New development of mechanics and application for unsaturated soils and special soils are systematically summarized. The contents of the paper consist of developing equipment, basic property, theoretical model and application in engineering. Attention is paid to the advancing front scientific problems, such as stress theory and constitutive model of unsaturated soils, as well as the thermodynamical characteristics of buffer material. In the progress of basic property of unsaturated soils and special soils, the moisture retention, water and air migration, structural fabric evolution, strength, stress theory, constitutive model and numerical analysis are discussed in the paper in detail. Regarding research advance of special soils, 16 kinds of soils are discussed, and the loess and expansive soil widely distributed in China, as well as buffer material for geological disposal repository of high-level radioactive waste are emphatically introduced. The relative problems such as earth pressure, humidifying deformation, creep properties，immersion test, slope, dynamic property and geologic hazard are also discussed in detail. In addition, practical application of theoretical results and functional technology are introduced. Finally, some proposals for further research are presented.

Rock salt has been recognized as a highly suitable medium for geological storage of oil, gas and radioactive wastes because of its low-permeability, high-ductility, low-creep strength and capacity for self-healing. The self-healing of damage, as a significant part of damage evolution of rock salt, has important influence on the stability and permeability of rock salt in excavation disturbed zone (EDZ). The research progress of damage self-healing property of rock salt is summarized from the aspects of mechanism, influencing factors and constitutive models, and the research advances in damage self-healing property of rock salt in China are summarized. In the EDZ, damage healing can occur under three different mechanisms: mechanical closure, diffusive healing driven by surface energy reduction and healing by recrystallization. The major factors that may affect crack healing are stress, temperature, initial damage, humidity, chemical environment and so on. The MDCF model and the Lux/Hou model which consider the self-healing characteristics of salt rock damage are introduced. Furthermore, several key research directions on the damage self-healing of layered salt rock in China are put forward.

A simplified method based on the load transfer approach is proposed for the working performance analysis of single energy piles. In the method, the load transfer function is chosen as a hyperbolic curve, and the unloading and reloading characteristics of pile-soil interface during temperature cycling are simulated by Masing's criterion. The accumulation of plastic deformation is approximated by reduction of stiffness during reloading. The location of the null point can be naturally determined by solving the governing equations through the matrix displacement method. The pile displacement, the axial force, the shaft resistance, and the base resistance can also be obtained. The proposed method is validated by comparing the predicted values with the experimental data collected from literatures. Finally, the long-term performance of single energy piles is studied with an example. The computed results indicate that the thermal cycles increase the settlement of free pile top and decrease the stress of fixed pile top. The influence of the thermal cyclic loading is related to the static load level and the degree of the stiffness degradation of the surrounding soil.

The holistic analysis of all the pores within the range of experimental measurements is often performed when studying the fractal characteristic of soil pores under compression. However, this studies show that the fractal behavior of large pores has great difference with that of small pores, especially their response to compression. To illuminate the different fractal characteristics, the different responses of large and small pores under compression, and describe their variation laws, the pore-size distribution data of Wuhan clay with different dry density are obtained by mercury intrusion method. Afterward, these pore-size distribution data are analyzed and fitted to obtain the fractal dimensions based on fractal theory. The result shows that, there is a special critical pore-size in the pore volume and pore-size distribution curve. The distribution laws of pores larger and smaller than critical pore-size, as well as their responses to compression deformation, are significant different. The pores larger than the critical pore-size are defined as large pores and those smaller than the critical pore-size are defined as small pores. The distribution of small pores has stronger natural fractal characteristic, and does not vary with the dry density, which is referred to as intrinsic fractal characteristic. The distribution of large pores is far from the intrinsic fractal characteristic, which indicates that its fractal behavior is weaker than that of small pores. With the increasing of dry density, the fractal characteristic of large pores is gradually enhanced to continually approach the intrinsic fractal characteristic of small pores. Therefore, the intrinsic fractal characteristic of small pores can be used as a compacted reference indicator of clay, and the essence of compression process is that the large pores adjust to a stronger fractal distribution under compression and gradually approach the reference indicator.

Reasonable and accurate evaluation of rock brittleness is the precondition of engineering practices, such as the assessment of rock burst risk and fracturing of oil and gas reservoir. In this paper, the applicability and limitation of energy drop coefficient for characterizing the failure process of brittle rock are analyzed in detail. In order to evaluate the brittleness of rocks more effectively, based on the stress-strain curve of the whole process of rock failure and the energy drop coefficient, a revised energy drop coefficient is developed by considering the ratio of released elastic energy in the total energy of the pre-peak stage. It is considered that brittleness is a comprehensive manifestation of releasable elastic energy stored in large quantities in the pre-peak stage and released rapidly in the post-peak stage. The experimental data of marble and granite under different confining pressures are analyzed and compared. It is found that the revised energy drop coefficient can not only reflect the brittle-ductile behavior of same rock under different confining pressures, but also effectively evaluate the degree of brittleness of different rocks under same confining pressure. In addition, the influences of Poisson’s ratio and damage variable on rock brittleness evaluation are discussed, the brittleness of granite is found greater than that of marble under each confining pressure with the increase of Poisson’s ratio; and with the increase of damage variable, the brittleness of granite is firstly greater than that of marble and then less than. The test results verify the reliability of revised energy drop coefficient, which may be expected to provide some references for rock brittleness evaluation.

