New Trends in Rock Materials Mechanics and Engineering Geology

The open excavation and concealed construction method is widely adopted for the construction of bias double-arch tunnels. However, the mechanical behavior of the tunnel during the whole construction period by using the open excavation and concealed construction method is not well understood, and the basis for construction organization and optimization is lacking. Based on an open-buried double-arch tunnel on Xiajuan Road, Changsha City, China, on-site monitoring was carried out in terms of the deformation of the steel arch in the primary lining, the stress of reinforcement in the secondary lining, and the deformation of the surrounding rock during the construction process. The correlation between the vault settlement rate and the steel arch strain was analyzed. The results show that the maximum vault settlement and settling rate of the left and right caverns occur at different locations due to different supporting conditions. The peripheral displacement experiences a process of convergence inward and extension outward. The compressive steel stress in the secondary lining of the right cavern is greater than that in the left cavern, except for the points at the arch waist. The backfill above the left cavern reduces the loading on the lining of the right cavern, but it increases the loading on the left cavern. The bias effect of the open-buried double-arch tunnel is well controlled and balanced when the open excavation and concealed construction method is adopted. Full article

Understanding the brittle fracture behavior of rock is crucial for engineering and Earth science. In this paper, based on acoustic emission (AE) and laser Doppler vibration (LDV) monitoring technology, the staged damage behaviors of rock-like materials with different brittleness degrees under uniaxial compression are studied via multiple parameters. The results show that the brittleness degree determines the fracture mode. As the specimen’s brittleness degree increases, the tensile failure increases and shear failure decreases. AE activity is enhanced at the crack damage point. With an increasing specimen brittleness degree, different instability precursor information is shown during the unstable crack growth stage: the AE b value changes from the fluctuating to continuously decreasing state, and the natural frequency changes from the stable fluctuation to upward fluctuation state. The AE b value near the stress drop is the smallest, and it decreases with an increasing brittleness degree. The natural frequency reduction indicates the rock-like fracture. The natural frequency is a symbolic index that reflects staged damage characteristics and predicts the amount of energy released by brittle failure. These findings provide guidelines for rock stability monitoring and provide support for better responses to stability evaluations of rock slopes, rock collapses, and tunnel surrounding rock in engineering. Full article

This paper focuses on a new test method and theoretical model for measuring and evaluating the reopening pressure during hot dry rock hydraulic fracturing. Firstly, rock blocks of four lithologies were collected from the hot dry rock strata. Hydraulic fracturing tests at high temperatures in real-time were conducted using drilled cubic specimens and drilled cubic specimens with a pre-crack. Breakdown pressure, reopening pressure, and fracture toughness were measured, respectively. In addition, Brazilian splitting tests at high temperatures in real-time were performed using Brazilian disc specimens to measure tensile strength. Secondly, an empirical equation for evaluating the reopening pressure during hot dry rock secondary fracturing was developed based on fracture mechanics and hydraulic fracturing theory. Third, the values calculated by the new equation, considering breakdown pressure, fracture toughness, and tensile strength, were compared to the values determined by the classical equation and to measurement results. It was found that the new equation predicted closer reopening pressure to the measurement results, regardless of the lithology of the hot dry rock. Moreover, with increasing temperature in the specimens, the error between the value calculated by the new equation and the measurement value remained low. In contrast, the difference between the classical equation predictions and the measurement results was widened. In addition, the reopening pressure was positively correlated with tensile strength and fracture toughness. Variations in lithology and temperature affected tensile strength and fracture toughness, which then changed the hot dry rock reopening pressure. Full article

The construction of the relation between the critical energy release rate, $G_{Ic}$, and the mode I fracture toughness, $K_{Ic}$, is of great significance for understanding the fracture mechanism and facilitating its application in engineering. In this study, fracture experiments using NSCB and CCCD specimens were conducted. The effects of specimen sizes, loading rate and lithology on the relation between $G_{Ic}$ and $K_{Ic}$ were studied. $G_{Ic}$was calculated by integrating the load–displacement curve according to Irwin’s approach. Based on the measured $K_{Ic}$ and $G_{Ic}$ of the rock specimens, a relation between $G_{Ic}$and $K_{Ic}$ was found to be different from the classical formula under linear elasticity. It was found that both specimen size and loading rate do not influence this relation. Full article

In order to study the deformation and failure characteristics of rocks under different cyclic loading and unloading paths, three stress path tests were conducted, and acoustic emission (AE) monitoring was conducted simultaneously. The mechanical characteristics and AE characteristics under different stress paths were analyzed, and the influences of the different stress paths on the energy dissipation and deformation damage were investigated. The law of energy evolution considering viscoelasticity under different stress paths was obtained. The concept of ultimate damage energy and its calculation method was proposed. The results show that the “hardening effect” of sandstone and granite under the constant lower limit (CLLCL) is the most significant in maximizing the mechanical property. The CLLCL imparts a stronger elastic property to rocks than the variable lower limit (VLLCL) does, while the VLLCL causes more damage to rocks than the CLLCL. A significant linear relationship between the proportion of damage energy and the proportion of elastic energy was discovered. Based on this linear relationship, the ultimate damage energy can be calculated for sandstone and granite. The evolution of the damage variable based on damage energy was compatible with the real damage condition, which validates the ultimate damage energy calculation method. The research results lay a theoretical foundation for the design and construction of geotechnical engineering. Full article

