Search

Soil-structure interfaces (SSI) are common in geotechnical structures, and understanding their shear behavior is essential for effective design. However, the coupling effects of particle shape and interface roughness on SSI remain understudied. This study addresses this gap by employing five types of super-ellipsoid particles with varying asphericity (η) values to model non-spherical particles. Interface shear tests with different roughness levels (Rn) were conducted using Discrete Element Method (DEM) simulations. The results show that both ηand Rnsignificantly influence shear strength, localized shear band thickness, and soil fabric, with two types of coupling effects: single-factor dominance and double-factor interaction. The influence on coordination number (Cn) and probability distribution of normalized contact force is more straightforward. Specifically, non-spherical particles exhibit a higher initial Cndue to enhanced interlocking, while Rnhas a lesser impact. The normalized contact force at the interface follows an exponential distribution, similar to pure soil, and is largely independent of ηand Rn. Notably, the shear zone is divided into three equal parts for soil fabric analysis. These findings offer new insights into SSI, contributing to more effective and safer geotechnical designs.

This study aims to develop a rational theoretical model for cutterhead-soil interaction. The cutterhead-soil interaction mechanism is divided into two components: the cutting action of the cutter on the soil and the extrusion of the cutterhead on the soil. By enhancing the Mckyes–Ali model, we analyze and deduce the force state of the cutter during shield tunneling, obtaining a calculation method for determining the force on the cutter. Additionally, we conduct an in-depth analysis of the extrusion effect of the cutterhead on the soil during shield tunneling, utilizing the fundamental solution of the Kelvin problem. Based on these theoretical calculations, we validate the tunneling thrust and cutterhead torque of the shield using our self-developed multi-functional large-scale shield tunneling test platform. The test results demonstrate that the tunneling thrust and cutterhead torque derived from the established cutterhead-soil interaction model in this paper are relatively close to the experimental monitoring values. This provides a theoretical foundation for establishing reasonable shield tunneling loads.

Flexural performance of joints is critical for prefabricated structures. This study presents a novel channel steel-bolt (CB) joint for prefabricated subway stations. Full-scale tests are carried out to investigate the flexural behavior of the CB joint under the design loads of the test-case station. In addition, a three dimensional (3D) finite element (FE) model of the CB joint is established, incorporating viscous contact to simulate the bonding and detachment behaviors of the interface between channel steel and concrete. Based on the 3D FE model, the study examines the flexural bearing mechanism and influencing factors for the flexural performance of the CB joint. The results indicate that the flexural behavior of the CB joint exhibits significant nonlinear characteristics, which can be divided into four stages. To illustrate the piecewise linearity of the bending moment-rotational angle curve, a four-stage simplified model is proposed, which is easily applicable in engineering practice. The study reveals that axial force can enhance the flexural capacity of the CB joint, while the preload of the bolt has a negligible effect. The flexural capacity of the CB joint is approximate twice the value of the designed bending moment, demonstrating that the joint is suitable for the test-case station.

This paper conducts a theoretical analysis of ground settlements due to shield tunneling in multi-layered soils which are usually encountered in urban areas. The proposed theoretical solution which is based on the general form of the Mindlin's solution and Loganathan-Poulos formula can comprehensively consider the in-process tunneling parameters including: unbalanced face pressure, shield-soil friction, unbalanced tail grouting pressure, unbalanced secondary grouting pressure, overloading during tunneling and the ground volume loss. The method is verified by comparing with the field data from the Qinghuayuan Tunnel Project in terms of the ground surface settlements along the longitudinal and transverse direction. Due to the local settlement or heave caused by the certain tunneling parameters, the ground surface settlements calculated using current solution along the longitudinal direction presents an irregular S-shaped curve instead of the traditional S-shaped curve. Results also find that the effect of the unbalanced secondary grouting pressure and the overloading during tunneling cannot be ignored.

With the burgeoning emphasis on sustainable construction practices in China, the demand for green building assessment has significantly escalated. The overall evaluation process comprises two key components: The acquisition of evaluation data and the evaluation of green scores, both of which entail considerable time and effort. Previous research predominantly concentrated on automating the latter process, often neglecting the exploration of automating the former in accordance with the Chinese green building assessment system. Furthermore, there is a pressing requirement for more streamlined management of structured standard knowledge to facilitate broader dissemination. In response to these challenges, this paper presents a conceptual framework that integrates building information modeling, ontology, and web map services to augment the efficiency of the overall evaluation process and the management of standard knowledge. More specifically, in accordance with the Assessment Standard for Green Building(GBT 50378-2019) in China, this study innovatively employs visual programming software, Dynamo in Autodesk Revit, and the application programming interface of web map services to expedite the acquisition of essential architectural data and geographic information for green building assessment. Subsequently, ontology technology is harnessed to visualize the management of standard knowledge related to green building assessment and to enable the derivation of green scores through logical reasoning. Ultimately, a residential building is employed as a case study to validate the theoretical and technical feasibility of the developed automated evaluation conceptual framework for green buildings. The research findings hold valuable utility in providing a self-assessment method for applicants in the field.

