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CONTENTS
Volume 26, Number 5, September10 2021
 


Abstract
According to the results of a survey of retaining structures damaged by the Wenchuan earthquake, the damage to gravity retaining walls accounted for 97.1% of the total damage to retaining walls. Among gravity retaining structures, embankment gravity retaining walls with nonuniform slopes are more prone to be disturbed under seismic conditions. However, relatively few studies have been performed to calculate the seismic earth pressure on such structures. In this study, a simplified approach is presented to calculate the seismic earth pressure on embankment gravity retaining walls with nonuniform slopes. In the proposed approach, the equations are derived based on the primary assumptions of the Mononobe–Okabe theory and the limit equilibrium state of the quadrilateral slip soil wedge. To verify the applicability of the proposed approach, a large-scale shaking-table test was conducted to obtain the distribution of the seismic earth pressure, the magnitude of earth pressure resultant force, the resultant force action point, and slip surface of an embankment gravity retaining wall with a nonuniform slope, under various peak ground accelerations. A comparison indicates that the calculated results were in agreement with the experimental results, implying that the proposed approach is valid for calculating the seismic earth pressure on embankment gravity retaining walls with nonuniform slopes.

Key Words
embankment gravity retaining wall with nonuniform slope; peak ground acceleration; seismic earth pressure; shaking-table test

Address
Honglue Qu, Yuanyuan Deng, Qindi Hu, Xue Huang and Chenxu Wang: School of Geoscience and Technology, Southwest Petroleum University, No. 8, Xindu Avenue, Xindu District, Chengdu, Sichuan, China

Abstract
This paper presents a novel similarity solution for drained spherical cavity expansion in overconsolidated soils, which creatively incorporates the large strain into similarity solution. The salient feature of the present solution lies in that it properly represents the large deformation associated responses of the overconsolidated soil during cavity expansion. The logarithmic strain components are reasonably incorporated into the similarity solution, which is a general solution technique that has been widely used to solve cavity expansion problems, to creatively account for the large deformation of soils during cavity expansion in such a solution framework. The competent modified unified-hardening (UH) model is employed to properly represent the unique behavior of overconsolidated soils during expansion, where three-dimensional strength characteristics of the soil are taken into account as well. The partial differential governing equations under Eulerian description are transformed into a set of first order ordinary differential equations under Lagrangian description and further solved as an initial value problem by MATLAB. The present method is verified by comparing with the modified Cam-clay model based solutions and an extensive parameter analysis is subsequently conducted for soils with different overconsolidation ratio. The unique expansion behaviors in the overconsolidated soils including the peak strength behavior, strain-hardening/softening and shear dilatancy behaviors are discussed in a comprehensive and in-depth manner.

Key Words
drained expansion; large deformation; overconsolidated soil; parameter analysis; similarity solution; spherical cavity

Address
Hanbo Zheng and Fayun Liang: Department of Geotechnical Engineering, Tongji University, 1239 Siping Road, Yangpu District, Shanghai, P. R. China

Hao Zhang: Department of Civil Engineering, Shanghai Normal University, 100 Haisi Road, Fengxian District, Shanghai, P. R. China

Abstract
Because of a wide distribution range, sudden occurrence, and high frequency of rockfall disasters on the slope of open-pit mines, it is difficult to effectively control the rockfall disasters in open-pit mines. The slope stabilities of slopes of 13 typical sections in the Changshanhao open-pit mine were calculated using 3DEC software, and the vulnerable area of each slope section was determined. These areas were analyzed as high-incidence areas of rockfalls. Combined with the field geological conditions, the slopes of the W6 and W8 sections where rockfall disasters easily occur were selected to study the motion characteristics of rockfalls, including the trajectory, landing distribution, bouncing height, and total kinetic energy using Rocfall software. According to different distribution characteristics of high-incidence areas of rockfall disasters on a slope, the gravel cushion and protective net methods are proposed to control rockfall disasters. The effectiveness and reasonableness of prevention methods were validated using numerical simulation, proving a good basis for scientific prevention and control of rockfall disasters in open-pit mines.