As an advanced spatial technology, topography-sensing technology is comprehensive, macroscopic, and intuitive. It shows unique advantages for rock structure interpretation and has important guiding significance for the research of the shear performances of rock–mortar interface under cyclic load in rock mass engineering. In this paper, cyclic shearing tests combined with the shear surface topography-sensing technology are employed to investigate the evolution characteristics of the interface morphology and the strength deterioration of the rock–mortar interface. Primarily, mortar and three types of rocks are used to prepare different rock–mortar interfaces, which are then applied to cyclic shear loading under two constant normal stresses. Subsequently, the shear strength degradation and dilatancy characteristics of rock–mortar interfaces with varying shear times are discussed. In addition, on the basis of the non-contact three-dimensional topography-sensing technology, the apparent three-dimensional point–cloud coordinate information of rock–mortar interface before and after each shear loading is obtained, and the apparent three-dimensional topography parameters of rock–mortar interface are calculated, according to which the influences of normal stress and lithology on the topography of interface subjected to cyclic shearing loading are analyzed. Full article

The excavation of hard rock roadways in coal mines is often in the environment of underground water and high ground temperature, and it is easy to be affected by the dynamic load, which leads to roadway destruction and increases the difficulty of roadway support. The ring sandstone specimens with different inner diameters (0~25 mm) were treated with temperature and water coupled, and the dynamic compression test was produced by the Hopkinson pressure rod device (SHPB). The experimental results indicate that the coupling effect of temperature and water reduces the dynamic performance of sandstone specimens. XRD test results showed that the composition of sandstone specimens did not change before and after warm water coupling, and no new substances were found. Dynamic properties of ring sandstone specimens with different inner diameters weaken with the increase in inner diameters. With the increasing inner diameter of ring sandstone specimens, the energy dissipation per unit volume increases the dynamic compressive strength decreases, and the degree of breakage increases. Fracture morphology, average strain rate, and dynamic peak strain of ring sandstone specimens increase with inner diameter. Full article

The rock or rock mass in engineering often contains joints, fractures, voids, and other defects, which are the root cause of local or overall failure. In response to most of the current constitutive models that fail to simulate the nonlinear fracture compaction deformation in the whole process of rock failure, especially brittle rocks, a piecewise constitutive model was proposed to represent the global constitutive relation of rocks in this study, which was composed of the fracture compaction empirical model and the damage statistical constitutive model. The fracture empirical compaction model was determined by fitting the expressions of fracture closure curves of various rocks, while the rock damage evolution equation was derived underpinned by the fracture growth. According to the effective stress concept and strain equivalence hypothesis, the rock damage constitutive model was deduced. The model parameters of the fracture compaction empirical model and damage statistical constitutive model were all calculated by the geometrical characteristics of the global axial stress–strain curve to guarantee that the models are continuous and smooth at the curve intersection, which is also simple and ready to program. Finally, the uniaxial compression test data and the triaxial compression test data of different rocks in previous studies were employed to validate the models, and the determination coefficient was used to measure the accuracy. The results showed great consistency between the model curves and test data, especially in the pre-peak stage. Full article

Lead–zinc tailings are the typical solid wastes in mines with high yield and low utilization rates in some countries at present. They are mainly stockpiled in tailings reservoirs, occupying massive land resources and threatening the health of the environment. One of the advantages of building material production in sustainability is the ability to utilize large amounts of industrial solid wastes, and the use of lead–zinc tailings in building materials is an effective way to meet the dual needs of environmental protection and economic development. This paper reviews the progress of utilizing lead–zinc tailings as building materials and mainly summarizes the status of lead–zinc tailings in cement, geopolymer, concrete, building brick, and foam ceramic. According to previous research, lead–zinc tailings contain large amounts of silica–alumina oxide, which can be used in the production of cement clinker. The addition of lead–zinc tailings to the sintered material can reduce the sintering temperature. The active components contained in lead–zinc tailings can be used in concrete instead of cement or in the preparation of geopolymers. Meanwhile, lead–zinc tailings can also be used as a fine aggregate. However, there are few studies on the durability of building materials with lead–zinc tailings. Additionally, most of the research results of building materials are in the laboratory stage, which are difficult to be promoted. In view of these problems, corresponding suggestions and prospects are given in the end in order to provide a reference for the research on the utilization of lead–zinc tailings. Full article

