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Volume 10, Number 3, March 2016

Charts are used extensively in slope practical application to meet the need of quick assessment of rock slope design. However, Charts for estimating the shear strength of the rock mass of a slope are considerably limited. In this paper, based on the Hoek-Brown (HB) criterion which is widely used in rock slope engineering, we present charts which can be used to estimate the Mohr-Coulomb (MC) parameters angle of friction φ and cohesion c for given slopes. In order to present the proposed charts, we firstly present the derivation of the theoretical relationships between the MC parameters and σci/(γH) which is termed the strength ratio (SR). It is found that the values of c/σci and φ of a slope depend only on the magnitude of SR, regardless of the magnitude of the individual parameters σci (uniaxial compressive strength), γ (unit weight) and H (slope height). Based on the relationships between the MC parameters and SR, charts are plotted to show the relations between the MC parameters and HB parameters. Using the proposed charts can make a rapid estimation of shear strength of rock masses directly from the HB parameters, slope geometry and rock mass properties for a given slope.

Key Words
shear strength parameters; strength ratio; Hoek-Brown; charts assessment

(1) Ling Wan, Zuoan Wei:
State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing, 400044, China;

(2) Ling Wan:
Chongqing Key Laboratory of Heterogeneous Material Mechanics, Chongqing University, Chongqing, 400044, China;

(3) Jiayi Shen:
Institute of Port, Coastal and Offshore Engineering, Zhejiang University, Hangzhou, 310058, China.

Simplified techniques based on in situ testing methods are commonly used to assess seismic liquefaction potential. Many of these simplified methods were developed by analyzing liquefaction case histories from which the liquefaction boundary (limit state) separating two categories (the occurrence or non-occurrence of liquefaction) is determined. As the liquefaction classification problem is highly nonlinear in nature, it is difficult to develop a comprehensive model using conventional modeling techniques that take into consideration all the independent variables, such as the seismic and soil properties. In this study, a modification of the Multivariate Adaptive Regression Splines (MARS) approach based on Logistic Regression (LR) LR_MARS is used to evaluate seismic liquefaction potential based on actual field records. Three different LR_MARS models were used to analyze three different field liquefaction databases and the results are compared with the neural network approaches. The developed spline functions and the limit state functions obtained reveal that the LR_MARS models can capture and describe the intrinsic, complex relationship between seismic parameters, soil parameters, and the liquefaction potential without having to make any assumptions about the underlying relationship between the various variables. Considering its computational efficiency, simplicity of interpretation, predictive accuracy, its data-driven and adaptive nature and its ability to map the interaction between variables, the use of LR_MARS model in assessing seismic liquefaction potential is promising.

Key Words
multivariate adaptive regression splines; logistic regression; seismic liquefaction potential; interaction; basis function; limit state function

(1) Wengang Zhang:
Key Laboratory of New Technology for Construction of Cities in Mountain Area, Chongqing University, Ministry of Education, Chongqing 400045, China;

(2) Wengang Zhang:
School of Civil Engineering, Chongqing University, Chongqing 400045, China;

(3) Wengang Zhang, Anthony T.C. Goh:
School of Civil and Environmental Engineering, Nanyang Technological University, 639798 Singapore.

The investigation of stress wave propagation in a medium with initial stress has very important application in the field of engineering. However, the previous research less consider the influence of initial stress gradient on wave propagation. In the present paper, the governing equation of wave propagation in elastic continuum material with inhomogeneous initial stress is derived, which indicated that the inhomogeneous initial stress changed the governing equation of wave propagation. Additionally, the definite problem of wave propagation in material with initial stress gradient is verified by using mathematical physics method. Based on the definite problem, the elastic displacement-time relationship of wave propagation is explored, which indicated that the inhomogeneous initial stress changed waveform and relationship of displacement-time histories. Furthermore, the spall process of blasting wave propagation from underground to earth surface is simulated by using LS-DYNA.

Key Words
inhomogeneous initial stress; mathematical physics; wave propagation; governing equations

(1) Ming Tao, Zhenghong Chen, Xibing Li, Huatao Zhao, TuBing Yin:
School of Resources and Safety Engineering, Central South University, Changsha, Hunan, China;

(2) Ming Tao:
Western Mining Group Co., Ltd, Xining, Qinghai, China.

With the mining depth continuously increasing, gas emission behaviors become more and more complex. Gas emission is an important basis for choosing the method of gas drainage, gas controlling. Thus, the accurate prediction of gas emission is of great significance for coal mine. In this work, based on the sources of gas emission from the heading faces and the fluid-solid coupling process, we established a gas continuous dynamic emission model, numerically simulated and applied it to the engineering. The result was roughly consistent with the actual situation and shows the model is correct. We proposed the measures of reducing the excavation distance and borehole gas drainage based on the model. The measures were applied and the result shows the overproof problem of gas emission disappears. The model considered the influence factors of gas emission wholly, and has a wide applicability, promotional value. The research is of great significance for the controlling of gas disaster, gas drainage and pre-warning coal and gas outbursts based on gas emission anomaly at the heading face.

Key Words
gas emission; gas pressure; stress; gas drainage

(1) Key Laboratory of Coal Mine Gas and Fire Prevention and Control of the Ministry of Education, China University of Mining and Technology, Xuzhou 221116, China;

(2) School of Safety Engineering, China University of Mining and Technology, Xuzhou 221116, China.

