To explore the variation of water retention capacity of expansive soil at different temperatures, the calibration curves of Whatman No.42 filter paper were measured by vapor equilibrium method at 5, 25, 40 ℃ and 60 ℃, and the bilinear calibration equation considering temperature effect was established. The results show that the water retention capacity of the filter paper decreases with the increase of temperature, and the effect on the high suction section of calibration curve is weaker than the low suction section. On this basis, Nanning expansive soil is taken as the research object, and the soil-water characteristic curves of Nanning expansive soil at different temperatures are measured by filter paper method. It is found that the water retention capacity of Nanning expansive soil decreases with the increase of temperature, but the influence of temperature depends on matric suction, especially when it is above 40 MPa, the water-retention capacity of Nanning expansive soil remains unchanged with temperatures. To probe into the microscopic mechanism of the change of water retention capacity of Nanning expansive soil under temperature, some samples were selected for mercury intrusion porosimetry test and adsorption bound water test. Based on the test results, the microscopic mechanism of water retention capacity change of Nanning expansive soil was analyzed from the physical mechanism of the interaction between each phase and each phase interface.

The strength and deformation characteristics of coarse-grained soil are closely related to the initial gradation and dry density during specimen preparation. To study the strength and deformation characteristics of coarse-grain materials with different gradations and densities, a simple and generalized method for calculating the skeleton void ratio of coarse-grained soil is proposed. The results of laboratory tests show that there is an obvious monotonic variation between the skeleton void ratio obtained by this calculation method and the mechanical properties of coarse-grained soil. When the specimen size is consistent, with the decrease of the skeleton void ratio, the failure shear stress increases, the failure friction angle increases, and the cohesion decreases. Also, as the skeleton void ratio decreases, the average initial tangent elastic modulus increases and the average initial tangent Poisson's ratio decreases. On the whole, the smaller the skeleton void ratio, the greater the strength and stiffness of the coarse-grained soil. Based on this, a scaling method of coarse-grained soil with equivalent skeleton void ratio is proposed in this paper.

Calcareous sand is a type of marine biogenic sand, which is the main material for the hydraulic filling of islands and reefs in the South China Sea. Studying dynamic characteristics of calcareous sand is of great significance to the development and utilization of resources in the South China Sea. In actual engineering, calcareous sand is mainly affected by wave loading that changes both in amplitude and principal stress direction. The effect of wave loading is quite different from that of fixed principal stress axes loading. Therefore, torsional shear apparatus that can simulate wave loading are used to carry out a series of undrained tests on saturated calcareous sand, mainly to study the influences of cyclic stress ratio (CSR) and relative density (D_r) on the characteristics of pore water pressure. The results are further compared with quartz sand, finding that differences in particle shape leads to the different pore water pressure development patterns between calcareous sand and quartz sand. In addition, the energy method is introduced to preliminarily examine the development of accumulated energy loss. On the basis, a model considering different relative densities is established to describe the relationship between pore water pressure and accumulated loss energy.

Salt caverns have good stability and air-tightness, and thus are ideal places for storage of natural gas, oil, hydrogen, etc. The oil blanket used in the conventional salt caverns created by solution mining has problems such as poor dissolution inhibition effect and heavy oil contamination, which cannot meet the requirements of green mine construction. As a substitute, gas blanket has attracted much attention. However, its application is hindered due to great difficulty in control, and the complex geological conditions of salt rock strata in China. To this end, the characteristics of gas blanket control at different cavern construction stages were analyzed first, and then the methods for predicting the thickness of gas blanket and calculating the gas injection amount at different stages were proposed based on the analysis of the pressure balance at the gas-liquid interface. Combined with an example of a well in the groove construction period, the recommended thickness of gas blanket and its fluctuation range were given, and the variation law of the gas blanket thickness and the gas injection amount with the cavern construction progress was proved. Finally, the key problems related to the application of gas blanket were discussed. The results showed that the gas blanket thickness is mainly controlled during the groove construction and roof formation periods, and the gas-liquid interface position is mainly controlled during the cavern construction and cavern repair periods. It is suggested that the average gas blanket thickness during the groove construction period should not be less than 0.3 m. The thickness of gas blanket fluctuates rapidly at the beginning of the groove construction period, and thus a larger gas blanket thickness should be set up and the nitrogen should be replenished in time. Then the gas blanket thickness tends to be stable, and the gas replenishment interval can be gradually extended. With the increase of cavern construction time, the single gas replenishment volume becomes larger and larger, and the cumulative gas replenishment volume increases linearly as a whole. During cavern construction, the wellhead gas pressure and the gas pressure at the gas-liquid interface increase first and then decrease linearly, and the wellhead gas pressure change shall be monitored in real time. The cost of gas blanket is close to that of oil blanket, but the environmental benefits are significant, and the discharged nitrogen and wellhead gas injection facilities can be reused to save costs. The position of gas-liquid interface should be monitored on site in real time by combining optical fiber monitoring and neutron logging.

