In order to analyze the flow deformation of sand under zero effective stress and shearing condition, traditional ring-shear apparatus is modified with the transparent box for specimen visualization. By analyzing the expansion of transparent box and comparing the shear tests of standard sand, the rationality of the ring-shear apparatus after the reformation is validated. By analyzing the shear stress-strain curves of saturated suspension plastic sand under unconsolidated undrained condition, strain softening is found in the shear strength. And by analyzing the effective stress of saturated suspended plastic sand, it is proved that the saturated suspended plastic sand in the visual ring shear tests is in zero effective stress state. The results show that the shear deformation of the saturated suspended plastic sand under the consolidated undrained condition is obviously discontinuous. Fracture occurs directly on the shear plane. The shear deformation of the saturated suspended plastic sand under unconsolidated undrained condition has distinct flow characteristics. The deformation characteristics are related to the shear rate. Under the low shearing rate, the shear flow deformation only forms on the shear plane and shows curved trajectory. But under the high shear rate, the shear flow deformation is totally incline, and consistent with the flow deformation of viscous fluid.

The spatial distribution of the root system has a significant effect on the shear strength of the composite soil. In recent years, the rapid development of the transparent soil test technology provides suitable technical support for visual observation of plant root distribution. Based on the transparent clay manufactured by Carbopol Ultrez 10, the distribution patterns of two plant root systems (tall fescue and vetiver) were visually observed in the growing processes. The growth of rhizomes in natural sand and natural clay was also carried out for comparative analysis. Based on the vane shear test method, the strengths of tall fescue root reinforced composite soil with different spatial distributions (such as vertical, inclined, intersect and mixed) were measured in detail. The optimum root content, root enhancement effect coefficient, and surface reinforcement effect were also discussed. The results show that the optimal root content in the transparent clay material is about 0.35%, and the root enhancement effect coefficient of the mixed root system is the largest, about 1.4-1.5 under this experimental condition.

The uniaxial compression mechanics test was carried out by simulating the osmotic pressure generated by the centrifugal test. The influence of the penetrating force on the mechanical properties of the filling body was studied, and the deformation characteristics of the filling body sample were discussed with the change of the osmotic pressure. The results show that as the penetration force increases, the interval of the stress-strain curve of the sample decreases first and then increases, the interval of the elastic phase shrinks, and the yield stage is not obvious. From low osmotic pressure to high osmotic pressure in the test process, the failure mode of the sample is successively characterized by tensile failure and shear failure, the number of cracks generated increases, and the morphology tends to be more complicated. On the basis of the mechanical test, a damage-softening constitutive model of the filling specimens with different osmotic pressures is established, considering the stress-strain relationship of the specimen in the compaction stage. The verification results show that the theoretical curve and the experimental curve are highly consistent. The model is suitable for analyzing the uniaxial compression mechanics of filling bodies with different osmotic pressures. The study provides a reference for the development of supergravity centrifugal simulation and underground seepage experiments.

Calcareous sand is a special type of rock soil developing in the ocean. This marine sediment with irregular shape has different mechanical properties from the land originated sand. On one hand, microscopic 3D imaging was conducted in this paper for comparing the micro properties of calcareous and quartz sands. It can be found that calcareous sand particles are multi-angular and flatter in comparison with quartz sand. On the other hand, the effect of different particle fraction contents on compressive deformation properties of calcareous sand was investigated in compression tests. Then the 3D morphology was used to discuss the effect mechanism from a microscopic viewpoint. Quartz sand was used as a reference for comparison. It is shown that the compressibility of calcareous sand is 1.6-2.6 times that of quartz sand under the same gradation and compactness. The effect of the coarse fraction (5-1 mm) content in the gradation plays the most significant role in this feature. When the content of coarse particles is less than 25% and the mass ratio of middle and fine particles (M) is constant, there is the worst coarse fraction content causing the greatest compressibility of calcareous sand. With the increase of the mass ratio of middle and fine particles, the worst coarse fraction content decreases, and an empirical formula is proposed.

The use of aged steel slag as geotechnical backfill material is one of the main ways of recycling waste steel slag. According to the engineering classification method of soil, the waste steel slag is divided into gravel steel slag, coarse steel slag and fine steel slag. For the gravel steel slag, the dynamic triaxial tests were carried out by considering the influencing factors, such as consolidation stress ratios, vibration frequencies, confining pressures and gravel contents. The relationships between dynamic strength and vibration times, dynamic strain and vibration times, pore water pressure and vibration times, dynamic stress and dynamic strain of the gravel steel slag samples were analyzed. The calculation model of saturated sand dynamic pore pressure proposed by Seed and Finn was used to analyze the types of dynamic pore pressure curves of gravel steel slag. Compared with the anti-liquefaction strength of the traditional gravel soil, the anti-liquefaction characteristics of gravel steel slag are better. In the practical engineering, gravel steel slag can be used to replace traditional sand, gravel soil, sand gravel and sand pebbles as backfill materials, to solve the shortage problem of gravel resources.

By introducing the energy consumption ratio (?), the axial cyclic loading test was carried out to study the energy evolution of sandstones under different confining pressures. The evolution law of ? was analyzed during the full stress-strain process, and then the damage deformation was further explored under cyclic loading. The test results showed that five stages of ? were corresponding to the stages of full stress-strain curves, which were divided into linear decline, stable development, slow increase, sudden increase and gently change, presenting a spoon-shaped evolution feature. It fully reflected the relationship of energy transformation and degree of damage development during the deformation evolution of specimens. In general, the energy consumption ratio (?) reduced as the confining pressure increased. At the same strain level, with the increase of confining pressure, the difference of ? at the stages of linear decline and stable development decreased, then it increased gradually at the stages of slow increase and sudden increase, and finally it decreased to a stable value at the stage of gently change. The variation of material parameters was analyzed, and then a theoretical formula of stress-strain evolution under cyclic loading was deduced by considering the confining pressure and evolution law of ?. The formula was well fitted with test results, which verified its rationality.

