This paper investigated the lateral ultimate bearing capacity of rigid pile in sloping ground. Firstly, the effective embedment depth of equivalent rigid piles of flexible piles and the mechanical characteristic of laterally loaded rigid piles are introduced. Secondly, two failure modes for the soil in front of laterally loaded piles are proposed under different directional loads at the top of piles (pointing toward and away from slope). Then, the ultimate bearing capacies of the rigid pile under different directional loads are derived on the basis of the upper limit theorem of limit-equilibrium analysis, and the rationality of the proposed method is verified by field tests. Finally, effects of the slope, internal friction angle, cohesion and load direction on the ultimate bearing capacity are investigated and some general conclusions are drawn. At the meantime, a fitting formula for the lateral ultimate bearing capacity of the rigid pile in sloping ground that considering the slope angle is proposed on the basis of the analysis results. References and guidance for design of piles in sloping ground are provided, which are valuable in both theoretical and engineering applications.

Soil-bentonite vertical cutoff wall is extensively applied to containment of urban industrial lands. Chemical compatibility of soil-bentonite backfill exposed to chemical solutions, i.e., hydraulic conductivity and its amplitude, is of importance to evaluate containment performance. Chemical compatibility of sand-bentonite backfill permeated with lead-zinc mixture (Pb-Zn), hexavalent chromium (Cr(VI)), and calcium (Ca) solutions was studied via flexible wall permeability test. The resulting hydraulic conductivity of the backfill permeated with Pb-Zn and Ca solutions considerably increases compared with the result obtained from uncontaminated specimen due to the squeeze of the double layer around bentonite particles. The hydraulic conductivity can not meet the requirement of anti-seepage when Pb-Zn concentration increased to 500 mmol/L. In contrast, limited increase in hydraulic conductivity is found when the backfill is permeated with Cr(VI) solutions. This is attributed to the fact that Cr(VI) exists in anionic complex rather than exchangeable cation. Predicting method for hydraulic conductivity of sand-bentonite backfills is developed based on the concept of bentonite void ratio and swell index of bentonite exposed to the corresponding inorganic solution.

By using the GDS dynamic triaxial apparatus tests, the effect of freeze-thaw cycles on dynamic stress, dynamic modulus, dynamic modulus ratio and damping ratio of silty sand under different negative temperatures has been investigated in this study. It is found that under the same dynamic strain, the freeze-thaw cycles are negatively correlated with dynamic stress and dynamic modulus, but positively correlated with dynamic modulus ratio and damping ratio. With the increasing of freeze-thaw cyclic numbers, the dynamic stress and dynamic modulus decrease while the dynamic modulus ratio and damping ratio increase. The normalized fitting models for the dynamic modulus ratio versus the shear strain and the damping ratio versus the shear strain have been presented by regression analysis. The freeze-thaw cycles have a significant effect on the initial dynamic modulus and the maximum damping ratio. With the increasing of freeze-thaw cyclic numbers, the initial dynamic modulus decreases and the maximum damping ratio increases. The effects of freeze-thaw cycles on the initial dynamic modulus and the maximum damping ratio under different negative temperatures have also been analyzed, and the calculation formulae of the number of freeze-thaw cycles correlation coefficients have been given. The results indicate that the effect of freeze-thaw cycles on dynamic characteristics of silty sand is obvious with decreasing of the temperature, and the dynamic characteristics after five freeze-thaw cycles are relatively stable. It is suggested that the dynamic parameters after five freeze-thaw cycles can be used as the basic parameters for the dynamic response analysis.

Many landslides along the bank have reactivated after the impoundment in the Three Gorges Reservoir Area (TGRA). In order to study the landslide deformation characteristic subjected to fluctuation of reservoir water level, a large-scale centrifuge test model was designed based on typical landslide with rectilinear sliding surface in TGRA. The deformation images, the curves of pore water pressure (PWP) and earth pressure (EP) vs. time were obtained by high-speed cameras and pore water pressure and soil pressure sensors during the modelling of two cycles of reservoir fluctuation. The results could be summarized as follows: in the initial stage of the water level drawdown, the PWP and EP gradually decreased. When the water level fell for 15 minutes, the frontal body pull apart and down, the middle and rear parts of the landslide had a creep movement and compaction process dominated by vertical displacement, and the deformation stopped two minutes after the water level stopped falling. When the reservoir drawdown again, the frontal part slid along the original fracture zone, and no obvious deformation occurred in the middle or rear parts. In addition, when the reservoir water infiltrated into the landslide for the first time, the PWP in the slope lag behind the water level obviously, whereas the lag effect had diminished during the next time. The landslide is greatly affected by the hydrodynamic pressure of reservoir drawdown and its deformation has a retrogressive characteristic. The creep compaction behavior improved the stability of the middle and rear parts of the landslide gradually. Therefore, no deformation occurred during the water storage later, and the experimental phenomena coincide with the deformation characteristics of actual reservoir landslide. It reveals the deformation mode and evolution trend of the landslide in TGRA subjected to reservoir fluctuation, which provides a basis for the geohazard prevention.

