During the tunnel boring machine (TBM) excavation of tunnel engineering, the soft-hard composite strata are widely encountered. Under the action of TBM cutters, the failure characteristics of soft-hard interbedded rock mass are clearly different from those of the homogeneous rock mass. By using the RMT-301 rigidity testing machine, fracture tests were carried out on rock-like specimens with various combinations of soft-hard interbeds. The monitoring data by acoustic emission (AE) and a high-speed camera were recorded as well during the testing process. Furthermore, we discussed the effects of the soft-hard interbed on rock breaking by the TBM cutter along its axial direction. Testing results show that the degree of rock fragmentation by TBM cutters was not only affected by properties of the cutter-acting layer but also strength ratio of the cutter-acting layer to the pressure-bearing layer. The spalling zone found in the plate specimen revealed the compressed plastic zone under the action of cutters. When the cutter-acting layer was the same but with a softer pressure-bearing layer, a greater crushing scope was observed in the cutter-acting layer along the direction perpendicular to the tool penetration. The characteristics of aggregation distribution were found on the plane localization point in the AE events of the plate specimen. In the aggregated area, the cutter-acting also exhibited a tendency to perpendicular to the loading direction of the cutter, when materials of the pressure-bearing layer changed from relatively hard to soft. Thus, it is proved that the distribution of the AE plane location to great extent reflects the damage degradation inside the specimen.

Successful installation of bucket foundations, a common foundation in ocean engineering, is a prerequisite for normal use. Static pressure sedimentation tests on the bucket foundations with different length-to-diameter ratios are performed in homogeneous silty clay to determine the change of pressure inside and outside the cylinder wall and the cylinder end during the static pressure sedimentation process. The results show that the inner pressure is in the form of double broken line. The outer pressure increases linearly, and the lateral extrusion of the wall is the main reason for the inner pressure generation. The soil squeezing effect in the interior wall is much significant than the exterior wall. The soil squeezing extent of the exterior is small on the upper portion and large on the lower portion of the foundation, which has a linear relationship with the IFR. The tip resistance is directly related to the strength of the soil. According to the standard, based on the undrained shear strength and the CPT, the lateral and tip resistance can be calculated accurately. Due to the difference of soil squeezing effect, ? and kf will take larger value when the inner resistance is calculated. The major part of resistance is tip resistance, and then lateral resistance becomes the major during installation. The resistance and the development of soil plug are not sensitive to the speed range of 0.1-0.2 cm/s. The soil squeezing effect and resistance characteristic of bucket foundations with length-to-diameter ratio between 1 and 2 are similar.

One of the effective aseismic reinforcement methods in rockfill dam is to improve the overall stability of rockfill at the upper part of the dam. Hence, a polyurethane foam adhesive (PFA) was firstly applied to reinforce rockfill materials, which can obviously enhance the shear strength and efficiently reduce the permanent deformation of the mixed material. A series of dynamic triaxial shear tests was conducted to investigate residual deformation behaviors of the PFA-reinforced rockfill materials under different confining pressures, consolidated stress ratios, cyclic stress ratios and PFA ratios. Testing results show that the residual deformation increased with increasing dynamic stress ratio or confining pressure in the PFA-reinforced material. Under the conditions of confining pressure of 300 kPa, the consolidation ratio of 1.5 and dynamic stress ratio of 0.4, the residual strain of PFA with a high content of 2% was 74% lower than that of rockfill at the same conditions. Thus, it is proved that the PFA can significantly reduce the residual deformation of the rockfill. The parameters in Sheng Zhujiang residual deformation model were also comparatively analyzed with the data of PFA-reinforced rockfill materials.

Evaluation of ground liquefaction hazards (e.g. the triggering and the post-liquefaction consequences) is essential for the seismic design and operational safety of infrastructures. To investigate the evaluation capability of different ground motion intensity measures (IM), the present study conducts a series of dynamic centrifuge model tests under 50 g centrifugal acceleration. A level saturated sand model ground is shaken 20 times with different amplitudes of input motion to obtain both liquefied and non-liquefied case histories. Then the calculation procedures of the peak ground acceleration amax, the earthquake-induced cyclic stress ratio CSR, the Arias intensity Ia and the filtered accumulative absolute velocity CAV5 are presented based on the recorded base motion. All these IMs are processed and checked by the model test data. The analyses indicate that, several types of IMs have similar ability to evaluate the liquefaction triggering. There are obvious IM thresholds from the generation of excess pore pressure to the initial liquefaction trigger. Several types of IMs have differences in the evaluation ability of post-earthquake settlement. Ia and CAV5 perform better than amax and CSR, and the possible reasons are preliminary explained. This study presents basis for reliable evaluation of liquefaction catastrophe by selecting appropriate ground motion intensity index.

Residual stress along piles has a great influence on bearing capacity of pipe pile jacked into red clay with an upper soft layer and a lower harder layer. Using self-developed equipment, indoor model tests are conducted to measure close-end single pipe pile and pile group jacked into layered red clay foundation. The variation of residual stress of single pile and pile group and their time effect with three kinds of diameters are analyzed. The results indicate that the residual stress along pile shaft increases first and then decreases from top of the pile to the bottom. The distribution of residual stress shows a broken line. For a typical red clay foundation with a hard top layer soil and soft lower layer, the residual stresses at pile shaft and pile tip are much smaller when the bearing stratum is hard plastic red clay layer or the plastic layer. However, the residual stress will increase when the piles puncture into better bearing layer. In the early stage of completing jacking single pile, the time effect of residual stress at pile shaft performs significantly. The stress value decreases, and exponentially decays to a lower stable value after the single pile being re-pressed as the rest period keeps going. If residual stress being ignored, the pressure value at pile shaft gotten by static load tests decreases. In this test, more than 7.97% of pile side friction above neutral surface is predicted, while less than 2.29% of pile side friction and 2.29% of pile tip resistance below neutral plane is predicted.

