The pressure balance method is adopted in calculating the stability against the inrush of excavation in the current criterion. The effects of soil strength and excavation size are not considered in this method. Therefore, the method gives a conservative evaluation of the situation approaching the critical artesian pressure. Aiming at these problems, firstly, the safety factor is defined according to the principle of shear strength reduction in this paper. The existing method considering soil shear strength along slip surfaces is improved by adopting effective stress analysis and considering the passive zone of excavation. Then, a new calculation method for inrush resistance is proposed based on the elastic plate theory. Subsequently, the results of the finite-element method with reduced shear strength are compared with those of above calculation methods under the plane strain condition. And the effects of the excavation length-width ratio for the improved and proposed methods are further analyzed. Finally, the analysis of an engineering practice is carried out. The analysis shows that compared with the existing methods, the improved and proposed methods in this paper can better reveal the trends of excavation stability against inrush with the change of the artesian pressure and improve the economy on the premise of ensuring the safety of engineering practice.

The dynamic shear characteristics of the reinforcement–soil interface affect the stability and durability of reinforced soil–rock mixture subgrades. A series of static and dynamic direct shear tests was conducted on the soil–rock mixture–geotextile interface using a large dynamic direct shear apparatus under different rock contents (0%, 25%, 50%, 75% and 100%). The effects of normal stress amplitude (10, 20, 30, 40 and 60 kPa) and normal loading frequency (0.5, 1.0 and 2.0 Hz) on the shear response of the interface were analyzed. The test results indicate that the shear strength of the upper and lower boundaries of the interface first increases and then decreases with the increase in rock content. This is positively correlated with the normal stress amplitude, while negatively correlated with the normal loading frequency. An increase in rock content amplifies the interface dilatancy effect, while increases in stress amplitude and loading frequency reduce the interface dilatancy effect. The enhancement of the interface friction effect can be attributed to increased rock content and stress amplitude. An empirical formula for the interface friction coefficient, as a function of rock content, stress amplitude, and loading frequency, has been established. This formula coincides well with the test results.

Pre-bored grouted planted pile is a new type of eco-friendly pile foundation. The combination of the lower section of PHC nodular pile and the pile base expansion greatly improves the vertical bearing capacity of single pile. A lot of application practices have been achieved in Jiangsu, Zhejiang and Shanghai regions, but limited to the current research status, the bearing capacity of enlarged grout base is not clear. Based on the in-situ self-balanced loading test, the ultimate compressive bearing capacity of the enlarged grout base of the pre-bored grouted planted pile is investigated. The research results reveal that the measured ultimate bearing capacity of the enlarged grout base of the pile is 40% higher than that calculated by the specifications. The back analysis of the test results shows that the ultimate end resistance reduction coefficient of Shanghai ⑦ layer of silt is 0.72-0.81, which is significantly higher than the recommended value of 0.50-0.55 in the specifications. The bearing capacity of the enlarged grout base of the pile is mainly controlled by the end bearing capacity, and the required displacement value for its full bearing capacity is about 0.03 times the pile diameters. The enlarged grout base of the pile accounts for 64% to 67% of the bearing capacity of pre-bored grouted planted pile, and the structural integrity of the enlarged grout base plays a key role in the working performance of the pre-bored grouted planted pile.

Accurate analyzing the scope of tunnel excavation failure zone has important guidance and engineering significance in determining support parameters reasonably. This study focuses on the identification methods of tunnel surrounding rock failure zone, specifically the continuous medium analysis method and the continuous-discontinuous method represented by the finite element-discrete element coupling method (FDEM). Firstly, the continuous medium analysis method and FDEM identification criteria for surrounding rock failure are studied. Then the rock mass is divided into elastic rock elements and elastic-plastic interface elements. Based on the concept of equivalent continuous model, the relationship between the mechanical parameters of interface elements and rock elements and rock mass element is mathematically derived. The connection between the parameter values of these two methods is established for the first time, resolving the challenge of determining values in the continuous-discontinuous method. Finally, the ranges of surrounding rock failure zones simulated by these two methods during the excavation process of railway tunnels with different lithology and cross-sections are compared. According to the range of mechanical parameters for each level of surrounding rock mass in the specification, the range of values for the main failure parameters of surrounding rock, such as penalty parameter and fracture energy, in FDEM, is given for each level of surrounding rock. The simulation results of railway tunnel excavation with different lithology and cross sections using the continuous medium method represented by FLAC^3D and FDEM method show that the plastic zone obtained by the continuous medium method, and the failure zone obtained by the plastic limit strain, as well as the crack growth zone and failure zone obtained by the continuous-discontinuous method, are generally consistent in terms of distribution range, shape and failure mode. The method proposed in this article for determining the failure parameters of surrounding rock in FDEM is verified as reasonable and feasible.