The presented research introduces a novel hybrid deep learning approach for the dynamic prediction of the attitude and position of super-large diameter shields - a critical consideration for construction safety and tunnel lining quality. This study proposes a hybrid deep learning approach for predicting dynamic attitude and position prediction of super-large diameter shield. The approach consists of principal component analysis (PCA) and temporal convolutional network (TCN). The former is used for employing feature level fusion based on features of the shield data to reduce uncertainty, improve accuracy and the data effect, and 9 sets of required principal component characteristic data are obtained. The latter is adopted to process sequence data in predicting the dynamic attitude and position for the advantages and potential of convolution network. The approach’s effectiveness is exemplified using data from a tunnel construction project in China. The obtained results show remarkable accuracy in predicting the global attitude and position, with an average error ratio of less than 2 mm on four shield outputs in 97.30% of cases. Moreover, the approach displays strong performance in accurately predicting sudden fluctuations in shield attitude and position, with an average prediction accuracy of 89.68%. The proposed hybrid model demonstrates superiority over TCN, long short-term memory (LSTM), and recurrent neural network (RNN) in multiple indexes. Shapley additive exPlanations (SHAP) analysis is also performed to investigate the significance of different data features in the prediction process. This study provides a real-time warning for the shield driver to adjust the attitude and position of super-large diameter shields.

Displacement measurement is crucial across various fields, and this study introduced an innovative system using vertical graphene (VG) for this purpose. The system incorporates cantilevers and wedge structures to minimize graphene material deformation. The study delves into the sensing mechanism of flexible VG sensors, involving sliding, crack propagation, carbon nanofragment contact changes, and tunneling effects in graphene sheets. Additionally, the impact of temperature annealing and aging treatment on VG sensor stability was explored, along with an assessment of VG bars’ temperature sensitivity. The results show that the VG sensor’s relative resistance change rate increases with temperature up to 70 °C, with decreased stability beyond that point. Calibration tests demonstrated the sensor’s performance, revealing a measurement range of 0–30 mm, a sensitivity of 20%, and a resolution of 0.0094 mm. The hysteresis error was measured at 0.33%, with repeatability and accuracy errors at 10.39% and 7.47%, respectively. These outcomes underscore the sensor’s potential for diverse sensing applications.

This paper presents a case study of the clogging of a slurry-shield tunnel-boring machine (TBM) experienced during tunnel operations in clay-rich argillaceous siltstones under the Ganjiang River, China. The clogging experienced during tunneling was due to special geological conditions, which had a considerably negative impact on the slurry-shield TBM tunneling performance. In this case study, the effect of clogging on the slurry-shield TBM tunneling performance (e.g., advance speed, thrust, torque, and penetration per revolution) was fully investigated. The potential for clogging during tunnel operations in argillaceous siltstone was estimated using an existing empirical classification chart. Many improvement measures have been proposed to mitigate the clogging potential of two slurry-shield TBMs during tunneling, such as the use of an optimum cutting wheel, a replacement cutting tool, improvements to the circulation flushing system and slurry properties, mixed support integrating slurry, and compressed air to support the excavation face. The mechanisms and potential causes of clogging are explained in detail, and the contributions of these mitigation measures to tunneling performance are discussed. By investigating the actual operational parameters of the slurry-shield TBMs, these mitigation measures were proven to be effective in mitigating the clogging potential of slurry-shield TBMs. This case study provides valuable information for slurry-shield TBMs involving tunneling in clay-rich sedimentary rocks.

This paper presents a simplified elastic continuum method for calculating the restraint effect of isolation piles on tunneling-induced vertical ground displacement, which can consider not only the relative sliding of the pile‒soil interface but also the pile row–soil interaction. The proposed method is verified by comparisons with existing theoretical methods, including the boundary element method and the elastic foundation method. The results reveal the restraining mechanism of the isolation piles on vertical ground displacements due to tunneling, i.e. the positive and negative restraint effects exerted by the isolation piles jointly drive the ground vertical displacement along the depth direction from the original tunneling-induced nonlinear variation situation to a relatively uniform situation. The results also indicate that the stiffness of the pile‒soil interface, including the pile shaft‒surrounding soil interface and pile tip-supporting soil interface, describes the strength of the pile‒soil interaction. The pile rows can confine the vertical ground displacement caused by the tunnel excavation to the inner side of the isolation piles and effectively prevent the vertical ground displacement from expanding further toward the outer side of the isolation piles.