Studying the permeability characteristics of acid-contaminated undisturbed loess can provide cost-effective engineering measures for the treatment of contaminated sites. Distilled water was used as the exudate. The permeability variation of the undisturbed loess was studied by using GDS triaxial permeameter under erosion by hydrochloric acid, nitric acid and sulfuric acid. The mechanism analysis was carried out from the change of microstructure of acid-contaminated undisturbed loess. The test results show that under the same consolidation stress conditions, the permeability coefficients of different types of contaminated undisturbed loess decrease with the increase of acid concentration. As the of acid concentration increases, the connection mode of contaminated undisturbed loess skeletons changes from point-to-point contact to point-to-surface contact and surface-to-surface contact. The dissipation of large pores and the increase of small pores decreases the effective seepage pores, and therefore decreases the permeability coefficient of the contaminated undisturbed loess. Under the same experimental conditions, the sequence of the permeability of different types of contaminated undisturbed loess is: sulfuric acid

Based on the large-distributed silty clay in the impact basin of the lower Yellow River, the dynamic triaxial apparatus and the strain controlled triaxial apparatus were conducted to investigate the undrained shear strength of the silty clay after vibration under different confining pressures and over-consolidated ratios. It is shown that the shear behavior of the sample after vibration is similar to that under over-consolidated state. Compared with the shear behavior before vibration, it can be found that the vibration has little influence on the shear strength when the similar over-consolidated ratio (SOCR) is less than 1.25; while SOCR is larger than 1.25, the shear strength of the sample decreases rapidly and the failure pore pressure ratio decreases firstly and then increases. By comparing the shear strength after unloading under the different SOCR and the same confining pressures, it can be concluded that the shear strength increases with the over-consolidated ratio (OCR) by exponential relation. And the increase of the shear strength caused by SOCR is more obvious than OCR. In addition, the shear strength ratio also increases with the increase of the SOCR and the OCR. Therefore, the OCR can be adopted to evaluate the foundation strength after dynamic load if it is difficult to carry out dynamic test in practice.

Rockmass may be in a creep state for a long time during underground mining. The failure progress of surrounding rock mass may be accelerated due to the mining disturbance. The rockmass failure is usually later than the mining activites and shows an obvious time lag effect, which brings difficulty in predicting the occurrence of engineering disaster. Given this problem, impact-creep tests of rock specimens were conducted under multi-cycle drop weight using a rock rheology-impact test machine. The changing law of axial strain of sandstone specimens was analyzed. The influence of creep state, impact times of drop weight and impact energy on the deformation and failure characteristics of creep rock were discussed. In terms of energy point of view, the failure rule of creep rock was explained under impact disturbance. The test results show that under the same rock creep state, the internal rock damage increases gradually with the increase of impact energy and impact times. The formation process of the damage zone is accelerated and the energy utilization rate is increased, which leads to the accelerated creep failure of rock samples. The impact disturbance causes the accumulated elastic strain energy within rock specimen to be released directionally along the damage zone and damage occurs. The research results provide a theoretical basis for the prediction of delayed rockburst disasters.

As a buffer material for nuclear waste storage, bentonite-sand mixture tends to shrink under high temperature and suction conditions, which affects the safety operation of engineering projects. Therefore, it is of great practical significance to study the shrinkage characteristics of bentonite-sand mixture. This paper investigates the influence of sand content and compactness on desiccation shrinkage characteristic of saturated compacted sample of bentonite-sand mixtures placed at custom designed thermostatic chamber. It is shown that water evaporation in the process of desiccation can be divided into deceleration and residual stages. In the former stage, the water migration is dominated by the dry density, while the final residual water content is mainly affected by bentonite content. An increase in the initial dry density and decrease in the bentonite content can coordinate the deformation of the mixture and hence reduce the anisotropy of shrinkage deformation. The bentonite content M and the initial dry density ?? are the key physical parameters affecting the drying-shrinkage process and have a close correlation to the Cornelis model parameters and the final pore ratio e0. At a given dry density, the microstructures of compacted samples tend to densify as M decreases, thereby effectively inhibiting the development and evolution of cracks during the drying-shrinkage process.

Clay minerals in very weak cemented rock mass are often high in content. Due to the argillaceous cementation, the cementation of this rock is poor and sensitive to water, and has strong plasticity. Based on the principle of soil consolidation and lever loading, an experimental device for regenerative structure formation of very weakly cemented rock mass was developed independently, and the method of graded loading and consolidation stabilization was determined. At the same time, the rock samples of regenerated structure rock mass with very weakly cementation at different moisture ratios were formed, and its formation condition and process was revealed. Uniaxial and triaxial compression tests were performed on the rock samples with different moisture ratios, the deformation laws of the rock samples, and the relationships between strength parameters and stress state and moisture ratio were revealed. The total stress-strain curve characteristics of the structural rock samples were analyzed, and the evolution law of volumetric strain was revealed. By analyzing the failure modes of uniaxial and triaxial compression tests of the rock samples, it was found that the failure modes of the rock samples are greatly affected by moisture ratio of cementation.

The consolidation characteristics of rigid pile composite foundation is a key factor affecting the progress of the project. To study the consolidation properties of rigid pile composite foundation under external load, the equal strain assumption was modified based on stress-strain characteristics of rigid pile and its surrounding soil. Considering the smearing effect, the consolidation behavior of surrounding soil and underlying stratum, the governing equations for the average excess pore water pressure within the surrounding soil and the underlying soil were developed. According to the boundary conditions of a time-dependent loading and additional stress varied with time and depth, the analytic solutions of consolidation degree were derived based on the consolidation theory of double-layered ground. The proposed method was validated by numerical simulation method. The factors that affect consolidation properties were systematically analyzed. It shows that the analytical solutions have great agreement with the numerical simulation results. The average consolidation rate strongly depends on the penetration ratio of the rigid pile. The average consolidation rate is slower than that of natural ground when the ratio is small. The average consolidation rate of rigid pile composite foundation with a greater penetration ratio and a smaller pile end resistance coefficient is faster than that of natural ground. With the increase of pile penetration ratio, the ratio of the constrained modulus of the pile to that of the soil and the ratio of the constrained modulus of the cushion layer to that of the soil, the overall consolidation rate of the composite foundation is accelerated. With the increase of the replacement rate, the overall consolidation rate of the composite foundation decreases.