Inorganic materials with strong compatibility and durability are widely used in the conservation of earthen sites, and those with especially loose structure has been the research focus of earthen sites reinforcement. Micro-nano Ca(OH)₂ has a range of characteristics, including small molecular structure, significant reinforcement effect and good durability. Take the UNESCO world heritage site at Suoyang City as an example, we prepared the loose soil samples with the density of 1.5 g/cm3, then, the samples are enforced by micro-nano Ca(OH)₂ suspension with concentration of 5%, 7.5% and 10%, respectively. Through the tests of air permeability, color difference, unconfined compressive strength and shear strength, it is found that the decrease value of air permeability is within 2%, and the color difference (ΔEab*) treated by 5% and 7.5% micro-nano Ca(OH)₂ suspension is less than 4, to certain degree, which is acceptable. The compressive strength and shear strength are improved after three rounds of reinforcement using the suspension with concentration of 7.5%. Meanwhile, the unconfined compressive strength increases by 9.8%, and the cohesion of soil increases by 34%. The internal friction angle grows up by 9°. The soil-water characteristic curve shows that micro-nano Ca(OH)₂ has a good inhibitory effect on the volumetric shrinkage of soil samples. The reinforcement mechanism is revealed by scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermogravimetric analysis. It is found a series of physicochemical reactions occurred in the alkaline environment after the treatment of micro-nano Ca(OH)₂. From the physical perspective, loose samples are enhanced by filling, wrapping, and mosaic. In terms of chemical perspective, the carbonation of calcium hydroxide forms new calcareous cements, which is the primary reason of reinforcement. This study reveals that micro-nano Ca(OH)₂ has potential for the anti-weathering and reinforcement of earthen sites.

The water retention characteristics of intact and remolded loess in full suction range were tested by combining pressure plate apparatus and vapor equilibrium method. The shear tests of intact and remolded loess under high suction were carried out by the unsaturated triaxial apparatus. At the same time, scanning electron microscope (SEM) and mercury injection apparatus (MIP) were used to conduct microscopic tests to investigate the influence of structural differences on the hydromechanical behavior of unsaturated loess. The test results show that with the increase of suction the degree of saturation and water content of intact and remolded loess decrease, and the void ratio decreases slightly as well. Since the initial void ratio of intact and remolded loess is almost the same, the total mercury intrusion volume of their mercury intrusion tests is close. The pore structure morphology and dominant pore size range of intact and remolded loess obtained from SEM and MIP tests are different, and the structural properties vary, resulting in different soil-water characteristic curve in different suction ranges. The stress-strain relationship of intact and remolded loess mostly displays softening, and the remolded loess with a suction of 3.29 MPa shows hardening behavior. With the increase of suction, the cohesion and peak strength of both the intact and remolded loess increase significantly, and the volumetric deformation changes from shear shrinkage to dilatancy. Because the intact soil has certain structure and strong cementation, the increased magnitude of its cohesion will be greater than that of the remodeled soil, and the peak strength will be higher than that of the remodeled soil, while the internal friction angle is basically the same.