The development of urban underground space (UUS) is of great significance for sustainable urban development because it has potential to solve many urban problems. However, the development of UUS is limited because there are still a lot of constraints and challenges. To better understand the constraining factors of developing UUS and improve the development and utilization of UUS, this study conducts a comprehensive survey of existing literature retrieved from the Web of Science Core Collection database. Five main constraining factors, including the limited geological conditions, high cost, lack of natural light and ventilation, high incidence, and difficulty in collecting data and information on UUS, have been discussed to better understand how they affect the development of UUS. Based on the survey, the critical success factors of developing UUS, such as the effective governance structure, planning system for integrating UUS into urban development, coordination of the design of ground and underground, delineation of land property rights of UUS, and application of information techniques in the use of UUS, have been identified and discussed. In addition, knowledge gaps in the studies on development of UUS have been identified. Finally, the research trends and future directions have been proposed for better understanding and practice of UUS development.

Based on a cross-river tunnel of Wuhan Metro Line 8, we present a two-dimensional discrete element model for shield attitude adjustment considering the effect of overbreak cutters. The shield shell mechanics under the influence of over-excavation rate, over-excavation orientations, and overburden load are simulated, and the tunneling mechanics law and the ultimate range during the adjustment of the shield attitude are investigated. The simulation results indicate the following: (1) The greater the over-excavation rate, the smaller the force exerted by the soil layer in the negative direction of the shield movement; therefore, increasing the over-excavation rate is helpful in expanding the range of shield attitude adjustment. (2) The shield is stressed symmetrically while conducting positive and negative horizontal adjustments in the soil layer, which has a symmetrical distribution, but vertical upward adjustment is more difficult than vertical downward adjustment. (3) With the increase in overburden load, the space of the shield attitude adjustment is gradually reduced at the same over-excavation rate. A good engineering application was achieved in this project using the simulation model. It is recommended to use the attitude adjustment method by controlling the tunneling parameters. In difficult situations such as high overlying loads, the over-excavation cutter can be used to assist in adjusting the shield attitude.

This study analyzed the passive arching effect under eccentric loading by developing a series of trapdoor discrete numerical models. The numerical models were validated by comparison with laboratory test results. The deformation pattern, soil arching ratio, force chain distribution, and coordination number under various surcharge magnitudes and deviation distances were analyzed. The numerical results showed that the deformation diagram of soil particles can be divided into three zones: principal displacement zone, transition zone, and static zone. With an increase in the surcharge magnitude, the range of the principal displacement zone decreased, but the range of the transition region increased. The curve of the soil arching ratio on the trapdoor can be divided into three phases, which can be well characterized by the tangent modulus. The passive arching effect is degraded by a surcharge. The ultimate soil arching ratio could be approximated as a W-shaped distribution along the +x-direction. With an increase in the trapdoor displacement, the force chain on the trapdoor gradually expanded outward to form an inverted funnel shape. The most powerful force on the trapdoor was mainly distributed on its edge. The average coordination number decreased gradually as the trapdoor moved upward.

This research explores the potential for the evaluation and prediction of earth pressure balance shield performance based on a gray system model. The research focuses on a shield tunnel excavated for Metro Line 2 in Dalian, China. Due to the large error between the initial geological exploration data and real strata, the project construction is extremely difficult. In view of the current situation regarding the project, a quantitative method for evaluating the tunneling efficiency was proposed using cutterhead rotation (R), advance speed (S), total thrust (F) and torque (T). A total of 80 datasets with three input parameters and one output variable (For T) were collected from this project, and a prediction framework based gray system model was established. Based on the prediction model, five prediction schemes were set up. Through error analysis, the optimal prediction scheme was obtained from the five schemes. The parametric investigation performed indicates that the relationships between Fand the three input variables in the gray system model harmonize with the theoretical explanation. The case shows that the shield tunneling performance and efficiency are improved by the tunneling parameter prediction model based on the gray system model.

Large quantities of waste engineering spoil (WES) from shield tunnelling is produced and require proper disposal, and the pollution risk of heavy metal that cannot be ignored. The previously proposed flocculation-solidification integrated process (FS) has shown its advantages in water-separation and precipitate-solidification. Further exploration is needed on the effectiveness of this process in controlling heavy metal. The content of heavy metals (As, Cr, Cd, Cu) in the supernatant and the leaching solution from mud cake were determined, the retention mechanism of FS for heavy metals was discussed. The results showed that the amount of heavy metals migrating to the external environment were reduced to 0.02 % – 6.21 % after treatment from 0.20 % – 26.58 %, with the migration ratio in the flocculation stage being 0.02 % – 6.20 %, in the solidification stage being 0.00 % – 0.12 %. The forms of heavy metals were transformed into stable states, and the retention effect was evident in the early stages of treatment, the concentrations of Cu/Cd in the supernatant were reduced to low levels after 0.5 h, while the concentration of As decreased by more than 50 %. Furthermore, the addition of sodium dodecyl sulfate (SDS) enhanced the retention effect, compared to group without SDS, the concentrations of heavy metals in supernatant were reduced by 2.21–68.26 % with SDS, which may be due to the changes in the surface charge characteristics of WES, thereby hindering the migration of heavy metals. This study confirms the effectiveness of FS in controlling heavy metals, providing support for waste slurry disposal.