Compared with traditional equal section pile, belled wedge pile has advantages of high unit material utilization, large pile side friction and tip resistances. However, there is little research focused on the quantitative model test on its vertical and lateral bearing capacities The bearing capacities of belled wedge pile embedded in sand under vertical load, lateral load, and surcharge load are tested experimentally to measure the pile shaft, tip resistances, lateral earth pressure, down-drag displacement, and drag load. At the same time, the bearing capacities of equal section pile with the same concrete usage are compared. The mechanism and differences of these piles are preliminary discussed. The results show that the vertical compressive bearing capacity of belled wedge pile are nearly 2.33 times that of equal circular pile, the side and tip resistance are higher than circular pile; the lateral bearing capacity of belled wedge pile is nearly 1.48 times that of circular pile, the larger diameter of the upper part of belled wedge pile and the expanded tip improve the lateral bearing capacity. Comparing with circular pile, the wedge angle can effectively reduce the down-drag displacement of pile top. It presents as one effective ways to reduce the negative friction resistance to the pile foundation by converting the traditional pile type into the belled wedge pile.

In this study, conventional triaxial tests were conducted to systematically investigate the strength characteristics of loess under the conditions of drying-wetting cycles. We proposed the methods for calculating structural strength and decay intensity of loess, and then discussed the effects of confining pressure and water content on structural strength and decay intensity. The relationship between structural strength and decay intensity was studied as well. The results show that the structural strength and decay intensity decrease with increasing water content and reveal a good logarithmic function with water content. The structural strength and decay intensity increase with the increase of confining pressure, which had a good linear function. The attenuated strength value of undisturbed loess after several drying-wetting cycles is almost equal to the sum of attenuated strength value of remolded loess and structural strength. It is proved that the action of the wetting-drying cycle not only broke the original structure of undisturbed loess, but also made the undisturbed and remolded loess have the same structure of soil mass.

To comprehensively evaluate the improvement effects of cement improvement on mechanical properties of argillaceous-slate coarse-grained soil, cyclic dynamic loading and monotonic loading tests under undrained condition are conducted using large-scale static-dynamic triaxial apparatus. The cyclic dynamic responses of the modified soil and the static and dynamic properties under the monotonic loading with medium and low strain rates are examined. The results show that, in cyclic loading tests, both the confining pressure and the loading frequency are the key factors influencing the dynamic elastic modulus and the damping ratio, respectively. The dynamic strength under cycle loading decreases in logarithmic scale with cycle number. The ratio of dynamic strength to static strength of cement-improved argillaceous-slate coarse-grained soil under monotonic loading increases significantly with the strain rate increasing. Compared with the properties of untreated soil, stiffness of improved raises remarkably whereas viscous damping decreases. The effect of strain rate on strength under monotonic loading becomes remarkable. The static strength also increases greatly. There is no difference in the internal friction angles in soil treatment while the cohesion increases significantly through the cement.

Failure mode of mechanically stabilized earth (MSE) wall in slope areas exhibits as the integral sliding of the backfill region along the slope. Particularly, the reduction of backfill strength obviously exacerbates the deformation of the wall. In this study, a novel micropile reinforcement scheme was proposed to investigate this failure mode. Finite element models of MSE wall of the slope before and after reinforcement were established and further validated by scaled model tests. Based on different natural conditions of the slope and the backfill strength, multivariate analysis was performed numerically to compare the stress and deformation behavior of MSE wall before and after micropile reinforcement. The results indicate that the reinforcement of micropiles can effectively prevent the sliding of backfill region along the slope. The displacements of the wall were decreased by 6.25% to 46.9%, according to different natural conditions of backslope. Moreover, the more obvious decrement was found when the backslope friction angle was lower. Based on different backfill strengths, the displacements were reduced by 6% to 56.1%, and the reduction was greater when the backfill strength was lower. In addition, the earth pressure and deformation of backfill soil declined greatly as well. Therefore, the results can provide an important guidance for the application of micropile-MSE wall in the practical engineering of road construction in mountainous areas.

Soil freezing characteristic curve (SFCC) represents the relationship between the freezing temperature and unfrozen water content. The SFCCs of clay samples saturated by different concentrations of NaCl solution are obtained using the nuclear magnetic resonance (NMR) and the cold bath. The effect of pore solution at different concentrations on the SFC is analyzed. It is shown that with the increase of the solution concentration, the freezing characteristic curve moves upwards, that is, at the same unfrozen water content, the freezing temperature decreases with the increase of the concentration. It is mainly because the osmosis potential induced by salt solution lowers the total potential of soil water, which in turn depresses the water freezing point. The freezing temperature is related to the energy status of liquid water in frozen soils. The total pore water potential includes the matric potential and the osmosis potential, where the matric potential includes capillary and adsorption and the osmosis potential depends on the concentrations of pore solution. When the unfrozen water content of the sample is very low, the adsorption effect is available. At this time, the unfrozen water is adsorbed on the soil particles in the form of adsorbed film. Similar to the unsaturated soils, a relationship between intermolecular forces and adsorbed water film is used to describe the soil freezing characteristic curve at low water potential. Combined with osmotic potential, the freezing characteristic curves at different concentrations are simulated, and the fitting results are in good agreement with the experimental data.

