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CONTENTS
Volume 19, Number 3, October30 2019
 

Abstract
A new approach of analyzing the displacements and stress of the surrounding rock for shallow tunnels excavated under non-axisymmetric displacement boundary conditions on a vertical surface is investigated in this study. In the proposed approach, by using a virtual image technique, the shear stress of the vertical ground surface is revised to be zero, and elastic solutions of the surrounding rock are obtained before stress revision. To revise the vertical normal stress and shear stress of horizontal ground surface generated by the combined action of the actual and image sinks, the harmonic functions and corresponding stress function solutions were adopted. Based on the Boussinesq\'s solutions and integral method, the horizontal normal stress of the vertical ground surface is revised to be zero. Based on the linear superposition principle, the final solution of the displacements and stress were proposed by superimposing the solutions obtained by the virtual image technique and the stress revision on the horizontal and vertical ground surfaces. Furthermore, the ground settlements and lateral displacements of the horizontal and vertical ground surfaces are derived by the proposed approach. The proposed approach was well verified by comparing with the numerical method. The discussion based on the proposed approach in the manuscript shows that smaller horizontal ground settlements will be induced by lower tunnel buried depths and smaller limb distances. The proposed approach for the displacement and stress of the surrounding rocks can provide some practical information about the surrounding rock stability analysis of shallow tunnels excavated under non-axisymmetric displacement boundary conditions on a vertical surface.

Key Words
shallow tunnel; non-axisymmetric displacement boundary; virtual image technique; linear superposition principle; ground settlement

Address
Ling Wang: 1.) School of Civil Engineering, Central South University, No.22, Shaoshan South Road,
Central South University Railway Campus, Changsha, Hunan Province, People\'s Republic of China
2.)Department of Environmental Design, Hunan University of Technology and business, No. 8 569, Yuelu Road,
Hunan University of Technology and Business, Changsha, Hunan Province, People\'s Republic of China

Jin-Feng Zou, Tao Yang and Feng Wang: School of Civil Engineering, Central South University, No.22, Shaoshan South Road,Central South University Railway Campus, Changsha, Hunan Province, People\'s Republic of China


Abstract
This study focuses on an improved prediction model to determine the limiting grouting pressure of compaction grouting considering the ground surface upheaval, which is caused by the three-dimensional conical shearing failure. The 2D-dimensional failure curve in Zou and Xia (2016) was improved to a three-dimensional conical shearing failure for compaction grouting through coordinate rotation. The process of compaction grouting was considered as the cavity expansion in infinite Mohr-Coulomb (M-C) soil mass. The prediction model of limiting grouting pressure of compaction grouting was proposed with limit equilibrium principle, which was validated by comparing the results in El-Kelesh et al. (2001) and numerical method. Furthermore, using the proposed prediction model, the vertical and horizontal grouting tube techniques were adopted to deal with the subgrade settlement in Shao-huai highway at Hunan Provence of China. The engineering applicability and effectiveness of the proposed model were verified by the field test. The research on the prediction model for the limiting grouting pressure of compaction grouting provides practical example to the rapid treatment technology of subgrade settlement.

Key Words
compaction grouting; limiting grouting pressure; cavity expansion; three-dimensional conical shearing failure; subgrade settlement treatment

Address
Liang Li, Zhou-Chen Xiang, Jin-Feng Zou and Feng Wang: School of Civil Engineering, Central South University, No.22, Shaoshan South Road, Central South University Railway Campus, Changsha, Hunan Province, People\'s Republic of China


Abstract
The physical models are useful to understand the soil behaviour. Hence, these tools allow validating analytical theories and numerical data. This paper addresses the design, construction and implementation of a physical model able to simulate the soil liquefaction under different cyclic actions. The model was instrumented with a piezoelectric actuator and a set of transducers to measure the porewater pressures, displacements and accelerations of the system. The soil liquefaction was assessed in three different grain size particles of a natural sand by applying a sinusoidal signal, which incorporated three amplitudes and the fundamental frequencies of three different earthquakes occurred in Colombia. In addition, such frequencies were scaled in a micro shaking table device for 1, 50 and 80 g. Tests allowed identifying the liquefaction susceptibility at various frequency and displacement amplitude combinations. Experimental evidence validated that the liquefaction susceptibility is higher in the fine-grained sands than coarse-grained sands, and showed that the acceleration of the actuator controls the phenomena trigging in the model instead of the displacement amplitude.

Key Words
Guamo sand; pore-water pressure excess; soil liquefaction; soil modelling

Address
Fausto Molina-Gómez and António Viana da Fonseca: Faculty of Engineering (FEUP), CONSTRUCT-GEO, Universidade do Porto, Porto, Portugal

Bernardo Caicedo : Department of Civil and Environment Engineering, Universidad de Los Andes, Bogotá, Colombia

Abstract
A finite element approach is presented to examine ground vibration characteristics under various moving loads in a homogeneous half-space. Four loading modes including single load, double load, four-load, and twenty-load were simulated in a finite element analysis to observe their influence on ground vibrations. Four load moving speeds of 60, 80, 100, and 120 m/s were adopted to investigate the influence of train speed to the ground vibrations. The results demonstrated that the loading mode in a finite element analysis is reliable for train-induced vibration simulations. Additionally, a three-dimensional finite element model (3D FEM) was developed to investigate the dynamic responses of a track-ballast-embankment-ground system subjected to moving loads induced by high-speed trains. Results showed that vibration attenuations and breaks exist in the simulated wave fronts transiting through different medium materials. These tendencies are a result of the difference in the Rayleigh wave speeds of the medium materials relative to the speed of the moving train. The vibration waves induced by train loading were greatly influenced by the weakening effect of sloping surfaces on the ballast and embankment. Moreover, these tendencies were significant when the vibration waves are at medium and high frequency levels. The vibration waves reflected by the sloping surface were trapped and dissipated within the track-ballast-embankment-ground system. Thus, the vibration amplitude outside the embankment was significantly reduced.

