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• Potential of using a PSAS to improve the properties of sand for use as a backfill material. • Appropriate water content w of the PSAS-treated sand reduces the swelling potential of PSAS treated sand. • Significant lower strength development of PSAS-treated sand compared with OPC-treated sand under same mixing conditions. • PSAS-treated sand is a suitable replacement of OPC-treated sand. • XRD profiles show that the formation of CaCO 3 is dominant in the PSAS-treated. The aim of this study is to investigate the potential of using a paper sludge ash-based stabilizer (PSAS) to improve the properties of sand proposed to be used as a backfill material around underground pipes. The swelling potential and strength of the sand treated with PSAS are investigated by conducting a series of laboratory tests. Similar tests are conducted on sand treated with ordinary Portland cement (OPC). Swelling potential tests show that the PSAS-treated sand with a water content of 0% show significant expansion during soaking, similar to the OPC-treated sand. However, the test results reveal that an appropriate moisture content of the PSAS-treated sand reduces its potential for expansion, depending on the duration of its temporary placement at the construction site. Unconfined compression tests show that the compressive strength of the PSAS-treated sand is significantly lower than that of the OPC-treated sand under the same mixing conditions, even though the chemical composition of PSAS is relatively similar to that of OPC. The increase in compressive strength with the curing time is more gradual in the PSAS-treated sand than in the OPC-treated sand, suggesting that the former is easier to re-excavate. X-ray diffraction profiles showed that the formation of calcite is dominant in the PSAS-treated sand, and that berlinite may be an additional contributor to the increase in strength of PSAS-treated sand in the long term. [ABSTRACT FROM AUTHOR]

Time-delayed spalling is proposed to describe the time-dependent splitting failure near the tunnel periphery, which occurs in several days or several months after excavation. This kind of failure has been frequently encountered in a deep TBM tunnel, endangering workers' security and delaying the construction schedule. In this paper, two typical time-delayed spalling cases were systematically introduced, including geological and supporting conditions. Based on field observation, microseismic monitoring and laboratory creep tests, the characteristics and mechanism of time-delayed spalling were investigated. Results showed that time-delayed spalling is a stress-induced time-dependent failure in the vicinity of tunnel surface and appears as flake or plate-like splitting fracture subparallel to the free surface. Although the failure region where time-delayed spalling happened is intact, discontinuities are scattered in the peripheral region. Time-delayed spalling is sensitive to boundary conditions and timely support is an essential method for preventing time-dependent spalling. This research is helpful to the tunnel excavation under similar geological conditions and provides foundations for the prevention of time-delayed spalling. • This paper makes an all-around introduction to the evolution process and mechanism of time-delayed spalling. • The spatial-temporal characteristics of fracture activities of time-delayed spalling were investigated. • The fundamental drivers of time-delayed spalling and the effective prevention method were analysed. [ABSTRACT FROM AUTHOR]

With the rapid expansion of underground engineering, accurate settlement estimation during foundation excavation using monitoring data has gained prominence. Previous studies have typically overlooked data patterns, relying solely on time-series models, which yielded limited accuracy and short-term predictability. To address these issues, this paper performs a thorough pattern analysis covering both the temporal and spatial properties, and proposes a spatiotemporal modeling method grounded in explainable artificial intelligence technique. A real-world engineering case study is conducted to validate the effectiveness of the proposed method. Counterintuitively, the results reveal a weak temporal effect within the settlement data, with only the last step playing a dominant role, whereas the spatial correlation among measuring points is notably more significant. Compared to conventional models, the proposed method consistently outperforms, achieving significantly higher R2 scores and excelling in long-term estimation with reductions of at least 78% in RMSE, 80% in MAE, and 72% in MAPE. • Spatiotemporal pattern analysis and XAI modeling for estimation are performed. • Pattern analysis results shows weak temporal correlations of settlement. • Spatial correlations in measuring points persist across construction stages. • The method yields notably smaller RMSE, MAE, and MAPE than conventional models. • SHAP analysis results highly align with the patterns uncovered by data analysis. [ABSTRACT FROM AUTHOR]

Reliable predictions of time-dependent diaphragm wall deflections in deep excavations in soft soils are crucial for managing potential damage to the surrounding environment. Bayesian updating offers a rational method for refining these predictions by using monitoring data. The inconsistency in monitoring data necessitates an examination of the impact of using different datasets on Bayesian updating. This paper presents a Bayesian updating of time-dependent deflections of diaphragm walls in deep excavations in soft soils using different datasets. The soft soil creep model is utilized to simulate the time-dependent behavior of soil. Bi-directional long-short memory neural networks are employed as surrogate models. Different updating strategies with varying numbers of data in the datasets are adopted for Bayesian updating and illustrated with the Taipei National Enterprise Center project. The results show that incorporating more monitoring data in the datasets for Bayesian updating does not guarantee better predictions unless the consistency of the monitoring data used is ensured. Additionally, the Bayesian updating process more accurately predicts short-term deflections than long-term ones, likely due to the higher consistency in short-term construction processes. It is advisable to review the construction processes to ensure the consistency of the monitoring data before selecting the appropriate dataset. [ABSTRACT FROM AUTHOR]

Optimizing the cutter changing process for tunnel boring machines (TBMs) is crucial for minimizing maintenance costs and maximizing excavation efficiency. This paper introduces TunnRL-CC, a computational framework that utilizes reinforcement learning to autonomously determine cutter-changing strategies. TunnRL-CC's realistic simulation models cutter wear under varying rock conditions, including hard rock and blockyness. A reinforcement learning agent is trained to learn optimal cutter-changing policies based on a reward function that balances cutter conditions and operational costs. The agent demonstrates innovative decision-making, adapting to changing excavation conditions. TunnRL-CC's proposed methodology significantly differs from traditional cutter changing practices, which rely heavily on operator experience. Although TunnRL-CC has not been applied in practical projects, its theoretical basis and comprehensive computational experiments demonstrate its capability to significantly improve TBM cutter maintenance procedures. [Display omitted] • A cutter wear simulation for hard rock tunnel boring machine advance was developed. • A predictive maintenance system for TBM cutters is implemented. • The system is reinforcement learning based and parameter optimization was done. • The learned cutter changing policy considers geotechnical and economic conditions. [ABSTRACT FROM AUTHOR]

To investigate the impact of shield side-crossing on existing piles and provide an efficient tool for assessing its deformation behavior pre-construction, this paper introduces a two-stage analysis method. Initially, by relying on the Mindlin solution and considering four parameters (palm face additional thrust, shield friction, grouting pressure and stress release) and the cumulative effect of ground deformation resulting from shield tunneling, the three-dimensional displacement field and stress field of the surrounding rock during shield tunneling are derived. Subsequently, based on the Pasternak foundation beam theory, the response characteristics of piles are analyzed by utilizing the obtained stress field. The rationality of the method is verified by field monitoring, numerical simulation and traditional Mindlin solution. The findings indicate that the cumulative deformation effect induced by shield tunneling on the front stratum should be considered and that the stratum response value calculated by the traditional method is relatively small. Accurate determination of the foundation beam parameters in each layer and consideration of the continuous deformation of piles are essential in composite layers. The pile segmentation calculation is employed to minimize errors. The grouting reinforcement scheme for the pile periphery soil should be carefully considered in construction, considering both cost and reinforcement effectiveness. [ABSTRACT FROM AUTHOR]

