查看更多>>摘要：? 2022Underground coal mining is characterized by the formation of extensive pillars. Coal pillars serve various purposes, and their instability failure characteristics play a vital role in safety mining. Considerable studies have been conducted over the last few decades on pillar instability and failure analyses. It was concluded that pillar failure for system instability is governed by both the strength of the pillars and the load acting on the pillars. There are several methodologies to evaluate pillar failure for instability; however, each method has its own applicable conditions, and none of them are applicable to all circumstances. This study focuses on methodologies (theoretical models, numerical simulations, and field measurements) for estimating pillar system loads and strengths. In the theoretical model, pillar failure criteria are significant factors for calculating coal pillar strength, and the primary factors for instability evaluation are noted. The general steps of the numerical simulation methods are summarized and analyzed. The finite element method is the most widely used method, whereas the discrete element method has become popular in recent years. Pillar stress, deformation, and fracture development are the main concerns when assessing pillar failure characteristics in field measurements. Finally, we list primary study interests (pillar failure analysis in abandoned and deep coal mines) on coal pillar failure analysis in future studies based on the development of underground coal mining.
查看更多>>摘要：? 2022 Elsevier LtdIn the present work, an improved smooth particle hydrodynamic (SPH) method is proposed for flow process and mechanism simulation of debris avalanche in mining waste dump. In this method, a modified stable kernel function for SPH is constructed, by which the compression stability can be easily achieved. Also, an adaptive smooth length scheme is proposed to overcome instability and inaccuracy caused by the large difference of neighboring particle numbers at different locations. Based on this theory, a fast particle search method is developed to march this changing smooth length and a modified cam-clay model is employed into SPH. Taking No. 2 waste dump in Nanfen iron mine as an example, the catastrophe scale and the impact scope are analyzed by the proposed method, and the accuracy of the proposed method is verified by field-measured data in a slippery event. The model is calibrated with the scale of damage, sliding range and flow accumulation form, especially the sliding distance. Moreover, the evolutionary mechanism of the long-distance landslide in the dump is investigated. Via parameters obtained by analogy, the sliding process and sliding speed are predicted for Heigou waste dump in Jingtieshan iron mine. Furthermore, influencing factors such as interface roughness and flow path are analyzed and the sliding influencing range and impact speed on the barrage dam are studied, which shows that the impacts on some dams exceed the design impact. Finally, based on those simulations, the prevention and mitigation countermeasures of Heigou waste dump are suggested.
查看更多>>摘要：? 2022 Elsevier LtdShale and coal samples were selected to clarify the tensile failure of layered sorptive rocks under the co-influence of bedding planes and loading conditions. Results indicate that, for these two rocks, tensile strength exhibited anisotropy. As loading rates rises, inverted Trumpet-shaped trend lines is proposed to reflect bedding effects with loading effects. The tensile strength of shale increases linearly with the bedding angle rises, while the value of coal shows great dispersion. The former is greater than the latter. An ultimate loading rate exists for shale and coal. Empirical relations were established to describe tensile strength with varying loading rate and bedding angle. Under the co-influences of bedding plane and loading conditions, more complex failure modes happened for coal and shale samples. Hydraulic fracturing along the direction of 60° (for shale reservoirs) or 45° (for coal reservoirs) to the bedding plane is more likely to produce a complex fracture network.
查看更多>>摘要：? 2022The effect of mechanical heterogeneity on the low cycle fatigue (LCF) properties of a 9–12% Cr martensitic steel welded joint with Ni-based weld metal are studied using smooth and hourglass specimens based on a local strain approach. The results indicate that the smooth specimens of the welded joint fracture at the softened weld metal (WM) due to the strain concentration. Moreover, the strain–life curves of the smooth specimens of the welded joint are close to the strain–life curves of the WM smooth specimens after the local strain approach considering the mechanical heterogeneity of welded joints is adopted. The LCF properties of the inter-critically heat-affected zone (ICHAZ) are obtained through hourglass specimens based on the local strain approach. The LCF properties of the base metal (BM), WM, and ICHAZ in the welded joint are compared to investigate the relationships of the LCF properties of the welded joint and different microzones.
查看更多>>摘要：? 2022 Elsevier LtdMost of urban ground collapses and tunnel failures are caused by joint leakage of shield tunnel lining. This paper conducts a series of model tests and particle flow simulations aiming to investigate the geo-hazards and explore the associated failure mechanism due to tunnel leaking. Based on critical width of leaky joint, taking leaky joint location, overburden depth and height of overlying water level as influencing factors, the settlement of the sand layer and the law of the water and sand loss is effectively predicted. Then, the focus is on designing a seepage tracer device to explore the distribution of the seepage field and its flow line variation. Finally, the particle flow numerical model of tunnel-sand is employed for the soil arching effect and flow line changes during seepage erosion to discover the fine scale influences of sand particle migration and loss around the shield tunnel on the surrounding environment.