Two methods are proposed for the determination of the ultimate bearing capacity of cave roofs. Method 1: assuming that the punching body is a truncated cone, the ultimate bearing capacity of cave roofs can be determined by applying tensile stress and shear stress simultaneously on failure surface using limit bearing method. Method 2: assuming that the punching body is a rotating body with an unknown curve as the generatrix, the expression of the generatrix and the ultimate bearing capacity is obtained by the limit analysis method. The ultimate bearing capacity of the roof is obtained by partial derivatives. Laboratory model experiments of the ultimate bearing capacity of cave roofs are conducted. The failure modes and the corresponding ultimate bearing capacity are obtained when the roof’s thickness varies from 1D to 5D. The measured data is in good agreement with theoretical calculation result. The study shows that the punching shear failure mode happens when roof’s thickness varies from 1D to 3D, and the failure pattern has a surface of revolution with a curve shape. When roof’s thickness reaches 4D, a failure mode of tearing damage and punching shear failure occurs. Plastic failure develops when roof’s thickness reaches 5D. The ultimate bearing capacity increases linearly with the increase of roof’s thickness from 1D to 4D in the same span-diameter ratio. When roof’s thickness reaches 5D, the ultimate bearing capacity of the cave roof is close to the ultimate bearing capacity of bedrock.

In China, rock salt deposits are typically characterized by interlayers, which are mostly distributed in Yunying and Pingdingshan areas. In the construction and operation processes of salt caverns, gypsum interlayers are soaked in corrosive solutions (e.g., brine and oil). To investigate fracture toughness and weakening mechanisms of gypsum interlayers under corrosive environment, we conducted a series of cracked chevron-notched Brazilian disk (CCNBD) tests. The CCNBD specimens suggested by ISRM were prepared in the laboratory and were soaked in four different liquids (i.e., water, half saturated brine, saturated brine and acidic oil) under three different temperatures (i.e., 20, 50 and 80 ℃). The soaking time for specimens was one month. Moreover, the results of soaked specimens are compared with those of dry ones. The results indicate that fracture toughness of gypsum significantly decreases with the increase of temperature when soaked in a given liquid. By contrast, the fracture toughness of gypsum approximately remains constant at the same temperature. The degree of fracture toughness of gypsum after water and brine immersion is greater than that of acidic oil. The weakening of gypsum soaked in water and brine is attributed to the combined effects of water, temperature, and chlorine ions. Specially, the effect of water-temperature contributes to a severe weakening, but the chlorine ions have little effect. The weakening mechanisms of gypsum soaked in acidic oil are chemical reactions and dehydration. Petroleum acid (naphthenic acid) reacts with gypsum to produce calcium naphthenate, which can be dissolved in the oil phase. During this process, the dissolution of calcium naphthenate in the oil phase promotes the forward reaction. Consequently, the study is significant for the evaluation of the leakage risk of storage caverns in bedded salt deposits.

Effects of confining pressure and water content on failure strain energy density of frozen silty sand are investigated in a comprehensive experimental program of triaxial compressive test under the condition of various confining pressures and a wide range of water content. The results show that when the water content is about 30.6%, the frozen soil is prone to plastic failure, while brittle failure occurs at other water contents. The influence of confining pressure on failure strain energy density can be divided into low confining pressures phase, medium confining pressures phase and high confining phase. And water content has an important effect on the boundary confining pressure. Two types of the effect of water content on failure strain energy density are observed. When confining pressure is low (50 kPa), failure strain energy density begins to increase with increasing the water content, and reaches a maximum (600 kPa) at water content of 30.6%. Then, as the water content continues to increase, the damage energy density decreases. When the water content reaches 60 kPa, the further increase of the water content no longer affects the damage energy density, i.e., the damage energy density of the frozen soil is close to that of the ice. When the confining pressure is high (≥ 500 kPa), there is no initial increase in the failure strain energy density compared to the low confining pressure stage.

This study aims at investigating the deformation behavior of rock salt as reservoir medium under long-term operation. Uniaxial creep experiments were conducted on rock salt specimens for 359 days, and the law of real-time acoustic emission (AE) signal was also monitored during the test. The results show that three stages of AE were identified in the uniaxial creep experiment. The cumulative AE event location indicates that the distribution of AE signals at each stage corresponds to the positions of deformation and failure of the specimen. Meanwhile, the relationship between accumulative AE event and the creep strain was approximately linear, which proves that the number of AE events can be used to establish the creep constitutive model of rock salt. Hence, a constitutive model of rock salt damage evolution was developed based on AE data. In addition, parameters in the constitutive model were determined by fitting experimental data with the least squares method. Fitting curves show that the proposed creep constitutive model can well describe three creep characteristic stages of rock salt .

A non-coaxial constitutive model is proposed based on the Gram-Schmidt orthogonalization process employed in the yield vertex non-coaxial theory. The flow rule is revised in this model. The model corrects the original flow rule, where the non-coaxial flow direction is defined as the projection of the unit stress increment direction in the orthogonal direction of the reference principal stress, and is associated with the plastic scalar factor. In addition, a new form of plastic function is derived according to the dilatancy equation in the generalized stress state. Based on the state-related sand model, the new non-coaxial model and the uncorrected model are used to simulate the hollow cylindrical single shear test and the hollow cylindrical torsional shear test on Toyoura sand. The simulation results are compared with the experimental data, and the results show that new non-coaxial model can more reasonably reflect the non-coaxial phenomenon and its variation in the test, especially for the monotonic shear test in the direction of the fixed principal stress axis.

