The fiber bundle model(FBM) and acoustic emission(AE) tests of sandstone under uniaxial force controlled compression are carried out to study the fracture characteristics of heterogeneous materials. The failure of fiber elements in fiber bundle model is analogous to the acoustic emission signal. The results show that: At low stress stage, FBM ignored the occasional avalanche processes, but FBM characterized acoustic emission characteristics well in high stress stage. The distribution of avalanche sizes and AE events both had double power-law behavior, and the probability distribution function(PDF) of simulations and tests share the similar power exponents and inflection points. Simulation and experimental results show a behavior analogous to the second-order phase transitions, and branching ratio ξ could be as a suitable order parameter to describe this transition. Moreover, near to the critical point, the evolution of branching ratio came from FBM and AE tests are consistent.

The interactions between liquid phase and solid matrix in unsaturated clays can be divided into capillary effects and physicochemical effects according to their formation mechanism. The physicochemical effects (that is, the adsorption effects) become significant at low saturation degrees. However, current strength models for unsaturated soils almost are established on the basis of capillary mechanism; and the contribution of adsorption effect to soil strength is neglected. Furthermore, the existing strength models for unsaturated soils apply only to compressive-shear soils but not to the tensile and tensile-shear soils. A binary-medium compressive-shear strength model is firstly proposed, involving the capillary and adsorption effects. The unsaturated clay is assumed to consist of two ideal parts, i.e. the ideal capillarity part and the ideal adsorption part, and then the corresponding ideal strength formulas are established. Furthermore, a participation function is used to reflect the degrees of capillary effects and adsorption effects. A tensile-shear strength model of unsaturated clays is secondly developed considering the various combinations of tensile-shear in unsaturated soils based on the compressive-shear strength model; and then the tensile-shear coupling strength formulas are obtained. Finally, predictions are performed on the compressive-shear strength and tensile-shear strength. Comparison between predicted results and existing test results shows that the proposed model can well describe the strength of unsaturated clays.

As an important mean for soil reinforcement, chemical solidification can consolidate soil particles with the reaction of chemical materials. Lignosulfonates are used to consolidate loess. Based on the limit moisture content test, thermal conductivity test, uniaxial compressive strength test, loading-unloading test, stress relaxation test and x-ray diffraction, the physical property and mechanical properties of lignosulfonate solidified loess are studied; and then the reinforcement mechanism of lignosulfonate is analyzed from the angle of energy dissipation and mineral phase. The reaearch results show that under air-dry conditions sodium lignosulfonate aggravated salinization of loess, and show unsatisfactory effect on improving the strength of loess. But with the increase of calcium lignosulfonate’s dosage, the plasticity index and thermal conductivity of solidified loess reduced; and the strength of samples improved significantly. For instance, the uniaxial compressive strength of loess even reached 11.81 MPa with 5% addition amount of calcium lignosulfonate and the curing age of seven days. The stiffness of the solidified loess is significantly increased under the action of calcium lignosulfonate, under the same strain level the energy consumption is greatly increased and the rate of stress relaxation is improved. Results of X-ray diffraction tests assisted that calcium lignosulfonate can react with the clay minerals in the loess to produce quartz and carbonate minerals, so as to strengthen the siliceous and calcareous cementation between the soil particles; finally, make the soil structure more compact. It is a new type of curing material worthy of further study.

The mechanical behavior of rock material is strongly influenced by confining pressure and strain rate. It is of great significance to establish a unified strength criterion taking account of complex stress state and strain rate in the rock dynamics analysis. A series of strength data obtained from uniaxial compression test, triaxial compression test, Brazilian test on sandstone under strain rates of 10-5-102.32 s-1, are applied to assess the applicability of generalized Hoek-Brown strength criterion and to analyze the strain rate effect on the material parameters. The results show that the strength rule of sandstone can be reasonably described by the generalized Hoek-Brown strength criterion from low tensile stress region to relatively high compressive stress region under the same strain rate. The parameters both uniaxial compressive strength and parameter a show a slight increase at lower strain rate, and show a dramatically nonlinear increase at higher strain rate, whereas parameter m almost does not change with different strain rates. Therefore, the function relationships between the material parameters and a of the generalized Hoek-Brown dynamic strength criterion and strain rate can be established. On this basis, a new generalized Hoek-Brown dynamic strength criterion is proposed taking account of strain rate from the region of 10-5-102.32 s-1. The physical mechanisms of strain rate and confining pressure effects on dynamic strength of sandstone are further studied.

The finite element method(FEM) is a powerful numerical analysis technique, which is applied widely in the simulation of geotechnical engineering structures. As the limitation of element shape in traditional FEM and the geometrical complexity of structures, such as layered construction and complicated material partition etc, a versatile and high-quality meshing discrete algorithm is comparatively difficult to implement, resulting in the majority time is consumed in element generation, which hinder the rapid process of automated analysis. In this paper, a swift analysis method combining the quadtree discretization and nonlinear polygon scaled boundary finite element method(PSBFEM) is developed to conduct the elastoplastic simulation of geotechnical structures. The static and seismic response of a typical core wall dam is modelled, and the validity of presented method is verified by comparing with the FEM. Simple operation, flexibility of the meshing, rapid generation and high-quality can be revealed in the proposed method, where the cumbersome human intervention can be decreased significantly, so as to provide a powerful technique for the rapid automatic analysis of complicated structures. There will be more meaningful research value and engineering significance to explore three-dimensional application of the method.

In order to analyze the influences of pore number and pore size on mechanical properties of marble, uniaxial compression tests are carried out on marble with different pore numbers and pore sizes; and with CT scanning of the specimens before and after destruction the characteristics of the spatial distribution of damage crack are studied. The results show that: (1) With increase of number or diameter of hole, elastic modulus, the peak strength, crack stress ,and crack stress level of hole gradually decrease. (2) With increase of the number or diameter of hole, tensile crack and shear crack increase while the far field crack decrease in the process of specimen failure; and the failure mode of the specimen is gradually transited from tensile failure to shear failure after the specimen failure; meanwhile, damage degree increased gradually. (3) Containing hole specimen under the condition of uniaxial compression, the failure process in the direction of before and after showing from one party to the other gradually failure, and in the direction of up and down showing from hole to the up and down gradually failure. (4) Under the condition of uniaxial compression with hole sample, and the damage distribution in the direction of before and after is decreases from one party to the other, while in the direction of up and down is performed gradually decrease from the hole to the up and down but it’s important to note that due to the superimposed effect of injury the maximum damage surface of the porous specimen is not located at the round hole but at the center of the two circular holes.