查看更多>>摘要：? 2022 Elsevier LtdThe present research aims to figure out the impact of setting accelerators on calcium leaching utilizing a hybrid decision-making method termed entropy weight – technique for order preference by similarity to an ideal solution (EW-TOPSIS). To fulfill this objective, a model test device was developed to carry out the experiment of calcium leaching in sprayed concrete. Three different types of setting accelerators were considered as the control variables in the experiment. Then, Ca2+ ions concentration, pH value, and flow of drainage solution were considered as indicators to evaluate the effect of each setting accelerator on calcium leaching. Meanwhile, the relationship between the three indicators was analyzed using the response surface method (RSM). Findings showed that relatively high dosing of setting accelerators had an inhibitory effect on calcium leaching of sprayed concrete. Additionally, the environment with a high pH value is more potential to experience calcium leaching.
查看更多>>摘要：? 2022 Elsevier LtdRevealing the mechanism of sand gushing triggered by failure of tunnel face in water-rich sandy dolomite strata contributes to the safe construction of tunnels. In this paper, we find that sandy dolomite and the water environment are the key factors causing sand gushing through geophysical prospecting at the tunnel face where 12,000 m3 sand surge occurred. Through the flow-solid coupling model, the extrusion deformation at the tunnel face is the main deformation form in the tunnel of water-rich sandy dolomite strata. The influence of different factors on the deformation value of the tunnel face is from strong to weak: sandification degree, head height, and tunnel depth. Combined with the study of pressure arch characteristics of the model, the limit equilibrium theory considering seepage effects and pressure arch characteristics is proposed. We get that sand gushing will occur in the tunnel in the intensively sandy dolomite strata where the head exceeds 80 m. For the intensively sandy dolomite strata with head below 80 m, the stability of the tunnel face is controlled by the degree of seepage damage. According to the reason of sand gushing, the comprehensive control measures consisting of risk identification by over-detection, double-layer close-packed pipe shed, grouting sealing technology and dewatering technology, and Milling and blasting combined construction method are proposed, and the effective control of tunnel working face is realized in practical application.
查看更多>>摘要：? 2022 Elsevier LtdThe large deformation is a common engineering problem during tunnel excavation. For brittle rock tunnels, the large deformation is closely related to the rock mass structure. In this study, taking the Guanshan tunnel as an example, large deformation of a deep-buried brittle rock tunnel in a strong tectonic active area was analyzed. The large deformation was explained in terms of the surrounding rock (diorite) mechanical properties and the development and evolution of macro and microcracks. The results showed that the diorite in the Guanshan mountain is characterized by high strength and brittleness. However, numerous microcracks are developed in the diorite, which can easily induce a cataclastic brittle failure of the surrounding rock by the transformation of the stress field. In terms of the spatial distribution, the macro and microcracks in the surrounding rock have a good unified relationship, whose development mechanism is related to strong tectonic activity. The stress environment of the surrounding rock changed during the tunnel excavation. A borehole camera revealed that the large deformation of the Guanshan tunnel is synthetically influenced by the macro and microcracks in the surrounding rock. The deformation includes the relaxation of the original macrocracks, fracture of the microcracks, and rock dilatation caused by the opening of the microcracks, among which the fracture of microcracks is the dominance. This study provides a new concept for analyzing large deformation in brittle rock tunnels, indicating that the negative effects on the stability of the surrounding rock induced by the development and evolution of microcracks should be fully considered in strong tectonic active areas.
查看更多>>摘要：? 2022This study describes an investigation of the load–deflection response of the material used for production of polymeric pipes. Three point bending tests were performed on curved pipe samples to evaluate their flexural properties, namely the flexural strength, the modulus, the strain to failure and the mode of failure. Effects of various configurations and parameters are investigated: effect of internal or external loading, effect of notch, impact of aging, combined effect of notch and aging. In addition, FE models are established to predict pipe material response under flexural loading. From the main results, the average flexural stress–strain response of pipe material is characterized by a linear portion curve, followed by a non-linear deformation up to the ultimate failure stress. A ductile behavior was observed, but with a brutal rupture at the peak flexural stress. The flexure behavior of the pipe material depends also on the configuration, and it behaves differently under internal and external loading. The presence of notch in pipe material reduces its mechanical performance. A significant decrease of flexural properties was observed for hydrothermal aged pipe samples. The combined effect of both hydrothermal aging and notch affects dramatically the flexural performance of pipe material. Consequently, the service life of pipe structures risks to be reduced. Finally, a coupled experimental–numerical approach for the characterization of pipe material behavior under flexure loading has shown a good correlation, and therefore, the efficiency of the established FE model to predict the flexural response of pipe structures.
查看更多>>摘要：? 2022 The Author(s)This paper aims to study the effect of asynchronous axial-torsional strain-controlled loading histories on fracture surface behavior of thin-walled tubular X5CrNi18-10 (304/304L) austenitic steel specimens. Tests under pure axial loading and pure torsional loading are also conducted to better segregate the effect of multiaxiality. The fractures surface topographies were examined through the profiles over the entire surface with the support of an optical measurement system. Then, features of the post-failure fractures were related to the loading conditions and the fatigue life. The outcomes indicate that the multiaxial loading path significantly affects the surface topography. Overall, fracture surface parameters increase for higher fatigue lives. Based on the dialectic relationship, a fatigue damage model able to estimate the fatigue lifetime under asynchronous axial-torsional loading histories has been successfully developed. The fracture surface topology parameters collected from both sides of the same specimen lead to comparable results which reinforces the applicability of the proposed approach.
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