This paper takes the ZF3806 working face of Shuiliandong Coal Mine in Binxian County, Shaanxi Province as the engineering background. Aiming at the problems of the development of surrounding rock cracks and roof breakage encountered in the process of roadway excavation and support and based on the composite beam theory, the method of layered grouting reinforcement of roadways is proposed according to the deformation and failure of the roadway roof and the internal drilling conditions. At the same time, combined with the splitting grouting mechanism, the roadway is strengthened and supported by layered grouting of “shallow bolt grouting + deep cable grouting”. The “shallow” and “deep” form a complete and stable composite beam support structure. After grouting, the bending moments of “shallow” and “deep” support beams decrease by 20.78 × 10⁶ N·m and 26.50 × 10⁶ N·m, respectively. The support scheme is applied to the field test, and the grouting effect is analyzed and monitored. The research results show the layered grouting support scheme of “shallow bolt grouting + deep cable grouting” can significantly improve the structural integrity of the roadway roof. The displacement of the two sides is within the controllable range, and the support role of the bolt and cable is entirely played through grouting. The roof displacement of the roadway is reduced by 65% on average, and the bolt failure and steel belt fracture are significantly reduced, which effectively controls the deformation and damage of the roadway and reduces the maintenance cost of the roadway while ensuring safe mining. The study’s findings could be useful in treating broken surrounding rock in other coal mine roadways. Full article

Compared with other natural fibers, coir fiber has good strength characteristics and long-term anti-biodegradation ability. At present, most studies on randomly distributed coir fiber-reinforced soil have focused on cohesionless soil or granular soil. In this paper, the influence of randomly distributed coir fiber on the deviatoric stress and shear strength index of red clay with different fiber content was assessed by a consolidated undrained (CU) triaxial compression test. Since the hyperbolic variational character of the stress–strain relation of the samples conformed to the hyperbolic hypothesis of the Duncan–Chang model of nonlinear elastic model, the Duncan–Chang model was used to fit it, and the influences of fiber content and confining pressure on the parameters of the Duncan–Chang model were studied. The fiber content was determined by testing to be 0%, 0.2%, 0.25%, 0.3%, 0.35% and 0.4% of the dry soil mass. It has been found that coir fiber distributed in a random radial manner can significantly increase the deviatoric stress of red clay, and thus can be effectively used in the case of soil and fiber mixing. The cohesion of the red clay first increases and then decreases with the increase in fiber content, with an optimum content of 0.3%. The internal friction angle changes little with increasing fiber content. Full article

At present, the treatment of tailings is mostly carried out in the form of stacking in tailings ponds, resulting in a huge waste of mineral resources and a major threat to the environment and ecology. Using tailings instead of a part of the cement to make cementitious materials is an effective way to reduce the accumulation of tailings. In this paper, lead–zinc tailings-based cementitious materials were prepared by using lead–zinc tailings, fly ash, and ordinary Portland cement, and the effects of four factors on the mechanical properties of lead–zinc tailings, as well as fly ash content, cement content, and water–binder ratio were studied by orthogonal experiments. The corresponding relationship between the factors and the properties of cementitious materials was determined, and the optimization and prediction of the raw material ratio of lead–zinc tailings-based cementitious materials were realized. The test showed the ratio of raw materials to be at the lowest price ratio. Synchronously the ratio that meets the minimum strength requirements was predicted. When the proportion of fly ash:lead and zinc tailings:cement = 30:40:30 and the water–binder ratio was 0.4, the predicted compressive strength of the prepared cementitious material achieved 22.281 MPa, which meets the strength requirements, while the total content of lead–zinc tailings and fly ash was the highest at this time. Full article

In this paper, model tests on a plain soil slope and a bamboo-rooted slope under slope top loading were carried out to analyze the slope surface displacement, the change in earth pressure, and the failure mode of the slope. Furthermore, the influence of rainfall on the deformation and mechanical properties of bamboo-rooted slope sliding was studied. The results show that: (1) the failure mode of the plain soil slope was block sliding failure, while the failure mode of the bamboo-rooted slope was progressive backward failure. (2) Under the slope top load, the slope displacement shows the rule that the top of the slope was large and the foot of the slope was small. The presence of bamboo rhizomes had a negligible effect on the slope displacement, but it significantly contributed to the sliding area’s increase. (3) Compared with the plain soil slope, the earth pressure in the area of the foot of the slope under the same level of the load was elevated more obviously by the bamboo-rooted slope, which indicates that bamboo rhizomes could play a specific role in reinforcing the slope. Still, the scope of its influence was limited and mainly concentrated in the shallow soil. (4) There was a significant increase in the displacement of the bamboo-rooted slope under rainfall conditions, and the magnitude of the upward slope earth pressure was small in the process of step-by-step loading. The test results may have important guiding significance for the in-depth study of the instability law and disaster prevention in bamboo forest areas. Full article