Consolidated undrained triaxial shear tests on undisturbed saturated Nanyang expansive clay have been performed in both reduced triaxial compression (RTC) and reduced triaxial extension (RTE) stress paths with three axial consolidation stresses (160 kPa, 240 kPa and 320 kPa) and three unloading rates (0.02 kPa/min, 0.2 kPa/min and 2 kPa/min) by GDS triaxial system. The influence of unloading rate on shear strength, pore-water pressure and effective stress path was analyzed. Test results showed that the stress-strain relationship was in hyperbolic under different unloading rates for RTC and RTE. The undrained shear strength increased with the increase of unloading rate from 0.02 kPa/min to 2 kPa/min. The pore pressure of the rate at 0.02 kPa/min was the minimum under two stress paths with the consolidation stress from 160 kPa to 320 kPa. Considering the change of the unloading rate parameter ρ0.02, the undrained shear strength increased 5.6% and 4.8% with every tenfold increase of the unloading rate. The rate effects on undrained shear strength were greater in reduced compression tests than those in reduced extension tests. The failure pattern of the undisturbed expansive soil sample was related to the shear rate and micro crack, demonstrating the coexistence of the main shear zone and the sub shear zones at low unloading rate. For the case of high unloading rate, the main shear zone was the only failure pattern.

In this paper, a large-scale shaking table test of the free field with the soil liquefaction was conducted under horizontal ground motion excitation. The temporal and spatial response of the free field under earthquake excitation was analyzed. The results showed that when the excited earthquake was small, the dynamic response of liquefiable site and pore pressure ratio at different buried depths of soil was small, whereas the peak acceleration from bottom to top enlarged. This indicated that the model foundation was in the linear elastic phase. When the seismic record of 0.3g Wenchuan earthquake was inputted, the pore pressure accumulated rapidly and the pore pressure ratio of the topsoil layer reached 1. The model foundation showed obvious nonlinear response characteristics after liquefaction. The peak acceleration in the liquefiable soil layer was not significantly enlarged, while there was an increasing trend of response acceleration from bottom to top. The results of this paper can be used for comparative analysis and verification of numerical simulation in the future

The lower enlarged composite pile is a newly developed uplift pile. The uplift mechanism of the lower enlarged composite pile is analyzed by combining theoretical analysis and field experiments. Based on this, the theoretical model and calculation parameters of uplift bearing capacity of the single pile for this pile type are proposed. The results show that the lateral resistance of the lower enlarged pile is enhanced by the effect of the upper resistance under a certain thickness of overlying soil layer. The mobilization factor can be 1.6 when calculated by empirical parameter method under testing conditions. The uplift bearing capacity of the upper non-enlarged composite pile is weakened by the influence of the upper resistance of the enlarged section, and the mobilization is decreased. When the pile diameter of the upper non-enlarged section is smaller than that of the enlarged section, the uplift bearing capacity of the lower enlarged composite pile is calculated by considering only the lateral resistance of the enlarged section and the upper resistance. The reliability and practicability of the model and theoretical method are verified through comparison with experimental results. The research results can be used as a reference for engineering design.

Consolidate drained shear tests were carried out on saturated natural silty sand using stress-controlled static triaxial shear apparatus. The samples of 50% relative denseness were prepared using dry-tamping method and wet-tamping method while the consolidation drained shear tests were carried out in three kinds of stress path conditions of CTC, TC and RTC. The experimental results of stress-strain relationship, volumetric strain rule and shear strength indexes were obtained, and the influence of sample-preparing methods on experimental results was studied. The results shows that, in three different stress paths, the samples of dry-tamping method have strain softening and shear dilatation phenomenon, while the samples of wet-tamping method have strain hardening and shear contraction phenomenon. The peak values of principal stress difference from dry-tamping method are all higher than those of wet-tamping method, and the difference between peak values of two sampling methods under CTC is larger than others. The dilatancy of samples under RTC is the most obvious, CTC is the least, and TC is between them. All of the effective internal friction angles obtained from dry-tamping method are bigger than those obtained from wet-tamping method. In the same sample-preparing method, the effective internal friction angle of CTC is almost the same as it of RTC, and at the same time, the angle of TC is relatively close with that of RTC. The influence of stress path on effective internal friction angle is much less than that of sample-preparing methods.

Studying the stability characteristics of silt sand slope under different seepage boundary conditions is of great significance to safety evaluation and disaster prevention of slope failure. An indoor slope model test system was developed. The model tests of slope instability under upper boundary infiltration, lateral boundary infiltration and bottom boundary infiltration were carried out respectively. The time histories of volumetric water content, pore water pressure, matrix suction at different positions inside the slope and failure process of the slope were analyzed and discussed. The results showed that soil changed from unsaturated state to saturated state in local place of the slope, the matric suction disappeared, and finally unstable regions and destruction formed on the slope surface under different seepage boundary conditions. Failure modes caused by upper boundary infiltration, lateral boundary infiltration and bottom boundary infiltration can be described as local shallow failure, multi-level retrogressive failure, and surface slide failure, respectively. By monitoring the volumetric water contents at different positions of the slope, an early warning system for slope instability caused by seepage can be proposed.

Due to the advantages in lightness, wear-resistance, permeability and high-damping, the rubber particles are mixed with sand to be applied as the lightweight fillers for slopes, subgrades and retaining walls. Thus, in this paper, the liquefaction potential and the dynamic pore water pressure of saturated rubber-sand mixtures with different rubber contents are investigated through the cyclic triaxial tests. The results show that the resistance to liquefaction significantly increases with the increase of rubber content in the rubber-sand mixtures. In addition, the liquefaction strength curve can be described by a power function. By taking the influence of rubber content, the normalized liquefaction strength curve of rubber-sand is obtained. The evolution models of dynamic pore pressure ratio under different test conditions are established, which are obviously influenced by the initial cyclic stress ratio and rubber content. It is observed that an evident upward migration of rubber particles occurs in the 10% rubber content mixtures when the intitial cyclic stress ratio exceeds 0.4. Based on the mesoscopic contact and movement state of particles, the migration mechanism of rubber particles is revealed.