The stability of steep bedding slope is generally better under static force condition, but lots of instable fracture phenomena occurred in this type of slop during “5.12” Wenchuan earthquake. A special dynamic deformation failure mode, toppling deformation, is found in steep soft-hard alternative bedding slope by field investigation. Based on existing knowledge and a failure case, i.e. Shuimogou soft-hard alternative bedding of steep slope in Wenchuan County, Sichuan, the mechanism of toppling deformation and the characteristics of dynamic response of this type of slope under strong earthquake are studied by centrifugal shaking table test. On slope surface, acceleration amplification factor increases first, then decreases, and finally increases with the increase of elevation. The dynamic response shows two peak values at 1/3 of slope height and slope shoulder. At the same horizontal height, the closer to the slope surface, the greater the magnification factor of acceleration, which means that the free face effect of slope rock-soil body is more significant. Experiment reveals the instability mechanism of this slope: under the repeated actions of strong earthquake loads, differential shear failure occurs between soft rock and hard rock, rock-soil body sliding along the dominant layer is hindered, the rock-soil body nearby slope toe bends and uplifts; the potential sliding surfaces are not connected completely, under the tremendous horizontal inertia force of earthquake, shattered rock stratum at slope shoulder generates cantilever beam bending toppling toward free face, so that the entire slope undergoes tension fracture slippage?lower bending?upper toppling instable fracture.

To investigate the influence of soil particle-size gradation on geogrid-sand interface, a series of large-scale direct shear tests, cyclic direct shear tests and post-cyclic direct shear tests is performed on geogrid and sand with three particle-size gradations. The interface shear stress, shear displacement and vertical displacement are analyzed in direct shear tests and cyclic direct shear tests. The influence of cyclic shear history on interface behavior is studied through the comparison and analysis of the results from direct shear tests and post-cyclic direct shear tests. Results show that, in direct shear tests, the shear softening phenomena occur on geogrid-sand interfaces under different soil particle-size gradation, which is more significant under higher vertical normal stresses. In cyclic direct shear tests, the shear hardening phenomena appear on geogrid-sand interfaces under different soil particle-size gradation, and the interface of geogrid-good graded sand has the highest shear strength under the same cyclic number. The apparent interfacial peak adhesion and apparent residual adhesion decrease with the cyclic shear tests, while friction angle increases with the cyclic shear tests. The post-cyclic shear strengths of three types of geogrid-sand interfaces in direct shear tests are higher than those of monotonic direct shear tests.

The repetitive shear test and anisotropic shear test of structural planes with the same morphology have always been challenging in the experimental study of shear mechanical properties of rock mass which are of significance to the mechanical response during excavation and stability analysis, evaluation and control of engineering rock masses. The key to this challenge is to reproduce the structural plane topography for the same type of rock. Based on 3D scanning and 3D carving techniques, a large number of marble structural plane samples with three different roughness are reproduced. To investigate the anisotropy of shear characteristics, direct shear tests are conducted on marble joint samples with same surface morphology under different normal stress conditions. The results show that under the same normal stress but different shear directions, the shear strengths, dilation characteristics and shear failure characteristics of marble joint samples with the same surface morphology are obvious anisotropic. The anisotropy of shear strength is largely dependent on the anisotropy of joint roughness. With increasing normal stress, the anisotropy of shear mechanical characteristics of rock joint gradually decreases. The 3D carving technique is a good method to investigate the anisotropy of shear characteristics of natural rock joints and can play an important role in further study of this problem.

As the research demands develop in the seismic reinforcement of bridge foundation on slope in engineering practice, a shaking table model test of bridge foundation on a slope reinforced by the front and back row anti-slide piles is introduced, in which the dynamic loading is applied in form of sine waves with different frequencies and peak accelerations. This study emphasis on the analysis of mechanical responses of the bridge foundation and anti-slide piles, and the developing process of landslide and dynamic response performance. Results show that the front and back row anti-slide piles should keep a proper distance to the bridge foundation, so that the mechanical responses of bridge pile foundation are more reasonable. As the dynamic load of upper structure affect bridge foundation greatly, the strain decreases along pile depth and the strain attenuation is related with soil resistance. When the back row anti-slide piles are cracking, the pile strain decreases significantly and the unloading effect appear in soil pressure behind piles. However, there is potential bearing capacity on pile strength. The landslide failure starts in the section dangerous in stability. The frequency-band coupling effect produce gradually before the back row anti-slide piles reaching the limit loading in vibration, and then the unloading effect take over after the limit loading state.

Rock size is an important factor influencing its mechanical behavior. Rock burst is a special mechanical response of rock under complex stress conditions. The study of size effect on rock behavior in rock burst is of great importance. A modified true-triaxial apparatus and acoustic emission (AE) monitoring system made by Physical Acoustics Corporation are used to perform laboratory rockburst simulation tests on granite specimens with different heights. The fracture characteristics of rock are observed, and the AE waveforms spectra characteristics are studied. The experimental results indicate that the critical failure stress of rock samples has an increasing trend as the sample height decreases. The fracture surface characteristics of rock after rockburst have undergone a transition from splitting tension failure to shear failure with the decrease of specimen height. Meanwhile, AE energy rate, which can reflect rock damage, increases gradually as the sample height decreases, indicating faster release rate of AE energy. Using fast Fourier transform (FFT) to process extracted waveform files at typical stages, it can be found that rock samples with different heights have a similar variation in the major frequency, which transits from low frequency to high frequency and finally back to low frequency. The most important characteristic frequency, is located in the lower frequency ranges of 90~120 kHz. The high frequency part of the spectrum characteristics varies with the height of the specimen.