For investigating the performance of load shedding culvert (LSC), model tests were conducted first. The performance of LSC was compared with those of imperfect-trench-installation culvert (ITC) and embankment-installation culvert (EC). Vertical earth pressure and horizontal earth pressure were measured in the model tests. Then, a theoretical model was established, and the formula for calculating the vertical earth pressure on the top slab of LSC was deduced. The proposed theoretical model was validated by comparing the results with those from model test. Research results illustrate that the LSC, compared EC, can effectively reduce the vertical earth pressure on the top slab. Comparing with ITC, LSC can not only improve the load reduction effect on the top slab but also reduce the horizontal earth pressure on the culvert sidewall. Theoretical results of the vertical earth pressure on the LSC top slab were consistent with the model test results, which indicate that the proposed theoretical model is correct and applicative.

A gradation equation with one parameter is derived to describe continuous gradation of coarse-grained soil. The basic properties of the gradation equation are studied, and the ability of the gradation equation to reflect two typical gradation curves of continuous gradation is analyzed. The applicability of the gradation equation is verified by several gradation curves of coarse-grained soil used in earth-rock dam engineering, and the range of ? deduced for the gradation is well represented. The study shows that the gradation equation can reflect the two typical hyperbolic and sigmoidal, gradation curves. The range of gradation parameter is 0–1. the curve gradation equation expresses is hyperbolic for small value of the parameter, and is sigmoidal for large value of the parameter. The gradation equation widely applies for gradations of different coarse-grained soils used in earth-rock dam, and it is more practical than fractal gradation equation and continuous gradation equation. The equation parameter greater than 0.13 implies well representation of the gradation, which provides a basis for the gradation design of coarse-grained soil for earth-rock dam.

Regarding the influence of seepage on face support pressure and ground collapse mode in shallow shield tunnel excavation, an experimental system composed of a shallow shield tunnel excavation-seepage model and a setup of measurement and data acquisition is designed and established, with consideration of pore water pressure in the excavation chamber and face plate opening ratio. The saturated soil pressures and pore water pressures at the face and settlements of surrounding strata are measured under various steady-state seepage conditions, as the soil input into the excavation chamber is gradually increased. Correspondingly, numerical simulations and limit equilibrium calculations are carried out. The major findings are: the effective earth pressure at tunnel face decreases as excavation volume loss increases, but plateaus after reaching a limit value; the necessary support pressure for face stability is related to the allowable collapse range of the stratum, the limit effective earth pressure, i.e. the minimum necessary support pressure at the tunnel face corresponds to the stratum limit collapse range. Seepage increases the limit effective earth pressure of excavation face, which shows roughly linear relationship with the hydraulic head difference between excavation face and ground surface. Seepage may increase the limit collapse range of the soil ahead of the tunnel face, but has little effect on the limit collapse range of the soil behind tunnel face; if the relative hydraulic head difference between tunnel face and ground surface is small (less than or equal to 0.33), seepage will mainly increase soil settlements, while the stratum limit collapse range only increases slightly; if the relative hydraulic head difference is large (greater than 0.33 and less than 1.00), seepage will enlarge the stratum limit collapse range, whereas the maximum settlement of stratum decreases slightly; if the relative hydraulic head difference is very large (greater than or equal to 1.00), the influences of seepage on both the settlement and limit collapse range of stratum have essentially reached their limits. The stratum limit collapse range may be divided into three zones stacking vertically: an inverted pyramid at the bottom within the height of tunnel face, an inverted prismoid at the top within a certain depth range below the ground surface and an inverted prismoid of a certain height in between; out of these three zones, the tapered angles of the inverted pyramid increase in longitudinal and transverse directions when the relative hydraulic head difference increases, and they exert the most significant influence on the limit collapse range of stratum.

Cusp catastrophe theory models of the rock slope instability under open blasting load were built based on the two-dimensional mechanical instability model considering the factors of blasting dynamic load. According to the established model, the influences of the amplitude and frequency of blasting dynamic load on the slope stability were discussed, and the dynamic critical instability height of the slope was derived, the criterion of the slope instability was also proposed. The result reveals that the possibility of slope instability increases with the increase of amplitude of the dynamic load, the decrease of frequency and the increase of trailing edge crack depth; the stability of slope is dynamic, and with the increase of incident angle of stress wave, the possibility of slope failure is increasing under blasting load. Taking two slopes in Dagushan Open-pit Mine as examples, the dynamic safety factor and the dynamic self-stability critical height of the slope are calculated, and the rationality of the proposed slope instability criterion is verified by the actual stability of the slope at present. It provides a certain theoretical support for preventing the dynamic instability of slope rock mass in the process of blasting excavation in open-pit mine.

The mechanical behavior of layered stone is much influenced by the weak bedding planes. To further explore how the layered structure influences the fracture characteristic of layered sandstone, a series of three-point-bending tests on sandstone specimens with different inclination angles was conducted and the anisotropy of fracture toughness and fracture pattern was discussed. Then a numerical model based on cohesive elements was proposed to simulate the fracture of semi-circular sandstone specimens under three-point-bending test and the effects of bedding strength on the fracturing behavior of semi-circular bending(SCB) specimens with different inclination angles were discussed by simulation with the proposed model. The results show that fracture toughness and fracture pattern are anisotropic under the influence of the inclination angle of the bedding and fracture toughness increases with the increase of bedding strength for a fixed inclination angle. In addition, the influence of joint strength on the fracture toughness is greater for lower inclination angles and the fracture patterns are not only influenced by joint strength, but also related to the inclination angle. Fracture patterns of θ = 0o specimens are almost not influenced by the joint strength, and the specimens all split along the bedding plane with tensile failure; tensile or shearing failure along the bedding plane occurs on θ = 30o specimens and the crack length along the bedding plane increases with the decrease of joint strength; when the joint strength is higher, tensile failure along the bedding plane occurs on θ = 45o specimens and tensile failure crossing the bedding plane occurs on θ = 60o?90o specimens, while shearing failure along the bedding plane occurs on θ = 45o?90o specimens when the joint strength becomes lower. Furthermore, the maximum shearing length occurs on θ = 45o specimens. In addition, the impacts on the crack initiation angle and crack propagation path caused by both bedding strength and inclination angle are discussed based on the numerical results. The findings in this paper may enrich the theory of fracture mechanics on layered rock.