The heterogeneity of particle and pore distribution and its resulting bottleneck effect are the main reasons for the hysteresis effect of soil and water characteristic curves (SWCC) on unsaturated soil. In this paper, the fractal theory is introduced to consider the microscopic fractal characteristics of the pore sizes and the seepage path of unsaturated soils. A capillary model is proposed for describing the seepage of water in unsaturated soil. In the proposed model, the pore size of unsaturated soil is simplified into a series of capillary tubes with different pore sizes, and the pore sizes and tortuosity are assumed to conform to fractal laws. On this basis, the equation of saturation Se-head height h of unsaturated soil during the wetting and drying processes is obtained to describe the characteristic equation of the hysteresis effect of SWCC. In addition, the characteristic equation of saturation Se-relative hydraulic conductivity coefficient Kr is established. Compared with the existing methods, this model can better simulate the hysteresis effect of SWCC of unsaturated soil. Finally, the essence of the hysteresis effect of unsaturated soil in the wetting and drying processes is compared and analyzed. It is revealed that the fundamental reason for the hysteresis effect is the heterogeneity of the pore size in the soil.

A geological model test of large 3D YTLH soil-rock combination was carried out to analyze the internal displacement, convergent deformation, face extrusion displacement and radial pressure of surrounding rock under the three states (hard plastic, soft plastic, flow plastic) and two different depths (12 m, 24 m). The results show that the internal displacement difference of surrounding rock presents the characteristics of ‘minimum on arch crown and maximum at both sides’, and the displacement difference of vault is less than 20% and the value of side wall is greater than 91%. The 4.5 m long anchor bolt on the arch has little effect on the vault, but the tensile effect of anchor bolt on side walls is fully exerted. The pre-convergence rates of hard plastic, soft plastic and flow plastic nearly reach 65%, 70%, and 80%, and the influence ranges on excavation face are 0.5D, 0.6D, and 0.8D, respectively, which shows different failure modes of vertical type, drum out type, and slump type. The stress release rate of hard plastic is the smallest, followed by soft plastic and flow plastic, and the maximum stress release rate of flow plastic is over 70%. Excess stress release should be avoided to lose stability in the actual engineering. The reasonable deformation allowance of double-line shallow-buried loess tunnel is recommended as follows: hard plastic formation (55-70 mm of vault, 15-20 mm of side wall), soft plastic formation (166-180 mm of vault, 40-50 mm of side wall), and flow plastic formation (290-300 mm of vault, 125-140 mm of side wall). The reserved deformation between vault and side wall can be set by curve transition with non-equal quantity.

With the stereo development and utilization of underground space, problems related to structure interaction are increasingly important in underground approaching construction projects. This paper proposed an analytical method based on cavity expansion (contraction) theory in geomaterials to solve the problem of tunnel excavation under-crossing a displacement pile. By adopting the unified clay and sand model and the large-strain assumptions, a mechanical model for tunnel-pile interaction was established in regards to the two dimensional problem. With the influence of tunneling volume loss, a reduction factor of pile bearing capacity was proposed, and the load-settlement response was then employed to predict tunneling-induced pile settlement. The analyses indicated that tunnel volume loss induced the reductions of both pile shaft and pile end bearing capacities, as well as the stiffness of surrounding soil, which all led to pile failure. Additionally, relationships to link tunnel volume loss to tunnel-pile distance, bearing capacity reduction factor, initial safety factor, and soil initial state parameters were obtained at pile failure, which ultimately contributes to understanding of the mechanisms of tunnel-structure interaction and the stability of underground structure.

Leaching tests under 12 kinds of stress combination were carried out to explore the weakening effect of soluble salt on the strength of compacted loess (Q2) during leaching. The ion concentration, soluble salt content and ultimate normal stress with different times of infiltration were determined. The results showed that the ion concentrations, the soluble salt amount and shear strength decreased in a step-like manner during leaching. With regard to the stress combination, the leaching stress (s) affected the form and hysteresis of the curves of ion and soluble salt; the confining pressure ( ) changed the smoothness of the curve; the soluble salt residue was positively correlated with s and . To measure the difference of soluble salt content under different , the average difference index ( ) was defined, and the index was positively proportional to s. To evaluate the process of leaching, the relative change amount of soluble salt content ( ) was defined as the dissolved salt ratio. When the value was less than 1%, the leaching process was determined to be stable. In terms of shear strength, the ultimate normal stress ( ) decreased with the decrease of relative soluble salt; s determined the intensity of the initial weakening; the difference of between different confining pressures weakened with the increase of s. The three characteristics of indicate that the occurrences of weakened strength and deformation in the leaching process are the result of the combined action of stress and changes in the soluble salt. Finally, the strength weakening formula considering the combined effect of soluble salt and stress was established.

China is an earthquake-prone country. The micro-pile composite structure is a new type of flexible supporting structure, and its supporting effect on the soil slope under the earthquake action has become a significant problem. Therefore, the dynamic characteristics of the micro-pile composite structure on the reinforced soil slope were studied by large-scale shaking table test under mixed loading. The test results demonstrate that the micro-pile composite structure achieves an ideal effect on the reinforcement of the soil slope under the earthquake action. With the increase of the peak value of the El wave acceleration, the peak acceleration and the dynamic pressure of the pile body in the front and back rows increase gradually. With the increase of the peak value of the input El-Centro acceleration, the response effect of the soil pressure is also more significant. The earth pressure and acceleration often reach the maximum values at the upper and lower 1/3 positions of the slide surface, the top of the cantilever end and the bottom of the anchorage section, which should be paid attention to these positions in practical engineering design and application. The research results can provide support for the seismic design of similar landslides in similar areas.

The Q3 loess is widely distributed in the northwest of China, and most of them present significant structural characteristics. With the development of the national “The Belt and Road” Initiative, as the northwest loess areas along the silk road will usher in a new tide of construction. The structural deformation characteristics of loess are very complex. In-depth study of the structural damage and deformation characteristics of loess under compression and shearing conditions is of great significance for constructing the constitutive relation of loess in theoretical research and field engineering application. Through the three-axis isotropic compression test and the three-axis shear test, the ball stress damage ratio of the loess structure, the ball stress damage ratio and the shear stress damage ratio are proposed. According to the elastic and plastic strain of the plastic potential line, and its yield function, the damage ratio of loess is introduced to the yield function, and expressed under structural damage. The rationality of selecting the plastic volumetric strain as the hardening parameter is verified. According to the relationship between hardening parameter and the test parameters, damage constitutive model of structural loess under the condition of compression and shear is derived. By comparing the measured stress-strain curves with the calculation from the constitutive model, we can see that the constitutive model can better reflect the structural damage evolution and deformation process of loess under compression and shearing condition.