The two-dimensional steady-state seepage field of the foundation pit under suspended waterproof curtains support considering the phreatic surface is studied analytically, and an analytical method for solving the phreatic surface is given. According to the symmetry, the half section of the foundation pit is taken, and it is divided into three regular regions based on the continuity conditions of the boundary. The variable separation method is used to express the water head distribution in the three regions as a series solution. The explicit solution of the seepage field in each region is obtained by combining the continuity conditions between regions and the orthogonality conditions of the series. The water table is determined based on the condition that the total water head satisfied by the water table is equal to the position water head. The analytical solution in this paper is compared with the results of laboratory tests and finite element analysis, the results verify the correctness of the analytical solution, which has higher efficient computational efficiency than that of the finite element numerical method. Performing a parametric analysis of the phreatic surface location, it was found that the insertion depth of waterproof curtain, the width and depth of foundation pit have a non-negligible effect on the phreatic surface location. As the thickness of the cross section increases, the position of the phreatic surface gradually decreases, and the distance from the bottom of the curtain to the top surface of the confining stratum has a linear relationship with the position of the phreatic surface on the waterproof curtain, without considering the extreme conditions. As the size of the foundation pit increases, the location of the phreatic surface shows a downward trend. The influence of the inner half width of the foundation pit on the phreatic surface is significantly smaller than that of the distance from the bottom of the curtain to the top surface of the confining stratum, this influence decreases with increasing the inner half width. The location of the phreatic surface decreases as the depth of the foundation pit increases, and the depth of the foundation pit has a relatively large influence on the location of the phreatic surface.

Immersion of loess can form compacted saturated loess or uncompacted saturated loess, and their engineering properties are significantly different. Based on the tests and data statistics of 22 loess sites in the Xi’an area, this paper systematically studied the basic physical and mechanical properties of the uncompacted saturated loess for the first time, revealed the fundamental reasons for its water-saturated weak property and large deformation due to water loss, and summarized the physical and mechanical characteristics of the uncompacted saturated loess in Xi’an area. The above research results can provide a basis for scientific research and engineering practice to strictly distinguish two types of saturated loess and formulate technical measures by classification. It is concluded that: uncompacted saturated loess is a kind of soil in which collapsible loess is not fully compacted, and macropore structure still exists in the immersion process. It is exposed in Q₃ loess or the upper part of Q₂ loess. It has a large void ratio, high water content, medium and high sensitivity, medium and high compressibility, low bearing capacity and strength, and is generally in soft plastic or flow plastic state. It is distributed adjacent to the compacted saturated loess, collapsible loess, and paleosol, forming a combination of soft and hard strata.

1. National Field Observation and Research Station of Landslides in Three Gorges Reservoir Area of Yangtze River, China Three Gorges University, Yichang, Hubei 443002, China; 2. State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan, Hubei 430071, China

The new frame ventilated anchor is an independently developed flexible support structure for frozen soil slope, which has a broad application prospect. In order to explore the cooling effect and mechanical effect of the new frame ventilation anchor, a multifunctional frozen soil laboratory box was designed, and it has the functions of loading, changing angle, adapting to the shaking table, and can simultaneously measure the temperature, moisture, wind speed and internal force. And a permafrost model slope reinforced by the frame ventilation bolts was erected to investigate the variation laws of temperature, moisture, wind speed and internal force of frame ventilation bolts subjected to freeze-thaw cycles. The closer to the anchor bolts, the more obvious the change of soil temperature and moisture. The frame ventilation anchor can absorb the cold energy and transmit and diffuse it along the axial and radial direction, with good cooling effect and maintaining the frozen state of frozen soil slope. The wind speed change law in the anchor bolt is consistent with the change of the external wind speed. A large external wind speed can motivate a more remarkable cooling effect of the frame ventilation anchor bolt. In a freeze-thaw cycle, the axial force of the anchor bolt changes in a parabola, and the axial force in the freezing period is greater than that in the thawing period. And the internal force of frame in freezing period is 2-3 times that in thawing period. The results can provide guidance for the design and engineering application of the new frame ventilation anchor.

