State Key Laboratory for Geomechanics and Deep Underground Engineering

Strength and deformation behaviors of rockfill materials, key factors for determining the stability of dams, pertain strongly to the grain crushing characteristics. In this study, single-particle crushing tests were carried out on rockfill materials with nominal particle diameters of 2.5 mm, 5 mm and 10 mm to investigate the particle size effect on the single-particle strength and the relationship between the characteristic stress and probability of non-failure. Test data were found to be described by the Weibull distribution with the Weibull modulus of 3.24. Assemblies with uniform nominal grains were then subjected to one-dimensional compression tests at eight levels of vertical stress with a maximum of 100 MPa. The yield stress in one-dimensional compression tests increased with decreasing the particle size, which could be estimated from the single-particle crushing tests. The void ratio-vertical stress curve could be predicted by an exponential function. The particle size distribution curve increased obviously with applied stresses less than 16 MPa and gradually reached the ultimate fractal grading. The relative breakage index became constant with stress up to 64 MPa and was obtained from the ultimate grading at the fractal dimension (α=2.7). A hyperbolical function was also found useful for describing the relationship between the relative breakage index and input work during one-dimensional compression tests.

In this paper, a new technology combing the variational iterative method and an integral transform similar to Sumudu transform is proposed for the first time for solutions of diffusion and heat equations. The method is accurate and efficient in development of approximate solutions for the partial differential equations.

Since the 1960s, mining science and technology in China has experienced two technical innovations, i.e. the “Masonry Beam Theory (MBT)” and “Transfer Rock Beam Theory (TRBT)”. Based on those theories, the conventional mining method (being called the 121 mining method) was established, consisting of excavating two tunnels with a pillar left for mining a working panel. However, with increasing mining depth, engineering geological disasters in the underground caverns have been frequently encountered. In addition, the use of the coal-pillar mining results in a large amount of coal resources unexploited. In order to address the problems above, the “Roof Cut Short-Arm Beam Theory (RCSBT), being called the 110 mining method)” was proposed by He Manchao in 2008. The 110 mining method features the mining of one coal seam panel, excavating necessarily only one roadway tunnel and leaving no pillars. Realization of the 110 mining method includes the following steps: (1) directional pre-splitting roof cutting, (2) supporting the roof by using high Constant Resistance Large Deformation bolt/cable (CRLD), and (3) blocking gangue by hydraulic props. This paper presents an overview of the principles, techniques and application of the 110 mining method. Special emphasis is placed on the numerical simulation of the geostress distribution found in the mining panel using the 110 method compared to that of the 121 method. In addition, the stress distribution on the “short beam” left by the roof cutting when performing the 110 method was also investigated using both numerical simulation and theoretical formulation.

Aiming at soft rock ground support issues under conditions of high stress and long-term water immersion, the ground failure mechanism is revealed by taking the deep-water sumps of Jiulong Mine as the engineering background and employing field investigation, tests of rock structure, mechanical properties and mineral composition. The main factors leading to the surrounding rock failure include the high and complex stress state of the water sumps, high-clay content and water-weakened rock, and the unreasonable support design. In this paper, the broken and fractured rock mass near roadway opening is considered as ground small-structure, and deep stable rock mass as ground large-structure. A support technology focusing on cutting off the water, strengthening the small structure of the rock and transferring the large structure of the rock is proposed. The proposed support technology of interconnecting the large and small structures, based on high-strength bolts, high-stiffness shotcrete layer plugging water, strengthening the small structure with deep-hole grouting and shallow-hole grouting, high-pretensioned cables tensioned twice to make the large and small structures bearing the pressure evenly, channel-steel and high-pretensioned cables are used to control floor heave. The numerical simulation and field test show that this support system can control the rock deformation of the water sumps and provide technical support to similar roadway support designs.

In this paper we propose a new model for the fractional Maxwell fluid within fractional Caputo-Fabrizio derivative operator. We present the fractional Maxwell fluid in the differential form for the first time. The analytical results for the proposed model with the fractional Losada-Nieto integral operator are given to illustrate the efficiency of the fractional order operators to the line viscoelasticity.

