The consolidation of unsaturated soil is of great significance to road engineering, soft foundation soil improvement, etc. Based on the one-dimensional consolidation theory of unsaturated soil proposed by Fredlund and Hasan, the governing equations for pore water pressure and pore air pressure in the soil are established. The initial conditions and a type of time-dependent mixed nonhomogeneous boundary conditions of single-layer unsaturated soil are presented which constitutes the solution of 1D consolidation of unsaturated soil. The homogenization of nonhomogeneous boundary conditions and the eigenfunction expansion method are adopted to derive exact analytical solutions in time domain for the dissipation of pore water pressure and pore air pressure in the soil. Finally, the method proposed in this paper is validated by experimental comparison, and several examples are used to analyze the effects of exponentially changing boundary conditions on the dissipation of pore water pressure, pore air pressure, and deformation of unsaturated soils. The results show that the speed of exponential change of pore pressure on the boundary or flux across the boundary has significant effect on the consolidation process of unsaturated soil.

Considering the physical and mechanical properties change continuously along the depth in non-homogeneous foundation, the linear transformative relationship is analyzed between the phase velocity and group velocity of the inhomogeneous elastic body waves and the solution of corresponding homogeneous elastic foundation. Firstly, based on the basic equations of elastodynamics, the analytical expressions for the phase velocity and group velocity of the planar elastic body waves in any non-uniformly changing foundation are obtained. Compared with the classical solution of the elastic wave phase velocity of the homogeneous foundation, it is found that the solution of the non-homogeneous foundation can be expressed linearly with the solution of the homogeneous foundation, thus the similarity conversion between the two solutions is obtained. At last, as a numerical example, considering the power law relationship of material properties change continuously along the thickness in the non-homogeneous foundation, the influence of foundation non-uniformity, Poisson's ratio and phase angle on the similarity conversion coefficients is analyzed. The calculation results show that, with the help of the classical solution of elastic wave velocity in homogeneous foundation, the solution of wave velocity in non-homogeneous foundation can be converted into the calculation of the similarity conversion coefficients, thereby simplifying the solution process.

In order to investigate the response law of moisture content to the characteristic stress and acoustic emission characteristics of red sandstone, the uniaxial compression tests of red sandstone under different moisture content conditions were conducted using RMT-150C rock mechanical pressure testing machine and PCI-Ⅱ AE win acoustic emission system. The physical and mechanical parameters and characteristic stress evolution mechanism of red sandstone under water erosion are analyzed, and the evolution law of acoustic emission (wide and narrow-band) time series mode under different moisture content conditions is also investigated. At the same time, the damage evolution model of red sandstone is constructed based on cumulative acoustic emission event number and statistical mechanics theory. The results show that: 1) The P-wave velocity decreases first and then increases with the increase of moisture content. When the water saturation reaches a critical value, the P-wave velocity will drop to the lowest value. 2) The acoustic emission signal received by the narrow-band receiving sensor is closely related to the friction between the particles in the red sandstone, and the acoustic emission signal received by the wide-band receiving sensor is intrinsically related to the evolution of the internal cracks in the red sandstone. 3) The moisture content has a significant effect on the acoustic emission event rate (wide-band) at the stage of unstable crack propagation, and has a minor effect on the ratio of characteristic stress to peak strength, but it has a relatively obvious effect on the strain percentage at each stage. With the increase of moisture content, the failure mode of red sandstone specimens gradually changes from brittle failure to ductile failure. 4) As the moisture content increases, a "backward" change trend can be observed for the active period of acoustic emission event rate (narrow-band), and the acoustic emission modes of dry, natural, and saturated rock samples correspond to mass shocks, pre-main-later shocks and swarm shocks type, respectively. (5) According to the damage model based on the cumulative number of acoustic emission events (wide and narrow-band), the damage process of red sandstone can be divided into four stages: initial damage stage, stable damage development stage, accelerated damage development stage and damage destruction stage.