In order to ascertain the concealed bedrock and its spatial distribution in an urban low-resistance coverage area of a typical lacustrine basin in Hunan Province, a multi-method comprehensive experimental study was carried out in Dingcheng District, Changde City where there are multiple sets of strata and fault structures. In this study, the wide-area electromagnetic method and microtremor survey were utilized on the basis of traditional methods, including the high-density resistivity method and controlled-source audio-frequency magnetotelluric method, to infer the concealed Cambrian limestone, fault structure, and vertical distribution of strata and the results were verified by drilling. The results indicate that the wide-area electromagnetic method is effective to explore the bedrock and concealed structure in urban geological survey. The microtremor method has an obvious effect on the detection of the Cretaceous and Quaternary silty strata within 100 m. The study may provide references for similar projects in this area. Full article

Considering sandstone’s heterogeneity in the mesoscale and homogeneity in the macroscale, it is very difficult to describe its time-dependent behavior under stress. The mesoscale heterogeneity can affect the initiation and propagation of cracks. Clusters of cracks have a strong influence on the formation of macroscale fractures. In order to investigate the influence of crack evolution on the formation of fractures during creep deformation, a time-dependent damage model is introduced in this paper. First, the instantaneous elastoplastic damage model of sandstone was built based on the elastoplastic theory of rock and the micro-heterogeneous characteristics of sandstone. A viscoelastic plastic creep damage model was established by combining the Nishihara model and the elastoplastic damage constitutive model. The proposed models have been validated by the results of corresponding analytical solutions. To help back up the model, some conventional constant strain rate tests and multi-step creep tests were carried out to analyze the time-dependent behavior of sandstone. The results show that the proposed damage model can not only reflect the time-dependent viscoelastic deformation characteristics of sandstone, but also provide a good fit to the viscoelastic plastic deformation characteristics of sandstone’s creep behavior. The damage model can also reproduce the propagation process of mesoscopic cracks in sandstone upon the damage and failure of micro-units. This research can provide an effective tool for studying the propagation of microscopic cracks in sandstone. Full article

Phyllite is widely distributed in nature, and it deserves to be studied considering rock engineering applications. In this study, uniaxial compression tests were conducted on foliated phyllite with different foliation angles under dry and water-saturated conditions. The impacts of water content and foliation angle on the stress–strain curves and basic mechanical properties of the Phyllite were analyzed. The experimental results indicate that the peak stress and peak strain decrease first and then increase with increasing foliation angle as a U-shape or V-shape, and the phyllite specimens are weakened significantly by the presence of water. Moreover, an approach with acoustic emission, digital image correlation, and scanning electron microscopic is employed to observe and analyze the macroscopic and mesoscopic failure process. The results show that tensile microcracks dominate during the progressive failure of phyllite, and their initiation, propagation, and coalescence are the main reasons for the failure of the phyllite specimens. The water acts on biotite and clay minerals that are main components of phyllite, and it contributes to the initiation, propagation, and coalescence of numerous microcracks. Finally, four failure modes are classified as followed: (a) for the specimens with small foliation angles α = 0° or 30° (Saturated), both shear sliding and tensile-split across the foliation planes; (b) for the specimens with low to medium foliation angles α = 30° (Dry) or 45°(Saturated), shear sliding dominates the foliation planes; (c) for the specimens with medium to high foliation angles α = 45° (Dry) or 60°, shear sliding dominates the foliation planes; (d) for the specimens with high foliation angles α = 90°, tensile-split dominates the foliation planes. Full article

Under conditions of low or medium stress, rocks that are in the compression state exhibit perceivable nonlinear elastic characteristics. After a comprehensive review of the existing nonlinear elastic models of rocks and joints, we proposed a new unified nonlinear elastic model. This new model contains two parameters with clear definitions, namely, the initial elastic modulus E_ni and the modulus change rate m. This model covers a variety of existing models, including the simple exponential model, BB model and two-part Hooke’s model, etc. Based on the RMT experimental system, a large number of uniaxial compression tests for dolomite, granite, limestone and sandstone were performed, and their nonlinear deformation stress‒strain curves were obtained and fit with the unified nonlinear elastic model. The results show that the rocks have obvious nonlinear elastic characteristics in their initial compression stage, and that the unified nonlinear elastic model is able to describe these phenomena rather well. In addition, an empirical formula for predicting the uniaxial compressive strength of the rock was constructed, corresponding to the unified nonlinear elastic model. Full article

Mining of closely spaced multilayer orebodies brings the problems of significant disturbance between adjacent mining layers and drastic structural changes in surrounding rock, which brings the need for a more effective stope support method. Previous research has made sound analysis on filling or bolt support, but neither of them can solely provide ideal support effects. Thus, a novel bolt-filling support method is proposed by utilizing the synergistic effect of rock bolts (cable bolts) and filling. Numerical simulation and similarity experiments were conducted in this research to analyze the support effect of this method for multilayer ore mining. For numerical simulation, the distinct-element modelling framework PFC2D (Particle Flow Code in 2 Dimensions) was applied for four support scenarios based on the calibration of the microscopic parameters of particles in vanadium shale ores. The numerical simulation results show that the number of fractures decreases from 1311 without support through 652 with 95% filling support to 410 with bolt-filling support, which is resulted from the redistribution of the force chains due to support change. On the other hand, a 300 cm ×180 cm × 40 cm similarity model with a geometry similarity constant of 100 was established based on the 4# rock layer profile of Mount Shangheng. Two parts of similarity experiments were conducted to investigate the strains around the stopes in multi-layer ore mining for three support scenarios. The experiment results prove that the highest strain is in the center of the roof on the upper goaf, and the roof-bolt filling support induces smaller strains than zero support and conventional filling support. Finally, an effective bolt-filling support system has been developed and validated, which can improve the safety and the stability of the roofs and interlayers during the mining process of closely spaced multilayer orebody by reducing the overall load and fractures in surrounding rock. Full article