In the shaking table model test on liquefiable sandy soil, the duration, frequency, energy and other characteristics of ground motion have changed after the seismic record time is compressed according to the time similarity ratio, and it will have a significant impact on the dynamic response of liquefiable foundation under seismic loading. The time compression ratio is the only variable in this series of shaking table model tests, and the effects are analysed by the characteristics, such as macroscopic phenomena, acceleration, pore water pressure. The effect of dynamic response of liquefied site in the shaking table tests with seismic record after time holding compression is researched in this paper. Results show that when the PGA of the input ground motion is similar, liquefied site may not be liquefied if the seismic record time is compressed. The longer the duration, and the greater the energy of the ground motion, excess pore water pressure accumulates rapidly, and the phenomenon of soil liquefaction and the filter isolation effects are obvious. According to the results of the tests, it is suggested that the original ground motion could be directly adopted by the shaking table tests regarding liquefaction as research objective.

In order to clarify the concept confusion and to avoid repeated calculation of the force in the groundwater condition, the characteristics of three kinds of groundwater forces in soil, namely pore water pressure and buoyancy and seepage force, are discussed. It is emphasized that the pore water pressure in seepage environment is related to water depth and hydraulic slope according to the energy conservation theory. Then the equivalent relationships for two volume forces (buoyancy and penetration) to the boundary force (pore water pressure) are discussed. The calculation method of groundwater force acting on the separate soil skeleton and the unity of soil skeleton and pore water in a seepage environment is explored. The former should use seepage force and effective gravity of soil particle to calculate equilibrium. The latter should use pore water pressure and saturated gravity of soil to calculate equilibrium. Then the improper use of the groundwater force in present codes for landslide stability analysis related to landslide control engineering is discussed in this paper. In addition, the calculation deviation caused by the improper use of the groundwater force is illustrated in an engineering example. The results show that two problems exist in the relevant specification: pore water pressure is calculated without considering hydraulic slope angle and the concept of pore water pressure and buoyancy are confused. Both cases will cause partial conservative design and engineering management based on the latter case will arise large economic waste.

Experimental model tests and numerical modelling were carried out to reveal characteristics of the concentration field of flow field in a double-well water-soluble cavity with the small spacing in the layered salt rock. Based on a dimensional analysis method, a similar model experiment platform was established to simulate the flow field in the cavity during its construction. The flow field migration law of the cavity and the intra-cavern concentration were measured by the dyeing method and a time averaging method respectively. It is found that the higher the flow rate was, the higher the limit height of the plume was. However, the change rate of concentration in the cavern decreased and the concentration of the outlet declined. The variation of the height of casing pipe actually changes the initial space position of freshwater relative to the cavity. The change of the interlayer occurrence state can be seen as changing the spatial position of the interlayer in the cavity, and interlayer in different regions change the movement trend and the range of action of the cavity flow field. 3D numerical calculation was conducted by using the Fluent software. The same stratified results were obtained as them from experiments in the laboratory, which verified the general rule of flow field from tests. However, in terms of velocity distribution, it was found that the flow field at the bottom was not macro-flow, which was dominated by natural convection, diffusion and sedimentation.

A series of undrained cyclic triaxial tests under coupling effects of cyclic deviator stress and cyclic confining pressure is conducted on Ningbo remoulded saturated soft clay by using GDS cyclic triaxial system. The coupling effects of cyclic deviatoric stress and cyclic confining pressure on undrained dynamic behaviors are studied. The influences of cyclic confining pressure and vibration frequency on permanent axial strain and pore pressure are further analysed. The experimental results show that under undrained condition, coupling of cyclic deviator stress and cyclic confining pressure limits the development of the cumulative plastic strain of saturated soft clay to some extent. With the increasing of the slope of loading paths ? and vibration frequency f, the permanent axial strain decreases. The relationships between permanent axial strain rate and cyclic time are identical under different stress paths and frequencies. The relationship between strain rate and cyclic time are more obviously affected by the slope of loading paths ? comparing with the loading frequency, and the strain rate decreases with the increase of ?. However, the curves of strain rate under different vibration frequencies almost coincide with each other. On the other hand, the maximum pore water pressure increases with the increase of cyclic confining pressure and decreases with the increase of vibration frequency. Based on the test results, a linear relationship between the permanent strain rate and cyclic time is established in log-log scale coordinates system.

Biogenic coral-reef limestone is distinct from the traditional geological rock. In this study, Hopkinson pressure bar tests on coral-reef limestone are conducted to investigate the dynamic fracture morphology and dynamic properties of coral-reef limestones of the South China Sea. Research results show that the high-strength and dense coral-reef limestone with vertical sedimentary evolution has high elastic wave velocity and uniaxial compressive strength; the tensile failure of coral-reef limestone mainly occurs along axis under uniaxial impact loading, and mainly in the weak parts such as the cementation surfaces between the bio-component, coral gravel and coral algae; the dynamic stress-strain model of reef limestone has obvious compaction stage, which is different from normal rock; the dynamic compressive strength of coral-reef limestone is more sensitive to the strain rate than that of normal rock；the energy density of the coral-reef limestone is linearly related to the incident energy and the dynamic compressive strength, and it shows a power function relationship with the strain rate. The dynamic mechanical properties of coral-reef limestone has an important guiding significance for the reef engineering practices such as blasting excavation, impact crushing, earthquake proof and antiknock design.