• A two-stage analysis method is proposed for analyzing the issue of local crack expansion in buildings under the influence of pit construction. • A three-dimensional fluid–solid coupling model of pit construction was established, along with a local structural crack expansion model based on XFEM. • The numerical model takes into account the initial cracks in the building and analyzes the impact of the size of these initial cracks. • Crack expansion control measures for damaged buildings are proposed. In response to safety concerns arising from pit construction near existing damaged buildings, this paper introduces a two-stage analysis method. Initially, the finite element method is utilized to construct a comprehensive model of pit excavation, enabling the analysis of building settlement and internal forces induced by the construction activity. Subsequently, the resulting building settlement vectors are employed as displacement loads in a localized structural model established via the extended finite element method. This facilitates the examination of crack propagation within the damaged building under settlement influence. Application of the proposed method to a new pit construction scenario reveals a maximum differential settlement of the building at 5.35 mm. As building settlement increases, crack propagation within the building follows a slow-fast-slow trend, with an approximate crack propagation length of 9.6 m and an average depth of 0.13 m. Notably, deeper and longer initial cracks exacerbate wall crack propagation, leading to cracks penetrating the wall when initial crack depths exceed 100 mm. Furthermore, crack propagation extends to the slab, resulting in a 10.2 m long of crack when initial crack depth is 66 mm. A case study demonstrates the effectiveness of the proposed two-stage analysis method in addressing crack propagation issues in existing buildings during pit construction. [ABSTRACT FROM AUTHOR]

Abstract In this short paper, the semi-empirical model introduced by Zheng et al. (2018) for evaluating the tunnel displacements induced by adjacent excavation was extended to a probabilistic model. To this end, the input parameters of the problem were defined as random variables with certain means and standard deviations. A reliability model was then established and solved by the Monte Carlo method. The results showed that the probability of exceedance fell sharply by increasing the tunnel displacement so that the probability of tunnel displacement of larger than 41 mm was less than 5%. Moreover, the reliability sensitivity analysis showed that the excavation depth and tunnel burial depth mostly affected the small range of tunnel displacements between 0.5 and 10 mm. However, the maximum impact of the retaining structure displacement and the horizontal distance of the tunnel from the excavation site were found to fall in medium and large (0.5 to larger than 21 mm) ranges of tunnel displacement. Having the exceedance probability curve presented in this paper, the exceedance probability for any desired value of the tunnel displacement is available, which can be used for safety evaluation and risk assessment of existing tunnels close to the surface excavations. [ABSTRACT FROM AUTHOR]

Abstract Tunnels are becoming more popular in the transportation system, which makes it imperative to study the surrounding soil tunnel stability. However, in previous studies, researchers generally regarded soil as an isotropic and homogeneous material, which is not consistent with real conditions. Therefore, on the basis of the upper bound theorem, the influence of the anisotropy and non-homogeneity of soil on the earth pressure and the failure mechanism of shallow square tunnels is studied in this paper. The failure mechanism of the surrounding soil for excavation tunnel is obtained using a discrete technique. Considering the anisotropy and non-homogeneity of soil, the earth pressure formula is derived and the optimal solution is obtained. Compared to other results, it is shown that the present approach is feasible and effective. In addition, taking the tunnel of Daganxi II, Longyong expressway of Hunan province as an example, a numerical calculation is conducted, in which the displacement field corresponds to the theoretical one proposed in this paper. After discussing the impact of the anisotropy and the non-homogeneity of soil on earth pressure, the tunnel stability is studied with the presence of the pore water pressure. The effect of pore water pressure and the change of the water table level are then investigated. [ABSTRACT FROM AUTHOR]

The aim of the paper is to simulate the response of a deep excavation supported by sheet pile walls and lime-cement columns. The application of the deep mixing technique using lime-cement products in deep excavations changes the initial state of the natural soil and creates substantial displacements associated with the installation effects. In this paper, the influence of lime-cement stabilisation was investigated using the finite element method for an instrumented braced excavation. The 2D finite element analyses were performed with advanced constitutive models for both natural clay and stabilised soil, exploiting the laboratory test made on both field mixed and laboratory mixed stabilised clay samples. The numerical results show that taking account of installation effects provides realistic predictions of deformation, excess pore water pressure evolution, as well as the structural forces in the struts. [ABSTRACT FROM AUTHOR]

Site contamination is a global concern because of the potential risks for human health and ecosystem quality. Every contaminated site has its own specific characteristics and the increased availability and efficiency of remediation techniques makes the choice of remediation alternative increasingly complicated. In this paper an attributional Life Cycle Assessment (LCA) of the secondary environmental impacts of a site remediation is performed and its results are monetized using two different monetization techniques, namely Stepwise 2006 and Ecovalue 08. Secondly, we perform a social Cost-Benefit Analysis (CBA) on the same case study using the same data sources. The case study used in this paper entails the soil and groundwater remediation of a tar, poly-aromatic hydrocarbons (PAH) and cyanide contamination of a school ground by a former gas plant. The remediation alternative chosen in this case study is excavation with off-site thermal treatment of the contaminated soil. The outcome of the social CBA, stating that the remediation project is socially beneficial in the long term, is critically compared to the outcome of the different LCA monetization methods. This comparison indicates that monetized LCA is a good complement to social CBA when it comes to the assessment of secondary environmental impacts. Combining the two methods provides decision makers with a more extensive and detailed assessment of the soil remediation project. [ABSTRACT FROM AUTHOR]

Buckets are a vital substructure of all digging machines, and are intended for the realisation of the fundamental machine function - soil excavation. This paper presents the results of the experimental-numerical investigation of the cause of the bucket wheel excavator SRs 470 buckets failure. The chemical composition and mechanical properties, the impact toughness, hardness, tendency to cracks and the microstructure were determined using appropriate tests. Experimental examinations of working and residual stresses were performed using strain gauges. The superposition of the experimentally determined working and residual stresses and the calculation of the total principal stresses were conducted using the originally developed procedure presented in this paper. The bucket working stress state was calculated by applying the linear finite element method. Conclusions based on the investigation results show that the main reasons for the buckets failure were the ‘design-in defects’ - oversights made during the procedures of geometrical shaping and material selection. Furthermore, high values of residual stresses, as well as the cold cracking observed on the welded joint of the knife and the bucket body, suggest that the ‘manufacturing-in defects’ also played a significant role in the failure. The superposition of influences of the ‘design-in defects’ and the ‘manufacturing-in defects’ has conditioned the appearance and propagation of long-term fatigue cracks, leading to the total destruction of the buckets. The fact that buckets' failure appeared due to oversights made during geometrical shaping, material selection and manufacturing further points to the importance of the critical approach implementation during the design phase of the earthmoving machines working devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • Simulate the actual working environment of coal mine. • Simulate the process of human body inhaling coal dust. • To monitor the characteristics of coal dust inhaled. The external flow field of roadheader in Daliuta Coal Mine is numerically simulated, and breathing process of drivers is experimented in this paper. The airflow field of the whole tunnel is divided into three parts. The wind speed in the breathing area is determined to be 1.8 m/s. The relationship between dust concentration and time in respiration area is y = -0.0357x2 + 8.5541x-1.2298. The condition concentration of dust capture test is 81–508 mg/m3. The experimental results show that the D 90 and D 50 of environmental and bionic throat dust particles decrease with the increase of dust concentration. The increase of environmental dust concentration has a greater impact on dust with particle size larger than 6.5 μm. Dust concentration (ppm) inhaled by the driver = 0.057* Dust concentration in the environment (mg/m3). This study is expected to provide theoretical support for the prevention and control of dust occupational hazards. [ABSTRACT FROM AUTHOR]

