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Soil-fluid retention (SFR) is considered a fundamental unsaturated property with a wide application from transient flow analysis, and strength prediction to constitutive modeling. Previous research has led to a consensus that soil microstructure can significantly affect retention properties. Furthermore, the soil microstructure is subject to changes due to variations in the sampling method and pore fluid chemistry. Therefore, this study aims to explore the influence of multiple factors, including sample preparation technique, dissolved salt concentration and cation type, on soil-fluid retention and volumetric behavior in a systematic manner. The results of tests conducted by employing the axis translation and filter paper methods are interpreted in detail based on some complementary scanning electron microscopy and micro-CT scan experiments. Furthermore, the repeatability of the test results is validated through some control tests. The results reveal a higher retention capacity for reconstituted samples compared with the compacted ones independent of the solute concentration. In contrast, both the SFR and shrinkage are suppressed by the addition of sodium chloride to the pore fluid independent of the sample preparation method. It is also found that the SFR capability of potassium cation is less than that of sodium cation at the same concentration. The SFRs are quantified and compared in terms of air entry/air expulsion suction, hydraulic hysteresis and desorption/adsorption rates. The interpretation of the results in light of the diffuse double-layer theory is supported by microstructural observation and provides insights into the SFR of lean clays exposed to saline environments with different types of salt species. [ABSTRACT FROM AUTHOR]

In projects such as highway bridges and offshore wind farms, understanding the kinematics of soil layers and their displacement is important for accurately predicting the behavior of caissons and monopiles under lateral loads. To better predict the distribution of soil deformation around the foundations, this paper presents an extensive usage of the energy-based variational method in laterally loaded deep foundations (caissons or monopiles) with very large diameters. By adding an assumption of soil deformation in multilayered soils, the displacement distribution around the foundations can be better described. The responses of deep foundations were obtained by minimizing the potential energy and virtual work of the foundation-soil system. After that, static lateral loading tests on two caissons with the same embedment depth of 36 m and the same diameter of 6 m were performed, and the displacement field in soils and the deflection profiles of the caissons were measured. Results show that the lateral displacement and the decay distribution fields calculated from the theory in this paper agree with the measured data from the static loading tests and the corresponding finite differential method (FDM) results. At last, a series of case studies performed by MATLAB and FDM analyses were also conducted to study the influence of uz on the response of foundations, as well as the influence of foundation parameters and soil modulus on the value of ϕz. [ABSTRACT FROM AUTHOR]

This paper presents a versatile interface direct shear test apparatus developed for systematically investigating the shear behaviour of geotechnical interfaces. The apparatus can support the testing of several particle–continuum as well as continuum–continuum interfaces and can also accommodate different configurations of testing, viz. conventional and fixed-box interface shear testing, by a simple rearrangement of the different components. The apparatus facilitates the visualisation and measurement of the deformation of geotextiles under pull-out loading, particle kinematics and the acoustic behaviour of soil–continuum interfaces by accommodating advanced deformation-measurement devices like digital cameras for digital image correlation (DIC) and sensors for acoustic emission (AE). The paper describes the design of all the components of the apparatus and the results of the interface shear tests of different particle–continuum and continuum–continuum interfaces. The repeatability of the test results is verified through multiple tests on the same interface. Results of the interface shear tests indicating the sensitivity of the apparatus for the different modes of testing are also presented. The provisions such as the shear box with a transparent side wall, the moving platform with an interchangeable transparent bottom and the capability to accommodate AE studies facilitated a detailed understanding of various types of interfaces. The DIC results provided insights into the shear zone formation at the dilative interfaces and the deformation of a geotextile under a pull-out load. The AE studies provided a new perspective on the response of particle–continuum interfaces. [ABSTRACT FROM AUTHOR]

Over 90% of Australia's surfaced roads are unbound pavements with sprayed seals. However, achieving complete impermeability with these seals is challenging, leading to some moisture exchange between pavement layers and the environment. As moisture fluctuations influenced by climatic factors significantly affect the structural performance of particularly unbound granular layers, there is a pressing need to enhance Australian pavement design by incorporating climatic effects to meet better pavement performance. Hence, the current study numerically evaluates the degree of moisture saturation ( S r) variations of pavement layers under different Australian climates. This paper reveals how ambient climate impacts the moisture variations of pavement layers based on the results of 126 numerical simulations performed. Results indicated that the annual rainfall is not an appropriate parameter to decide the service moisture condition of the UGM layer, but the ratio between annual rainfall and annual pan evaporation ( P PE ) combined with the saturated permeability of the seal ( K s) is found to be a better indicator. More importantly, this study develops a novel empirical model to predict the service moisture condition of the UGM layers aiming to advance the current Australian pavement design guide. Furthermore, a correlation between pavement moisture and a widely used climatic index, Thornthwaite Moisture Index (TMI ) is presented in this study. Furthermore, this paper proposes a novel approach to integrating climatic factors into the current Australian pavement design of unbound pavements with thin seals. This study enhances understanding of the complex relationship between climate and pavement moisture by taking a multi-dimensional approach. [ABSTRACT FROM AUTHOR]

Soil being a naturally formed material, the prediction and analysis of anchor uplift capacity incorporating the inherent variabilities in the soil properties is essential. This paper presents a probabilistic analysis of horizontal strip anchors in spatially varying soil using the multivariate adaptive regression splines (MARS) as a prediction model. The use of MARS in spatially varying soils is proposed, and its advantage over the conventional expensive Monte Carlo simulations is reported in this paper. The soil cohesion and friction angle have been modeled as lognormal random fields, and the influence of the spatially distributed soil properties on the anchor uplift capacity is assessed in the current study. Furthermore, a comparison between the deterministic and reliability-based design methodologies is presented, and their implications on the design of foundation are discussed. The results indicate that the code-specified factor of safety (FOS) value of 1.5 does not fulfill the target probability of failure ( P f ) values recommended in probabilistic design. A minimum FOS = 2 is required to satisfy the P f ≤ 0.001 criteria, which is usually recommended for the design of foundations. [ABSTRACT FROM AUTHOR]

Rockburst (equal to strainburst in this paper), a typical catastrophic geohazard, poses a major threat to the safety of employees and infrastructure in deep rock engineering. Fortunately, accidents can be reduced or eliminated by predicting rockburst accurately, and the sound signals generated during rockburst are useful information for the prediction. In this paper, a two-step method for predicting rockburst using sound signals was proposed, which mainly includes two steps. Step 1: the wavelet scattering network is first used to extract the features of sound signals corresponding to the macrocracking phenomena (e.g. particles ejecting, slabbing, and fragments ejecting) during rockburst, and then these phenomena are classified by the integrated usage of the k-nearest neighbour (KNN) classification algorithm and voting. Finally, according to the nature of these phenomena, which occur sequentially before rockburst, the rockburst development stages can be recognized by the classification results. Step 2: the possibility of rockburst occurrence is determined by identifying the rockburst precursors in the evolutionary characteristics of the sound signals, such as which the Mel-frequency cepstral coefficient rate and energy rate both decrease sharply and the amplitude difference activity exhibits a distinct change from a significant decrease stage to a low-level stage for a duration and then to a dramatic increase stage. Furthermore, case studies show that the two-step method accurately recognizes the rockburst development stages and determines the possibility of rockburst occurrence in a multilevel and progressive way. Therefore, it is feasible to predict rockburst under deep rock engineering. [ABSTRACT FROM AUTHOR]

