To investigate the destruction characteristics of intact structural loess under loading conditions, triaxial shear tests are conducted on Q2 intact loess. Based on the experimental results, a structural variable parameter m of soil is defined, which can consider the spherical stress, deviatoric stress, matric suction and other factors. By means of method for calculating the structural parameter m based on the experiment, the relationships among shear strength parameters c, and structural parameter m are found out, the curve equations of m with c, are deduced, respectively. By introducing the curve equations into Drucker-Prager (D-P) criterion, a modified yield criterion applicable to Q2 intact loess is established. The modified yield criterion can consider the structural effect of intact Q2 loess and describe the structural characteristics of loess very well. Besides, the yield surface reflecting the impact of structural parameters is drawn. The rationality of the modified yield criterion is verified by comparing the results of the modified yield criterion with those obtained from the triaxial tests.

Cemented soil in anti-seepage engineering usually directly or indirectly encounters underground corrosive media environment, which may lead to decrease or even failure in impermeability. For this purpose, the permeability tests are conducted on the cemented soil with different cement ratios under the sewage and clean water conditions, respectively. The effects of curing ages on the permeability of cemented soil are investigated, and the evolutions of ion concentration in cemented soil after permeating are also analyzed. The result shows that for the samples soaked under clean water curing condition, their permeabilities decrease gradually with increasing curing age, and this decreasing rate becomes more slowly when the curing age exceeds sixty days. For the specimens soaked under sewage curing condition, their variations of permeabilities are similar with those of specimens with the curing age less than sixty days under clean water curing condition. However, an increase in the permeability is observed when the curing age exceeds sixty days. This phenomenon is attributed to the erosion effects of sewage on cemented soil. Under both clean water and sewage curing conditions, the permeability decreases gradually with the increase of cement content. With the increasing of curing age, the concentrations of Ca2+, Mg2+, Cl? and SO42? in cemented soil gradually increase under sewage curing condition, whereas the concentrations of Mg2+, Cl?, SO42? gradually decrease under clean water curing condition. The research results can provide technical parameters for the impermeability and durability design of cemented soil in anti-seepage engineering, which have an important engineering significance.

Both the special engineering geological properties and the complex engineering dynamic stability problems are closely related to the wave-induced dynamic response of pore pressure in seabed sediment in the Yellow River estuary. Four typical sites on the intertidal flats of the Yellow River delta are selected to simulate the wave action on the intact seabed sediments. Various testing methods, such as pore water piezometer test, field sediment strength test and sampling/laboratory geotechnical experiments, are employed to determine the variations in pore pressure and strength of the undisturbed seabed sediments at different stages under the cyclic loading. It is shown that during the cyclic loading process, the excess pore pressure response of undisturbed seabed sediment can be separated into 5 stages including gradual accumulation, partial dissipation, rapid accumulation, accumulated liquefaction and complete dissipation, which correspond to five processes of sediment strength variation including attenuation, increase, attenuation, loss and recovery, respectively. The grain size composition and structural strength dominate the excess pore pressure response. The wave-induced liquefied depth of intact seabed sediment is significantly affected by the initial physical properties such as dry density, void ratio, saturation degree, etc. To a large extent, the relative amount of fine grained components also controls the liquefaction characteristics of sediment in the Yellow River estuary.

The soil in the coastal reclamation area is generally very poor, embedded with thick soft oozy soil layers. The soil can produce great consolidation settlement under the effect of late filling. Different types of surcharges have an important effect on the bridge pile foundation, and reduce the bearing capacity of pile. Balanced surcharge and unbalanced surcharge mainly affect the settlement and the horizontal displacement of pile, respectively. Combined with the Taizhou Bay bridge project construction, three piles are selected to conduct balanced surcharge loading test, and another three piles are designed to conduct unbalanced surcharge loading test to study the bearing characteristics of pile foundation under different balance surcharges. The field test results show that the negative friction of pile side is caused mainly by balanced surcharge. When the surcharge load is up to 4 m and area is 24 m×16 m, the total negative frictional resistance is up to around 2 687 kN, and the depth of neutral point is about 29.5 m, nearly being 0.36 times the pile length. The development of negative frictional resistance changes with time. The unbalanced surcharge load mainly affects the pile foundation to produce soil arching effect, and gives rises to a large horizontal displacement of pile. In the unbalanced surcharge loading test, the surcharge mainly affects the area in the range of 20 m from the ground, the maximum horizontal displacement in soil appears around 4 to 5 m off the ground, and the maximum horizontal displacement of pile appears at the top of the pile.

The pendulum-type wave is one of the block rock mass inherent dynamic characteristics in deep mining. To study the propagation regularity of deep block rock mass pendulum-type wave, a method combined theory analysis with laboratory experiments is adopted; the pendulum-type wave propagation characteristics under shock load are discussed. In the experiment, twelve pieces of granite and rubber interlayer material are used to establish the experimental model, and the TST5915 dynamic data acquisition system is used for monitoring signals. Acceleration response curves are obtained in homogeneous interlayer and part of thickened interlayer medium, and pendulum-type wave dynamic model theory is also used for analysis. The results show that in the transmission process of pendulum-type wave between the blocks, the frequency is not affected by the energy, but the energy determines the attenuation time of the wave. When the viscosity increases in the block medium, the acceleration amplitudes are declined, but it has no effect on the acceleration attenuation cycle, and the main factors influencing the acceleration attenuation is the energy magnitude of the shock load. The experimental research will provide certain basis for studying dynamic transmission characteristics of pendulum-type wave in the future.

