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CONTENTS
Volume 14, Number 4, March20 2018
 

Abstract
Strength of loess that experienced cyclic freeze and thaw is of great significance for evaluating stability of slopes and foundations in loess regions. This paper takes the frequently encountered loess in the Northwestern China as the study object and carried out three kinds of laboratory tests including freeze-thaw test, direct shear test and SEM test to investigate the strength behaviors of loess after cyclic freeze and thaw, and the correlation with meso-level changes in soil structure. Results show that for loess specimens at four dry densities, the cohesion decreases with freeze-thaw cycles until a residual value is reached and thus an exponential equation is proposed. Besides, little change in the angle of internal friction was observed as freeze-thaw proceeds. This may depend on the varying of soil structure, based on which a clue can be found from the surface morphology and mesoscopic scanning of loess specimens. Clearly we observed significant changes in surface morphology of loess and it tends to aggravate at higher water contents or more cycles of freeze and thaw. Moreover, freeze-thaw cycling leads to obvious changes in the meso-structure of loess including lowering the particle aggregates and increasing both the proportion of fine particles and porosity area ratio. A damage variable dependent on the ratio of porosity area is introduced based on the continuum damage mechanics and its correlation with cohesion is discussed.

Key Words
loess; freeze and thaw; strength; cohesion; damage variable

Address
Jian Xu, Zhangquan Wang and Jianwei Ren: School of Civil Engineering, Xi\'an University of Architecture and Technology, Xi

Abstract
With rapid economic growth, numerous deep excavation projects for high-rise buildings and subway transportation networks have been constructed in the past two decades. Deep excavations particularly in thick deposits of soft clay may cause excessive ground movements and thus result in potential damage to adjacent buildings and supporting utilities. Extensive plane strain finite element analyses considering small strain effect have been carried out to examine the wall deflections for excavations in soft clay deposits supported by diaphragm walls and bracings. The excavation geometrical parameters, soil strength and stiffness properties, soil unit weight, the strut stiffness and wall stiffness were varied to study the wall deflection behaviour. Based on these results, a multivariate adaptive regression splines model was developed for estimating the maximum wall deflection. Parametric analyses were also performed to investigate the influence of the various design variables on wall deflections.

Key Words
wall deflection; braced excavation; multivariate adaptive regression splines; case histories; parametric analysis; finite element analysis

Address
Yuzhou Xiang: School of Civil Engineering, Chongqing University, Chongqing 400045, China

Anthony Teck Chee Goh: School of Civil and Environmental Engineering, Nanyang Technological University, 639798, Singapore

Wengang Zhang: 1.) School of Civil Engineering, Chongqing University, Chongqing 400045, China
2.) Key Laboratory of New Technology for Construction of Cities in Mountain Area, Chongqing University, China

Runhong Zhang:School of Civil and Environmental Engineering, Nanyang Technological University, 639798, Singapore

Abstract
Deformation of rock masses is not only related to rock itself, but also related to discontinuities, the latter maybe greater. Study on crack propagation at discontinuities is important to reveal the damage law of rock masses. DDARF is a discontinuous deformation analysis method for rock failure and some modified algorithms are proposed in this study. Firstly, coupled modeling methods of AutoCAD-DDARF and ANSYS-DDARF are introduced, which could improve the modeling efficiency of DDARF compared to its original program. Secondly, a convergence criterion for automatically judging the computation equilibrium is established, it could overcome subjective drawbacks of ending one calculation by time steps. Lastly but not the least, relationship between the super relaxation factor and the calculation convergence is analyzed, and reasonable value range of the super relaxation factor is obtained. Based on these above modified programs, influences on crack propagation of joint angle, joint parameters and geo-stresses

Key Words
crack propagation; discontinuous deformation analysis method for rock failure (DDARF); coupled modeling methods; convergence criterion

Address
Yunjuan Chen and Xin Zhang: School of Civil Engineering, Shandong Jianzhu University, Ji

Abstract
The study of the mining effect influenced by a normal fault has great significance concerning the prediction and prevention of fault rock burst. According to the occurrence condition of a normal fault, the stress evolution of the working face and fault plane, the movement characteristics of overlying strata, and the law of fault slipping when the working face advances from footwall to hanging wall are studied utilizing UDEC numerical simulation. Then the inducing-mechanism of fault rock burst is revealed. Results show that in pre-mining, the in situ stress distribution of two fault walls in the fault-affected zone is notably different. When the working face mines in the footwall, the abutment stress distributes in a \"double peak\" pattern. The ratio of shear stress to normal stress and the fault slipping have the obvious spatial and temporal characteristics because they vary gradually from the higher layer to the lower one orderly. The variation of roof subsidence is in S-shape which includes slow deformation, violent slipping, deformation induced by the hanging wall strata rotation, and movement stability. The simulation results are verified via several engineering cases of fault rock burst. Moreover, it can provide a reference for prevention and control of rock burst in a fault-affected zone under similar conditions.