Rock cores retrieved from deep rock masses may be permanently damaged on account of the stress release occurring during the drilling process. The quantification of core damage is important for accurate evaluation of the rock strength at depth. This paper presents a laboratory simulation of the core drilling process under high in situ stress conditions. The study aims to quantitatively evaluate sampling damage from both macro and micro perspectives using mechanics tests and microscopic observations. The observed decrease in core specimen integrity with increasing sampling confining pressure is in line with practical engineering findings, thus validating the experimental method utilized in this paper. The test results show that the porosity of the core increases and P-wave velocity decreases as the sampling confining pressure increases, which indicates that the structure of the core is significantly changed by the sampling damage. The stress–strain curve exhibited increased nonlinearity and acoustic emission events at the initial stage of loading, indicating an increase in sampling damage with rising sampling pressure. The uniaxial compressive strength and Brazilian tensile strength of the cores drilled at 40 MPa are reduced by about 21% and 28%, respectively, compared to the undamaged rock, indicating that the effect of core damage on the rock strength cannot be ignored. Microstructural observations further reveal that the crack density of the cores drilled at 40 MPa is four times higher than that of the intact rock. Additionally, the development of microcracks shows obvious directionality, with microcracks preferentially developing perpendicular to the drilling direction. Stress path analysis of the cores indicates that the sampling damage may be primarily caused by tensile stresses. This study provides a better understanding of the mechanisms underlying sampling damage and core disking. [ABSTRACT FROM AUTHOR]

Historically, seepage failure has always been the primary cause of failures and accidents of earth dams after overtopping. However, research on the reliability of earth dams against seepage failure remains scarce. Meanwhile, the influence of the uncertainty of the soil–water characteristic curve (SWCC) on the reliability of dams against seepage failure is still unclear. In this study, the van Genuchten–Mualem model is used to describe SWCC, and its uncertainty is characterized by discretizing SWCC fitting parameters a and n into cross-correlation lognormal random fields. Based on the random finite element method, this paper systematically studies the influence of the heterogeneity, autocorrelation, and cross-correlation of hydraulic parameters Ks, a, and n on the reliability of a dam against seepage failure. Sensitivity analysis indicates that Ks and autocorrelation distance crucially affect the reliability of the dam against seepage failure. Additionally, this paper also emphasizes and proves that considering the correlation between the hydraulic conductivity field and the critical hydraulic gradient field has a significant impact on evaluating the reliability of earth dams against seepage failure. However, this subtle but important potential characteristic has not been paid attention to in previous studies. [ABSTRACT FROM AUTHOR]

In the tunneling driven by large diameter slurry shield (SS), the working face is at risk of passive failure when the overburden is insufficient or the support pressure is excessive. This paper examines the partial progressive failure of the tunnel face by developing a hybrid mechanism which incorporates the failure zone into the complex movement. The failure blocks include a translational and a rotational one, and a spatial discretization technique is used to construct the velocity discontinuity between the blocks to ensure compatibility. To identify the failure extent of the face, the incipient failure origination is introduced. A kinematic approach is utilized to determine the upper bound solution for support pressure. By optimizing, the minimum support pressure is searched and the failure mechanism is gained in response. Additionally, this study performs the parametric analysis to discuss the influences of the factors such as frictional angle, cohesion, overburden depth, ground surface surcharge, and slurry weight on incipient failure origination as well as support pressure. The numerical analysis included in the framework of finite element limit analysis is carried out for verification. This paper ends with the validation of the current solution by re-examining the previous case. [ABSTRACT FROM AUTHOR]

The paper presents a rigorous analytical approach to predicting the load–settlement behavior of axially loaded piles embedded in sandy soils, adopting the advanced SANISAND model. The problem of the soil state around the pile during loading is formulated as a system of first-order ordinary differential equations, which can be solved as an initial value problem. The derived load–settlement (t–z) curve is then implemented into the load-transfer method to determine the pile's load–settlement behavior in sands and the deformation mechanism of the soil around the pile during axial loading. To verify the proposed analytical approach, a FEM simulation is performed with a user-defined subroutine, demonstrating its capacity to capture the dilatancy behavior of sands as the pile moves downwards. Additionally, a parametric analysis is conducted to assess the influence of the initial void ratio on the stress–strain relationship of the sandy soil around the pile during the loading process. The proposed analytical approach is also compared with a well-established finite-element model and a centrifuge test. The results indicate that the present approach can well predict the elastoplastic load–settlement response of the pile and reflect important phenomena observed from pile tests. [ABSTRACT FROM AUTHOR]

Although the cardioid-shaped traffic loading path can be implemented using hollow cylinder apparatus, the preparation of inherently anisotropic sand with different bedding plane angles could be difficult. Consequently, the macro-scale response of inherently anisotropic sand under traffic loading has not been adequately investigated to reveal the underlying microscopic mechanism. In this paper, elongated particles with various aspect ratios were used to approximate the natural sand particles, and uniform three-dimensional specimens with different bedding plane angles were generated using discrete element method based on a modified version of under-compaction method. The cardioid-shaped loading path was implemented using an advanced servomechanism that can apply arbitrary loading paths. The internal structure of specimen was quantified through a contact-normal-based fabric tensor, which could describe the load-bearing structure of granular specimens. The interplay between the macro-scale observations and the fabric evolutions was elucidated. The influences of both bedding plane angle and aspect ratio on the accumulations of volumetric strain and generalized shear strain are not monotonic, with the largest strains at the bedding plane angle of 45° and the aspect ratio of 1.4. Results provide useful insights into the underlying mechanism of the deformation behavior of inherently anisotropic granular materials under traffic loading. [ABSTRACT FROM AUTHOR]

Soil setup has a significant contribution to the performance of jacked piles in natural clays with structure characteristics. In this paper, a series of model pile tests are conducted to investigate the pile setup in structured clays, focusing on the influence of soil structure on time-dependent pile response. Three artificially structured clays are prepared as model soils to avoid the sampling challenge of undisturbed clays. The model tests are capable of modeling pile response through installation, equalization, and loading, and hence the initial structure and stress-induced structure degradation of clays, as well as the following thixotropic effect and reconsolidation of disturbed clays, can be adequately incorporated. Meanwhile, the behaviors of the piles and pile–soil interface are constantly monitored by the measurement system during and after pile installation. The results demonstrate that by increasing the cement content of structured clays from 0 to 4%, the penetration resistance is almost doubled, and the pore water pressure (PWP) and radial stress of the pile–soil interface located 20 cm from the pile toe increase by 1.27 and 1.38 times, respectively. A higher cement content in model soils leads to a quicker dissipation of excess pore water pressure (EPWP) due to the presence of a larger void structure and a smaller zone of damage caused by pile driving in structured clays. The growth rate of the ultimate bearing capacity of piles increases sharply with the cement content. The normal stress of the interface first decreases slightly and then grows dramatically with the mobilized shear stress during static loading tests. [ABSTRACT FROM AUTHOR]