In order to address the issues about significant thermal disruption and carbon emissions associated with the use of cement for solidifying frozen soil, calcium carbide slag was used as an alkali activator to activate metakaolin based geopolymer for soil solidification. In this research, the impacts of metakaolin and calcium carbide slag contents, curing temperature and curing age on the compressive strength of the solidified soil were investigated. Geopolymer solidified soil and cement solidified soil were compared in parallel. The curing mechanism was studied by X-ray diffraction and electron microscope scanning. Test results indicate that there is an optimal content of metakaolin and calcium carbide slag. When the content is lower than the optimal content, it plays an active role. On the contrary, it will have a negative effect. The optimal content of metakaolin and calcium carbide slag is 10% and 6%, respectively. The compressive strength of the optimal content sample cured at 20 ℃, –2 ℃ and –10 ℃ for 28 days is 3.783 MPa, 1.164 MPa and 0.901 MPa, respectively. The main products of metakaolin based geopolymer activated by calcium carbide slag are amorphous hydrated calcium silicate and hydrated calcium aluminate gel, which contribute to the improvement of compressive strength of solidified soil. The compressive strength of geopolymer solidified soil cured at –2 ℃ and –10 ℃for 28 days is 69% and 76% lower than that cured at 20 ℃, respectively. Due to the expansion of the pores in the frozen state which is related to the ice crystal, the growth of cracks is promoted, the efficiency of geological polymerization reaction is reduced and the amount of polymerization products is reduced. Compressive strength of the samples increases with the increase of curing age, because of the more silicon-aluminum grid structures produced by the geological polymerization reaction, the lower the porosity of the solidified soil and the internal structure of the soil is intertwined to form a denser structure. The geopolymerization reaction is less affected by low temperature. Compressive strength of geopolymer solidified soil cured at 20 ℃, –2 ℃ and –10 ℃ for 28 days is 1.07, 1.13 and 1.19 times that of cement solidified soil, respectively. The research results lay a theoretical foundation for the application of geopolymer in subgrade soil reinforcement in frozen soil area.

The undrained behavior of sand is mainly dependent on its initial state. To better understand and reveal this feature, the characteristic state lines, namely the loosest consolidation line (LCL), the static liquefaction dividing line (LDL) and the quasi steady-state dividing line (QDL), which are related to the undrained behavior of sand in the e-lnp plane, are presented firstly. Based on the theory of shear yielding and dilatancy, a simple method used to determine QDL is given, and the existence of LDL is demonstrated by introducing the normal compression line (NCL) of sand. Subsequently, the initial state of sand is divided into four characteristic subareas, which can be referred to as the static liquefaction subarea I, the strain softening subarea II, the quasi-steady state subarea III and the strain hardening subarea IV, and sand shows the similar undrained behavior when its initial state places in the individual subarea. Finally, the theoretical and engineering applications of subarea are analyzed.

The coral sand in the project site is mainly composed of coral sand and gravel with wide gradation characteristics, and its coral gravel content is distributed from 20% to 90%. Its liquefaction characteristics are quite different from quartz sand. The application of the current liquefaction evaluation method to the coral reef sand site will lead to the design of liquefaction remediation being uneconomical or unacceptable. In this study, the sands from islands and reefs of the South China Sea and the coral reefs of East Timor were taken as the research objects to conduct the original gradation dynamic triaxial test. A liquefaction evaluation method was developed based on the relationship between the liquefaction resistance CRR and the relative density D_r, and a comparative analysis was carried out through the centrifuge vibration test. The results show that under the same ground motion conditions, the excess pore pressure ratio generated by the dynamic triaxial test is larger than that of the model test; when the duration increases to 30 weeks (corresponding to magnitude 8), the soil liquefaction depth is up to 20 m, which effectively proves that the coral reef sand site has the potential risk of liquefaction under the action of strong earthquakes. In addition, through the calculation of liquefaction discrimination, it is verified that the accuracy rate of the liquefaction evaluation method based on the “CRR-D_r” relationship is 82.5%, and the inconsistent results are conservative for the working conditions, which can be applied to engineering liquefaction mitigation design.