A model test is carried out to study the distribution of surrounding rock pressure and its mechanical characteristics based on open excavation section of Xinzuofang unequal-span double-arch tunnel of Lanzhou-Chongqing railway. Test results show that lateral pressure acting on the tunnel is smaller than the vertical stress of surrounding rock, and lateral pressure at the crown is smaller than that at the bottom of side wall, moreover, lateral pressure coefficient of small hole side is about 0.55 on average, while the big hole side is about 0.65. The stress of surrounding rock on the top of middle wall is bigger than that on the crown; the surrounding rock stress of big hole side is about 1.2 times that of the small hole. The tunnel is in a small eccentric bending state, and thrust stress in big hole is about 20% to 30% greater than that in small hole side; the destroy of tunnel structure firstly occurs at hance and invert near the middle wall in succession, finally the whole structure collapse; thus, the hance and invert near the middle wall are the place that should be focused on in the design and construction. Based on the above, the mode of surrounding rock pressure distribution is obtained finally. The results can directly provide guidance for the design and construction of Xinzuofang tunnel; what’s more, it’s also helpful to improving the design and construction concepts related to the unequal-span double-arch tunnel.

In this paper, a triaxial experimental apparatus is developed to investigate the frictional sliding behavior of fissures in limestone. Slide-hold-slide (SHS) tests, velocity stepping (VS) tests and permeability tests are conducted on the limestone core samples under both dry and wet conditions. Time-dependence and sliding stability are firstly studied through SHS tests and VS tests, respectively, and then the effect of water on the frictional behavior of fissures is further analyzed. Meanwhile, the permeability of fissures is measured during the sliding process in permeability tests. SHS tests show that frictional strength of fissures exhibits significant time- and stress- dependent behavior. The decreasing magnitude of frictional strength at the controlled time and the healing magnitude after re-sliding are proportional to the controlled time intervals, but inversely proportional to the effective confining stress. In addition, the frictional behavior is obviously influenced by water. However, VS tests demonstrate that frictional strength of limestone increases with increasing sliding velocities, which indicates the velocity-strengthening behavior. Finally, it can be seen from a series of permeability tests under varied effective normal stresses from 1 to 3 MPa is carried out, the permeability declines sharply with the increase of effective confining stress, and even decreases gradually with sliding process at each level of effective confining stress.

The suction-controlled triaxial shear tests were conducted on unsaturated weakly-expansive soil experiencing different suction histories over a wide range of suction. The maximum suction was applied by using the vapor equilibrium method for high suction and the axis translation technique at low suction. The results show that at the same net stress and suction, the stress-strain curves of the specimens subjected to drying-wetting cycle are situated at a higher level and a smaller contractive volumetric strain occurs during shearing, and the stress-strain curves of the specimens experiencing larger suction also raise up and a smaller contractive volumetric strain can be observed during shearing. Furthermore, the stress-strain and volumetric strain behaviors become more and more similar to the deformation characteristics of overconsolidated soil with the increase of the imposed maximum suction. The reason for the above phenomena is that the specimen experiences a larger suction as the specimen experiences a larger pre-consolidation pressure. Meanwhile, the shrinkage characteristics of weakly-expansive soil become significant due to water loss. After experiencing a larger suction, the void ratio decreases significantly, and thus the specimen exhibits the deformation characteristics similar to the overconsolidated clay during shearing. Therefore, in order to characterize the stress-strain relationship and the strength of unsaturated weakly-expansive soil, the specimen volumetric shrinkage caused by suction history should be considered.

Based on the unified hardening (UH) model of reconstituted soil, a UH constitutive model is developed for structured clay. In this model, the dynamically moving normal consolidation line (MNCL) instead of the static normal consolidation line(NCL) is used as the reference line in determining the reference stress; and a proper increment evolution equation is proposed for the MNCL to describe the soil structural decay. The proposed structured soil UH model can reasonably simulate many behaviors of the structured soil, including the isotropic compression, strain hardening, strain softening, shear-induced shrinkage, shear-induced expansion, undrained shear decompression softening and coupling effect between soil structure and soil density. Compared to the original UH model, the structured soil UH model includes 3 new model parameters, which reflect the soil structure degree, the structure decay rate and the plastic flow rule, respectively. Comparisons between the test results and the model predictions of the three natural soils indicate that the structured soil UH model can reasonably describe the main features of the behavior of the structured soil.

Deep mining water inrush has the characteristics of sudden, hysteretic nature and strong induced disaster, and studying the water inrush channel genesis, evolution and disaster causing mechanism become the key to the control of deep mine water inrush. A lot of water prevention practice and control theory confirm that the fault water inrush channel generally occurs in the structure and strata contact surfaces, based on which concealed structure block body water inrush criterion model is established, besides, the theoretical criterion of water inrush is obtained by using shear failure theory. By means of the deep confined water, the activation and the evolution of the water conduction channel in the bottom of the pressure water are simulated. A similar solid-fluid coupling material is developed, and the feasibility analysis of the material is selected to simulate the fault failure. Experiment shows the whole process of floor crack formation, concealed fault propagation, water inrush channel of concealed fault floor directly under the action of mining stress disturbance and high pressure water. Mechanism of lagging water inrush from coal floor in confined water body under stress field and seepage field coupling is revealed, and the formation of water inrush path of the spatial variation is analyzed and discussed through the interpretation of the monitoring data and the phenomenon, which provides new methods and knowledge for the study of deep mining water inrush structure.

