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CONTENTS
Volume 16, Number 6, December30 2018
 

Abstract
The stability of shallow cavities with an arbitrary profile is a difficult issue in geotechnical engineering. This paper investigates this problem on the basis of the upper bound theorem of limit analysis and the Hoek-Brown failure criterion. The influence of pore pressure is taken into consideration by regarding it as an external force acting on rock skeleton. An objective function is constructed by equating the internal energy dissipation to the external force work. Then the Lagrange variation approach is used to solve this function. The validity of the proposed method is demonstrated by comparing the analytical solutions with the published research. The relations between shallow and deep cavity are revealed as well. The detaching curve of cavity roof with elliptical profile is obtained. In order to facilitate the application of engineering practice, the numerical results are tabulated, which play an important role in tunnel design and stability analysis of roof. The influential factors on potential collapse are taken into consideration. From the results, the impact of various factors on the extent of detaching is seen intuitively.

Key Words
three-dimensional; shallow cavity; arbitrary profile; pore water pressure

Address
W.J. Luo: School of Civil Engineering and Architecture, East China Jiaotong University, Nanchang, 330013, China

X.L. Yang: School of Civil Engineering, Central South University, Changsha, 410075, China

Abstract
A major concern in deep excavation project in soft clay deposits is the potential for adjacent buildings to be damaged as a result of the associated excessive ground movements. In order to accurately determine the wall deflections using a numerical procedure such as the finite element method, it is critical to use the correct soil parameters such as the stiffness/strength properties. This can be carried out by performing an inverse analysis using the measured wall deflections. This paper firstly presents the results of extensive plane strain finite element analyses of braced diaphragm walls to examine the influence of various parameters such as the excavation geometry, soil properties and wall stiffness on the wall deflections. Based on these results, a multivariate adaptive regression splines (MARS) model was developed for inverse parameter identification of the soil relative stiffness ratio. A second MARS model was also developed for inverse parameter estimation of the wall system stiffness, to enable designers to determine the appropriate wall size during the preliminary design phase. Soil relative stiffness ratios and system stiffness values derived via these two different MARS models were found to compare favourably with a number of field and published records.

Key Words
wall deflection; braced excavation; soil stiffness ratio; case histories; multivariate adaptive regression splines; inverse analysis

Address
Wengang Zhang: 1.) Key Laboratory of New Technology for Construction of Cities in Mountain Area, Chongqing University, Chongqing 400045, China
2.) School of Civil Engineering, Chongqing University, Chongqing 400045, China
3.) Key Laboratory of Rock Mechanics in Hydraulic Structural Engineering, Ministry of Education, Wuhan University, Wuhan 430072, China

Runhong Zhang: School of Civil Engineering, Chongqing University, Chongqing 400045, China

Anthony. T. C. Goh: School of Civil and Environmental Engineering, Nanyang Technological University, 639798, Singapore

Abstract
Centrifuge model tests were used to simulate pile-raft composite foundation and pile-geogrid composite foundation with different pile spacing for researching the time effect of negative skin friction of rigid piles in high-speed railways. The research results show that the negative skin friction has a significant impact on the bearing capacity of composite foundation. Pile-raft composite foundation has higher bearing capacity compared to pile-geogrid composite foundation to reduce the effect of negative skin friction on piles. Both the foundation settlement and negative skin friction have significant time effect. The distribution of skin friction can be simplified as a triangle along the pile. The neutral point position moves deeper in the post-construction stage at larger pile spacing. For pile-geogrid composite foundation, the setting of pile-cap affects the position of neutral point in the post-construction stage. Reinforced cushion with geotextile may promote the better performance of cushion for transmitting the loads to piles and surrounding soils. Arching effect in the cushion of the composite foundation is a progressive process. The compression of the rigid piles contributes less than 20% to 25% of the total settlement while the penetration of the piles and the compression of the bearing stratum below the pile tips contribute more than 70% of the total settlement. Some effective measures to reduce the settlement of soils need to be taken into consideration to improve the bearing capacity of pile foundation.

Key Words
embankment engineering; negative skin friction; rigid pile composite foundation; pile-cushion interaction; centrifuge model test; time effect

Address
Changdan Wang and Peijun Guo: 1.)Key Laboratory of Road and Traffic Engineering of the Ministry of Education, Tongji University, 4800 Cao

Abstract
This study investigates the feasibility of adopting the results of the UC (unconfined compression) test to assess the total cohesion of the unsaturated soil. A series of laboratory tests were conducted on samples of unsaturated lateritic soils of northern Taiwan. Specifically, the unconfined compression test was combined with the pressure plate test to obtain the unconfined compression strength and its matric suction of the samples. Soil samples were first compacted at designated water content and then subjected to the wetting process for saturation and the subsequent drying process to its target suction using the apparatus developed by the authors. The correlations among the matric suction, the unconfined compression strength and the total cohesion were studied. As a result, a simplified method to estimate the total cohesion using the unconfined compressive strength is suggested. The calculated results compare reasonably with the unsaturated triaxial test results. Current results show good performance; however, further study is warranted.