Calcareous sand, as a porous medium deposited in marine environment, is an ideal material used for a protective cushion. A total of 83 SHPB tests were conducted on calcareous sand sampled from South China Sea and silica sands bought from Fujian Province with identical grain size distributions and relative densities. The curves of stress wave transmittance, shock response and energy absorption efficiency were obtained. The effects of strain rate, relative densities and moisture content on the impact characteristics of two kinds of sand were analyzed. It is found that the stiffness of calcareous sand is only 10% that of silica sand under the same load and boundary conditions. Because of the existence of inner pore, the attenuation of shock wave in calcareous sand is greater than that in quartz sand. Within the bearing capacity, reducing relative density and increasing water content can effectively improve energy dissipation effect of protective cushion of calcareous sand.

liquefaction and sand boiling are common failure phenomenon during the suction penetration for bucket foundation. However, the jacked penetration can avoid such failure phenomenon. The jacked penetration tests of bucket foundation with different sizes is designed in the laboratory. The earth pressure internal and outer the bucket body is discussed in the process of penetration, meanwhile, the soil displacement field is obtained by using digital image processing technology. Test results show that the soil plugging effect of bucket foundation appears when the penetration depth reached 1 times of the diameter of bucket, and the incremental filling ratio of soil plug is about 0.7 after penetration. The penetration resistance and the inner earth pressure of bucket increase linearly with the penetration depth during the penetration, then exponentially grow when the penetration depth reaches half times of the height of bucket shirt. The soil plug is more effective with 10 cm in diameter of bucket, and the height of soil plug is 15 cm. There is a soil arching effect inside the bucket, a passive soil arch is formed first at the end of bucket, then destroyed as the penetration depth increase, and the active soil arch form.

To investigate the acoustic emission (AE) characteristics and damage evolution process of salt rock during the long creep process, uniaxial creep AE tests were carried out by using a large-scale programmed rheometer and the PAC Sensor-highway II AE monitoring instrument at Sichuan University. The strain law and AE test results of the long creep process of salt rock were analysed, and the evolution process of the whole creep damage was discussed in detail. The results show that the salt rock undergoes an initial attenuation creep stage, a steady creep stage and an accelerated creep stage during the creep period of about one year, in which the steady creep rate is basically maintained at 6×10-5 d-1. The variation of characteristic parameters of AE in the whole creep process is basically consistent with the creep strain trend, showing an "active-quiet-active" trend. According to the AE parameter characteristic curve, the salt rock can be predicted to begin the accelerated creep stage at 300 days, and it is more accurate than the creep strain trend line, which provides experimental fundamentals for the construction of the gas storage. According to the characteristics of temporal and spatial evolution of AE, the damage path of the long-duration creep damage of the salt rock is from the form of "end-central-whole part". The change trend of the damage variable based on the AE ringing counts is consistent with the creep strain trend. Moreover, the fractal dimension of AE in the whole process of the salt rock shows a "decreasing-fluctuating-rising" trend, which indicates that the AE undergoes a process from disorder to order and then to disorder, and changes with the creep rate curve consistent. The inflection point of fractal dimension is consistent with that of AE in predicting an accelerated creep inflection point, and further analysis shows that the fractal dimension of AE is basically fluctuating up and down at the value of 2. The damage variable rate is basically stable at around 0.002 d-1.

The unsaturated intact loess has obvious structural characteristics which significantly affect its mechanical behaviors. However, introducing structural characteristics into multi-field coupled analysis of collapse deformation for unsaturated loess foundation has not been widely reported, and further research is urgently needed in this field. Based on the established elastoplastic damage constitutive model for unsaturated intact loess combining water – gas migration law of unsaturated loess, a new elastoplastic damage seepage-consolidation coupled model is presented in this paper, which considers the influence of structural damage. The concrete expressions of the governing equations of the new coupled model in the two-dimensional coordinates are derived, and the governing equations are discretized in time domain and space domain by Galerkin method, respectively. At the same time, the concrete expressions of each element of the modulus matrix are obtained, and a multi-field coupling finite element program named after ULEDSC is compiled. Large field immersion test of loess foundation is simulated by this new program (taking in-situ soaking test of the self weight collapsible loess site in Heping town, Lanzhou city, Gansu province as an example). The pore pressure, displacement and damage fields during wetting and subsequent drying processes are obtained in this paper, which reveals the multi- field coupling response of self weight collapsible loess foundation because of the action of water and self-weight of loess. The research results in this paper can give scientific basis for the project design of loess area, and the new compiled finite element program is a powerful tool to solve the problem of loess collapsibility.

Water-rock interaction is one of the most important causes of surface weathering, structure damage and strength reduction of rock. Water-rock interaction is also a classical problem of research field of rock and soil mechanics. In order to investigate the deterioration characteristics and mechanism of acoustic wave properties of red-bed sandstone in Lanzhou City, Gansu Province, a series of dry-wet cycle tests with different salt solutions is conducted. The research results show that the mass, P-wave and S-wave of red-bed sandstone specimens gradually decrease with the increasing of the number of dry-wet cycles with salt solution, especially with sulphate solution. Furthermore, it is easier for the samples perpendicular to the direction of bedding plane than the samples parallel to the direction of bedding plane to get deteriorated. Based on the P-wave spectrum analysis, the sulphate solution causes more energy loss than the sodium chloride solution. For the same salt solution, there is a highly positive correlation between the energy loss and the salt solution concentration. During the deterioration process, there are two types of deterioration, the end-face pulverization and rupture along the bedding plane. The microstructure analysis indicates that the cementation weakening of mineral particles and void increasing of rock due to the dry-wet cycles with salt solution are the main reasons of degradation of red-bed sandstone acoustic wave properties. Research results have important implications for the long-term slope stability evaluation of red-bed sandstone, and the evaluation and control of weathering disease of stone cultural heritage.