In order to investigate the strength characteristics of lateritic clay in a wide range of suction, a series of constant water content direct shear tests is carried out on the unsaturated Guilin lateritic clay. With regard to the suction applied, the suctions can be imposed by using the pressure plate method and vapor equilibrium method. The effect of soil density on soil-water characteristic curve can be ignored, and thus the test under constant water content is that at constant suction. The test results show that with the increase of suction, unsaturated shear strength and total cohesion increase first and then decrease, and reach a maximum values at suction of 7 MPa. The internal friction angle does not change significantly when the suction is higher than 7 MPa, indicating that the suction contributes to the shear strength by changing the cohesion in a high range of suction. When suction is higher than 70 MPa, shear strength varies slightly with increase of suction. Finally, by using results of mercury intrusion porosimetry tests, strength characteristics of Guilin lateritic clay in a wide range of suction are explained from the perspective of pore-size distribution.

In practice, rock mass is neither subjected to pure creep of pure relaxation but to a stress-strain synchronously varies with the lapse of time. Using the visual triaxial compression servo-control test system, the generalized stress relaxation tests are carried out under different confining pressures in different regions including creep and relaxation. The experimental results show that there is different conditions of strain and stress in rock mass, which include strain and stress increase at the same time, strain increase but stress decrease, strain and stress decrease at the same time; creep and relaxation are special cases of generalized stress relaxation of rock. Confining pressure effects of rock mass depend on the condition of generalized stress relaxation; confining pressure curbs the deformation in the condition of axial deformation increasing; and confining pressure promotes the deformation in the condition of axial deformation decreasing. In this paper, the study of generalized relaxation test under triaxial stress is carried out using the generalized stress relaxation test. And the generalized stress relaxation characteristics of the rock under confining pressure are compared and analyzed, so as to provide some guiding and reference significance for the further study of triaxial generalized stress relaxation test.

In order to improve the prediction accuracy of frozen soil temperature field and reduce the testing work load of thermal parameter, the inversion formula of unfrozen water content is deduced based on the thermal conductivity and the three-phase composition of soil, water and ice in saturated frozen soil. According to the two-phase structure of dry soil or saturated soil, a formula for predicting thermal conductivity of soil minerals is derived. The specific heat and thermal conductivity of silty clay are measured at different negative temperatures; and the unfrozen water contents of silty clay under different negative temperatures are calculated respectively through the recurrence method for unfrozen water content by specific heat and the inversion formula for unfrozen water content by thermal conductivity established in this paper. The thermal conductivity, specific heat and latent heat of frozen soil at different negative temperatures are determined based on the measured and inversed values of unfrozen water content. The thermal parameters calculated by the unfrozen water content are entered into ABAQUS; and the calculated values of frozen soil temperature field with different thermal parameters are obtained. The calculated values of each temperature field are compared with the measured values of the model test. The results show that the reducing testing work load of thermal parameters is feasible from the viewpoint of the unfrozen water content of frozen soil; and the thermal parameters obtained from the inversion of unfrozen water content based on the Johansen method can better predict the frozen soil temperature field.

Pore pressure is a very important parameter in rock mechanics. In previous publications, influence of uniform pore pressure on fracture toughness was considered; however effects of nonuniform pore pressure on fracture properties are not found. A three-point bending test device that controls pore pressure and confining pressure respectively is designed. With this device three-point bending tests are conducted on specimens of different pore pressures. Specimen and fixture are placed in the confining pressure chamber, and the specimen is enclosed in rubber membrane. A 2D fluid-solid coupling model of finite element is built by XFEM; and the numerical model is verified and calibrated against the crack opening displacement measured by LVDT; and the deformation of crack tip monitored by digital imaging technology. The pore pressure distribution and crack propagation parameters near crack tip is in the rock fracture process are obtained. The results show that there is a low pore pressure zone in the front of the crack tip during rock fracture process. The low pore pressure zone forms a nonuniform pore pressure distribution near the crack tip, which leads to greater mode I fracture toughness than that under uniform pore pressure. The fracture toughness and the pore pressure gradient of low pore pressure zone are positively correlated.

Ferrous sulfate(FeSO4) is used to stabilize chromium-contaminated soils. Leaching test, alkaline digestion test and sequential extractions test are conducted to investigate the variation of stabilize properties of FeSO4 treated chromium-contaminated soils along with particle size and pH. The results show that the leaching concentration(hexavalent chromium and total chromium), hexavalent chromium content of the soil are decreased significantly with particle size decreased. Sequential extractions test show that: with the decreased of particle size, the weak acid soluble fraction(F1) of chromium content decreased, while the reducible(F2) and oxidisable(F3) changed oppositely. The hexavalent chromium leaching concentration and hexavalent chromium content were decreased significantly with pH decreased; while the total chromium leaching concentration changed oppositely. There is a threshold value for pH in terms of its influence on chromium speciation. The weak acid soluble and oxidisable fraction of chromium content decreased with the pH decreased before its reached the threshold value; while the reducible changed oppositely. The weak acid soluble of chromium content increased with the pH decreased after its reached the threshold value; while the reducible and oxidisable fraction changed oppositely. The changing in stabilized properties and risk assessment of stabilized soil can be attributed to the change of chromium speciation.

Three types of AE signals are obtained by carrying out the tunnel rock burst simulation experiment and clustering rock explosion signal. The acoustic emission signals which have the characteristics of the precursory anomaly, large energy and small quantity, are preferred as precursor characteristic signals of rockburst. Before the rockburst, the precursor characteristic signal of rockburst appeared densely; it is shown obvious precursory anomaly. The window functionis used to carry out the quantitative analysis of temporal density of precursor signal and put forward the quantitative index——time intensity which can measure timing evolution characteristics of signal. Before the rockburst, the precursory signal appeared densely, is greater than or equal to 3. This situation firstly appears can be as the precursor information of rockburst; therefore the early warning threshold a can be set to 3. Based on optimization of rockburst precursor signal and early warning threshold extraction, with the help of BP neural network, intelligently identify rockburst precursor signal. The time window function is used to calculate value of precursor signal. When value of precursor signal start to achieve rockburst warning threshold ( ≥a), it starts to warn rockburst. Therefore, a real-time warning method of rockburst based on AE data of tunnel rockburst simulation experiment is established so as to provides a new idea for the construction of early warning method of rockburst.