Rockslides along a stepped failure surface have characteristics of stepped deformation characteristic and it is difficult to predict the failure time. In this study, the deformation characteristics and disaster prediction model of the Fengning granite rockslide were analyzed based on field surveys and monitoring data. To evaluate the stability, the shear strength parameters of the sliding surface were determined based on the back-propagation neural network and three-dimensional discrete element numerical method. Through the correlation analysis of deformation monitoring results with rainfall and blasting, it is shown that the landslide was triggered by excavation, rainfall, and blasting vibrations. The landslide displacement prediction model was established by using long short-term memory neural network (LSTM) based on the monitoring data, and the prediction results are compared with those using the BP model, SVM model and ARMA model. Results show that the LSTM model has strong advantages and good reliability for the stepped landslide deformation with short-term influence, and the predicted LSTM values were very consistent with the measured values, with a correlation coefficient of 0.977. Combined with the distribution characteristics of joints, the damage influence scope of the landslide was simulated by three-dimensional discrete element, which provides decision-making basis for disaster warning after slope instability. The method proposed in this paper can provide references for early warning and treatment of geological disasters.

We have derived explicit analytic formulas for the linear growth rate and the frequency in the combination of Kelvin–Helmholtz (KH) and Rayleigh–Taylor (RT) instabilities in fluids with continuous density and velocity profiles. It is found that the density gradient effect (i.e., the density transition layer) decreases the linear growth rate in the RT instability (RTI), especially for the short perturbation wavelength. The linear growth rate for the KH instability (KHI) is increased by the density gradient effect but decreased by the velocity gradient effect (i.e., the velocity transition layer). The frequency in the KHI is reduced by both the density gradient effect and the velocity gradient effect. In most cases, both the linear growth rate and the frequency are decreased by the combination of density and velocity transition layers, i.e., the combined effect of density and velocity gradients stabilizes the KHI. The density gradient effect has an opposite influence on the linear growth rates of the RTI and KHI. Therefore, in real system, there is a competition between the growths of the RTI and KHI which plays an important role in the material transport or mixture. If the widths of density and velocity transition layers have the same dimensionless values, the combined linear growth rate in the combination of KHI and RTI increases with the acceleration but decreases with the width of density (velocity) transition layer.

Strain-based condition evaluation has garnered as a crucial method for the structural health monitoring (SHM) of large-scale engineering structures. The use of traditional wired strain sensors becomes tedious and time-consuming due to their complex wiring operation, more workload, and instrumentation cost to collect sufficient data for condition state evaluation, especially for large-scale engineering structures. The advent of wireless and passive RFID technologies with high efficiency and inexpensive hardware equipment has brought a new era of next-generation intelligent strain monitoring systems for engineering structures. Thus, this study systematically summarizes the recent research progress of cutting-edge RFID strain sensing technologies. Firstly, this study introduces the importance of structural health monitoring and strain sensing. Then, RFID technology is demonstrated including RFID technology's basic working principle and system component composition. Further, the design and application of various kinds of RFID strain sensors in SHM are presented including passive RFID strain sensing technology, active RFID strain sensing technology, semi-passive RFID strain sensing technology, Ultra High-frequency RFID strain sensing technology, chipless RFID strain sensing technology, and wireless strain sensing based on multi-sensory RFID system, etc., expounding their advantages, disadvantages, and application status. To the authors' knowledge, the study initially provides a systematic comprehensive review of a suite of RFID strain sensing technology that has been developed in recent years within the context of structural health monitoring.

Abstract The understanding of the weakening mechanism of tensile strength of rock subjected to cyclic wetting-drying is critical for rock engineering. Tensile strength tests were conducted on a total of 35 sandstone specimens with different wetting-drying cycles. The crack propagation process and acoustic emission characteristics of the tested samples were obtained through a high-speed camera and acoustic emission system. The results indicate that the tensile strength is observably reduced after cyclic wetting-drying, and the extent of the reduction is not only related to the number of wetting-drying cycle, but also closely related to the clay mineral content of the sample. In addition, as the cycles of wetting-drying increase, the effect of each single cycle on tensile strength get reduced until it becomes constant. Moreover, the crack initiation and penetration time is prolonged as the number of wetting-drying cycle increases, which indicates that cyclic wetting-drying weakens the rock stiffness and enhances the ductility of sandstone. Meanwhile, the acoustic emission characteristics of the tested samples further confirmed the ductile behaviour of the sandstone samples with increasing wetting-drying cycle. Furthermore, through the analysis of the microstructure and mineral composition of the samples with different wetting-drying cycles, it is concluded that the main weakening mechanisms of sandstones containing clay minerals are frictional reduction, chemical and corrosive deterioration.