The displacement discontinuity method (DDM) has been widely used for large-scale engineering problems, e.g., hydraulic fracturing related to metal mining and hydrocarbon extraction. However, there is a lack of detailed explanation for the implementation of 3D-DDM in closed-contour boundary problem, and applications to address asymmetric closed-contour boundary problem remains limited. In this paper, we have theoretically derived and elaborated the numerical procedure, identified the caveats of DDM in solving fracture-type and closed-contour boundary problems. Subsequently, we modified the analytical integral and differential expressions for the basic solution on 3D-DDM based on triangular elements and provided a more general suite of expressions. Additionally, implementation details including element traversal criteria and precautions against rigid body movement are introduced to address the asymmetric closed-contour boundary problem. The accuracy of the generalized 3D-DDM were verified through simulations involving a penny-shaped fracture and a spherical cavity. Finally, the generalized 3D-DDM was employed to elucidate the stress redistribution and interference with respect to the tunnel excavation. This study demonstrates that: (1) the modified analytical integral and differential expressions combined with the element traversal criterion and precautions against rigid body movement provide a detailed explanation of how 3D-DDM can be applied to asymmetric closed-contour boundary problem; (2) during tunnel excavation, the arch flanks and floor would suffer from the biggest damage risk; and (3) the interaction effect between adjacent tunnels plays a role when the tunnel spacing is less than eight times the radius of the arch. [ABSTRACT FROM AUTHOR]

The issue of pressurized tunnels has been sufficiently investigated in the literature; nevertheless, the long-term behavior of the problem, which is the case in very squeezing conditions, remains unexplored. From a practical standpoint, the development of a damaged zone around the tunnel, due to the poor quality of blasting for excavation, imposes an additional challenge in predicting tunnel responses. This paper introduces an analytical approach addressing both water seepage and the excavation damaged zone (EDZ) concerning the long-term behavior of lined circular pressurized tunnels. To achieve this goal, the rheological behaviors of the initial rock mass and damaged zone are modeled using the Burgers model, along with considering the time-dependent variation in the rock mass hydraulic conductivity. After the validation of the model, the conducted parametric studies reveal that rock mass and lining hydraulic conductivities, EDZ radius, and the Burger shear modulus are the most influential parameters. [ABSTRACT FROM AUTHOR]

• A spatiotemporal feature fusion-based deep learning (FFDL) framework is developed. • The FFDL framework is utilized to forecast synchronous excavation stability. • It's designed with feature fusion, deep learning, and global sensitivity analysis. • Feature fusion-based indicators are generated for excavation database preparation. • A case study is conducted to verify the applicability of the FFDL framework. Under rapid urbanization, analyzing and perceiving synchronous excavation stability is essential to generate valuable and foresightful information in identifying and mitigating potential risks in deep excavations. Although the existing forecasting methods can achieve high accuracy in the safety state perception of deep excavations, it is prone to lack proper consideration of the monitoring item's fusion and cause error and uncertainty via the single-parameter risk evaluation. To address it, this paper proposes a spatiotemporal feature fusion-based deep learning (FFDL) framework to implement the feature fusion-based data analysis and time-series forecasting on the factor of safety (FS) on behalf of excavation stability, and global sensitivity analysis. The fusion indicators and proposed FFDL framework are validated through a comprehensive case study encompassing 100 typical metro station constructions. The feature fusion-based data analysis results confirm the statistical significance of fusion indicators, contributing to establishing a high-quality spatiotemporal sequential database. As for the real-time prediction, the Bayesian optimization CNN-LSTM model provides a reliable prediction of excavation stability and the relative errors in the training and testing datasets do not exceed 1% and 3% in construction duration. It also enhances the predictive accuracy and outperforms the existing models LSTM, GRU, BiLSTM, and CNN-LSTM, reaching an average improvement of 38%, 32%, and 32% in RMSE, MAE, and MAPE, respectively. Furthermore, the proposed model has an excellent generalization performance in accurately predicting the excavation stability of the other ten excavation cases with an average relative error of 5.37%. In short, this work contributes to not only providing a new perspective in risk management by integrating feature fusion-based indicators and excavation stability but also verifying the applicability of the proposed framework. [ABSTRACT FROM AUTHOR]

• The classification and mechanism of effect of deep excavation on existing tunnels are presented. • The prediction methods for influence zone of deep excavation on existing tunnels are summarized. • The prediction and control methods of excavation-induced tunnel displacement are summarized. • The research gaps are clarified and future prospects are put forward. Foundation pit excavation near existing tunnels has become increasingly common in cities. Excavation-induced unloading can inevitably affect existing tunnels and threaten their operational safety. This paper reviews the state-of-the-art developments and future trends in this issue. First, we discussed the technical requirements for tunnel protection and the necessity for predicting and controlling tunnel displacement. Thereafter, the classification and mechanical mechanisms of the effects of foundation pit excavations on existing tunnels are introduced. Further, the determination methods used for the influence zone of foundation pit excavation on existing tunnels are discussed, aiming at solving the question of 'how far is the influence?'. In addition, the prediction methods used for the excavation-induced tunnel displacement are discussed, aiming at solving the question of 'how big is the influence?'. Finally, the control methods used for the excavation-induced tunnel displacement are discussed, aiming at solving the question of 'how to deal with the influence?'. Consequently, we clarified the research gaps and outlined future directions. Thus, this study is expected to function as a reference for engineers to guarantee the safety of existing tunnels affected by foundation pit excavations. [ABSTRACT FROM AUTHOR]

A high concentration of dust in a fully-mechanized excavation face is a serious threat to the safety of production underground and miners’ health. This paper discusses the use of a novel air curtain generator and proposes a novel dust control and prevention technique. Based on the k-ε two-equation turbulence model, Hertz-Mindlin model and the CFD-DEM coupled interface compiled with C++ language, this paper firstly constructs a simulation model of the coupling between airflows and dust in a fully-mechanized excavation face, and then simulates the airflow fields and dust fields under forced/exhaust ventilation conditions with and without a novel air curtain generator being utilized. The results show that when only the forced/exhaust ventilation was used, a high concentration of dust spread throughout the entire tunnel space and no effective air curtain was formed. Furthermore, after the air curtain generator was turned on, as the radial-to-axial forced air ratio ( P FQ ) increased, the horizontal vortex in the front of the head-on section weakened gradually, and the originally disordered airflows behind the heading machine moved uniformly towards the head-on section. As the P FQ further increased, the distance ( d ) between the formed air curtain and head-on section decreased overall; through a curve fitting, this relationship can be written as: d = −5.247 ln( P FQ ) + 13.569. When the P FQ > 5:5, the average negative-pressure-induced dust-exhaust capacity increased, the distance between the formed air curtain and the head-on section decreased, and the re-entrainment of dust did not take place in a straightforward manner. Finally, some field measurements were carried out in order to validate the simulated results, with the subsequent comparison showing that the numerical simulated results were basically accurate. [ABSTRACT FROM AUTHOR]

This paper addresses the problem of assessing the stability conditions of shallow excavations of circular shape, namely circular sections of long cylindrical tunnels or spherical cavities, in purely cohesive ground by means of a scalar factor of safety as it is traditionally done for the case of slopes in the practice of geotechnical engineering. The paper presents a closed-form statically admissible solution for cavities in dry ground that allows a conservative estimation of the scalar factor of safety to be made. The effects of the geometry of the excavation, whether a section of cylindrical tunnel or a spherical cavity, the depth of the cavity in relation to its radius, and the effect of the support pressure and ground surcharge load in relation to the cohesion of the ground, on the factor of safety are examined. A quantitative analysis for determining how conservative the results from the analytical solution are with respect to results obtained with a commercial software implementing the finite-difference method is presented. The analysis indicates that the values of factors of safety predicted with the analytical solution are within 80% of the values of factors of safety predicted with the numerical (finite-difference) solution. A quantitative comparison of values of factors of safety and required support pressure obtained with the analytical solution and with other published solutions is presented. Factors of safety obtained with Terzaghi (1943) limit equilibrium model are shown to be both conservative and non-conservative depending on the combination of input values considered for the model. Values of required support pressure predicted with the proposed analytical solution are shown to be similar to the ones predicted numerically by Davis et al. (1980). An extension of the proposed statically admissible model to account for water in the ground is also presented. Cases of shallow cavities of circular shape in saturated cohesive ground with a water surface at or above the ground surface, and limiting conditions of flooded and dry openings are considered. Stability conditions for flooded openings in saturated ground are shown to generally improve, while stability conditions for dry openings in saturated ground are shown to worsen, in comparison with the same equivalent cavities in dry ground. [ABSTRACT FROM AUTHOR]