The development of a prediction method for the lateral pressure exerted on expansive soil retaining walls with geosynthetic inclusions has been identified as vital for the design of such structures when saturation of the backfilled expansive soil is achieved. It is assumed that the deformations of expansive soil are composed of swelling deformation due to water absorption by the soil and compression deformation induced by external loads. Within the tenets of elasticity, equations were devised to estimate the elastic modulus and swelling force of expansive soil, respectively. Parameters for these equations were determined through the swelling tests on the expansive soil with loadings. Based on the interaction relationship between the geosynthetic inclusions and the backfilled expansive soil, a practical prediction method for the lateral pressure exerted on expansive soil retaining walls with geosynthetic inclusions was developed when the expansive soil reached saturation, and its performance was fully validated by model tests of the expansive soil retaining wall with soilbag and expanded polystyrene geofoam (EPS) inclusions, respectively. It was observed that the lateral pressures calculated using the proposed method exhibited a well agreement with experimental measurements.

Natural gas hydrates are considered as one of the most important potential alternatives for energy shortage, and depressurization is believed to be the most economic effectiveness for hydrate exploitation. The exploitation induces solid hydrate dissociation, liquid / gas generation and migration, heat transfer and skeleton deformation, showing strong thermo-hydro-mechanical (THM) coupling behavior of sediments. These processes will trigger geotechnical hazards, such as borehole inclination and reservoir collapse. A THM coupling numerical model for hydrate exploitation was developed based on the open-source FEM platform OpenGeoSys. In detail, the kinetic reaction equation was implemented to represent the liquid / gas generation during gas hydrate dissociation. Air and water mass balance equations were introduced to illustrate the phase change between liquid and gas phases. Besides, the nonlinear complementary problem (NCP) combined with the choice of special primary variables was adopted to strictly constrain the liquid / gas saturation, and kinetic reaction rate was connected to the source / sink terms of governing equations. The model was validated and verified through a test and a large-scale numerical model, and the effects of pore water compressibility on the THM coupling response of hydrate-bearing sediments were discussed. Results show that the model was numerically stable in dealing with the nonlinear problems of phase change among solid, liquid and gas phases, and of phase appearance / disappearance of pore fluids caused by hydrate dissociation; the hydrates dissociate from near to far regions, and the produced gas / liquid gradually migrated to the driving well and reached a steady state, where the gas / liquid saturation tended to be stable; due to the influence of air dissolution, the evolution of gas phase saturation lagged behind that of the liquid saturation; the pore water compressibility had a non-negligible effect on the dissipation of pore pressure and skeleton deformation under large pore pressure.

Shear band and crack evolution are very important for landslides. Crack is the weakest area in soil, and there is a lack of effective methods to analyze the meso-structure damage in shear bands quantitatively. To reveal the influence of cracks in granite residual soil on shear deformation and failure, CT scanning was used to obtain volume images of the sample at different loading stages during triaxial loading. Based on the digital volume correlation (DVC) method, a crack classification method is established according to the connectivity characteristics of cracks before and after loading. The cracks can be divided into eight kinds: obsolete, brand-new, isolated, split, combined, compound-brand-new, compound-isolated, and compound-mixed cracks. The results show that the brand-new cracks and compound-type cracks are closely related to the shear band evolution. With the increase of axial strain, the brand-new cracks and compound-brand-new cracks are in an increasing trend. When axial strain is 12%, the volume content of the brand-new cracks is more than 50%, the compound-isolated cracks exhibit rapid attenuation, and the compound-mixed cracks tend to increase first and then decrease. At the early stage of shear band initiation, a few new cracks are formed in the shear band, which accelerates the development of the shear band as the cracks are the weakest area. With the development of the shear band, a large number of new cracks cause more serious damage to the meso-structure in the shear band. Finally, the coupling effect of shear bands and cracks destroys the soil strength.