The existing aerated anchor has some shortcomings, such as small bearing capacity, explosive air bag, and unapplication in engineering. By adding end baffle and side guard plate for air bag of aerated anchor, the aerated anchor with end baffle and the aerated anchor with side guard plate was invented respectively. The aerated inflation controlled anchor was then developed by adding the earth-squeezing steel plate in the structure of the anchor, which changes the way of transmission of the anchor. It has the advantages of large bearing capacity, stable performance and complete recovery, and the overall structure of this anchor is simpler and more practical. Full-scale indoor and outdoor tests of the three kinds of anchors were carried out respectively. The maximum aeration pressure of the aerated inflation controlled anchor in tube piece type can reach 0.6 MPa, which is 5 times the existing aerated anchor. The maximum ultimate bearing capacity of the anchor section per meter is 40 kN, which is 60 times the existing aerated anchor. At the same time, the formulas for calculating the bearing capacity of the aerated inflation controlled anchor in tube piece type are deduced and verified, and facilitates the practical application of the anchor.

Red sandstone is widely distributed in China, and its disintegration is very significant due to changes in water content. The red sandstone samples from Zhuzhou area of Hunan Province were used to conduct laboratory static and disturbed disintegration tests. Then, an evolution model of gradation curve of particle disintegration of red sandstone was established based on the Weibull distribution, and the model parameters λ and k were analyzed, the value and change rate of the two parameters reflect the evolutionary process of particle disintegration and breakage of red sandstone. Moreover, on the basis of established model, the calculation formula of the relative disintegration ratio was obtained, and the correctness of the formula was verified. Furthermore, according to the test results and the values of model calculation, the similarities and differences between the slaking durability index and the disintegration ratio, and the effects of different test methods on the test results were discussed. Finally, the feasibility of application of Weibull distribution model to the evolution of rock particle disintegration is verified based on the existing researches.

Arching effect is a common phenomenon in the systems of soil-structure interaction, and has been found to be inevitably affected by dynamic loading. The present study is devoted to investigate the evolution process of soil arch under the cyclic loading. To this end, a series of tests was conducted by using a trapdoor apparatus equipped with a cyclic loading system. By using particle image velocimetry (PIV) together with a set of dynamic load cells, evolution behaviors of the soil arch are observed and analyzed, including the geometric features, particle displacement fields and variation of vertical stresses. Based on the test results, it is found that the settlement of moving gates generates a void area over the trapdoor with a triangular boundary as the soil arch is initially formed. After applying cyclic loads, the structural boundary of the void area gradually extends vertically and moves upward to the filling surface, while the displacement region spreads in a fan-shaped patterns and extends to the sides with increasing base angles. Depending on the differences of initial trapdoor displacements and cyclic loads, two typical categories of the final stability of soil arch under cyclic loading are identified in the tests, namely the new stable cases and collapse cases. The results show that soil arch with a larger initial trapdoor displacement is more likely to experience a final collapse, as the void area extends along the filling height and a vertical slip surface is generated. The stability of soil arch under is related to the supporting effect of the accumulated soil within the void area to the lower boundary of the soil arch.

The permeability is an important parameter which reflects the moisture movement in unsaturated soil. In this paper, a soil column device is designed combining instantaneous profile method and filter paper method to determine permeability function. The device includes a continuous water supply system at the upper part and a soil column composed of soil sample with a cylinder and filter paper at the lower part. During the infiltration, the mass of soil samples and filter papers are measured to determine the water content profile and hydraulic head profile. Then the soil-water characteristic curve and permeability curve are calculated by these data. The Malan loess and the first layer of paleosol from Zhengning, Gansu province are tested. The results show that the method covers a wide range of suction from 1 to 105 kPa, and permeability coefficient range of 10?5?10?13 m/s. This method is simple, inexpensive, and available for both intact and remolded soil. Moreover, several common statistical permeability models including Childs & Collis-Geroge model, Fredlund model, van Genuchten model, and Priesack & Durnerare model are used to predict the permeability curve of the two soils. The results show that the predicted results are consistent with the measured results in low suction range, while they are not in high suction range.

To investigate the dynamic response of pile group foundation on liquefiable ground subjected to horizontal and vertical (bidirectional) coupling earthquake excitations, a shaking table model test for a dynamic interaction system with liquefiable ground- pile group foundation-frame tube structure was conducted. Different types of earthquake motions were selected as the excitations for the shaking table test, and then the influence of bidirectional coupling earthquake excitations on the dynamic response of liquefiable ground and pile group foundation were analyzed by comparing the test results of soil acceleration, excess pore water pressure and pile group strain subjected to horizontal unidirectional and bidirectional coupling excitations. The results indicate that under the bidirectional coupling earthquake excitations, the vertical peak acceleration of liquefiable soil gradually increases with the decrease of buried depth; the liquefaction effect of saturated sand is related to the bidirectional coupling earthquake excitations and the type of input earthquake motions; besides, compared with the horizontal earthquake excitation, the peak strain in the central and bottom of pile group foundation are larger than those under the bidirectional coupling earthquake excitations, the variation of peak strain of pile top is different; also, the swaying and tilting of the pile group system of the building structure are exacerbated by the bidirectional coupling earthquake excitations. The research results are of great significance to both the seismic design of pile group on liquefiable foundation and disaster prevention and mitigation.