This study focuses on empirical modeling of the strength characteristics of urban soils contaminated with heavy metals using machine learning tools and their subsequent stabilization with ordinary Portland cement (OPC). For dataset collection, an extensive experimental program was designed to estimate the unconfined compressive strength (Qu) of heavy metal-contaminated soils collected from a wide range of land use pattern, i.e. residential, industrial and roadside soils. Accordingly, a robust comparison of predictive performances of four data-driven models including extreme learning machines (ELMs), gene expression programming (GEP), random forests (RFs), and multiple linear regression (MLR) has been presented. For completeness, a comprehensive experimental database has been established and partitioned into 80% for training and 20% for testing the developed models. Inputs included varying levels of heavy metals like Cd, Cu, Cr, Pb and Zn, along with OPC. The results revealed that the GEP model outperformed its counterparts: explaining approximately 96% of the variability in both training (R2 = 0.964) and testing phases (R2 = 0.961), and thus achieving the lowest RMSE and MAE values. ELM performed commendably but was slightly less accurate than GEP whereas MLR had the lowest performance metrics. GEP also provided the benefit of traceable mathematical equation, enhancing its applicability not just as a predictive but also as an explanatory tool. Despite its insights, the study is limited by its focus on a specific set of heavy metals and urban soil samples of a particular region, which may affect the generalizability of the findings to different contamination profiles or environmental conditions. The study recommends GEP for predicting Quin heavy metal-contaminated soils, and suggests further research to adapt these models to different environmental conditions.

ABSTRACTSophora davidiiis a cross-pollinated plant with important ecological protection and medicinal value in China, but its seed yield is low due to backward and nonstandard production technology. Therefore, we divide the flowering period of Sophora davidiiinto initial, full and final flowering period, measuring the floral morphology, pollen viability, stigma receptivity, nectar volume and nectar concentration, foraging behavior of pollinators, fertilization physiology, seed yield and quality through field observation and indoor testing to explore whether the flowering period affects the floral traits, pollinator behavior and seed production of plants. Our results revealed that the nectar volume, nectar concentration, pollen viability and stigma receptivity at full flowering period were the highest. The single visit time and visit time per flower of Chinese honey bees were the longest in the full flowering period, while the number of transfer, visit frequency and number of touching stigma were the least. The visiting number of the bees was the most and the most active in the full flowering period. The bees pollination not only improved the pollen amount, germination rate, pollen tube length and the ovule number of S. davidii, but also their effect was the most obvious in full flowering period. The principal component analysis showed that pollination by Chinese honey bees during the whole flowering period of S. davidiiwas the best way to produce seeds. We can conclude that flowering period affects flower traits, foraging behavior of pollinators, seed yield and quality of S. davidii.

Marine concrete contains a high volume of supplementary cementitious materials, which benefits low-carbon concrete production. However, they may also increase the risk of cracking and accelerate the carbonation due to the pozzolanic reaction. Theoretically, the CaO-based expansive agent (CEA) can inhibit shrinkage cracks and introduce external calcium sources that aid in the carbonation resistance of concrete. A comprehensive understanding of the impact of CEA on the carbonation resistance of marine concrete is currently scarce. In this study, marine concretes with varying dosages of CEA were exposed to 20 % CO2for 28 days. The carbonation depth, carbonation coefficient, air permeability, pore structure characteristics and CO2buffer capacity of concrete were investigated. When the CEA dosage was less than 6 %, the carbonation resistance and air permeability approached the reference groups in normal-strength concrete (NSC) and high-strength concrete (HSC). However, more than 6 % CEA significantly decreased the carbonation resistance of concrete, particularly for HSC. For NSC, there was an excellent correlation between the carbonation coefficient and compressive strength, while for HSC, the carbonation coefficient correlated well with porosity. Also, CO2buffer capacity was essential to assess the carbonation resistance of marine concrete.

The hydration process of calcium sulfoaluminate (CSA) and aluminate cement (CAC) is influenced by their composition and calcium sulfate sources. Increasing the calcium sulfate content promotes ettringite generation; however, exceeding the optimal threshold may cause volume instability. This study aims to optimize sulfate levels in CSA and CAC by adjusting the SO3/Al2O3molar ratios. Contour maps were used to analyze how different sulfate sources and calcium sulfate levels affect strength development, ettringite formation, and volume stability. Both gypsum and anhydrite similarly improved compressive strength in CAC and CSA at equivalent SO3/Al2O3ratios. However, gypsum caused more significant expansion than anhydrite at equivalent SO3/Al2O3ratios, as indicated by the higher expansion values in gypsum-rich regions. The SO3/Al2O3molar ratio is crucial for regulating ettringite formation, enhancing compressive strength, and ensuring volume stability in CSA and CAC systems. Maintaining this ratio below 1.0 enabled the addition of sufficient calcium sulfate to achieve optimal performance.