Loess is widely distributed in China and is markedly structural, differences plane strain problem exist in loess engineering. With the help of a true triaxial apparatus of Xi'an University of Technology, axisymmetric triaxial tests and plane strain test on the intact Q3 loess with different moisture contents are conducted under different confining pressures in order to study the strength evolution characteristics, the differences of strength, and failure modes. The results show that the intact loess of low water content is prone to brittle failure and the stress-strain relationship curve is softening under low consolidation confining pressure. However, with the confining pressure increasing, it hardens. Confining pressure enhances the strength of intact loess; moisture content attenuates the strength of intact loess. In brief, the failure strength of loess is closely related to moisture content, confining stress and spherical stress state. With the moisture content increasing, cohesion effect reduces obviously; while internal friction angle decreases slightly. Under the same conditions, the strength under plane strain condition is 1.1-1.4 times, larger than that under axisymmetric triaxial condition. The loess sample exhibits lateral dilatancy shear failure with single shear band under axisymmetric triaxial state, and shear shrinkage lateral dilatancy failure under plane strain state.

Threshold fines content FCth is an important parameter to assess the grains contact state and the mechanical properties of sand-silt mixtures. Systematic laboratory tests are performed on 38-group test results for 14 types sand-silt mixtures. The FCth of the mixtures are evaluated by the traditional approaches in literature using different physical and mechanical properties. Furthermore, the factors affecting the FCth of the mixtures are discussed preliminarily. The results show that as the grains size difference of sand-slit mixtures increasing, the FCth determined by the static test results will be obviously higher than those by the dynamic test results. The Rahman’s empirical formula can not predict the mean threshold fines content well. The traditional approach using the maximum and minimum void ratio of clean sand or clean silt, can predict the of the mixtures with round-like grains observed in laboratory tests well. However, the of the mixtures with angular-like grains obtained by the traditional approach are obviously lower. The analysis indicates that the mean grain size ratio Rd is an important physical index for evaluating . It is seen that an increase in Rd causes a decrease in of the mixtures with Rd up to 10, thereafter causes an increase in the and remains constant ultimately. A new empirical formula is thereby established and validated based on Rd.

To investigate effects of the concentration and composition of the pore solution on the mechanical properties of the expansive soil, free swelling rate tests and direct shear tests are performed on Guangxi expansive soils containing different concentrations of NaCl and CaCl2 solutions. The experimental results show that with the increase of solution concentration, the free swelling rate decreased rapidly and then decreased gradually. When the concentration is the same, the free swelling rate of expansive soil containing NaCl solution is slightly larger than that of CaCl2 solution; the strength and the cohesive of soil decrease with the increase of concentration; however, the influence of solution concentration on the internal friction angle is smaller. Analysis of the test results shows that the expansive soil surface has a negative charge fixed, the particle surface will form electric double layer; as the concentration of salt solution increases, the thickness of the double layer decreases, the repulsion between particles decreases, the intergranular stress increased, soil particle sedimentation, reducing the free swelling rate; meanwhile, the higher cationic chemical price, the greater cationic radius, the more significant effects on the double layer; therefore CaCl2 solution has a greater effects on the free swelling rate than NaCl solution. On the other hand, the salt solution can change the structure of expansive soil from agglomeration to flocculation. The salt solution will increase the intergranular stress, increasing the strength of the expansive soil; however, structural changes can reduce the strength. The above two influencing factors have the opposite trend to the strength, for Guangxi expansive soils, the effect of the structure larger than the effect of intergranular stress.

The mechanical features based on unloading mechanical parameters are not accordant with the mechanical characteristics of rock under unloading condition; in order to construct strength criterion which is widely used and accordant with characters of unloading rock, the work and results are carried out as fellows. Firstly, different initial damage levels between unloading experiment of rocks and underground engineering under excavation unloading conditions are discassed. Secondly, the internal relations between elastic strain energy, the second invariant of stress deviator, the second invariant of stress tensor and Poisson’s ratio are explored. Thirdly, the internal relations between elastic strain energy and strength criterion are also explored. Lastly, based on elastic strain energy, the mechanical features of rocks under unloading condition are studied by using loading mechanical parameters. The experiment results show that existed strength criterion is possible to violate the first thermodynamic law or the law of conservation of energy. It is suitable to increase or decrease for the limited bearing loads of rock under the range of unloading condition based on elastic strain energy, and the mechanism of above-mentioned result is analyzed.

The mechanical properties of coarse-grained materials are closely related to material state, such as confining pressure, density, lithology, gradation, etc. The effect of material state on mechanical properties of coarse-grained materials is investigated by large-scale triaxial tests under isotropic consolidation and drained shear conditions. Test results show that the strain hardening and shear contraction are strong at small dry density. Softening and dilatancy are become stronger as dry density increases. Lithology also has significant effect on mechanical properties of coarse-grained materials. The strain softening and dilatancy are stronger when the lithology is stiffer. Gradation has important effect on mechanical properties of coarse-grained materials. Under same coarse sand and fine gravel content, the coarse-grained material has small strength and big dilatancy for small content of coarse gravel. The void ratios of specimens of different confining pressures are tend to their critical void ratios and show a good linear relationship in logarithmic coordinate system of average normal stress. The normalization of Rowe dilatancy model parameter is good for influence factors of material state, such as confining pressure, density, lithology and gradation, which means the Rowe dilatancy model can well reflect the effect of material state on mechanical properties of coarse-grained materials.

Gobi is a common geological formation in Northwest China. The gobi gravel soil is made up of the coarse-grained soil, the fine-grained soil, and the bond particles among them. Gobi gravel soil contains soluble salts and exhibits salt cementation, which makes it different from other soil-rock mixtures. In this study, the pH values and the soluble concentrations are tested on gobi gravel soil obtained from Xinjiang Autonomous Region and Gansu Province. The mechanism and the type of salt cementation are analyzed. The microstructure, mineral composition, and bond character of structural soil particles were examined by the techniques of X-ray, SEM, and moss-Bauer spectroscopy to investigate the physicochemical mechanism of bond forces. According to the results on the mineral composition and the microstructure, the possible chemical bond types and the physicochemical mechanism of bond forces were suggested. Finally, the mechanical model and the corresponding formulae of the relationship between the shear parameter and the cementation were established, in which the content and distribution of the cementing agent was suggested as the variables. The cohesion values were calculated and compared to the in-situ shearing test results. The results show that the essence of chemical bond is the formation of the ionic bond by the non-metal atoms in the minerals or CaCO3 (for example, by the oxygen atom). The magnitude of this chemical bond force is determined by the ionic bonds. In addition, the contribution of the salt cementation must be taken into consideration in the determination of the shearing strength for gobi gravel soil.