In northern regions, the long-term serviceability of infrastructure founded on frozen ground is adversely affected by climate warming. Rates of change in temperature, which are not identical spatially and temporally, can remarkably dictate the magnitude and evolution of permafrost degradation. Investigating such impacts requires a non-isothermal rate-dependent geomechanical constitutive model for ice-contained geomaterials. In this paper, a critical-state thermo-elasto-viscoplastic (TEVP) constitutive model is developed for modeling time- and temperature-dependent behavior of frozen soils using the concepts of thermo-elasticity and thermo-viscoplasticity. Solid phase stress (defined as the excess of total stress over fluid pressure), in addition to the cryogenic suction, are considered as the two independent stress state variables to establish the model. The proposed model is able to satisfactorily capture the rate-dependent behavior of frozen soils observed in the experimental tests reported in the literature. [ABSTRACT FROM AUTHOR]

The principal stress rotation is often studied by considering the uniaxial rotation of principal stress. In this paper, the stress path on biaxial rotation of principal stresses is considered. The hollow cylindrical apparatus was used to achieve the principal stress rotation around the second stress principal axis. A novel specimen preparation device was developed, which was used to achieve the principal stress rotation around the third principal stress axis. The influence of principal stress biaxial rotation on the dense sand behavior was investigated under undrained conditions. The results revealed that the deformation properties of dense sand were closely associated with the stress direction dependence of the soil. An increase in the inherent anisotropy changed the slope of the effective stress path and the phase transition pore pressure, influenced the shear dilatancy and shear shrinkage characteristic of sand. Likewise, an increase in the stress-induced anisotropy changed the shape of the effective stress path, the development of pore pressure, the shear dilatancy and shear shrinkage characteristic of sand. More importantly, deformation properties of sand were affected by the coupling of the two factors, which was predominantly controlled by stress-induced anisotropy. [ABSTRACT FROM AUTHOR]

Examination of the microstructure and mineral composition of Callovo-Oxfordian (COx) claystone revealed the presence of clay matrix intruded by a large amount of mineral inclusions such as carbonate and quartz. This claystone can be damaged when wetted/dried due to the swelling/shrinkage of clay matrix, or when subjected to mechanical loading due to the loss of bonds formed among mineral grains. The damage of COx claystone was evidenced in the literature by analysing its pore size distribution curves after wetting/drying and mechanical loading, obtained from the mercury intrusion porosimetry (MIP) tests. In this paper, a damage coefficient accounting for the physics of damage (i.e. generation of cracks) was adopted, corresponding to the proportion of cracks in the total porosity. This coefficient enables the description of the effect of cracks on the overall mechanical behaviour of COx claystone. Based on the MIP results, the evolution of the damage coefficient with the effective stress and plastic volumetric strain was identified for COx claystone, during both the hydration and the oedometer compression processes. [ABSTRACT FROM AUTHOR]

Biological-formed fossilized diatom sediments have unique physical, electrical, and mechanical properties due to the shape, internal open porosity, and brittleness of the individual particles. The presence of diatoms strongly influences the overall behavior of soils. However, engineers and researchers find this influence challenging to quantify because measuring fossilized diatom content is elusive. This paper uses simple physical, electromagnetic, and mechanical engineering measurements to characterize the response of the artificial soils prepared with known amounts of fossilized diatoms under different pore-chemistry fluid and mechanical environments. Soils with high fossilized diatom content tend to retain high quantities of water even under high NaCl-concentration pore fluid. This response results from the internal porosity and is not a function of electrical forces on the particle surface. Furthermore, internal porosity governs electrical and mechanical properties under different pore fluid environments. Despite having elevated Liquid Limits, soils with high fossilized diatoms content do not deform while drying and changing pore fluid salt concentration. However, fossilized diatoms are brittle and offer high compressibility and low particle crushing stress (around 2–4 MPa). Our results show that simple physical and index tests can help assess the effect of fossilized diatoms' in soils, and provide a framework to predict the engineering properties of natural soils containing a wide range of fossilized diatoms even when diatom content cannot be precisely measured. [ABSTRACT FROM AUTHOR]

Two centrifuge shaking table tests were carried out to investigate the seismic response of a subway station structure in liquefiable interlayer site. For the centrifuge shaking table test of underground structures, there is no precedent for the model preparation of the liquefiable interlayer site for reference. In the paper, some model making techniques were proposed for the liquefiable interlayer site, including the preparation of liquefiable interlayer site (clay consolidation, sand saturation and assembly of interlayer site), structural waterproof treatment, releasing initial pore pressure in the sand layer during centrifugal loading. The model tests obtained ideal results, which achieved the experimental goal of studying the seismic response of subway station structure in liquefiable interlayer site. The research conclusions are as follows. The vertical inertia effect of the overlying soil could significantly increase the axial pressure on the columns of an underground frame structure and then, reduce its horizontal deformation capacity. The columns are the weak components of a subway station structure, which are easy to be damaged under earthquake. The ends of a column are the vulnerable parts and were prone to damage. The classification standard of the limits of relative displacement ratio for underground structure proposed by Du et al. (Du et al. in Earthq Eng Struct Dyn 50:655–672, 2021) is reliable and can provide a method for earthquake damage response evaluation of an underground structure. [ABSTRACT FROM AUTHOR]

This paper presents the results of field tests performed to investigate the bearing capacity of Drilling with a prestressed concrete (DPC) pipe pile under different end sealing and side grouting conditions. The High Strain Dynamic Testing (HSDT) was conducted to evaluate the bearing characteristics of full-scale DPC pipe piles. Moreover, base resistance theoretical formula considering end sealing effect and shaft resistance theoretical formula considering side grouting effect are presented. The theoretical results were compared with the recommended values of specification for traditional pipe piles and tested values to demonstrate the rationality of theoretical formulas and the superiority of end sealing and side grouting. Furthermore, the effects of sediment under the sealing concrete and grouting conditions on the bearing capacity of a single pile were discussed in detail to reveal the influencing mechanisms of end sealing and side grouting. The result showed that the presented base resistance theoretical formulas can estimate the effect of end sealing on the ultimate base resistance of DPC pipe piles with good accuracy. For 1 m pipe piles, end sealing increases the base resistance by up to 103.5% at most compared to unsealing pipe piles; total shaft resistance of piles with double or multi-pipe grouting is more than 37% higher than the recommended maximum value of traditional pipe piles in the pile foundation specification. In addition, the base resistance was significantly affected by the sediment thickness under the sealing concrete. The hole wall time-dependent deformation caused by drilling and unloading affected the side grouting significantly. [ABSTRACT FROM AUTHOR]

Rainfall-induced shallow landslides often turn into flows. These phenomena occur worldwide and pose severe hazard to infrastructure and human lives on mountainous areas. Risk assessment, and the design of mitigation measures, can both be informed by back-analysis of previous events. However, shallow instabilities are frequently spread over a large area, with the generated flows occurring in sequences, or surges. Conventionally, back-analysis exercises tackle the problem by simulating runout as a single event, with all surges happening simultaneously. This simplification has repercussions that have not been explored in the literature so far, and whose impact in hazard assessment practice is unclear. Therefore, a novel time-resolving procedure is proposed in this paper, which can for the first time be applied to resolve instability sequences of arbitrary duration. The methodology discretizes the event, detecting instabilities at equally spaced time intervals as a function of rainfall. Thanks to this, the post-failure behaviour of each surge can be tracked by a runout model, with a separate simulation performed every time a new instability is detected. The methodology robustness is tested on two documented case studies. The results reveal that, under some conditions, the time-resolving procedure can lead to significantly different results in terms of runout path, flooded area, and flow heights. This leads to criticism on how back-analysis is conventionally applied, prompting for a review of historical cases. [ABSTRACT FROM AUTHOR]