Due to the effect of sorting by hydraulic dredger fill, the foundation of dredged coral reef in the South China Sea contains fine calcareous silt interlayer with uneven thickness. Compared with coarse-grained calcareous sand, calcareous silt presents higher compressibility, lower bearing capacity and larger settlement deformation, which adversely affect the safety of buildings on coral reefs. In this paper, the characteristics of primary and secondary consolidation settlement, consolidation time and consolidation rate of calcareous silt were obtained through laboratory consolidation tests, for better understanding the engineering properties of calcareous silt and calculation of coral reef foundation settlement. The calcareous silt shows 0.03?0.37 MPa?1 of the compression coefficient and 6.67?54.79 MPa of the compression modulus. Compression coefficient is directly proportional to moisture content and inversely proportional to dry density. Compression coefficient lower than 0.1 MPa?1 and compression modulus more than 20.0 MPa occurs in moderately dense and dense calcareous silt with water content of less than 15% as low compressibility soil, but loose calcareous silt is moderately compressible. Compared with quartz sand under the same dry densities and moisture contents, the compression coefficient of quartz sand is higher than that of calcareous silt, while the compression modulus is lower than that of calcareous silt. Under the same dry density and water content, both Hangzhou Bay silt and calcareous silt show moderate compressibility. However, the compressive modulus of calcareous silt is slightly larger than that of Hangzhou Bay silt, and its compressive coefficient is slightly smaller. When the load exceeds 200 kPa, the degree of consolidation of calcareous silt reaches 0.95 in the first 5 hours of the consolidation test. Therefore, it suggests 24 hours for the consolidation time of calcareous silt under loading less than 200 kPa but 5 hours under loading greater than 200 kPa for the testing efficiency.

the evolution of the critical state of TDA-graded aggregates is essential to safety for TDA application in railway roadbed, but the investigations on effects of TDA on the critical state are rare. This paper presents an experimental investigation on the stress strain relationship of TDA-graded aggregates through large scale triaxial apparatus by consolidation and drainage conditions. In total, 12 groups of specimens were carried out considering four volumetric TDA content and three confining pressures. The experimental results show that the shear properties of the TDA sub-ballast mixture are characterized as strain-softening when the TDA volume content is less than 20%, and show strain hardening when the TDA volume content is greater than 20%. And the critical state line (CSL) in space, and relationship between the TDA content and the values of parameters of CSL is linearity. In consequence, the strain-stress of TDA-graded aggregates based on the critical state line characteristics was predicted, and compared to the corresponding measured values with good agreement. It highlights the feasibility of the new formula for the TDA-graded aggregates. These experimental findings are helpful for modeling aggregates with TDA inclusion.

To investigate the effect of high temperature on physical and dynamic mechanical properties of limestone, basic physical tests were conducted on limestone specimens at room temperature and high temperature treatment from 100 ℃ to 800 ℃. Moreover, dynamic impact compression tests under the same loading conditions were also conducted using SHPB test device. Test results indicate that the main mineral composition of limestone is calcite and dolomite. At room temperature, the limestone has a compact structure. With the increase of treating temperature, the dolomite gradually decomposes into micro-sized particles, and the surface color of test specimens gradually changes from off-white to white. Moreover, the volume of test specimens increases, while its mass, density and P-wave velocity decrease. These variation rates are closely related to the temperature. Dynamic compression stress-strain curves of limestone specimens under different high temperatures are basically consistent. A small increase followed by a significant decrease can be observed for both the dynamic compressive strength and dynamic elastic modulus with the increase of the temperature. An obvious negative quadratic function relationship is also found between these dynamic parameters and the treating temperature, and the maximum value is observed at 200 ℃. However, parameters including the dynamic strain and strain rate of test specimens, and the treating temperature are in a positive quadratic function relationship. The failure modes of specimens transit from brittle to ductile brittle, and damage degree is the lowest at 200 ℃. The damage degree increases with the increase of temperature, and the size of limestone fragments gradually decreases, which basically becomes powder at 800 ℃.

In this study, laboratory tests of the air-booster vacuum preloading method with different air-boosting depths were performed on the Tianjin dredged slurry of high water content. The law of gas migration in soil was used to analyze the reinforcement mechanism and the reinforcement factors. Test results show that the drainage, settlement, dissipation of excess pore water pressure as well as the vane shear strength were significantly improved when air boosting is operated on the lower part of drainage board. In the initial stage of consolidation of the fluid-plastic soil, the injected gas is easy to form bubbles and to move upwards rapidly under the action of buoyancy, which drives the deep soil particles to move upwards and disturbs the soil like stirring, so that the dredged slurry was reinforced more uniformly; while as water content of the dredged slurry gradually decreased, the gas in soil would form a closed space with a certain pressure, leading to increased pressure between the plastic vertical drain and the gas injection pipe; in the later stage of consolidation, the gas expanded in soil, which forms micro-fracture cracks to accelerate the water dissipation in the soil and improves the drainage reinforcement effect.