Key Words
normal fault; mining-induced stress; fault slipping; rock burst

Address
Jin-Quan Jiang and Pu Wang: State Key Laboratory of Mining Disaster Prevention and Control Co-founded by Shandong Province and the Ministry of Science and Technology, Shandong University of Science and Technology, Qingdao, China

Li-Shuai Jiang: School of Mining and Safety Engineering, Shandong University of Science and Technology, Qingdao, China

Peng-Qiang Zheng: Department of Resources and Civil Engineering, Shandong University of Science and Technology, Tai

Abstract
Currently, layered geogrid method (LGM) is the commonly practiced technique for reinforcement of slopes. In this paper the geogrid-box method (GBM) is introduced as a new approach for reinforcement of rock-soil slopes. To achieve the objectives of this study, a laboratory setup was designed and the slopes without reinforcements and reinforced with LGM and GBM were tested under the loading of a circular footing. The effect of vertical spacing between geogrid layers and box thickness on normalized bearing capacity and failure mechanism of slopes was investigated. A series of 3D finite element analysis were also performed using ABAQUS software to supplement the results of the model tests. The results indicated that the load-settlement behavior and the ultimate bearing capacity of footing can be significantly improved by the inclusion of reinforcing geogrid in the soil. It was found that for the slopes reinforced with GBM, the displacement contours are widely distributed in the rock-soil mass underneath the footing in greater width and depth than that in the reinforced slope with LGM, which in turn results in higher bearing capacity. It was also established that by reducing the thickness of geogrid-boxes, the distribution and depth of displacement contours increases and a longer failure surface is developed, which suggests the enhanced bearing capacity of the slope. Based on the studied designs, the ultimate bearing capacity of the GBM-reinforced slope was found to be 11.16% higher than that of the slope reinforced with LGM. The results also indicated that, reinforcement of rock-soil slopes using GBM causes an improvement in the ultimate bearing capacity as high as 24.8 times more than that of the unreinforced slope.

Key Words
stabilization; rock-soil slope; geogrid-box method; layered geogrid method, laboratory model; numerical model

Address
Gholam Moradi and Arvin Abdolmaleki:Faculty of Civil Engineering, University of Tabriz, Tabriz, Iran

Parham Soltani: Department of Textile Engineering, Isfahan University of Technology, Isfahan 84156-83111, Iran

Masoud Ahmadvand: Dimond Consulting Engineers Company, Tehran, Iran

Abstract
One of the significant problems in the design of onshore pipelines in seismic areas is their stability in case of liquefaction. Several model tests and numerical analyses allow investigating the behavior of pipelines when the phenomenon of liquefaction occurs. While experimental tests contribute significantly toward understanding the liquefaction mechanism, they are costly to perform compared to numerical analyses; on the other hand, numerical analyses are difficult to execute, because of the complexity of the soil behavior in case of liquefaction. This paper reports an overview of the existing computational methods to evaluate the stability of onshore pipelines in liquefied soils, with particular attention to the development of excess pore water pressures and the floatation of buried structures. The review includes the illustration of the mechanism of floating and the description of the available calculation methods that are classified in static and dynamic approaches. We also highlighted recent trends in numerical analyses. Moreover, for the static condition, referring to the American Petroleum Institute (API) Specification, we computed and compared the uplift safety factors in different cases that might have a relevant practical use.

Key Words
liquefaction; pipeline; flotation; computational methods

Address
Massimina Castiglia and Filippo Santucci de Magistris: Di.B.T Department, Structural and Geotechnical Dynamics StreGa Lab., University of Molise, via de Sanctis, 86100 Campobasso, Italy

Agostino Napolitano: PRG Onshore Pipeline Specific Engineering, Saipem S.p.A., via Toniolo 1, 61032 Fano (PU), Italy

Abstract
Samples composed of coal and rock show different mechanical properties of the pure coal or rock mass. For the same coal seam with different surrounding rocks, the frequency and intensity of rock burst can be significantly different in. First, a method of measuring the strain variation of coal in the coal-rock combined sample was proposed. Second, laboratory tests have been conducted to investigate the influences of rock lithologies, combined forms and coal-rock height ratios on the deformation and failure characteristics of the coal section using this method. Third, a new bursting liability index named combined coal-rock impact energy speed index (CRIES) was proposed. This index considers not only the time effect of energy, but also the influence of surrounding rocks. At last, a new approach considering the influences of roof and/or floor was proposed to evaluate the impact capability of coal seam. Results show that the strength and elastic modulus of coal section increase significantly with the coal-rock height ratio decreasing. In addition, the values of bursting liability indexes of the same coal seam vary greatly when using the new approach. This study not only provides a new approach to measuring the strain of the coal section in coal-rock combined sample, but also improves the evaluation system for evaluating the impact capability of coal.