The mechanical behavior of granular materials is characterized by strong nonlinearity, which is known to be directly linked to the details of the underlying microstructure of contacts, or fabric. The incremental behavior in different loading directions can be obtained by performing a series of axisymmetric stress probing on the specimens. Since the macro- and micro-scale response in different loading directions cannot be obtained experimentally on the very same specimen, discrete element method is employed in the present study, and the stress probing tests on the Rendulic plane are carried out on the specimens of different stress histories, stress states and particle size distributions (PSD). Simulation results indicate that the classic plasticity theories are unable to describe all the observed features when the specimens have different stress histories. However, a linear correlation between the deviatoric strain and the deviatoric part of the contact-normal-based fabric can be obtained. For the specimens with the same relative density, only confining pressure is found to have a significant effect on the linear factor while the linear factor seems to be insensitive to the variation of the stress ratio, stress history and PSD. Since the anisotropy of sand and therefore the impact of stress histories can be characterized by the deviatoric part of the fabric tensor, these observations would provide the necessary micro-scale physical basis for the development of elasto-plastic incremental constitutive relations of granular soils.

The site investigation on earthquake damage shows that tunnels in the active fault zone suffer the most serious disasters. To investigate the longitudinal response of tunnels crossing the active fault under the dislocation, this paper proposed and verified an analytical solution of longitudinal mechanical behavior for tunnels. The active fault zone has worse mechanical properties and is the place where the main dislocation occurs. Therefore, the tunnel is divided into three parts in the longitudinal direction, including dislocation affected zone, transient zone and non-influence zone. Assuming that these three zones have different model parameters and calculation modes, an analytical mechanical model of the tunnel is formulated based on the double-parameter Pasternak elastic foundation beam. The proposed model satisfies the continuity of deformation and stress along the longitude direction. Analytical solutions agree well with the numerical simulation results and the laboratory mock-up test observations, demonstrating its good capacity. Analytical results reveal that the tunnel internal force and deformation show a significant increase in the active fault zone under the dislocation. The longitudinal deflection of the tunnel is similar to the dislocation while it has a reverse deflection at the junction zone between the fault zone and the foot or hanging wall. For the dislocation of normal fault, the longitude moment reaches its maximum value at the junction zone between the fault zone and the foot or hanging wall, and a tensile and compressive zone appear in the crown of tunnel on the side of the foot and hanging wall respectively. Shear force in the active fault zone is also bigger than that in the foot and hanging wall. All above responses result in the serious disasters in the fault zone, which is consistent with the site investigation results. Therefore, the proposed analytical solution could be used for the tunnel longitude response analysis under the dislocation. Finally, sensitivity analyses of the ground coefficient and the fault width are performed and useful results are summarized, which can provide technical supports for the tunnel design and construction in the active fault zone.

Due to the characteristics of environment protection and economy, microbial remediation technology in concrete industry has attracted much attention nowadays, however, the repair efficiency is greatly affected by the alkaline environment. Therefore, it is of great significance to improve the efficiency of the technology and the quality of repair work. In this paper, the accelerating effect of Al2O3 on microbial calcification in high alkaline environment was investigated. Concrete specimens with different crack widths were repaired by adding Al2O3, during which the pH value and urea content of the leaching solution were monitored. After repairing, the repairing effect was evaluated by acoustic time value, CaCO3 formation efficiency and unconfined compressive strength. The results showed that Al2O3 could reduce the inhibition of alkaline environment on bacteria and enhance the urease activity and calcification efficiency. The addition of Al2O3 reduced the pH of the leaching solution from 12 to 9, while the urea utilization rate increased significantly, up to 81%, thus significantly shortened the repair time. The acoustic time value of specimens with addition of Al2O3 is close to that of specimens without cracks, which is significantly better than that of non-added specimens. After Al2O3 addition, the formation rate of CaCO3 in 2 mm cracked specimens was 77.32%, which is way higher than that of 20.98% specimens without Al2O3 addition. The strength recovery of repaired specimens increases with the decrease of crack width, and the strength recovery of repaired specimens with Al2O3 addition is much higher than those of the specimens without Al2O3. Therefore, the addition of Al2O3 can effectively improve the efficiency in concrete repairing process, reduce the repair time, and provide important reference for the rapid and efficient repair of cracks by microorganisms in future practical projects.

A strain-softening model with broad applicability is proposed with respect to the Hoek-Brown (H-B) criterion based on forty triaxial test results of different hard and soft rocks. Firstly, based on the test results, the three-parameter power-type confining pressure function is verified to be correct for describing the relationship between the post-peak critical plastic stain and confining pressure for different types of rocks, and is introduced into the definition expression of the plastic internal variable. Then, the rationality of the different parameters for describing the softening parameters of the strain-softening model based on H-B criterion is compared and analyzed. It is found that the parameter GSI is best suited for the description. Moreover, the evolution of GSI with the plastic internal variable in the post-peak stage is studied, and a widely applicable nonlinear model is established. By comparing it with the other existing models, it shows that the proposed model can describe the nonlinear evolution of strength parameters of H-B criterion in the post-peak stage more correctly with fewer parameters. The model is applied in the software ABAQUS by adopting the non-associate flow rule. Finally, by simulating the different laboratory tests of rocks, it is proved that, with good applicability, the proposed model can correctly characterize the strain-softening and dilation behavior in post-peak stage of hard and soft rocks under different confining pressures. By comparing it with the models of constant critical plastic strain or constant dilation angle, respectively, it is found that the simulated stress-strain curves by the proposed model are more closely in line with the test results.

The freezing point and freezing characteristic curves of saturated remolded silt with solution (NaCl, Na2CO3) were measured by thermocouple and nuclear magnetic resonance method. Upon comparing the NaCl and Na2CO3 solutions, the effects of initial salt content on freezing temperature and unfrozen water content were studied. The results show that the freezing temperature of soils decreases with the increase of initial salt content; the freezing temperature of saturated soils with NaCl solution is lower than that of the corresponding pure solution with the same concentration. But the freezing temperature of saturated soils with Na2CO3 solution (<0.6 mol/L) is higher than that of the pure solution. At the same temperature, the content of unfrozen water in soils increases with the initial salt content of NaCl, but does not change obviously with the initial salt content of Na2CO3. The mechanism analysis shows that the salt type and salt content have different effects on soil water potential. Based on the improved generalized Clapeyron equation, the freezing temperature of salt-bearing soil was introduced into the prediction model of unfrozen water content. The quantitative expression of unfrozen water content of soil was obtained, and compared with the measured data with considering the effect of salt content. It is verified that the model can reasonably predict the unfrozen water content of saline soils at different temperatures.