Geogrid is used to reinforce the trackbed by increasing the confining pressure and reducing the vertical cumulative settlement and lateral displacement of ballast. In order to further study the reinforcement mechanism of geogrid reinforced ballast, pull-out tests of single and double-layer geogrids with large and small apertures under static load were carried out by using self-designed equipment, and the influences of grid aperture, reinforcement depth and number of layers on pull-out resistance were analyzed. The standard values of pull-out resistance at different depths were obtained by single-layer tests, and the coefficient of double-layer reinforcement was proposed to quantify the reinforcement capacity of double-layer geogrids, and the best laying way was also discussed. Double-layer geogrids with aperture size of 65 mm placed in 200-300 mm were simulated by DEM. The distribution of internal stress chain and contact force vector of geogrid reinforced ballast during pull-out process were analyzed from the micro view. The results show that, for the graded ballast, the geogrid with 65 mm aperture performed better than that with 32 mm aperture; the ultimate pullout resistance of double-layer laying was greater than the sum of the standard values of the two-layer laying. The double-layer reinforcement effect is related to the geogrid aperture and the layer spacing. The simulation results also verified the superposition of reinforcement effect between the two-layer geogrids during pull-out process, and the distribution of normal contact force vector showed that the double-layer geogrid had interlocking reinforcement effect.

To study the strength and deformation of municipal solidified sludge after different freeze-thaw cycles, the sludge solidified by CJYT-1 solidifying agent was tested through true triaxial tests. The stress-strain relationship and the strength and deformation characteristics after freeze-thaw cycles number of 0, 1, 3, 5, 8, 10 are obtained, and the influence of intermediate principal stress ratio b and the number of cycles N on the soil strength parameters (including cohesion c′ and internal friction angle ?′ ) are studied. The results of the freeze-thaw cycle test show that the unconfined compressive strength and density of the solidified sludge gradually decrease with the increase of the number of freeze-thaw cycles, and the change slows down and stabilizes after 8 cycles. The cohesion and the internal friction angle both increase with the increase of b. Compared with b=0, when b=1, the growth rate of and can reach 16.77% and 12.3%, respectively. As the number of cycles N increases, the failure strength of the soil gradually decreases, and the failure stress ratio Mb generally decreases. The dilatancy of the specimen does not change significantly. The cohesion and internal friction angle decrease with the increase of freeze-thaw cycles N. Based on the two commonly used, Lade-Duncan and Matsuoka-Nakai failure criteria, combined with the true triaxial test data of solidified sludge, a failure criterion suitable for solidified sludge is proposed, and the -b relationship curve of the criterion is analyzed. Comparing the failure criteria proposed in the article, Lade-Duncan and Matsuoka-Nakai failure criteria, the test results are closer to the failure criteria in the article.

Taking the large-scale toppling failure counter-tilt slope in Changshanhao open-pit mine in Inner Mongolia as engineering background, a layered counter-tilt slope geological generalized physical model was constructed based on similar theory. Physical model tests were performed under three different conditions: unreinforced, ordinary PR anchor cable reinforcement, and constant resistance and large deformation (NPR) anchor cable reinforcement. Then infrared thermal imaging system, strain monitoring system and digital speckle displacement measurement system were used comprehensively to monitor the temperature field, strain field and displacement field respectively during the entire counter-tilt slope excavation test. Finally the deformation characteristics and instability mechanism of layered counter-tilt slope were investigated, and the reinforcement effects under different reinforcement measures were compared and analyzed. The research results show that the deformation process of counter-tilt slope has obvious deformation characteristics of "superimposed cantilever beam". Its toppling mechanism is mainly manifested in three stages: initial crack formation, crack development, and sliding surface penetrating and slope instability. The PR anchor cable failed during the excavation and could not resist the large deformation of the slope. In contrast, the NPR anchor cable has the characteristics of high constant resistance, large deformation and energy absorption, which can effectively prevent the occurrence of counter-tilt slope instability and provide a new way for slope engineering reinforcement.

As a kind of special soil, granite residual soil is widely distributed in the southeastern part of China and usually leads to engineering accidents due to its special structure. In this paper, a series of triaxle tests was conducted on the slope residual soil from Bozhi County, Zhaoqing City, Guangdong Province, to study the strain and pore pressure characteristics of structural granite residual soil under triaxial stress state as well as the structural yield characteristics of granite residual soil, which could provide useful reference for corresponding projects. Triaxial compression tests were conducted on undisturbed soil, remolded normal consolidated soil and remolded over-consolidated soil. The results showed that both undisturbed soil and remolded over-consolidated soil had certain structural characteristics, and had an obvious dilatancy during the drained shear test. The stress-strain curves of both undisturbed soil and remolded over-consolidated soil showed strain softening. The excess pore pressure of both undisturbed soil and remolded over-consolidated soil increased first and then decreased during the undrained shear test, while the excess pore pressure of undisturbed soil decreased more. The undrained shear strength of over-consolidated soil was consistent with the SHANSEP theory and the test constant was 0.67. The normalized stiffness of remolded normal consolidated soil decreased slowly with loading process going on, and it yielded completely when =15%. The normalized stiffness curves of undisturbed soil and remolded over-consolidated soil were not consistent with each other, and the structural yielding occurs at =1.5% and =1% respectively, and the overall failure occurs at =15%. In addition, the larger the confining pressure was, the more similar the structural curve of the structural soil was to the disturbed soil.