A series of undrained dynamic triaxial tests is carried out to investigate the evolution patterns of pore water and accumulative dissipated energy during the vibration-induced liquefaction of saturated loess, and the effects of confining pressure, dynamic stress amplitude and consolidation stress ratio on them are discussed. The results show that the pore water pressure and dissipated energy of saturated loess gradually build-up with the increase of cyclic loading times during vibration-induced liquefaction. The consolidation confining pressure inhibits the increase of pore water pressure and consumes more energy. Larger dynamic stress amplitude leads to faster increase in pore water pressure and less energy consumption. Under the isotropic consolidation, the increase of pore water pressure causes the effective stress to be 0, thus triggering the initial liquefaction. However, under anisotropic consolidation, the specimen usually reaches the strain criterion for liquefaction first, while the pore water pressure does not increase to the confining pressure level, and the larger consolidation stress ratio leads to the lower pore water pressure and less cumulative dissipated energy during liquefaction. The pore water pressure is closely related to the cumulative dissipated energy, and normalized pore water pressure u/σ₀ and the cumulative dissipated energy W/W_f are less influenced by the confining pressure, dynamic stress amplitude and consolidation stress ratio and can be expressed uniformly in a hyperbolic model

The weakening of physical and mechanical properties of weathered granite often has a great impact on engineering stability. Therefore, it is of great significance to study the failure characteristics of granite with different weathering degrees. Combining the qualitative description of the core characteristics and the quantitative evaluation index of wave velocity ratio, the granite rocks collected from the reservoir area of Wuyue Pumped Storage Power Station in Henan Province were divided into three groups: slightly weathered granite, weakly weathered granite and strongly weathered granite. The fragments generated from granite rocks during uniaxial compression tests were collected, and their quality and scale characteristics were analyzed. Then, the corresponding relationship between fragment fractal dimension and wave velocity ratio was established. Meanwhile, the MATLAB software was employed to calculate the fractal dimension of the cracks on the main rupture surface. The results show that weathered granite rocks mainly produce coarse grain fragments and the proportion of fragments in coarse group gradually increases with the increase of weathering degree. Strongly weathered rocks produce blocky fragments in a small proportion and have a narrow range of the length-thickness ratio, indicating weak dynamic failure characteristics. Besides, their fragment shapes are single and mainly have plate-like structure. With the decrease of weathering degree, the proportions of blocky fragments increase and the dynamic failure characteristics become more apparent. The fractal dimensions of fragments have an increasing trend with the increase of the wave velocity ratio. Compared with the fragment quality, width and thickness, the fragment quantity and length are the main factors affecting the fractal dimension and are also the main parameters reflecting the fractal characteristics of granite with different weathering degrees. Moreover, the crack fractal dimensions of rupture surface for weakly and slightly weathered granite rocks increase significantly with the increase of wave velocity ratio, while for strongly weathered granite rocks there is no obvious change. It implies that the cracks of weakly and slightly weathered granite rocks have a higher degree of self-similarity, more complex structure and require more energy for their initiation and propagation

The structure of a rock mass directly controls its mechanical and hydraulic properties, and the distribution of rock block volumes can directly reflect the structural characteristics of the rock mass. Currently, many studies simplify the joint surfaces as planes and ignore the influence of roughness on the volume of rock blocks. In this study, the Hurst exponent (H) and root-mean-square height (Rq) were used to characterize joint roughness, and the influence of joint roughness on the quantity and volume distribution of rock blocks was investigated. The results show that: (1) H and Rq control the roughness of the joint, and the roughness increases with the increase of Rq and decreases with the increase of H; (2) the quantity of rock blocks is generally positively correlated with joint roughness, that is, it increases as the roughness increases; (3) the influence of Rq and H on the distribution of rock block volumes is mainly achieved by changing the proportion of small-volume blocks, and the mean and median volumes of rock blocks decrease as the roughness increases; (4) when the joints are orthogonal and spaced closely, the variation in the quantity of rock blocks can be divided into three stages with respect to the roughness: a stable stage, an initial growth stage, and a rapid growth stage, where Rq and H jointly control the relative distribution range of each interval. Finally, based on the data collected by photogrammetry, we establish a joint model of the rock mass, and study the distribution of rock block volumes in a slope along a certain highway in Dalian, which verifies the correctness of the above conclusions.