Geotechnical engineering often encounters high temperature environment. It is important to study the mechanical properties of rock samples printed in 3D subjected to high temperature treatment to promote the application of 3D printing technology in engineering field. Using GS19 sand and furan resin as printing substrates, rock samples with highly consistent internal structure were prepared by 3D printing technology and the mechanical properties of rock samples printed in 3D subjected to different temperature treatments were studied. The reasons for the change in mechanical properties of rock samples printed in 3D at different temperatures were analyzed from the microscopic level by scanning electron microscopy. The optimal temperature of 3D printed rock samples are proposed and the failure characteristics of 3D printing rock samples with prefabricated cracks after optical mechanical temperature action are studied. The uniaxial compressive strength and splitting tensile strength of 3D printed rock samples increase first and then decrease with increasing temperature. The optical mechanical temperature is 150 ℃. After the optical mechanical temperature effect, the failure process of 3D printed rock samples with different inclined cracks includes four stages, i.e. compaction, micro-crack initiation, stable crack propagation and penetration failure. The initial crack initiation locations appear at the prefabricated cracks, but with the change in inclination of prefabricated cracks, the propagation path always tends to the direction of load loading and is approximately centrosymmetrical.

In practical engineering, the overburden deformation is difficult to be monitored by conventional testing methods. Therefore, the Brillouin frequency shift (BFS) analysis and Brillouin optical frequency domain analysis (BOFDA) technology are adopted in this research to solve the problem. Based on the coal mining processes in the field, a 4 200 mm × 250 mm × 1 600 mm (length, width and height, respectively) overlying strata model is established in the laboratory. The deformation charactistics of overlying strata during the excavation are tested through the four horizontal sensing fibers and five vertical sensing fibers embedded in the model. By comparing the experimental results with the measured displacements obtained by close range photography digital image processing technology, the relationships between the optical fiber frequency shift values, strata working face weighting and the evolution of overburden structure are revealed through the comprehensive analysis of the characteristics of mining overburden activity and the law of strata pressure appearance. Besides, the characterizing method of the development and evolution range of two zones based on optical fiber frequency shift value are also obtained. The study shows that the BOFDA technology can be used to monitor the characteristics of mining overburden activity and the law of strata pressure appearance using BFS analysis. The test results provide theoretical and experimental support for the field application of distributed optical fiber testing technology in monitoring the "two zones" deformation of overlying strata in coal mines.

A rainfall infiltration test model which enables the measurement of the volumetric water content of soil is designed. The distribution and variation of the initial water content under rainfall infiltration are obtained through the test. Based on these results, a novel method for shallow stability analysis of earth slopes subject to rainfall infiltration is proposed by combining the unsaturated shear strength theory and the limit equilibrium method. The proposed method is then applied to study the stability of a soil slope along the Qili connecting line of Hang-Xin-Jing expressway. The main findings are as follows: the inverse proportion function characterized by water content distribution parameter A, correction coefficient λ and μ can be used to describe the initial water content distribution of soil in natural state; with the increase of A value, the initial stability of the slope decreases, and the sensitivity of rainfall to slope instability also decreases; when the rainfall intensity is the same, the greater the initial surface water content is the shorter the rainfall time needed to cause the slope instability; and when rainfall time is the same, the greater the initial surface water content is the smaller the rainfall intensity needed to cause the slope instability. Under the same groundwater level, the rainfall intensity is inversely proportional to the rainfall time needed to cause the slope instability.

In order to explore the deformation mechanism and influencing factors of the short cantilever beam under the technology of pillarless mining with gob-side entry retaining by roof cutting and pressure relief, the roof structure and motion process are analyzed, and the mechanical model of the short cantilever beam roof is established. Based on the principle of function, a calculation formula for the deformation of the short cantilever beam roof in the three stages of the early, middle and late stages is derived. The influencing factors and sensitivity of the short cantilever beam roof in each deformation stage are discussed, and the corresponding control ideas are put forward according to the main control factors in each deformation stage. The results show that the deformation of the short cantilever beam roof in the early stage is small. At this stage, the elastic modulus of basic roof, the strength of support in roadway and roof, and the height of short cantilever beam have a significant influence on it. In the medium-term stage, the deformation is large, and is significantly affected by the bulking coefficient, the modulus of the short cantilever beam roof and the width of the roadway. The roof is in a relatively stable state at the later stage, and the deformation is basically no longer changed. A countermeasure of phased main control factors, namely timely high-strength support in roadway + roof cutting plan optimization was proposed for the S12012 working face of Ningtiaota coal mine. Good effect of field application was verified.

The anchorage of suspension bridge is divided into tunnel-type anchorage and gravity anchorage. The tunnel-type anchorage can effectively use the geological conditions of the anchored area and requires less engineering in comparison with the gravity anchorage. It is also characterized with high cost performance and low disturbance to surrounding environment. However, the tunnel-type anchorage has yet to form a relatively complete, quantitative design method with its current design and construction mainly depend on engineering experience. Combined with the tunnel-type anchorage project of China’s first railway suspension bridge, four failure modes of tunnel-type anchorage are summarized and analyzed, that is, the interface failure of side wall of anchorage, the failure of inverted cone platform, the failure of slope sliding, and the compression failure of anchorage. The calculation model is established according to the typical failure mode, and the corresponding simplified calculation formula of bearing capacity is derived based on the limit equilibrium theory. The sensitivity analysis of the key design parameters is carried out by using the finite element method. The design and calculation method of tunnel-type anchorage are given, and a relatively complete design for the project is provided to set an example. The research results can help future design of tunnel-type anchorage of railway suspension bridge.