Loess is highly structured and water sensitive. Water-induced geohazards due to human activities and natural factors are of great concern, especially the loess slope with a saturated base. The failure process of a bottom-saturated loess slope was reappeared in this research based on a centrifuge test using the intact loess model. Monitored by the video, the PIV technique and the pore water pressure and soil pressure, the failure mode of the loess slope was analyzed. The main conclusions are as follows. The bottom of the model is thoroughly saturated when the acceleration is increased to 80g and there exists multiple failure forms on the slope model including sliding failure, collapse failure and internal subsidence failure. The PIV results indicate that the fractures on the surface of the model occur before the sliding failure and the collapse failure. The sliding failure and collapse failure both occur on the high pore-water pressure area though the pore-water pressure distribution is nonuniform at the bottom of the model. The sliding failure process in the model is the same as that of the field landslide following the process of base saturation, tensile fractures occurring, small backward sliding, water level increasing and large backward sliding. The results can provide reference for the model test study on undisturbed loess and the multi-failure mechanism of in-situ landslide especially in the long term irrigated loess areas.

To study the influence of unloading on complicated geotechnical structures such as cast-in-place piles, tunnels, etc, a simplified solution model of cavity reverse expansion considering elastoplastic unloading in drained soil is established. In this model, the superposition method is adopted in the derivation of stresses. In the reverse plastic zone, the non-correlated Mohr-Coulomb criterion, the assumption of large strain and ignoring the elastic strain are adopted. This study shows that the reverse expansion process can be divided into an elastic and two elastoplastic stages. When the cavity pressure is restored to the initial value, the radius of both cylindrical and spherical cavities cannot revert to the initial value, and there is still a certain range of stress weak zone around the cavity. Compared with the classical in-situ expansion solution, the yield surface development, stress variation and stress field around the cavity tend to be the same when cavity pressure increases to a certain value. The assumption of ignoring the elastic strain in the plastic zone will lead to a smaller displacement and a larger ultimate expansion pressure of the simplified solution, but it has no effect on the stress-related quantities. Compared with the Tresca solution, the proposed model takes into account the effect of internal friction angle and is closer to the actual soil mass. A plane strain model of cavity reverse expansion is established by numerical simulation, and the stress analysis results are basically consistent with that of theoretical model.

Regarding the anisotropic elastic modulus of sands, the effect of various stress states on the compressional wave (P-wave) and shear wave (S-wave) velocities along multi-directions measured using two pairs of horizontal and vertical bender elements installed on the sample is investigated. A cross-anisotropic stiffness matrix is fully determined based on the measured elastic wave velocities and the evolution of the anisotropy degree of elastic wave velocity with stress ratio is presented. The test results indicate that there exists a power relationship between the elastic wave velocities and the confining pressure in isotropic stress states. Meanwhile, the elastic stiffness of Toyoura sands in the horizontal direction is less than that in the vertical direction, indicating an initial fabric anisotropy. During anisotropic consolidation along a triaxial compression path, the velocities of elastic wave propagating along the vertical direction increase, while those propagating along the horizontal direction first remain constant then decrease as the ratio of vertical stress to horizontal stress increases. Moreover, the anisotropy degree of the stress normalized elastic wave velocity in the sands first keeps almost constant then increases with the increase of the ratio of vertical to horizontal stress, which is attributed to the evolution of soil micro fabric during anisotropic loading.

The foundation pit excavation and dewatering break the equilibrium stress field of the surrounding soil layer and negatively affect the underlying shield tunnel. The analytical solution of the longitudinal deformation of the underlying tunnel caused by foundation pit excavation and dewatering is proposed using a two-stage analysis method. In the first stage, Mindlin elastic solution and effective stress principle are used to calculate the additional stress caused by excavation and dewatering. In the second stage, the shield tunnel is treated as a Timoshenko beam resting on the Pasternak foundation to simulate the interaction between the tunnel and soil. The analytical solution of the longitudinal tunnel deformation is derived from the superposition method. By comparing with the monitoring data of engineering examples, the correctness of the proposed method is verified, and the influence of the excavation length, width, depth, tunnel burial depth, dropdown, and relative position of the foundation pit on the longitudinal displacement of the tunnel is further analyzed. The results show that with the increase of excavation length, width, and depth, the maximum uplift of the tunnel increases. The tunnel deformation decreases with the increase in tunnel burial depth. With the increase of the dropdown, the uplift decreases, and the settlement value increases. With the increased distance between the tunnel axis and the foundation pit center, there are a decreasing area of the uplift, an increasing area of the settlement, and a decreasing area of settlement.