The increase/decrease change of water content is one of important factors for shear strength of unsaturated soils. Direct shear tests are done on the compacted soils under continue drying conditions. The results show that the behavior of shear strength changes significantly during the drying conditions. The peak value of shear strength occurs under lower water content conditions. And the strain softening characteristic is demonstrated during the shear process, whereas the strain strengthening characteristic is shown under higher water content conditions. The shear strength model is developed by combining the soil-water characteristic curve (SWCC) and suction stress characteristic curve(SSCC), which can be used to predict the shear strength of unsaturated soil accurately. Compared to the measured data, the model can predict the evaluation of suction strength under a continue drying condition only using the determined soil-water retention curve and shear strength parameters under the fully saturated state. The measurement can be simplified and the tested time can be saved greatly when the model is used in practice. Furthermore, the nuclear magnetic resonance (NMR) technique is used to determine the distribution of pore water in soils on the same samples for shear strength tests. The measured data are used to explain the strength evolution of clayey soils under different water contents from microscopic analysis.

By means of axial loading and unloading of confining pressure, a series of unloading triaxial tests with different unloading rates and different confining pressures is performed using MTS815 rock test system to understand exactly the influence of unloading rate on strength of Beishan granite. Unloading rate is 0.1, 1.5, 2.0 MPa/min,respectively axial loading rate is 10 times of unloading rate of confining pressure; initial confining pressure is set as 5, 10, 15, 20, 30 MPa, axial and circumferential deformation are recorded by axial and circumferential extensometer; influence coefficient is put forward by elastic energy. The results show that: Specimens all show brittle fracture properties; strength increase with unloading rate increasing; c increase with unloading rate increasing; but φ remain the same with unloading rate increasing. The effect of unloading rate on strength, c and φ is caused by stress adjustment hysteresis and extra tensile stress. Influence coefficient is put forward based on elastic energy to determine unloading rate on destroy severity, destroy severity increase with influence coefficient increasing; in the same confining pressure influence coefficient increase with unloading rate increasing, which indicate unloading rate promote destroy severity. but in the same unloading rate influence coefficient decrease with confining pressure increasing, which indicate confining pressure reduce destroy severity.

Calcareous sand is generally saturated with salt water in marine environment. Conductivity is an important parameter in salinity evaluation which can reflect the salinity of the water. Therefore, the conductivity of calcareous sand has great significance in water quality evaluating of calcareous sand in marine environment. In this paper, we selected an exposed open calcium sand on a calcareous sand island, and buried triple sensors of soil conductivity, volumetric water content and temperature at the depths of 0.5, 1.0, 1.5 m to monitor the calcareous sand conductivity and volumetric water content. The relationship between calcareous sand conductivity and pore water conductivity is analyzed based on conductivity and volumetric water content site observation, conductivity indoor testing and Manta2 water quality sensor verification of calcareous sand with different gradations. The results show that the conductivity of calcareous sands has linear relationship with the volumetric water content and the conductivity of pore water respectively, and then promote a calculation model for the conductivity of calcareous sand.

In this paper, the variation rules of kinetic parameters, dynamic mechanical properties and failure form of saturated granite under low temperature from 25 ℃ to – 40 ℃ are investigated by means of split Hopkinson pressure bar(SHPB) dynamic impact experiment system. Experimental results show that, under high strain rate condition, the peak stress of saturated granite changes like a "乁" glyph with decreasing temperature. The peak strain decreases first, then increases, and the inflection point temperature is –10 ℃. The failure mode of specimen is significantly affected by temperature. Under the impact of high strain rate, the damage variable which is represented by energy dissipation can accurately reflect the macroscopic fracture characteristics of saturated granite in different low temperature conditions. The peak strain and damage variable change with temperature shows that when low temperature is within a certain range, the strength of the frozen granite is not only affected by the degradation of ice, instead, the strength of the saturated granite increases with the low temperature. The research results possess important reference value for the engineering planning, design and construction of similar rock mass blasting excavation in alpine region.

To meet the requirements of geotechnical material for engineering in loess area, a series of tests on loess with long age improved by lime or fly ash to investigate the effects of original soil type, admixture material and admixture amount on shear strength and permeability, and to reveal the microstructure and reaction mechanism. Some conclusions are concluded as follow: the strength development and the stable age of lime soil and lime-ash soil mainly owe to working time of lime and fly ash; the change of hydration reaction rate makes the influence of admixture amount on lime soil show age effect; the granularity of original soil has the most important influence on shear strength and permeability; the strength development is not synchronous with the development of permeability of same improved soil, so the standard age should be different and should be distinguished in practice work. According to the influence of various factors on shear strength and permeability, engineering design shall distinguish the type of original soil at first; and then select improvement mode and admixture amount based on demand nature on the premise of ensuring curing age.

Angola Quelo sand possesses the characteristics of softening and collapsibility when immersed with water; it is of significance to study its permeability for engineering. The permeability coefficient of natural and compacted Angola Quelo sand is measured by laboratory variable head penetration test and double-ring water infiltration test. Based on the test data, the ranges of permeability coefficient of natural and compacted Quelo sand is summarized; the relationship between permeability coefficient and void ratio is analyzed. In addition, the surface water infiltration laws of Quelo sand stratum are discussed. The test results show that the brown-red Quelo sand in the upper stratum is high permeability coefficient and poor water retention; so the surface water is easy to infiltrate into underground, whereas the permeability coefficient of the variegated Quelo sand in the lower stratum is low, which has the conditions for forming perched water, and it will be detrimental for engineering. There is an approximately logarithmical function relationship between permeability coefficient and void ratio of the natural brown-red Quelo sand; however, the variegated Quelo sand in lower stratum does not show this regularity. The permeability coefficient of the compacted brown-red Quelo sand is still higher, and anti-seepage effect is poor.