Thin sandstone is a widely used building material; however, its compressive behavior is not well understood. Four groups of cylinders were manufactured in a factory to investigate the uniaxial compressive behavior of red sandstone. Uniaxial compression tests were performed to determine the compressive behavior and failure mode of the specimens. The geometry of the stress–strain diagram varied among the four groups. The critical strain generally increased with a decrease in the height of the cylinder, whereas the compressive strength exhibited an inverse trend. The experimental diagrams were normalized with the peak stress and corresponding critical strain to represent the stress–strain diagram of each group of cylinders. A formula consisting of two parabolas was employed for regression to obtain a representative mathematical expression of the diagram. The correlations between porosity, compressive strength, and elastic modulus were evaluated based on empirical expressions. Normalized strength was employed to evaluate the size effect on the diameter and length–diameter ratio (L/D) of the cylinder; the latter provided a better prediction of the experimental results than the former. A new expression in terms of L/D was proposed based on the regression analysis of the experimental results. This study is beneficial for the engineering application of sandstone as a construction material. Full article

Predicting the strength evolution of fiber-reinforced cement mortar under freeze-thaw cycles plays an important role in engineering stability evaluation. In this study, the microscopic pore distribution characteristics of fiber-reinforced cement mortar were obtained by using nuclear magnetic resonance (NMR) technology. The change trend of T₂ spectrum curve and porosity cumulative distribution curve showed that the freeze-thaw resistance of cement mortar increased first and then decreased with the fiber content. The optimal fiber content was approximately 0.5%. By conducting mechanical experiments, it is found that the uniaxial compressive strength (UCS) of the samples exhibited the ‘upward convex’ evolution trends with freeze-thaw cycles due to cement hydration, and based on fractal theory, the negative correlation between UCS and D_min was established. Eventually, a freeze-thaw strength prediction model considering both porosity and pore distribution was proposed, which could accurately predict the strength deterioration law of cement-based materials under freeze-thaw conditions. Full article

Previously conducted studies have established that gaseous water sorption of mudstone is widespread in nature. The deterioration of its uniaxial compression properties during gaseous water sorption can cause engineering problems. However, related studies were currently in the initial stage of this research direction. On the one hand, there were few studies on the deterioration characteristics of the uniaxial compression properties of mudstone in this process. The results might not be applicable to all projects. On the other hand, its microstructure changes in this process were unclear. Therefore, to obtain the deterioration characteristics of uniaxial compressive performance during gaseous water sorption for offering scientific reference to the geotechnical engineering of mudstone in the central Sichuan region of China, red-bed mudstone was used as a research material. A swelling test and uniaxial compression tests were carried out. To clarify microstructure changes for advancing the depth of research on the effects of gaseous water on mudstone, scanning electron microscopy (SEM) tests were performed. As a result of this study, formulas were first established that could correctly characterize the deterioration of uniaxial compressive strength (UCS) and elastic modulus when the moisture absorption rate increased. Secondly, the dependence was obtained, which was the relationship between both the UCS and elastic modulus and moisture absorption time. Finally, microstructure changes were revealed during gaseous water sorption. Full article

Reviewing literature revealed that the studies on the bearing characteristics of pile foundations mainly focuses on clay, ordinary sand, loess, saline soil, and other areas. However, few studies on the bearing characteristics of the pile foundation in calcareous sand were conducted. Besides, existing traditional studies ignored the variation of soil compression modulus with depth, and the effect of void ratio on the transverse bearing characteristics of the pile foundation in a calcareous sand area were not well understood. In response of these problems, this study conducted a theoretical investigation on the transverse bearing characteristics of the pile foundation in a calcareous sand area. The transverse bearing characteristics of the pile foundation were derived based on the Pasternak foundation model and the Winkler foundation model, incorporating the heterogeneous distribution of compressive modulus with buried depth. The calculation results of the Pasternak foundation model are closer to the observed results than the Winkler foundation model. Therefore, the following research on the transverse bearing characteristics of the pile foundation in the calcareous sand area adopts the Pasternak foundation model. Then, the effects of the pile length, pile diameter, pile elastic modulus, horizontal load, bending moment, and void ratio on the transverse bearing characteristics of the pile foundation in a calcareous sand area were thoroughly analyzed. Furthermore, the difference between the transverse bearing characteristics of the pile foundation in a calcareous sand area and a quartz sand area was discussed. Results show that the horizontal displacement of the pile top in a calcareous sand area is greater than the quartz sand area under the same conditions. Full article