Through the plane charge loading test, the anti-explosion performance of different height-to-span ratio structures under explosion load of plane charge is studied. Based on the previous structural effect tests of intense explosion, the damage characteristics corresponding to different failure grades of supporting structures in hard rock under the action of intense explosion are analyzed. The macroscopic damage forms of structures with different height-to-span ratios are described in detail and the damage mechanism of structures is revealed. The test results indicate that the damage characteristics and damage grades of three types of structures with different height-to-span ratios vary under the same loading conditions. Firstly, in the structural test section with a height-to-span ratio of 1.17, extrusion and compression-shear damage occur at the arch, and there is a moderate blockage in the tunnel. The structural test section is severely damaged. Secondly, in the structural test section with a height-to-span ratio of 1.50, the arch foot produces a through compression-shear failure zone, and the straight wall is damaged by tensile stripping. The tunnel presents medium stripping, and a large amount of concrete accumulation is formed on the bottom plate. This structural test section is moderately damaged. Lastly, the structural test section with a height-to-span ratio of 1.00 is mainly damaged by splitting and stripping, with slight stripping in the tunnel and a small amount of concrete accumulation on the bottom plate. This structural test section is moderately damaged. The comprehensive analysis shows that the structural type with height-to-span ratio of 1.00 has the best anti-explosion performance.

The existing Masing-type nonlinear soil constitutive models encounter the problem of relatively complex loading-unloading rules (eg, the "extended Masing" rule) to describe the soil stress-strain hysteresis curve under the irregular cyclic loadings such as earthquakes. It will lead to a large number of state variables during the solution, which is inconvenient to be implemented. At the same time, the existing (improved) models primarily match the shear modulus reduction curves with the damping ratio curves rarely being matched. In this paper, to overcome the above problems, a new irregular loading-unloading rule is proposed based on modified damping. The rule overcomes the "upper boundary rules", and only the current reversal point and historical maximum (minimum) point need to be stored, which greatly reduces memory. Meanwhile, it accounts for the effect of soil shear modulus and the damping ratio curve simultaneously to modify damping ratio. Then, a new nonlinear constitutive model is proposed and implemented into the Abaqus software based on the Matasovic back-bone curve and the proposed loading-unloading rule. The correctness of the proposed loading-unloading rule is verified by comparing numerical results of the site seismic response of Mississippi Bay with the results calculated by the Deepsoil software where the Davidenkov Chen Zhao (DCZ) model is adopted. To further validate the practical applicability of the proposed model, the seismic response analysis of KSRH10 site of Japan KiK-net is conducted and compared with the record of acceleration time history and spectral acceleration.

In order to systematically study the densification mechanism of landslide dam material during rolling dynamic compaction, based on the self-designed model device for rolling dynamic compaction and particle image velocimetry technology, the effects of different construction parameters on the deformation and particle displacement of the landslide dam material foundation were studied. The test results showed that the rolling dynamic compaction process is a combination of impact and rolling. Due to the horizontal impact, the deformation of the foundation under the impact point is asymmetric. The combination of "high speed and low-weight roller" construction parameters would improve the impact effect, and weaken the compaction effect, resulting in poor surface smoothness of the foundation. The maximum displacement during the reinforcement occurred when the arc surface of the triangular impact wheel was in contact with the soil. Afterwards, due to the rise of the center of the impact wheel, the foundation appeared partially elastical rebound. The increase of roller speed promotes the impact energy transfer to the deeper depth, but the improvement width is limited. The increase of roller weight promotes energy transfer to both horizontal sides, but the improvement depth is limited. For the Yigong landslide dam material foundation in the model test, the optimal towing speed for the rolling dynamic compaction is about 0.75 m/s. The results could provide a theoretical basis for the reinforcement of impact rolling of the shallow layer of landslide dam foundation.

Based on the mechanism of hydraulic damage of the surface layer of ballastless track subgrade bed, a hydraulic damage control measure of setting polyurethane crushed stone waterproof bonding layer on the surface layer of subgrade bed is proposed. By establishing three groups of test models of graded crushed stone group (J-0), permeable polyurethane crushed stone group (J-5) and dense polyurethane crushed stone group (J-10), the static and dynamic characteristics, fatigue characteristics and waterproof characteristics of polyurethane crushed stone waterproof bonding layer are studied. The results show that the residual strain of J-10 is 2.6×10–6 under static loading and unloading, and the maximum displacement is about 1.0 mm. It has a good deformation adaptability with the surface layer of the subgrade bed and an obvious energy consumption. Under the action of the train dynamic load, it can reduce the amplitude of dynamic deformation and dynamic stress on the surface of the subgrade bed and increase the expansion range of dynamic stress. Under the action of the long-term dynamic cyclic load, the dynamic response of structural layer of J-0 and J-5 increases significantly after water injection, while the dynamic response of J-10 remains basically stable after 10 000–20 000 times loading. During the test, J-10 can effectively prevent water from entering the crushed stone layer on the surface of the subgrade bed, while water continuously infiltrates in J-0 and J-5, causing the erosion of fine particles of graded crushed stone. The research work has an important application value for the treatment of hydraulic damage on the surface of ballastless track subgrade bed in rainy areas.