In order to study the law of thaw consolidation for high ice content permafrost embankment, a nonlinear constitutive relationship was incorporated into the original linear large strain thaw consolidation theory and a piecewise interpolation function was used to implement the nonlinear relationship between compression modulus and void ratio. Numerical simulation method of thaw consolidation was further modified. Validity of this work was verified by the monitored data of Qinghai-Tibet highway. The analysis results shown that the thaw consolidation calculation accuracy of high ice content embankment can be notably improved by the modified thaw consolidation theory and numerical simulation method. Further analysis indicated that the interactive effects between thermal and mechanical field can be further reasonably described by the nonlinear stress-strain relationship. The thawing consolidation degree of frozen soil is affected by effective thawing consolidation time and characteristic drainage length, which is completely different from the development law of thawing roadbed. The thaw consolidation degree increases in the early stage of roadbed operation, while with the development of time, the degree of consolidation decreases continuously after reaching the peak value. This is mainly due to the increase of characteristic drainage length and the shortening of effective melting and consolidation time caused by the continuous increase of melting depth. Therefore, the nonlinear constitutive relationship must be employed to calculate the stability design parameters, such as thaw depth, settlement and consolidation degree when the high ice content permafrost embankment was involved.

The roof of the stope in the western region is thick and hard. The broken rock often forms large key blocks. The stability of the surrounding rock is poor with leads to strong support response. Thus, investigating the dynamic structural mechanical behavior of blocks is of great significance to the control of stope surrounding rocks in the western region. According to the dynamic structure formed by the relative rotation of key blocks, a kinematic mechanical analysis model is established. In this study, according to the change of geometric relationship between blocks, the relationship between the extrusion area and the angle of rotation is derived, and the dynamic process of the relative rotation of blocks is divided into three rotation stages. Based on the "voussoir beam" theory, the relationship between the extrusion force and the rotation angle of blocks in different stages is deduced, the structural stability and mechanical behavior are analyzed. Combined with the instability conditions, the working resistance of support is taken as the response characteristic, finding the most unstable position of the structure during the turning process, and then a method of calculating support working resistance is developed, and its correctness of the formula is proved by practical cases. The theoretical calculation results show that: with the increase of the rotation angle θ, the extrusion force T1 generally shows an increasing trend. When the blockness i<1, T1 increases or decreases in a quadratic parabola with θ change. However, when i>1, the curve gradually shows a linear change. As the blackness is large, the increase rate of T1 with θ is smaller. From the analysis of instability conditions, it can be revealed that the large key blocks are prone to slip instability in the early stage of rotation, but its anti-rotation deformation instability ability is relatively strong. For the characteristics of large blockness, weak self-stability of the structural and strong response of the support, it is necessary to design a reasonable support working resistance. By analyzing the stress conditions in the three rotation stages, it is found that the most unstable block is at the critical angle between the initial and middle rotation stage. Finally a formula of calculating the working resistance of support is given in the state of instability.

The design of underwater tunnel has special requirements for the thickness of the frozen wall. To improve the frozen wall design of the contact channel in the Maliuzhou waterway section of the Zhuji Intercity Rail Transit Project, based on the fluid-solid coupling theory, the finite difference method is adopted to analyze the stability of the underwater tunnel numerically. By simulating underwater tunnel with different frozen wall thickness, the responses of underwater tunnel stability to the thickness of frozen wall are discussed and the optimizaitons of frozen wall ticknesses are done. The results of simulation show: compared with the non-permeability model, the fluid-solid coupling model has the same distribution of stress on the frozen wall, but the overall values are obvious larger, which means the effect of water cannot be ignored. Due to the existence of water, the frozen wall tends to be “homogeneous” and the stress concentration phenomenon is alleviated, but the distribution range of high shear stress is expanded, which increases the risk of shear damage, and the frozen wall is changed to be under the tension from the pressure, which decreases structural stability. The deformation of the frozen wall is intensified under influence of the fluid-solid coupling and increase with the decreases of the thickness until the thickness of the model reaches 2.0 m or more, where the deformation of the frozen wall is basically stable. The plastic zones of the fluid-solid coupling models mostly exist at the arched areas on both sides, no plastic zone is formed in the models with 3.0 m and 2.5 m thickness, the plastics are formed in the opposite sides of the model with 2.0 m thickness, the plastic zone is almost going through in the models with 1.5 m thickness, the damage zone is formed obviously at frozen wall arch of the model with 1.0 m thickness. The thickness of 2.5 m is selected as the optimized thickness of the frozen wall. This optimized thickness is directly applied to the design of the No.4 communication channel, which is constructed by a freezing method. Through the on-site monitoring test, the validity and the effectiveness of the optimization scheme are verified, which means this optimization scheme has essential promotion and application value for the design of frozen wall thickness in similar projects.

It is difficult for traditional bolt-shotcrete support to meet the requirements of deformation control in soft rock tunnel, therefore yielding support becomes an important means to control deformation. The circumferential yielding support sets up the yielding device in the circumferential direction of the tunnel in order to realize the rigid-flexible-rigid characteristics of the supporting structure. From the perspective of energy transformation in tunnel excavation-support process, the principle of circumferential yielding support is clarified in this paper. The main factors affecting the deformation of the support structure are analyzed using the analytical method of structural mechanics, and the mechanical characteristics of traditional support and circumferential yielding support are compared using the finite element software ABAQUS. The following conclusions are drawn: the initial support is a typical compression-bending member. The circumferential yielding support causes the yielding device to buckle through the circumferential pressure, which balances with the internal force of the support structure. It is hence possible to achieve a certain support resistance while controlling the surrounding rock stress by shortening the circumference. The circumferential yielding device should be set at places where the bending stress is relatively small. The shear stiffness and bearing capacity of the device should be ensured with the characteristics of "strong shear and weak compression". The circumferential yielding support has the mechanical characteristics of rigid-flexible-rigid, which can be adapted to the rheological characteristics of soft rock with high geo-stress.