This paper investigates the response of finned piles in sand subjected to static lateral load through laboratory tests and full-scale field tests. Firstly, model tests were carried out on free headed single piles of different shaft diameters with and without fins in sand to explore the performance of the piles under lateral loading. The results obtained from monotonic loading tests on three series of piles of three different combination of fins and pile shaft diameters were presented. The effect of fins on improving the stiffness and ultimate lateral capacity of the piles was discussed. An equivalent diameter was proposed for a finned pile, which enabled the experimental results to be back calculated using an available elasto-plastic solution for laterally loaded piles in sand. Secondly, field tests were conducted on laterally loaded Starfin screw piles in loose to medium dense sand. The proposed approach was then used for the analysis of the measured response of Starfin screw piles and further validated against measured test results from fully instrumented finned piles in overconsolidated dense sand. The results show that the proposed equivalent diameter and approach for the analysis of finned piles provided the most satisfactory match to the measured data, ranging from the initial elastic state to the ultimate limit state. [ABSTRACT FROM AUTHOR]

This paper describes a new simple and inexpensive method for accurately measuring the three-dimensional deformation of soil specimens during triaxial tests. The method incorporates a cost-effective image capture system that can be applied to any triaxial apparatus as well as an automated post-image analysis approach for processing the images acquired during triaxial tests. Image capture is performed using multiple low-cost Raspberry Pi cameras and accessories placed outside the triaxial chamber. The system employs particle image velocimetry, camera calibration and stereophotogrammetry to determine the spatial variation in axial and radial sample strains as samples are loaded. It is demonstrated that axial and radial displacements can be measured with an accuracy of 1–2 μm, respectively, and it is verified by comparison with data from triaxial tests on sand samples that the full nonlinear stiffness–strain degradation of soil samples from fully elastic conditions can be determined without the need for any additional sensors. [ABSTRACT FROM AUTHOR]

The effects of interstitial fluid on the behaviors of two approaching particles play an important role in the rheology of granular–fluid mixtures. In this paper, an Euler–Lagrange model is developed to study the effects of interstitial fluid on the frictional behaviors of particle contacts which is resolved by the discrete element method (DEM). A formulation of the friction coefficient for immersed particle contacts, involving the effects of interstitial fluid viscosity and pressure, is proposed based on the results of a laboratory experiment. The enhancement effect of the porosity of granular materials on the inter-particle friction coefficient is taken into account. For the inter-particle normal contact force, an existing empirical formula of the coefficient of restitution for immersed particle collisions is adopted. The model is verified in the laboratory experiment of collisions between a single particle and a solid wall in both air and water. The model is further validated by simulating subaerial granular landslides into water down an inclined slope. Without the effects of interstitial fluid on the inter-particle friction coefficient, the propagation velocity of subaerial landslides intruding into the water and the generated tsunami wave is underestimated. Moreover, if the enhancement effect of the landslide porosity is excluded, the propagation velocity of the landslide and the generated wave are overestimated. [ABSTRACT FROM AUTHOR]

Soil thixotropy plays an important role in many engineering practices, which recently has been drawn an increasing attention by many researchers. In this paper, an experimental investigation on the thixotropy of deepwater marine clays in the South China Sea was carried out. The thixotropy-induced changes of undrained shear strength were measured by fall cone method, and the microscale evolution of soil structure, particularly the change of various types of water, was observed and quantified via employing scanning electron microscopy and thermogravimetric analysis, respectively. The test results show that the thixotropy strength ratios of all deep-sea clays increase quickly at the early stage (before about 10 days), then followed by a gradually lower increasing rate with prolonged time. The microstructural evolution of clay during thixotropic hardening is characterized by the transformation from a dispersed structure with parallel-arranged particles to a well flocculated one. The different types of water and their changes of mass fraction with thixotropic time could be well classified and quantitatively measured by thermogravimetric analysis, in which both the weakly and strongly bound water contents decrease, with the corresponding increase in the free water fraction. The thixotropic mechanism was then revealed from the perspective of the microstructural evolution and the adjustment of the thickness of bound water. The recovery of strength is majorly attributed to the forming and strengthening of inter-particle bonds or contacts and the adjustment of bound water layer. This research could help to provide a deeper insight into the inner reason of soil thixotropy. [ABSTRACT FROM AUTHOR]

A stress-dependent porosity and permeability model is proposed to predict the microstructure evolution and the physical properties and mechanical behavior of deformable hydrate-bearing sediments (HBS) with various hydrate growth patterns under engineering disturbance. First, according to Hertzian contact theory and the proposed mesoelastic–plastic damage model (Gurson-DP model), the correction formula of the pore size under the influence of the effective confining pressure and the overburden pressure is given, and the stress-dependent porosity model is derived. Second, the fractal capillary bundle model is used to describe the stress-dependent permeability of HBS with different hydrate saturations considering the grain-cementing hydrate and the universal-growth hydrate. Finally, the proportions of hydrates with various growth patterns, such as pore filling (PF), wall coating (WC), and grain cementing (GC), are determined based on the equivalent flow assumption to reasonably evaluate the hydrate growth habit in HBS. This paper comprehensively studies the stress-dependent porosity and permeability models of deformable HBS and thus, provides a theoretical basis for quantitative evaluation and prediction of the physical properties (such as porosity and permeability) and mechanical behavior of HBS. [ABSTRACT FROM AUTHOR]

Boreholes excavated in porous rocks exhibit a variety of inelastic deformation patterns. This paper investigates how nucleation, propagation, and coalescence of compaction zones, including those resulting from compaction localization, affect the mechanics of excavated boreholes in high-porosity rock formations. For this purpose, a recently developed controllability framework able to differentiate among multiple modes of compaction banding is used to guide the interpretation of numerical simulations for boreholes excavated in porous rock. The goal is to explain the link between heterogeneous deformation patterns forming around the excavated zone and in situ stress conditions. To carry out the analyses, the theory is combined with a strain-hardening constitutive law calibrated against Berea sandstone laboratory evidence, thus capturing the stress-dependence of both homogeneous and heterogeneous compaction. The resulting simulations of idealized boreholes show that the inelastic compaction around the excavated zone depends dramatically on the far-field stress state, leading to transitions from isotropic-distributed plastic deformation modes under in-plane isotropic stress states, to dog-ear-, slot-, and/or butterfly-shaped inelasticity in the presence of strongly anisotropic in situ stress. It was found that each of these scenarios can be explained in terms of controllability indices computed at locations exhibiting inelastic response, thus establishing a link between the computed modes of global borehole deformation and multiple types of compaction localization processes (e.g., compactive shear bands, shear-enhanced compaction bands, and pure compaction bands). [ABSTRACT FROM AUTHOR]