With the rapid development of traffic infrastructure construction in western mountain area, the lining-stratum interaction mechanism of mountain tunnel under seismic effects has attracted increasing attentions. Based on the prototype of a regular two-lane highway tunnel section with V-grade surrounding rock, a static pushover model test for mountain tunnel was conducted. The variations of stratum displacement, stratum strain and ground pressure with pushover distance were carefully studied, and the lining-stratum interaction mechanism was thoroughly discussed. The test results show that: the lining-stratum interaction can be generally divided into compacting stage, overturning stage, and dragging stage. The stratum tends to circumferentially flow along the lining perimeter from the springing line in the overturning stage, and then drives the lining to shift together in the dragging stage. The stratum near the springing line experiences predominantly radial compression, forming a compression deformation zone, while the stratum near the lining shoulder mainly undergoes circumferential compression, forming a slip deformation zone. The response of the ground pressure on the left and right sides are exactly opposite. Specifically, the ground pressure in the compression deformation zone on the right side is greater than its counterpart on the left side, while the ground pressure in the slip deformation zone on the right side is less than its counterpart on the left side. These researches can provide some experimental basis and technical support for the anti-seismic calculation of mountain tunnels based on response displacement method.

The treatment of the hydraulic fill coral sand ground starts to attracted a lot of attentions with the development of marine island reef engineering. By using self-developed laboratory vibroflotation instruments, vibroflotation tests on of saturated coral sands ground are conducted to analyze dynamic response regularity during vibro-compaction, such as dynamic pore water pressure and horizontal earth pressure. The characteristics of settlement and relative density are also investigated. The results indicate that loose coral sands can be improved to medium density after two times of double-point vibro-compaction; meanwhile, the most obvious effect to relative density appears at the point where vibrator works, and the middle or deeper areas are better improved than the surface areas. The maximal excess pore water pressure appears at the stage of vibrator penetration. The excess pore water pressure starts to attenuate at the beginning of vibration retention. A significant descend of excess pore water pressure happens when vibrator starts to lift. The peak excess pore water pressure of the second penetration is obviously smaller than that of first penetration. The excess pore water pressure ratio contours exhibits parallel distribution during vibro-compaction. The shallow horizontal earth pressure of coral sands shows an increase with both penetration and extraction of vibrator, while the deep horizontal earth pressure presents a decrease.

The seepage of sandy foundation would lead to the collapse of foundation and the destruction of engineering structure. A series of large-scale sand column seepage model experiments war carried out by microorganism-bentonite combined mineralization method. The discussion in-depth was conducted for the effects of sand particle size, slurry liquid-solid ratio and treatment cycles on the permeability, internal erosion characteristic and bentonite and calcium carbonate precipitation distribution of sand. Moreover, the stability of sealing and the microstructure were thoroughly investigated and the treatment effect of microorganism-bentonite combined mineralization method was evaluated. It was found that this method could improve the seepage prevention effect and the stability of sealing of sand, and the permeability coefficient of samples could be reduced by up to 4 orders of magnitude. In addition, the erosion rate during the permeation process was also reduced by several times and reached as low as 0.51 g/(s·m²). Based on the effect of bentonite and calcium carbonate precipitation on sand sealing, the anti-seepage mechanism of microorganism-bentonite combined mineralization method was analyzed. The results show that the microorganism-bentonite combined mineralization method is feasible and efficient in the seepage control of sand, which will provide an important reference for the application of microbial mineralization technology to engineering anti-seepage problems.

A three-dimensional soil-water characteristic surface model considering deformation is established to study the effect of deformation on the soil-water characteristics and the hysteresis effect of unsaturated loess. It is established by first constructing a relationship between water content and pore ratio under constant suction conditions, and then introducing the effect of suction. The model can describe the change of water content with pore ratio and suction during wetting or drying of loess with different initial pore ratios. Wetting and drying tests on loess show that the water content under constant suction conditions is linearly related to the pore ratio, which verified the theoretical assumptions of the model. Additionally, soil-water characteristics of equal pore ratio state can be determined from the model, and by comparing them with the experimental results, it is found that the deformation caused by suction in the drying path has a greater influence on soil-water characteristics, which will reduce the characteristic parameters and suppress the hysteresis effect.