By carrying out triaxial unloading test under different stress paths on rock, the complete stress-strain curves, deformation characteristics and its strength criterion are studied. The test results show that the relation between lateral strain and confining pressure firstly is linear, and then is nonlinear in the total stage of unloading confining pressure. And its growth rate is about 3 to 5 times the growth rate of the axial strain. It shows obvious lateral dilatancy, and the degree of dilatancy is related to the unloading path. According to the area that is enclosed by confining pressure and volumetric strain curve, it can be seen that the greater the confining pressure is before unloading, the more the energy releases. Deformation modulus decreases gradually with the unloading confining pressure, and increases with the initial confining pressure; the relation between deformation modulus and confining pressure shows negative exponential distribution overall. At the same unloading paths, the reduction of the deformation modulus increases with the increase of initial confining pressure. The Poisson′s ratio rises up continually, and the variation law with the confining pressure can be well described by nonlinear. Failure characteristics of rock are mainly shear failure. The strength characteristics of rock can be well characterized by using the Mohr strength criterion of power function. These conclusions provide reliable theoretical reference and guiding significance for the deep mining of the underground metal mine.

Based on the triple-shear unified strength criterion and shear strength of unsaturated soil in terms of two state stress variables, a triple-shear unified solution of shear strength for unsaturated soil is obtained with considering the effects of the intermediate principal stress, strength disparity of materials and strength criterion. A formulation of Terzaghi’s ultimate bearing capacity for unsaturated soil foundation is developed, and validated through the feasibility analysis and example demonstration. In addition, the influences of various factors, including intermediate principal stress effect, strength criterion, matric suction, effective internal frictional angle and effective cohesion, are discussed on the ultimate bearing capacity of unsaturated soil foundation. The results show that the intermediate principal stress and strength criterion have significant impact on the ultimate bearing capacity, namely, the more remarkable the intermediate principal stress effect, the higher the ultimate bearing capacity is. It is also shown that the consideration of intermediate principal stress can fully mobilize the soil strength and the strength criterion plays an important role in predicting the ultimate bearing capacity. The matric suction has dual effects on the Terzaghi ultimate bearing capacity of strip foundation. In low matric suction region, the ultimate bearing capacity increases linearly with the increase of matric suction and attains its maximum when the matric suction reaches the air-entry value. In high matric suction region, the ultimate bearing capacity decreases gradually and finally maintains constant. Moreover, the Terzaghi ultimate bearing capacity increases dramatically as the effective internal frictional angle and effective cohesion increase.

The Harbin to Dalian Passenger Dedicated Line (HDPDL) is the first high-speed railway designed, constructed and operated in cold regions in China. The unique engineering geological condition along the HDPDL and the stringent engineering requirements pose severe challenges to the stability of subgrade in cold regions. In order to monitor the stability and freezing characteristics of the subgrade, the typical subgrade sections are selected in different freezing zones. The structure style of subgrade has a remarkable disparate impact and restriction on the freezing characteristics of high-speed railway subgrade in cold areas through analyzing the monitoring data of the first freezing and thawing period after operation. By comparing the middle section of cutting with the embankment near the entrance and exit of cutting, it is found that in this embankment section, there exists thicker frozen interlayers for a long time. The temperature difference between the cutting and the embankment increases with the increase of latitude. It is also found that there is a certain thickness of high-temperature frozen soil in embankment in April every year. In the same region, the maximum freezing depth of embankment is 20 to 50 cm deeper than that of cutting. However, the maximum deformation of cutting is 2 to 5 mm larger than that of embankment, and this difference becomes larger as latitude increases in spring thawing period, the change rate of frozen depth of cutting section fluctuates dramatically around 0; at this moment, the deformation exhibits a rise in mutation manner while the freezing depth change rate of embankment is located in the range of negative, and the obvious mutation in deformation of embankment is not be observed.

The MTS-810 vibration triaxial testing machine is used to study the change law of damping ratio of frozen clay and loess with different loading frequencies, confining pressures and temperatures. The results show that for frozen clay, the damping ratio firstly decreases and then gradually increases with the increase of dynamic strain amplitude under the conditions mentioned above. For frozen loess, the damping ratio firstly decreases and then tends to be a stable value with the increase of dynamic strain amplitude. Damping ratios of frozen clay and frozen loess decrease with the increase of loading frequencies, and changes slightly with the increase of confining pressure under the same dynamic strain amplitude. The change of damping ratio is insignificant with the confining pressure when the temperature is in the range of -0.2 to -1 ℃, the value of damping ratio of frozen soil at the temperature of -2 ℃ is apparently less than that at the temperature of -0.2 to -1 ℃. Damping ratio is greatly affected by frequency at a relatively low dynamic stress level and is greatly affected by temperature at a relatively high dynamic stress level. In the whole loading process, damping ratio is minimally affected by confining pressure. The influence of frequency on frozen loess is greater than that on frozen clay when the dynamic strain amplitude is at relative low level. With the increase of dynamic stress, the influence of frequency on frozen loess is gradually less than that on frozen clay. In the whole loading process, temperature has greater influence on frozen loess than on frozen clay, while confining pressure has less influence on frozen loess than on frozen clay.