It is easy to observe the development of vertical joints of aeolian loess on the edge or shore of a plateau, and these vertical joints can readily induce loess disasters due to changes in the water environment. The vertical joints of loess were investigated in this study. The developmental laws of vertical joints of loess in horizontal and vertical directions were summarized based on their meso-microscopic developmental characteristics. The display forms, transformation mechanisms and the micro-mesoscopic structural basis for forming vertical joints of loess were observed on different evaluation scales. Based on the sedimentary dynamics of loess, the vertical developmental mechanism of vertical joints was discussed. Studies had shown that vertical joints formed gradually during the historical sedimentary process and were the product of diagenesis. It was proposed that the pore concentration zone and vertical tubular channel in loess were the micro-mesoscopic structural basis for the development of vertical joints, for which the results of a three-dimensional CT scanning test provided strong evidence. The vertical joints exhibit different forms on different evaluation scales. Under external actions (wet and dry cycling and loess pile thickening), the vertical joints in the micro-meso-sub-macro point of view can be developed in an upward scale (expansion characteristics) or downward scale (decay characteristics), and they can transform between the two scales. This is referred as the scale conversion mechanism. The vertical developmental mechanism of vertical joints of loess was also proposed based on this.

NMR technique was used to test the micro-structural characteristics of the saline soil solidified with different proportions of water glass, lime and fly ash, lime and fly ash and water glass respectively. Combined the unconfined compression strength tests, the solidified effect of saline soil was analyzed, and the microstructure characteristic mechanism of strength cause was discussed. The results showed that the pore characteristics of different solidified soil were quite different. The macro-pores in saline soil solidified with lime and fly ash were reduced, while the total pore volume in saline soil solidified with water glass, lime and fly ash was decreased, but the macro-pores were increased. The pores in saline soil solidified with water glass were increased, but the pore volume decreased with the increase of water glass concentration. The compression strength of the soil solidified with water glass, lime and fly ash was greater than that of other solidification schemes, but its pore structure was not optimal, which indicated that the effect of cement between particles on solidification was much greater than that of pore characteristics.

To predict the settlement of low reinforced embankments on soft soil foundation with high accuracy, the pavement structure is modelled as a Euler-Bernoulli beam, and the reinforced embankment is simulated as composite materials and simplified as Timoshenko beams considering the lateral shearing. The soft soil foundation is simulated by the three-parameter Kerr elastic foundation model considering the stress diffusion. To derive the governing differential equations, the energy balance equation is developed, and the principle of stationary total potential energy is used. Based on the eigenvalue differential method, the differential governing equations of settlement deformation of embankment are derived, and the analytical solutions for the settlement, shear stress and bending moment of reinforced embankment on Kerr foundation are established. The effects of the thickness and the elastic modulus of soft soil foundation and the reinforcement position on the stress and settlement of the reinforced embankments are analyzed. The results show that the Kerr foundation model can simulate the settlement of reinforced embankments with higher accuracy than Winkler and Pasternak models.

This research focuses on the double-layer soft clay foundation with an upper soft layer and lower hard layer in Tianjin coastal area. The bearing property and failure mode of the double-layer soft clay grounds are studied by laboratory load test and numerical simulation. The results show that the P-S curves of double-layer soft clay foundation have an obvious concave-convex turning point due to the reinforcement effect of the underlying sedimentary soil, which is different from the reclaimed homogeneous ground. What’s more, the position of the turning point is closely related to the width-thickness ratio. The smaller the width-thickness is, the later the turning point appears, and the less significant reinforcing effect of underlying sedimentary soil is. Numerical results demonstrate that the failure modes of the double-layer soft clay grounds are trivially affected by the thickness of upper soft soil layer, all of them are general shear failure. The failure mode of the double-layer soft clay grounds varies from punch-shear failure mode to local shear failure mode with increasing the width of the load plate. When the width of the load plate is more than 3.0 m, the general shear failure mode occurs.

Prefabricated diaphragm wall is constructed through factory prefabrication and site jacking, which is more civilized and environmentally friendly, and it is an important research direction in rail transit pit support engineering in China. The key for the construction of prefabricated diaphragm wall is the jacking process control of the sheet pile with large section. During the design stage, it is particularly important to consider how to evaluate jacking resistance and perform slurry control. In order to evaluate the jacking resistance of prefabricated diaphragm wall, a series of model pile experiments is conducted. From which, lateral resistance and tip resistance of different preformed slurry situations are studied. With the experimental results, preformed slurry control standard is proposed for prefabricated diaphragm wall deadweight and preloading jacking. According to the final results of the model pile jacking experiments, a jacking resistance evaluation model for prefabricated diaphragm wall is established, the reliable control standard for preformed slurry situation is determined, and the related software is developed. Our results show that for prefabricated diaphragm wall deadweight jacking with 1.2 m width, the slurry density could not exceed 1.15 g/cm3, and for preloading jacking with 30 ton additional pressure, the slurry density could not exceed 1.33 g/cm3.

High-fill culverts have been widely used in expressway in the western mountainous area of China. A series of damage occurs in culvert structure because of the large load of high fill and earth pressure concentration caused by the stiffness difference between the culvert and surrounding soil filled. In order to relieve the stress concentration and eliminate the structural damage, a new culvert structure is proposed, i.e., two load shedding blocks are set on both sidewalls of the general cover-plate culvert as an integral structure. The U-type load-shedding hole between two load-shedding blocks is ?lled with compressible material. The model test and numerical simulation were conducted to investigate the stress characteristics of the load-shedding culvert on the flexible foundation. The numerical simulation results are consistent with the measured results in model test. In addition, the influences of rigid and flexible foundation on stress states of load-shedding culvert are discussed. The load-shedding effect under the condition of flexible foundation is found better than that of rigid foundation, the stress states of the culvert are more reasonable. Hence, the ground treatment relevant to flexible foundation should be paid more attention in practical project, the requirement of post-construction settlement is more important than the foundation stiffness.