Studies on the clamping effect and failure mode of the tunnel-type anchorage are still insufficient, leading to many difficulties in the optimization of design philosophy of the tunnel-type anchorage. In this work, the bearing characteristics, bearing mechanics and the failure mode of the tunnel-type anchorage were analyzed through 2D laboratory model tests. Besides, the influences of wedged angle and burial depth on the bearing capacity and failure mode were studied as well. This work reveals the essence of the clamping effect of the suspension bridge tunnel-type anchorage to some extent. Main conclusions are given as follow: First, additional stress is generated when the anchorage moves with a crescent accelerated velocity and squeezes the surrounding rock. The clamping effect results in resistance and the surrounding rock and soil start to bear the main cable load jointly. Second, the bearing capacity of the tunnel-type anchorage is contributed by gravity and the clamping effect. The clamping effect will play a role only when the gravity effect fails to balance the main cable load. From the view of economy and security, it is necessary to rationally design the size of the anchorage to ensure the role of the clamping effect. Third, the bearing capacity of the tunnel-type anchorage is also influenced by the wedged angle and it is necessary to optimize the wedged angle to obtain the maximum bearing capacity. Fourth, the bearing capacity of the tunnel-type anchorage increases linearly with the burial depth. Thus, in the actual project, the burial depth should be determined according to the bearing capacity, the construction difficulty, as well as economy. Finally, the initiation and propagation of the cracks is associated with the response of the stress and displacement. There is no crack initiation when the anchorage and surrounding rock are relatively static. The formation time of the failure mode corresponds to the nonlinear displacement stage of anchorage acceleration.

X-section cast-in-place concrete (XCC) pile is a typical non-circular cross-sectional pile of which the mechanical characteristics are different from a traditional circular pile, namely the “geometrical effects”. So far, a rigorous theoretical method that considers the geometrical effects is still not given. To investigate the influence of geometrical effects of vertically loaded XCC single pile embedded into homogeneous soil on pile foundation settlement, the differential equations governing the displacements of the pile-soil system based on variational principles are obtained, which accounts for both vertical and horizontal soil displacements. The conformal mapping technique is applied to the governing differential equations in the physical plane with a complicated boundary. With the aid of Matlab software, a finite difference program is developed to solve the governing equations, yielding semi-analytical solutions of pile and soil displacement functions. The pile displacement function is selected to verify the convergence of the developed program. The pile displacement obtained from the present method is exactly the same as the existing theoretical solution. Compared with the finite element analysis, the solution for the XCC pile from our analysis is in reasonable agreement. Finally, parametric studies, which focus on the major effect factors of pile settlement, are conducted, and the geometrical effects of XCC pile are investigated by means of comparing the normalized head pile of stiffness with circular piles with the same area and the same perimeter. After that, a fitting equation for the percentage increase of the normalized pile head stiffness of the XCC pile relative to the circular pile with equal cross-section is given.

In order to investigate and analyze the damage mechanism and evolution rule of the physical and mechanical properties of granite under the action of multiple high temperature-water cooling cycle at different temperatures, high temperature-water cooling cycle test, uniaxial compressive strength test, ultrasonic test were carried out. The results show that: 1) At the same temperature, an increase in the number of high temperature-water cooling cycle results in the initiation and expansion of the internal fractures of the rock sample, which is manifested by the gradual increase of the mass loss rate of granite samples. And the compressive strength and elastic modulus decrease firstly, then increase slightly, and finally continue to decline. 2) When the number of high temperature-water cooling cycle is the same, an increase of temperature leads to a continuous increase in the mass loss of the granite samples, and a continuous decrease in the compressive strength and elastic modulus. 3) Temperature has a large effect on the P-wave velocity of granite. As the temperature increases, the wave velocity decreases rapidly and the amplitude becomes unstable. 4) The increase of temperature and the number of high temperature-water cooling cycle both increase the damage degree of rock samples and the damage variables. 5) With the increase of temperature and the number of high temperature-water cooling cycle, the rock sample gradually softens, and its uniaxial compression failure mode transitions from splitting tensile failure to conical shear failure. The number of cracks on the surface gradually increases during failure. Additionally, tree-like cracks appear when the temperature is up to 400 ℃ and gradually penetrate the entire surface. It is concluded that the physical and mechanical properties of granite will be severely degraded after high temperature-water cooling cycle.