The procurement of high-quality aggregates is a global problem. In Chile, mining companies are in the process of developing massive underground projects that require the extensive use of Portland cement concrete (PCC), approximately 60%–75% of which is aggregate. Currently, mining projects transport all the required aggregate to the site from stockpiles that can be more than 100 km away, while mining excavations produce millions of cubic meters of waste rock (WR) that are disposed of in landfills. The use of WR in PCC seems to be a sustainable solution for the production of PCC, but decision-makers lack the tools to support a sustainable decision based on CO 2 emissions and operation costs. This paper proposes a methodology that uses stochastic simulation tools to evaluate CO 2 emissions and operation costs to decide when it is sustainable to use WR in PCC for underground mining projects. The main objective of this paper is to provide a methodology to quantify CO 2 emissions and the cost of transporting natural aggregate versus recycling WR for PCC production in tunneling operations. A sensitivity analysis is also presented, which considers scenarios that include natural aggregate transportation distances of 50, 60, 70, 80, 90, and 100 km, and 0%, 25%, 50%, 75%, and 100% replacement of natural aggregate with recycled WR in PCC. The results indicate that the use of WR leads to reductions in CO 2 emissions only for natural aggregate transportation distances of greater than 70 km owing to the emissions produced when recycling WR. In addition, 100% replacement of natural aggregate with recycled WR leads to a greater reduction in CO 2 emissions than that obtained in scenarios in which a percentage of the required natural aggregate is obtained from WR. In terms of costs, 100% replacement of natural aggregate with recycled WR is the most economical alternative for most scenarios; however, the cost reduction varies with the required transportation distance of natural aggregate. It is concluded that using 100% recycled WR in PCC leads to lower CO 2 emissions and costs as compared to the traditional approach in which the natural aggregate is procured from a site located at a distance of 70 km or more from the construction site, under model assumptions. [ABSTRACT FROM AUTHOR]

Construction of an underground complex in congested urban areas calls for excavation of a group of foundation pits, referred to as a pit complex, which are usually surrounded by existing facilities. In such circumstances, the safety of the pit complex and facilities during the construction are of great concern. This paper presents a case of an underground complex construction in Shanghai soft clay. A pit complex composed of two deep excavations was excavated for a Comprehensive Transport Hub (CTH) and a commercial retail area and pedestrian concourse known as South Square (SS), which were connected to an operating metro station and a railway station. During the excavation, potential deformation of metro tracks and railway tracks were expected due to extensive soil unloading. To safeguard the railway and the subway, a zoned and staged construction technology was proposed, in which several temporary partition walls were constructed in addition to necessary supporting structures, to allow the large-scale deep excavations to be divided into several independent small-scale excavations. This paper discusses the rational construction sequence of these excavations as well as reinforcement measures in detail. The construction technology was examined by extensive field data. It is found that the maximum horizontal displacement of diaphragm walls ranged between 0.05% H e and 0.4% H e , where H e is the excavation depth. The vertical displacements of the railway tracks were well controlled, whereas the metro tracks heaved significantly due to unloading effect. [ABSTRACT FROM AUTHOR]

In the last decades mechanized tunnelling with Tunnel Boring Machines (TBMs) has spread, due to the sensible technological developments, allowing for higher advancement rates, huge excavation diameters (up to 17 m) and lower excavation costs. Methane inflows from gassy rock masses may represent a serious hazard in underground excavations and could cause expensive delays and, at worst, tragic accidents to workers. Consequently, if methane-air mixtures may be present, a safety engineering system should be designed and set up before starting the excavation works in order to prevent fires or explosions. Due to the impossibility to prevent the contemporary presence of explosive gas-air mixtures and ignition sources, TBMs have never been adopted for tunnelling in gassy rock masses until 2011 (excluding the tunnels excavated with TBM, where methane gas hazard was underestimated, consequently producing delays and unpredicted expenses). The paper describes the safety engineering system developed for the excavation of the Sparvo twin tunnels (Italy) with EPB–TBM. The machine (Herrenknecht S-574) was specifically designed to prevent the risk of having explosive gas-air mixtures and ignition sources in the same place and at the same time, hydraulically confining the volumes inside the machine. After a brief description of the case study, the paper illustrates the design criteria, the technological solutions adopted for the construction of the Herrenknecht S-574 and the operating procedures. Then, the paper focuses on examining and interpreting the methane monitoring results during Sparvo tunnel construction, that highlight the presence of huge volumes of methane. The developed safety engineering system allowed tunnelling without interruptions even with sensible gas flows. Current limits and possible improvements to the safety system described are also discussed. [ABSTRACT FROM AUTHOR]

In this paper, the relationship between the dynamic surface subsidence and overburden separated strata has been studied under the condition of sedimentary coal measure strata. When the underground coal seam is mined, the ground surface subsidence will be caused. The surface subsidence is caused by the goaf clearance passing along the overlying strata up to the surface. During the course, the bed-separation space would be generated and its size directly affected the value of mining goaf passing up to the ground - the surface subsidence. It shows that the surface subsidence is closely related with overburden separated strata. Therefore, the research on the dynamic development law of overburden separated strata contributes to recognition and prediction of surface dynamic subsidence, which is the important basis for the control of mining subsidence damage. In this paper, the whole processes form cracking, propagation, to closure of the mining overburden separated strata are analyzed in the first chapter. The various steps of surface dynamic subsidence, from the initial step, the active step, and then to the recession are researched. And then the corresponding relationship between the surface dynamic subsidence and overburden separated strata is studied and its model is established for analyzing factors of geological and mining that influenced this relationship. At last, a similar material model for coal measure strata in sandy shale is established and carried on the excavation experiment of coal seam. Then by use of the test, the development law of mining overburden separated strata is studied, and the space-time corresponding rule of the surface subsidence and overburden separated strata is analyzed. And on this basis, we find the relationship between the surface subsidence and overburden separated strata. Based on allometric growth of mining overburden separated strata, which would provide a new research and analysis method for control and prevention of mining subsidence damage, we establish the model of mining subsidence. [ABSTRACT FROM AUTHOR]

Time-Lapse Electrical Resistivity Tomography (TL-ERT) is an effective geophysical method for monitoring groundwater migration for its high sensitivity to the conductivity changes of the rock mass. However, existing Time-Lapse resistivity inversion still has two problems to be appropriately improved: false anomalies in initial model propagating into subsequent inversions and the limitation due to equal sensitivity to resistivity variations along different directions. In this paper, Time-Lapse resistivity inversion is improved with two additional approaches. First, prior temporal gradient constraint is applied into Time-Lapse inversion equation to enhance the sensitivity to the vertical or horizontal variation of the model parameters evolved over time during iteration. Second, the observation datasets are normalized with the same ratio before inversion to filter the false anomalies of initial model and to highlight the significant information on model changes over time. The effectiveness of the improvement is verified by a numerical inversion test and a physical model test. Furthermore, this paper describes the successful application of the improved Time-Lapse resistivity inversion method to monitor the groundwater migration caused by water inrush in tunneling located at Cen-xi tunnel, Guangxi Province of China. Surface ERT arrangement in the site has appropriately indicated the existence of the subsurface runoff pathway of underground water, and then Cross-hole ERT were implanted to monitor the groundwater migration. The results acquired by the proposed Time-Lapse inversion method could effectively provide guidance to hazard management and groundwater environmental recovery in the site. [ABSTRACT FROM AUTHOR]