Aim of this study is to investigate the influence of blasting excavation construction on roadway support bolt. Based on the theory of structural dynamics, the vibration law of bolt under blasting seismic waves is deduced theoretically, including the variation of displacement, vibration speed and axial force on bolt with time. The result shows that the velocity and axial force of the bolt in the free section decrease exponentially, while the axial force, the axial velocity and the shear stress of the bolt in the anchorage section change sinusoidally, and the overall performance increases first and then decreases. The anchorage length has a great influence on the vibration effect of the bolt. The stress state of the bolt varies with the anchorage length of the bolt. On the premise that the tensile strength of the bolt is satisfied, the length of the anchorage section can be reduced appropriately. Shear stiffness has a certain effect on the vibration of the bolt. The greater shear stiffness lead to the greater shear stress between bolt rod and anchoring mortar. Therefore, in order to prevent the bolt from shear failure, the anchorage material with smaller shear stiffness should be chosen as far as possible. The research results have some guiding significance for improving the safety technology in excavating blasting.

Under the same or similar external conditions, the similarity degree of internal structure and external performance of landslide can be clearly demonstrated by the similarity of movement of landslide monitoring points. Thus, it is of important theoretical value and practical significance to use appropriate similarity evaluation method. In this paper, a method based on motion-angle-difference is proposed to evaluate similarity of movement of landslide monitoring points. The velocity of landslide deformation is converted to angle, and the acceleration of landslide deformation is converted to motion-angle-difference. By comparing the motion-angle-differences, the similarity of different landslide monitoring points could be accurately evaluated. In view of the sufficient data, the three dimensional motion-angle-difference is proposed. In this way, not only the distinguishable responses of each monitoring point to the same external influencing factors are emphasized, but also the scale effect can be effectively eliminated. Through a set of experiments, the applications of this method have generated great results, such as partition evaluation of similarity of different monitoring points on the same landslide, evaluation of similarity of different landslides in the Three Gorges Reservoir Region, and displacement prediction of similar landslide monitoring points.

The Jiguanshanliangzi high-steep slope is taken as a typical case study in Wudongde hydropower station near Chin-sha River. Based on seismic monitoring of the slope surface, firstly, after inputting horizontal and vertical Ricker wavelets at the elastic slope model bottom, it is found that the low modulus of rock mass materials at the slope top is easily amplified after the excitation of the horizontal Rick wavelet. The surface convex topography is easy to produce resonance amplification when the vertical Rick wavelet is excited. The predominant frequencies of the top surface are consistent with the measured values. Secondly, comparative analysis of the slope stability and dynamic response characteristics are performed when inputting the real Wenchuan and Ludian earthquake acceleration records. It can be found that the slope may have three different potential slip surfaces at different locations under the static condition. However, when inputting the above two seismic waves, the deformation and failure occur only at the slope top position. When inputting the Wenchuan seismic wave, the shear strain increment of the top slip surface is significantly greater than that when inputting Ludian seismic wave. The tension failure zone is observed at the slip surface and the horizontal and vertical residual deformation is not convergence. The slope is at the state of instability after the earthquake. When inputting the Ludian seismic wave, there is no tensile failure zone observed at the slip surface and the residual deformation is convergence, which means that the slope is stable after the earthquake. The slope of horizontal and vertical acceleration at the slope top surface appears significantly enlargement due to a low modulus material, showing obvious site effect. In addition, the surface acceleration is generally greater than the corresponding values within the slope, especially at the location of convex topography. The amplification factor of horizontal acceleration at the slope top after inputting the Wenchuan seismic wave is greater than that after inputting the Ludian seismic wave, but the vertical acceleration amplification factors are essentially the same.

A high-precision microseismic(MS) monitoring system was installed to evaluate the stability of the #5, #6 bus-bar tunnels at Lianghekou hydropower station during excavation. The dangerous areas of underground powerhouse during excavation were delineated through real-time monitoring of MS accumulation and analyzing frequency of microseismic signal in gathering area. Based on previous exploration data and site excavation progress, and with the aid of UDEC discrete element program, the deformation distribution and failure mechanism of bus-bar tunnels after excavation were revealed. The MS activities were closely related to excavation of underground powerhouse. The excavation of #5, #6 bus-bar tunnels resulted in the accumulation of MS events and the increasing of stress gauge reading. The free surfaces formed by excavation were prone to instability. The high frequency components of MS signal decreased at first and then increased before surrounding rock fractured. Displacements at the top arch of bus-bar and the upstream side wall of main transformer chamber were remarkable and presented tensile failure after excavation. The research results provide important references for excavation and reinforcement of underground powerhouse at Lianghekou hydropower station.

The moment estimations, such as mean and variance of samples, are quite uncertain in the context of limited geotechnical parameters, which may lead to a large bias in reliability analysis. The same small sample X may come from different populations W*, and the biases between the population mean and variance and the corresponding moment satisfy the law of t and χ2 distribution under assumption of normal distribution. Based on conditional probability principle, virtual population space ?POP and corresponding occurrence probability space ?OCC composed of W* are constructed. The Monte-Carlo simulation methods is used to obtain the failure probability space ?FAI for a simple soil slope. Underlying the full probability formula, a momentary weighting method, denoted by MWM, is proposed to calculate reliability index ?T. The numerical examples show that MWM could effectively narrow the ?T range, and simultaneously reduce the uncertainty caused by parameter estimation error. The mean value of ?T converges to the true value, showing good validity and unbiasedness. Aiming at the characteristics of single batch sampling in actual investigation work, MWM can reduce the distortion degree of reliability analysis in large occasional moment estimation bias cases.

