The gas in the seabed sediment exists in the seabed soil as discontinuous gas phase, existing theoretical studies seldom consider the gassy seabed environment, and there are few studies on the additional deformation of the tunnel lining caused by the seepage force induced by the wave dynamic pressure. Firstly, the control equation of gas-water mixed flow is obtained by Biot consolidation equation, and the pore water pressure response around the tunnel lining is obtained by combining with Stokes second-order nonlinear wave theory suitable for shallow water. Secondly, the superposition method is used to consider the oscillatory pore pressure and cumulative pore pressure in the seabed soil caused by waves, and the maximum pore water pressure and seepage force that may appear around the lining are taken as the most unfavorable load cases. The displacement variation law of the tunnel lining during service under the action of wave seepage force is obtained in combination with the exponential decay model to describe the lining deterioration effect. Finally, accuracy of the theoretical analysis in this paper is verified by the experimental monitoring data and numerical simulation. Parameter analyses are made on the wave period, water depth, seabed shear modulus, seabed gas content, tunnel radius, burial depth and lining deterioration. The cumulative effect of wave pressure propagating into the seabed and excess pore water pressure can be weakened when the seabed gas content increases. The extreme pore pressure around the tunnel lining decreases and the phase lag occurs with the increase of the gas content in the seabed. The external seepage force and the radial displacement of the lining decrease significantly with increasing the gas content in the seabed. Larger wave period and shallower seawater depth can significantly increase the wave pressure on the seabed surface, and induce greater seepage force around the tunnel lining, resulting in greater radial displacement. Reducing the radius and depth of the tunnel can effectively weaken the influence of the seepage force caused by the accumulated pore water pressure. When the lining deterioration coefficient is constant, the influence of excess pore water pressure caused by waves in the seabed with lower gas content is more significant, and the lining produces large radial displacement, which is not conducive to the normal service of the tunnel.

Seismic active earth pressure is the primary load for retaining wall design in high earthquake-intensity areas. Based on the relative position relationship among water table, crack depth and wall heel, this study firstly presented three mechanical models of seismic active earth pressure on retaining walls in unsaturated soils with cracks, which corresponded separately to high/medium/low water tables. The pseudo-dynamic method was then employed to calculate the seismic effect of sliding soils behind a retaining wall. The solution of seismic active earth pressure on inclined retaining walls for changing water table was derived by adopting mechanical principles of unsaturated soils and the limit equilibrium method. The iterative steps to be easily conducted were provided, and the proposed solution was compared with the results of theoretical analysis and the shaking table test available in the literature. Finally, the influences of water table, crack depth and unsaturated soil characteristics on the seismic active earth pressure coefficient were discussed. The results show that the proposed solution well considers the effects of water table, crack depth and unsaturated soil characteristics, which can be degraded to the classical earth pressure equation. Additionally, it agrees well with the existing theoretical solution and measured data of the shaking table test. Consequently, the proposed solution has an important theoretical significance and good application prospect. The influences of water table, crack depth, matric suction, suction distribution and suction angle on the seismic active earth pressure are all apparent. In order to optimize the seismic design of a retaining wall, engineering measures should be taken to maintain stable existence of matric suction, suction distribution, low water table and small crack depth.

Roughness of rock fracture has a significant influence on the seepage characteristics of fracture. The point cloud data of rock fracture surface was collected by three-dimensional (3D) optical scanning system. The joint roughness coefficient (JRC) and surface roughness ratio (Rs) were calculated by SURFER and GEOMAGIC STUDIO, and the quantitative relationship between JRC and Rs was established. The effects of JRC and Rs on the fracture seepage characteristics in limestone were investigated by conducting seepage tests under the coupling effect of stress, seepage and chemical interaction. The results show that JRC is a logarithmic function of Rs, with the R-squared (R2) of 0.912 8. The maximum relative error (MRE), mean absolute error (MAE) and root mean square error (RMSE) between the proposed characterization formula and seepage test results are 6.93%, 0.34 and 0.27, respectively. JRC shows quadratic function and logarithmic function with the seepage flow and permeability at stable period, respectively. The fitted relationships of Rs and each parameter are consistent with that of JRC. The larger JRC is, the smaller the seepage flow and permeability are. The values of JRC and Rs of the fracture surface increase under the coupling effect of HMC (hydrological- mechanical-chemical) three fields. The characterization method proposed in this study can be used to estimate the surface roughness of rock fracture. Meanwhile, the value of JRC can be applied to predict the seepage flow and the permeability at stable seepage period.