Key Words
gravel cushion; rockfalls; slope vulnerable area; stability analysis; 3DEC software

Address
Chun Zhu: 1.) School of Earth Sciences and Engineering, Hohai University, Nanjing, 210098, China
2.) State Key Laboratory for Geomechanics & Deep Underground Engineering, Beijing 100083, China

Manchao He and Zhigang Tao:State Key Laboratory for Geomechanics & Deep Underground Engineering, Beijing 100083, China

Qingxiang Meng: Research Institute of Geotechnical Engineering, Hohai University, Nanjing 210098, Jiangsu, China

Xiaohu Zhang: School of Civil Engineering, Guizhou University of Engineering Science, Bijie, Guizhou, 551700, China

Abstract
An increase in failure of geotechnical structures is a significant concern in seismic-prone areas. The purpose of the study is to propose a closed-form solution for the seismic active pressure acting on a retaining wall with backfill subjected to uniform surcharge considering the propagation of both shear and primary waves. The proposed study considers the damping ratio by assuming soil as Kelvin-Voigt material. The proposed methodology satisfies boundary conditions at the surface of the backfill due to surcharge. The deduced acceleration profile is considered for the estimation of inertial forces due to critical wedge and surcharge. The study reveals that the maximum seismic active pressure coefficient occurs when the normalized input frequency is equal to π/2. It is observed that the surcharge magnitude does not affect both horizontal and vertical acceleration profiles. The parametric study presents the influence of various static and dynamic properties of the backfill soil on the distribution of seismic pressure acting on the wall. The coefficient of earth pressure obtained from the proposed method is in good agreement with the existing pseudo-static methods. It is concluded that the effect of shear wave propagation on earth pressure is relatively dominant as compared to that of primary wave propagation.

Key Words
active pressure; damping ratio; modified pseudo-dynamic analysis; primary wave velocity; shear wave velocity; surcharged backfill

Address
Godas Srikar and Satyendra Mittal: Department of Civil Engineering, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand-247667, India

Abstract
In the mining industry, significant progress and increased mineral production cause waste disposal issues which is one of the crucial problems in mining operations. It leads to both environmental and economic issues. Particularly, wastes from the production of metallic sulfide ore cause serious environmental pollution. In the last three decades, waste has been stored in underground openings in a controlled manner as paste-fill. Paste-fill is created by waste, water, and chemical additives. In this paper, two types of wastes were chosen to investigate the usability of tailings as paste-fill material. A lead and zinc underground mine was selected as a research site located in Balikesir, Turkey. First of all, several tests were conducted to analyze the physical, chemical, and mineralogical characteristics of paste-fill materials. Then, one of the design of experiment methods was used to create different mixtures of paste-fill specimens by changing the binder ratio and water content as input variables for four curing times. Finally, the strength properties were obtained as output variables, and an optimum mixture of paste-fill was determined. The results show that the tailings can be used as paste-fill material to achieve environmental and economic benefits and provide a safe working environment.

Key Words
design of experiment; paste-fill; tailings, underground mining; waste disposal

Address
Omer F. Ugurlu: Department of Mining Engineering, Faculty of Engineering, Istanbul University-Cerrahpasa, Istanbul, Turkey

C. Atilla Ozturk: Department of Mining Engineering, Faculty of Mines, Istanbul Technical University, Istanbul, Turkey

Abstract
The effect of heat treatment and the bedding orientation on the tensile properties, the central strain and failure patterns of bedded sandstone specimens were studied under Brazilian test conditions. The laboratory test results show that the tensile strength decreases with increasing bedding orientation at different temperatures, which indicates the bedded sandstone possesses prominent anisotropy in tensile strength. The anisotropy coefficient first increases and then decreases with the increasing temperature. For all temperatures, both V-strain and S-strain present a decreasing trend with increasing bedding orientation. However, for all bedding orientations, the S-strain first increases and then decreases, but V-strain continues to increase with increasing temperature. Furthermore, the failure patterns of the failed specimens are generally classified into three categories: central across the bedding planes (CF), fracture along the bedding planes (LA) and the mixed fracture patterns of the two. Finally, the evolution of the internal structure of the disk specimens after different heat treatments was investigated by SEM tests. The specimen profile looks smoother and denser at 400oC and 600oC, but at 800oC and 1000oC, the internal structure of the specimen is sharply deteriorated by thermal reactions.

Key Words
bedded sandstone; bedding orientation; failure patterns; heat treatment; tensile properties

Address
Xinshuai Shi: 1.) College of Energy and Mining Engineering, Shandong University of Science and Technology, Qingdao 266590, PR China
2.) State Key Laboratory for Geomechanics and Deep Underground Engineering, China University of Mining and Technology, Xuzhou 221116, PR China
3.) Graduate School of Engineering, Nagasaki University, 1-14 Bunkyo, Nagasaki 852-8521, Japan

Yujing Jiang: 1.)College of Energy and Mining Engineering, Shandong University of Science and Technology, Qingdao 266590, PR China
2.) Graduate School of Engineering, Nagasaki University, 1-14 Bunkyo, Nagasaki 852-8521, Japan