Rockbursts frequently occur in deep underground excavations in a sudden or violent ejection of blocks of rocks from excavation walls. In addition to understanding rockburst mechanisms, rockburst control is an important issue for the safety of mining operations. Bolts and anchors are efficient measures to control rockbursts and permit the efficient exploration of underground excavations in mines. As mining depths increase, anchor and bolts with larger extension and higher loading capacity are needed. This paper introduces a Constant Resistant Large Deformation (CRLD) bolt which has been developed at the State Key Laboratory for Geomechanics and Deep Underground Engineering (GDUE), in Beijing, China. Static and dynamic tests were developed for this type of bolt. Advancements in Hopkinson tests were recently developed for CRLD bolts and Split-Hopkinson Tension Bar (SHTB) experiments for these bolts were performed. This paper presents the SHTB equipment and the results obtained with one and two CRLD bolts, as well a deep analysis of the obtained results. To better understand the complex nature of the problem, numerical simulations using several softwares were done for the case of one bolt, which had the dual goal of verifying the experimental and numerical results. In addition, the numerical predictions permit one conducting analysis the behavior of the bolt while targeting the development of large deformations. Finally some relevant conclusions are drawn. [ABSTRACT FROM AUTHOR]

• The pressure fluctuation occurred during the tunnel construction. • Numerical simulation and experiments are both carried out to analyze the causes. • The breakdown of the filter cake is the main cause of the pressure fluctuations. • Compressed air breaks through filter cake, which causes pressure fluctuations. The Wuhan Metro Line 8 Crossing River Tunnel Project suffered manifest pressure fluctuations when opening the excavation chamber of the slurry shield. In this paper, numerical simulation and air pressure test are both carried out to analyze the causes of the pressure fluctuation. The analysis results show that the air pressure applied on the excavation face during the opening of chamber lies in the safe region, excluding the possibilities of active and/or passive excavation face failures. Then, calculated by empirical formula, the pressure on site is lower than the hydraulic fracture pressure, which means the pressure fluctuation is not related to the hydraulic fracture. At last, by air pressure tests, the break through pressure of the filter cake is found much smaller than the air pressure on site. Therefore, it is concluded in this paper that the quality of the filter cake does not meet the design standard, and the breakdown of the filter cake is the main cause of the observed pressure fluctuations on the excavation face. Furthermore, the mechanism of filter cake breakdown is investigated experimentally. [ABSTRACT FROM AUTHOR]

Compared with concrete pile, the steel pipe pile has an advantage as high stiffness, high bearing capacity, high bearing capability, high quality and short construction term. Construction of deep foundation pit causing the unloading of neighborhood soil, inevitable role in the steel pipe pile foundation building. Combining with the actual measurement engineering data and numerical result, the deep foundation pit at the typical station on Xiamen metro line 1 is taken as the engineering background of this paper, the dynamic response of the steel pipe pile foundation during construction of neighborhood deep excavation was studied. The results indicate that, Under the condition of soil-rock compound stratum in Xiamen city, when the steel pipe pile location away from the edge of deep foundation pit 2h (h: depth of deep excavation), the displacement of the steel pipe pile was generally small. The settlement displacement of concrete pile foundation and steel pipe pile foundation are basically the same, the horizontal displacement of the steel pipe pile foundation has a simple linear distribution. the horizontal displacement of the concrete pile foundation has obvious inflection point, under inflection point, the same as the steel pipe pile foundation, above inflection point, the horizontal displacement two times than the steel pipe pile foundation. The results of this paper providing a reference to similar projects. [ABSTRACT FROM AUTHOR]

Conductor pipes are the first part of an oil well to provide the initial structural foundation and they are normally installed into the ground by using impact hammers both onshore and offshore before any drilling operation. However, it is possible that conductor pipes do not reach the design depth and therefore relief drilling is needed. Nowadays offshore relief drilling is performed by using drill strings with drill bit of jack-up rigs. However, this operation is both time-consuming and expensive. This paper analyzes the use of an alternative solution, developed for supporting the installation of conductor pipes. Two mathematical cutting models were used to theoretically assess the net relief drilling time based on two geotechnical parameters, i.e. cohesion and friction angle. By comparing the theoretical results with three drill logs of an offshore project performed in the UK with another drill rig with similar geometries, it is shown that the preliminary models seem to match the net drilling time registered on the field. The results shown in this paper have to be carefully interpreted and cannot be applied to future projects as the net drilling time values have to be considered as theoretical. [ABSTRACT FROM AUTHOR]

Underground tunnel excavation using the drill-and-blast method often results in underbreak occurrences due to improper blasting parameters and complex geological environment. This underbreak phenomenon has a profound impact on tunnel safety, stability and construction costs. Traditional approaches for predicting underbreak extent (UE) through field measurements and theoretical models exhibit limitations in terms of accuracy and efficiency. Consequently, it is urgent to develop a novel approach for UE prediction in tunnelling operations. In this paper, extreme gradient boosting (XGBoost) is first applied as the foundational algorithm, and slime mould algorithm (SMA) is implemented for tuning hyper-parameters of XGBoost. Meanwhile, six chaotic maps are integrated with SMA to initialize the population and improve the optimization performance. Subsequently, a dataset of 250 samples is collected from three underground mines in China, involving ten influential factors (RMR , uniaxial compressive strength (UCS), vertical principal stress (σ v), lateral pressure coefficient (λ), excavation area (EA), powder factor (PF), specific charge (SC), advance length (AL), periphery hole burden (HB)and periphery hole spacing (HS)). Additionally, four indices, i.e., coefficient of determination (R 2), variance accounted for (VAF), mean absolute error (MAE) and root mean square error (RMSE), are used to evaluate the comprehensive performance of these proposed COSMA-XGBoost models and four common machine learning models. Finally, a parametric sensitivity analysis is performed, and the optimal intelligent model is applied in practical tunnelling projects. The results indicate that chaotic optimized SMA models have better convergence ability and higher accuracy compared with the original SMA model. Notably, the PSMA-XGBoost model outperforms other models as the R 2, VAF, MAE and RMSE values for the testing set are 0.979, 95.79%, 4.176 and 4.884, respectively, whereas 0.968, 94.25%, 4.274 and 5.012, respectively for training set. EA , RMR and UCS exhibit significant effects on UE. In practical tunneling projects, the engineering application of the PSMA-XGBoost model demonstrates its feasibility and efficiency in predicting UE within underground tunnels. [ABSTRACT FROM AUTHOR]