Toppling failure is a common instability mode for counter-inclined slopes, but the failure mechanisms involved present an ongoing engineering challenge in the geotechnical field. This study analyzes the instability failure mode of large-scale toppling failure at a counter-inclined slope on the southwestern stope of the Changshanhao open-pit gold mine. An instability failure is found here that mainly comes through two forms; one is the flexural-toppling and vertical fractures that form due to induced toppling failure at front-edge faults, the other one is bending-toppling failure and vertical fractures that form in trailing-edge steeply dipping faults. A simple mechanical mechanism for toppling failure is then established based on superimposed cantilever beam theory. By applying the maximum tensile stress strength criterion of brittle failure, a computational formula is derived for the depth to which vertical fractures extend in counter-inclined toppling failure, taking the effect of blasting vibration load into account. The relationship between the structural parameters of a cantilever beam slice and slope stability under blasting vibration are investigated. Geophysical evidence for the depth of fracturing and the related failure mechanism is then obtained using the transient surface wave method. The results of this geophysical prospecting indicate that it is feasible to simplify the rock formation as a cantilever beam slice and investigate the toppling failure of a counter-inclined rock slope under blasting vibration load using a quasi-static method. The applicability of the present research to this region is thus validated, indicating that this approach can also provide useful input for other similar engineering applications.

In recent years, with the increasing depth of coal mining around the world, traditional shallow geology mechanics are no longer suitable for the research on deep geological problems. In terms of deep mining, soft rock roadways in inclined rock formations show different deformation types compared with soft rock roadways in shallow horizontal strata. Based on the –1000 m track contact roadway in Qishan Mine of Xuzhou, physical model tests on the failure process of 45° and 60° inclined layered soft rock formations are carried out using physical models. The real-time monitoring of strain inside the model during the failure of soft rock formation is conducted to explore the failure mechanisms of 45° and 60° inclined layered soft rock formations in terms of in-depth high self-weight stress and horizontal tectonic stress. FLAC3D is also used for numerical simulation and comparative analysis. The roof and floor of the tunnels through 45° and 60° inclined formations fail on the left, and left and right walls fail near the bottom. The maximum displacement of the roof and floor of the 60° inclined formation is larger than that of the 45° inclined formation, and the maximum amount of deformation of left and right walls of the 45° inclined formation is larger than that of the 60° inclined formation, indicating failure features of different steeply inclined layered soft rocks roadways under high lithostatic stress and horizontal tectonic stress can provide a theoretical basis for mining and support of deep roadways.

In this paper, the interface width effects (i.e., the density gradient effects or the density transition layer effects) on the Rayleigh–Taylor instability (RTI) in the weakly nonlinear (WN) regime are investigated by numerical simulation (NS). It is found that the interface width effects dramatically influence the linear growth rate in the linear growth regime and the mode coupling process in the WN growth regime. First, the interface width effects decrease the linear growth rate of the RTI, particularly for the short perturbation wavelengths. Second, the interface width effects suppress (reduce) the third-order feedback to the fundamental mode, which induces the nonlinear saturation amplitude (NSA) to exceed the classical prediction, 0.1λ. The wider the density transition layer is, the larger the NSA is. The NSA in our NS can reach a half of its perturbation wavelength. Finally, the interface width effects suppress the generation and the growth of the second and the third harmonics. The ability to suppress the harmonics’ growth increases with the interface width but decreases with the perturbation wavelength. On the whole, in the WN regime, the interface width effects stabilize the RTI, except for an enhancement of the NSA, which is expected to improve the understanding of the formation mechanism for the astrophysical jets, and for the jetlike long spikes in the high energy density physics.