In this study, four groups of different types of bridge foundation model are tested to research the horizontal bearing behavior of caisson-pile composite foundation in lab based on the Qiongzhou Strait bridge project. The Q-s curve and horizontal ultimate bearing capacity of these four groups of foundations in sandy soil layer are obtained. Pile bending moment and shear force of pile shaft are analyzed in detail. At the same time, the load sharing ratio of caisson and piles is discussed. The results show that the horizontal ultimate bearing capacities of a single caisson foundation are increased by 1.2 times, 1.6 times and 2 times respectively with adding skirts, steel pipe pile, or steel pipe pile and the skirt. The maximum bending moment point is in the middle of the pile shaft, i.e. at about 0.5 m under the mud surface. The horizontal load is borne mainly by the upper caisson foundation and soil layers above the middle upper part of pile. The maximum shear force is found at the joint of pile top of steel pipe and caisson pile, where the reinforcement measures should be taken in practical engineering. The research achievements could provide a better reference for design or construction of caisson-pile composite foundation.

By combining the technologies of particle image velocimetry (PIV) and close-range photogrammetry, a procedure for geotechnical physical modelling using artificial synthetic transparent soil is developed. The soil deformation caused by the shallow foundation settlement (SFS) are measured and recorded non-intrusively. The conventional model test using natural soils is employed for the purpose of comparison. The transparent soil is made of a pore solution, the refractive index of which is matched with the refractive index of fused quartz. Transparent soil model is sliced by using a laser light sheet and digital images of soil deformations caused by SFS are captured. The MATLAB-based software, Geo-PIV, is employed to obtain the generated displacement fields. The results show that the SFS-induced disturbance zone is enlarged in transparent soil, the maximum shear strain expands by about 1.5 times, and the range of surface heaving increases by 30-50% in transparent soil compared with those in natural soil; however, the movement trends of soil elements in transparent soils are generally similar to those in natural soils, indicating that the proposed modelling methodology has applicability to mechanism study to some extent.

A series of long-term 1D oedometer test on compacted loess has been conducted using a high pressure consolidometer. It is found that the compacted loess has remarkable creep deformation and the proportion of the creep deformation in total deformation can come up to 6%-23%. The creep deformation proportion goes higher as the water content of the sample increases and the compaction degree reduces. And the creep deformation proportion decreases with the increase of stress level. A nonlinear creep model, which can well describe the rules of post-construction settlement of compacted loess, is proposed. The validity of model is verified by comparing the results from proposed model with those from the layer-wise summation method. The proposed model is employed to examine the variation law of the post-construction settlement under the conditions of the different water contents and compaction degrees. It is found that there exist logarithmic relationships between the post-construction settlement and the compaction degree/ water contents. Supposing the velocity of the post-construction settlement v < 0.1 mm/d is the stabilized standard, the high embankment settlement trends to be stable in 200 to 650 days after construction. The higher the compaction degree is, the lower the water content is, the longer the time up to stable required is.

Deep filtration effect widely exists and plays an important role in the process of permeation grouting in porous media. Based on the mass conservation equation, linear filtration law and seepage continuity equation as well as Darcy law, a theoretical model is developed for three-dimensional slurry frontal surface. The migration of the slurry frontal surface migration and the variation of the permeability coefficient of the deposition layer are examined based on in-situ grouting test; the measured values are compared with the theoretical ones. It is shown that the permeability coefficient varies as the frontal surface migration. At the constant grouting pressure, the deep filtration effect is more significant, and the slurry diffusion distance is shorter when the water-cement ratio is smaller. At the same diffusion distance, the permeability coefficient of the deposit layer above grouting point source is larger than that below the grouting point source, due to the influence of gravity effect. The grouting diffusion distance and the permeability coefficient of the deposit layer at a specified point are positively correlated with the water cement ratio. The above result has practical bearing, in which it can help construction designs.

In this study, a new media atomizing nozzle was adopted by rainfall simulation equipment for centrifugal model tests. Three comparative tests were conducted to simulate the behaviors of the deposits slope under the conditions of the rainfall and grid support. The scale of the centrifuge model to prototype was selected as 1:80. The displacement field of deposits slope was measured by a high-speed flash photography system, which had characteristics of non-contact and fixed-spot and was combined with program of particle image velocimetry (PIV). It was found that deposits slope was very stable without rainfall, but with increasing rainfall time, the settlement at top of slope and the horizontal displacement at surface of slope were both enlarged. Particularly, obvious deformation was observed on the surface of slope. Under continuous intensive rainfall, the slope failure mode was different from the traditional circular slide, since the slope failed layer by layer until a ‘debris flow’ was generated. However, the stability of the slope was significantly enhanced once protective geogrids were applied. Thus the application of geogrid supports efficiently improve the slope stability under rainfall conditions.

An improved variable-water head permeameter is used to simulate the water migration in dredged sludge during the dewatering process. By determining the permeability coefficient and the filtration constant, the seepage volume and the filtrate volume, the water content and the porosity of the mud cake, the influences of different vacuum loading methods (with different durations and loading gradients) are examined on the filtration and seepage of the dredged sludge during the dewatering process under the vacuum load level of 100 kPa. It is found that the filtration and seepage occur simultaneously under the vacuum loading condition. During the 1 h loading, the filtration prevails for 40 minutes, whereas the seepage dominates in the following 20 min. When the vacuum loading gradient increases from 1 time/ 1 h (gradient: 100 kPa) to 5 times/ 1h (gradient: 20 kPa), as the vacuum loading gradient decreases, the permeability coefficient and filtration constant increase, and the dehydration of dredged sludge is significant. The smaller the vacuum loading in the early stage is, the more effective the dehydration is.