This research develops a hybrid approach that integrates light gradient boosting machine (LightGBM) and non-dominated sorting genetic algorithm II (NSGA-II) to optimize the tunnel boring machine (TBM) performance during excavation. The TBM operational data are first extracted and meta -models are established to estimate the key TBM performance, including the penetration rate, over/under excavation ratio, and energy consumption. An optimization process is proposed by adopting NSGA-II and the technique for order preference by similarity to an ideal solution (TOPSIS) analysis to determine ideal operational parameters. The developed approach acts as a useful tool that assists tunnel construction automation and improves TBM performance under different in-situ conditions. Real data from a tunnel project in Singapore is utilized as a case study to examine the applicability and efficiency of the proposed approach. The results indicate that (1) The proposed meta -model provides reliable estimation with an average RMSE and MAE of 2.604 m m / m i n and 3.402 m m / m i n for TBM's penetration rate(O 1), 0.0211 and 0.0324 for over/under excavation ratio (O 2), and 15.512 k w h and 23.088 k w h for energy consumption (O 3), respectively. The prediction accuracy is better than the state-of-the-art methods; (2) The TBM's performance can be optimized by the proposed approach with an average improvement of 33.14 %, 1.32 %, and 17.95 % for O 1 to O 3 , respectively, and an overall improvement of 39.60 %; (3) The overall reliability of TBM operation improved after optimization with a significant reduction in data variance by 91.16 %, 76.92 %, and 97.35 % for O 1 to O 3 , respectively. This paper contributes to proposing a novel method that integrates LightGBM with NSGA-II in resolving the complex TBM operation problem by considering the major performance indexes including excavation efficiency, safety, and energy consumption during TBM operation. [ABSTRACT FROM AUTHOR]

Due to the great uncertainty and complexity in the underground environment, precious risk perception in underground construction is a highly challenging problem. Excessive false-positive alarms (FPA) and false-negative alarms (FNA) generated by the unreasonable setting of early-warning values are the main causes to affect the safety of engineering in underground construction. Aiming to reduce the FPA and FNA in risk assessment of an excavation procedure, this paper provides a novel data-driven optimization framework for early-warning threshold modification based on massive field monitoring data. The multi-objective expected value optimization (MEVO) approach is applied to achieve the goal of unsupervised and multivariate modification tasks. Firstly, the objective functions of the MEVO approach are established with the combination of grey relational analysis and Cosine similarity measure. Secondly, the expected values of objective functions are calculated based on the expert evaluation method and Monte Carlo simulation. Finally, the sample sequence generated from observed monitoring data satisfying the expected values is selected as the optimal solution. A case study is utilized to verify the effectiveness and applicability of the proposed approach. The result from the case study indicates that: (1) The proposed approach modifies the multivariate early-warning values to decrease the number of alarms with a reduction ratio of 12% in the training set; (2) The early-warning frequency under the modified values is lower than that under the original values during the whole excavation stages in the testing set; (3) The modified threshold values fall within the threshold intervals based on expert evaluation method, which are capable of improving risk assessment in current practice. In short, our proposed approach enables a more accurate and intelligent evaluation of the risk state by formulating more credible criteria. It contributes to serving as a reliable decision tool for ensuring construction safety during deep excavation. [ABSTRACT FROM AUTHOR]

Strainburst is an unstable rock failure phenomenon that occurs at deep excavations' boundaries due to the excavation-induced stress concentration and a "soft" loading environment. A critical task for researchers is to predict the possibility or risk of strainburst occurrence. In this paper, the local mine stiffness (LMS) of a tunnel determined by a novel calculation method is compared to the post-peak characteristic stiffness (PCS) of surrounding rock masses having different brittleness to discriminate strainburst occurrence, which is verified with simulated stable and unstable rock failure occurring in a calibrated deep tunnel model established by UDEC. The reliability and accuracy of the LMS calculation method are further examined by comparing excess energy's analytical and numerical results. The relative difference is 11.3 % and 2.5 % regarding the measurement of the Richter magnitude. As a result, a new rockburst indicator, called strainburst stiffness factor (SSF), is proposed to predict strainburst risks based on the analysis of stiffness differences. The prediction results of SSF were successfully validated on two real-life examples where the data was matched with the "5.5″ rockburst event in the Zofiowka Coal Mine and the "11.28″ rockburst event in the Jinping II Hydropower Station. The proposed indicator provides an effective tool to predict strainburst risks, which can further improve the safety of workers and equipment when constructing deep excavations in mining and civil engineering projects. • The reliability and accuracy of a novel method for calculating the local mine stiffness of a tunnel are verified. • A new indicator of strainburst prediction is proposed and developed based on the stiffness theory. • The effectiveness of the new rockburst indicator is validated with reported strainburst cases. [ABSTRACT FROM AUTHOR]

• Responses of tunnels induced by river excavation in soft soils is evaluated. • Various protection measures of excavation-induced tunnel deformation are studied. • An effective soil reinforcement for mitigating tunnel deformation is proposed. • A well-documented case history is presented. The excavation of river channel in soft soils has an inevitable influence on adjacent metro tunnels. This paper investigates the effect of river channel excavation on the underlying metro tunnels and corresponding protective measures based on an engineering project in Fuzhou city, China. A three-dimensional finite element model is developed to calculate the vertical and horizontal displacements and diametrical distortion of tunnels under different excavation sequences and soil reinforcement measures. Real-time monitoring of the vertical and horizontal displacements and diametrical distortion of tunnels is carried out and analyzed in detail. The results show that the vertical displacements and diametrical distortion of tunnels are primarily caused by the excavation of the river directly above the tunnels, while the horizontal displacements are induced by the excavation of the river next to the tunnels. A combination of cement slurry with a portal form and concrete with a plate form is recommended to reinforce the bottom soil of rivers and protect the operational tunnels. The accuracy of the calculation model and the effectiveness of the protection measure are confirmed by using on-site measurements. The findings can provide useful reference for the safety assessment and protection measures of similar projects. [ABSTRACT FROM AUTHOR]

• Derivation of the displacement boundary function considering the lining-soil interaction. • Correction of ground loss considering vertical movement and geological conditions. • Quantification of the effects of radial contraction, vertical translation and lining deformation on ground movements. This paper presents an improved analytical solution for the prediction of ground movements based on the ground loss correction. The boundary function of ground displacement composed of radial contraction, vertical translation of tunnel and tunnel ovalization is derived. The displacement analytical solution is further optimized by the equivalent ground loss rate components corrected from both the vertical translation of the tunnel and the geological conditions. Field measurements from eight tunnel cases are used to validate the capability and applicability of the proposed solution. Finally, the influence of the three deformation components mentioned above on ground deformation is explored. The results demonstrate that in practice, while the focus is on the quality and timing of grouting to control ground loss, the vertical translation of the tunnel should also be strictly controlled. The research results in this paper can provide a new simple and reliable calculation method for predicting the ground movements induced by circular tunnel excavation. [ABSTRACT FROM AUTHOR]

• Various engineering risks of high and steep slope near river and reservoir are analyzed. • In view of various risks during excavation of the foundation pit near high and steep slope, several effective reinforcement measures are proposed. • The finite difference software FLAC3D is used to simulate the evolution process of slope deformation, and the deformation law of steel tubular pipe pile is analyzed. • The plastic deformation law of reserved thin-walled rock wall is studied, and the stress characteristics of support beam in foundation pit are found. The intake of water diversion project is generally located on the bank slope above the large reservoir or deep water area of a river. Due to the influence of water level change and hydraulic action, the rock mass of bank slope is seriously weathered and broken, leading that the rock mass has low strength and is easy to collapse or landslide. In this paper, the water intake engineering of the long-distance diversion project in central Shanxi Province is selected as the research object. The multi-point displacement meter is used to monitor the slope deformation after anchorage and concrete retaining wall support. Based on the FLAC3D V6.0 software, the numerical simulation of the excavation process of the steep reinforced river bank slope is carried out, and the long-term deformation of the slope is predicted. The excavation scheme of retaining outer thin-walled rock wall as water cofferdam is proposed. The excavation process of foundation pit, which is supported with concrete-filled steel tubular pile reinforcing cofferdam and concrete supporting beam, is simulated. It is found that the upper part of the steep slope supported by anchor cable and concrete retaining wall is stable, and the large deformation and plastic failure of the water-retaining thin rock wall are mainly affected by the disturbance of foundation pit excavation. The concrete-filled steel tubular pile support avoids the collapse of the reserved thin-walled cofferdam, and the horizontal beam in the foundation pit improves the stress state of the external wall of the foundation pit. The research results of this paper reveal the evolution mechanism of rock mass deformation and failure during excavation of foundation pit on steep bank slope, and provide guidance for excavation and support of foundation pit for similar bank slope. [ABSTRACT FROM AUTHOR]