Small-strain stiffness of saturated clay and its directional dependence are critical for the design of deep excavations in soft soils and the evaluation of excavation impacts on adjacent infrastructure. Though many constitutive models have been proposed to capture the behavior of fine-grained soils at small strains, they are in general too complex to be incorporated into the simplified analyses of excavation-induced ground movements and soil-structure interaction. Moreover, in these models, small-strain moduli are normally assumed to be isotropic and hence independent of loading directions. In this study, based on the concept of intergranular strain (IGS), we propose a simple and easily calibrated hypoelastic model for saturated clay with anisotropic small-strain stiffness. The model considers direction-dependent moduli at very small strains, non-linear degradation of stiffness with strain levels, recent stress history effects, and stress-dilatancy relation. By comparing against the results of stress probe tests on natural Chicago clay, it shows: 1) The proposed model can reasonably represent the degradation of stiffness at small strains, the stress-strain relationships at large strains, as well as the development of excess pore pressures and soil dilatancy. Also, the model can well approximate advanced elastoplastic models. 2) Compared with the existing Overlay model, the IGS model can better replicate the dependence of small strain stiffness on the intermediate stress path rotations between monotonic and full reversal loading. 3) Anisotropy can noticeably influence the soil stiffness at very small strains such that soil specimens characterized by smaller stress path rotations can feature higher initial shear modulus. With the increase in strain levels, nevertheless, recent stress history becomes the dominant factor in affecting small-strain characteristics of clay.

Due to the long-term landing and take-off of aircraft, the development characteristics of the cumulative plastic strain of silt foundation will change. The influences of loading frequency and degree of compaction on the long-term cumulative plastic deformation of compacted silt under different dynamic stress amplitudes were studied based on dynamic triaxial test. The test results show that the cumulative plastic strain evolution type of compacted silt under different cyclic stress ratios can be divided into three types: plastic shakedown, plastic creep and incremental failure. In addition, the degree of compaction affects the cumulative plastic strain and the ratio of critical cyclic dynamic stress. And the loading frequency has a significant influence on the increase rate of cumulative deformation in the early stage of loading. In addition, the elastic behavior is obviously influenced by the degree of compaction, with the dynamic modulus increasing with the increase of compactness. Based on that the evolution characteristics of cumulative plastic strain of compacted silt showing a stable type, a model of cumulative plastic strain of compacted silt was proposed, in which the influences of degree of compaction and loading frequency were considered. It was found that the fitting parameters had a good linear relationship with the cyclic stress ratio under the same degree of compaction and loading frequency during model parameter fitting. Based on the analysis of the correlation among the parameters, the relationships between these parameters and cyclic stress ratio, degree of compaction and loading frequency were determined.

Rock bolts have been widely used as the reinforcement of jointed rock mass. To explore the shear behaviors of bolted rock joints, the influences of two locking modes, i.e., two-end locking and no-locking, on the shear characteristics of bolted rock joints were studied based on the indoor direct shear tests. The enhancement of the shear strength of the bolted rock joints influenced by normal stress and prestress was analyzed. During the test, the variation laws of the axial forces at varying monitoring points of the bolt were recorded by strain gauges, and the axial force mechanism of the bolt under different locking modes was studied. The deformation characteristics of the bolt after shear test were carefully examined and the influence of normal stress on the bending deformation of the bolt was analyzed. The results show that the shear stress-displacement curves of the locking bolted joints at both ends can be divided into three stages, i.e., the initial elastic stage, elastoplastic stage and plastic hardening stage. The shear stress-displacement curves of the unlocked bolted joints can be divided into three stages, i.e., the initial elastic stage, elastoplastic stage and plastic softening stage. The locking mode has a significant impact on the shear strength and the axial deformation of bolt. Compared with the no-locking mode, the lock at both ends is more conducive to the shear resistance. Based on the analysis of the plastic hinge position of bolt after shear test, it shows that the normal stress has an important influence on the plastic hinge position, and the distance between the plastic hinge points decreases with the increase in the normal stress. Finally, an analytical model was proposed to predict the position of the plastic hinge. The new model takes into account the influence of the normal stress, which agrees well with the experimental results.

There is a time interval between adjacent trains in the railway line in service, thus the long-term loading of trains on the subgrade is composed of the vibrational loading when the train is passing and the intermittent loading when train passed away, namely the intermittent cyclic loading. A series of dynamic triaxial tests with continuous loading and intermittent loading (single-stage and multi-stage) was conducted to study the deformation of subgrade under the intermittent cyclic loading of trains. The cumulative plastic strain under intermittent loading was studied, and the prediction models were proposed. Results show that the resistance of the sample to cyclic loading was improved and the cumulative plastic strain was reduced due to the loading intermittence. The cumulative plastic strain showed "phased growth" under intermittent loading instead of the "smooth growth" under the continuous loading. Finally, the hyperbolic model based on the time-hardening approach could better predict the cumulative plastic strain of the stable and critical samples under intermittent loading. The research can provide guidance for further understanding of the deformation characteristics and settlement prediction of railway subgrade.

