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CONTENTS
Volume 29, Number 2, April25 2022
 


Abstract
Instability of bolted rock mass has been a major hazard in the underground coal mining industry for decades. Developing effective support guidelines requires understanding of complex bolted rock mass failure mechanisms. In this study, the dynamic failure behavior, mechanical behavior, and energy evolution of a laboratory-scale bolted specimens is studied by conducting laboratory static-dynamic coupled loading tests. The results showed that: (1) Under static-dynamic coupled loading, the stress-strain curve of the bolted rock mass has a significant impact velocity (strain rate) correlation, and the stress-strain curve shows rebound characteristics after the peak; (2) There is a critical strain rate in a rock mass under static-dynamic coupled loading, and it decreases exponentially with increasing pre-static load level. Bolting can significantly improve the critical strain rate of a rock mass; (3) Compared with a no-bolt rock mass, the dissipation energy ratio of the bolted rock mass decreases exponentially with increasing pre-static load level, the ultimate dynamic impact energy and dissipation energy of the bolted rock mass increase significantly, and the increasing index of the ratio of dissipation energy increases linearly with the pre-static load; (4) Based on laboratory testing and on-site microseismic and stress monitoring, a design method is proposed for a roadway bolt support against dynamic load disturbance, which provides guidance for the design of deep underground roadway anchorage supports. The research results provide new ideas for explaining the failure behavior of anchorage supports and adopting reasonable design and construction practices.

Key Words
bolted rock; crack propagation; dissipation energy; dynamic mechanical properties; split Hopkinson pressure bar; static-dynamic coupled loading

Address
Pengqi Qiu: College of energy and mining engineering, Shandong University of Science and Technology, 579 Qianwangang Road, Qingdao, China;
College of mining engineering, Taiyuan University of Technology, 18 Xinkuangyuan Road, Taiyuan, China
Jun Wang, Jianguo Ning, Xinshuai Shi and Shanchao Hu: College of energy and mining engineering, Shandong University of Science and Technology, 579 Qianwangang Road, Qingdao, China


Abstract
A rockburst is a common disaster in deep-tunnel excavation engineering, especially for high-geostress areas. An anomalously low friction effect is one of the most important inducements of rockbursts. To elucidate the correlation between an anomalously low friction effect and a rockburst, we establish a two-dimensional prediction model that considers the discontinuous structure of a rock mass. The degree of freedom of the rotation angle is introduced, thus the motion equations of the blocks under the influence of a transient disturbing force are acquired according to the interactions of the blocks. Based on the two-dimensional discontinuous block model of deep rock mass, a rockburst prediction model is established, and the initiation process of ultra-low friction rockburst is analyzed. In addition, the intensity of a rockburst, including the location, depth, area, and velocity of ejection fragments, can be determined quantitatively using the proposed prediction model. Then, through a specific example, the effects of geomechanical parameters such as the different principal stress ratios, the material properties, a dip of principal stress on the occurrence form and range of rockburst are analyzed. The results indicate that under dynamic disturbance, stress variation on the structural surface in a deep rock mass may directly give rise to a rockburst. The formation of rockburst is characterized by three stages: the appearance of cracks that result from the tension or compression failure of the deformation block, the transformation of strain energy of rock blocks to kinetic energy, and the ejection of some of the free blocks from the surrounding rock mass. Finally, the two-dimensional rockburst prediction model is applied to the construction drainage tunnel project of Jinping II hydropower station. Through the comparison with the field measured rockburst data and UDEC simulation results, it shows that the model in this paper is in good agreement with the actual working conditions, which verifies the accuracy of the model in this paper.

Key Words
anomalously low friction; intensity; prediction model; rockburst; tunnel

Address
J.W. Zhan: College of Civil Engineering, Fujian University of Technology, Fuzhou, China
G.X. Jin: College of Ecological Environment and Urban Construction, Fujian University of Technology, Fuzhou, China
C.S. Xu: School of Civil, Environment and Mining Engineering, the University of Adelaide, Adelaide
H.Q. Yang and J.F. Liu: School of Civil Engineering, Chongqing University, Chongqing, China
X.D. Zhang: College of Civil Engineering, Fuzhou University, Fuzhou, China