Coral sand is a special geotechnical medium formed by dead corals and shellfish after a long time of physical and chemical weathering. Coral sand particles are easily broken, and their mesoscopic structures have great influence on the macroscopic mechanical properties of reef foundation. However, some technical problems such as the quantification of sand particle morphology, have not been solved. The PartAn particle morphology observation system is used to study the multi-angle projection images of the same soil particle, and a variety of parameters are used to evaluate the morphology of sand particles. Thus, morphology characteristics of coral sand particles are accurately distinguished: dendrite, rod, flake and block, which is suitable for the rapid measurement of a large number of sandy gravel samples with different shapes. Meanwhile, the obtained test data can also be used as the database of numerical simulation, providing data resource support for the random generation of irregular particles. Experiments are carried out to analyze the morphologies of 170 thousand individual particles quantitatively, and they have a high reliability in statistics because of a large amount of database. At the same time, the interference effect of human factors caused by the manual selection of the samples before the test is avoided. The coral sand fractal data with a high degree of realism provide a reliable method for the quantification of breakage of the coral sand particle under load.

To study the combined influence of chemical corrosion and the freeze-thaw on the damage and creep characteristics of rock, the quartzite and quartz sandstone of Dadongshan tunnel are adopted to be the test specimens. After being soaked in different chemical solutions and subjected to freeze-thaw cycles with different cycle times, the rock specimens are scanned by the electron microscope to analyze themicroscopic characteristics of rock surface. The triaxial creep tests are carried out to analyze the combined influence of chemical corrosion and freeze-thaw on the parameters of instantaneous strain, creep strain, creep rate and long-term strength of rock. The results show that the rock is damaged under combined influence of chemical corrosion and freeze-thaw cycle, the degree of damage increases with the increase of freeze-thaw cycle time, and the influence of chemical solutions increases by the following orders, HCl solution, NaOH solution and NaCl solution. The creep mechanical parameters of rocks change obviously with the change of freeze-thaw times and solution environment. With the intensification of chemical corrosion and the freeze-thaw cycle, the fracture morphology of rock has a tendency to change from brittleness to ductility. It can be indicated that, in the damage process of rock specimens, the freeze-thaw cycle and chemical corrosion promote each other mutually, since the combined influence of two-factor on rock damage and creep characteristics are greater than the influence of single factor.

A series of resonant column tests was carried out on undisturbed silty clay and silt in the same borehole from surface to bedrock in the estuary of the Yangtze River. Then the variation law of dynamic shear modulus G with soil depth H was explored within various strain ranges in the same undisturbed soil. It was found that the G in the various strain ranges of undisturbed silty clay and silt increased regularly with the increase of H. Meanwhile, the maximum dynamic shear modulus Gmax linearly increased with the increase of H, whereas the attenuation relationship of G decreased with the increase of H. The experimental results showed that the G of the undisturbed soil was correlated with the soil depth H. Based on the soil depth H and Hardin model, the G prediction method was put forward accordingly to predict the Gmax of each kind of undisturbed soil at different depths and their G within various strain ranges. According to the comparison and analysis of three kinds of G prediction methods, the G prediction method based on soil depth H was the most advantageous. In addition, the applicability of the method was further verified by re-processing the data of undisturbed marine soil in Bohai sea area.

The South China Sea shows strategic significance for China's economic development, resource exploitation, and maintenance of national land integrity. At present, China has built a series of coral reef islands in the South China Sea by the means of reclamation. A number of structures, such as buildings, breakwaters and airports etc., have been built on these reclaimed coral reef islands. As the foundation materials, calcareous sand’s response to extreme ocean wave and strong seismic wave play an important role in evaluating the stability of these structures on these reclaimed islands. In this study, taking the coral reef island reclamation project in the South China Sea as the engineering background, a series of tri-axial cyclic tests is performed for the calcareous sands sampled from reclaimed islands, to investigate their dynamic mechanical properties. The experimental results show that the calcareous could become partially liquefied under cyclic loading in undrained condition. While they can’t become liquefied in drained condition. In undrained condition, the relationship between normalized residual pore pressure u/ and cycle times ratio N/Nf is found in accordance with the inverse sine development model proposed by Seed. Furthermore, the relationship curves between the dynamic deformation modulus of all calcareous sand samples and their corresponding normalized strain ?m /?r all overlap on one hyperbolic line, indicating that the relationship between the dynamic deformation modulus and normalized strain ?m /?r of calcareous sand is independent on dry density, particles size gradation.

Through the large-scale shaking table test, the distribution of peak pressure near the sliding surface was analyzed. The seismic signal has the characteristics of short duration and non-stationarity. Based on the characteristics, the horizontal-loaded El waves were decomposed to analyze the dynamic response in different frequency bands by using wavelet packet analysis, which has the properties of uniform frequency band division and time-frequency localization. The test results show that the dynamic soil pressure is usually highest at the position near the sliding surface. Moreover, the dynamic soil pressure is abrupt at the heights of 25 cm and 45 cm along the pile body, respectively, which should be paid attention to in practical engineering. The frequency bands those greatly affect the dynamic pressure of micro-piles are the first frequency band (0.1-6.26 Hz) and the second frequency band (6.26- 12.51 Hz). In the engineering application, the resonance between the seismic waves in these two frequency bands and the micro-piles should be avoided. At 25 cm of pile height, the dynamic soil pressure values on the hill and river sides of micro-piles at the rear row are higher than those of micro-piles in the front row, while at 45 cm of pile height, the dynamic soil pressure values on the hill and river sides of micro-piles in the front row are higher than those of micro-piles at the rear row.