The Central Plains are located in an area that experiences seasonal freeze-thaw cycles, which can have significant effects on the soil structure of soil relics. To determine if lime-metakaolin (L-MK) is a feasible alternative to natural hydraulic lime (NHL) for earth site restoration work, tests were conducted using lime, metakaolin and silty sand from the site as main raw materials. Mass loss, unconfined compressive strength and splitting tensile strength tests were carried out on L-MK improved silty sand soil undergoing different numbers of freeze-thaw cycles to study its strength characteristics in depth. X-ray diffraction (XRD) thermogravimetry (TG), and scanning electron microscope (SEM) microscopic tests were also performed on some samples to reveal the internal mechanism of strength deterioration law of L-MK improved soil. Results indicate that L-MK improved soil has better freeze-thaw cycle resistance than NHL improved soil under the experimental mix ratio. Increasing the content of metakaolin improves the strength of L-MK improved soil. As the number of freeze-thaw cycles increases, the strain softening characteristics of L-MK improved soil show a weakening trend, and unconfined compressive strength and tensile strength decrease monotonically. After 30 freeze-thaw cycles, the unconfined compressive strength and splitting tensile strength of L-MK improved soil are about 3.79 and 1.16 times higher than that of NHL improved soil, respectively. The variation of strength is consistent with hydration products such as CSH and C₄AH13 generated by hydration reaction under the influence of freeze-thaw cycle for L-MK and NHL improved soil.

As transmission line projects continue to expand into the western mountainous regions of China, the need for more transmission tower foundations on steep hillsides has increased. However, research on the uplift bearing deformation characteristics of pile foundations under high-intensity wind and snow scenarios on sloped ground is lacking, and current specifications are insufficient. Therefore, laboratory model tests were conducted on rock-socketed uplift piles on both flat and sloped ground to investigate load-displacement curves, ground deformation and crack propagation, failure mode, axial force of pile, side friction of pile, and relative displacement between the pile and rock. ABAQUS numerical simulation results were compared to the model test results to validate the reliability of the numerical model and investigate the influence of steepness (slope angle) on the bearing capacity and deformation characteristics of rock-socketed uplift piles. The results demonstrate that the load-displacement curves for flat and sloped ground have similar steep shapes, and sloped ground can have an adverse impact on the bearing capacity and deformation characteristics of rock-socketed uplift piles. The decrease in pile bearing capacity is positively correlated to the steepness of the slope, with a decrease of 0%–12.8% for slopes of 0º–30º and up to 25.9% for a slope of 45º. Bedrock failure surfaces mainly occur in the downhill slope within a range of 3.2d(d is pile diameter), as well as within a fan-shaped range of 120º, while the failure range on adverse slopes is about 1d, which is different from symmetrical and composite failure on flat ground. When the load on the top of the pile reaches approximately 80% of its ultimate bearing capacity, visible cracks can be observed in flat or downhill areas of sloped ground. These research findings offer a scientific basis for improving the design and specifications of uplift resistance capacity in transmission tower foundations on sloped ground.

This study aims to investigate the problem that segment of shield tail is easy to float up in surrounding rock formation. Based on the self-developed gravity testing system of grouting, the nonlinear variation law of grouting buoyancy is obtained, and based on the equivalent continuous beam theory, a refined longitudinal uplift model of shield tail segment is established. The model can comprehensively consider the time-varying of grouting, the nonlinear distribution characteristics of grouting buoyancy and the cumulative effect of construction steps. The reliability of the model is verified by using the actual floating test results of shield construction in an underground pipe gallery in Guangzhou. The results show that with the increase of the pressure difference of the grouting and the permeability of the strata, the dissipation speed of the grouting buoyancy presents an increasing trend, and the uplift values of shield tail segment exhibits a decreasing trend. When the shield tunnels are in strongly weathered pebbly sandstone formation, the uplift characteristic curve follows the law of first increasing and then decreasing, and finally floating stably. Under an action of 20 kPa differential pressure, the maximum uplift value of segment is 151.74 mm, the value of which is 39.2 m away from the shield tail, and finally floating stably near 70 m away from the shield tail. At this time, the uplift value is 145.2 mm. The longitudinal model of segment upward movement further reveals the influence mechanism of grouting consolidation law on its uplift characteristics. The model has good reliability compared with the measured results. The results can be used to predict the uplift deformation of segment induced by grouting buoyancy and provide a theoretical basis for similar projects.