Key Words
unsaturated soil; matric suction; total cohesion; unconfined compressive strength

Address
Horn-Da Lin and Xu-Hui Wang: Department of Civil and Construction Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan

Chien-Chih Wang: Department of Civil Engineering and Geomatics, Cheng Shiu University, Kaohsiung 83347, Taiwan

Abstract
A new mechanical model for predicting the vibration of a pipe pile embedded in longitudinally layered visco-elastic media with radial inhomogeneity is proposed by extending Novak\'s plain-strain model and complex stiffness method to consider viscous-type damping. The analytical solutions for the dynamic impedance, the velocity admittance and the reflected signal of wave velocity at the pile head are also derived and subsequently verified by comparison with existing solutions. An extensive parametric analysis is further performed to examine the effects of shear modulus, viscous damping coefficient, coefficient of disturbance degree, weakening or strengthening range of surrounding soil and longitudinal soft or hard interbedded layer on the velocity admittance and the reflected signal of wave velocity at the pile head. It is demonstrated that the proposed model and the obtained solutions provide extensive possibilities for practical application compared with previous related studies.

Key Words
analytical solution; dynamic response; inhomogeneous soil; viscous-type damping; pile-soil interaction; pipe pile

Address
Chun Y. Cui, Kun Meng and Zhi M. Liang: Department of Civil Engineering, Dalian Maritime University, Dalian, 116026, China

Ya J. Wu: Department of Civil Engineering, Shanghai University, Shanghai, 200072, China

David Chapman:School of Engineering, University of Birmingham, Birmingham, B15 2TT, U.K.

Abstract
A simple prediction procedure was investigated for calculating the stresses and displacements of a circular opening. Unlike existed approaches, the proposed approach starts each step with a radius increment. The stress for each annulus could be obtained analytically, while strain increments for each step can be determinate numerically from the compatility equation by finite difference approximation, flow rule and Hooke\'s law. In the successive manner, the distributions of stresses and displacements could be found. It should be noted that the finial radial stress and displacement were equal to the internal supporting pressure and deformation at the tunnel wall, respectively. By assuming different plastic radii, GRC and the evolution curve of plastic radii and internal supporting pressures could be obtained conveniently. Then the real plastic radius can be calculated by using linear interpolation in the evolution curve. Some numerical and engineering examples were performed to demonstrate the accuracy and validity for the proposed procedure. The comparisons results show that the proposed procedure was faster than that in Lee and Pietrucszczak (2008). The influence of annulus number and dilation on the accuracy of solutions was also investigated. Results show that the larger the annulus number was, the more accurate the solutions were. Solutions in Park et al. (2008) were significantly influenced by dilation.

Key Words
new prediction procedure; strain-softening; circular opening; stress and displacement; GRC

Address
Feng Wang and Jin-Feng Zou: School of Civil Engineering, Central South University, No.22, Shaoshan South Road, Central South University Railway Campus,
Changsha, Hunan Province, 410075, People

Abstract
Soil stabilization is an essential engineering process to enhance the geotechnical properties of soils that are not suitable for construction purposes. This study focuses on using coconut coir, a natural fibre to enhance the soil properties. Lime, an activator is added to the reinforced soil to augment its shear strength and durability. An experimental investigation was conducted to demonstrate the effect of coconut coir fibers and lime on the consistency limits, compaction characteristics, unconfined compressive strength, stress-strain behaviour, subgrade strength and durability of the treated soil. The results of the study illustrate that lime stabilization and coir reinforcement improves the unconfined compressive strength, post peak failure strength, controls crack propagation and boosts the tensile strength of the soil. Coir reinforcement provides addition contact surface, improving the soil-fibre interaction and increasing the interlocking between fibre and soil and thereby improve strength. Optimum performance of soil is observed at 1.25% coir fibre inclusion. Coir being a natural product is prone to degradation and to increase the durability of the coir reinforced soil, lime is used. Lime stabilization favourably amends the geotechnical properties of the coir fibre reinforced soil.