The rock specimens prepared by traditional rock core drilling method have the disadvantages of unclear internal structures in the same batch and large differences in mechanical properties, and the specimens prepared by inserting joint method have the disadvantages of difficulty in controlling prefabricated joints, low precision and long cycle. 3D printing technology overcomes the deficiencies of the traditional specimen preparation methods, but its shortcomings are low strength and high plasticity of the prepared specimens. Non-jointed complete specimen A-1-1 and non-consecutive parallel four-joint specimen B-1-1 were produced using 3D printing technology. Then vacuum drying and uniaxial compression tests were carried out on these specimens. Moreover, CT scanning test and internal fracture 3D reconstruction were performed on specimen B-1-1. We obtained the stress-strain curve, apparent fracture mode of the specimens and internal crack distribution of specimen B-1-1 after uniaxial compression. Experimental results indicate that: the comparison between the stress-strain curves of specimen A-1-1 and the undried specimen shows that the strength and plastic deformation of vacuum-dried specimens have been greatly improved, which provides references for the applicability of 3D printing specimen in rock mechanics field. The stress-strain curve of specimen A-1-1 is similar to that of the rock, and the apparent cracking mode of specimen A-1-1 is similar to that of the medium sandstone, indicating 3D printing specimen can be used in the mechanical study of similar rock. The ‘wing-shaped flat-necked funnel-shaped’ fracture mode is the main failure mode to lose the bearing capacity of the non-consecutive parallel four-joint specimen, and the generation, expansion, and penetration evolution of cracks under uniaxial compression are the combination of the complex tensile-shear group. Besides, the internal fracture mode and apparent fracture mode are different, and the apparent fracture mode cannot accurately characterize the internal fracture mode.

Ferrous sulfate (FeSO4) was used to stabilize chromium-contaminated soils. Leaching test, alkaline digestion test and sequential extraction test were conducted to investigate the effects of particle size and organic dosage on the stability properties and risk assessment of FeSO4-treated chromium-contaminated soils, respectively. Results showed that the leaching concentration (hexavalent chromium and total chromium) and hexavalent chromium content decreased significantly with the decrease of particle size, but decreased with the increase of organic dosage. When Fe(II)/Cr(VI) molar ratio was three, the Cr(VI) and total Cr leaching concentrations were about 4.68 mg/L and 8.9 mg/L, respectively, which were lower than the Identification standards for hazardous wastes: identification for extraction toxicity (GB/T5085.3－2007) of China. Furthermore, when Fe(Ⅱ)/Cr(VI) molar ratio was three and organic dosage was 5%, the amount of Cr(VI) in the soil was 28.3 mg/kg, lower than the threshold allowed by Environmental quality standards for soils (GB15618－2008) for industrial and commercial reuse of China (Cr(VI)<30 mg/kg). However, the residential land reuse (Cr(VI)<5 mg/kg) was only achieved by adding the organic dosage of 10%. Sequential extraction test showed that with the decrease of particle size, the weak acid-soluble fraction of Cr content decreased, the Cr content in the reducible state increased, while the Cr content in the oxidisable state was slightly affected. In addition, organic matter transformed Cr from weak acid-soluble fraction and reducible fraction to oxidisable fraction. The changing in the stability properties and risk assessment of stabilized soil can be attributed to the change of chromium speciation.

The upper structure and foundation of offshore wind turbines (OWTs) bear huge lateral environmental loads over the life time. Meanwhile, there is a high probability of the seismic load acting on the foundation of OWTs simultaneously. In this paper, a loading device was designed to impose initial lateral environmental loads, and a set of centrifuge dynamic model tests on a monopile in sand ground were setup. Thus, the monopile dynamic tests under jointed load condition were realized from the physical model scale. The centrifuge shaking table test shows that the bending moment of the pile after shaking under jointed load conditions is greater than its initial bending moment. The bending moment of the pile after the earthquake at a partial depth in the saturated sand is about four times than the initial bending moment. In addition, it is found that the lateral displacement at the pile head accumulated during the shaking process. The lateral displacement of the pile head after the earthquake is 1.3 times of the initial lateral displacement. The coupling effect of monopile for offshore wind turbines under jointed load condition poses a great challenge to the safe service of OWTs and deserves attention in the design of OWTs foundation.

The modified stress method is adopted in this paper to consider the effect of anisotropy on soil strength. This method introduces the fabric tensor to adjust the relative magnitudes of stress components in different directions, so that anisotropic soil can be equivalent to isotropic soil in the modified stress space. By substituting the modified stress tensor for the ordinary stress tensor, the Mohr-Coulomb strength criterion can be developed to be cross-anisotropic. The form of the criterion remains unchanged, while strength parameters are still constant and independent of the loading direction. This paper compares the relation curves between the internal friction angle and the loading direction according to three different modified stress formulas and analyzes the effect of fabric on the variation of the internal friction angle. Continuous and regular failure envelops are drawn in the deviatoric plane. Meanwhile, triaxial compression and true triaxial test results of different anisotropic geomaterials are predicted. Finally, the cross-anisotropic Mohr-Coulomb criterion is used to calculate the passive earth pressure on the retaining wall in the horizontally sedimentary stratum. The obtained expression is simple and explicit, which verifies the practicability of the modified stress method.

Based on the bounding surface model developed for saturated sand under cyclic loading, a 3D model is introduced into three-dimensional stress space by means of the modified generalized Mises method. The model incorporates the state-dependent dilatancy and the hardening rule of using historically maximum loading surface as the bounding-surface to simulate the changes of stiffness and dilatancy and contraction of saturated sand under drained conditions. In virtue of the concept of substepping integration scheme, an explicit integration procedure of the bounding-surface model for saturated sand under cyclic loading is proposed. By utilizing user subroutine interface of finite element method (FEM) software, the explicit integration procedure is incorporated into FEM software. Hence, a finite element model consists of one single soil element is created to simulate triaxial compression experiments of Toyoura sand subjected under monotonic and cyclic loading respectively. As a result, the effectiveness of the explicit integration scheme demonstrated its performances in accurately obtaining stress-strain relation and dilatancy and contraction phenomenon of Toyoura sand under both monotonic and cyclic loading. Moreover, the high stability and convergence of the explicit integration scheme are validated for relatively small strain increments by setting up increments with various sizes.