The tunnel boring machine (TBM) tunnelling has been successfully applied worldwide in recent years, and TBMs provide continuous support to the tunnel face by using the freshly-excavated wet soil or slurry which completely fills up the work chamber under pressure. Under extremely unfavorable geological and hydrogeological conditions, however, face instabilities may occur. In fact, the excavation face support pressure for TBM in soft ground determines the construction safety and surface deformation. A visual platform for calculating the excavation face support pressure conveniently, TBM Studio, is constructed by computer programming based on the suggested models. In this visual platform, the influence of stratified soils can be considered. Furthermore, a comparison of the results of Alaskan way tunnel and Qianjiang tunnel by different calculation models is done, the differences between different models are revealed. In addition, the effects of the stratified soil layers’ self-stability on excavation face stability in complex strata are also discussed, demonstrating that it is crucial for determining quantitatively the relationships between the effective support pressure required and the hydraulic head in the soft ground.

With the development of city construction, it is common to see more and more cross construction phenomena of the ground engineering and the underground engineering, which unavoidably contributes to the effect of the new construction on the existing construction. Therefore, on the premise of ensuring the safety of the existing construction, how to construct new projects has become one of the important issues for numerous scholars. In this paper, the finite element numerical simulation analysis method of ABAQUS and the simplified specification corner-points method are applied to analyze comparatively an engineering construction adjacent to the existing underlying tunnel. On this basis, the effects of the pit excavation and its subsequent construction on the underlying existing tunnel are evaluated. The field monitoring data demonstrate that the two methods, i.e. the numerical analysis method and the traditional theory of soil mechanics method, are coincidently available in such engineering construction which has clear boundary and explicit load and can secure engineering. The research also shows that the two-dimensional analysis model not only has the smaller calculation workload, but also has more security compared with a three-dimensional model considering practical engineering conditions.

Based on the laboratory and in situ seismic piezocone tests (SCPTU), comprehensive analyses of soils sampled from the Yangtze River floodplain at the Nanjing Fourth Bridge site were conducted, including the fine division of the soil layer, permeability evaluation of clayey soils and hydraulic conductivity prediction. It is shown that the measured parameters of SCPTU (qt、fs、u2) can be used effectively for profiling the highly layered and heterogeneous deposits in the Yangtze River floodplain, especially for identifying the soil interfaces, thin permeable or impermeable interlayers. Based on the dissipation of excess pore pressure in the process of SCPTU testing, the permeability of the complicated mixed soils can be evaluated. Based on SCPTU, the predicted kh values show significant discreteness. It is observed that the lab measured kh values are generally lower than those estimated from SCPTU within 1-2 orders of magnitude. The results from Burns & Mayne method (2002) can be used in the planning phase of civil engineering works. It is suggested that such an enhanced seismic piezocone test should be considered to be a new tool for the dewatering design of foundation pit engineering.

Since there is only one exponential formula which is used to adjust the rheological convergence rate in the exponential rheological model of 3 parameters, 6 parameters, 7 parameters and Merchant model and H-K model, the deformation of rockfill dam in early impounding period and later impounding period cannot be reflected reasonably at the same time. While the 9 parameters power function rheological model, which can reflect the deformation of rockfill dam well, is inconvenient for mathematical operation. By the way of analogy with compound exponential formula for thermal and mechanical of concrete, a compound exponential rheological model, which can better reflect the rheological deformation law of rockfill dam and is convenient for mathematical operation, is advised from phenomenological perspective, and the finite element calculation formula is deduced based on compound exponential rheological model. Example analysis shows that only taking two compound exponential formulae, with two exponential coordinate adjustment, can better reflect the rheological deformation law of rockfill dam and is convenient for mathematical operation. While one exponential formula is a special case of compound exponential formula, and it cannot reflect the deformation of rockfill dam in later impounding period well.

The material property of soil significantly differs from that of pile, inducing the relative sliding or separation between soil and concrete pile during earthquake. The strong nonlinear contact behavior can directly affect the stress states of pile and soil near the interface, thus affecting the seismic response of superstructure. The real pile-soil interface does have a certain thickness due to the constraint relationship of concrete on pile, and the contact zone of related volumetric law does exist. A user-defined element (UEL) program based on modified Desai thin interface element is developed and then inputted into ABAQUS. In the modification process, Rayleigh damping is added into the interface element to simulate energy dissipation in the process of strong nonlinear contact behavior between soil and pile. Hyperbolic model is adopted in normal and tangential constitutive relation. Certain behavior pattern rules of modified Desai element on pile-soil interface are made to simulate the contact states such as bonding, sliding, separation and reclosing. A fine 3D pile-soil-structure model is developed to improve the effect of the modified Desai’s interface element on the dynamic response of superstructure. The result provides an instructive guideline for engineering design in time-history analysis.

