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CONTENTS
Volume 11, Number 4, October 2016
 

Abstract
Steep rock slope with water-filled tension crack will happen to overturn around the toe of the slope under seismic loading. This failure type is completely different from the common toppling failure occurring in antidipping layered rock mass slopes with steeply dipping discontinuities. This paper presents an analytical approach to determine the seismic factor of safety against overturning for an intact rock mass slope with water-filled tension crack considering horizontal and vertical seismic coefficients. This solution is a generalized explicit expression and is derived using the moment equilibrium approach. A numerical program based on discontinuous deformation analysis (DDA) is adopted to validate the analytical results. The parametric study is carried out to adequately investigate the effect of horizontal and vertical seismic coefficients on the overall stability against overturning for a saturated rock slope under two water pressure modes. The analytical results show that vertically upward seismic inertia force or/and second water pressure distribution mode will remarkably decrease the slope stability against overturning. Finally, several representative design charts of slopes also are presented for the practical application.

Key Words
rock slope with water-filled tension crack; overturning failure; discontinuous joint plane; analytical solution; design charts; horizontal and vertical seismic coefficients

Address
(1) Yanjun Zhang, Tingkai Nian:
School of Civil Engineering and State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian 116024, China;
(2) Defeng Zheng:
School of Urban and Environmental Science, Liaoning Normal University, Dalian 116029, China;
(3) Lu Zheng:
Institute of Disaster Mitigation and Reconstruction, Sichuan University, Chengdu 610065, China.

Abstract
Underground tunnelling is one of the sustainable construction methods which can facilitate the increasing passenger transportation in the urban areas and benefit the community in the long term. Tunnelling in various ground conditions requires careful consideration of the stability factor. This paper investigates three dimensional stability of a shallow circular tunnel in a layered soil. Upper bound theorem of limit analysis was utilised to solve the tunnel face stability problem. A three dimensional kinematic admissible failure mechanism was improved to model a layered soil and limiting assumptions of the previous studies were resolved. The study includes calculation of the minimum support pressure acting on the face of the excavation in closed-face excavations. The effects of the characteristics of the layers on the minimum support pressure were examined. It was found that the ratio of the thickness of cover layers particularly when a weak layer is overlying a stronger layer, has the most significant influence on the minimum tunnel support pressure. Comparisons have been made with the results of the numerical modelling using FLAC3D software. Results of the current study were in a remarkable agreement with those of numerical modelling.

Key Words
minimum support pressure; stability; layered soil; upper bound; tunnel

Address
(1) Nima Khezri:
UTM Construction Research Centre (UTM CRC), Block C09, Level 1, Institute of Smart Infrastructure and Innovative Construction, Universiti Teknologi Malaysia, 81310, Skudai, Johor, Malaysia;
(2) Hisham Mohamad:
Civil and Environmental Engineering Department, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 32610 Perak, Malaysia;
(3) Behzad Fatahi:
School of Civil and Environmental Engineering, University of Technology, Sydney, Australia.

Abstract
A modified grey clustering method is presented to systematically evaluate the risk of water inrush in karst tunnels. Based on the center triangle whitenization weight function and upper and lower limit measure whitenization weight function, the modified grey evaluation model doesn't have the crossing properties of grey cluster and meets the standard well. By adsorbing and integrating the previous research results, seven influence factors are selected as evaluation indexes. A couple of evaluation indexes are modified and quantitatively graded according to four risk grades through expert evaluation method. The weights of evaluation indexes are rationally distributed by the comprehensive assignment method. It is integrated by the subjective factors and the objective factors. Subjective weight is given based on analytical hierarchy process, and objective weight obtained from simple dependent function. The modified grey evaluation model is validated by Jigongling Tunnel. Finally, the water inrush risk of Shangjiawan Tunnel is evaluated by using the established model, and the evaluation result obtained from the proposed method is agrees well with practical situation. This risk assessment methodology provides a powerful tool with which planners and engineers can systematically assess the risk of water inrush in karst tunnels.

Key Words
karst tunnel; water inrush; risk assessment; triangular whitenization weight function; grey clustering method

Address
Geotechnical and Structural Engineering Research Center, Shandong University, Ji

Abstract
In this paper, five different quantitative parameters were proposed for the characterization of the primary roughness which is the component of surface morphology that prevails during large strike-slip faults of more than 50 m. These parameters are mostly the anisotropic properties of rock surface morphology at various scales: (i) coefficient (ka) and degree (δa) of apparent structural anisotropy of surface; (ii) coefficient (kr) and degree (δr) of real structural anisotropy of surface; (iii) surface anisotropy function P(φ); and (iv) degree of surface waviness (Ws). The coefficient and degree of apparent structural anisotropy allow qualifying the anisotropy/isotropy of a discontinuity according to a classification into four classes: anisotropic, moderately anisotropic/isotropic and isotropic. The coefficient and degree of real structural anisotropy of surface captures directly the actual surface anisotropy using geostatistical method. The anisotropy function predicts directional geometric properties of a surface of discontinuity from measurements in two orthogonal directions. These predicted data may subsequently be used to highlight the anisotropy/isotropy of the surface (radar plot). The degree of surface waviness allows qualifying the undulation of anisotropic surfaces. The proposed quantitative parameters allows their application at both lab and field scales.

Key Words
rock joint; surface roughness; anisotropy; geostatistical method; waviness

Address
Université du Québec en Abitibi-Témiscamingue (UQAT), Research Institute in Mining and Environment (RIME), 445, boul. de l'Université, Rouyn-Noranda, Quebec, J9X 5E4 Canada.