Pipe-shed support is a commonly used auxiliary construction method for tunnel engineering in complex geological environments, and it mainly relies on the micro-arch effect between pipes to play a supporting role. The formation and failure of micro arches are closely related to the spacing between pipe-sheds. After considering the lateral earth pressure and the non-uniform distribution of micro-arch section stress, the shape of the rational arch axis is determined and its standard equation of micro-arch is derived. By combining the failure conditions of micro-arch, a calculation method of rational pipe-shed spacing is obtained. Several engineering cases are adopted to verify the proposed method and the rationality of the method is validated by comparing with existing calculation methods of pipe-shed spacing. On this basis, the main parameters affecting the pipe-shed spacing are analyzed. The results show that the pipe-shed spacing is negatively correlated with the vault load. The pipe-shed spacing increases linearly with the increase of pipe-shed diameter and soil cohesion, and increases in nonlinear with the internal friction angle of soil. Significantly, the increase of internal friction angle of soil has an increasing impact on the pipe-shed spacing. However, the influence of the above parameters on the pipe-shed spacing is weakened with the increase of load.

The pore structure characteristics of tight rocks have an important impact on the displacement behavior between CO₂ and water, as well as the flow characteristics of CO₂. The residual water saturation will ultimately affect the efficiency and safety of CO₂ geological storage. Therefore, it is of great significance to further explore the CO₂-H₂O two-phase displacement characteristics of tight cores. In this study, the two-phase displacement characteristics and its influencing factors of natural low-permeability cores from deep reservoirs in Ordos Basin were visualized using nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) techniques. After qualitative and quantitative characterization of core pore structure, it is found that displacement patterns are closely related to core pore structure. Cores with strong heterogeneity and anisotropy are more conducive to the formation of fingering phenomena, while cores with large porosity and high permeability show piston-like displacement pattern. Fingering phenomena contributes to the migration of gas phase and can lead to the premature breakthrough of CO₂, resulting in high residual water saturation and low displacement efficiency.

The frequent occurrence of buried pipeline accidents caused by the ground collapse and subsidence makes it urgent to carry out experimental studies on the mechanical response under different subsidence effects. A systematical survey of the pipeline strain, earth pressure and soil deformation was conducted considering the effects of ground subsidence and collapse. The result showed that due to the arching effect at the top of the pipeline, the strain and earth pressure firstly increased and then decreased with the extension of the collapse zone, while they increased as the subsidence zone extended during the collapse and settlement. In the subsidence and collapse zones, the pipeline along the axial direction exhibited a saddle shape with both ends convex and concave in the middle. Pipeline deformation was more significantly affected by the subsidence. When the subsidence and collapse were both 50 mm, the maximum strain at the top, bottom and middle of the pipeline increased by approximately 18.8%, 249% and 273% compared to the ground collapse, respectively. It could be seen by comparing the ratio of the increasing area to the decreasing area of earth pressure around the pipeline λ that λ in the subsidence was increased by 78% compared with that in the collapse; therefore, the pipeline was subjected to larger earth pressure during the subsidence. Based on the modified Marston calculation model, a method for predicting the vertical earth pressure during ground subsidence was proposed, and the accuracy of the method was verified using the model test results.

Dynamic information about the cutter force, such as peak load, growth rate and frequency, is critical to maintaining the stability of the tunnel boring machine system and controlling cutterhead vibration. The current cutting force prediction formula cannot meet the solutions of the thrust and vibration of the cutterhead. Based on the idea of discrete modeling, the one-dimensional penetration of the traditional cavity expansion theory is extended to high-dimensional rotary rock test. The influence of rock mass parameters and operating parameters on the force is studied. And the full-scale rotary cutting test is used to verify the theory. The results show that the increases in installation radius, speed and penetration cause an increase in the volume of rock mass extruded by the cutter, and an acceleration in the boundary velocity of the core. It contributes to increase in the growth rate of cutter force and frequency of the cutterhead vibration. The higher strength of the rock mass leads to higher force peak value, growth rates and lower frequencies. The dynamic cutting force model differs from the test results within 5%, indicating the accuracy of the model.