With the rapid development of urban construction, new structures inevitably induce the secondary loading on the top of existing high fill open-cut tunnel. In order to characterize the influence of the new secondary loading due to backfilling on vertical earth pressure on the top of high fill open-cut tunnel, the relationship between the geogrid deformation and the soil settlement is established by using the elastic theory of soil settlement, based on the formulation of earth pressure on the load reduction structure. Meanwhile, the effect of the secondary loading is considered. The method for calculating vertical earth pressure on the top of high fill open-cut tunnel before and after the load reduction is further improved. Numerical analysis models are established, and the numerical results are compared with the results obtained from the proposed procedure in this paper. The results show that the theoretical results are close to the numerical results, with the same regularity. The load reduction measure has a great impact on the backfill earth pressure on open-cut tunnel. The higher the fill, the more significant the effect of load reduction, and the smaller the practical earth pressure on the top of open cut tunnel. The calculation of vertical earth pressure on the top of open-cut tunnel under the secondary loading should consider the influence of soil settlement rather than a simple superposition.

Landslide often exhibits characteristics of multi-stage destruction in practical engineering. However, the most dangerous slip surface and corresponding minimum safety factor are only concerned in general computing and design, this often leaves security risk. Considering the softening characteristics of geomaterial, a theoretical framework of effective simulation and evaluation of landslide multi-stage destruction is established with FLAC3D and Matlab software platform. Taken landslide in low-rent housing area of Dangjiaba in Xunyang county as an example, the process of forming multi-slip surfaces is revealed by progressive evolution of plastic shear strain, plastic tensile strain and shear strain increment and so on. It is shown that time and space sequences are not necessarily corresponding sequence. The temporal sequences of multi-slip surfaces are first-class main slip surface, second-class main slip surface and sub-slip surface; the spatial sequence is first-class master slip surface, sub-slip surface and second-class main slip surface. The number of slip surfaces is equal to the number of tension cracks in collecting on-site. The entry location of first-class main slip surface is in excellent agreement with the tension crack in the frontal part of landslide, but the positions of second-class master slip surface and sub-slip surface have little error with the tension crack on-site. The distribution and magnitude of strength parameters in the slip surfaces gradually change with the development of slip surface from peak strength to residual strength, this is the root reason why the multi-slip surfaces of landslide can be simulated effectively. The evolution of vector sum safety factors according the temporospatial distribution of material parameters in the multi-slip surfaces is obtained. It turns out that there are three different sequences of safety factors in the process of forming the multi-slip surfaces of landslide. It illustrates the active and passive relationships among all slip surfaces in the formation process.

The saturated soil exits widely on the earth. The soil should be considered as two phase medium of solid and fluid. The equivalent viscous-elastic artificial boundary element is studied regarding the effects of energy radiations of solid-fluid medium based on the u-p type of Biot equation of saturated soil. The wave input is realized by the equivalent load of earthquake on the node of artificial boundary. Its calculation precision is verified by comparison the examples. A nonlinear finite dynamic model of saturated soil-subway station is proposed for analyzing the wave propagation of soil in two phase medium and comparing with the seismic response in saturated soil and single phase soil under earthquake. The numerical results are compared with the results obtained from shaking table test. The results are shown that it is more reasonable to use the characteristics of multi-pore medium to analyze foundation soil under earthquake motion than to use the single phased medium. The seismic response of saturated soil and underground structural interaction system is studied through analyzing the acceleration, displacements and internal forces of the key elements in the station.

The dynamic response of a low-filled piled embankment under traffic loading is closely related to its bearing capacity and stability. In this study, a series of discrete element numerical models of piled embankments is established by using PFC2D based on the previous indoor model tests. The microscopic parameters of embankment filling and soil between piles adopted in the discrete element model are calibrated by numerical biaxial tests and uniaxial compression tests, respectively. Meanwhile, the validity and feasibility of the discrete element model are verified by comparison of load-transfer efficacy between the discrete element results and experimental data. Then, a cyclic loading in an ideal sinusoidal wave is applied to the surface of a low-filled piled embankment, and the analyses of load-transfer efficacy, distribution of contact force and embankment settlement are performed in detail. Numerical simulation results indicate that the bearing capacity of soil arching in a low-filled embankment would be gradually weakening firstly under the cyclic loading and reach a steady state finally. Specifically, the weakening of soil arching performs as the decreases of the load-transfer efficacy in macroscopic and the difference between the contact forces upon piles and soil between piles in microscopic. Meanwhile, the weakening of soil arching would result in the aggravation of differential settlement on embankment surface.

Based on the pile active underpinning project of Xima Bridge in Fuzhou Metro Line I shield tunnel, considering the complex hyperstatic structures composed by bridge superstructure, bridge piles and soil masses, the numerical simulation and the field monitoring data are utilized jointly to study the inner force and displacement responses of hyperstatic structures under different jacking loads. The influences of superstructure stiffness and substructure stiffness on the determination of jacking load are emphasized. The reasonable jacking loads for two typical conditions (the piles under cap beam and abutment beam) are 1 800 kN and 2 600 kN respectively, which make the axial forces of underpinned piles reduce to zero. The field monitoring is also carried out during construction, and the displacement of bridge superstructure and the axial force of bridge pile from monitoring data are consistent with their counterparts from numerical simulations. Based on these results from numerical simulation and field monitoring, a simplified analytical method is further proposed to calculate the reasonable active jacking load by considering the stiffness ratio between the superstructure and substructure, which can provide some reference for the pile underpinning projects under similar scenarios.