Hongwen Jing, Yuan Gao, Zhenlong Zhao and Qian Yin: State Key Laboratory for Geomechanics and Deep Underground Engineering, China University of Mining and Technology, Xuzhou 221116, PR China

Yuanchao Zhang: Graduate School of Engineering, Nagasaki University, 1-14 Bunkyo, Nagasaki 852-8521, Japan

Abstract
A range of Pb(II) and Cu(II) contaminated silt columns were prepared to simulate heavy metal contaminated site, and citric acid was employed to flush the silt columns. The concentration of citric acid, flushing time and concentrations of Cu(II) and Pb(II) were considered to study the removal behaviors of heavy metals. The removal efficiency of Cu(II) was found much better than that of Pb(II). The total removal ratio of Cu(II) could reach 59.9-73.4% when using 0.005mol/L citric acid, whereas the removal efficiency decreased with increasing the concentration of citric acid because higher concentration of chelating agent could lead to decrease of permeability in soil. The removal efficiency of Pb(II) was not as good as Cu(II), with the maximum removal ratio only 16.7%, and higher citric acid concentration led to higher removal efficiency, because lower concentration of citric acid could be adsorbed on soil surface and caused inhibitory effect on Pb(II) removing. The removal ratio of Cu(II) was greater when the initial Cu(II) concentration was lower in the contaminated soil, however, the same 0.005 mol/L concentration of citric acid was not effective to remove Pb(II), and the removal behaviors of Cu(II) and Pb(II) from contaminated silts were rather different. Therefore, appropriate concentration of citric acid should be carefully chosen to flush the heavy metal contaminated site, and this study can provide some theoretical basis for remediating heavy metal contaminated site by soil flushing.

Key Words
citric acid; contaminated silt; flushing; heavy metal; removal

Address
Yan Wang: School of Civil and Environmental Engineering, Ningbo University, Ningbo 315211, China

Lin Tang: School of Ocean Engineering, Harbin Institute of Technology at Weihai, Weihai 264209, China

Likui Liu: China Construction Third Bureau Engineering Design Co. Ltd, Wuhan 430074, China

Abstract
Mining backfill is increasingly used in underground mines to fill stopes. Its successful application depends on the stability of barricades built to retain the backfill in stopes. The design of barricades requires a good estimation of pore water pressure (PWP) and total stresses during and after the deposition. On this regard, a large number of works have been published on analytical and numerical solutions. There are however very few experimental results with simultaneous measurements of PWP as well as horizontal and vertical total stresses that can be used to validate or calibrate the analytical and numerical solutions. For a specific project, field measurements are interesting in terms of representativeness to field conditions, but the results are very difficult to be correctly interpreted because the treated problem can involve a large number of uncertainties and the obtained results are due to combined effects of several influencing factors. Laboratory tests with simplified and well-controlled conditions are thus preferred. Until now, however, the most previous laboratory tests were conducted with dry backfill or with a tailings slurry instantaneously poured in a confining structure without simultaneous measurements of PWP as well as horizontal and vertical total stresses. Studies on the effects of filling rate and solid content of backfill on the variation of PWP and total stresses during the filling operation are absent. To fill these gaps, a series of column backfilling tests were conducted with simultaneous measurements of PWP as well as vertical and horizontal total stresses during and after the deposition of slurried backfill. When the filling rate is high, the test results showed that the PWP, horizontal and vertical total stresses increase at the same rate and equal to the iso-geostatic overburden pressure during the deposition of backfill slurry. Their peak values appear at the end of deposition. The backfill thus behaves like a liquid with little generation of effective stresses during the deposition. High filling rate and/or high solid content lead to high PWP and horizontal total stresses at the end of deposition. When the filling rate is small, the PWP and total stresses exhibit also peak values at the end of filling operation, but the vertical total stress at the center can continue increasing with time after the end of deposition due to the suspended sensor and occurrence of a phenomenon known as stress shielding effect. The results also showed that the settlement of settled backfill after the end of slurry deposition can generally exhibits a fast evolution rate stage, followed by a slow evolution rate stage. The duration of the fast evolution rate stage and the final settlement of the settled backfill increase as the solid content decreases. The final settlement after the end of slurry deposition is related to the solid content, not to the filling rate.

Key Words
column tests; consolidation; mining backfill; pore water pressure; settlement; total stresses

Address
El Mustapha Jaouhara, Jian Zheng and Li Li: Research Institute on Mines and Environment, Department of Civil, Geological and Mining Engineering École Polytechnique de Montréal, C.P. 6079, succursale Centre-Ville, Montréal, QC, Canada H3C 3A7



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