The micro-scale hydraulic-mechanical mechanism of unsaturated soil is still unclear, and the relevant microscopic experimental researches are insufficient. Aiming at the experimental requirements of observing the microscopic behavior of unsaturated soil, we developed a miniature triaxial test apparatus and a miniature soil-water characteristic curve test device for unsaturated granular soil, which bases on the similar experimental principle of conventional unsaturated soil test device and suits for μ-CT scanning system. Two devices have a miniaturized size, light weight, and high compatibility, which are able to achieve the non-destructive and dynamic high-resolution 3D tomography of unsaturated granular soil samples under unsaturated triaxial shear test and SWCC test respectively. The experimental accuracy and reliability of these two developed mini-devices were verified by comparing with the results of conventional triaxial test and conventional SWCC test devices respectively. We carried out in situ CT scanning tests of triaxial shear and unsaturated seepage, and obtained micrometer resolution 3D images. The multiscale evolution trends of the parameters obtained from the image analysis accurately reflect the macroscopic stress-strain relationships and global water-retention capacity characteristics of the in situ tests.

Seabed surface structures may be subjected to dynamic loads. In order to ensure the long-term stability of them, it is crucial to study the dynamic characteristics of deep-sea ultra-soft soil at seabed surface. Oscillatory shear tests were carried out on deep-sea ultra-soft soil with water content beyond liquid limit by an Anton Paar MCR302 rheometer with strain control mode. The variations of dynamic rheological parameters, dynamic shear modulus G and damping ratio l were studied. The test results showed that with the increase of shear strain, the deformation of deep-sea ultra-soft soil was dominated by recoverable elastic deformation and gradually transited to unrecoverable viscous deformation. By establishing the relationship between dynamic rheological parameters and dynamic shear modulus G and damping ratio l, the dynamic characteristics of deep-sea ultra-soft soil were discussed. According to the features of dynamic shear modulus G of deep-sea ultra-soft soil, the concept of peak reference strain was proposed, and the relationship between maximum dynamic shear modulus G_max and normalized water content w/w_p (w is the moisture content, w_p is plastic moisture content) was established. Compared with conventional clay, the G/G_max-γ (γ is shear strain)curve of deep-sea ultra-soft soil decreased faster and was less affected by plasticity index. The damping ratio of deep-sea ultra-soft soil was generally high, and increased rapidly with the increase of shear strain. Based on the experimental results, models suitable for describing G/G_max-γ、and λ-γ curves of deep-sea ultra-soft soil were proposed.

In the current code, the E_ak formula for active rock pressure of slopes sliding along gently inclined outward weak structural planes does not consider the water pressure of the trailing edge fractures, which leads to deviation in E_ak calculation. In view of this problem, according to the balance relationship and geometric conditions of the force system, the stress analysis and simplification are carried out considering the water pressure of the trailing edge crack, and the calculation formula of the active rock pressure is derived to determine whether there is an extreme point and its location. The research results show that the error of E_ak is 21.89%-100% without considering water pressure; E_ak has a maximum in the effective range. The dip angle of gently inclined rock stratum θ   and the friction angle in the structural plane φ  are compared, it is found that if θ >φ , the width of potential slip surface at the top of slope is generally 0.2-1.2 times of the slope height H; and if θ  ≤ φ  , the maximum value of E_ak appears on the slope. This study improves the calculation formula by classification, and analyses the correlation between the extreme point position and some factors including H. It is of theoretical and practical significance for the prevention and control of sliding slope along gently inclined soft outward inclined structural plane.