In order to study the deformation and failure characteristics of contact zone composite rock mass, the cement, sand and gypsum are used as similar material to make specimens with two different strength materials. By uniaxial compression test, influence of similar material strength and high strength material volume ratio on the mechanical properties of composite specimens is analyzed. The results show that: (1) The larger the strength ratio of the similar material, the greater the impact on the overall strength of the composite specimens; the change of the volume ratio of the higher strength material has a significant impact on the overall strength of the composite specimens. (2) When the similar material strength ratio is 1.74, the rupture plane passes through composite specimen end to similar material contact surface; when it up to 2.49, the rupture plane extends from contact surface to both ends of the composite specimen; when it to 4.33, the composite specimens failure gradually changes from both ends into low strength material end. (3) There is a corresponding relationship between variation of acoustic emission(AE) counts and damage location and shape of composite specimens. With strength ratio of the similar material increasing, AE counts of high strength material end gradually decreased and low strength material end gradually increased. The study provides a theoretical reference for the strength analysis of contact zone composite rock mass.

To study the effect of precipitation and drought weather on soil shear strength, a series of quick shear tests is performed on karst red clay samples sampled from Yanshan area of Guilin city, which have been subjected to several wetting/drying cycles. The experimental results show that after several drying and wetting cycles, the red clay samples under fully saturated conditions have no significant peak value in their shear strain-shear stress relationship, showing strain hardening behavior, whereas the oven-dried samples have significant strength peak values, showing strain softening behavior, and their strength tend to be stable as the development of strain. With the increase of the drying/wetting cycle number, both cohesion and frictional angle gradually decrease for both fully saturated and oven-dried samples. Both the cohesion and internal friction angle of oven-dried samples are larger than those of the fully saturated samples, showing more significant variations. In order to study the effects on shear strength and strength parameters of soil samples, the volume changes of the soil samples are also measured after different cycles of wetting and drying. It is found that with the increase of the number of cycles, the volume of the sample decreases first and then remains unchanged.

Tensile cracks influence the stability of loess slopes, which has become a key problem in the stability analysis of slopes and even the study of loess landslides. The previous studies based on the elastic semi-infinite spatial theory aren't in accordance with the real strain state of soil unit near the tip of cracks. Based on the soil mechanics for unsaturated soils and the maximum tensile strain strength theory, a new equation of limit depth of cracks is established. In the equation, the soil-water characteristic curve variables are obtained via pressure plate extractor tests. Mechanism of the tension cracks and influence of the variables on tension cracks is also analyzed. The comparison between results of the equation and actual values show that are much closer each other.

To overcome the shortage of study on fracture evolution and monitoring of rockburst in roadways(tunnels), biaxial compression comparative tests are carried out on rectangular granite samples under the constraint of one side by monitoring the whole process using ultrasonic plane testing method. The method of determination of homogeneity and wave velocity is obtained. The mechanism of rockburst and the regularity of ultrasonic wave waveform are analyzed and discussed. The results show that the hard rock presented obvious layer burst phenomenon and the core of rockburst is located in the inner stress concentration zone before the critical bursting. The evolution process of stratified burst of hard rock can be revealed by means of the waveform of ultrasonic plane testing method; the velocity of ultrasonic wave is decreasing in the process of loading; arrival time of the subsequent wave has not obvious change in the earlier stage and metaphase periods; however, the arrival time of the later period is obviously increasing; and the subsequent wave amplitude is generally decreasing in the loading process; the wave amplitude is increasing before the burst. The application of ultrasonic plane testing method in the field of hard rock monitoring is discussed, stratified burst of hard rock can be predicted based on the variation of waveform and wave velocity and nondestructive monitoring of surrounding rock is realized; the damage evolution process and prediction can be further revealed by the damage variables.

The compressive strength of the fiber-lime-fly ash-saline soil is affected by the salt contents and reinforcement modes. Unconfined compressive tests are conducted on lime-fly ash-saline soil and fiber-lime-fly ash-saline soil in the condition of nine salt contents(0.5%, 1.5%, 2.5%, 3.5%, 4.5%, 5.5%, 7.0%, 8.5% and 10%) and six reinforcement modes (the whole sample, the top1/3, the top 1/2, the middle 1/3, the bottom 1/2 and the bottom 1/3 of sample). The results show that both the compressive strength and the failure strain increase with increasing salt content which is less than 7%, and decreases with increasing salt content which is more than 7%. When the fibers are added to the middle 1/3 of the sample, the compressive strength is the largest, which is reduced to the whole, the bottom 1/2, the top 1/2, the bottom 1/3 and the top 1/3 of sample. The compressive strength is basically the same when the reinforcement mode is the bottom 1/2 and the top 1/2, and that of the reinforcement modes is the bottom 1/3 and the top 1/3. The All stress-strain curves of lime-fly ash-saline soil and fiber-lime-fly ash-saline soil are strain softening. The soil has the best deformation resistance when the sample is reinforced entirely. Fiber reinforcement can counteract the damage caused by salt expansion and moisture absorption softening of solidified soil due to high salt content. The deformation resistance of fiber-lime-fly ash-saline soil is best when the whole sample is reinforced fibers.

Stepped wetting tests with stress free and compression experiments under controlled matric suction are performed on remolded Q3 loess by using refitted consolidation apparatus for unsaturated soils. The soil-water characteristic curves and compression stress-strain curves are obtained. Meanwhile, the relationship between saturation and matric suction and that between water content and suction are studied. The law of compressive yield stress varying with matric suction and that of collapsibility coefficient varying with matric suction are also studied. The results show that when the suction of unsaturated remolded loess is large, the strength of it is large and the compression deformation is small. And the structural yield pressure of unsaturated remolded loess is larger. When the suction is constant, with the increasing of pressure, the collapsibility coefficient shows a tendency of first increased and then decreased. Under the same net compression stress, the greater the matric suction of unsaturated soil is, the larger the collapsibility coefficient change sand vice versa. Once the (p = 200 kPa) is in excess of 0.1, the matrix suction will approximately exponentially increase with it.