Adjacent construction around metro tunnels is a common situation in urban cities, which usually leads to the disturbance of surrounding soils and existing tunnels. Based on the influence zone theory, construction risks can be described in a graded manner. However, the calculation of the influence zone in existing research is mostly based on a single indicator, which is difficult to adapt to the increasingly stringent requirements of real projects. To address this limitation, a normalized method for the influence function and a weighted combination method for multi-indicators were proposed. These methods can combine any number of indicators to obtain an integrated result of the influence zone, facilitating direct guidance of engineering. Based on a case study of the Metro construction in Qingdao, a series of numerical simulations and calculations of the integrated influence zone was carried out. The results show that the shape of the integrated influence zone in this case is a necked bottle, i.e., the new tunnel causes a greater influence when it is below the existing tunnel. The change of soil layer and the weight of indicators both play important roles on the shape of the influence zone. The relevant conclusions and methods provide a basis for the safety assessment of similar projects.

This study conducted both experimental and numerical investigations on the capillary water absorption into AAS materials with varying mix proportions. The results demonstrate that the capillary water absorption of AAS mortars adheres to the square root of time (SRT) law until wetting front reaches the top surface of specimen. The isopropanol (IPA) absorption of AAS mortars also follows the SRT law, and the measured intrinsic capillary sorptivity Sintfor IPA and water are quite close. Through theoretical modeling and numerical simulation, the capillary absorption kinetics of different AAS mortars can all be accurately quantified using the Richards equation, regardless of the water retention curve model employed. These results suggest that the microstructure of AAS materials studied herein is stable during capillary water absorption. This may be attributed to the viscous characteristics of AAS materials, arising from the irreversible collapse and rearrangement of the nanostructure of C-A-S-H gels during drying.

This study presents a framework for predicting geological characteristics based on integrating a stacking classification algorithm (SCA) with a grid search (GS) and K-fold cross validation (K-CV). The SCA includes two learner layers: a primary learner's layer and meta-classifier layer. The accuracy of the SCA can be improved by using the GS and K-CV. The GS was developed to match the hyper-parameters and optimise complicated problems. The K-CV is commonly applied to changing the validation set in a training set. In general, a GS is usually combined with K-CV to produce a corresponding evaluation index and select the best hyper-parameters. The torque penetration index (TPI) and field penetration index (FPI) are proposed based on shield parameters to express the geological characteristics. The elbow method (EM) and silhouette coefficient (Si) are employed to determine the types of geological characteristics (K) in a K-means++ algorithm. A case study on mixed ground in Guangzhou is adopted to validate the applicability of the developed model. The results show that with the developed framework, the four selected parameters, i.e. thrust, advance rate, cutterhead rotation speed and cutterhead torque, can be used to effectively predict the corresponding geological characteristics.

The soil water characteristic curve (SWCC) is an important tool in soil science and geotechnical applications. Most previous studies on SWCCs are limited to one to three drying‐wetting cycles, mainly because SWCC measurement is complex and time‐consuming. The numerous models that have been proposed to predict hysteresis in SWCCs. In this paper, a novel simplified equation is proposed based on the van Genuchten model, whereby SWCC hysteresis can be easily predicted from the initial drying SWCC. The theory for describing the main wetting curve and main drying curve considers the ink‐bottle effect and entrapped air. Laboratory experiments on silicon micro‐powder (SMP) and Guangxi Guiping clay (GGC) were conducted to determine SWCCs for five drying‐wetting cycles. The proposed equation was verified using the experimental SMP data and data from the literature. The predicted hysteretic SWCCs are in good agreement with the experimental data.

Energy piles are a new type of heat exchange systems with buried pipes in a pile foundation, which optimize a ground source heat pump system for the utilization of shallow geothermal energy. In this study, based on the principle of similarity, the thermo-mechanical behavior of the model energy pile with a large cross-section in saturated sandy soil was experimentally evaluated. The pre-cast model concrete pile with a diameter of 0.2 m and length of 1.5 m was buried in saturated sand in a steel box with dimensions of 2.5 m × 2.5 m × 2.0 m (length × width × height). The pile was heated using water in the polyethylene (PE) pipe, which was connected to a water cycle temperature controller. At a constant inlet water temperature of 55 °C, three thermal cycles were carried out with the same heating and cooling periods and different water flow rates. The temperature distributions in the pile and soil, in addition to the pore pressure, soil pressure, and displacement of the pile, were monitored to clarify the thermo-mechanical behavior of the pile and soil. The heat transfer efficiency was analyzed based on the temperature difference and water flow rates. The measured strain at different locations in the pile under cyclic thermal loading revealed that the uneven strain that developed in a pile body should be considered for its long-term application. Furthermore, focus should be directed toward the long-term unrecoverable displacement of the energy pile due to the thermal plastic strain and thermal consolidation of the soil.