It is essential to understand the in situ stresses underground for engineering design and ground stability control in mining, geotechnical and petroleum engineering. Determination of the complete 3D stresses is particularly difficult due to the complex conditions underground. Overcoring and some other methods have been used in the past. They are either very expensive to implement or are based on some pre-assumptions. A recently developed alternative method is based on differential-direction drilling (D3 method). By this method, the complete 3D in situ stresses can be estimated through measurements of diametrical borehole deformation in multiple non-parallel planes. The D3 method has overcome the theoretical hurdle of using 2D data to find a 3D solution to the in situ stresses. It has five mathematical models to fit the anticipated field conditions. This paper, as a follow-up, considers practical applications of the D3 method and analyzes a few key factors which may affect its application. The minimum space angle between measurement planes and the minimum number of measurement directions in each plane (or around a borehole) are determined. The effects of measurement errors and selection of a proper model for a specific site condition are also analyzed. A statistical approach is applied to help detect erroneous measurement data and search for the best-fit solution. Practical drilling patterns in mining and petroleum engineering are also suggested. [ABSTRACT FROM AUTHOR]

Slurry tailings storage in large impoundments has been largely used worldwide for a long time, as their cost is very competitive. However, recent disasters have brought to light the need to better comprehend the mechanics of the materials stored and to search for disposal alternatives to overcome the drawbacks. One possibility is the filtered tailings disposal (dry stacking) which requires a better understanding of the material's response in a dewatered (through filtration) and compacted condition. This paper compares two tailings from the same beneficiation (treatment) plant with different gradings and mineralogy, related to the beneficial processes they undergo. A series of triaxial tests comprising isotropic compression without shearing specimens, as well as isotropic compression followed by drained (CID) and undrained (CIU) shearing, and K-compression followed by undrained (CKU) shearing specimens were conducted over a range of confining pressures and initial compaction degrees. The experimental program allowed the evaluation of convergence for normal compression lines (NCLs) and the analysis under the light of critical state soil mechanics for the stress–strain response of the tested materials. The research outcomes show that changes in iron ore tailings gradings due to different production processes and the use of different compaction degrees had an influence on its behavior (compression and shearing) at lower stress levels, while at higher stresses levels, this difference is erased and there is a convergence for unique and parallels NCL and CSL on ν–ln p′ plane with a spacing of 2.71. On the p′–q plane both tailings showed a unique and similar CSL. [ABSTRACT FROM AUTHOR]

In this paper, the evolution of nanoscale pores, covering inter-particle pores and inter-layer pores, in illite-dominant clay during consolidation is monitored using small angle X-ray scattering (SAXS) and nitrogen gas adsorption (N2GA) techniques. No obvious change observed in the characteristic peaks of SAXS intensity curves during consolidation suggests that the intra-particle structure of the clay, including interlayer spacings, is not affected by mechanical loading, at least up to 4 MPa. The N2GA test results show that the volume of inter-particle pores inside the aggregates does decrease gradually as the compression proceeds, which is accompanied by a gradual reduction in specific surface area, probably due to the rearrangement of the particles composing the aggregates. The inter-particle pores are compressed as a whole during consolidation instead of the progressive collapse in an ordered manner, from the larger to the smaller. By comparing the pore-size distributions of illite-dominant clay obtained by MIP (mercury intrusion porosimetry) and N2GA techniques, it is found that the shapes of the two distributions in the common measurement range are obviously not matched, essentially due to the sequential nature of the drying and wetting processes. While filling the research gap in the evolution of intra-aggregate pores during consolidation, this study also shows that the N2GA technique and SAXS measurement used in conjunction with each other appear as a powerful approach for clay nano-pores identification. [ABSTRACT FROM AUTHOR]

This paper reevaluated the disadvantages of existing observational methods using both theoretical and laboratory consolidation settlement–time (S–t) relationships. Two observational methods that account for the effect of sampling range were developed by using the Taylor model as a substitute for Terzaghi's solution. The significance of the sampling range effect in predicting the end of consolidation settlement (S100) and the consolidation coefficient (cv) was verified through application to the above S–t data. The further application of the proposed methods to three case records with some prerequisites produced slightly higher S100 and lower cv values compared with two routine methods and indicated that the back-analyzed S–t curves correlated excellently with the in situ monitored curves. The latter finding may support the hypothesis that the in situ consolidation settlement curves are the family of laboratory consolidation settlement curves. In this case, consolidation-based prediction was applicable to such in situ consolidation settlement, thereby suggesting that both in situ and laboratory consolidation settlement curves behave with an identical cv value as verified in a homogeneous clay deposit. The above approach was also confirmed to be applicable to prolonged yet incompletely measured settlement data. [ABSTRACT FROM AUTHOR]

The mechanism of flow liquefaction in granular soils under drained conditions compared with that under undrained conditions is a subject of great interest. This paper discusses the diverse views in relation to the initiation of instability and the conceptual difficulties brought by the discrepancies. It is shown that the constant shear drained (CSD) stress path is not a conventional stress-controlled test, and overlooking this fact may result in misleading conclusions. The difficulties inherent in the CSD tests have resulted in different criteria for the detection of the onset of instability in experiments and thereafter to different views. Through systematic simulations for the CSD, ACU and ICU stress paths under a range of initial states, it is shown that the instability line in the stress space is state dependent, and its gradient can be well related to the state parameter defined using the critical state concepts. For a given soil, the relationship is nearly unique regardless of the CSD, ACU or ICU stress path, and the critical state concepts and the second-order work criterion work well. Theoretically, it is shown that the conditions for instability under the drained and undrained stress paths are the same, regardless of the constitutive models chosen. [ABSTRACT FROM AUTHOR]

The interfaces play a key role in many engineering problems involving geologic materials. In particular, slope stability analyses of ancient landslides (that were subjected to large displacements along a slip surface) need the formulation of ad hoc interface elements. The mechanical response of slip surfaces in clays is affected by hydro-chemo-mechanical interactions and by rate effects and this paper presents the formulation of an innovative zero-thickness interface element for dealing with these kinds of effects. The proposed interface element is an extension of the modified zero-thickness element proposed by Goodman et al. (J Soil Mech Found Div ASCE 94:637–659, 1968). In addition to solid displacement, we consider the flow of water and the diffusion of a single salt in the fluid phase. Terzaghi's effective stress principle is used leading to the usual hydro-mechanical coupling within the interface element. The fluxes of water and salt are considered in the longitudinal and in transversal directions of the interface element. For the constitutive relation, we propose an innovative nonlinear elastic energy that improves the numerical convergence in the occurrence of interface opening. The Mohr–Coulomb yield surface is used for the plastic regime in which we considered the effects of strain rate and salt concentration on the shearing behaviour of the interface element. The proposed element has been implemented in a user-defined subroutine of ABAQUS. The typical effects of salt concentration and displacement rate and the typical model responses for the longitudinal and transversal fluxes of salt and pore fluid are discussed in detail. Finally, the proposed interface element is validated through the comparison with experimental results. [ABSTRACT FROM AUTHOR]