The long-term train loads can result in problems such as strength attenuation, excessive cumulative settlement and even subsidence in sandy soil foundations and filling materials, which can jeopardize train operation safety. To understand the mechanism of the disease, it is necessary to explore the cumulative plastic deformation and pore water pressure characteristics of saturated sand under intermittent loading. Therefore, dynamic triaxial tests under continuous and intermittent loading with different dynamic amplitudes and confining pressures were performed. The test results showed that: (1) The cumulative plastic deformation-loading cycle curve of saturated sand exhibited a “zigzag” pattern. The intermittent effect led to unloading rebound and significantly reduced the accumulated plastic deformation of sand in the later loading stage, which can transform the failure mode from “destructive” to “stable” under continuous loading. (2) For plastic stability and plastic creep, the pore water pressure-loading cycle curve showed a ladder shape. In the first dynamic loading stage, the pore water pressure increased rapidly with loading cycle while drainage occurred during the intermittent stage, causing pore water pressure was dissipated and approached or equaled zero, resulting in denser sand soil. In the subsequent loading stage, the cumulative amplitude of pore water pressure decreased significantly. For the incremental failure type, the pore water pressure increased rapidly and the specimen was damaged in the first loading stage. (3) A prediction model characterizing the two-stage development of cumulative plastic strain of sand under intermittent loading was established and its prediction effect was good. (4) Intermittent effect increased the resistance of sand to plastic deformation. The cumulative plastic strain of sand was overestimated and the dynamic strength was underestimated under continuous loading. The cumulative deformation characteristics and its mechanism of saturated sand under cyclic intermittent loading can be deeply understood.

Three-point bending tests were conducted on laminated composite rock specimens composed of fine sandstone. A CCD camera was used for observation and a digital speckle correlation method was adopted. The mechanical characteristics of the contact surface were analyzed during the whole process of deformation and damage of the laminated composite rock. The results are as follows. (1) With the application of load, the horizontal strain fields on the surfaces of the upper and lower specimens show alternating tensile and compressive strain zones with vertical distribution, and this phenomenon is especially obvious near the interlaminar contact surface. (2) The overall interlayer sliding displacement was fluctuating. The value of interlayer sliding displacement gradually increased with a maximal slip value of 0.174 mm as the load increased. (3) The value of horizontal stress on the contact surface fluctuated due to varying interlayer contact condition. The vertical stress curve between layers was “V” shaped distribution. (4) The interlayer friction coefficient changed continuously during the loading process, and it reduced from 3.5 to 0.2 in the early sliding stage, and remained at 0.15 in the stable sliding stage. (5) The deformation energy density curves of the upper and lower layers have the same trend, and the contact surface deformation energy density reached the maximum value of 4.2 J/m3 at the peak loading moment. The above research results can provide useful reference for remote rock interface DIC monitoring and rock sliding study taking values.

In the South-to-North Water Diversion Project, a large number of expansive soil slopes slid due to the long and gently inclined fissures. The micropiles had achieved good application in the rescue and reinforcement project of the expansive soil slopes. The study on the reinforcement mechanism and the influence of parameters of micropiles in reinforcing the soil slope with long and gently inclined fissures is of great significance for the design of such projects. Based on the actual project of reinforcing expansive soil slope with micropiles, the thrust was applied on the sliding body along the direction of the fissure surface, and the failure tests of the non-piled slope with different angles of the gently inclined fissure were carried out. After taking the pile length, row spacing and pile position as influence parameters, the model tests of micropile-reinforced soil slope with long and gently inclined fissures were carried out, the displacement characteristics of the slope and the stress characteristics and the reinforcement effect of the micropile were analyzed. The test results showed that the micropile had a good anti-slide reinforcement effect for the slope with gently inclined fissures, and could maintain the anti-slide resistance at a high level. The anti-slide resistance provided by micropiles increased with the increase of pile length (anchorage ratio), while the increase efficiency decreased with the increase of pile length. It was suggested that the anchorage ratio of micropiles should be 0.5 when the pile is arranged at upper 1/3 position of the slope, and less than 0.65 when it is arranged at lower 1/3 position of the slope. The distribution of bending moment and shear force of the piles was reversed S-shape, and the maximum values were located near the fissure surface. The double-row piles can enhance the toughness of the slope to resist damage. When the row spacing was 200 mm (10 times the pile diameter), the front and rear rows of piles can well coordinate, which could give full play to the anti-slide effect and greatly increased the anti-slide thrust of the slope.