Despite decades of research, superhydrophobic surfaces still rely on a stable air layer that is plagued with problems, such as poor pressure stability, the inability to self-heal, and the failure to repel organic liquids or complex mixtures with low surface tension, and this seriously restricts their applicability. To address these limitations, new Nepenthespitcher plant-inspired materials with a continuous liquid layer have been proposed, which are defined as slippery lubricant infused porous surfaces (SLIPS) that rely on a stable liquid layer. They show pressure stability, self-healing, and omniphobic properties with extremely low contact angle hysteresis for almost all liquids (such as blood, oil, and even butane, where γ 13 mN m−1). However, these surface functions will be diminished over time due to the depletion of the lubricant layer by various factors, including evaporation, solubility, shearing, the loss of the cloaking layer or the wetting ridge, etc.Therefore, it is critical to improve the stability of the lubricant layer for the preparation of stable and durable SLIPS. In this review, we mainly focus on how to enhance the stability of the lubricant layer and reduce the loss of lubricants to prolong the longevity of SLIPS. We start from the design principles, which should ensure that the substrate can be infiltrated and wetted by the lubricant rather than by external droplets. Thereafter, the effects of the physical properties of the lubricant (e.g.viscosity, vapor pressure, surface tension, etc.) and the type of structure (flat vs.rough, nanoscale vs.microscale vs.hierarchical, closed-cell vs.open-cell) on prolonging the lifetimes of SLIPS are discussed. Finally, a variety of physical and chemical methods have been explored, which aim to maintain a stable lubricant layer through capillary force, chemical interactions, swelling or by an embedded lubricant reservoir, as well as to maintain stimuli-responsive SLIPS that avoid unnecessary lubricant loss by employing microcapsules that lock up the lubricants or a phase changeable lubricant.

Water evaporation loss occurs during multistep outflow experiments from the soil surface and the outflow vessel. The main focus of this paper is to introduce an improved pressure plate instrument that can correct for the error of water evaporation loss on the unsaturated hydraulic conductivity. Experiments using silicon micropowder (SMP) and Guangxi Guiping clay (GGC) were conducted with an improved instrument. The results showed that the measured value of the water content will be overestimated and the unsaturated hydraulic conductivity will be underestimated without considering the water evaporation loss.

Artificially cemented soils have been widely used as filling materials in highway and railway construction. The shear strength evolution of filling materials upon moist variation can determine the stability of subgrade and embankments. This study conducted water retention tests, MIP tests, and multi-stage triaxial shear tests on cement-treated granite residual soil (GRS) to determine its water retention curve (WRC) upon free drying, pore structure, and peak shear strength qf, respectively. The water retention behavior and shear strength evolution upon free drying were modeled based on the dual-porosity structure of cement-treated GRS and the effective stress principle, respectively. Results show that the drying-WRC is bimodal and higher cement dosage yields a more severe decrease in the water retention capacity within a specific suction range. For a given confining pressure, the peak shear strength qfincreased with increasing cement dosage or suction value s. The peak shear strength qfalso solely depends on the suction value in the peak stress state. In addition, the cement-treated GRS has a bimodal pore size distribution curve, and its macro- and micro-void ratios remain almost unchanged after free drying. The bimodal drying-WRC of the cement-treated GRS can be modeled by differentiating the water retention mechanisms in macro- and micro-pores. Moreover, using the macro-pore degree of saturation as the effective stress parameter χ = SrM, the qf–pf′relationship (where pf′is the effective mean pressure at failure) under various suction and stress conditions can be unified, and the qf–srelationships at various net confining pressures σ3,netcan be well reproduced. These findings can help design subgrade and embankments constructed by artificially cemented GRS and assess their safe operation upon climate change.

In earthquake-prone areas, mountain tunnels often suffer from seismic damage when traversing active fault zones. To capture the seismic behavior of mountain tunnel under the action of active faults motion, the rate and state friction (RSF) relation is introduced to define the stick–slip dynamic behavior of a fault. The RSF relation is implemented in the finite element methods (FEMs). Numerical simulations of triaxial patch tests indicate that the RSF method can effectively capture the stick–slip dynamics. To reproduce the seismic damage to Daliang tunnel caused by slip of the Lenglongling fault, a three-dimensional (3D) numerical model including tunnel structure and plates of the fault is established. Seismic waves triggered by fault slip are then reproduced using the model. The simulation results show that the waves are dissipated while travelling and that their amplitudes decrease with depth. The failure of the tunnel lining is captured, and its seismic responses, including the displacement and strain of the structure, are extracted for various fault strike angles. The simulations are consistent with the observations, and it indicates that the movement of the simulated tunnel structure adjacent to the fault surface is significantly greater than those in the foot wall and in the middle of the fault. This study has the potential to provide a more direct means of understanding the seismic action of infrastructure induced by earthquakes. Seismic waves are no longer needed as input to the numerical simulation and instead, the earthquakes are generated by directly modeling the stick–slip motion of the fault.