Abstract
The catastrophic earthquake-induced failure of slopes concentrically distributed at near-fault area, which indicated the special features of near-fault ground motions, i.e. horizontal pulse-like motion and large vertical component, should have great effect on these geo-disasters. We performed shaking table tests to investigate the effect of both horizontal pulse-like motion and vertical component on dynamic response of slope. Both unidirectional (i.e., horizontal or vertical motions) and bidirectional (i.e., horizontal and vertical components) motions are applied to soft rock slope model, and acceleration at different locations is reordered. The results show that the horizontal acceleration amplification factor (AAF) increases with height. Moreover, the horizontal AAF under unidirectional horizontal pulse-like excitations is larger than that subject to ordinary motion. The vertical AAF does not show an elevation amplification effect. The seismic response of slope under different bidirectional excitations is also different: (1) The horizontal AAF is roughly constant under horizontal pulse-like excitations with and without vertical waves, but (2) the horizontal AAF under ordinary bidirectional ground motions is larger than that under unidirectional ordinary motion. Above phenomena indicate that vertical component has limited effect on seismic response when the horizontal component is pulse-like ground motion, but it can greatly enhance seismic response of slope under ordinary horizontal motion. Moreover, the vertical AAF is enhanced by horizontal motion in both horizontal pulse-like and ordinary motion. Thence, we should pay enough attention to vertical ground motion, especially its horizontal component is ordinary ground motion.

Key Words
near fault; pulse-like ground motion; seismic response; shaking table tests; vertical ground motion

Address
Chongqiang Zhu and Hualin Cheng: Department of Geotechnical Engineering, College of Civil Engineering, Tongji University, Shanghai 200092, China
Yangjuan Bao: Department of Geotechnical Engineering, College of Civil Engineering, Tongji University, Shanghai 200092, China;
Department of Civil Engineering, Shanghai University, Shanghai 200444, China
Zhiyi Chen and Yu Huang: Department of Geotechnical Engineering, College of Civil Engineering, Tongji University, Shanghai 200092, China;
Key Laboratory of Geotechnical and Underground Engineering of the Ministry of Education, Tongji University, Shanghai 200092, China

Abstract
Complex geological conditions have a great influence on the mining of coalbed methane (CBM), which affects the extraction efficiency of CBM. This investigation analyzed the complicated geological conditions in the Liujia CBM block of Fuxin. A geological model of heterogeneities CBM reservoirs was established to study the influence of strike direction of igneous rocks and fault structures on horizontal well layout. Subsequently, the dual-porosity and dual-permeability mathematical model was established, which considers the dynamic changes of porosity and permeability caused by gas adsorption, desorption, pressure change. The results show that the production curve is in good agreement with the actual by considering gas seepage in matrix pores in the model. Complicated geological structures affect the pressure expansion of horizontal wells, especially, the closer to the fault structure, the more significant the effect, the slower the pressure drop, and the smaller the desorption area. When the wellbore extends to the fault, the pressure expansion is blocked by the fault and the productivity is reduced. In the study area, the optimal distance to the fault is 70 m. When the horizontal wellbore is perpendicular to the direction of coal seam igneous rock, the productivity is higher than that of parallel igneous rock, and the horizontal well bore should be perpendicular to the cleat direction. However, the well length is limited due to the dense distribution of igneous rocks in the Liujia CBM block. Therefore, the horizontal well pumping in the study area should be arranged along the direction of igneous rock and parallel plane cleats. It is found that the larger the area surrounded by igneous rock, the more favorable the productivity. In summary, the reasonable layout of horizontal wells should make full use of the advantages of igneous rock, faults and other complex geological conditions to achieve the goal of high and stable production.

Key Words
CBM; horizontal well drainage; intrusive igneous rock; pressure distribution; sealing fault

Address
Bing Qin,Wei-Ji Sun and Bing Liang : Institute of Mechanics and Engineering, Liaoning Technical University, Fuxin 123000, China
Zhan-Shan Shi: Institute of Mining, Liaoning Technical University, Fuxin123000, China;
Liaoning Academy of Mineral Resources Development and Utilization Technical and Equipment
Research Institute, Liaoning Technical University, Fuxin 123000, China
Jian-Feng Hao: Institute of Mining, Liaoning Technical University, Fuxin123000, China

Abstract
An accurate analysis of structures supported on soft soils and subjected to seismic loading requires the consideration of the soil-foundation-structure interaction. An important aspect of this interaction lies with the energy dissipation due to soil material damping. Unlike advanced constitutive models that can induce energy loss, the use of simple elastoplastic constitutive models requires additional damping. The frequency dependent Rayleigh damping is a formulation that is frequently used in dynamic analysis. The main concern of this formulation is the correct selection of the target damping ratio and the frequency range where the response is frequency independent. The objective of this study is to investigate the effects of the Rayleigh damping parameters in soil-pile-structure and soil-inclusion-platform-structure systems in the presence of soft soil under seismic loading. Three-dimensional analyses of both systems are carried out using the finite difference software Flac3D. Different values of target damping ratios and minimum frequencies are utilized. Several earthquakes are used to study the influence of different excitation frequencies in the systems. The soil response in terms of accelerations, displacements and strains is obtained. For the rigid elements, the results are presented in terms of bending moments and normal forces. The results show that when the frequency of the input motion is close to the minimum (central) frequency in the Rayleigh damping formulation, the overdamping amount is reduced, and the surface spectral acceleration of the analyzed pile and inclusion systems increases. Thus, the bending moments and normal forces throughout the piles and inclusions also increase.