When soil structures are analyzed with numerical method, effective stress-based nonlinear soil models are used to predict soil deformation or liquefaction. However, model parameter calibration often becomes an obstacle to the practical applications of the model because of the uncertainties and lack of appropriate laboratory test results. In this paper, the state dependent dilatancy concept is incorporated into the existing bounding surface model, it makes soils failure conform to critical state. Based on the piezocone penetration test (CPTu) results, a procedure is proposed to calibrate a bounding surface model for simulating liquefaction and ultimate failure under monotonic or cyclic loading. The in situ residual strength is utilized as critical state obtained from laboratory tests，it is used to calibrate the parameters related to critical state line. A relationship between soil liquefaction resistance and equivalent number of cycles is developed based on published CPT-based liquefaction triggering charts, together with correlations between a magnitude scaling factor and number of equivalent cycles to liquefaction, further the procedure is introduced to calibrate unloading plastic modulus simply. Based on the profiles of piezocone penetration test, examples to illustrate the calibration procedure of the model parameters are presented finally.

The bearing capacity of shallow foundations is significantly affected by stratum uncertainty, mainly including geological uncertainty and spatial variability of soil properties. The influence of geological uncertainty and soil spatial variability on the bearing capacity of shallow foundations has been separately investigated in previous studies. This study aims to develop a general probabilistic computational framework to reveal the effects of geological uncertainty and spatial variability of soil properties on the bearing capacity of shallow foundations, in which the geological uncertainty is simulated by Markov random field and the soil spatial variability is characterized using log-normal random field in different strata considering variations of the vertical scale of fluctuation. Based on the borehole and soil data collected from Mawan, Shenzhen, shallow foundation bearing capacity analysis is performed according to the proposed computational framework. The subset simulation method is used to accelerate the calculation of the reliability of each scenario, and reduction factors are proposed to reduce the calculation results to different degrees with the aim of simplifying the consideration of spatial variability. Contribution indexes are defined to quantify the effects of the geological uncertainty and spatial variability of soil properties on the bearing capacity results of shallow foundations. The results show that the traditional deterministic bearing capacity calculation will overestimate the bearing capacity of shallow foundations without considering the stratum uncertainty. When the number of boreholes is sparse, the geological uncertainty has a greater influence on the calculation results; when the number of boreholes is sufficient, it is mainly dominated by the spatial variability of soil properties.

The DC resistivity method is an economical and efficient engineering geophysical detection method. It has been widely applied in engineering detection due to its high sensitivity to a water-bearing geological body. The linear inversion is now mainly used in the data imaging and interpretation of the DC resistivity method in real applications. However, its inversion results are easy to fall into the local optimum, which may lead to a wrong imaging result as well as the geological interpretation. The unsupervised inversion method can use both the physical laws and data mining. It could get rid of the dependence on the real model, and can retain the feasibility of global search ability in the real data. Based on the unsupervised inversion method, we developed a deep learning boundary characterization method based on multi-scale edge features. To solve the problem of the fuzzy boundary of inversion imaging, we proposed a multi-scale inversion method of resistivity based on convolution wavelet transform by drawing on the experience of multi-scale inversion in seismic and electromagnetic exploration. On this basis, we used the multi-scale inversion objective function as the loss function to correct the network gradient, and thus effectively improved its boundary characterization ability. We carried out field tests in the No. 1 air shaft project of the Shanghai regional airport connecting line. Taking the detection of the leakage point of the diaphragm wall of the 5th foundation pit as an example, we verified 15 low resistance anomalies to guide the reinforcement of the foundation pit, which proves that the method is feasible and effective.

Exploiting methane hydrate induces deformation and damage to the reservoir, leading to a series of geotechnical engineering problems. Therefore, to achieve safe and effective extraction of hydrates, it is necessary to research the shear deformation characteristics of methane hydrate-bearing sediments(MHBS). The thermo-hydro-mechanical-chemical (THMC) microscopic contact model was utilized to account for hydrate cementation effects and their sensitivity to environmental temperature and pressure. In addition, the flexible boundary was applied to triaxial numerical tests to ensure the full evolution of shear bands. The microscopic mechanism of onset and development of shear bands was studied by considering macro and micro variables such as strain localization, porosity, average pure rotation rate (APR), bond failure, and spatial distribution of shear band. The results indicate that the flexible boundary used in the triaxial shear test effectively represents the stress-strain and volumetric response of MHBS while ensuring the free deformation of the sample. The shear band has already begun to germinate and to develop during the initial strain hardening stage and becomes more pronounced once it reaches the strain softening stage. Considerable disparities exist in macro- and microscopic parameters, including particle rotation and porosity alterations, both within and outside the shear band. Furthermore, hydrate cementation exerts a dual impact on its host sand. On the one hand, it enhances its strength characteristics, and on the other hand, as a weak link in the shear process, it takes the lead in failure, thus contributing to the emergence of shear bands. The research results have reference value for understanding the mesoscale evolution mechanism of MHBS deformation.