Microseismic source location is the core of microseismic monitoring technology in coal mining; it is also the advantage of microseismic monitoring technology compared with other monitoring methods. The source location method directly determines the accuracy and stability of the source location results. Based on the problem of non-benign arrays of microseismic monitoring sensors in the coal mining process, a fast location method of microseismic source in coal mining based on the NM-PSO algorithm is proposed. The core idea of the NM-PSO algorithm is to use the particle swarm optimization (PSO) algorithm for global optimization, reduce the size of the solution space and provide the optimized initial value for the Nelder Mead simplex algorithm (NM), and then use the fast iteration characteristics of the NM algorithm to accelerate the convergence of the model. The NM-PSO algorithm is analyzed by an example and verified by the microseismic source location engineering. The NM-PSO algorithm has a significant improvement in the source location accuracy. The average location errors in all directions are (5.65 m, 5.01 m, and 7.21 m), all Within the acceptable range, and they showed good universality and stability. The proposed NM-PSO algorithm can provide a general fast seismic source localization method for different sensor array deployment methods, which significantly improves the stability and result in the accuracy of the seismic source localization algorithm and has good application value; this method can provide new ideas for research in microseismic localization in coal mining. Full article

By improving the ZWT model, a principal structure model applicable to both soft and hard materials under dynamic loading conditions was obtained. Dynamic mechanical experiments were conducted using SHPB to obtain stress–strain curves for coal rock and foam concrete. The ZWT intrinsic model was simplified according to the dynamic impact characteristics of concrete, and the intrinsic model was established by introducing macroscopic damage quantity D and correction factor δ. The stress–strain curves of coal rock, foamed concrete, steel fiber concrete, granite, lightweight foamed concrete, and EPS concrete at different strain rates were used to validate the present constitutive model and prove the correctness of the model. Full article

The rockburst simulation test is conducted by utilizing a mineral-containing marble specimen. The loading condition is set to the three directions, each loading on five surfaces except for a single free surface. The whole test procedure is monitored in real time by using a PCI-II acoustic emission monitoring system and a high-speed camera. According to the test outcomes, rockburst is a process in which energy is rapidly released from the free surface. Rock block and rock plate are buckled and ejected from the free surface and a severe rockburst process is accompanied by spray rock powder. An explosion sound can be heard during the process, which can be analyzed by signal processing techniques. The failure mode of the specimen is a splitting-shearing composite failure, and the free surface becomes a rockburst destruction surface. A V-type rockburst pit is formed in the ejection area. The effective acoustic emission signal of the whole test process is decomposed and reconstructed using five-layer wavelets to produce six frequency band sub-signals. In addition, the wavelet energy and its energy distribution coefficients are assessed for various frequency bands, and the proportion of each dominant frequency band within each period is computed. Finally, it was found that the dominant frequency band is 125~250 kHz, while the suboptimal frequency band is 250~500 kHz. The succeeding features are noticed to be used as predicted features for the rockburst disaster. Namely, acoustic emission signals arise in large numbers and the energy distribution coefficient of the dominant frequency band concentrates above 0.4. The proportion of dominant frequency band appears in continuous valley type and keeps below 80%, while the proportion of suboptimal frequency band appears in continuous peak type and keeps above 20%. Full article

The serrated structural plane is the basic unit of structural plane morphology. However, the understanding of its internal stress distribution, failure mode and crack evolution law was not clear enough in previous studies. In this paper, the shear mechanical properties of the serrated structural planes were studied by numerical simulation, and the crack evolution law of the serrated structural planes and the effects of four microscopic parameters on the shear properties were analyzed. The results show that: (1) the number of microcracks increases with the increase in normal stress; the crack expansion rate is slow before the shear stress reaches the peak. After the shear stress reaches the peak, the crack expansion rate continues to increase, and the microcracks keep sprouting and expanding, and the number of microcracks tends to stabilize when the shear stress reaches the residual shear strength. (2) The particle contact stiffness ratio $k_n{}^{\ast }/k_s{}^{\ast }$ and parallel bond stiffness ratio $k_n/k_s$ were negatively correlated with the shear strength; and the particle contact modulus $E$ and parallel bond modulus $E^{\ast }$ were positively correlated with the shear strength. As the particle contact modulus $E$ and parallel bond modulus $E^{\ast }$ increase, the peak shear displacement gradually decreases. The parallel bond stiffness ratio $k_n/k_s$ has a negative correlation with the peak shear displacement. This study is expected to provide theoretical guidance for the microscopic parameter calibration and shear mechanical analysis of serrated structural planes. (3) Several XGBoost, WOA-XGBoost, and PSO-XGBoost algorithms are introduced to construct the quantitative prediction model, and the comparative analysis found that WOA-XGBoost has the best fitting effect and can be used for the prediction of shear strength. When using this model to calculate the weight shares of micro-parameters, it was found that $k_n{}^{\ast }/k_s{}^{\ast }$ has the greatest influence on shear strength, followed by $E^{\ast }$; $E$ and $k_n/k_s$ had the least influence. Full article