The energy release of brittle rock has critical characteristics under stress, In order to understand the statistical distribution law of acoustic emission(AE) avalanche energies and waiting-times in rock loading process before and after critical point, uniaxial compression tests were carried out in the laboratory. The AE characteristics of the loading stage before and after the critical point are obtained; and then the distributions of the functions in the loading states are analyzed, The results show that: (1) It is found that the process of rock samples from the uniform random expansion to the strip concentration until the final penetration through the evolution of AE centers, the cumulative energy(2.8×108 aJ) and the cumulative counts(6.68×105) of AE had mutations before crack coalescence, marking reach the critical point. (2) The probability density function(PDF) of AE energies conforms to be the power-law distribution in 4 magnitudes of the loading stage before and after the critical point. (3) The waiting-time follows the two-power law within any energy interval; each energy region follows the same power-law distribution in a small waiting-time interval( <0.1 s); different energy region will have different power-law characteristics in a large waiting-time interval( > 0.1 s); (4) Combining statistical distributions law of energy with waiting-time, the distribution law of AE signals in the critical state is consistent with the whole process; and the energy signals of the whole process distribution mainly concentrates on the loading process after the critical point.

In physical similarity simulation experiments, the similarity between the physico-mechanical properties of similar materials and the physical properties of simulated prototypes is the key to the success of physical similar simulations. In order to determine the physico-mechanical properties of physical similar materials, three factors and four levels of orthogonal experiments are used; and the influence of three factors, such as sand binder ratio, density and residual moisture content, on the uniaxial compressive strength, elastic modulus and Poisson's ratio of similar materials are studied by using the similar materials composed of sand and gypsum. The results show that the factors affecting the degree of uniaxial compressive strength from big to small in turn for the sand binder ratio, density, residual moisture content; and the uniaxial compressive strength increases with the increase of density but decreases with the sand ratio and residual water content increases. The factors affecting the degree of elastic modulus from big to small in turn for the sand binder ratio, density, residual moisture content; and the elastic modulus increases with the increase of the density, decreases with the increase of the sand binder ratio. The factors affecting the Poisson's ratio from big to small in turn for the residual water content, density, sand binder ratio; and the Poisson's ratio increases with the increase of density and residual water content, but not to the sand binder ratio. The density, sand binder ratio and residual moisture content have a certain interaction with the uniaxial compressive strength; but they do not exist on the elastic modulus; and the density, sand binder ratio have a certain interaction with the Poisson's ratio of similar materials. The regression equation of the ratio of sand to shell, density and residual water content on uniaxial compressive strength, elastic modulus and Poisson's ratio is obtained; and it is of great significance for the design of similar materials.

In light of the issues on frequent destruction derived from slump and shallow landslide of loess slope after rainfall, the study mainly focuses on revealing internal moisture-heat change process of unsaturated loess slope under rainfall infiltration and sunshine evaporation. This research employed a laboratory loess slope model, regulated the rainfall-insolation cycle, and monitored the temperature, moisture and surface displacement. The results show that the depth affected by internal temperature and water infiltration of unsaturated loess slope is limited; in the range of 30~40 cm, under conditions of rainfall and sunshine. These show that, generally, the destruction depth of loess slope with slump and instability is limited, which mostly is a shallow slump. With the change of rainfall and sunlight, the slope surface displacement in the model occur a slight deformation on expansion or contraction.

Aiming at the disadvantages of rockburst proneness criterion in application of tunnel boring machine(TBM) tunnel construction stage, a novel rockburst predictive method applying to tunnel construction stage is proposed, considering the key influence factors of rockburst such as the in-situ stress, the rockmass integrality, the rock strength and construction disturbance during tunnel construction. Firstly, the uniaxial rockmass strength based on Hoek-Brown strength criterion is estimated, by introducing five parametric attributes of rock strength , brittleness coefficient , the quantitative geological strength index (GSI), the excavation disturbance factor D and the maximum in-situ stress .Then, a novel rockburst predictive index is put forward by the strength-stress ratio method of engineering rockmass; and the corresponding threshold values of the new index are presented. Case studies for application further verified the feasibility and reliability of the novel index, so as to provide a practical method for the study of rockburst prediction.

A new method for assessment of karst ground collapse stability is presented for ground stability assessment at a covered karst area. Based on data of karst geological survey and karst disaster assessment from Tangshan city, the ground stability condition is investigated; and 5 major factors that might affect the karst ground stability are selected as independent variables, and then a logistic regression model for stability assessment of karst ground collapse is established. This model not only meets goodness-of-fit test, but also have good performance in stability and forecast accuracy. The presented model can carry out the quantitative analysis for qualitative factors, and the factors investigated are relatively easy to obtain; thus the logistic regression method for karst ground collapse stability can be widely applied to covered karst area.

Rockburst disaster prediction is still an unsolvable global problem in underground rock engineering construction at present; to predict the rockburst intensity grade, a prediction method of rockburst intensity classification of finite intervals cloud model based on index distance and uncertainty measure is proposed to overcome the measured index values of certainty and uncertainty, intensity classification are of fuzzy and random in predicting. The evaluation index system of rockburst intensity classification forecasting is first established based on a comprehensive analysis of the rockburst mechanism and the Mass function of each index is calculated by the ridge function, the weight coefficients are second obtained based on the index distances and uncertainty measure. Then the normal cloud theory is modified and used to calculate the cloud characteristics for each evaluation index in rockburst classification, which generates the cloud drops in finite intervals, combined the measured index values with the corresponding weights the comprehensive degrees of certainty are obtained; and the rockburst level is identified by the weighted average principle in the end; the uncertainty and randomness mapping between the semantic variable and the evaluation index value are realized. The actual cases are introduced to further explain the calculation flow of the prediction model; and comparing with other theory methods shows that the model proposed is effective for rockburst classification to a certain extent; and its accuracy is higher than the other methods, so as to provide a novel idea for similar engineering problems.

This study aims to research mechanical properties of deep mixed ground under condition of different confining pressures and different thickness ratios between hard rock and soft rock. The cement and kaolinite have been used as simulation materials to make the artificial mixed ground; and then the mechanical tests and numerical simulation FLAC3D are used to study the influence of various surrounding pressures and different thickness ratios on the mechanical properties. The results show that the artificial mixed ground can satisfy the need of strength difference. And the mixed ground has the strain hardening phenomenon when the confining pressure ascends, then this phenomenon disappears due to the discordant deformation between the soft and hard rock, and the irregular fractures increase in the soft part of the mixed ground. It is also shown that the mechanical properties of deep mixed ground are controlled by the rock in majority without considering the structural plane effect. The numerical simulation and the mechanical tests show similar stress-strain curves and both indicate that deformation of mixed ground mainly occurs in the soft part.