The existing multivariate composite foundation uses two or more kinds of piles to strengthen the foundation soil in order to improve the bearing capacity and accelerate the consolidation of the foundation. In this paper, a consolidation model of permeable concrete pile composite foundation, which has the advantages of both bulk material pile and rigid undrained pile, is proposed. In the practical project, the compression amount of rigid pile and soil is not equal, which is inconsistent with the equal strain condition. For this reason, this work abandons the traditional equal strain hypothesis, considers the amount of penetration of the pile to the cushion and underlying layer, and modifies the traditional equal strain hypothesis. At the same time, the parabolic change of horizontal permeability coefficient of soil in disturbed area and the blocking effect of fine particles on water seepage in permeable concrete pile are considered. Besides, the governing equation and solution of this kind of consolidation problem and the expression of consolidation degree of composite foundation are given. The solution of consolidation degree of composite foundation is also discussed. Finally, the solution of this work is compared with other composite foundation solutions, the consolidation behavior is analyzed, and the influence of pile resistance caused by pores of permeable concrete pile on the consolidation velocity of foundation is verified.

The deformation-bearing law of rock at the post-peak stage is of great significance to the stability control of the surrounding rock in the fragmented zone of the roadway. To study the rupture evolution and bearing characteristics at the post-peak stage of the rock, the uniaxial compression tests with different multiples of the peak strain value as the control strain were carried out on sandy mudstone, and the nonlinear fractal theory was applied to elucidate the distribution pattern of the post-peak ruptured masses. Based on the test results, a mechanical analytical model for rock samples containing penetrating fracture surfaces in the post-peak phase was established. The results show that: (1) The complete stress-strain curve of sandy mudstone presents two forms of post-peak stress drop, i.e. "single peak" and "multi-peak". (2) The post-peak specimen damage mode gradually changes from tensile damage under low-multiples peak strain to shear slip damage under high-multiples peak strain. (3) The fractal dimension of the internal fragments of the specimen is greater than that of the surface fragments for the same strain, and both of them have a significant positive correlation with the multiple of the post-peak strain of the specimen. (4) The continuous failure mode of rock at the post-peak stage is related to the characteristics of the contact fracture surface between fragments, and the fragments will only slide along the fracture surface within a certain dip angle range. The established analytical model can accurately explain the fracture-bearing characteristics and fragmentation distribution of the sandy mudstone at the post-peak stage.

Since two or more anti-seepage walls are usually required in the present design of dam foundation, the anisotropic steady-state seepage of dam foundation with anti-seepage walls at both ends is analytically studied in this paper. The soil is divided into four regular regions, the anisotropic soil layer is converted into the equivalent isotropic soil layer by coordinate transformation, and the water head distribution in the four regions is expressed as a series solution by using the separation variable method. The explicit analytical solution of the anisotropic seepage field of the dam foundation with anti-seepage walls at both ends is obtained by combining the continuity conditions between regions. The analytical solution in this paper is reduced to the seepage flow under isotropic conditions, the uplift pressure at the dam bottom, the analytical solution and numerical results of conformal transformation are compared. The head value under anisotropic conditions is compared with the calculation results of the finite element software. The results are in good agreement, which verifies the correctness of the analytical solution in this paper, and the analytic solution has a higher accuracy than the analytical solution of conformal transformation. Finally, a parametric analysis of the seepage field at the base of the dam shows that soil anisotropy has a non-negligible effect on seepage at the base of the dam, and that, all other things being equal, the seepage volume and outlet hydraulic gradient of a soil with a larger ratio of vertical to horizontal permeability coefficient will be smaller than those of a soil with a smaller ratio of vertical to horizontal permeability coefficient; the maximum lift pressure of a soil with a larger ratio of vertical to horizontal permeability coefficient will be larger than that of a soil with a smaller ratio of vertical to horizontal permeability coefficient.