In this paper, improved physics-informed neural networks (PINNs) with hard constraints (PINNs-H) are introduced to simulate the variation of the excess pore water pressure in the nonlinear consolidation problems with continuous drainage boundary conditions. In the PINNs-H, we modify the network architecture to automatically satisfy the corresponding initial and boundary conditions accurately, and obtain high-precision soil consolidation behaviors. The accuracy and effectiveness of the presented PINNs-H are demonstrated on two examples of the nonlinear consolidation models. Specifically, the results indicate that based on less training data, we may better predict the consolidation behaviors through the PINNs-H. Furthermore, the training data required by the PINNs-H is significantly less than the grid point data of the finite difference method (FDM), and the PINNs-H exhibits a better memory advantage. For the inverse problem, we find that on the basis of less observed data of the excess pore water pressure, the PINNs can provide a great estimate to the interface parameters of the continuous drainage boundary conditions, and effectively resist the noise interference. We also use the PINNs and PINNs-H to identify the nonlinear factor, and reveal that PINNs-H can provide high-precision predicted results, whereas the PINNs fail. [ABSTRACT FROM AUTHOR]

Due to the periodic changes of climate, cracks are widely developed in expansive soils, leading to the destruction of soil integrity, the deterioration of physical strength, and eventually the instability of the expansive soil slope and other disasters. In this paper, a deep learning-based modeling method was proposed for soil crack networks characterization through steps of segmentation, quantification and simulation. Inspired by the U-Net convolutional neural network, a dilated convolution module was added to the backbone to enhance the crack segmentation capability and a subpixel edge detection algorithm was followed for accurate crack edge detection. Then, a deterministic or stochastic method was designed for crack network simulation. A case study of an expansive soil slope on the bank of Wadong Main Canal in the Pi-Shi-Hang Irrigation District, China, was conducted. Results show that the dilated U-Net model gained 0.24 and 0.25 improvement in F1-score and IoU (Intersection over Union) comparing to the conventional segmentation method (Otsu) and crack edge precision was further improved by 5.38%. The performances of proposed method including the image labeling, effect of crack thickness and environmental conditions, etc., are also explored. To validate the simulated crack network, crack areas at different depths were measured through X-ray images. Comparing with the simulation result, mean error rate of 1.05% was achieved. Thus, the proposed method can efficiently characterize soil crack networks using the field acquired crack images. [ABSTRACT FROM AUTHOR]

In soft soil layers, piles are frequently loaded laterally by horizontal soil movements. In many cases, the lateral pressure acting on piles due to horizontal soil movements is calculated with empirically or analytically based approaches, respectively. However, most of these design approaches do not consider possible influences on the resulting pile loads. This paper presents the results of model tests and numerical simulations on single piles and pile groups in cohesive soil subjected to lateral loads which were carried out to overcome limitations of available design approaches. Based on extensive small-scale 1 × g-model tests and numerical investigations with the finite element method, influencing factors on the lateral pressure, such as the roughness of the pile–soil interface, the pile size, the pile shape and the pile spacing were identified. A parametric study with the numerical model quantified the most relevant factors influencing the development of lateral pressure on piles due to adjacent surface loads and lead to the development of a simplified analysis approach. [ABSTRACT FROM AUTHOR]

The load transfer mechanism of laterally loaded pile groups is very complicated, and the analysis method is affected by many factors. This paper presents a field test study on lateral responses of large diameter cast-in-place isolated single piles with free head and pile groups with fixed head to investigate the pile group effect. Boreholes are drilled, and relevant field and laboratory tests are carried out to obtain main physical mechanical parameters and the soil profile of the site. Results of lateral loads, lateral displacements and bending moments measured in the field are reported and discussed. A group efficiency factor-based calculation method applicable to laterally loaded pile groups is derived according to a series of full scale and centrifuge tests. An existing group efficiency factor-based calculation method is compared with the proposed method. And three other measured test results are used to verify the calculated results. The comparison results show that the proposed method provides good predictions of load–displacement responses of pile groups. [ABSTRACT FROM AUTHOR]

In the realm of constructing urban underground spaces, it is imperative to address the impact of tunnel leakage on the surrounding environment. This paper introduced a theoretical analysis to investigate the localized water leakage's influence on adjacent pile foundations. A pore pressure distribution function, accounting for localized leakage water, was formulated. Integrated with the seepage control equation, this function facilitated the calculation of additional stress imposed on piles due to tunnel localized water leakage. Employing the Pasternak foundation model, an analytical solution was developed to assess the lateral performance of adjacent piles under localized water leakage conditions. This approach was compared with numerical simulations to validate the reliability of soil seepage fields and pile lateral performance resulting from localized tunnel leakage at different positions. Through comprehensive parameter analysis, it was observed that the width of the leakage joint significantly influenced pile lateral responses, manifesting in three distinct stages: linear increase, nonlinear gradual augmentation, and stabilization. Different positions of the lining leakage joint yielded varying effects on adjacent piles' lateral responses, with closer proximity intensifying the impact on the pile. When leakage joints were situated near the pile toe, a pronounced negative bending moment was generated. Furthermore, this study summarized the influence range of tunnel localized leakage adjacent to piles. It established that the maximum pile-tunnel horizontal distance inducing lateral pile responses due to tunnel localized leakage was set at 8 times the pile diameter (8 Dp). Additionally, tunnel leakage influences should be considered when the pile length exceeded 0.6 times the depth of the tunnel axis. [ABSTRACT FROM AUTHOR]

Unsaturated soil is widely distributed around the world but less considered in design due to the absence of a convenient analysis method in practice. The Morgenstern–Price (MP) method incorporating the extended Mohr–Coulomb shear strength equation provides a reliable approach to evaluate slope stability in such conditions. However, this method is time-consuming due to the need for a tedious trial-and-error process in determining the scaling factor, which involves complex iterations during each trial. Furthermore, since the relatively complicated nature of unsaturated soil, a dense slice division is necessary to obtain reliable results, making the analysis even more cumbersome. In this paper, an improved MP method for unsaturated soil slope stability analysis is presented, which eliminates the need for a dense slice mesh by employing only a few strategically placed Gauss points along the slip surface. Moreover, the trial-and-error process for determining the scaling factor with the corresponding complex iterations is replaced by an efficient search algorithm with a more concise iteration process, resulting in a more convenient implementation of the proposed method. Extensive examples are provided to validate the effectiveness of the proposed improved MP method, indicating its potential as an accurate and efficient analysis method for unsaturated soil slopes in practical application and relative study involving repetitive analyses. [ABSTRACT FROM AUTHOR]

This research work presents a comprehensive experimental study of frost heave in a fine-grained material to investigate the effects of top freezing (TF) and bottom freezing (BF) mechanisms with ice lens formation. A novel test device was built to investigate artificial ground freezing (AGF)-related temperature and load boundary conditions. This paper includes 62 frost heave experiments and test observations up to 10 days. The long test duration allows a precise examination of ice lens growth during thermal steady state when the frost line remains largely stable and the ice lens grows. This state corresponds to the holding phase of a practical in situ AGF implementation where the cooling is used to maintain the frozen body thickness. The freezing observations show that BF heaving is larger than TF heaving in most cases. This is caused by the more favorable hydraulic conditions caused by gravitational effects and vertical cracking that occurs during ice lens formation due to suction. This facilitates water accumulation at the ice lens. An applied load reduces the differences between BF and TF conditions beyond a certain value which corresponds to an overburden capable of preventing the formation of the longitudinal cracks. [ABSTRACT FROM AUTHOR]