To study the permeability of saturated clays with different stress histories under ramp loading, the one-dimensional consolidation and seepage tests are carried out using modified GDS triaxial apparatus, and the change of the permeability coefficient of remolded silty clay in Luochuan, Shaanxi Province is studied. The results show that permeability coefficients of normally and over-consolidated saturated clays decrease nonlinearly with the increase of the consolidation stress, and the void ratios of these two soils are consistent with the trend of change of the permeability coefficients with the consolidation stress. The compressibility and permeability of soil in the over-consolidated state are much smaller than that in the normally consolidated state. The permeability coefficient and void ratio decrease with the increase of the osmotic pressure difference under a constant consolidation stress. Finally, the measured values are compared with the permeability coefficients calculated by the modified Darcy permeability coefficient formula, modified Kozeny-Carman formula, Stokes porosity permeability coefficient formula and degree of consolidation and seepage formula in Ref. [12]. The results reveal that the permeability coefficients calculated using the modified Kozeny-Carman formula are in good agreement with the measured values. Therefore, the modified Kozeny-Carman formula is recommended to predict the permeability coefficient of Luochuan saturated clay.

Helical piles are widely used in power transmission lines and photovoltaic engineering. It has many advantages, such as convenient construction, large bearing capacity, etc. However, the precision of the existing theoretical calculation method for estimating the uplift bearing capacity of the helical pile is still not satisfying. Based on the cavity expansion method, through the Tresca criterion, a modified approach to estimate the uplift bearing capacity of the helical pile was proposed. Full-scale model tests on the uplift bearing capacity of helical piles were carried out, and the tensile load-displacement response was measured. The uplift bearing capacity of the helical piles tested was obtained with consideration of different failure interpretations. Based on the comparison between the predicted uplift bearing capacity of the helical piles using the method proposed in this paper and the results obtained from the literature, the accuracy and reliability of the theoretical calculation method herein are verified. The results show that the uplift bearing capacity coefficient of the helical anchor increases with the increase of the buried depth of the first helix, and its upper limit value is mainly restricted by the rigidity index of the soil. Compared with traditional calculation methods, the theoretical calculation method in this paper is more accurate, which has about 10% calculation error.

To study the shear deformation mechanism and strength characteristics of vibroflotation crushed stone column composite foundation in sandy silty soil, two model tests of crushed stone pile composite foundation with different displacement rates of pile were carried out by using large stacking ring shear apparatus. The relationship between shear stress and shear displacement, deformation of composite foundation under different stress states are systematic analyzed. The test results show that: 1) The sandy silty composite foundation has a feature of elastoplastic object and the stress level S=0.5 can be used as the elastoplastic object’s dividing line roughly. 2) In the process of large deformation destruction of composite foundation, the stone columns and soil have a good deformation consistency, meanwhile, the shear deformation is inhibited with the increase of displacement rate of pile. 3) At present, a few specifications in China suggest that the number of stress ratio of pile with soil is 1 for the shear strength calculation of composite foundation, which means that only pile area replacement is considered. As a result, the calculation results of shear strength are close under different pile replacement rates. The permutation rate of 22.7% has a 1.32° gap compare with 40.3% while the pile replacement rate of 22.7% has a 3.65° gap compare with 40.3% in the model test. It indicates that the reinforcement mechanism of stone columns on composite foundation should not be limited to the factor of displacement rate, the change of drainage effectiveness of composite foundation factor should also be considered.

The natural seawater was used to carry out the experiment of microbial culture and microbial-induced calcium carbonate precipitation (MICP) to strengthen calcareous sand. First, the effect of seawater on microorganisms was studied through the growth and reproduction of microorganisms and the change of urease activity. Then, the effect of seawater on the strengthening effect of MICP was evaluated according to the changes of calcareous sand permeability and unconfined compressive strength (UCS) before and after MICP treatment. Finally, the mechanism of the effect of seawater on the strengthening of calcareous sand by MICP was analyzed by SEM and XRD tests. The results show that: 1) natural seawater leads to a lag in the growth of microorganisms, but the number of microorganisms and urease activity in the stable stage are not significantly different from those in fresh water environment; 2) the effect of using seawater to strengthen calcareous sand by MICP is less different than that under fresh water condition, the permeability coefficient of calcareous sand can be reduced by an order of magnitude, and the UCS value can reach 1.7 MPa; 3) under the condition of natural seawater, the MICP process is controlled by seawater composition, microorganisms, calcium ion concentration, urea concentration and pH. The main crystal form of calcium carbonate is calcite, which can fill the intergranular pores and make the sand particles cement as a whole, which is the main reason for the improvement of mechanical properties of calcareous sand.