To accurately evaluate the safety of foundation pit construction in soft soil area and its impact on the surroundings, the time and space influencing factors during excavation cannot be ignored. In this paper, based on the excavation of a deep foundation pit in the soft soil area of the Yangtze River floodplain, a 3D finite element model was established considering the combination of bottom-up and top-down constructions, and the calculated values of horizontal displacement of the diaphragm wall were compared with the measured values to verify the reliability of the finite element calculation. Based on theoretical analysis, numerical calculation and measured data, the influence coefficient of corner effect and equivalent horizontal resistance coefficient were used to measure the influence of spatio-temporal effect on the deformation of supporting wall, and the calculation method of the diaphragm wall deformation considering spatio-temporal effect was proposed. The necessity of the spatio-temporal effect and the rationality of the proposed method in the design of foundation pit in soft soil area were verified by engineering examples. The results can provide beneficial reference for the calculation of deep foundation pit deformation in soft soil area.

Since the mechanical behavior of the convex corner is complex due to surcharge near the excavation, it is of great importance to evaluate the influence of changes in strut position on the convex corner. Field monitoring and numerical simulations were used to analyze the influence law of the changes of strut position on the deformation and stress characteristics of the convex corner area. The axial force of inner strut, the lateral earth pressure on the pile, the horizontal displacement of the pile, the settlement of adjacent building and the bending moment of the pile were obtained. The research results show that the depth of strut position that is too high or too low is unfavorable to the coordinated deformation and the force of the retaining system. In contrast, the optimal strut position in this analysis is between 0.33 and 0.50 times the depth of the excavation (0.10–0.33 times the depth of the pile).

For the reliability analysis of rock tunnel stability, considering the difficulty in obtaining the statistical data on rock mass parameters, there is the potential inadequacy when using the probabilistic reliability method; on the other hand, the rock tunnel stability is intimately pertinent to a variety of failure modes, meaning it is necessary to consider the issue on structural system reliability. First, based on the interval theory, the uncertainty parameters were represented by adopting the interval variables. Subsequently, aiming at the coexistence of multiple failure modes in rock tunnel engineering, the concept of structural system reliability was introduced, and then a structural system reliability method to calculate the reliability index and assess the rock tunnel stability based on the non-probabilistic interval theory was established. On this basis, the rationality of the proposed method was verified via the engineering example. Finally, the fluctuation range of the uncertainty parameters was defined to further analyze the influence of different parameters in each failure mode on the corresponding reliability index and the system reliability index. The results show that the non-probabilistic reliability index of each failure mode decreases with the increase of the range of interval variables, and the same parameter in various failure modes causes different effects. In addition, the change of uncertainty parameters also leads to the variations in the main failure modes that affect the structural system stability of rock tunnel.

The shear strength vibration degradation of the rock discontinuities is of great significance to analyze and evaluate the dynamic stability of rock slope. Based on the rock dynamic test, the strength vibration degradation coefficient equation of the rock discontinuities affected by multiple factors was obtained. Then, combined with the limit equilibrium theory and the principle of dynamic vector method, the UDEC program was used for calculation, and its built-in Fish language was used to program to update the strength characteristic parameters of the rock discontinuities in real time and capture the seismic inertia force of slope at any time of earthquake duration, and the minimum average safety coefficient method was adopted to solve the final dynamic stability evaluation index. Thereby, a dynamic algorithm of slope dynamic stability coefficient considering the strength vibration degradation of the rock discontinuities was proposed. The results show that: (1) The strength vibration degradation coefficient of the rock discontinuities is a dynamic variable that depends on the response value of the number and amplitude of cyclic shearing and the relative motion speed between rock blocks. (2) The algorithm is applied to the calculation example of the dynamic stability of slope with the through-type and straight rock discontinuities. The analysis results show that in the dynamic action time history, the attenuation of the dynamic stability coefficient of slope considering the strength vibration degradation of the rock discontinuities is more obvious than that without considering the effect, i.e. the calculation results of the former are more in line with the actual observation, which verify the feasibility of the proposed algorithm. (3) The minimum strength vibration degradation coefficient of the rock discontinuities decays gradually in the form of negative exponential function with the time-history change of dynamic excitation. The larger the initial cohesion (internal friction angle) of the rock discontinuities is, the smaller the slope angle (layer inclination) or dynamic load amplitude (frequency) is, the larger the minimum dynamic stability coefficient of slope during the earthquake duration is, and the relatively stronger the final dynamic stability of slope is at this time.