With the development of the technique for constructing the cast-in-place piles with high frequency vibratory hammers, the cast-in-place piles have been widely used in construction engineering. The penetration mechanism of the pile sleeve driven by high frequency vibratory hammers remains unclear, and particularly the squeezing effect in the sleeve penetration has yet to be investigated. In this paper, a finite elements and infinite elements coupling model is developed for simulating the sleeve penetration process driven by high frequency vibratory hammers, and used to study the squeezing effects such as ground heaves, lateral soil displacement and excess pore pressure generation. The results indicate that the horizontal displacement induced by soil compaction increases with the increase of sleeve penetration depth, and for the vertical compaction displacement, the heave increases in shallow soil layers and the settlement increases in deep soil layers as the sleeve penetration depth increases. The maximum compaction displacement lags behind the sleeve penetration depth. The reason for heave in shallow soil layers is that the horizontal stress increment causes an increase in the vertical stress, and the depth of heave interface increases with the increase of dynamical load amplitude, while decreases with the increase of vibration frequency. The excess pore pressure increases with the increase of sleeve penetration depth, and exhibits an exponential attenuation trend as the radial distances increases.

It is much more significant for assessment of probability distribution of large samples of geotechnical parameters to study the stability and reliability of geotechnical engineering in some important geotechnical engineerings. Thus normal information spread estimation method (NISEM) is proposed to generate probability density functions of geotechnical parameters with large samples based on the optimal bandwidth which is received by the minimum mean integrated square error. The method proposed in this paper based on the information spread principle, instead of assuming the fitting test of classical probability distribution curves, makes full use of the data sample provided from the view of the test sample and the information theory. It presents the mathematical and physical performances more fully and tight. The influence of bandwidth on the results of information diffusion estimation has been studied by the inference of probability density function of compression index (Cc). The results show the reasonability of NISEM, which is used to infer probability density function of geotechnical parameters with large samples. At last, probability density functions of rock and soil shear strength parameters have been inferred by using NISEM. By K-S test, the correctness and practicability of NISEM are verified.

The traffic load transfers from track, roadbed, and tunnel structure to foundation, generating cyclic dynamic stress and excess pore water pressure in soil, inducing settlement of shield tunnel. A vertical coupling dynamical model of metro train, track, tunnel and foundation is developed and used to analyze the effect of differential settlement of tunnel foundation on subway traffic load. A three-dimensional numerical model is established based on the engineering background of the subway tunnel near the Stadium Station of Shanghai Metro Line 1. Combined with the calculation formulas of accumulated plastic strain and cumulative pore pressure, the influence of train speed on the long-term settlement of subway foundation without tunnel uneven deformation is analyzed and compared to the case with tunnel differential deformation. It is shown that the larger the amplitude of soil vibration is, the faster the amplitude attenuation becomes while the train speed gradually increases. The longitudinal differential settlement has significant adverse effect on the operation of subway tunnel. As the train speed increases, this effect becomes more significant. When the tunnel differential settlement is small and the track condition is good, tunnel operation settlement decreases as the metro driving speed increases. However, the long-term settlement of tunnel significantly increases as vehicle speed increases, while the foundation differential settlement becomes pronounced and the track irregularities are significant.

A contact model for rock is established and imbedded into a DEM software by summarizing the bond granule tests. DEM simulation of uniaxial compression test on the pre-cracked Lac du Bonnet granite is performed, and then stress distributions are further analyzed and compared with the theoretical results. Different fracture criteria are employed to predict the crack initiation angles that are compared with theoretical ones. The results show that the failure modes obtained from DEM simulation are similar to experimental results, and stress distributions in DEM simulation are qualitatively similar to theoretical values. When the angle of pre-crack is small, the lateral stresses are compressive and tensile. The compressive strains concentrate at two edges, resulting in the tensile strains in the up- and downward cracks. When the angle of the pre-crack is large enough, the stress concentration is unobvious, leading to a discrepancy between the DEM and theoretical results. The crack extension angle resulting from uniaxial compression measured from DEM tests are in good agreement with those acquired from experimental tests. These angles are consistent with theoretical predictions by the maximum circumferential stress criterion and the maximum energy release rate criterion.

The coarse aggregate can show significant particle breakage characteristics under external force loading. Studying the particle breakage process is one of the research focuses at present. Based on one coarse particle failure mechanism, a numerical model for particle breakage is developed, in which the nonlinear contact H-Z model and a density-control method are introduced and the variation of a single particle breakage strength and diameter are considered. Based on the proposed model, the biaxial shear test of coarse aggregate is carried out and compared with the laboratory test results. It is shown that the proposed particle breakage numerical model can describe well the relationship between deviatoric stress and axial strain, and the relationship between volume strain and axial strain. The particle breakage ratio obtained by numerical simulation is consistent with the results obtained by laboratory test. The normalized particle breakage ratios under different confining pressures are practically coincident, and can be fitted by a hyperbolic curve function without considering particle breakage in sample preparation and consolidation processes. As the confining pressure increases, the particle breakage ratio increases, and the final grading curve of sample coincides with that proposed by Einav, which has a fractal dimension of 2.6.