With the reduction of shallow resources, the degree of damage and the frequency of dynamic hazards, such as deep rock bursts and impact ground pressure, are increasing dramatically. However, the existing support materials are incapable of meeting the safety requirements of the refuges and roadways under a strong impact force. To effectively solve these problems, a novel negative Poisson's ratio (NPR) anchor cable with excellent properties, such as impact resistance and the ability to withstand large deformation, is proposed. In the present study, a series of field tests and numerical simulations are conducted to investigate the mechanical and support characteristics of NPR anchor cables under blast impact. Laboratory mechanical tests show that NPR anchor cables can maintain constant resistance and produce large deformation under the action of multiple drop hammer impacts. According to the results of field tests, the roadway supported by conventional anchor cables was unable to endure the blast impact, while the roadway supported by NPR anchor cables was able to withstand the severe impact equivalent to a Class 3 mine earthquake. The dynamic response of the NPR anchor cable that supports the roadway under explosion is investigated using the innovative coupled modeling approach that combines the finite element method and the discrete element method, and the support effect of the NPR anchor cable is verified. The study shows that the NPR anchor cable has a superior impact and blast resistance performance, and a broad application prospect in the support of chambers and roadways that are at high risk of rock bursts and impact ground pressure.

This study aims to investigate the effect of admixture glacial acetic acid on the setting time, compressive strength, and hydration temperature of magnesium phosphate cement.

The new Fourier-like integral transforms ?(?)= ? ???? ?(t)e-ikt dt, ?(?)= 1/????? ?(t)e-i?t dt, ?(?) 1/? ???? ?(t)e-it/? dt, ?(?)= ????? ?(t)e-it/? dt are addressed for the first time. They are used to handle a steady heat transfer equation. The proposed methods are efficient and accurate.

Abstract The changes associated with the cutting roof and release pressure mining method in the three zones that are susceptible to spontaneous combustion in the goaf with “Y” type ventilation system were studied. For the investigated underground coal mine working face, its three zones of spontaneous combustion have a “U” type ventilation system for the traditional mining method and a “Y” type ventilation system for the cutting roof and release pressure mining method. These systems were monitored using a beam tube method, and the evolution characteristics of spontaneous combustion of the three zones was analysed. The monitoring data showed that when using a traditional mining method with a “U” type ventilation system, the scattered tropical zone converts into the oxidation heating zone after 68.5 m in the goaf, and the suffocative zone presents after 85.5 m. For the cutting roof and release pressure mining method together with a “Y” type ventilation system, the scattered tropical zone converts into the oxidation heating zone after 84 m in the goaf, and the suffocative zone appears after 198.8 m. Compared to traditional mining, the width of the oxidation heating zone increases when using the cutting roof and release pressure method. To prevent spontaneous combustion of the goaf, the comprehensive techniques of the pressure balance for fire control, ground fissure sealing, working face sealing, retained roadways guniting and inert gas fire extinguishing have been used in the studied coal mine. The CO concentration of the goaf is less than 300 ppm during the mining process. Safe mining of the tested working face shows that the cutting roof and release pressure technique can be applied to control the coal seam spontaneous combustion.