The effect of the shearing velocity on filled joints is significant for the safety and stability of engineering rock mass under dynamic loads. To study the effect of the shearing velocity on shear mechanical properties of filled joints, sands were used as the filled material and the granite was used as joint wall. By using the RMT–150C servo-testing system, direct shear tests were conducted on filled joints to investigate the effects of normal stress, shearing velocity and filled thickness on shear mechanical properties. Experimental results show that the shear stress-displacement curve of the filled joint belongs to the yield shear type, and it can be further divided into three phases: elastic stage, transitional stage and slip stage. At the slip stage, the shear stress continually increased with increasing the shear displacement, and the increase amplitude was related to the normal stress. With the rapid growth of the shear rate, the shear strength and frictional angle increased slightly. The shear stress-displacement curve of the elastic phase was fitted by a hyperbolic form to study its non-linear process and the fitting result turned out to be good. Two new parameters, namely the initial stiffness and stiffness influence coefficient, were defined to describe shear deformation characteristics of the joint. Experimental results show that the initial stiffness increased sharply with increasing the shearing velocity to a high value. As the normal stress increased, the initial stiffness increased linearly, while the stiffness influence coefficient decreased obviously. Moreover, the effects of filled thickness on these two parameters were dependent on the normal stress. For the planar filled joint without roughness, both of the shearing velocity and filling thickness obviously have greater influence on deformation characteristics of the joint than on shear strength.

The aim of this study is to investigate the effects of anchoring mode and bedding on mechanical properties of anchored rock. Similar materials were used to precast bedding rocks and standard specimens with 0° and 90° bedding were made in the laboratory. Anchor bolts made of #45 steel were applied to perform end anchoring and full-length anchoring, and thus, three kinds of specimens were obtained by end-anchoring, full-length anchoring and non-anchoring, respectively. The uniaxial compressive strength (UCS) and deformation of specimens were obtained by using MTS815 rock mechanical experiment system. The results show that the UCS of rock was enhanced by the anchor. Specifically, the UCS increment was influenced by the bedding direction and anchoring mode. For anchored specimens with the same bedding, the UCS increment of full-length anchored rock was greater than that of the end-anchored rock. For the specimens with the same anchoring method, the increase amplitude of UCS of anchored specimen with 90° bedding was higher than that of the anchored specimen with 0° bedding. It is found that failure modes of anchored specimens are affected by anchoring types and they are further divided into shearing extension and shearing offset. Failure modes of anchor in anchored specimens are not affected by anchoring methods, and both of anchoring methods slipped between rock mass and grouting interface. However, the differences between the end anchorage and the full-length anchorage are that the latter has longer bond length between the anchor and rock, the higher bond strength was, and the more and thicker rock debris were after failure.

Swelling mudstone is one type of special soft rock with a feature of collapsing under drying and wetting cycles. Water immersion tests were conducted in laboratory to examine disintegration behavior of Yanji swelling mudstone under drying and wetting cycles. On the basis of grain size distributions, relative base entropy is proposed to measure the disintegration behavior, and is compared with disintegration ratio. The results show that the groups of different grain sizes change greatly at the initial 3 cycles, and then tend to be stable. With the increase of the number of wetting and drying cycles, the coarse particle content gradually decreases, the fine particle content increases. The particle size changes from the homogeneous to the heterogeneous state, then back to the homogeneous state. There is a significant negative linear relationship between relative base entropy and disintegration ratio. The relative base entropy decreases with the increase of disintegration ratio, implying reasonable and feasible measurement of the grain size distributions using proposed relative base entropy method. The relative base entropy decreases gradually with the increase of the number of drying and wetting cycles, and finally tends to be stable, which agrees well with the changes in the grain size distribution and its derived indexes. Hence, the feasibility and applicability of the proposed approach are verified again, and the relative base entropy can be a new useful index for the quantitative analysis of the disintegration of swelling mudstone. After the excavation of cutting slopes, waterproofing and moisturizing measures should be taken in time to prevent the disintegration and argillitization of swelling mudstone.

Since various water-induced geological disasters occur in the red-bed mudstone, it is important to study disintegrating states of red-bed mudstone under dry and wet cycles. A series of wet and dry cycle tests was conducted on mudstone samples from Triassic Badong Formation. After each cycle, every group of screened particles was weighed, and morphological parameters of rock sample were also obtained using an image processing technique. With the combination of the fractal geometry theory and the gray relational analysis, the fractal characteristics of size distribution and the morphological characteristics of rock particles were gained. Thus, a new model was established to evaluate the stability of the red-bed mudstone. The results show that rock particles with a size larger than 10 mm disintegrated dramatically, which mainly occurred in former eight times cycles and tended to stop after 12 times cycles. Corresponding to the evolution of disintegration process, the fractal dimension of size distribution rapidly increased and stabilized at around 2.20 by the end of disintegration. Meanwhile, both the circularity of rock particles and the dimension of covering boxes showed correlations with disintegrating degree and eventually stabilized when the disintegration ended. From the gray relational analysis, the variation characteristics of circularity of the red-bed mudstone well reflect its disintegrating state. Therefore, the stability evaluation of the red-bed mudstone has a significant guidance in engineering construction.