The relative permeabilities for water-air two-phase flow in rough-walled fractures of rock are significant parameters on multiphase flow and hydro-coupling analysis in fractured rock engineering. According to the capillary theory and cubic law, the rough-walled fractures are conceptualized as a large number of parallel plates of different apertures, and a relative permeability model for water-air two-phase flow in rough-walled fractures is proposed on the basis of micro structure of rough-walled fractures. The theoretical model is validated by the comparison with experimental data from two different rough-walled fractures with distinguished spatial distributions. No matter for water phase or air phase, the proposed model can satisfy the experimental data better than X model, V-C model and Corey model. In order to evaluate the feasibility of the proposed model on rough-walled fractures with different spatial distributions, a numerical approach is developed to generate the aperture distribution based on random successive addition method, and to perform water-air two-phase flow process based on the invasion percolation model, respectively. On the basis of a large number of numerical results, predictions of the proposed model are consistent with the calculated data and presents better goodness of fit than X model, V-C model and Corey model. This more reliable analytical model can be used for better understanding the multiphase flow and hydro-coupling analysis in fractured rock.

The high-level waste geological repository is in a multi-field coupling environment of thermo-hydro-mechanics (THM), and multi-field coupling analysis is required when performing safety assessment on the high-level waste repository. However, the excavation of the high-level waste repository caused the stress redistribution of the surrounding rock near the wall, consequently generated damage and resulted in changes in the thermal parameters (T), seepage parameters (H) and mechanical parameters (M) of the surrounding rock, and their spatial distributions are not homogeneous, which will have a significant impact on the THM coupling evolution process during the operational period. By analyzing the coupling mechanism of thermo-hydro-mechanics of high-level waste repository, and the distribution and evolution law of surrounding rock damage in repository, the damage variable and damage evolution criterion are defined. The damage variable is related to thermal parameters, seepage parameters, mechanical parameters and multi-field coupling parameters (Biot coefficient, Biot modulus and temperature drainage coefficient) and then the damage of surrounding rock is linked with thermo-hydro-mechanical fields. An elastoplastic damage thermo-hydro-mechanical multi-field coupling numerical model is established. Then, the established model is used to simulate the surrounding rock heating test of the high-level waste geological repository in Mont Terri, Switzerland. The numerical and experimental values are compared, the effect of excavation-induced damage on evolution of temperature field, seepage field and stress field are discussed, and the evolution law of excavation-induced damage under multi-field coupling is also analyzed.

Groundwater withdrawal can cause reduction of hydraulic level in pumped aquifers and result in land subsidence. One of distinguishing features of land subsidence is the long-term accompanying deformation of soil layer, resulting from rheological characteristics of soil. In this study, an approach for land subsidence evaluation is presented based on Biot’s consolidation theory. By using semi-analytical numerical principle and viscoelastic rheological theory, the numerical scheme for coupled deformation of soil layer is derived. In the scheme, the compressible pore constituent and viscoelastic characteristics of soil skeleton can be taken into account. The proposed method does not involve numerical integrations and is naturally appropriate for decoupled parallel computing. A FORTRAN computer program is developed for the land subsidence analysis based on the above numerical scheme. After rheological models are adopted, the validities of the present method and computer program are verified by comparing the present results with the existing solutions. It can be shown that the proposed numerical results can accurately reflect the lag effect of deformation due to viscosity of soil layers. Moreover, more numerical example experiments have been conducted to investigate the influences of soil layer permeability, compressibility of pore fluid and viscosity of skeleton on long-term deformation.

In order to overcome the inefficiency of existing numerical calculation programs in calculating the contact slip law of complex fracture surfaces, a new numerical calculation method was proposed by absorbing the idea of boundary element method. In this algorithm, all grids were located at the boundary of rock blocks, and the interaction force between rock blocks and the displacement of rock blocks were calculated by using the explicit difference method. The algorithm was validated by two simulation experiments, i. e. the ball sliding on the parabolic surface and the dumbbell sliding on the inclined surface with different inclinations. The results show that: the algorithm can accurately describe the contact between objects and accurately calculate the normal displacement between blocks. The algorithm can accurately judge the "sliding state" and "stable state" of the object. The error between the numerical and analytical results of friction force is less than 10?10. When calculating the variation of bearing capacity during slip of fracture surface, the calculation results of the new method are consistent with those of the finite element method, but the calculation efficiency of the new method is significantly improved.

Periodic oscillation method is a new method for permeability measurement of porous media. It exhibits advantages of short testing period, good stability and high precision. However, it has not been widely used for low permeability measurement in laboratory due to lack of systematic research. In this paper, the effects of different porosities and medium permeabilities on the permeability measurement results of the periodic oscillation method are numerically analyzed. In addition, the applicability of different forms of periodic waves in the permeability measurement is discussed. Conclusions from the study results can be drawn as follows. First, both the porosity and permeability can affect the process of gas pressure transfer. Second, the initial pressure equilibrium process in medium may not be needed for the periodic oscillation method as the measurement results are almost unaffected by the initial pressure distribution after a certain period of time. Third, compared with sinusoidal wave, square wave exhibits a more notable influence on the pressure response of the downstream gas. Moreover, it is observed that square wave, triangular wave and sawtooth wave are easier to be loaded in practice. Finally, based on the numerical analysis, it is suggested to use the square wave instead of sinusoidal wave in the periodic oscillation method. This study will be helpful to guide the application of the periodic oscillation method test in low permeability measurement.