This paper examines the effect of different geological and mining factors on roof stability in underground coal mines by combining field observations, laboratory testing, and numerical modeling. An underground coal mine in western Pennsylvania is selected as a case study mine to investigate the underlying causes of roof falls in this mine. Three-dimensional distinct element analyses were performed to evaluate the effect of different parameters, such as the variation of immediate roof rock mass strength properties, variation of discontinuity mechanical properties, orientations and magnitudes of the horizontal in-situ stresses, and the size of pillars and excavations on stability of the immediate roof. The research conducted in this paper showed that the bedding planes play an important role on the geo-mechanical behavior of roofs in underground excavations. Therefore, an appropriate numerical modeling technique which incorporates the effect of discontinuities should be employed to simulate the realistic behavior of the discontinuous rock masses such as the layered materials in roof strata of the underground coal mines. The three-dimensional distinct element method used in this research showed the capability of this technique in capturing the important geo-mechanical behavior around underground excavations. [ABSTRACT FROM AUTHOR]

The paper reports some geotechnical aspects of the design and construction of the San Pasquale Station, intermediate along Line 6 and located close to the sea and at the same time within one of the most fascinating district of the city known as Chiaia borough. The station required an excavation deeper than 25 m, almost entirely located in pyroclastic sand below the groundwater table. The main shaft is 85.5 m long and 24.1 m large, containing also the whole length of the pedestrian platform while a single large section tunnel, built before the excavation of the station shaft, accommodates the two operating rail tracks. In the paper monitoring data will be presented and discussed. Settlements and horizontal displacements represent certainly very significant outcomes among the observed data. Their variations along with time and main construction steps are first of all presented in the paper. The monitoring data have also been submitted to a process of careful interpretation based on the use of numerical analyses to better understand the interaction of deep excavation with urban area. The FEM code Plaxis has been adopted for such a purpose adopting advanced constitutive soil models which are available in the code library. [ABSTRACT FROM AUTHOR]

• Similar materials suitable for the rockburst model test are configured by orthogonal proportioning tests and physical mechanics tests. • The rockburst mechanism of rock mass with structural planes in underground chamber excavation is studied by model test and numerical simulation. • The failure modes and laws of surrounding rock mass with different structural planes during chamber excavation are obtained. Natural rock mass generally contains discontinuous structural planes, such as joints, fractures and faults, which have great influence on the occurrence of rockburst. The rockburst mechanism of rock mass with structural planes in underground chamber excavation is studied by means of model test and numerical simulation in this paper. Firstly, quartz sand, barite powder, gypsum powder, cement and water are selected as raw materials to configure the similar materials suitable for the rockburst model test. Secondly, four working conditions of none structural plane, single structural plane, multiple structural planes and through structural plane are designed, and the corresponding rockburst model tests are carried out. The stress and displacement laws of surrounding rock during excavation are analyzed. Finally, the numerical calculation of chamber excavation is conducted under the above four working conditions and the model test is verified. The failure modes and laws of surrounding rock mass with different structural planes during chamber excavation are obtained. The results show that: (i) After the tunnel excavation in rock mass with single structural plane, the tension of structural plane and the expansion of fractures occur, accompanied by small-scale rockburst. (ii) After the tunnel excavation in rock mass with multiple structural planes, the stress level of surrounding rock mass decreases significantly and no rockburst occurs, but the surrounding rock is prone to large-scale collapse or spalling. (iii) After the tunnel excavation in rock mass with through structural plane, the fractures appear in the vault and arch bottom and expand rapidly, accompanied by rockburst phenomena such as granules ejection. The research results of this paper are of great significance for understanding the deformation and failure mechanism of rock mass with structural planes in the underground chamber excavation. [ABSTRACT FROM AUTHOR]

Tunnel excavation in mountainous or sloping regions can sometimes reactivate or accelerate landslide phenomena with a potential important impact on the stability of such constructions. The problem of tunnelling-induced landslides, that represents an important issue for many areas of the world, is very complex to analyse and demanding to solve. In addition, there are very few well documented case histories in literature. The paper presents the case of the Val di Sambro twin tunnels excavated in a structurally complex formation, in a geomorphological setting characterised by landslides of various areal sizes, whose depth was not well known before tunnelling. After a description of the main technical features of the tunnels, the geological setting and the geomechanical site conditions, the paper illustrates and comments the most significant outcomes of the monitoring system in the Southern zone of the tunnels, one of the areas where the major deformative phenomena occurred. The Val di Sambro tunnels represent a unique case study for the large amount of monitoring data collected before and during the tunnel excavation through an integrated system, consisting of various measure methods (inclinometers, piezometers, underground and surface topographic measurements, SAR interferometric technique). The combined use of surface, subsurface, underground and satellite data allowed analysing the characteristics of the landslide movements before the tunnel excavation and in relation to the tunnel construction. [ABSTRACT FROM AUTHOR]

The paper is dedicated to the case history of a 13 m wide, 17 m high and 40 m long service tunnel at Toledo Station, previously constructed in a deep open shaft and belonging to the Line 1 of the Napoli underground network. The existing Line 1 has been recently extended with a new stretch consisting of five new stations connected by twin rail tunnels for a total length of about 5 km. Toledo Station main shaft is located by a side of the line and it is connected to the pedestrian platforms by the above mentioned large size service tunnel. The station is situated in the historical center of the city of Napoli, under a deeply urbanized area. In Fig. 1 a longitudinal section of the main shaft of the station and of the large service tunnel with the above and surrounding buildings is sketched. The focus of this paper is on the settlement caused by the tunnel excavation and on the use of the Artificial Ground Freezing (AGF) technique to allow the safe excavation of the large crown of the service tunnel, located about one half in a silty sand layer and one half in yellow tuff, well below the groundwater table. [ABSTRACT FROM AUTHOR]

In deep sea mining, the vertical transport of excavated material from the seafloor to a vessel at the sea surface is a key process. Stationary flow is preferred, and blockage of the riser would terminate the entire operation. For a blockage to occur there needs to be accumulation of material, the formation of a solid plug, and the plug needs to exert sufficient friction on the riser wall. The formation of a blockage is a complex chain of events, described in detail in this paper. The hypothesis presented in this paper on the formation of plugs and on the conditions for a blockage to occur is checked with the results of a unique experiment. We developed a test setup in which the conditions for riser blockage are enforced. We were able to conduct a reproducable blockage experiment, which shows that the mechanism presented in this paper is a very accurate description of the blockage process. To ensure safe operations and high production levels, the transport system needs to be designed for maximum flow assurance. Knowledge of the mechanism and conditions for riser blockage can be used in the design of feeding systems and strategies for the vertical transport system. [ABSTRACT FROM AUTHOR]