Freeze-thaw weathering of rock mass is mainly controlled by several factors, such as lithology, structure of rock mass, saturated water and temperature. In this study, the freezing and thawing strain tests were carried out on four kinds of fractured rock from the cold zone of Xinjiang. The strain processes of dry and saturated fractured rock were obtained under freezing and thawing conditions, respectively. It is found that the saturated fractured rock under eight strain stages, while the dry fractured rock experienced five strain stages. The swelling-shrinking ratio of saturated fractured rock was defined under the freezing and thawing action. Furthermore, the fitting relationships between the ratio of different lithology and freezing-thawing cycles were gained. At the same time, the variation law of strain in the process of cyclic freezing and thawing was analyzed, which revealed that the maximum micro-strain of fractured rock at the frost heave stage increased with the increase of the cycle number. Besides, the freeze-thaw strain tests on jointed rockmass were conducted under different constant temperatures, and the fitting relationships between strain and different constant temperatures were obtained as well. Testing results demonstrate that the ratio increased with increasing the freezing and thawing cycle. Moreover, the variation degree of swelling-shrinkage rate was related to rock porosity characteristics. In addition, saturated jointed rockmass was highly sensitive to the temperature during the freezing and thawing process, and the damage was reflected as the thermal and frost heaving damage.

Consolidated undrained triaxial shear tests on thawed saturated clay with different initial compaction degrees were conducted under different strain rates and confining pressures to study the effect of strain rates on the mechanical properties of the thawed saturated clay. The stress-strain characteristic curve, pore water pressure, secant modulus (E50), peak strength, residual strength and shear strength index of thawed saturated clay were analyzed. The results show that when the strain rate increases, the peak and residual strengths of the saturated clay first increase then decrease, then continue to increase; but the secant modulus E50 increases continuously. The strain rate does not change the strain magnitude corresponding to the deviatoric stress peak. The initial compaction does not affect the strain value corresponding to the peak strength of the thawed saturated clay. And the initial compaction degree has little effect on the development trend of pore water pressure of thawed saturated clay at confining pressure of 120 kPa and strain rate of 0.15% / h. The effect of initial compaction is significant as the strain rate exceeds 1.5% / h. The confining pressures have great impact on the developments of the pore water pressures and the strain values at the peak strengths. With the increase of confining pressure, the strain value and the pore water pressure corresponding to the peak strength of the thawed saturated clay increase. Internal fraction angles decrease with the increase of strain rates when the strain rates slower than 15%/h, but increase with the increasing strain rates when the strain rates exceed 15%/h. Cohesion of the thawed saturated clay increases with the increase of strain rates. The results of this study imply theoretical significance to understand the effect of increasing the strain rate of molten soil.

It is known that bedrock fault movement can cause the deformation of overlying soil during an earthquake. However, the mechanisms of fault propagation in layered cemented soil and the influences of pre-existing fracture on soil have not yet been fully understood. In this study, four centrifuge tests were conducted on 9-layered soil of clay and sand to investigate the effects of cementation and tip depth of pre-existing fracture. Centrifuge testing results show that the layered uncemented soil was subjected to deform by the shear force after normal faulting. Then, an upside down trapezoidal distribution of uneven settlement area was formed, and a shearing localization zone was also developed above the bedrock fault. When the uneven settlement finally reached the ground surface, tensile ruptures were formed at the top of the unsaturated clay layer. The bending deformation found in the layered cemented soil induced the shearing and tensile ruptures. The depth of surface fault ruptures in cemented soil was greater than that observed in the uncemented soil. In layered cemented soil, with increasing the tip depth of pre-existing fracture, the dip angle of the rupture initiating from the tip of the pre-existing fracture increased, and the surface fault rupture moved towards the hanging wall.

To resolve the problem of large deformation of tunnel in shale caused by groundwater during construction in Northwestern Hubei, softening microscopic mechanisms and mechanical properties of water-saturated shale were investigated. At different water-saturated times, the water absorption and microstructure characteristics of shale were examined using X-ray diffraction, natural water absorption experiments and scanning electron microscope (SEM). Then evolution laws of strength and deformation parameters under different water-saturated times were analyzed by uniaxial compression tests. Experimental results show that, with the increase of saturation time, the water absorption of shale increased logarithmically, but the peak compressive strength and elastic modulus of shale decreased logarithmically. It is found that mechanical properties of shale changed rapidly within 20 days until stabilized after 50 days. As the chlorite and muscovite minerals in shale expand with the water, with increasing saturation time, the fine mineral particles were gradually stripped from the dispersed the lamellar structure. As a result, a large number of loose, porous flocs were produced. Due to the effect of hydration, the compact layer microstructure of shale became loose, and cementation among mineral particles was destroyed gradually, resulting in the growth of pores and cracks. Finally, the strength of shale and the ability to resist deformation were decreased, and the fracture surface became dense and interconnected.

An experiment is conducted to determine the active earth pressure for soil with limited width behind a retaining wall in translational motion. The test results show that a continuous failure surface of limited-width soil behind a retaining wall passes through the wall toe and a fixed point. Based on the variational limit equilibrium method, a specific equation for the curve of the slip surface is deduced with logarithmic helical curve. The distribution of active soil pressure and soil pressure intensity with a limited width behind wall are derived using thin-layer element method. Comparing with the results of laboratory observations and Coulomb earth pressure, the result by the proposed method is closer to the measured value than the classical earth pressure method. The distribution of the active earth pressure is analyzed under different ratios n of the width to height of the backfill. The results show that the active earth pressure increases with the increasing of n, but approaching to a constant value as n reaches a threshold of limited width of 0.55.