Abstract
The greenschist in the Jinping II Hydropower Station in southwest China exhibits continuous creep behaviour because of the geological conditions in the region. This phenomenon illustrates the time-dependent deformation and progressive damage that occurs after excavation. In this study, the responses of greenschist to stress over time were determined in a series of laboratory tests on samples collected from the access tunnel walls at the construction site. The results showed that the greenschist presented time-dependent behaviour under long-term loading. The samples generally experienced two stages: transient creep and steady creep, but no accelerating creep. The periods of transient creep and steady creep increased with increasing stress levels. The long-term strength of the greenschist was identified based on the variation of creep strain and creep rate. The ratio of long-term strength to conventional strength was around 80% and did not vary much with confining pressures. A quantitative method for predicting the failure period of greenschist, based on analysis of the stress.strain curve, is presented and implemented. At a confining pressure of 40 MPa, greenschist was predicted to fail in 5000 days under a stress of 290 MPa and to fail in 85 days under the stress of 320 MPa, indicating that the long-term strength identified by the creep rate and creep strain is a reliable estimate.

Key Words
greenschist; hard rock; creep behaviour; creep stage; creep rate; long-term strength

Address
(1) Qing-Zhao Zhang, Ming-Rong Shen, Wen-Qi Ding:
Department of Geotechnical Engineering, College of Civil Engineering, Tongji University, Shanghai, SH 200092, China;
(2) Qing-Zhao Zhang, Hyun-Sic Jang, Bo-An Jang:
Department of Geophysics, Kangwon National University, 1 Kangwondaehak-gil, Chuncheon, Gangwon-do 24341, Republic of Korea;
(3) Ming-Rong Shen, Wen-Qi Ding:
Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education, Tongji University, Shanghai, SH 200092, China.

Abstract
A series of three-dimensional (3D) parametric finite element analyses have been performed to study the influence of the relative locations of pile tips with regards to the tunnel position on the behaviour of single piles and pile groups to adjacent tunnelling in weathered soil. When the pile tips are inside the influence zone, which considers the relative pile tip location with respect to the tunnel position, tunnelling-induced pile head settlements are larger than those computed from the Greenfield condition. However, when the pile tips are outside the influence zone, a reverse trend is obtained. When the pile tips are inside the influence zone, the tunnelling-induced tensile pile forces mobilised, but when the pile tips are outside the influence zone, compressive pile forces are induced because of tunnelling, depending on the shear stress transfer mechanism at the pile-soil interface. For piles connected to a cap, tensile and compressive forces are mobilised at the top of the centre and side piles, respectively. It has been shown that the increases in the tunnelling-induced pile head settlements have resulted in reductions of the apparent factor of safety up to approximately 43% when the pile tips are inside the influence zone, therefore severely affecting the serviceability of the piles. The pile behaviour, when considering the location of the pile tips with regards to the tunnel, has been analysed in great detail by taking the tunnelling-induced pile head settlements, axial pile forces, apparent factor of safety of the piles and shear transfer mechanism into account.

Key Words
numerical modelling and analysis; piled foundations; soil-structure interaction; shear transfer mechanism; weathered soil

Address
(1) Cheol-Ju Lee, Young-Jin Jeon, Sung-Hee Kim:
Department of Civil Engineering, Kangwon National University, Korea;
(2) Inn-Joon Park:
Department of Civil Engineering, Hanseo University, Korea.

Abstract
The crest of the Pubugou central core rockfill dam (CCRD) cracked in the first and second impounding periods. To evaluate the safety of the Pubugou CCRD, an inversion analysis of the constitutive model parameters for rockfill materials is performed based on the in situ deformation monitoring data. The aim of this work is to truly reflect the deformation state of the Pubugou CCRD and determine the causes of the dam crest cracks. A novel realcoded genetic algorithm based upon the differences in gene fragments (DGFX) is proposed. It is used in combination with the radial based function neural network (RBFNN) to perform the parameters back analysis. The simulated settlements show good agreements with the monitoring data, illustrating that the back analysis is reasonable and accurate. Furthermore, the deformation gradient of the dam crest has been analysed. The dam crest has a great possibility of cracking due to the uncoordinated deformation, which agrees well with the field investigation. The deformation gradient decreases to the value lower than the critical one and reaches a stable state after the second full reservoir.

Key Words
high central core rockfill dam; dam crest cracks; monitoring data analysis; parameters back analysis; uncoordinated deformation

Address
(1) Wei Zhou, Shao-Lin Li, Gang Ma, Xiao-Lin Chang, Yong-Gang Cheng, Xing Ma:
State Key Laboratory of Water Resources and Hydropower Engineering Science, Wuhan University, Wuhan, 430072, China;
(2) Shao-Lin Lip:
Changjiang Institute of Survey, Planning, Design and Research, Wuhan 430010, China.

Abstract
This study aimed to develop upper and lower bounds to predict the tunnel support pressure under the pile tip during the circular tunnel excavation. Most previous studies on the upper and lower bound methods were carried out for the single ground structures, e.g., retaining wall, foundation, ground anchor and tunnel, in the homogeneous ground conditions, since the pile-soil-tunnel interaction problem is very complicated and sophisticated to solve using those bound methods. Therefore, in the lower bound approach two appropriate stress fields were proposed for single pile and tunnel respectively, and then they were superimposed. In addition, based on the superimposition several failure mechanisms were proposed for the upper bound solution. Finally, these upper bound mechanisms were examined by shear strain data from the laboratory model test and numerical analysis using finite element method.

Key Words
pile-soil-tunnel interaction; upper and lower bounds; tunnel support pressure; stress field; superimposition; upper bound mechanism; shear strain

Address
Department of Civil Engineering, Seoul National University of Science and Technology, 232 Gongneung-ro, Nowon-gu, Seoul 139-743, Republic of Korea.


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