Key Words
track-embankment-ground system; vibration response; finite element model; moving train load; fast Fourier transform

Address
Qiang Fu and Yang Wu: School of Civil Engineering, Guangzhou University, Guangzhou Higher Education Mega Center, 230 Wai Huan Xi Road, Guangzhou 510006, P.R. China


Abstract
Taking top-coal caving mining face (TCCMF) as research object, this paper considers the combination of top-coal and immediate roof as cushion layer to build the solution model of support resistance based on the theory of elastic foundation beam. Meanwhile, the physical and mechanical properties of coal-rock combination influencing on strata behaviors is explored. The results illustrate that the subsidence of main roof in coal wall increases and the first weighting interval decreases with the increase of top-coal and immediate roof thicknesses as well as the decrease of top-coal and immediate roof elastic modulus. Moreover, the overlying strata reflecting on support has negative and positive relationship with top-coal thickness and immediate roof thickness, respectively. However, elastic modulus has limit influence on the dead weight of top-coal and immediate roof. As a result, it has similar roles on the increase of total support resistance and overlying strata reflecting on support in the limit range of roof control distance. In view of sensitive analysis causing the change of total support resistance, it can be regards as the rank of three components as immediate roof weight > overlying strata reflecting on support > top coal weight. Finally, combined with the monitoring data of support resistance in Qingdong 828, the validity of support resistance determined based on elastic foundation beam is demonstrated, and this method can be recommended to adopt for support type selecting in TCCMF.

Key Words
support resistance determination; elastic foundation beam; coal-rock combination; sensitive analysis

Address
Zhanbo Cheng: 1.) School of Energy and Mining Engineering, China University of Mining and Technology-Beijing, Beijing 100083, China
2.) Coal Industry Engineering Research Center of Top-coal Caving Mining, Beijing 100083, China
3.) School of Engineering, University of Warwick, Coventry CV47AL, U.K.

Shengli Yang, Lianghui Li and Lingfei Zhang: 1.) School of Energy and Mining Engineering, China University of Mining and Technology-Beijing, Beijing 100083, China
2.)Coal Industry Engineering Research Center of Top-coal Caving Mining, Beijing 100083, China

Abstract
Due to top-coal and immediate roof as cushion layer connecting with support and overlying strata, it can make significant influence on strata behaviors in fully mechanical top-coal caving working face (TCCWF). Taking Qingdong 828 working face as engineering background, FLAC3D and UDEC2D were adopted to explore the influence of top-coal thickness (TCT), immediate roof thickness (IRT), top-coal elastic modulus (TCEM) and immediate roof elastic modulus (IREM) on the vertical stress and vertical subsidence of roof, caving distance, and support resistance. The results show that the maximum roof subsidence increases with the increase of TCT and IRT as well as the decrease of TCEM and IREM, which is totally opposite to vertical stress in roof-control distance. Moreover, although the increase of TCEM and IREM leading to the increase of peak value of abutment pressure, the position and distribution range have no significant change. Under the condition of initial weighting occurrence, support resistance has negative and positive relationship with physical parameters (e.g., TCT and IRT) and mechanical properties (e.g., TCEM and IREM), respectively.

Key Words
coal-rock combined body; fully mechanized top-coal caving face; overlying strata behavior; numerical simulation

Address
Zhanbo Cheng: 1.)School of Energy and Mining Engineering, China University of Mining and Technology-Beijing, Beijing 100083, China
2.) Coal Industry Engineering Research Center of Top-coal Caving Mining, Beijing 100083, China
3.) School of Engineering, University of Warwick, Coventry CV47AL, U.K.

Weidong Pan and Xinyuan Li: 1.) School of Energy and Mining Engineering, China University of Mining and Technology-Beijing, Beijing 100083, China
2.) Coal Industry Engineering Research Center of Top-coal Caving Mining, Beijing 100083, China

Wenbin Sun: College of Mining and Safety Engineering, Shandong University of Science and Technology, Shandong 266590, China

Abstract
Evaluating the stability of the excavation face of the cross-river shield tunnel with good accuracy is considered as a nonlinear and multivariable complex issue. Understanding the stability evaluation method of the shield tunnel excavation face is vital to operate and control the shield machine during shield tunneling. Considering the instability mechanism of the excavation face of the cross-river shield and the characteristics of this engineering, seven evaluation indexes of the stability of the excavation face were selected, i.e., the over-span ratio, buried depth of the tunnel, groundwater condition, soil permeability, internal friction angle, soil cohesion and advancing speed. The weight of each evaluation index was obtained by using the analytic hierarchy process and the entropy weight method. The evaluation model of the cross-river shield construction excavation face stability is established based on the idea point method. The feasibility of the evaluation model was verified by the engineering application in a cross-river shield tunnel project in China. Results obtained via the evaluation model are in good agreement with the actual construction situation. The proposed evaluation method is demonstrated as a promising and innovative method for the stability evaluation and safety construction of the cross-river shield tunnel engineerings.

Key Words
cross-river tunnel; shield construction; stability of the excavation face; AHP-entropy weight method; ideal point evaluation model

Address
Yiguo Xue, Xin Li, Daohong Qiu, Xinmin Ma, Fanmeng Kong, Chuanqi Qu and Ying Zhao: Geotechnical and Structural Research Center of Shandong University, Jinan, Shandong, China

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