•Urban Underground Space (UUS) presents a strategic approach for sustainable urban development.•A systematic framework is presented to assess UUS’s carbon reduction potentials.•UUS released approximately 547 Mt of carbon emissions during construction phase in 2020.•Geothermal resources have significant potential for carbon sequestration in UUS sector.

Blister beetles of Epicauta impressicornishave attracted attention because they contain a large amount of cantharidin (CTD). To date, however, the synthesis and transfer of CTD in adults of E. impressicornisare largely unknown. Here, we showed that the larvae E. impressicornisare capable of synthesizing CTD and they consume CTD during pupation. Before sexual maturity, both male and female adults synthesized a small amount of CTD, while after sexual maturity, males produced larger amounts of CTD, but females did not. The newly synthesized CTD in males first appeared in the hemolymph and then accumulated in the reproductive system. During the mating, the males transferred CTD to the reproductive system of females. In addition, a farnesyl pyrophosphate synthase (FPPS) gene was identified in male E. impressicornis. RNA-seq analysis, quantitative RT-PCR, and RNA interference analyses were conducted to investigate expression patterns and the functional roles of E. impressicornisFPPS (EiFPPS). Our results indicate that EiFPPSis highly expressed in the fat body of males. Moreover, the knock-down of EiFPPSled to a significant decrease in CTD synthesis. The current study indicates that EiFPPSis expressed in the fat body to regulate CTD synthesis in male E. impressicornisblister beetles.

To improve the safety and scale of helium storage, large-scale or strategic helium storage in underground salt caverns can be implemented. Salt caverns leached from bedded salt formations have been considered as potential underground storage sites for helium in China. However, the salt formations are typical lacustrine sedimentary rocks with an interbedded structure, thus the sealing feasibility of such salt caverns must be evaluated before they can be used. To this end, the helium seepage equation in deep strata and permeability evolution function are derived with the help of experimental results and theoretical analysis. Based on these, a helium seepage model considering slippage effect and threshold pressure gradient is proposed to evaluate the sealing properties of salt caverns for helium storage. The analysis results indicate that it is feasible to use bedded salt mine formations for helium storage when the formations permeability parameters and reservoir design parameters meet the long-term tightness evaluation criteria, including permeability, porosity, salt pillar width, salt roof thickness and operating pressure and duration. More importantly, specific recommendations are provided for the operation parameters, design parameters and formation permeability thresholds of salt caverns for ensuring helium storage safety while maintaining stable cavern operations. The threshold permeability of the target salt formations should be approximately 1×10-18m2to ensure tightness. The minimum and maximum operating pressure are recommended to be 10 MPa and 18 MPa respectively for 50 years of this helium storage. The salt pillar width should be 300 m, and the salt roof thickness should be 40 m.

Given the increasingly notable segmentation of underground space by existing subway tunnels, it is difficult to effectively and adequately develop and utilize underground space in busy parts of a city. This study presents a combined construction technology that has been developed for use in underground spaces; it includes a deformation buffer layer, a special grouting technique, jump excavation by compartment, back-pressure portal frame technology, a reinforcement technique, and the technology of a steel portioning drum or plate. These technologies have been successfully used in practical engineering. The combined construction technology presented in this paper provides a new method of solving key technical problems in underground spaces in effectively used cross-subway tunnels. As this technology has achieved significant economic and social benefits, it has valuable future applications.

Rectangular tunnels are often encountered in geotechnical engineering. To clarify the mechanical mechanism of the stresses around tunnels, this study presents new analytical approximant solutions for evaluating stresses around tunnels under arbitrary stress boundary conditions. The solutions consist of two parts: one is the solution for a half-plane before excavation, and the other is the solution for a half-plane with tunnels. The second part can be further decomposed into solutions of a half-plane without tunnels subjected to virtual tractions along the ground surface and solutions of an infinite plane with tunnels loaded by virtual tractions along tunnel boundaries. An efficient iterative procedure is proposed for determining the two sets of unknown virtual tractions, which are transformed into equivalent concentrated forces to simplify the computational process. The solutions agree very well with the results obtained by the finite element method. A parametric study is finally performed to investigate the influences of the tunnel buried depth, the tunnel shape, and surcharge loads on the stresses along the ground and around tunnels. The new proposed solutions potentially provide a potential alternative approach for preliminary designs of future rectangular tunnels.