To explore the influence of tunnel axis stress on rockburst, rockburst model tests were performed to reproduce the rockburst process of the tunnel. Under different intermediate principal stress conditions, the tests were carried out on cubic granite specimens with prefabricated holes by using the true triaxial rockburst test system. The whole rockburst process was monitored by a real-time video observation system and an acoustic emission system under true triaxial loading conditions. The test results show that no macroscopic damage, particle ejection, rock fracturing and block ejection are the four main stages of the whole rockburst process. The higher the intermediate principal stress is, the shorter the time between the ejection of the particles and the block injection is, the longer the splitting duration is, the shorter the ejection duration but more severe is. With a higher intermediate principal stress, the splitting failure is more obvious under the Poisson effect resulting from the tangential first principal stress and the axial intermediate principal stress. Besides, a higher stress level is required for rockburst, and the risk of rockburst in the tunnel is reduced. However, once the stress concentration level is high enough to induce rockburst, the rockburst intensity is higher.

How to correctly calculate the sinking resistance of caissons has been a difficult problem in the design of caisson structure. In order to comprehensively study the sinking resistance and distribution law of the caisson, the sinking simulation of the caisson in four different depth conditions is carried out through the centrifuge model test. Side pressure, earth pressure on foot blade incline, earth pressure on tread of foot blade and deformation of the earth surface have been analyzed. The results show that the side pressure increases first and then decreases, and its value and distribution can be simplified by piecewise function. Distribution of earth pressure on foot blade incline is cubic polynomial. With the increase of the depth of the foot blade, the soil pressure of incline and tread significantly increases, and the resistance ratio of incline and tread per unit width remains the same. Sinking of caisson will lead to subsidence of the earth surface outside the caisson, subsidence of the earth surface adjacent to caisson wall inside the caisson, and uplift of the earth surface which has a certain distance away from the caisson. The experimental and analytical results reported in this study can provide reference for theoretical research and engineering design.

Ratio of safety margin (RSM) provides a rational tool for establishing the quantitative relationship between the safety criteria of deterministic design and reliability-based design and for verifying the universality of safety criteria. However, the existing definition of RSM is only applicable to design situations, where the response (e.g., safety factor FS of stability against sliding of retaining wall) follows normal and/or lognormal distributions. This paper proposed a generalized reliability RSM (RRSM) based on the cumulative probability distribution function of FS. The generalized RRSM is applicable to design situations with FS following arbitrary probability distributions and overcomes the limitation resulted from the normal and/or lognormal assumption. This makes the RSM principle feasible in general design situations. Based on the generalized RRSM, it is proved that equality between RSM of FS and RRSM guarantees the equivalence between safety criteria of deterministic design and reliability-based design (i.e., identical feasible design domains) when FS follows normal and/or lognormal distributions. Similarly, it is also proved that equality between RSM of FS and generalized RRSM guarantees the equivalence between safety criteria of deterministic design and reliability-based design when FS follows arbitrary probability distributions. Calibration of allowable FS based on generalized RRSM is illustrated through a gravity earth retaining wall example. Results obtained from RRSM and generalized RRSM are compared for validating the calibration results based on generalized RRSM.

Taking the new type prestressed subgrade as the research object, theoretical formulas for calculating the diffusion coefficient of additional stress perpendicular to the slope surface in an embankment induced by a prestressed reinforcement device (lateral pressure plate and prestressed bar) were derived based on the theory of elasticity. The presstress diffusion trends directly beneath the plate bottom as well as in the two external directions were analyzed. The results show that: 1) the applicable condition of the theoretical formulas requires that the net distance between the plate (with a side length of 0.9 m) and embankment shoulder should be not less than one time of the plate width; 2) the diffusion effects of the normal component force are much greater that those of the tangential component force; 3) due to the tangential component force, the total diffusion stress directly beneath the plate bottom presents a “raised abdomen” pattern and it gradually transits to a uniform “flat abdomen” pattern as the depth increases; 4) the maximum diffusion coefficient of the additional stress at different depths fluctuates on the plate centerline as the depth increases; 5) the diffusion effects in different zones show a descending order, i.e., directly beneath the plate bottom > the outside of the upper boundary > the outside of the left and right boundaries > the outside of the lower boundary, and the average effective diffusion depth in the two directions is about 1.6 m. A refined 3D FEM model using the ABAQUS software was established to verify the theoretical formulas. It was found that the finite element results (including at the embankment shoulder) agree well with the theoretical data, which demonstrates the validity and applicability of the theoretical formulas. Finally, the rational plate spacing was explored based on the distribution of the superimposed additional stress under the action of multiple lateral pressure plates to form a continuous, effective and relatively uniform preloading area at a certain depth. The prestressed reinforcement device can improve the stress state of the soil embankment and provide lateral constraints to the embankment slope, which is beneficial for the long-term stability of the subgrade.

The response of a monitoring point on a landslide to external factors over a period of time can be regarded as a current state of the landslide. The monitoring points on landslide show similar responses when they are stimulated by similar external factors under similar states. Accordingly, it is possible to analogize similar states and apply it to stability analysis, data correction and prediction of landslide. In this study, a similarity measurement method for multiple information data based on status element matrix was proposed. It not only ensured the similarity of the external factors, but also guaranteed the similarity of the current state of landslide to measure external factors and movement status of landslides. To verify the effectiveness of the method, 1 770 states of 34 monitoring points of 4 landslides in the Three Gorges reservoir area were used as status element matrix to perform similarity matching, and good results were obtained to predict displacement data of Baishui River landslide from January 2015 to June 2016. Based on the results, the similarity measurement method proposed was superior to the existing classic prediction methods such as back propagation neural network, support vector regression and so on.

In this study, two seismic failure mechanisms of L-shape retaining walls (i.e., long heel failure and short heel failure) were presented, and the failure mechanisms were influenced by geometric parameters and physico-mechanical parameters. The seismic stability of L-shape retaining walls and the determination method of sliding surface were investigated in this paper, and the critical condition of two failure mechanisms was defined. Based on the kinematical approach of upper bound theorem, the critical state equation of L-shape retaining wall was established, taking account of the occurrence of the second and third sliding surfaces condition. Then the multivariate function to calculate seismic acceleration coefficient was derived and optimized by extremum principle, so as to obtain the critical yield acceleration factor and the inclination of sliding surface. A case study and comparative analysis showed that the critical yield acceleration factor was smaller than that derived from the M-O method. When the heel of L-shape retaining wall was long enough, the angle between two sliding surfaces equaled to 90°-φ. It means that the result of using this method is the same as the result of slip-line field theory. When the heel of L-shape retaining wall was short, the angle between sliding surfaces was approximately 90°-φ.