The capillary interaction among particles is an important aspect of analyzing the mechanical properties of wet granules. By considering the interaction between two spherical particles and the inter-particle meniscus, exact solutions for geometry and matric suction of the interface of gas-liquid-solid are deduced by shooting method. The results by the proposed method are compared with the inter-particle forces obtained by the annular approximation method and the data fitting method to evaluate the accuracy of the two simplified methods. The characteristic curves of the suction stress caused by the capillary action between the two spherical particles are analyzed for different inter-particle spacings, different liquid-solid contact angles and different matrix suctions. The results obtained by the fitting method are better for the smaller volume of the liquid, and the result by the circular approximation is closer to the exact solution than that by fitting method for larger liquid volume. This study provides some theoretical guidance for understanding the suction in unsaturated soils and microscopic analysis of unsaturated soil mechanics.

The infiltration of irrigation water on Heifangtai loess plateau raises the groundwater level and saturates the deep soil all the time. Lixiviation caused by underground water takes away much salt and changes chemical components in pore water at the same time, which affects the strength of loess. In this study, the shear strength and physicochemical characteristics of loess are investigated using ring shear apparatus, laser particle size (LPS) analyzer, Zeta probe (potential measuring apparatus), inductively coupled plasma emission spectrometer (ICP-OES), ion chromatograph. The test results show that the curve of strength (internal friction angle)－soaking time is in a “spoon” shape. Based on the results of physical and chemical tests, mechanism of strength weakening of loess soaked in water is discussed. The cements (soluble salt) among loess particles dissolve in water rapidly, breaking the microstructure and making the internal friction angle decrease. At the same time, ion concentration in the pore water increases, and the ions exchanged with outer layer of clay particles, leading to a decrease in the thickness of adsorbed water of clay particle so as to make the internal friction angle increase slightly. With the increase of soaking time, gypsum dissolves in sodium chloride solution and coarse particles are dispersed into clay particles further, then the total thickness of electrical double layer increases, so the internal friction angle decreases slightly.

In the process of long-term operation of salt cavern storage, the surface subsidence prediction is important for the storage safety assessment. So far, there is no analytical model based on the theory of mechanics. The problem of the surface subsidence above salt cavern storage is similar to the one of boundary deformation of the sphere cavern with shrinkage force in the elastic half infinite space. By using the spherically symmetric displacement of the sphere cavern with shrinkage force in the elastic infinite space, the elastic analytical solution of the surface subsidence in integral form is derived with the principle of superposition. The surface subsidence is caused by the sphere cavern under a certain internal pressure in the half infinite space. Then, regarding volume deformation as elasticity and distortion as viscoelasticity Maxwell with the correspondence principle, the elastic analytical solution is transformed to be a viscoelastic analytical solution in integral form in space-time domain by Laplace transformation. In comparison with the results of numerical simulation, the accuracy of the elastic model is verified. Finally, the viscoelastic model is applied to predictive analysis of the surface subsidence in a salt cavern storage, and is compared with the observation data in cavern site, demonstrating the new model to be effective in predicting the surface subsidence and its development trend of the salt cavern storage. Therefore, the model can be expected to provide a theoretical method for subsidence prediction of salt cavern storage.

Based on Clough system stiffness model, this paper introduces a novel synthetic stiffness expression of strut system for excavation. This expression considered the wall stiffness, strut stiffness and the soil stiffness behind the wall, and thus it had substantial advantage to predict the deformation induced by excavation. Clough system stiffness, Bolton system stiffness and the synthetic system stiffness proposed in this paper were applied to measure the tilt of 469 retaining walls in 22 deep excavations of Tianjin subway line 6 engineering. The maximum deformation of the retaining structure in foundation pit decreased with the increase of the stiffness of the dimensionless composite support system. The deformation value tended to be constant, until increased to a certain value. When the mobilized undrained shear strength ratio of soil was further analyzed, it is found that the ratio of the soil behind the wall along Tianjin subway line 6 was less than 0.6. The upper limit value of this ration is 0.8, which indicates that the excavation engineering of Tianjin subway line 6 has sufficient safety reserves. Therefore, research results can provide significant reference for the economic and safety design of similar engineering.

Different geomorphologic zones of coral reef demonstrate different geological engineering behaviors and mechanical properties. In order to investigate the engineering behaviors and its regularity, a series of tests including plate loading test, deep spiral plate loading test, compaction test and resilience modulus test is conducted on different zones in Yongxing Island, South China Sea. Engineering mechanical parameters including bearing capacity, deformation modulus, rebound modulus of coral reef are obtained. The test results show that the bearing capacity and deformation modulus of artificial calcareous soil ground are higher than those of reef flat foundation and sand bar foundation. The bearing capacity of artificial calcareous soil ground ranges from 320 to 360 kPa, and its deformation modulus ranges from 95 to 200 MPa. The bearing capacity of ground satisfies the requirement of low-rise buildings. As settlement of calcareous ground accompanies instantaneously under loading, fast loading method can be adopted in the plate loading test. The bearing capacity of subgrade above underground water table increases with increasing depth, but decreases below underground water table. The modulus of resilience increases with compaction. It can reach a range from 472 to 730 MPa with the degree of compaction over 87%.