Water drives the decay of road subgrades such as frost heave in cold areas and collapse in saline soil areas, which influences the safety and comfort of vehicle transportation. This paper proposes a novel geotechnical material, namely hydrophobized soil, as a subgrade fill material to mitigate water-induced degradation of subgrade. Hydrophobized soil has a low affinity to water and therefore can prevent the subgrade from water infiltration, enhancing the volume stability of subgrades. To demonstrate its feasibility, the hydrophobicity and its durability were investigated in this study. A one-year outdoor weathering test on hydrophobized soil columns was conducted, with the hydrophobicity measured. The results show that hydrophobized sand has different durabilities and exhibits different degradations depending on the chosen hydrophobizing agent and its concentration. Based on the testing results and capillary rise model, the design of hydrophobic hydraulic barrier in subgrade was discussed at the end. [ABSTRACT FROM AUTHOR]

In this paper, the deformation response of the stratum in the vicinity of a tunnel is investigated based on a case study in Tianjin. A method to predict the surface settlement in the case of double-track curvature shield tunneling is also proposed. The research methodology consists of analytical calculations, finite element analysis as well as field monitoring. Straight shield tunneling and curvature shield tunneling are modeled, each with a single-track shield and a double-track shield, and their operational parameters are compared. The influence of overcutting and existing tunnel on ground movement is also discussed. The salient observations from the series of analyses are as follows: (a) The maximum settlement induced by curvature shield tunneling is much greater than that induced by straight shield tunneling, while the existing tunnel has little impact on stratum settlement in contrast, (b) the proposed method of predicting the surface settlement induced by double-track curvature shield tunneling fits well with the field-monitored data in the Tianjin case study, and (c) the location of the maximum ground settlement is deviated by the overcutting phenomenon, whereas the settlement of the soil above the excavated tunnel is reduced due to the presence of the existing tunnel. [ABSTRACT FROM AUTHOR]

An innovative approach that combines isogeometric analysis (IGA), limit analysis, machine learning, and the multivariate adaptive regression splines (MARS) model is presented in this paper to investigate sinkhole stability of circular cavity. The upper bound limit analysis method using IGA and second-order cone programming (SOCP) is employed to analyze circular cavity stability. Based on Bézier extraction, the non-uniform rational B-spline (NURBS) is used to generate a set of NURBS surfaces that define the boundary of the soil domain. The proposed approach is validated through comparative analysis with previous studies, demonstrating its effectiveness in accurately predicting soil stability. A large dataset consisting of 5000 randomly generated runs is used to train the machine learning algorithm that is integrated with the MARS model. The results show high accuracy, with a small mean squared error of 10–3, in predicting the undrained stability of circular cavities. The integration of IGA, limit analysis, machine learning, and the MARS model contributes significantly to advancing computational techniques for assessing soil stability. The proposed approach offers a comprehensive and precise tool for engineers and researchers, providing an accurate design formula for evaluating the undrained stability of circular cavities. [ABSTRACT FROM AUTHOR]

This paper reports the results of thermal spallation experiments on specially dried shale samples with 3 bedding orientations (0°, 45° and 90°) under 3 flame temperatures (899 °C, 1243 °C and 1559 °C) and the 3D thermal elastic finite element modelling. Under open flame heating, continuous spallation is observed with ejection of various spalls and popping sounds. After a period of spallation, tensile fractures are formed in the samples and grow perpendicular to the heating surface, except for a sample with bedding orientation of 90° under the low temperature. Increasing flame temperature promotes ejection, popping sounds and spallation rate, but reduces the spallation starting time, spallation duration, depression diameter and depression depth. The model shows that heating induces compressive stress in the surface layer and tensile stresses beneath it. The tensile stress is found to be sufficient to generate large tensile fractures. The ratio between the induced compressive and tensile stresses increases with increasing spallation depth but little affected by the flame temperature. The spallation compressive stress increases with temperature from 29 to 51% of the uniaxial compressive strength. This stress is shown to be sufficient to cause buckling of thin layers separated from the bulk of the rock. The size of the buckling layer is smaller than the size of the spallation zone leading to a mosaic pattern seen on the surface after spallation. The results are important for further understanding of the mechanism of thermal spallation of rocks as well as large scale spallation-like processes in the Earth's crust. [ABSTRACT FROM AUTHOR]

The soil–anchor interface mechanical behavior is of practical importance for the bearing performance of ground anchors. Element-scale pullout test is a simple, reliable, and economical technique to investigate the interface shear stress–displacement response of anchors. However, the influence range of boundary effect for the anchoring element-scale pullout specimens is poorly understood, particularly under the actual stress and construction conditions. In addition, there is still a lack of study on the mechanical behavior of soil–anchor interface subjected to ground pressure via element-scale pullout test. In this paper, an element-scale pullout test setup that can simulate ground pressure and construction method of ground anchors was specially developed, with details introduced carefully. A response surface function-based soil dry density prediction model was proposed for the test design. Comparison with the soil consolidation test results indicates that this model equipped with high fitting and prediction accuracy. Twenty groups of element-scale pullout tests with different ground pressures and anchor diameters were conducted. Based on the test design of the proposed model, the soil density and moisture content were almost the same for all specimens after consolidation. The shrinkage of anchor hole, interface shear stress–displacement response, and interface shear strength were discussed adequately. It is shown that the soil–anchor interface shear strength is hardly dependent on ground pressure under the actual construction method of anchors. The influence of boundary effect for the element-scale pullout test can almost be eliminated when diameter ratio of specimen to anchor exceeds 5.0 ~ 6.7. [ABSTRACT FROM AUTHOR]

The problem considered in this paper is the passive earth pressure determination under various rigid wall geometry with negative wall-soil friction. An exact solution based on statically admissible stress fields is employed to evaluate the impact of negative wall-soil friction and inclined walls on the design of retaining walls. A series of conservative solutions for the passive earth pressure coefficient in the presence of negative wall friction is obtained, shedding light on the load transfer mechanism of cohesionless backfill materials. While focusing on the passive earth pressure coefficient, the study further identifies the stress state transition zone in the backfill and the influence of wall inclination on passive earth pressure. In addition, the load transfer mechanism of cohesionless backfill material in a retaining wall is affected by various factors, including wall geometry, degree of negative wall friction, the direction of the major principal stress at the wall, and the position and orientation of the transition zone and line of stress discontinuity. It follows that comprehensive design charts involving various rigid wall geometry and negative wall-soil friction are provided for engineering practice. Overall, the study successfully characterizes the admissible stress field in the backfill of rigid retaining walls, contributing to the knowledge of retaining wall design under the effect of negative wall friction. [ABSTRACT FROM AUTHOR]