The settlement behaviors of high loess-filled foundation usually plays a critical role in later construction planning. In order to investigate the settlement behaviors and affecting factors of high loess-filled foundation, a long-term in-situ monitoring was carried out to monitor the settlement of a high loess-filled foundation, pore water pressure and internal sedimentation of the filling body. Monitoring results show that instant settlement and consolidation settlement caused by the overlying soil loading are the main components of the settlement of the original saturated loess foundation. Moreover, the settlement and the pore water pressure tend to be stable at the same time, while no obvious creep deformation occurs during this process. On the other hand, the settlement of unsaturated filled foundation is largely dependent on the exhaust conditions. For example, the initial post-construction settlement of the soil with better exhaust condition is even more than 2 times of the soil settlement under non-ideal exhaust condition. Thus, variation of exhaust conditions is one of the main reasons for the soil settlement difference between the centrifugal model test and the in-situ monitoring. Properly slowing down construction speed and reasonably arranging exhaust passages are helpful to shorten the time of post-construction settlement stabilization and save time for subsequent construction.

The traditional gob-side entry retaining with filling is cumbersome and slow, which cannot satisfy the requirements of modern high-intensity mining. Thus, a non-pillar mining technology by cutting roof is proposed to form a roadway along the empty. However, the design of key parameters is one of core problems of this technology, which has a great influence on the stability of gob-side entry retaining. In this study, theoretical analysis, numerical simulation and field tests are conducted to investigate the key parameters systematically at the 21304 working face of Chengjiao mine. We derive the formulas for the height and the angle of cutting roof by using the self-bearing of bulking rocks and the stability principle (S-R) of surrounding rock. A mechanical model of energy-cavity blasting is established and further used to determine the explosive payload and spacing of borehole in combination with numerical simulation and field tests. The results show that the mechanical relationship between the roof and stratum of mining goaf can be cut off if the designed parameters of cutting roof are proper. Additionally, the roof can collapse along pre-cutting and gangue of bulking rock can support the overlying roof. Moreover, the rotary sinking, disturbance to roadway and deformation of surrounding rock of roadway are all controlled by cutting roof. The key parameters for the 21304 working face of Chengjiao mine are obtained by theoretical calculation, numerical simulation and field tests. The field application indicates that the lateral roof of roadway can be quickly cut down into the roadside after robbing and all indicators can meet the requirements of this site.

Thirty-four compressed air drainage wells with an average depth of 15 meters were set up in an unstable landfill in Northwest China for slip control. The surface displacement, deep horizontal displacement and leachate level before and after control were compared to analyze the effect of slip control using the compressed air drainage wells. The results show that the maximum surface displacement rate is reduced from 237.3 mm/d to 78.7 mm/d after treatment with compressed air drainage wells, the maximum pumping rate of compressed air drainage wells is 255 m3/d, and the average pumping rate is 132 m3/ d, the pumping rate of the single drainage well is 3.88 m3/d. The compressed air drainage wells have low cost and short construction period, and have good effect on landfill slip control, which can provide reference for landfill slip control.

Prestressed anchor cable is the main engineering measure for stability control of surrounding rock mass in large underground caverns. Aiming at the problem of unloading stability of rock mass excavation and long-term bearing safety of anchor support system in high-stress area, the long-term in-situ monitoring results of systematic anchor cable are deeply analysed. In this paper, we investigate the stress characteristics and space-time variation of the anchor cable, and the time-dependent characteristics of the pre-stress of anchor cable in the underground powerhouse system of Jinping I hydropower station located in Southwest of China. The factors influencing the long-term safety of high bearing anchorage cable structure are discussed, and the long-term safety of anchoring system is evaluated with the numerical simulation method. The obtained results show obviously different from them in the conventional cavern. Most of the anchor cables for supporting deep rock mass of this underground cavern exceed the designed locking value, the load of the cable system is high, the continuous growth time becomes long, and the time effect characteristics is greatly significant. The main factors affecting the long-term bearing capacity of anchor cable include the creep of rock mass, initial tension stress of anchor cable, uneven stress of anchor cable. The analysis indicates that the anchorage cable long-term bearing safety is guaranteed.

Based on the analysis of the characteristics of uncovering coal seam in gas tunnel, we propose a method of directional hydraulic fracturing by waterjet slotting, and also develop the waterjet slotting guide device. A rapid elimination technology system is formed for the large cross-section gas tunnel excavated through multiple coal seams, which is further applied to a project of Chongqing-Guizhou high-speed railway. The results show that the fracturing of hydraulic cracks is governed by the waterjet slotting obviously, and always expands along the coherent plastic zone formed by the directional hole cutting and hydraulic fracturing cracks in the coal seam. The permeability of coal seam is increased by 35–187 times, and the average gas extraction efficiency is 4.28 times and 12.73 times higher than that of conventional fracturing in adjacent coal seam of the same tunnel and conventional extraction technology in the same coal seam of adjacent tunnel, respectively, and the time of uncovering coal seam is 50% less than the expected. Directional hydraulic fracturing effectively weakens the damage to the surrounding rock by high-pressure water, and the vault settlement and horizontal convergence of tunnel are reduced by 18.3% and 16.4%, respectively.

This study is to solve the problems of the low content and high gush of gas under high-intensity mining conditions in Tashan coal mine, and to make up the disadvantages of high cost and difficult operation of large-scale physical experiments and field tests. According to the geological and gas occurrence conditions of regional coal seam which covers 8101 working face in Tashan coal mine, numerical testing schemes were designed to optimise and analyse the gas pre-drainage effect in the extremely thick seam by using ground vertical boreholes. Based on the pore characteristics of coal-rock (body), we developed mathematical constitutive models of gas-solid coupling and permeability-damage coupling in the gas-bearing coal-rock (body) rupture process. A numerical model of gas drainage was established by using RFPA2D-Gasflow software, and the relevant physical parameters, simplified initial conditions and boundary conditions were established. The following results can be achieved through the above numerical tests. First, the reasonable borehole bottom location of ground vertical boreholes is at the bottom of coal seam. Then, on the basis of considering the drilling cost and the drainage effect, the reasonable borehole spacing between adjacent ground vertical boreholes is from 50 to 60 m. Meanwhile, the actual application effect of gas extraction by using ground vertical boreholes in 8101 working face demonstrates a good gas drainage effect when the borehole bottom location is at the bottom of coal seam and the borehole spacing is 50 m. To a certain extent, the rationality and feasibility of numerical tests are further verified.