This paper analyses the deformation and force behavior of a wood-piled island cofferdam based on the principle of equivalent bending stiffness. The horizontal deformation and bending moments in wood piles and the axial stress in tension bars on top of piles were both analyzed by the finite difference (FD) method. Except for the analysis of the cofferdam construction process, the influence of the pile length, the dam width, the tension bar interval, and the pile interval, among the commonly adopted parameters, were detailly examined in numerical simulations. In addition, a reinforced wood-piled cofferdam model by steel pipe piles has been established to quantify the effect of reinforcement. It was found that the dewatering inside the cofferdam was detrimental to cofferdam stability. The pile deformation reached maxima (roughly 0.6% of the pile length) at solidifying stage after dewatering. The changing trend of the cofferdam structure force within a safe district was consistent with the displacement. The dam width had a vital effect on the stability of the cofferdam, especially on the horizontal deformation. The steel pipe pile reinforcement scheme performed better in further deformation control, providing a new idea for island-type cofferdams with rigorous structural deformation control. Full article

Energy sustainability represents an important research topic for aiding decreasing energy dependence and slowing down climate changes. In this context, solutions using thermal energy storage through rock start to emerge, due to its natural benefits, when compared to more polluting alternatives. To understand whether a rock material can be considered a good thermal energy storage material for such solutions, it is necessary to evaluate the physical, chemical and thermal properties of such materials. Therefore, it becomes essential to understand how heat propagates in the rock and how voids influence the thermal properties. To achieve these goals, hematite ore from Moncorvo, Northeastern Portugal was used, in particular, to study the effect of grain size on thermal properties for three different sized lots. Chemical and physical changes between heated and unheated lots were detected using X-ray diffraction and particle size, as well as X-ray fluorescence analysis. Regarding thermal properties, a hot wire method approach was used with seven thermocouples. Additionally, a thermal inversion model to simulate the heat exchanges was also proposed, allowing changing the properties of the constituents, to fit the theoretical and experimental temperature curve. Furthermore, the model reveals how heat propagates inside the reservoir filled with hematite ore. Full article

The interface problem exists widely in building. Joints are interfaces of rock mass structures. To further study the influence of morphological characteristics on the shear mechanical properties of sawtooth joints, this paper prepared rock-like materials based on the similarity principle and carried out direct shear tests of sawtooth joints. The results showed that: (1) the peak shear displacement of joints first increases and then decreases with increasing normal stress, but the normal trend of stress during turning is different under different sawtooth angles. When the sawtooth angle of the joints is small, the decrease in shear stress between shear strength and residual shear strength is not obvious, and the rate of decrease is also small. (2) The shear strength of joints is positively correlated with normal stress. Using the Mohr–Coulomb criterion to analyze the shear strength of joints, it was found that the cohesion c and internal friction angle α of joints increased nonlinearly with increasing sawtooth angle, but their increasing trends were different. By introducing the function relation between cohesion, internal friction angle, and sawtooth angle into the classical shear strength equation, an empirical equation for the shear strength of joints was established in consideration of sawtooth angle. (3) There are two modes of shear failure for serrated joints: the “saw-toothed sliding gnawing failure mechanism” (SSG) and the “tensile fracture mechanism” (TFM). In the SSG, the shear failure mode of joints evolves in a slipping–gnawing–complete gnawing mechanism with increasing sawtooth angle and normal stress. The TFM mainly occurs at high sawtooth angles. This study provides a theoretical reference for the prediction and prevention of geological disasters. Full article

In recent years, heavy rain and waterlogging accidents in subway stations have occurred many times around the world. With the comprehensive development trend of underground space, the accidents caused by flood flow intruding complex subway stations and other underground complexes in extreme precipitation disasters will be lead to more serious casualties and property damage. Therefore, it is necessary to conduct numerical simulation of flood intrusion process under malfunction of flood retaining facilities in complex subway stations. In order to prevent floods from intruding subway stations and explore coping strategies, in this study, the simulation method was used to study the entire process of flood intrusion into complex subway stations when the flood retaining facilities fail in extreme rain and flood disasters that occur once-in-a-century. The three-dimensional numerical simulation model was constructed by taking a subway interchange station with a property development floor in Nanning as a prototype. Based on the Volume of Fluid (VOF) model method, the inundated area in the subway station during the process of flood intrusion from the beginning to the basic stability was simulated, and it was found that the property development floor has serious large-scale water accumulation under extreme rainfall conditions. Through the dynamic monitoring of the flood water level depth at important positions such as the entrances of the evacuation passages, and the analysis of the influence of the design structure and location distribution of different passages on the personnel evacuation plan, it was found that the deep water accumulation at the entrances of the narrow, long, and multi-run emergency safety passages are not conducive to the evacuation of personnel. Finally, the flow of flood water into the subway tunnel through the subway station was calculated. The research results provide certain reference and guidance for the safety design of subway stations under extreme rainfall climatic conditions. Full article