Tunnel Boring Machine (TBM) tunnelling in weak rock associated with high overburden is very demanding due to the difficulties in predicting the complex interactions between the rock mass, the tunnel machine, its system components, and the tunnel support during excavation/construction. These factors affect the performance and even the feasibility of a TBM drive (sticking of the cutterhead and jamming of the shield may occur). In this respect, several computational models such as the Convergence–Confinement Method (CCM), axially symmetric model and three-dimensional (3D) simulation have been developed in the literature. Among these models, this paper presents three modelling techniques (i.e., a 3D simulator using the Finite Element Method (FEM), an axisymmetric model using the Finite Difference Method (FDM) and an LDP (Longitudinal Displacement Profile) approach based on the CCM), and applies them to the Headrace Tunnel from the Kishanganga Hydroelectric Project in India. The three approaches are not considered to be alternatives but rather complementary to each other, depending on the real situation. The LDP approach is a simplified analytical method but is still efficient to provide a conceptual framework for evaluating the ground-shield interplay during mechanised excavation. The FDM axisymmetric model represents a powerful tool (i.e., with a large deformation scheme available) for the simulation of ground behaviour and its interaction with the machine components, especially in the case of weak rocks with high deformability. However, when the conditions violate the important assumptions underlying these two approaches, true 3D numerical analyses are necessary, which consider all the TBM components. Finally, the paper highlights the potentials of the 3D simulator to model the basic features (i.e., stepwise conicity of the shield, backfilling layer and anisotropic in-situ stress state) of a shield-driven deep tunnel, which determine the tunnel’s behaviour and its response to TBM advancement. The obtained results show that the 3D nature of the complex interactions and the in-situ state of stress, including the nonlinear behaviour can be better reproduced in a 3D simulation than in the other two methods. [ABSTRACT FROM AUTHOR]

In urban areas, subway construction inevitably imposes negative impacts on adjacent buried pipelines. During the recent construction of the Beijing subway, several ground failures have occurred due to the pipeline damages induced by tunnel construction. In this paper, a disastrous ground failure of such kind occurred during the Beijing subway Line 10 construction is presented, in which a sinkhole about 20 m long, 14 m wide and 12 m deep formed. Both the tunnel construction and the ground traffic were severely affected. The adopted remedial measures for this failure, including road restoration, dewatering, dredging and tunnel face reinforcement, are systematically illustrated. The probable mechanism of this failure is also analyzed and briefly discussed. The case presented in this paper can serve as a practical reference for the engineers practicing in the similar engineering field. [ABSTRACT FROM AUTHOR]

For the excavated clayey cover of a coal seam in open-pit mining, the shear strength is the most important issue after its deposition in landfills. For this purpose, an artificial lumpy material was investigated in this paper. A transition form between a reconstituted soil and natural lumpy soil governs the mechanics of the soils artificially deposited after the excavation. This paper presents triaxial and oedometer tests (including K 0 and isotropic consolidation tests conducted in triaxial cell) both on an artificial lumpy soil and its corresponding reconstituted form. Compression, permeability and strength of lumpy materials have been evaluated. When normalized by Hvorslev pressure, the shear strength of both lumpy materials and reconstituted soil lies on unique lines, with strength parameters of the lumpy materials lower than that of the reconstituted soil. Both the consolidation and triaxial test results indicate that the reconstituted soil, which exists in the inter-lump voids, plays a crucial role in the behaviour of lumpy materials. [ABSTRACT FROM AUTHOR]

• A novel tool-soil interaction model for a scoop sampler was developed and validated. • Work extends Mori model to account for soil cohesion, adhesion and surcharge effects. • Terramechanics models used to obtain interaction forces between sampler and soil. • Proposed model is compared and validated against earlier model in simulation studies. • In experiments, model predictions agree with measurements in cohesive, adhesive soil. Robotic systems have been developed and deployed for sample collection and geotechnical measurements of soil characteristics. A custom scoop-type robotic soil sampler has been designed and built for sampling operations. An earlier terramechanics model for scoop samplers proposed by Mori et al. is limited to describing the interaction forces in loose sands. This paper proposes an extended model which captures the interaction of a scoop-type sampler with a wider range of soils, including cohesive and adhesive mediums, and accounts for the effects of surcharge. The proposed model was compared to the Mori model in both simulation and laboratory experiments. The forces predicted by each model agree closely for loose sand, but differ in cohesive and adhesive mediums. The proposed model was experimentally tested on dry sand and on centrifuged tailings, a cohesive and adhesive soil. In both cases, the proposed model showed close agreement between measured and predicted forces. [ABSTRACT FROM AUTHOR]

• General decoupled method for reliability-based geotechnical design. • The method is robust to model complexity and parameter dimension. • Non-parametric and global estimation of failure probability functions. • Case study on the design optimization of deep excavation in Singapore marine clay. • Effects of statistical characteristics of soil properties on design is investigated. This paper presents a general decoupled method for reliability-based geotechnical design that takes into account the spatial variability of soil properties. In this method, reliability analyses that require a lot of computational resources are decoupled from the optimization procedure by approximating the failure probability function globally. Failure samples are iteratively generated over the entire design space so that their global distribution information can be extracted to construct the failure probability function. The method is computationally efficient, is flexible to implement, and is well suited for geotechnical problems that may involve sophisticated models. A design example of two-dimensional deep excavation against basal heave is discussed for Singapore marine clay where the density and normalized undrained shear strength of soil mass are modeled as random fields. Results demonstrate that the proposed method works well in practice and is advantageous over the coupled or locally decoupled reliability-based geotechnical design methods. [ABSTRACT FROM AUTHOR]

A number of landslides occur in the soil slopes overlying bedrock due to excavation. However, the excavation-induced deformation and failure behavior and the coupling influential mechanism of the bedrock and excavation have not been clearly elucidated, although they are essential for the stability analysis of slopes overlying bedrock under excavation conditions. In this paper, a series of centrifuge model tests was conducted on the slopes overlying bedrock under excavation conditions with different bedrock shapes. The slopes overlying different bedrocks experienced a significant progressive failure process under excavation conditions, and the slip surface gradually developed from the excavation area at the slope toe to the slope top. The failure mechanism of the slope that overlies the bedrock under the excavation condition can be illustrated by the significant coupling of the deformation localization and failure. There was a shear zone, where the shear strain was concentrated with a substantial increase rate. The displacement direction of the soil in the shear zone was consistent and invariable for a slope overlying the bedrock after the shear zone appeared. Excavation led to a significant influence area inside the slope overlying the bedrock, which was significantly affected by the shape of the bedrock: steeper bedrock corresponded to a wider significant influence area, and flatter bedrock corresponded to a narrower one. [ABSTRACT FROM AUTHOR]

This paper presents new archaeological material and first dates on Upper Pleistocene layers at the site of La Crouzade cave (Gruissan, Aude, France). The site was first excavated by T. and P. Héléna at the beginning of the twentieth century, and the excavations were recently completed during three years (2016–2018) of systematic campaigns. We obtained dates from Middle Palaeolithic layers using two methods: AMS 14C dates were obtained from bone and charcoal, and combined ESR-U series dating was undertaken on horse teeth. Together, these methods allowed us to date this Mousterian sequence to 49,776–44805 cal BP for the deepest level (layer C8) and from 42,000 ± 3000 years BP for the top (layer C6). The Upper Palaeolithic layers are preserved only as patches in the actual excavation area, but a date was obtained from a piece of charcoal collected from a small hearth preserved in the first layer (C5) above Middle Palaeolithic deposits, which indicates an age similar to that of a modern human maxillary previously analysed and re-dated here from 36,014 to 34402 cal BP, confirming its stratigraphic attribution. The Middle Palaeolithic lithics at the site were first described as para-Charentian cultural facies following typological analyses. The revision of the earlier collection supplemented with the new material, using a technological approach, allow to identify two layers dominated by Levallois production followed by discoid production (Layers C8 and C6) surrounding an original assemblage (layer C7), characterised by a dominant Levallois production completed by three secondary production systems of equal importance, including discoid, SSDA and a Quina-like production. The faunal spectrum predominantly comprises an assemblage of Pleistocene large mammals, and biochronological studies corroborate the dates obtained. [ABSTRACT FROM AUTHOR]