Conical polycrystalline diamond compact (PDC) cutter is a new type of PDC cutter with high impact and wear resistance, which has a very good drilling effect in hard, strong abrasion, and soft-hard interbedded formations. In order to reveal the hard-rock breaking mechanism of conical PDC cutters, the laboratory test and numerical simulation on the granite broken by the conical PDC cutter were carried out. The influence law of cutting depth and front rake angle on cutting force and rock breaking specific energy of the conical PDC cutter was analyzed. In the laboratory test, a high-speed camera and transparent K9 glass were used to observe the formation process of cuttings and the initiation and propagation of microcracks under the action of conical PDC cutters. The stress response and damage evolution characteristics during the rock breaking process were analyzed by numerical simulation. The surface morphology and fracture microscopic characteristics of cutting grooves and large-size cuttings were analyzed, and the mechanical model of conical PDC cutters to break granite was established. The results show that the granite breaking process can be divided into two stages: crushing and chipping. The effect of the front rake angle on the rock breaking process is relatively small, while the influence of cutting depth is significant. The cracks around the conical PDC cutter are mainly composed of compaction nucleation, longitudinal crack and transverse crack. The maximum propagation depth of the longitudinal and transverse cracks is 6.69 and 4.53 times the cutting depth, respectively. The compressive stress around the cutter tip is concentrated, the shear-compression failure occurs, an arc-shaped strip-like tensile stress zone is formed at the periphery of the compressive stress zone, and the tensile micro-cracks are induced at the boundary of the cutter tip and compressive stress zone. When the micro-crack propagates to the front of conical PDC cutters to form an arc-shaped tensile main crack, the block debris cracking occurs, which improves the rock breaking efficiency. Meanwhile, the tensile micro-cracks propagate to the rock inside and deteriorate rock strength, a bottom damaged area is formed, which improves the rock breakage efficiency of the subsequent cutting.

To clarify the creep damage mechanism of rock mass under the periodic variation of reservoir water level in the hydro-fluctuation belt, by considering the weakening effect of the water-rock interaction on the bond and the variation of material properties with time, we proposed a new discrete element method based on the parallel bond model in particle flow code (PFC) and implemented the creep simulation of water-rock interaction based on laboratory tests. The results indicate that under the failure stress level, the micro-crack growth behavior of the samples is similar to the creep strain and it consists of three stages: attenuation growth stage, stable growth stage, and accelerated growth stage. The ratio of the accelerated growth stage’s time to the total time of the micro-crack growth process increases with the period of the water-rock interaction. When the sandstone is damaged in the creep process, the proportion of shear cracks gradually increases with the period of the water-rock interaction and the distribution of inclination angles of micro-crack gradually scatters. The micro-cracks in the areas near the inclination angles of 65° and 115° increase, the tensile strength of the samples weakens and the shear strength increases. Under the water-rock interaction, the maximum cementation energy stored in the samples decreases and the strain with the same cementation energy stored in the samples increases, which is consistent with the rules observed in the field that the overall bearing capacity of the rock mass decreases and the deformation of rock mass increases. Because the method is feasible to simulate sandstone creep process under water-rock interaction, the study can provide theoretical support for the model study of reservoir bank slope rocks under the influence of reservoir water level fluctuation.

The compaction degree is an important parameter for evaluating the quality of soil compaction in many engineering constructions such as roads, housing construction, and water conservancy project, and it correlates with moisture content and electrical conductivity. Frequency domain reflectometry (FDR) can rapidly measure soil moisture content and electrical conductivity. Firstly, in this research, FDR was adopted to rapidly measure the values of soil moisture content and electrical conductivity regarding lateritic soil, expansive soil, and loess at varying compaction degrees. Secondly, the measured values of moisture content were calibrated in laboratory, and the calibration curves of the three soils were obtained accordingly. Thirdly, empirical relationships between compaction degree, moisture content and conductivity of the three soils were established using the partial least squares regression (PLSR) analysis method, and compared with the measured value. Fourthly, scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) tests revealed its mechanism from microscopic aspect. Finally, the predicted value of the compaction degree obtained by the fitting equation was verified, and an error evaluation system was established. The results show that such fitting equations based on the relationship between compaction degree, moisture content, and electrical conductivity have a high prediction accuracy. Therefore, the results in this work can provide a good reference for the rapid detection of soil compaction in roads, housing construction, water conservancy and other projects.