To select an appropriate notch prefabrication method and notch length for obtaining relatively accurate and reliable rock mode I fracture toughness (KIC), as well as to improve understanding on macro fracture process and meso-fracture characteristics in the rock three-point bending test, three methods, i.e., wire cutting, saw blade cutting and water jet cutting were used to prefabricate notch in granite and marble specimens for three-point bending test. The comparison of micro fracture characteristics among three different cutting methods was conducted with the application of scanning electronic microscopic. The test results show that the effect of wire cutting method on KIC is the smallest. In addition, three-point bending tests on granite and marble containing dimensionless notch length of 0.1, 0.2, 0.3, 0.4, and 0.5 show that KIC tends to increase firstly and then decrease with increasing notch length. The dimensionless notch length of ? =0.3 is recommended for obtaining the representative KIC. The macroscopic failure of rock specimen undergoes a process of initiation of localization zone, development of localization zone, crack initiation, and finally fracture propagation. The acoustic emission process of rock specimen is observed with an obvious brittle characteristic, the crack opening displacement curve is consistent with the trend of cumulative acoustic emission curve, and the evolution of crack opening displacement curve can be regarded as a macroscopic characterization of the specimen internal failure development process.

Branch-type anchor is a new type of bolt independently developed by the authors, which has broad application prospects. In order to explore the load-bearing characteristics of branch-type anchors, an indoor test model was constructed, and a series of pull-out tests was carried out for different embedding depths, branch diameters, and double-branch spacing. The corresponding load-displacement curves were obtained, and non-dimensional processing for part of the data was conducted to obtain the relationship curve between the buried depth ratio and the load factor. Finally, a simplified mechanical model was used to derive the calculation formula for the end resistance and the pull-out ultimate bearing capacity of the branch-type anchor. The research results show that there is a nonlinear relationship between the embedment depth and the ultimate bearing capacity, and a critical embedment depth exists. The plate diameter has the most significant impact on the pull-out bearing capacity, which has a linear growth relationship with the ultimate bearing capacity. The ultimate bearing capacity is 2?5 times higher than that of a straight bolt. The bearing capacity of the double plate can be fully used when the separation distance of the double plate is 4 times of the plate diameter. Since the soil is mainly sheared at the initial stage of loading, the initial slope of the load-displacement curve of the double-branch anchor is much larger than that of the single-branch anchor. The sudden change point of the slope of the relationship between the embedment depth ratio and the load factor is the critical embedment ratio, which is 3.02. The results obtained by this formula are basically consistent with those of the four testing groups, which verifies the validity of the calculation formula. The research results have important theoretical and practical significance for the design and engineering application of the branch-type anchor.

The integrity coefficient of rock mass is one of the important indice to evaluate the stability of engineering rock mass. Extensive research results show that the integrity coefficient Kv can comprehensively represent the integrity of rock mass. However, this parameter is difficult to obtain in frequent field tests. Therefore, a new integrity coefficient that can be easily obtained to represent the rock mass integrity is needed. Based on the literature review and a large number of engineering in situ data, this paper first studies the relationship between the volumetric joint count (Jv) and the integrity coefficient (Kv) of rock mass. A correction method of Jv representing Kv is then put forward considering the type of structural plane. The structural plane is divided into five categories according to the qualitative and quantitative properties of the structural plane. Moreover, the correction coefficient of structural plane, Jp, is determined based on the measured data. Comparing the Kv measured in the practical engineering, the Kv conversed from the international recommended standard value, the Kv conversed by the linear fitting, and the Kv conversed by the proposed correction method, it shows that the goodness-of-fit of the Kv conversed by the correction method and the measured Kv is the highest. The absolute residual reduce 58% and 32% compared to national recommended standard value and the linear fitting conversion, indicating that the conversion accuracy is higher. It is proved that the correction of the structural plane is feasible and exhibits promising application prospect in engineerings.

In this paper, the indirect boundary element method is extended to simulate near-fault ground motion of complex sites. Seismic amplification effect of alluvial valley under the successive dislocation of a strike-slip fault is quantitatively analyzed by a two-dimensional finite-fault kinematic model. First, hanging wall, footwall of the fault and alluvial valley are divided into different calculation domains. Second, the boundary integral equation is established by using the stress and displacement boundary conditions of different interfaces in the frequency domain. The virtual load density is obtained by discretization, and the seismic response in the frequency domain is solved. The time domain results can be obtained by Fourier transform. Further, the accuracy of the proposed method is verified by comparing with the analytical results. Finally, the amplification characteristic of near-fault ground motion of the alluvial valley is investigated. The influence of the varying parameters, such as the buried depth of the fault upper boundary, the dip angle of the fault, the fault distance of alluvial valley, and the fracture velocity of fault element, on the seismic response of the model are studied. The results show that the alluvial valley has an obvious amplification effect on the amplitude of near-fault ground motion, and the peak value of acceleration response spectrum of the analyzed model can be magnified by 4.64 times. In the interior of alluvial valley, the duration of ground motion is prolonged obviously, and long-period velocity pulse with larger amplitude appears. The near-fault ground motion damage has a typical concentration-effect: when the increase of the fault distance is 10 km, the half-space surface displacement approximately attenuates 50%. This study can provide a new and effective method for simulating near-fault ground motion of complex sites, and it is of great significance for seismic zoning of the complex site with near fault and seismic design of engineering structure.