The mesoscopic structure of real soil consists of numerous particles with different sizes, and yet the traditional reconstruction method of quartet structure generation set (QSGS) produces relatively uniform soil particles，which has significant discrepancy with the actual mesoscopic structure of soil. In order to remedy this deficiency, the QSGS is improved by considering the influences of porosity and autocorrelative function of soil, so that the mesoscopic structure reconfiguration closer to real soil is obtained. Based on the reconfiguration model combined with Lattice Boltzmann method , the D2Q9 model is applied to construct a two dimensional model for simulating mesoscopic seepage field of reconfiguration soil by setting the non-equilibrium extrapolation scheme at the inlet and outlet boundaries, and the bounce-back scheme at the soil particles’ boundary as well as the left and right boundaries. Meanwhile, according to a case study, a corresponding program is developed to simulate mesoscopic seepage field of reconstructed soil with constant inlet seepage velocity. The results show that the pore fluid preferentially flows through the channel with good connectivity. Meanwhile, the flow velocity is controlled by the whole connectivity of the channel. The velocity is much faster in whole-through-channel than that in partial-through-channel. Even if there exists a large pore space, the velocity still depends on whether or not it is on the channel with integral connectivity.

Acid etched fracture caused by acid fracturing is the main flow channel for fluid, thus, it is necessary to study the flowing rules of fluid in acid etched fracture. Four governing equations commonly used in fracture flow research and their applied conditions are introduced, among which Navier-Stokes equation is chosen as the governing equation for numerical simulation on acid etched fracture. In order to analyze the behavior of fluid flow through acid etched fractures and high-speed non-Darcy effect on fracture conductivity capacity, two kinds of fractures with different acid etching morphologies are reconstructed to solid models by using reverse engineering techniques, and flow experiments are carried out under different flow rates by using finite element numerical simulation. It indicates that, the acidized surface morphology and contact area of acid etched fracture have a great impact on the flow field distribution. The uniform etching fracture with smooth aperture distribution leads to stable flow pattern and low tortuosity, however, with the presence of obvious boundary layer effect caused by narrow fracture width and wide surface area, high viscous resistance will be generated while flowing. The channeling fracture with rough surface and complex aperture distribution results in unstable flow pattern and high tortuosity, and there is an obvious vortex under high flow rate, hence, increasing the inertial resistance loss. The necking phenomenon in contact area leads to circumfluence, and multiple acceleration-decelerations cause additional pressure loss. Meanwhile, with the increase in simulating flow rate, pressure drop and flow rate will gradually deviate from the linear relationship and present the non-Darcy flow phenomenon. The rougher the fracture surface is, the smaller the critical flow and critical Reynolds number are, the stronger the non-Darcy effect of fluid is under the same flow rate, the faster the conductivity capacity decreases.

The aim of this paper is to establish a digital model for characterizing the actual pore structure of coal and further simulating the gas seepage in coal. The computed tomography (CT) data of long-flame coal samples from Daliuta coalmine is obtained through the μCT225kVFCB high precision CT system. It is found that the minimum pore diameter in coal sample is 1.94 μm. Meanwhile, a new method is developed to convert CT three-dimensional (3D) data into CAD digital model, according to the reverse engineering technology and a Matlab language based 3D reconstruction program. As an example, a finite element model is established by Ansys software to simulate the gas seepage. Then the distributions of gas velocity and pressure in the coal pores are analyzed and hydraulic conductivities along X, Y and Z directions are also calculated. The results indicate that the permeability of coal exhibits anisotropy at microscale (<100 μm) and is greatly affected by coal structure. The newly developed CAD digital coal model can be used not only for finite element analysis, but also for discrete element analysis such as EDEM software. Therefore, this study broadens the application of 3D CT data and extends research areas of coal at microscale.

Rock quality designation (RQD) index is an important parameter for evaluating the quality of fractured rock mass and this index has been widely used in rock engineering. It is difficult to express the actual rock mass of the whole space region by RQD obtained from geological exploration drilling in specific location because of structural and random distribution of RQD in engineering rock mass. In order to make up the deficiency, the spatial interpolation method in statistics provides powerful means. By considering the anisotropy of RQD spatial distribution and the difficulty to describe the structure of RQD distribution in engineering coordinate system, a standard coordinate system could be established according to the space rotation matrix and zoom ratio matrix after getting the principal Hessian direction (pHd) of geological exploration drilling RQD in engineering coordinate system. Then Kriging interpolation method is introduced. Variation function is used to describe RQD structural changes in standard coordinate system, a mathematical model which is conforming to spatial variation is established and the interpolation calculation is made. At last, the prediction of RQD distribution in engineering coordinate system will be acquired by inverse transforming standard coordinate system. Using R programming language, the method is applied to engineering. The results show that this method can effectively predict the distribution of RQD in engineering rock mass, and make up the limitation of local drilling.

In consideration of the imperfection, randomness and ambiguity of the information for stability analysis of highway slopes, an improved fuzzy evaluation method is put forward to assess the stability of highway slopes based on the maximum entropy principle and the engineering fuzzy set theory. In this method, the comprehensive empowering method is adopted to determine the weight of index. The procedure makes full use of the information of the factors influencing stability of highway slopes, and uses the generalized weighted distance to represent the difference between slope sample and standard sample. The relative membership degree is obtained by conditions’ optimization, the grades of the slope samples are identified according to the weighted average principle. The procedure is applied to Changde-Jishou and Jishou-Huaihua highway in Hunan province to analyze the stability of rock slopes. It is found that the assessment results agree well with the results obtained with the fuzzy comprehensive evaluation method，the attribute recognition method and the practical condition of slopes, showing that the new procedure is more reasonable. Furthermore, the Shannon entropy value of the model is smaller, which indicates less uncertainty and higher reliability of the evaluated results.