This paper proposes an automated deep learning (AutoDL) framework for dynamic prediction and multi-objective optimization (MOO) on the driving position of the tunnel boring machine (TBM) to enhance tunneling reliability and efficiency. More specifically, AutoDL contains a standard process of data preprocessing, optimal hyperparameter tuning, algorithm selection, and model performance evaluation, which can intelligently learn the time-varying monitoring data collected by the smart sensors installed on TBM. It can return a prediction interval to well consider uncertainty, which is stable enough to raise the reliability of the prediction results. Later, the model from AutoDL serves as a meta-model for MOO-based decision-making to evidently control the four TBM position objectives, including shield head horizontal deviation, shield head vertical deviation, shield tail horizontal deviation, and shield tail vertical deviation. To validate the effectiveness of the proposed approach, it is applied in a TBM project for a natural gas backbone network between Changxing Island and Chongming Island in Shanghai. It is found that the proposed AutoDL can greatly reduce the requirements of professional knowledge of developers on model training. The deviation of the TBM driving position in each segment ring can be dynamically and accurately estimated in the form of both a single point and interval, reaching the average MAE of 1.051. Based on the intelligent model built by AutoDL, Nondominated Sorting Genetic Algorithm II (NSGA-II) is conducted to feasibly adjust TBM operational parameters. The average deviation of the four optimization objectives of the 66-ring data is decreased by 16.05%, contributing to reducing the occurrence of shield tunneling misalignment (STM). [ABSTRACT FROM AUTHOR]

Open-ended pre-stressed high-strength concrete (PHC) pipe piles are susceptible to progressive distortion and even failure in the vicinity of the pile toe during driving into stiff soil or rock strata. This paper presents an experimental investigation conducted as part of a power plant construction in Huainan, China. After 50 piles were driven in the initial phase, the toe of 9 piles were detected as damaged using the sonic echo testing method. In the second construction phase, four piles were instrumented with longitudinal and circumferential fiber optic cables, as well as discrete strain gauges. The recorded responses of pipe piles throughout their driving process are analyzed to reveal the causes of damages. The results show that a maximum circumferential tensile stress developed at a distance of 1/6 pile length above the pile toe, with its value three times greater than that in other cross-sections. This high circumferential stress results in transverse cracks and the failure of open-ended PHC piles and is believed to be related to the formation of soil plugs. The findings provide valuable insights into performance evaluation of driven open-ended PHC piles. [ABSTRACT FROM AUTHOR]

Unsaturated soils with bimodal pore structures, such as many residual and colluvial soils, are widespread in nature. Bimodal pore structures can noticeably influence their soil–water retention behaviour. Estimating the bimodal soil–water retention curve (SWRC) accurately has become critical in both theoretical research and engineering practice. In this paper, a novel equation to simulate the bimodal SWRC of unsaturated soils is proposed. The proposed bimodal SWRC equation not only provides higher simulation accuracy for bimodal SWRCs compared to other equations, but it also shows good agreement with experimental data from different types of soils. Moreover, the relationships between bimodal SWRC variables (i.e., air entry value, inflection point, and slopes at transition zone) and the best fitting parameters are presented. Finally, a practical approach is developed to estimate the bimodal relative permeability of unsaturated soils based on the proposed bimodal SWRC equation. The results are convincingly demonstrated that there is good agreement between the predicted and measured relative permeability coefficients of unsaturated soils in the literature. [ABSTRACT FROM AUTHOR]

Microbially-induced calcium carbonate precipitation (MICP) technology is a new method of soil improvement that has been proposed in recent years. However, the application of MICP technology is limited by its lower efficiency and higher cost. This paper proposes a cost-effective biogrouting method for strengthening the surface soil in a designated area of the in-situ dry sandy foundation, which with a wide range of possible applications. The unconfined compressive strength, permeability, and calcium carbonate precipitation in the soil reinforced by biosand and bio-slurry are analyzed and compared. The results show that biosand has a higher bacterial utilization rate and strengthens the reinforcement effect when the bacterial suspension is insufficient. The reduction in the use of bacterial suspension lower costs when the target reinforcement strength is predetermined. Biosand can be used to increase the efficiency of reinforcement and reduce costs by adjusting the proportion of fine particles added to decrease permeability and increase the final and early strength of the specimen. Biosand has excellent prospects for engineering applications such as reinforcement of coarse sand, rapid microbially induced calcite precipitation and in-situ soil improvement. [ABSTRACT FROM AUTHOR]

During the construction of tunnels in the Chinese Loess Plateau, the primary focus has traditionally been on the loess surrounding the tunnel. However, the swelling of paleosol and the low mechanical strength of loess in thick paleosol strata elevate the risks associated with tunnel construction. The distribution of loess and paleosol significantly influences tunnel stability. In this paper, we monitored the surrounding rock displacement and support structure pressure of a tunnel built within the thick paleosol strata. The thermal–mechanical coupling model was employed to simulate and calculate the swelling of paleosol, and the impact of loess and paleosol distribution on tunnel stability was thoroughly discussed. The results confirm the reliability of the thermal–mechanical coupling numerical model. At the vault and spandrel, where the interface lies between the thick paleosol strata and thick loess strata around the tunnel, the surrounding rock displacement initially increases and then decreases with the decrease in tunnel depth. However, the surrounding rock pressure exhibits an inverse variation, reaching a minimum when the interface is at the bottom of the lower bench. In areas with a thin loess layer around the tunnel, the surrounding rock displacement decreases, while the surrounding rock pressure increases with the reduction in the height of the thin loess layer. Furthermore, in comparison with surrounding rock with a full paleosol section, the displacement safety factor is 0.39–0.40 smaller, but the pressure safety factor is 1.21–1.24 larger when the interface is at the bottom of the lower bench. Simultaneously, the pressure safety factor is 0.17–0.41 larger, but the displacement safety factor is only 0.08–0.09 smaller with the thin loess layer in the upper bench. These findings provide a valuable theoretical reference for the construction of tunnels in thick paleosol strata and multi-strata environments with swelling soil and weak mechanical strength soil. [ABSTRACT FROM AUTHOR]

The creep and nonlinear damage behavior of rocks are two main factors that can cause large deformations and instability in tunnels. In this paper, uniaxial compression creep and triaxial compression tests were conducted to analyze the time-dependent and damage-induced strain-softening response of sandstone obtained from a water-conveyance tunnel in China. Using the test results, a new constitutive model was developed by coupling damage mechanics, Maxwell and Kelvin viscoelastic models, and the Mohr–Coulomb failure criterion. The model is formulated to describe both the full creep process (including the three stages of transient, steady, and accelerated creep) and the damaged-induced strain-softening behavior of the sandstone. The proposed model was validated against experimental data and was adopted to investigate the long-term safety of the segmental liner of the water-conveyance tunnel. The results showed that the differences between the rock peak and residual strength or between the initial and residual stiffness of sandstone increased as the confining pressure increased. In addition, the ratio between the crack damage stress and the peak strength increased initially with the increase in confining pressure and then decreased with a further increase in confining pressure. The ratio between creep deformation and total deformation increased with the increase in applied stress, and the specimen exhibited significant creep behavior at the final loading stage. Furthermore, the steady creep rate increased, and the viscosity coefficient decreased with the increase in loading stress. Good agreement was found between the values of failure strengths and shapes of stress–stain curves between the numerical simulation and experimental results under the uniaxial unconfined compressive creep test or triaxial compressive test. The axial load and bending moment of the tunnel segmental liner increased with the increase in the yield strength of concrete. The plot of axial force along the entire segmental liner ring varied greatly with time, while the plot of bending moment was less affected by time. [ABSTRACT FROM AUTHOR]