In subsurface engineering, grouting is an important measure to seal or strengthen fractured rock mass and reduce groundwater flow. Understanding the grout flow in rock fractures is significant to improve the grouting efficiency. The influence of grout material property on the grouting process in rock fractures saturated with a resident fluid is studied by visualized experiments. We present an experimental phase diagram of pattern formation and elucidate the relevant microscopic mechanisms. The experimental results show that the injection velocity and mass fraction in the grout significantly influence the displacement patterns in rough fractures, which is different from the displacement behavior with Newtonian fluid. During the displacement, the formation of different patterns is attributed to the local viscosity heterogeneity induced by the coupling effect of shear-thinning behavior and the spatial variability of fracture apertures. Decreasing injection velocity or increasing the mass fraction would stabilize the fluid-fluid interface and increase the area of initial stable region. The narrower aperture region of the fracture can only to be partially filled (with a low filling rate) by the polymer solution, except under the condition of very low flow rate and high mass fraction. The grout filling rate exhibits non-monotonicity with respect to flow rates. The displacement efficiency is significantly affected by displacement patterns, and thus we propose a theoretical model based on the interface stability analysis to elucidate the mechanisms behind the transition of displacement patterns. This work improves the fundamental understanding of grout flow in rough fractures and can provide a reference and technical guidance for evaluation and control of grouting efficiency in engineering practice.

An Archie resistivity correction model for volatile organic compound (VOC) contaminated clay was proposed by introducing the contaminant influence coefficient and correcting the porosity. Determination method of the four parameters (cementation exponent, saturation exponent, contaminant influence coefficient and coefficient of uniformity for pore micro-distribution) in the model was proposed based on the results of the Miller soil box test. The test results show that the formation factor of clay is positively correlated with porosity, which is different from the sandy soils, due to the effect of surface charge of clay particles on resistivity. The saturation exponent varies parabolically with the increase of volumetric moisture content and it increases linearly with the increase of porosity, whereby an empirical formula of saturation exponent considering both factors is proposed. The power function relationship between soil resistivity and volumetric water content and the linear relationship between soil resistivity and volumetric contaminant content were integrated to obtain the determination method of contaminant influence coefficient. The variation of coefficient of uniformity for pore micro-distribution with volumetric water content can be divided into three stages: steeply falling stage, leveling stage and slowly rising stage, and the occurrence state of pore water in soil is the main factor affecting a.

The excess pore water pressure (ue) in saturated coral sand with different relative densities (Dr) features complicated under complex cyclic loading conditions. In order to investigate its generation characteristics, a series of undrained cyclic shear tests subjected to 90º jump rotation of cyclic principal stresses with various orientations was conducted on such saturated coral sand. These laboratory cyclic tests by using the GDS hollow cylinder torsional apparatus showed that the patterns of ue generation in those test specimens are related to the paths of cyclic stress, levels of cyclic stress, and Dr. Then, the expression of excess pore water pressures ratio (ru) was established for different Dr values and cyclic loading modes. The unit cyclic stress ratio (USR) was introduced as a stress index for characterizing complex cyclic stress path, and the expressions of model parameters λ ₁ and θ based on USR and Dr were proposed. The established expression of ru can predict the generation of ru in saturated coral sand with various Dr under complex cyclic loading modes. Experimental data of different sand types in the literature independently verify the applicability of the proposed equation for ru.

It is essential to determine the mechanical properties of soils effectively during shield tunneling in the water-rich sandy pebble strata, which can be used to dynamically adjust the shield tunneling parameters. Since the conventional geological exploration cannot provide accurate strata parameters, the big data statistical analysis of stratum distributions and soil properties in Chengdu is conducted in combination with laboratory shear test and penetration test to explore the interaction between the mechanical properties of water-rich sandy pebble soils and the main parameters such as fines content, moisture content and water pressure. Test results show that with the increase in water content, the internal friction angle first decreases and then increases, while the interlocking force increases first and then decreases. The values of C and φ  decrease to a certain extent as the fines content increases from 1% to 6%. The formulae for describing the relations of two strength indices of soils (C and φ ) with the fines content and moisture content, as well as the equation for describing the relation between fines content and saturated moisture content, are derived. The feasibility of the proposed formulae is verified by fitting to the actual data. It is concluded that the failure pattern of the sandy pebble strata is piping type and the permeability of the sandy pebble strata declines as the fines content increases. Finally, the mechanism of the influences of tunneling parameters’ dynamic adjustment and the muck improvement process on construction is investigated by analyzing the characteristics of the excavated layers. The research results can provide a reference for the selection of the shear strength parameters of the water-rich sandy pebble soil layer used in empirical formula, value selection in numerical simulation, key tunneling technologies and construction plans in Chengdu area.