Key Words
dynamic analysis; numerical modelling; Rayleigh damping; rigid inclusion; pile

Address
Guillermo A. López Jiménez and Orianne Jenck: Univ. Grenoble Alpes, CNRS, Grenoble INP**, 3SR, F-38000 Grenoble, France
Daniel Dias: Hefei University of Technology, School of Automotive and Transportation Engineering, Hefei, China;
Antea Group, Paris, France

Abstract
Reusing the used pile has not yet been implemented due to the unpredictability of the bearing capacity evolution. This paper presents an analytic approach to estimate the sides shear setup after the dissipation of pore pressure. Long-term evolution of adjacent soil is simulated by viscoelastic-plastic constitutive model. Then, an innovative concept of quasi-overconsolidation is proposed to estimate the strength changes of surrounding soil. Total stress method (a method) is employed to evaluate the long term bearing capacity. Measured data of test piles in Louisiana and semi-logarithmic time function are cited to validate the effectiveness of the presented method. Comparisons illustrate that the presented approach gives a reasonably prediction of the side shear setup. Both the presented method and experiment show the shaft resistance increase by 30%-50%, and this highlight the potential benefit of piles reutilization.

Key Words
driven pile; long term; quasi-overconsolidation ; reuse; side shear setup

Address
Jifei Cui, Pingping Rao, Jian Wu and Zhenkun Yang: Department of Civil Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China

Abstract
Piled raft foundations are widely used and effective in supporting high-rise buildings around the world. In this study, a piled raft system was numerically simulated using PLAXIS 3D. The settlement comparison results between the actual building measurements and the three-dimensional (3D) numerical analysis, were in good agreement, indicating the usefulness of this approach for the evaluation of the feasibility of using a piled raft foundation in Ho Chi Minh City subsoil. The effects were investigated of the number of piles based on pile spacing, pile length, raft embedment on the settlement, load sharing, bending moments, and the shear force of the piled raft foundation in Ho Chi Minh City subsoil. The results indicated that with an increased number of piles, increased pile length, and embedding raft depth, the total and differential settlement decreased. The optimal design consisted of pile numbers of 60–70, corresponding to pile spacings is 5.5-6 times the pile diameter (Dp), in conjunction with a pile length-to-pile diameter ratio of 30. Furthermore, load sharing by the raft, by locating it in the second layer of stiff clay, could achieve 66% of the building load. The proposed model of piled raft foundations could reduce the total foundation cost by 49.61% compared to the conventional design. This research can assist practicing engineers in selecting pile and raft parameters in the design of piled raft foundations to produce an economical design for high-rise buildings in Ho Chi Minh City, Viet Nam, and around the world.

Key Words
3D FEM; high-rise building; Ho Chi Minh subsoil; load sharing; parametric study; piled raft

Address
Kamol Amornfa and Ha T. Quang: Department of Civil Engineering, Faculty of Engineering at Kamphaeng Saen, Kasetsart University,
Kamphaeng Saen, Nakhon Pathom, Thailand
Tran V. Tuan: Department of Civil Engineering, College of Engineering Technology, Can Tho University, Ninh Kieu, Can Tho, Viet Nam

Abstract
The face stability of shield tunnelling is the most important control index for safety risk management. Based on the reliability of the transparent clay (TC) model test, a series of TC model tests under different buried depth were conducted to investigate the progressive failure mechanism of tunnel face. The support pressure was divided into the rapid descent stage, the slow descent stage and the basically stable stage with company of the local failure and integral failure in the internal of the soil during the failure process. The relationship between the support pressure and the soil movement characteristics of each failure stage was defined. The failure occurred from the soil in front of the tunnel face and propagated as the slip zone and the loose zone. The fitted formulas were proposed for the calculation of the failure process. The failure mode in clay was specified as the basin shape with an inverted trapezoid shape for shallow buried and appeared as the basin shape with a teardrop-like shape in deep case. The implications of these findings could help in the safety risk management of the underground construction.

Key Words
failure mechanism; soil deformation; transparent clay; tunnel face

Address
Huayang Lei and Rui Jia: Department of Civil Engineering, Tianjin University, Tianjin, China 300072;
Key Laboratory of Coast Civil Structure Safety of Education Ministry, Tianjin University, Tianjin, China 300072
Saibei Zhai: Department of Civil Engineering, Tianjin University, Tianjin, China 300072;
Beijing Urban Construction Design & Development Group Co., Ltd., 5 Fuchengmen North Street, Beijing, China 100032
Yingnan Liu: Department of Civil Engineering, Tianjin University, Tianjin, China 300072


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