Porosity and permeability of two typical sedimentary rocks in coal bearing strata of underground coal mines in China, i.e., mudrocks and fine-grained sandstones, were comprehensively investigated by multiple experimental methods. Measured porosity averages of the helium gas porosity (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M1"><mml:mrow><mml:msub><mml:mrow><mml:mi>φ</mml:mi></mml:mrow><mml:mrow><mml:mi>g</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>), MIP porosity (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M2"><mml:mrow><mml:msub><mml:mrow><mml:mi>φ</mml:mi></mml:mrow><mml:mrow><mml:mi mathvariant="normal">M</mml:mi><mml:mi mathvariant="normal">I</mml:mi><mml:mi mathvariant="normal">P</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>), water porosity (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M3"><mml:mrow><mml:msub><mml:mrow><mml:mi>φ</mml:mi></mml:mrow><mml:mrow><mml:mi>w</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>), and NMR porosity (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M4"><mml:mrow><mml:msub><mml:mrow><mml:mi>φ</mml:mi></mml:mrow><mml:mrow><mml:mi mathvariant="normal">N</mml:mi><mml:mi mathvariant="normal">M</mml:mi><mml:mi mathvariant="normal">R</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>) of the twelve investigated rock samples range from 1.78 to 16.50% and the measured gas permeabilities (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M5"><mml:mrow><mml:msub><mml:mrow><mml:mi>K</mml:mi></mml:mrow><mml:mrow><mml:mi>g</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>) range from 0.0003 to 2.4133 mD. Meanwhile, pore types, pore morphologies, and pore size distributions (PSD) were determined by focused ion beam scanning electron microscopy (FIB-SEM), mercury intrusion porosimetry (MIP), and low-field nuclear magnetic resonance (NMR). FIB-SEM image analyses showed that the mineral matrix pores including interparticle (interP) and intraparticle (intraP) pores with varied morphologies are the dominant pore types of the investigated rock samples while very few organic matter (OM) pores were observed. Results of the MIP and the full water-saturated NMR measurements showed that the PSD curves of the mudrock samples mostly present a unimodal pattern and nanopores with pore diameter less than 0.1 μ m are their predominant pore type, while the PSD curves of the fine-grained sandstone samples are featured by a bimodal distribution. Furthermore, comparison of the full water-saturated and irreducible-water-saturated NMR measurements indicated that pores in the mudrocks are solely adsorption pores (normally pore size &lt; 0.1 μ m) whereas apart from a fraction of adsorption pores, a large part of the pores in the sandstone sample with relatively high porosity are seepage pores (normally pore size &gt; 0.1 μ m). Moreover, the PSD curves of NMR quantitatively converted from the NMR <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M6"><mml:mrow><mml:msub><mml:mrow><mml:mi>T</mml:mi></mml:mrow><mml:mrow><mml:mn fontstyle="italic">2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math> spectra by <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M7"><mml:msub><mml:mrow><mml:mi>T</mml:mi></mml:mrow><mml:mrow><mml:mn fontstyle="italic">2</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mrow><mml:mi>P</mml:mi></mml:mrow><mml:mrow><mml:mi>c</mml:mi></mml:mrow></mml:msub></mml:math> and weighted arithmetic mean (WAM) methods are in good agreement with the PSD curves of MIP. Finally, the applicability of three classic permeability estimation models based on MIP and NMR data to the investigated rock samples was evaluated.

In this paper, we investigate general fractional derivatives with a non-singular power-law kernel. The anomalous diffusion models with non-singular power-law kernel are discussed in detail. The results are efficient for modelling the anomalous behaviors within the frameworks of the Riemann-Liouville and Liouville-Caputo general fractional derivatives.

A blasting experiment was conducted on iron ore samples by considering multiple coupling charge coefficients. The resulting internal fracture and damage characteristics were quantitatively analyzed via computerized tomography (CT), scanning, and three-dimensional (3D) model reconstruction. The results show that the iron ore primarily displayed radial and circumferential cracks along the blast hole under an explosive load. When the decoupling coefficient was small, the crack surface was dominated by transgranular fractures in the form of intracrystalline fractures. As the uncoupling coefficient increased, the crack surface exhibited transgranular and intergranular coupled fracture modes. Using fractal theory to analyze crack distribution characteristics, as the decoupled coefficient increased, the body fractal dimension tended to decrease, and the degree of damage gradually decreased. The degree of damage reached a turning point when the decoupling charge coefficient was approximately 1.33. A numerical simulation suggested that the explosion energy transmitted to the iron ore and the effective stress decrease sharply when the decoupling coefficient exceeds 1.33. In some optimal uncoupling coefficient range, excessive fragmentation of the ore body is prevented, thereby allowing full use of the explosive energy.

Differential synthetic aperture radar interferometry (D-InSAR) is characterized mainly by high spatial resolution and high accuracy over a wide coverage range. Because of its unique advantages, the technology is widely used for monitoring ground surface deformations. However, in coal mining areas, the ground surface can suffer large-scale collapses in short periods of time, leading to inaccuracies in D-InSAR results and limiting its use for monitoring mining subsidence. We propose a data-processing method that overcomes these disadvantages by combining D-InSAR with the probability integral method used for predicting mining subsidence. Five RadarSat-2 images over Fengfeng coal mine, China, were used to demonstrate the proposed method and assess its effectiveness. Using this method, surface deformation could be monitored over an area of thousands of square kilometers, and more than 50 regions affected by subsidence were identified. For Jiulong mine, nonlinear subsidence cumulative results were obtained for a time period from January 2011 to April 2011, and the maximum subsidence value reached up to 299 mm. Finally, the efficiency and applicability of the proposed method were verified by comparing with data from leveling surveying.