According to the basic mechanics and kinematics laws of rockfall impacting backfilling shed tunnel, the theoretical calculation formula of rockfall impact load is derived from three aspects using Laplace transform: rockfall impacting semi-infinite backfill, rockfall impacting finite thick backfill, and considering the interaction between backfill and substructure. The theoretical formula is verified by numerical simulation and relevant test data, and is compared with the other calculation formulae. The research shows that the theoretical value obtained from the proposed formula and the results of numerical simulation and laboratory tests all have a relatively stable law. The theoretical values are 6%−41% larger than the numerical values, and the difference between the theoretical value and the 95th percentile value of Pichler test is within 6%. Although the theoretical value in this paper is larger than that of all the other formulae, it is more consistent with numerical data and test data, thus it can better represent the real rockfall impact load. The formula can reflect the influences of thickness and properties of backfill, i.e. the smaller the thickness of backfill, the greater the impact load, and the thickness amplification factor can be determined according to the h/r table. The dynamic interaction between the backfill and the structure leads to the increase of the impact load on structure, which can be defined as dynamic amplification factor; the larger the thickness of backfill, the smaller the dynamic amplification factor. The proposed theoretical formula can consider the influence of many factors such as rockfall size, rockfall shape, rockfall energy, and thickness and properties of backfill. Therefore, the theoretical value can be used to design structure of shed tunnel directly.

During the simulation of rainfall infiltration, the conventional rainfall boundary cannot accurately reflect the influence of the variation of ponding water depth on the actual rainfall infiltration calculation. To address this issue, the conventional rainfall boundary is improved by incorporating the diffusion wave approximation equation, which allows for the coupling of ponding water depth variations with actual infiltration during heavy rainfall events. To confirm the precision of the improved boundary, two classical experimental cases are tested. The improved boundary is subsequently applied to the simulation of an actual engineering scenario. It is revealed that: (1) the improved rainfall boundary is capable of achieving real-time dynamic conversion between flow and pressure boundaries; (2) when the rainfall boundary functions as the pressure head boundary, the location with the theoretically deepest ponding water depth on the slope surface, as calculated by the improved boundary, manifests at the slope toe. Conversely, when the rainfall boundary serves as the flow boundary during the later stages of rainfall, the ponding water depth becomes negligible, and the location with the theoretical deepest ponding water depth arises at the intersection of the flat slope surface and the steep surface.

The anti-seismic stability of dams built on overburden is a key challenge. In order to reveal the law of ground motion propagation in the overburden and the phenomenon of dam instability, centrifuge shaking table model tests were carried out by inputting site wave and windowed sine wave successively based on a prototype project. It is found that when the target peak acceleration of site wave is 0.53g, the peak acceleration of site wave transmitted to the dam crest is 0.773g and the acceleration amplification factor is 1.39 due to the energy loss and the filtering effect of the weak overburden. The acceleration amplification factor is less than the recommended value of 2.0 in the code. In the test of inputting windowed sine wave, the amplification factor of dam crest acceleration is 1.46, which also shows that the weak overburden has a certain attenuation effect on ground motion propagation. The dam seismic subsidence deformation revealed in the two tests conforms to the general law. However, due to the large thickness of the soft sand layer, the overall seismic subsidence rate is high. There is no obvious damage to the dam body after the first test, and some phenomena are observed such as a large number of rockfill falling, dam crest subsidence, dam slope extrusion arch, core wall cracking in the second test. Although limited by the test conditions, the size effect and boundary effect of the model may have some influence on the test results, some findings in the tests can provide a reference for the dynamically numerical simulation of dam resting on soft overburden.

To study the micro seepage characteristics of coal under different hydraulic load paths, a two-media seepage model based on the microstructure of coal is established through CT three-dimensional reconstruction technology. Three equivalent hydraulic loading paths are designed, i.e., constant velocity loading (LP1), conventional pulsating loading (LP2), and fast-loading and slow-unloading loading (LP3). The numerical simulation tests of water injection seepage of coal under different cyclic load paths are carried out. In addition, the self-built water injection device of coal is used to explore the macro damage under three loading paths. The results show that the connected fractures account for 73.49% of the pore-fracture structure and are the main factor influencing coal seepage. The pores with a diameter of 9−23 μm are the major part of the isolated pores, with the number and volume share exceeding 50%. The pore-fracture structure and loading path within the coal has an important influence on the seepage distribution characteristics of velocities and pressures. The average seepage velocity of LP1 fluctuates greatly along the intrusion direction, while the inhibition effect of LP3 is obvious, and the path of LP3 has a larger span over time than those of LP1 and LP2. Compared with LP1, the loading path of LP3 has the fatigue damage effect of pulsating load, and the damage degree is more severe than that of LP2. This research can provide directions for the study of coal microstructure and the optimization of technical parameters of coal seam water intrusion.