The reasonable value of soil constitutive parameters is an important prerequisite for numerical simulation. In order to accurately obtain the parameters of the modified Cambridge model for Huzhou soft soil, a parameter inversion method for the modified Cambridge model based on laboratory experiments and neural networks was developed for two typical soft soils in the region. Firstly, laboratory triaxial consolidation undrained tests and standard consolidation rebound tests were conducted, and based on the test results, the parameter inversion interval of the modified Cambridge model for typical soft soil in Huzhou region was determined. Secondly, based on the principle of orthogonal experimental design, numerical calculations were conducted on the lateral displacement of the retaining structure at different parameter levels during the excavation process of the foundation pit. Based on the numerical calculation results, 64 sets of PSO-BP neural network training samples were constructed. Finally, the constructed training set was used to invert the parameters of the modified Cambridge model for soft soils in Huzhou area. The critical state effective stress ratio (M₁, M₂), compression parameter (λ₁、λ₂), rebound parameter (κ₁、κ₂), and void ratio (e₁、e₂) of the two typical soft soil modified Cambridge model parameters obtained through inversion were M₁=1.076、λ₁ =0.050、κ₁ =0.021、e1=1.712，M₂=1.123、λ₂=0.038、κ2=0.012，e₂=0.967. The predicted deformation values of the retaining structure calculated through inversion parameters were in good agreement with the measured values, with a relative error of no more than 5%. Based on the inversion parameters, finite element numerical calculation was used to predict the deformation of the foundation pit, and the prediction results verified the accuracy of the inversion method. The influence of the number of neural network training samples and the number of input layer nodes on the inversion results of the Cambridge model parameters for soft soil correction was analyzed. The research results can provide parameter support and technical guidance for similar foundation pit projects in Huzhou area.

The seismic responses of three-dimensional (3D) concave topography sites were calculated by the combination method of finite element discrete model, the viscoelastic artificial boundary and the central difference integral formula, and the characteristics and differences of the influence of pyramid-shaped, hemisphere-shaped and prism-shaped concave topographies in homogeneous elastic half space on site ground motion were analyzed under the vertical incidence of P wave and SV waves. (1) The influence of different shapes of concave topographies on site ground motion is significantly different, namely, the prism-shaped concave topography>the hemisphere-shaped concave topography>the pyramid-shaped concave topography, but the differences between the different concave topographies are more manifested in the medium frequency range. (2) Concave topographies have a complex scattering effects on seismic waves. Whether it is vertically incident P wave or vertically incident SV wave (only vertical or horizontal seismic motion input), it can produce significant ground motions in both directions in and near the sag area, and while SV wave is vertically incident, the wave scattering of concave topography is more intense, and furthermore the amplitude of ground motion in vertical direction generated by SV wave is even greater than that in horizontal direction. (3) The concave topography may cause the topographical edge effect of ground motion, and the ground motion at the edge of prism-shaped concave is significantly amplified, while this effect is relatively weak in the pyramid-shaped and hemisphere-shaped concave topographies. The study reveals that the steep degree of the concave edge has a significant impact on site ground motion, and that the edge effect of concave topography may exist and is closely related to the steep degree of the concave edge. This research result gives an important hint for the analysis of practical engineering problems, that is, the rational treatment of concave edge parts should be paid special attention to when establishing a simplified analysis model of concave topography. The research results can be applied to the engineering construction in mountainous areas, especially bridge and dam construction, and provide a reference for its seismic fortification to consider the characteristics and differences of different shapes of concaves on site ground motion, especially the possible topography edge effect.