Key Words
coconut coir; lime; stress-strain behaviour; post-peak strength; CBR; durability

Address
Evangelin Ramani Sujatha: Centre for Advanced Research in Environment (CARE), School of Civil Engineering, SASTRA Deemed University, Thanjavur 613401, Tamil Nadu, India

A.R. Geetha, R. Jananee and S.R. Karunya:School of Civil Engineering, SASTRA Deemed University, Thanjavur 613401, Tamil Nadu, India


Abstract
Braced excavation systems are commonly required to ensure stability in construction of basements for shopping malls, underground transportation and other habitation facilities. For excavations in deposits of soft clays or residual soils, stiff retaining wall systems such as diaphragm walls are commonly adopted to restrain the ground movements and wall deflections in order to prevent damage to surrounding buildings and utilities. The ground surface settlement behind the excavation is closely associated with the magnitude of basal heave and the wall deflections and is also greatly influenced by the possible groundwater drawdown caused by potential wall leakage, flow from beneath the wall, flow from perched water and along the wall interface or poor panel connections due to the less satisfactory quality. This paper numerically investigates the influences of excavation geometries, the system stiffness, the soil properties and the groundwater drawdown on ground surface settlement and develops a simplified maximum surface settlement Logarithm Regression model for the maximum ground surface settlement estimation. The settlements estimated by this model compare favorably with a number of published and instrumented records.

Key Words
ground surface settlement; logarithm regression; braced excavation; water drawdown

Address
Runhong Zhang, Zhongjie Hou and Wei Wang: School of Civil Engineering, Chongqing University, Chongqing, China

Wengang Zhang: 1.) Key Laboratory of New Technology for Construction of Cities in Mountain Area, Chongqing University, Chongqing, China
2.) National Joint Engineering Research Center of Geohazards Prevention in the Reservoir Areas, Chongqing University, Chongqing, China
3.) School of Civil Engineering, Chongqing University, Chongqing, China

A.T.C. Goh: School of Civil and Environmental Engineering, Nanyang Technological University, Singapore

Abstract
Tunnel excavation leads to a disturbance on the initial stress balance of surrounding soils, which causes convergences around the tunnel and settlements at the ground surface. Considering the effective impact of settlements on the structures at the surface, it is necessary to estimate them, especially in urban areas. In the present study, ground settlements due to the excavation of East-West Line 7 of the Tehran Metro (EWL7) and the Abuzar tunnels are evaluated and the effect of the lateral earth pressure coefficient (K0) on their extension is investigated. The excavation of the tunnels was performed by TBMs (Tunnel Boring Machines). The coefficient of lateral earth pressure (K0) is one of the most important geotechnical parameters for tunnel design and is greatly influenced by the geological characteristics of the surrounding soil mass along the tunnel route. The real (in-situ) settlements of the ground surface were measured experimentally using leveling methods along the studied tunnels and the results were compared with evaluated settlements obtained from both semi-empirical and numerical methods (using the finite difference software FLAC3D). The comparisons permitted to show that the adopted numerical models can effectively be used to predict settlements induced by a tunnel excavation. Then a numerical parametric study was conducted to show the influence of the K0 values on the ground settlements. Numerical investigations also showed that the shapes of settlement trough of the studied tunnels, in a transverse section, are not similar because of their different diameters and depths of the tunnels.

Key Words
tunnel boring machine; ground settlement; numerical model; lateral earth pressure coefficient

Address
Mohammad-Reza B. Golpasand: Department of Civil Engineering, Seraj High Education Institute, Tabriz, Iran

Ngoc Anh Do: Hanoi University of Mining and Geology, Faculty of Civil Engineering, Department of Underground and Mining Construction, Hanoi, Vietnam

Daniel Dias: 1.) School of Automotive and Transportation Engineering, Hefei University of Technology, Hefei, China
2.) Grenoble Alpes University, Laboratory 3SR, Grenoble, France

Mohammad-Reza Nikudel: Department of Engineering Geology, Tarbiat Modares University, Tehran, Iran

Abstract
To evaluate the stability of a rock slope with one pre-exiting vertical crack, this paper performs corresponding probabilistic stability analysis. The existence of cracks is generally ignored in traditional deterministic stability analysis. However, they are widely found in either cohesive soil or rock slopes. The influence of one pre-exiting vertical crack on a rock slope is considered in this study. The safety factor, which is usually adopted to quantity the stability of slopes, is derived through the deterministic computation based on the strength reduction technique. The generalized Hoek-Brown (HB) failure criterion is adopted to characterize the failure of rock masses. Considering high nonlinearity of the limit state function as using nonlinear HB criterion, the multivariate adaptive regression splines (MARS) is used to accurately approximate the implicit limit state function of a rock slope. Then the MARS is integrated with Monte Carlo simulation to implement reliability analysis, and the influences of distribution types, level of uncertainty, and constants on the probability density functions and failure probability are discussed. It is found that distribution types of random variables have little influence on reliability results. The reliability results are affected by a combination of the uncertainty level and the constants. Finally, a reliability-based design figure is provided to evaluate the safety factor of a slope required for a target failure probability.

Key Words
rock slope; crack; probabilistic analysis; Hoek-Brown criterion; multivariate adaptive regression splines; response surface method

Address
J.Q. Zhu: Department of Civil and Architecture Engineering, Changzhou Institute of Technology, Jiangsu, China

X.L. Yang: chool of Civil Engineering, Central South University, Changsha, 410075, China


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