The sinking state prediction and optimal sensor placement are conducive to ensuring safe and steady sinking of open caissons and reducing monitoring costs. Based on LightGBM, a framework in the field of machine learning, a sinking state prediction model of super large open caisson is established. By using the monitoring data of the stress sensors at the bottom of the open caisson, the sinking speed of the open caisson, the height difference in the transverse direction and the height difference along the bridge direction are accurately predicted. Through the analysis of the sensor importance, the optimal sensor placement scheme that can meet the sinking state prediction accuracy is determined. The proposed sinking state prediction model and the optimal sensor placement method were applied to the super large open caisson sinking project of the main tower of Changtai Yangtze River Bridge. The results show that the model has high accuracy in predicting the sinking state of the open caisson, and the R² of the three prediction indexes is greater than 0.94. The important sensors for predicting the sinking state are mainly concentrated in the outer circle of the open caisson and the area near the transverse and longitudinal axes. Under the condition of satisfying the prediction accuracy of sinking state, the optimal sensor placement scheme can reduce the number of sensors by 45.5%. When the numbers of sensors in the optimal sensor placement schemes are same, the proposed optimization scheme is better than the scheme based on the correlation analysis of characteristic variables in terms of overall accuracy of sinking state prediction.

Currently, dewatering scheme is typically designed using the method of theoretical calculation and numerical simulation. The designed scheme, however, is far from the optimum, since the total pumping rate can be further optimized with engineering safety ensured. Based on the dewatering in the 2nd confined aquifer of a cut and cover tunnel belonging to the north part of Jiangyin-Jingjiang Yangtze River tunnel project, dewatering optimization is conducted combining the methods of linear programming (LP) and numerical simulation. In advance, the hydraulic conductivity is adjusted by simulating the pumping test. Then, the parameters required in the LP model are obtained with numerical simulation. The pumping wells with optimal locations and the corresponding pumping rates are further determined, and the results are compared with the ones in actual construction. It is found that more number of pumping wells and more rational well location usually result in lower total pumping rate and drawdown. For the cut and cover tunnel with gradually changing excavation depths along the tunnel, dewatering in the deepest excavation zone shows the highest efficiency, since the dewatering requirements of the subsequent zones with lower excavation depths may be met simultaneously. The dewatering optimization can significantly reduce the number of activated pumping wells, total pumping rate and environmental effect.

Uplift of the horizontal rectangular anchor plate is a typical three-dimensional problem. However, it is difficult to characterize the sliding surface of soil around the anchor plate in the limit state for its shape is affected by a combination of the length-width ratio and embedment ratio of the anchor plate. Combining the results of ABAQUS 3D numerical simulation and 2D sliding surface analysis, it is found that the geometric form of the 3D sliding surface in any horizontal section within its buried depth range can be described by a closed graph, including four segments of straight lines parallel and equal to the long and short sides of the anchor plate respectively and four segments of 1/4 arc. The horizontal distance between the straight line and the corresponding anchor edge is determined by the 2D sliding surface in the vertical symmetric plane in the center of the long edge. The shape of this 2D sliding surface depends only on the embedment ratio, and it can be characterized by the logarithmic spiral morphological function. Based on these understandings, a three-dimensional mechanical analysis model of uplift bearing capacity of the horizontal rectangular anchor plate was constructed for the first time, and four cases of the model were analyzed. Combining the decomposition and merging of the model, the mechanical limit equilibrium analysis of the isolation body was carried out. Then, the calculation method of uplift bearing capacity of the horizontal rectangular anchor plate was deduced. It is applicable in the whole range of the length-width ratio and embedment ratio. Compared with five test cases and three other calculation methods, the results show that the proposed method has the best performance in all kinds of sand ground with various relative densities, which shows good applicability.