To investigate scattering of plane qP-qSV waves induced by a convex topography with the transversely isotropic (TI) medium, the indirect boundary element method (IBEM) is used for the numerical simulation and the solutions of the plane qP-qSV waves scattering problem in both the frequency and time domain are given, respectively. In the process of solving, the calculation model is divided into open layered half-space region and close hill region, and the wave field is decomposed into free wave field and scattered wave field, the first of which can be solved by the direct stiffness method, and the second can be simulated by the dynamic Green’s function by applying the fictitious inclined uniformly distributed load. The results in frequency domain show that the different TI media can change the dynamic characteristics of hill and layered half-space, and alter the dynamic interaction mechanism between hill and layered half-space, making the surface displacements significantly different. The results in time domain indicate that the parameters of the TI media and incident directions of plane waves have significant effects on the propagation of qP-qSV waves around the hill. In addition, time domain results clearly show the transmission process of incident, reflected and scattered waves.

A coupled computational fluid dynamics (CFD) and discrete element method (DEM) model is established to capture the fluid-particle interactions in submarine landslide. The model is validated with experimental data of granular collapse in the literatures. Underwater granular collapse, as a paradigm of submarine landslide, is simulated with various initial aspect ratios, in detailed comparison with aerial granular collapse. The results show that CFD-DEM can well capture the key processes of submarine landslide, including its collapse, propagation, and deposition. Complicated interactions between water and grains are observed, such as the formation of vortex in water when the granular flow transits from vertical falling to lateral spreading. When the initial aspect ratio is high, the vertex in water can significantly modify the surface morphology of the final deposit. Compared to dry granular collapse, the underwater landslide generally leads to a shorter runout distance and thicker deposit; the loose materials on the surface are easily affected by the water flow.

A composite rigid-flexible pile-supported retaining wall (CRF-PSRW) including EPS cushion was proposed aiming for the treatment of high-filled expansive soil subgrade slope. The numerical model of CRF-PSRW used for high-filled expansive soil subgrade was established by FLAC3D. Based on the thermal-mechanical coupling model, the deformation of expansive soil was simulated with the change of humidity. The mechanical and deformation behaviors of CRF-PSRW in five different working conditions were compared and analyzed. The effects of thickness and stiffness of EPS cushion on the earth pressure and horizontal displacement of the CRF-PSRW were further investigated. The results show that the CRF-PSRW can obviously reduce the earth pressure of retaining wall, bending moment and shear force of anti-slide pile, and horizontal displacement of the structure. However, settlement and horizontal displacement of pavement are found to significantly increase. The compression amount of EPS cushion increases with the decrease of elastic modulus or increase of thickness. Then larger lateral deformation of the expansive soil is permitted, leading to reduction of the force and deformation of CRF-PSRW. In order to give full play to the decompression effect of flexible EPS cushion, the conditions of thickness and modulus of elasticity must be satisfied at the same time.The single cushion stiffness index is not enough to reflect the influence of EPS cushion..

Permeability coefficient is a main parameter to reflect the permeability of soil. Existent studies about influence of particle size and gradation on permeability coefficient of soil mainly focused on experiments. It is difficult to change a parameter completely independently because of the interaction of various variables in the experimental study, which results in considerable differences between the conclusions from different researchers. Under the condition that other parameters remain unchanged, numerical simulation can basically change a certain parameter independently to make up for the shortcomings of experimental methods. In this paper, the particle discrete element method is used to generate soil of porous media with different particle sizes, different porosities and gradations by adjusting the size of the control particles. Lattice Boltzmann method is used to simulate seepage in soil at meso-pore fluid scale. The results show that the lattice Boltzmann method can simulate soil seepage accurately and effectively. Main passageway phenomena and large particle size effect are found in the seepage process. The simulation results are in good agreement with those by Kozeny-Carman (K-C) formula, demonstrating the K-C formula is applicable to porous media with different gradations. The permeability coefficient increases with the increase of uniformity coefficient and the curvature coefficient. A formula for calculating permeability coefficient with gradation parameters is given. The formula is nearly equivalent to K-C formula, but the parameters in this formula can be measured easily.

With the rapid development of marine energy extraction, the demand for submarine pipelines has been increasing in recent years. The stability of pipelines during their service period directly affects the safety of the oil and gas exploitation, the workers’ life and the marine ecological environment. In view of the fact that submarine pipelines are vulnerable to the damage from landslides, a novel type of submarine pipeline with a double-elliptic contour is developed. Then, the effect and mechanism of disaster reduction of the pipeline under the impact of landslides are analyzed based on the computational fluid dynamics (CFD) method. The results show that the developed pipeline, no matter in a suspended or laid-on-seafloor status, can delay the separation of velocity boundary layer near the pipeline surface to reduce the influence of Karman Vortex Street. Thus, the drag force and lift force of pipelines imposed by submarine landslides are effectively reduced,with a maximum lessening percentage of 71.01% for drag force coefficients and 32.14% for lift force coefficients. Moreover, the equations for estimating the drag force and lift force coefficients of double-elliptic contour pipeline are recommended, which provides a new reference for the disaster fortification and mitigation engineering on submarine pipelines.