The reinforcement width and depth of trench face soil body of diaphragm wall should satisfy not only the requirement of stability of trench face but also the requirement of anti-sliding (anti-shearing) , anti-capsizing and anti-bending capability of reinforcement body. The paper first analyzes the relationship between the lots of influencing factors and the stability safety factors of trench face, and it also sums up the key influencing factors and the important controlling parameters which are the reinforcement width and depth. Then it puts forward the checking principle and the safety criteria for the anti-sliding (anti-shearing), anti-capsizing and anti-bending capability, and also presents the calculation methods of width and depth (length) of mixing pile reinforcement body. In addition it puts forward measures which can upgrade the stability of trench face by means of inserting steel material into mixing pile top and embedding steel material in guide wall and arranging mixing piles into outer arch in the plane. The verification of calculation methods of mixing pile reinforcement width and depth is carried out, and the calculus of being upgraded stability safety factors of trench face by means of inserting steel material into mixing pile top and embedding steel material in guide wall and arranging mixing piles into outer arch in the plane is also given. Finally, it provides the research prospect on this topic.

Lanzhou metro line 1 passes mainly through ②-10 and ③-11 sandy pebble strata, most of the line is under the groundwater level and the strata have high permeability. EPB (earth pressure balance) shield tunneling in such strata will not only easily lead to high torque and serious wear of cutterhead and screw convey, but also cause screw conveyor spewing, which lead to an engineering accident. Therefore, the properties of sandy pebble strata need to be improved to make the tunneling safe. Bentonite slurry and foam are selected to condition sandy pebbles. Slump, permeability coefficient and friction coefficient between the soil and steel tube are obtained by different conditioning schemes. When the slump is in the range of 15 to 20 cm, the optimal conditioning scheme which can meet the workability requirement, and can make the screw conveyor keep soil pressure balance, prevent spewing is determined by the theoretical calculation. Engineering practice shows that the effect of conditioning scheme with injection ratio of foam and slurry 7% and 8% respectively is remarkable, which can provides some guidelines for soil conditioning and screw convey anti-spewing during EPB shield tunneling in sandy pebble stratum with rich water in Lanzhou city.

In order to find out the supporting effect of advanced support in silty clay tunnel, the ground settlement, crown settlement, surrounding rock pressure, concrete shotcrete stress and grid steel frame stress are studied by the methods of field test and numerical simulation with the third-phase project of Harbin Metro Line 1 as the engineering background. The conclusions of the study are as follows: (1) Grout diffusion range is too small and uneven, the improving effect of current grouting capacity for soil is poor; the mechanical parameters of the slurry soil have not been raised too much; and its indexes are no different from those of the ordinary soil mass. (2) Silty clay stratum has a certain resistance to the deformation caused by tunnel excavation; the tunnel deformation can reach stability in a short time whether or not the advanced support exists or not. (3) There are obvious differences in lateral stress distribution of surrounding rock; and the grid steel stress increases rapidly in accordance with the increase of the surrounding rock pressure, illustrating that the time and spatial effects of the advanced support which improve uneven surrounding rock load and delay the release of surrounding rock pressure in the silty clay tunnel is not existent. (4) As the range of plastic zone is 1.5-3.0 m roughly and the small pipe do not go beyond the plastic zone on the radial, the supporting effect of them is actually the compaction effect they have on the surrounding soil, which increases its density but cannot reach the effect of arousing the self-supporting capacity of surrounding rocks. (5) The maximum stress of the grid steel frame is only about 30% of its yield strength and the concrete shotcrete layer maximum stress is only about 13.6% of its axial compressive strength, which means it has a sufficient strength reserve to ensure a greater safety.

It is difficult to estimate the detailed rock strength of excavating face timely and effectively when tunnel boring machine(TBM) advances, which results in it difficult to predict the risk of rockburst and TBM jamming. Based on previous research results and engineering practices, a method for estimating rock strength using TBM parameters is proposed for real-time in-situ estimation of rock strength. The equation of real-time estimation is established by the mechanical analysis between TBM specifications, excavation parameters and the rock strength. Then the relationships between the constants in the equations and the TBM specifications such as excavation(tunnel) diameter, cutter diameter are determined in this study on the basis of data collected at several tunnels. Typical TBM case studies for application further verified the wide suitability and reliability of the novel equations. The proposed method appears to be promising and feasible for real-time in-situ estimation of rock strength.

The flexible retaining technology with prestressed anchor has the advantages of safety, short construction duration and economic rationality for retaining excavation in weak rock, which has been widely applied to practice. Owing to the advantages of removal and economization of land resources in excavation projects in urban areas, a method of making centrifugal model with the pressured prestressed anchor is developed combining with the deep excavation project of Dalian Victory Plaza. The centrifugal model tests of flexible retaining structures with pressured prestressed anchor are carried out; the numerical models by FLAC are established for comparison and verification; the influences of the deformation of excavation, the horizontal earth pressure and the anchor types on the design value of the anchor prestress and their influences on the slipping zone are studied. The results show that: the different lengths of unbonded segment in pressured and tensioned anchor resulted in the demand of two types of anchor for the different design value of prestress; the centrifugal models with pressured prestressed anchor and the FLAC numerical model with tensioned prestressed anchor have obtained the linear slip zone with similar position; and the two are verified by mutual verification. The difference in the anchor types does not affect the damage mechanism of the excavation.

Grouting is the most commonly used method in the foundation treatment of hydraulic structures. It can block cracks or fractures of the dam foundation rock mass to meet the design requirements, such as seepage resistance, structural strength, etc. The fracture is the most basic structural surface of the water permeability and the filling degree of grout is the most direct manifestation of grouting effect. However, due to the hidden feature of the grouting project, it is difficult to obtain the filling characteristics of the cracks directly. At present, the indirect water pressure test is the most method in grouting evaluation. The 360°borehole wall image obtained by borehole camera technology is used to identify the characteristics of fracture filling. Then an evaluation index based on the characteristics of fracture filling is put forward, which is called borehole fracture filling integrity(BFFI). The relationship between BFFI and permeability is discussed and the function relation of two evaluation indexes is established using the cubic polynomial. Based on the conventional evaluation method of water pressure test, the BFFI standard for grouting effect evaluation is established. The method is applied to the Yalong River Tongzilin hydropower station test grouting workshop, verifying the reliability of the proposed evaluation method. The results show that: (1) The results of water pressure test method and the BFFI method grouting effect evaluation are consistent, so as to further illustrate the feasibility of BFFI method to evaluate grouting effect. (2) The evaluation of grouting effect can be carried out based on the technology of borehole camera, which can not only show the filling situation of the grout in the fractures, but also reflect the grouting effect. The method based on fracture filling characteristics provides a new idea for grouting effect evaluation.