Moving element method (MEM) is an efficient approach for dynamic analysis of structure under moving loads. However, a paucity of the research adopting the method for the dynamic analysis of the saturated porous media was found in literature. Based on the coupled dynamic field equation u-p formulation, MEM formulations of the transient-state and steady-state dynamic control equations are obtained. The accuracy and the effectiveness of the technology demonstrated through the results that are in general consistent with each other by the semi-analytical and numerical solution. An example of involving the moving load on the saturated pavement overlying elastic base course is analyzed based on MEM. The transient dynamic response and the steady dynamic response are explored. The results show that obvious transient effect comparing with the steady-state dynamic response is indicated by hydrodynamics. Based on the results of steady-state dynamic response, the influences of load velocity, drainage boundary and permeability coefficient on the dynamic response of saturated asphalt pavement are analyzed. The results of the study can provide a reference for analyzing the damage mechanism of asphalt pavement water stability under hydrodynamic action.

Earth pressure is one of the traditional research subjects in geotechnical engineering. With respect to the structural loess, shear strength and tensile strength are two aspects of structural loess strength characteristics. Therefore, the impact of tensile strength of loess on the earth pressure calculation needs to be evaluated reasonably. Based on the theory of joint strength considering tension and shear properties of loess simultaneously, a new formula of active earth pressure is derived to analyze equilibrium of active limit stress state. The formula is verified and compared with Rankine’s active earth pressure. Result shows that the active earth pressure based on the joint strength theory is larger than Rankine’s active earth pressure determined by traditional Mohr-Coulomb theory, and the tensile crack depth of soil behind wall is relatively small. Due to the overestimation of the tensile strength in Mohr-Coulomb strength theory, the value of Rankine’s active earth pressure is underestimated. However, the theory of joint strength based on tensile strength of loess can reasonably calculate the active earth pressure.

Although suffusion in the deep sandy gravel foundation probably cannot lead to seepage failure of the dam, fine grains inside the sandy gravel are lost. It results in increasing the permeability of the soil, but decreasing its strength and deformation modulus. The former causes the change of the seepage field of the foundation dam, which further induces the changes of deformation and stress of the dam body. While the latter reduces the deformation modulus and leads to the deformation and stress adjustment of the dam foundation. Since the stress and deformation of a dam and its foundation caused by suffusion bring some negative impact on the normal use and dam safety, quantitative assessment of the impact is urgently required for both of the design and operation management of such dams built on a deep internal instability sandy gravel foundation with a suspended cutoff wall. Therefore, a simulation method was proposed to investigate the effect of suffusion within the foundation on stress and deformation of the dam. A dam design with a typical suffusion suffered foundation was calculated and analyzed. It is found that in these two schemes, the effect of seepage fields on the stress and deformation of the dam foundation is much greater than that caused by the modulus decay. In general, the safety of the dam is not significantly reduced by the deformation and stress changes of the dam caused by suffusion.

In this paper, we prepared samples of grouting-reinforced fractured mudstone with different grouting contents and moisture conditions by simplifying the simulation of grouting process. Dynamic characteristics of grouting-reinforced fractured mudstone sampled were investigated by a split Hopkinson pressure bar (SHPB). Furthermore, the experimental process of SHPB test was simulated by using finite element software Ansys/LS-Dyna, and numerical results were analyzed and compared with experimental data. The results show that dynamic properties of samples were significantly influenced the grouting content. The best grouting effect was achieved when the degree of mudstone crushing was moderate and the slurry had a good pressure condition. In addition, the water content obviously affected the dynamic behaviors of samples with the same grouting content. In general, the higher water content resulted in smaller peak strength and elastic modulus. The stress-strain curve by numerical simulation was in good agreement with experimental one. The rationality analysis of the HJC model parameters shows that there is a strong correlation between the model parameters (A and B) and dynamic peak stress, and their values increase with the increase of strength.

To resolve problem of poor convergence in open-close iteration of discontinuous deformation analysis, an improved DDA method based on approximated step function and Lagrange interpolation is developed based on the relationship between the state of contact constraints within blocks and the block displacement. Hyperbolic tangent function is used to approximate the step function. The state of contact constraints within blocks is represented by block displacement using step function, which replaces the function of open-close iteration and avoids the problem of poor convergence in open-close iteration. The potential energy function of block system only containing the block displacement as unknown variable is derived with the principle of Lagrange interpolation. The extremum of general potential energy function is analyzed to obtain the block displacement. With the model of sliding block and underground chamber respectively, computational accuracy and computational speed of the improved DDA method are analyzed, and the correctness and the iterative stability of the improved DDA method is verified. Research shows that the improved DDA method based on approximated step function and Lagrange interpolation produces high precision, and it has a more stable and more robust computing convergence compared with the traditional DDA. Therefore, the improved DDA method based on approximated step function and Lagrange interpolation is a stable and effective numerical method and it provides a new approach for solving the problem of poor convergence in open-close iteration of discontinuous deformation.

To investigate the transient liquefaction stability of dense seabed soil beneath the offshore bridge under extreme wave loads, a finite element numerical model for simulating dynamic response of seabed is developed and solved by RANS equation and Biot equation. Accuracy of the proposed model is verified by experimental data from literatures. The distribution of the wave pressure field is applied to analyze the effects of the wave characteristics and the submerged depth on the transient liquefaction stability of dense seabed. Results of numerical simulation indicate that the submerged girder can significantly affect the wave pressure field, and the amplitude of the liquefied depth in front of the girder is greater than that in rear of the girder. The largest liquefied depth is located within the range of 1/10-1/8 distant from the front of the box girder. The amplitude of the liquefied depth increases with the increment of both wave height and wave period. The seabed in front of the box girder is the easiest to be liquefied when the box girder is just submerged while the seabed gets more stable with the increment of the submerged depth in rear of the girder. The results of the study can provide a reference for the safety analysis of cross-sea bridges.