Aiming at the foundation pit engineering in the typical stratum of Jinan, the hardening soil small-strain (HSS) model in PLAXIS 3D is adopted to establish the finite element model, and according to the actual monitoring data and the displacement back analysis, a general method of selecting the parameters for the HSS model in this typical stratum is obtained. Then the HSS model and the Mohr-Coulomb (M-C) model are analyzed by the simplified finite element analysis. The simulation results of the deformation of the retaining wall and the ground surface settlement behind the wall under different excavation depths are compared. The results show that the difference between the simulation results of M-C model and HSS model increases with the increase of excavation depth, and the results of HSS model are more in line with the actual deformation. Considering the difficulty and economy of parameters selection and the engineering applicability of the two models, it is suggested that when the excavation exceeds 15 m, the HSS model should be taken, otherwise, the M-C model should be taken. The research results have important reference value to guide the design of deep foundation pit and the investigation and selection of geotechnical engineering parameters.

The stability of the surrounding rock of the high sidewall draws great attention during the construction of the super large underground cavern. Based on geological conditions, geophysical prospecting, monitoring data and construction materials, the deformation evolution mechanism, spatial distribution pattern and failure mode of the surrounding rock are analyzed by using rock mechanics theory and FLAC3D numerical simulation. The research shows that in the vertical direction, the unloading response of the surrounding rock under 10 m of the excavation surface is intense. The surrounding rock deformation accounts for 50%-55% of the total deformation during this period. In the axial direction of the cavern, the influence area by excavation is concentrated in the range of twice the span of cavern, and the displacement increment caused by excavation takes up about 97% of the total unloading displacement change. The difference in the deformation of the surrounding rock is large at different depths due to the geological structural surface. Because of the soft plasticity of the weak interlayer, the strain energy release after the confining pressure is a slow process, and the aging shearing characteristics are obvious. During the layer-by-layer excavation process, the stress state of the surrounding rock in high sidewalls has undergone four stages: the accumulation of strain energy, stress release, stress adjustment, and stree stabilization. These research results provide significant references for similar projects.

Frost heaving deformation of the subgrade in the seasonally frozen region affects the running speed and safety of high-speed trains. Taking ordinary-graded macadam subgrade structure as the prototype, we established the thermal-mechanical coupling model of subgrade foundation and the external force model of subgrade whole structure. Then the temperature field, deformation field and structural mechanical parameters were calculated and compared with literature data, which further verified the reliability of the model. On this basis, three anti-frost heave structural models were established, including the cement stabilized gravel subgrade, thermal insulation strengthening layer with graded macadam subgrade, and thermal insulation strengthening layer with cement stabilized macadam subgrade. Finally, the frost heave deformation and stress characteristics were calculated. The results show that the thermal insulation strengthening layer and cement stabilized macadam filler can effectively reduce the frost heaving deformation of the subgrade. The frost depth and maximum frost heaving of the thermal insulation strengthening layer with cement stabilized macadam structure are the smallest, which are 0.8 m and 1.585 mm. Moreover, the thermal insulation strengthening layer can reduce the vertical stress of the surface layer of the subgrade, and the cement stabilized macadam with larger elastic modulus can accelerate the attenuation of vertical stress and reduce the stress of bottom layer of subgrade. The thermal insulation strengthening layer with cement stabilized macadam subgrade surface structure can provide references for the selection of high-speed railway subgrade structure in the seasonal frozen zone.

A numerical model, called VRCS1, is developed for large-strain consolidation of saturated soft soil stabilized by PVD under vacuum-surcharge combined preloading. VRCS1 accounts for large strain, material nonlinearity, non-Darcian flow, vacuum loss along PVDs, and partial drain penetration. The estimated settlement using VRCS1 is in good agreement with field measurement for a site at Ballina bypass, Australia. Based on the field soil parameters, we investigated the effects of staged surcharge, cyclic surcharge, vacuum-surcharge combined preloading, equal stress/equal strain at the upper boundary, and PVD penetration depth on the consolidation of soft soil foundation stabilized with PVDs. The simulation results show that the staged surcharge can reduce the peak value of excess pore pressure and thus improve soil stability. The cyclic load produces oscillation during the consolidation process, and the peak value of settlement appears later than the peak values of excess pore pressure and load. There are fundamental differences between vacuum loading and surcharge loading, and vacuum loading cannot be simply replaced by surcharge loading. The consolidation rate under the condition of equal strain at the top boundary is generally faster than that under the condition of equal stress, and the real condition is usually between these two conditions. When the penetration depth of PVD exceeds 0.9 times the thickness of the soil layer, the effect of accelerating consolidation by increasing the penetration depth is weak.

To prevent the loss of properties and human lives, it is of great significance to establish an accurate and reliable model for predicting the landslide time of high fill slope. On the basis of the summary of the displacement and velocity characteristics during the creep failure process of high fill slope, this paper proposes a practical model for predicting the medium and short-term landslide. The proposed model is based on the improved artificial bee colony algorithm by modifying the strain rate formula of Saito model. The time series of landslide displacement after entering the accelerated deformation stage are taken as the input, and then the predicted landslide time is obtained by inverting the practical model parameters through the artificial bee colony algorithm. Three cases of high fill slope landslides are taken as examples, and the accuracy and reliability of the practical model are verified by the displacement data of the monitoring points. Meanwhile, the results of landslide time predicted by this model are compared with those predicted by the traditional Saito series model. The results show that the practical model is more accurate and reliable than the two general Saito models in predicting the landslide time through the time series of landslide displacement.