This paper presents a systematic investigation of the effect of critical parameters on the peak pullout resistance of soil nails, including degree of saturation, grouting pressure, overburden pressure, and roughness conditions of soil nails according to both laboratory and field pullout test results. Influences of the above parameters on apparent coefficient of friction(ACF) are quantitatively investigated; and to facilitate the evaluation of influences of these parameters on ACF values, a normalized ACF is proposed for different pullout testing conditions. It is found that the dependence of ACF on overburden soil pressure is the highest (ACF ranges from 0-1) while this dependence is the lowest for degree of saturation of soils (ACF ranges from 0-0.18).

A new formation technology of post-grouting jacked steel pipe micropiles is presented, including mixture grout (tailing sands and cement mixed in water) ratio test and construction technology. Ratio tests are conducted to analyze the compression strength under influence of water-cement ratios and tailing sand mass-cement mass ratios. The compression tests on 7 short piles and 6 large piles are carried out at the field site; the relationships between mixture grout types, grouting methodology, mixture grout volume and ultimate compression bearing capacity are studied; and then the test results are also compared with the calculated results of standards in operation and miniature pile construction manuals and instruction of federal highway administration(FHWA). Research results show that the mixture grout early hardening is faster than neat cement grout and no significant difference of 28d strength; the strength and grouting technology can be met with w/c = 0.6 and s/c = 0.5; the ultimate compression bearing capacity of post-grouting micropiles increase by 75%-150%; the test results are 1.33 times that of the calculated values, and similar with that of the FHWA calculated values.

The high-stress level caused by the pile driving can result in grain breakage of sand around the pile, which is more serious for the very easily crushable sand. The grain breakage will lead to the reduction of pile bearing capacity, which can result in the instability of foundation structures even collapse. In this paper, a numerical simulation analysis to investigate the problem of the pile driving into the foundation of very easily crushable sand is performed by adopting a newly developed sand breakage model combining with the Coupled Eulerian-Lagrangian(CEL) method. The model parameters are first calibrated and validated through simulating a series of triaxial tests of Dog’s bay carbonate sand. Then, the centrifuge pile driving tests performed on Dog’s bay carbonate sand are simulated by using the CEL technique. The simulated results have a good agreement with the experimental measurements, which demonstrates that the adopted breakage model associating with the CEL for solving the pile driving is effective and feasible. All the comparisons indicate that the bearing capacity of the pile is significantly decreased due to the grain breakage. The results are helpful for the design and construction of the pile driving into the foundation of very easily crushable sand.

In order to reveal the failure mechanisms of the surrounding rock near caverns considering the influence of structural surface in deep highly-stressed condition, a finite/discrete element method combined approach is adopted to establish the numerical models of circular hole specimen containing pre-existing flaw, with particularly attention paid to the mechanical failure characteristics and the crack growth behaviors around the circular hole under the condition of different locations, lengths and dip angles of pre-existing flaw. A series of targeted supporting measures are put forward for each case. Research results show that (1) For the specimen without pre-existing flaw, extensional cracks will appear on the top and bottom of the hole primarily; then the splitting cracks will gradually emerge and coalesce on both sides of circular hole subsequently, which is similar to the slabbing failure near excavation boundaries. (2) The rocks on this side will present the totally shear-slip failure if there exists exposed pre-existing flaw on either side of the circular hole. Contrarily, it will exhibit tension and shear failure if there exists unexposed pre-existing flaw on either side of the circular hole. The damage degree of specimens containing unexposed pre-existing flaw may be more serious and intense compared with those with exposed pre-existing flaw, and is more prone to induce rockburst. (3) For those flaws where are located on top of circular hole, whether the flaws are exposed or not, the rockmass will present a local caving or collapse eventually. (4) With the increasing length of pre-existing flaw, the failure mode of upper rockmass will be transforming from local caving to global collapse eventually. (5) If the pre-existing flaw is on either side of circular hole, the released kinetic energy(damage degree) during failure process will present the tendency of increase firstly and decrease subsequently with the increasing dip angle of flaw, However, for the condition of pre-existing flaw located on top of circular hole, the damage degree of specimen will be the most intense and serious only when the dip angle of pre-existing flaw reaches 60º. Research results may provide guidance for engineering excavation, support design and stability analysis of rockmass containing flaws and faults.

In situ experiments were conducted in Beishan exploration tunnel(BET) in Beishan, Gansu, the most potential candidate site of Chinese high-level radioactive waste repository, to study the rock damage caused by blasting. Acoustic emission(AE) was monitoring during all the blasting process. Firstly, blasting damage stage and progressive damage stage are identified based on AE evolution for each blast round. Then the evolution of AE signal frequency is analyzed; and the damage mechanisms for blasting damage stage and progressive damage stage are analyzed based on AE signal characteristics. The thickness of excavation damage zone of each blast round is delineated by ground penetrating radar with high-frequency antenna. The thickness of each blast round is correlated well with the number of AE hits. At last, we analyze the displacement and AE characteristic in laboratory creep test and field displacement measurement test. Since AE evolution is a direct indictor of progressive damage process, AE can be used to describe the creep behavior and the damage state of rock mass.

For solving the deficiency of triaxial apparatus of frozen soil in matching the real-time scanning of medical CT in the low temperature environment, a new triaxial apparatus of frozen soils is developed successfully. The configuration of the apparatus and the technical difficulties that need to be overcome in the development process are also introduced. The apparatus can be used to complete the triaxial loading and unloading test in the low temperature environment. Meanwhile, the medical CT matched with the newly developed apparatus can realize the real-time dynamic scanning in the whole mechanical process. On this basis, the real-time CT scanning test of frozen loess under triaxial loading is conducted. The test results show that the parameters of the newly developed apparatus can meet the real-time CT scanning conditions of the frozen soil samples under triaxial loading and unloading. In addition, the high quality mesoscopic CT images of different load conditions are obtained; and then the test results are also analyzed and discussed. The development of the apparatus has provided a new technical means for establishing the relationship between the mesostructure and the macroscopic mechanical properties.