Discrete element method (DEM), such as particle flow code (PFC), has become one of the current highlights to investigate the particle breakage process in the geotechnical field. In this study, based on the point load crushing criterion considering the local stress concentration, a three-dimensional (3D) particle crushing model was established. Particually, the particle balance among particles before and after crushing is ensured by the Apollo filling and expansion method, and a size effect factor is used to characterize strength of particles with different sizes. Then, numerical simulations were performed on three types of sand with different degrees of breakage, namely silica sand, calcareous sand and Sacramento River sand. The comparisons of numerical and experimental results show that the established model can well describe compressive properties of granular materials with different degrees of breakage. Comparing with the failure criterion rooted in Mohr–Coulomb theory on the basis of mean stress, the criterion in the established model shows a better manner in reflecting the real fragmentation phenomena under the same loading condition. At the same time, the established model reveals the influence of crushing on the anisotropic dissipation and gradation evolution of granular materials.

Damage characteristics and damage evolution mechanism of post-peak fractured rock mass are critical for controlling the stability of surrounding rock in underground caverns, tunnels and other rock engineerings. Since the current study on damage and destruction characteristics of post-peak fractured rock mass is insufficient, and its understanding is not comprehensive, the potential engineering accidents may occur, such as large collapse and large deformation. In this study, a series of triaxial tests was carried out to investigate mechanical properties of the post-peak fractured rock mass. Then, the corresponding nonlinear damage characteristics were analyzed. Assuming that the rock damage satisfies the Weibull distribution rule, a constitutive equation of the fractured rock was deduced by introducing a damage variable. A nonlinear damage and failure criterion of post-peak fractured rock was established by combining with the energy dissipation principle and strain energy density theory. Based on the above principle, the calculation program of damage failure of post-peak rock was developed according to FISH language, and the simulation of the non-continuous process of post-peak fractured rock was realized using a continuous method. As a result, the damage and failure characteristics and its evolution rule of post-peak fractured rock mass were revealed. Furthermore, numerical results were compared with triaxial compression results. It turns out that the constitutive equation and the discriminant criterion can well simulate the nonlinear damage and rupture process of fractured rock. Therefore, this study can provide a new theoretical analysis method to effectively control the stability of surrounding rock.

In recent years, the mountain tunnel collapse accidents occur frequently in China, which results in heavy casualties and huge property damage. Hence, the real-time field monitoring of surrounding rock stability and the early safety warning have become one of the key issues in current mountain tunnel constructions. Firstly, this paper clarified all the relating concepts of the remote online monitoring technology, including its signal collection, transmission and background processing principle, focus control system (FCS) and general packet radio service (GPRS). Then, a new type of tunnel remote telemetry system was proposed. The system adopted the wired and wireless networking schemes in the tunnels, including the signal collection and transmission subsystem, the management analysis subsystem and the remote receiving subsystem. Finally, the system was applied to Dashizi tunnel with the high-risk collapse, the longest road tunnel in Ningbo. All-weather real-time high-frequency monitoring was recorded, including the deformation of surrounding rock, the stress of bolts, and the shotcrete stress between surrounding rock and steel arch. In addition, server + client mode was employed to achieve a high-speed transmission of remote data and multi-unit real-time monitoring. The obtained time-history curves (i.e., deformation, stress and pressure) were analyzed. It indicates that the deformation of surrounding rock of Dashizi tunnel shows a change of the step-like fluctuation and exhibits a mutation after blasting excavation. Meanwhile, it is found that the deformation of surrounding rock and the pressure of the shotcrete layer are greatly affected by the tunnel excavation disturbance. However, the overall trend of change basically undergoes rapid change at the early stage, a slow change at the middle stage and the gradual stability at the late stage. Through the remote online monitoring of the tunnel for nearly one year, it shows that the technology can realize the long-range telemetry and unattended warning of the stability of underground engineering surrounding rock, which has great application prospect.

Since the instability of dangerous rock mass exhibits as the sudden collapse of destruction, no obvious displacement characteristics can be identified. Thus, the application of conventional displacement monitoring techniques is difficult to achieve the purpose of monitoring and early warning. In addition, the stability of dangerous rock mass is influenced by the bonded area between dangerous rock block and bedrock, which is considered as one of the critical parameters. However, this bonded area is hard to obtain, which makes it difficult to evaluate the stability of the dangerous rock block. In this study, we assume that the rock block is homogeneous and isotropic, the main control structural plane is a single plane, the damping ratio of the system is less than 1 and the deformation is linear elastic deformation within the amplitude range. As a result, the vibration model of the dangerous rock mass can be simplified as a spring oscillator model. Then, the relationships among the natural vibration frequency of dangerous rock mass, the bonding area, the elastic modulus and the quality of dangerous rock mass were established by the theoretical derivation. Considering the limit equilibrium model, a new model based on natural vibration frequency was derived to evaluate the stability of dangerous rock mass. A dangerous rock block on the right bank of Baihebao reservoir was selected as the case study. A wireless vibration sensor (micro core) was fixed on the dangerous rock block to acquire data, which was converted to natural vibration frequency by the Fourier transform and other mathematical methods. Furthermore, the bonded area was determined according to the relationship among natural vibration frequency, rock block bonding area and elastic modulus. Finally, the stability evaluation of dangerous rock mass was completed using the new model. This case study verifies the feasibility of the proposed procedure with a faster rate and more accuracy than traditional methods.