Key Words
rock burst; coal-rock combined sample; impact capability; hard rock; impact energy speed

Address
Y.L. Tan, X.S. Liu and J.G. Ning: 1.)State Key Laboratory of Mining Disaster Prevention and Control Co-founded by Shandong Province and the Ministry of Science
and Technology, Shandong University of Science and Technology, Qingdao, China
2.) College of Mining and Safety Engineering, Shandong University of Science and Technology, Qingdao 266590, China

B. Shen:1.)State Key Laboratory of Mining Disaster Prevention and Control Co-founded by Shandong Province and the Ministry of Science
and Technology, Shandong University of Science and Technology, Qingdao, China
2.)CSIRO Energy, QCAT, 1 Technology Court, Pullenvale, Qld 4069, Australia

Q.H. Gu: College of Mining and Safety Engineering, Shandong University of Science and Technology, Qingdao 266590, China

Abstract
This paper focuses on the development of a new non-linear macro-element for the modelling of soil-foundation interaction. Material and geometrical nonlinearities (soil yielding and foundation uplift respectively) are taken into account in the present macro-element to examine the response of shallow foundations under monotonic and cyclic loads. Several applications of soil-foundation systems are studied. The results obtained from these applications are in very favourable agreement with those obtained through other numerical models in the literature.

Key Words
numerical modelling; macro-element; soil-footing systems; interaction; non-linear; cyclic loads

Address
Mourad Khebizi:Department of Civil Engineering, Mentouri University of Constantine, Algeria

Hamza Guenfoud and Mohamed Guenfoud:Civil Engineering and Hydraulic Laboratory, University of Guelma, Algeria

Abstract
The present study evaluates the interface shear strength between sand and different construction materials, namely steel and concrete, using direct shear test apparatus. The influence of surface roughness, mean size of sand particles, relative density of sand and size of the direct shear box on the interface shear behavior of sand with steel and concrete has been investigated. Test results show that the surface roughness of the construction materials significantly influences the interface shear strength. The peak and residual interface friction angles increase rapidly up to a particular value of surface roughness (critical surface roughness), beyond which the effect becomes negligible. At critical surface roughness, the peak and residual friction angles of the interfaces are 85-92% of the peak and residual internal friction angles of the sand. The particle size of sand (for morphologically identical sands) significantly influences the value of critical surface roughness. For the different roughness considered in the present study, both the peak and residual interaction coefficients lie in the range of 0.3-1. Moreover, the peak and residual interaction coefficients for all the interfaces considered are nearly identical, irrespective of the size of the direct shear box. The constitutive modeling of different interfaces followed the experimental investigation and it successfully predicted the pre-peak, peak and post peak interface shear response with reasonable accuracy. Moreover, the predicted stress-displacement relationship of different interfaces is in good agreement with the experimental results. The findings of the present study may also be applicable to other non-yielding interfaces having a similar range of roughness and sand properties.

Key Words
interface; surface roughness; direct shear test; peak interface angle; residual interface angle; constitutive modeling

Address
Manojit Samanta: Geotechnical Engineering Group, CSIR-Central Building Research Institute, Roorkee–247667, Uttarakhand, India

Piyush Punetha and Mahesh Sharma: Academy of Scientific and Innovative Research, CSIR-Central Building Research Institute,Roorkee 247667, Uttarakhand, India

Abstract
The influences of mineral content and porosity on ultrasonic wave velocity were assessed for ten hornfelsic rocks collected from southern and western parts of the city of Hamedan, western Iran. Selected rock samples were subjected to mineralogical, physical, and index laboratory tests. The tested rocks contain quartz, feldspar, biotite, muscovite, garnet, sillimanite, kyanite, staurolite, graphite and other fine grained cryptocrystalline matrix materials. The values of dry unit weight of the rocks were high, but the values of porosity and water absorption were low. In the rocks, the values of dry unit weight are related to the presence of dense minerals such as garnet so not affected by porosity. The statistical relationships between mineral content, porosity and ultrasonic wave velocity indicated that the porosity is the most important factor influencing ultrasonic wave velocity of the studied rocks. The values of P-wave velocity of the rocks range from moderate to very high. Empirical equations, relevant to different parameters of the rocks, were proposed to determine the rocks

Key Words
hornfels; mineral; porosity; fissure; wave velocity

Address
Davood Fereidooni: School of Earth Sciences, Damghan University, Damghan, Iran


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