To make the initial geo-stress field of rock masses obtained by the inversion analysis more realistic, three conditions are proposed, which are the initial geo-stress field of rock masses should be superposed by compressive stress fields, the tectonic load of boundary obtained by the inversion analysis should not be too large, and the constituent of stress fields obtained by the inversion analysis should be consistent with the constituents of the stresses field measured by the in-situ test. Based on the theory of multiple linear regression, in the inversion analysis of the initial geo-stress field of rock masses, the reason leads to negative, too large and insignificant regression coefficient is uncovered firstly. It is the multicollinearity between independent variables that may lead to negative, excessive and insignificant regression coefficient when the least square method is adopted to obtain the regression coefficients. Then, two sources of multicollinearity are given. The one is that a narrow range of measured in-situ stresses can lead to multicollinearity among independent variables. The other one is that using multiple equations to express the initial geo-stress field of rock masses which commonly leads to nearly completely multicollinearity between independent variables. Finally, some methods for detecting and avoiding multicollinearity are proposed, and applied in the inversion analysis of the initial geo-stress field of rock masses for the Banzhulin tunnel. Based on the results of this inversion analysis, it is found that ridge regression can replace the least square method to solve regression coefficients effectively if independent variables suffer from the multicollinearty.

In traditional geological modeling methods, the expression of the stratigraphic model is inaccurate and the stratigraphic boundary has a sawtooth phenomenon. Moreover, due to the large amount of model data, it cannot be smoothly loaded and rendered on the Web side. To solve these problems, this paper proposes a three-dimensional (3D) geological modeling method based on regular voxel splitting. This method first uses the boreholes and geological section data in the geological survey for data conversion and fusion, and encrypts the stratum vector point through the interpolation algorithm, and then constructs and divides the regular voxels, and designs 5 different regular voxel splitting types. At the same time, the data structure design of the voxel splitting model is carried out, and the irregular voxel metadata structure is analyzed and displayed through Three.js. Using this method, a 3D geological model was constructed based on the survey data of a certain area of Zhengzhou City, and the Web-side visualization was performed. Experiments have proved that the constructed model can accurately and smoothly express different stratigraphic structures, and can realize rapid rendering, spatial query and analysis of the internal information of geological bodies in the browser.

Local scour often occurs in hydraulic and ocean engineering. Wave-current coupling and pile diameter effect make this problem very complicated. In order to study the local scour characteristics of large diameter monopile under combined waves and currents, a numerical model was established in the CFD software FLOW 3D, and a physical model test was designed. By comparing the scour depth in the physical model test and the results in numerical simulation, the accuracy of numerical simulation was verified. Based on an offshore wind farm project, a field-scale numerical model of seabed and monopile was established. The waves were described by random theory and the turbulence was calculated by large eddy simulation method, and the local scour characteristics of a large diameter monopile under combined waves and currents were analyzed. The results show that the spatial development of local scour can be divided into three stages: longitudinal cutting, lateral spreading and stabilization. The maximum scour depth was 4.9 m in front of the pile, which was about 0.9 times of the pile diameter. Correspondingly, the time development of the local scour can also be divided into three stages: rapid growth, moderate growth and stabilization. After 20 hours, the maximum scour depth remained unchanged, and the local scour reached a stable state.

Soil is a multi-phase and multi-scale geomaterial that exhibits dramatically inhomogeneous and discontinuous physical nature. Conventional finite element method, which is conceptualized at a single macroscale and ignores the control mechanism of soil at the micro and meso scales, cannot reproduce and predict the multi-scale and hierarchical failure of soil. In order to investigate the influence of the physical details and kinematic characteristics of soil at the microscale associated with the global mechanical responses, a multi-scale particle micro-rotation theory is established according to the concept of the soil cell element model. The method is implemented into a multi-scale finite element code, and is used to reproduce and predict the depth of foundation plastic zone. The numerical simulation results show that the multi-scale coupling finite element model can relate the motion feature of soil particles at the microscale to the mechanical response of soil at the macroscale; the rotation displacements of soil particles concentrate upon the plastic zone and has an average value of 4°; the depth of foundation plastic zone increases as the size of soil particle and elasticity modulus of soil increases respectively. The concentration and development of plastic deformation, which is caused by the particle rotation leading to a degradation of the ability of strain transmission, are the micro-mesoscale physical mechanism of the trans-scale evolution of foundation plastic zone.