The concrete cutoff wall is the main anti-seepage structure of the rockfill dam resting on the deep overburden foundation, and is the key to ensuring the dam safety. Therefore, it is of great significance to accurately simulate the stress state of cutoff wall for evaluation of the rockfill dam resting on the deep overburden. Combining the incremental iteration method and the finite element-scaled boundary finite element coupling method (FEM-SBFEM), this paper realizes the trans-scale refined numerical analysis of the stress and deformation of the rockfill dam, which overcomes the low precision of the conventional midpoint increment method in solving local strong nonlinear problems. The characteristics of local large strain in band-shaped connected zone between cutoff wall and core wall and the bottom of cutoff wall are found. The overestimate of cutoff stress is due to the failure of conventional methods to describe local large strain of soil. The three-dimensional efficient refined analysis of cutoff wall of high asphaltic core dam on the super-deep overburden is performed by setting thin-layer elements to simulate the local large strain. The proposed trans-scale analysis method based on FEM-SBFEM-incremental iteration method-embedding thin-layer elements provides theoretical and technical support for the safety evaluation and design optimization of cutoff wall of rockfill dam resting on deep overburden.

A numerical model of the liquefaction horizontal free-field shaking table test was developed based on the completed large-scale shaking table test of liquefaction horizontal free field using the OpenSees finite element platform, and the numerical model was verified. Based on this, a free-field numerical model of the overall inclined foundation was established, and the non-cyclic dynamic response of the liquefaction lateral spreading site and the mechanism of liquefaction-induced lateral spreading were discussed. The results show that the established numerical model can effectively simulate the seismic response in liquefiable sites. There was significant relative displacement at the interface between liquefiable loose sand and overlying non-liquefiable layer. In the inclined site, the strain accumulation of saturated sand soil starts from the upper part of the loose sand layer and gradually develops downward. The increase of excess pore water pressure was not completely coupled with the accumulation of non-cyclic strain of the soil. The non-cyclic lateral displacement was controlled by the middle parts of the site. In the process of soil liquefaction, when the shear stress along the sliding surface is less than the initial static shear stress, lateral spreading starts, and the shear stress ratio of the saturated loose sand layer is in the range of 0.04−0.06, which is slightly smaller than the initial static shear stress ratio. In addition, it is found that liquefaction-induced lateral spreading requires a certain site inclination (greater than 0.5º). The lateral displacement of soil conforms to the cosine distribution pattern. With the increase of site inclination, the contribution of liquefiable deep soil to the overall lateral displacement is more significant.

The boundary and loading device of the physical model of laboratory geogrid pull-out tests are usually rigid, but the boundary conditions of the geogrid in engineering application cannot always correspond to the physical model boundary of laboratory pull-out test. In order to study the effect of boundary conditions on the pull-out test results, this paper uses three-dimensional discrete element method to carry out numerical simulation on the pull-out tests of geogrid-reinforced aeolian sand based on the laboratory triaxial and pull-out tests. The effects of four combination conditions, namely rigid top surface and rigid front wall (R_TR_P), flexible top surface and rigid front wall (F_TR_P), rigid top surface and flexible front wall (R_TF_P), and flexible top surface and flexible front wall (F_TF_P), on the macroscopic and mesoscopic characteristics of reinforced soil interface are studied. The relationship between pull-out force and pull-out displacement, interface shear strength, force chain, porosity distribution and particle rotation law were analyzed under different combination conditions. The displacement of rigid loading plate and flexible boundary particles, the deformation of geogrids under F_TF_P combination, and the evolution law of shear band during pull-out were examined. The results show that the rigid and flexible boundary of the front wall of the model has a great influence on the pull-out force curve pattern and interface friction angle. Under rigid front wall boundary conditions, the pull-out force and displacement curves are machining softening, while the pull force and displacement curves are approximately double-folded under the boundary condition of flexible front wall. When the front wall of the model changes from rigid to flexible, the friction angle of the interface decreases by 7º− 8º. When the normal pressure is less than 90 kPa, it is suggested that the peak reduction coefficients of the F_TR_P combination, R_TF_P combination and F_TF_P combination should be 0.9, 0.6 and 0.7, respectively. In the process of pull-out test, the specimen volumes under the four combinations expand and show dilatancy. The shear band thickness distributions of R_TR_P and F_TR_P are 5.38 and 10.79 times of the medium particle diameter. The shear bands of R_TF_P and F_TF_P have a wider distribution range. The research results are helpful to further reveal the interaction mechanism between geogrid and aeolian sand under rigid and flexible loading modes as well as rigid and flexible front wall boundary.