Rock mass, the heterogeneous natural material composed of rock and discontinuities, is an important part of engineering construction. Discontinuities affect the mechanical properties of natural rock mass and further threaten the stability of rock engineering. To study the failure characteristics of anchored structure plane with different JRC, jointed specimens with four different JRC were fabricated by pouring cement mortar. Specimens were tested under four different normal loads to figure out how JRC and anchorage angle affect the mechanical properties of anchored structure plane. Besides, acoustic emission (AE) testing technology was adopted to explore the AE characteristics of anchored structural plane under shearing. The results showed that there exists a positive correlation between the peak shear strength and JRC. The undulation shape of structural plane led to an obvious downward trend in the strain softening stage of the structural plane with JRC of 6–8 and 18–20. When the anchorage angle ranged from 45° to 60°, the potentiation of bolt was the most significant. Based on the AE results, the larger the normal stress, the more likely the cumulative count curves were to enter the fast growth phase before the peak. The characteristics of b-value curves are mainly related to the topography of structural planes and whether the bolt is deformed. In the direct shear test, the cumulative proportion of shear cracks was more than 85%, which is much higher than that of tensile cracks. The variation of cumulative tensile cracks goes through three stages: slow growth, rapid growth, and slow growth. Compared with the unanchored structural plane, the variation range of real-time tensile cracks of the anchored structural plane is large, and sometimes the proportion of real-time tensile cracks may reach 80%. Full article

High uncertainty is an inherent behavior of geotechnical materials. Nowadays, random field theory is an advanced method to quantify the effect of high uncertainty on geotechnical engineering. This study investigates the effect of spatial variable soil layers on deformations of deep excavation via the random finite element method. A procedure based on PLAXIS 2D software was developed to generate two-dimension random finite element models including multiple variables. Via the K-S test and S-W test, the excavation deformations basically followed lognormal distribution. With the growth of standard deviation of soil properties parameters, the distribution of excavation deformations becomes wider, and the failure probability increases. When the vertical scale of fluctuation ranges from 1 m to 25 m, the distribution of excavation deformations becomes wider. To analyze system reliability, this study proposed a fitted multiple lognormal distribution methods, which was a method with higher efficiency. The results indicated that system reliability was lower than single failure probability and sensitive to design level. The system failure probability will be over-evaluated or under-evaluated if the correlation between excavation responses is ignored. This study provided a novel method to quantify the effect of high uncertainty of soil layer on excavation responses and proposed an efficient method for system reliability analysis, which is meaningful for excavation reliability design. Full article

The stability of the interface between mortar and rock is very important in engineering construction. In this paper, the all-digital acoustic emission (AE) system is used to detect the direct shear test of the mortar-rock binary medium interface with different sawtooth angles under different normal stress states. The stress-displacement information and AE signal during the whole shearing process are extracted. The coupling relationship between stress and AE characteristic parameters is discussed. The quantitative relationship between sawtooth angle and shear strength of binary medium is established, and three AE characteristic parameters that can be used to predict structural instability are proposed. The research shows that: With the increase of the normal stress and the sawtooth angle, the shear strength of the mortar-rock binary medium increases. The relationship of that is obtained by least squares fitting. The shear stress-displacement curve is divided into five stages according to the change of deformation law. Through the analysis of AE characteristic parameters, it is found that increasing the sawtooth angle makes the AE count and AE cumulative count increase. Based on the analysis of the characteristic parameters of RA-AF, the changes of shear cracks and tensile cracks within the whole shearing process were obtained, respectively. In the process of binary medium shearing, the AE peak frequency is in the range of 120–340 kHz. Three acoustic emission parameters that can predict the macroscopic damage of binary media are obtained: the AE b value, the ratio of shear crack signals, and the number of signals with a peak frequency of 220 Hz to 320 Hz. Full article

In order to improve the impact resistance mechanical properties of bolt, the requirements of rock burst roadway support must be met. Based on the requirements that the anchor should have a reasonable deformation load threshold, high stroke efficiency, constant reaction force and stable repeatable deformation damage mode. A constant resistance anti-impact device was designed, and a new constant resistance energy-absorbing impact anchor rod was designed in combination with a conventional anchor rod, and the working principle of a constant resistance energy-absorbing impact anchor rod was given. ABAQUS finite element software was used to analyze the mechanical properties of bolt and the results showed that the constant resistance energy-absorbing anti-shock anchor has a stable and repeatable deformation damage mode under both static and impact loads, and the three indexes of the constant resistance energy-absorbing anti-shock anchor, such as yield distance, impact resistance time and energy absorption, are significantly better than those of the conventional anchor. The impact energy and impact velocity have less influence on the load-bearing capacity and stroke efficiency of the impact device. The impact velocity has less influence on the indices of the rod yield load, breaking load, absorbed energy and the yield distance of a conventional anchor and constant resistance energy-absorbing anti-stroke anchor, and the impact resistance time decreases non-linearly with the increase in the impact velocity. Full article