Frictional forces between soil and structural elements are of vital importance for the foundation engineering. Although numerous studies were performed about the soil-structure interaction in recent years, the approximate relations proposed in the first half of the 20th century are still used to determine the frictional forces. Throughout history, wood was often used as friction piles. Steel has started to be used in the last century. Today, alternatively these materials, FRP (fiber-reinforced polymer) piles are used extensively due to they can serve for long years under harsh environmental conditions. In this study, various ratios of low plasticity clays (CL) were added to the sand soil and compacted to standard Proctor density. Thus, soils with various internal friction angles (φ) were obtained. The skin friction angles (δ) of these soils with FRP, which is a composite material, steel (st37) and wood (pine) were determined by performing interface shear tests (IST). Based on the data obtained from the test results, a chart was proposed, which engineers can use in pile design. By means of this chart, the skin friction angles of the soils, of which only the internal friction angles are known, with FRP, steel and wood materials can be determined easily.

Key Words
skin friction; pile materials; design chart; direct shear test; interface shear test; surface roughness

Department of Civil Engineering, Firat University, Engineering Faculty, 23100, Elazig, Turkey.

Rock salt is a near-perfect material for gas storage repositories due to its excellent ductility and low permeability. Gas storage in rock salt layers during gas injection and gas production causes the stress redistribution surrounding the cavity. The triaxial cyclic loading and unloading tests for rock salt were performed in this paper. The elastic-plastic deformation behaviour of rock salt under cyclic loading was observed. Rock salt experienced strain hardening during the initial loading, and the irreversible deformation was large under low stress station, meanwhile the residual stress became larger along with the increase of deviatoric stress. Confining pressure had a significant effect on the unloading modulus for the variation of mechanical parameters. Based on the theory of elastic-plastic damage mechanics, the evolution of damage during cyclic loading and unloading under various confining pressure was described.

Key Words
rock salt; triaxial; cyclic loading-unloading; deformation; damage

(1) Jie Chen, Deyi Jiang, Jinyang Fan, Yi He:
State Key Laboratory of Coal Mine Disaster Dynamics and Controls, Chongqing University, Chongqing 400030, China;

(2) Chao Du:
China Southwest Geotechnical Investigation & Design Institute CO., LTD., 610052 Chengdu, China.

Most laboratory test research has focused on grouting efficiency in homogeneous reconstituted soft clay. However, the natural sedimentary soils generally behave differently from reconstituted soils due to the effect of soil structure. A series of laboratory grouting tests were conducted to research the effect of soil structure on the performance of compensation grouting. The effects of grouting volume, overlying load and grouting location on the performance of compensation grouting under different soil structures were also studied. Reconstituted soil was altered with added cement to simulate artificial structured soil. The results showed that the final grouting efficiency was positive and significantly increased with the increase of stress ratio within a certain range when grouting in normally consolidated structured clay. However, in the same low yield stress situation, the artificial structured soil had a lower final grouting efficiency than the overconsolidated reconstituted soil. The larger of normalized grouting volume could increase the final grouting efficiency for both reconstituted and artificial structured soils. Whereas, the effect of the overlying load on final grouting efficiencies was unfavourable, and was independent of the stress ratio. As for the layered soil specimens, grouting in the artificial structured soil layer was the most efficient. In addition, the peak grouting pressure was affected by the stress ratio and the overlying load, and it could be predicted with an empirical equation when the overlying load was less than the yield stress. The end time of primary consolidation and the proportion of secondary consolidation settlement varied with the different soil structures, grouting volumes, overlying loads and grouting locations.

Key Words
grouting efficiency; soil structure; grouting volume; overlying load; grouting location; primary consolidation

(1) Gang Zheng, Xiaoshuang Zhang, Yu Diao, Huayang Lei:
School of Civil Engineering, Tianjin University, Tianjin 300072, China;

(2) Gang Zheng, Xiaoshuang Zhang, Yu Diao, Huayang Lei:
Key Laboratory of Coast Civil Structure Safety, Tianjin University, Ministry of Education, China;

(3) Gang Zheng:
State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University, Tianjin 300072, China.

In this research work, an exact analytical solution for thermal stability of solar functionally graded rectangular plates subjected to uniform, linear and non-linear temperature rises across the thickness direction is developed. It is assumed that the plate rests on two-parameter elastic foundation and its material properties vary through the thickness of the plate as a power function. The neutral surface position for such plate is determined, and the efficient hyperbolic plate theory based on exact neutral surface position is employed to derive the governing stability equations. The displacement field is chosen based on assumptions that the in-plane and transverse displacements consist of bending and shear components, and the shear components of in-plane displacements give rise to the quadratic distribution of transverse shear stress through the thickness in such a way that shear stresses vanish on the plate surfaces. Therefore, there is no need to use shear correction factor. Just four unknown displacement functions are used in the present theory against five unknown displacement functions used in the corresponding ones. The non-linear strain-displacement relations are also taken into consideration. The influences of many plate parameters on buckling temperature difference will be investigated. Numerical results are presented for the present theory, demonstrating its importance and accuracy in comparison to other theories.

Key Words
thermal buckling; solar functionally graded plate; analytical modeling; neutral surface position

(1) Sidi Mohamed El-Hassar, Samir Benyoucef, Houari Heireche and Abdelouahed Tounsi:
Laboratoire des Structures et Matériaux Avancés dans le Génie Civil et Travaux Publics, Université de Sidi Bel Abbes, Faculté de Technologie, Département de Génie Civil, Algeria;

(2) Samir Benyoucef
Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria;

(3) Samir Benyoucef:
Algerian National Thematic Agency of Research in Science and Technology (ATRST), Algeria;

(4) Houari Heireche:
Laboratoire de Modélisation et Simulation Multi-échelle, Département de Physique, Faculté des Sciences Exactes, Département de Physique, Université de Sidi Bel Abbés, Algeria;

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