The combined finite-discrete element method (FDEM) numerical simulation method was used to study the prediction of the large deformation and its control of the weak surrounding rock in the deep tunnel under high in-situ stress condition. Firstly, the basic principle of the FDEM was introduced. Then the uniaxial compression, Brazilian disc and triaxial compression simulation tests were compared with laboratory experiments to calibrate the input parameters. Finally, the large deformation of the surrounding rock was simulated after deep tunnel excavation under high in-situ stress conditions; based on the solid modelling method, the reinforcement of the tunnel by using the method of rockbolt-shotcrete-grouting was simulated. The results show that the large deformation of the tunnel is primarily caused by the rupture and fragmentation of the surrounding rock. The shallow part is mainly a tensile failure, and the deep part is a shear failure. The shear failure angle is consistent with that of the uniaxial compression test result, 58°, the maximum crack propagation depth is 10.6 m, and the maximum surface convergence is 20.7 cm. The reinforcement method of rockbolt-shotcrete and rockbolt-shotcrete-grouting can effectively control the deformation of the surrounding rock, inhibiting the crack extension range (reduced to 5.8 m, 5.1 m). Besides, the convergence of the surrounding rock surface is greatly reduced (5.1 cm, 4.2 cm).

The upper bound approach based on rigid finite element method (RFEM) is one of the limit analysis methods, and it is an important method for stability analysis of soil slopes. However, there are still some key problems to be overcome in this method. Due to the assumption of rigidity, the plastic deformation energy of the system is stored only at the interfaces of all elements. Therefore, the accuracy of the approach is highly dependent on the alignment of the interfaces, which indicates that the accuracy is poor if an unstructured mesh is employed. To overcome this limitation, we propose a novel RFEM-based upper bound approach using perturbation method, according to the sequential limit analysis. Firstly, considering the rotation of elements, a novel second-order cone programming (SOCP) is put forward to construct the kinematically admissible velocity field based on RFEM. Secondly, a model for searching the critical slip surface is built by using sequential SOCP of RFEM-based upper bound approach and then solved by the nonlinear simplex and particle swarm optimization algorithm. From the analysis on stability problems of two benchmark soil slopes, the proposed method is verified. The main influence factors on computational efficiency and accuracy are also investigated in this paper. We have found that the type of mesh is a significant factor affecting the accuracy of the proposed method. It is necessary to consider the rotation of element in RFEM-based upper bound approach, which can not only improve the accuracy of the approach but also overcome the dependence of RFEM-based upper bound limit analysis on the alignment of interfaces.

Considering the Drucker-Prager constitutive model under Cosserat continuum theory, the finite element analysis of slope stability is conducted by coupling the characteristics of strength anisotropy and strain softening of soil. Numerical simulation is carried out by the secondary development of finite element software ABAQUS, and then the slope stability analysis is conducted based on the gravity increase method. The method of microstructure tensor combined with stress invariant is used to consider the anisotropy of cohesion, which is compared with the classical Casagrande anisotropy method commonly used in slope stability analysis. It is proved that the method of microstructure tensor combined with stress invariant is more reasonable in theory and numerical analysis. By simulating the relevant examples, it is found that strength anisotropy and strain softening have great effects on the overloading safety factor of the slope, especially when the slope angle is slow. The comparative study demonstrates that it is difficult to obtain the reliable overloading safety factor by the classical continuum finite element analysis coupling strength anisotropy and strain softening, and there is an obvious mesh-dependent defect. However, the Cosserat continuum finite element analysis can effectively overcome these problems and maintain the well-posedness of strain localization caused by the strength anisotropy and strain softening. Thus, the effective results are obtained.

Aiming at the three-dimensional ground motion simulation of alluvial basins in urban areas, the unique advantages of boundary element method (BEM) in dealing with wave motion in infinite domain and the high efficiency and large capacity of fast multipole algorithm (FMM) are brought into play. A simulation method suitable for broadband multi-degree-of-freedom model, fast multipole indirect boundary element method (FMM-IBEM) is developed. Through precision comparison and efficiency verification, it is found that FMM-IBEM can accurately and efficiently realize broadband simulation of ground motions in three-dimensional complex sites, and greatly reduce the storage and calculation. Then, the method is used to analyze a three-dimensional alluvial basin with complex shape and undulating bedrock surface in frequency domain and time domain. The results show that: incidence frequency, basin shape and location of the basin have different effects on the magnification of surface displacement of alluvial basins, and generally, the amplification effect in low frequency domain is higher than that in high frequency domain. Spectrum curves show multiple resonance bands, and the magnification effect of surface displacement in the middle and margin of alluvial basin is significantly different. Site selection of important projects should avoid seismic energy accumulation areas in alluvial basins.

The traditional peridynamic model is impossible to reflect characteristics of the internal stress in rock-like materials, which first increases, then reduces and finally damages. Based on the traditional bond-based peridynamic model, an improved model is proposed to reflect the characteristics of the stress and strain in rock-like materials. This new model makes up for the deficiency of the traditional one. The modified model was used to simulate the crack propagation process of rock specimens with a single crack under different prefabricated crack angles and tensile loads. The variation of the cracking angle under different prefabricated angles and tensile load conditions is analyzed. The results show that the prefabrication angle and tensile load affect the cracking angle. A small crack angle appears when the tensile load around the rock specimens is nearly equal, and the cracking angle increases first and then reduces under the condition of a certain tensile load. The model was also used to simulate crack propagation process of rock under uniaxial compression. Comparing the results of the numerical simulation with the results of the laboratory test, the validity of the proposed model is verified. The proposed model can well simulate the mechanical properties of rock materials under tensile loading conditions, and it presents a broad application prospect in rock numerical simulation.

Based on the Brillouin optical frequency domain analysis (BOFDA), the distributed optical fiber monitoring technology has been preliminarily applied in geotechnical engineering. The strain monitoring results show that there is a certain strain loss at the pretension section of the optical fiber with time after the pretension of the optical fiber. The strain loss is mainly caused by the fatigue characteristics of optical fibers. The strain loss caused by the fatigue of optical fibers is obviously disadvantageous to engineering monitoring to a large extent, which needs to be eliminated in practical monitoring. For the distributed optical fiber monitoring technology, two strain optical fibers (HY material, new strain optical fiber and polyurethane strain optical fiber) are selected to conduct point-fixed pretension in the laboratory ( ), and strain loss monitoring is carried out for 8 months. By comparing and analyzing the difference of strain loss between the two kinds of optical fibers, we obtain the variation rule of strain loss with time and the rate change of strain loss of optical fibers with the increases of temperature and humidity under pretension state. Given this, a point-fixed pretension method for tunnel deformation monitoring is studied using the distributed optical fiber monitoring technology, which provides theoretical basis and construction guidance for engineering application.