The construction of salt caverns for energy storage is of strategic significance, but the operation of underground gas storages in salt formations will cause surface deformation. The research and analysis of surface deformation is an important part of the stability evaluation of salt caverns for gas storage. From the perspective of classical mechanics theory, the analytical solution of surface deformation above salt caverns for gas storage is deduced. The surface displacement caused by the contraction of a salt cavern is regarded as the boundary displacement caused by the surface force acting on a spherical cavern in a semi-infinite space. The equivalent conversion of load form is carried out based on the mirror principle. The vertical subsidence and horizontal displacement of the surface of the elastic semi-infinite space is obtained. According to the elastic-viscoelastic correspondence principle, the viscoelastic solution of the surface displacement of the semi-infinite body, regarded as Maxwell body, can be obtained. A numerical model of a salt cavern for gas storage is established based on the engineering practice. The results of the analytical solution and the numerical simulation are compared and analyzed to verify the accuracy of the analytical solution. The analytical solution was applied to predict the surface displacement above a group of caverns, and the influence of the layout of salt caverns and cavern center spacing on the surface displacement is analyzed. The research results show that the regular triangular layout is slightly better than the square layout. The larger the cavern center spacing, the smaller the maximum surface subsidence. The proposed theoretical prediction model can provide a theoretical basis for controlling surface deformation for the construction of gas storage caverns.

With the rapid development of rail transit, effectively developing urban underground space (UUS) in the metro zone has become an important approach to expanding urban space. However, UUS is currently facing problems, such as an uneven distribution or even loss of vitality, which restricts the utilization efficiency of the space. Thus, we established a UUS environmental assessment system based on the “comfort-aesthetic-function-traffic-structure” using space syntax, instrumental measurement, and questionnaire surveys. By constructing a partial-least-square structural equation model, the internal relationships between the UUS environment and corresponding space vitality and space perception under different study areas, namely the underground transportation-oriented space (transportation space for short) and the underground commercial-oriented space (commercial space for short), were studied in detail throughout the working day. Results indicate the following: (1) the UUS in the metro zone environment influences spatial vitality. The vitality distribution of transportation space is significantly affected by the spatial traffic and structure. The vitality distribution of commercial space is significantly affected by the spatial function and traffic. (2) The environment of UUSs in the metro zone influences users's perception. The perception of transportation space is significantly affected by aesthetics and comfort. The perception of commercial space is significantly affected by aesthetic, comfort, and spatial functions. (3) The user's perception affects vitality, and the effect is more significant in commercial space. This study provides an in-depth understanding of the relationship between the complex environment and its spatial vitality as well as the spatial perception of the UUS in metro zones. Our research results provide a novel approach and theoretical basis for the development and application of UUS vitality in various cities.

A multi-step horizontal salt cavern (MSHSC) for energy storage has been drawing more attention, using retractable water-injection tubes to mine larger storage spaces between two boreholes. The retract distance per step best determines the shape of the cavern roof, and thus has an important influence on the stability of MSHSCs. This paper discusses the impact of the step distance on the stability and economy of MSHSCs. The geometry of MSHSCs with different step distances is obtained using our previously developed solution mining model. Geo-mechanical models are developed based on the geometry and the geo-conditions of Jintan salt mine in China. Then a series of static creep analyses are performed using FLAC3D software. Results show that smaller step distances mean higher stability risks during long-term operation. As the step distance is reduced, both the volume shrinkage and plastic zone volume increase. In the displacement contours after 30 years of operation, the large displacement zone increases significantly with decreasing step distance. However, the cavern volume and expected revenue increase with decreasing step distance, contrary to the stability parameters. Economic analysis with integrated stability considerations is conducted to give a balanced step distance. Volume shrinkage is considered in the calculation of effective cavern volume. Plastic zone volume is reflected in the space cost of MSHSCs, since it influences the thickness of the cavern top plate and the pillar width between adjacent caverns. Further, a comprehensive indicator of economic cost/expected revenue per unit volume of rock salt versus time is proposed, calculated, and compared. According to the comparison results, a medium step distance of 100 m or 125 m is recommended for the design of MSHSCs in a given salt layer, with the stability and economic considerations best balanced.

In this study, a refined numerical model for segmental lining of a shield tunnel, which contains detailed models of reinforcement and connecting bolts, is established using finite element software. The model is first validated by the results from a full-scale model test. Then, based on the load-structure method, this numerical model is adopted to investigate the internal force distribution and the transverse deformation characteristics of the shield tunnel when it is subject to local soil loosening. The influence of loosening position, loosening range, and loosening extent on the mechanical response is extensively studied through comprehensive numerical analyses. The results show that the main influence of local soil loosening on the ring is to disturb the force balance and change the constraint conditions, thus changing the deformation pattern and force state. After the loosening occurs, the bending moment of the ring in the loosening range increases and the axial force decreases. The vertical convergence of the ring is the largest and the equivalent stiffness of the ring is the smallest when the local soil loosened at the haunch and the loosening range α is 90°. The vertical convergence of the ring increases with increasing of the loosening extent, and the equivalent stiffness decreases linearly with increasing of the loosening extent. The results can enhance our understanding of mechanical behaviors of segmental lining associated soil loosening, and will show a possible way for detecting soil loosening based on the measured deformation and internal forces.