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CONTENTS
Volume 15, Number 4, July20 2018
 

Abstract
The mechanical behavior of the brittle material samples containing the internal and edge cracks are studied under direct shear tests. It is tried to investigate the effects of stress interactions and stress intensity factors at the tips of the pre-existing cracks on the failure mechanism of the bridge areas within these cracks. The direct shear tests are carried out on more than 30 various modeled samples each containing the internal cracks (S models) and edge cracks (E models). The visual inspection and a low power microscope are used to monitor the failure mechanisms of the tested samples. The cracks initiation, propagation and coalescences are being visualized in each test and the detected failure surfaces are used to study and measure the characteristics of each surface. These investigations show that as the ratio of the crack area to the total shear surface increases the shear failure mode changes to that of the tensile. When the bridge areas are fixed, the bridge areas in between the edge cracks have less strength than those of internal cracks. However, the results of this study show that for the case of internal cracks as the bridge area is increased, the strength of the material within the bridge area is decreased. It has been shown that the failure mechanism and fracture pattern of the samples depend on the bridge areas because as the bridge area decreases the interactions between the crack tip stress fields increases.

Key Words
bridge area; failure mechanism; crack propagation; direct shear test

Address
Hadi Haeri and Zheming Zhu: College of Architecture and Environment, Sichuan University, Chengdu 610065, China

Vahab Sarfarazi: Department of Mining Engineering, Hamedan University of Technology, Hamedan, Iran

Alireza Bagher Shemirani: Department of Civil, Water and Environmental Engineering, Shahid Beheshti University, Tehran, Iran


Abstract
A probabilistic study of a reinforced earth wall in a frictional soil using the surface response methodology (RSM) is presented. A deterministic model based on numerical simulations is used (Abdelouhab et al. 2011, 2012b) and the serviceability limit state (SLS) is considered in the analysis. The model computes the maximum horizontal displacement of the wall. The response surface methodology is utilized for the assessment of the Hasofer-Lind reliability index and is optimized by the use of a genetic algorithm. The soil friction angle and the unit weight are considered as random variables while studying the SLS. The assumption of non-normal distribution for the random variables has an important effect on the reliability index for the practical range of values of the wall horizontal displacement.

Key Words
reinforced earth walls; reliability analysis; surface Response methodology; limit states; approximate performance function; genetic algorithm

Address
Adam Hamrouni: 1.) Department of Civil Engineering, University of Skikda & InfraRES Laboratory, Univ. of Souk-Ahras, Algeria
2.) Grenoble Alpes University, Laboratory 3SR, Grenoble, France

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

Badreddine Sbartai:Department of Civil Engineering, University of Badji Mokhtar-Annaba & LMGHU Laboratory, Univ. of Skikda, Algeria

Abstract
In this study, we propose a three-dimensional simplified slope stability analysis using a hybrid-type penalty method (HPM). In this method, a solid element obtained by the HPM is applied to a column that divides the slope into a lattice. Therefore, it can obtain a safety factor in the same way as simplified methods on the slip surface. Furthermore, it can obtain results (displacement and strain) that cannot be obtained by conventional limit equilibrium methods such as the Hovland method. The continuity condition of displacement between adjacent columns and between elements for each depth is considered to incorporate a penalty function and the relative displacement. For a slip surface between the bottom surface and the boundary condition to express the slip of slope, we introduce a penalty function based on the Mohr-Coulomb failure criterion. To compute the state of the slip surface, an r-min method is used in the load incremental method. Using the result of the simple three-dimensional slope stability analysis, we obtain a safety factor that is the same as the conventional method. Furthermore, the movement of the slope was calculated quantitatively and qualitatively because the displacement and strain of each element are obtained.

Key Words
hybrid-type penalty method; slope stability; slip surface; safety factor; displacement; strain

Address
Kiyomichi Yamaguchi and Norio Takeuchi: Graduate School of Engineering and Design, Hosei University, Tokyo 162-0843, Japan

Eisaku Hamasaki: Adovantechnology Co., Ltd, Sendai 980-0013, Japan


Abstract
In this study, a method of electrochemical consolidation is applied. This method utilizes electro-osmosis, which is an effective ground improvement technique for soft clays, and soil treatment using lime, which is the oldest traditional soil stabilizer. The mechanism of lime treatment for soil involves cation exchange, which leads to the flocculation and agglomeration. Five representative laboratory tests-an electro-osmotic test and four electrochemical tests with various proportions of lime-were performed on dredged marine clay. The objectives of this study are to investigate the effect of electrochemical treatment and to determine the optimum dose for optimal consolidation performance of dredged marine clay. The results show that a better consolidation effect was achieved in terms of current, temperature, and vane shear strength by using electrochemical treatment. The best results were observed for the electrochemical test using 4% lime content.

Key Words
electro-osmosis, electrochemical treatment, lime, dredged marine clay, vane shear strength

Address
Xiaobing Li, Hongtao Fu and Jun Wang: 1.) College of Architecture and Civil Engineering, Wenzhou University, Wenzhou, Zhejiang, China
2.) Key Laboratory of Engineering and Technology for Soft Soil Foundation and Tideland Reclamation, Wenzhou University, Wenzhou, Zhejiang, China
3.)Innovation Center of Tideland Reclamation and Ecological Protection, Wenzhou University, Wenzhou, Zhejiang, China

Guohui Yuan: College of Architecture and Civil Engineering, Wenzhou University, Wenzhou, Zhejiang, China

Yuanqiang Cai: 1.) College of Architecture and Civil Engineering, Wenzhou University, Wenzhou, Zhejiang, China
2.) Innovation Center of Tideland Reclamation and Ecological Protection, Wenzhou University, Wenzhou, Zhejiang, China
3.) Key Laboratory of Soft Soils and Geoenvironmental Engineering, Ministry of Education, Zhejiang University, Hangzhou, Zhejiang, China

Abstract
In deep braced excavations, struts and walers play an essential role in the whole supporting system. For multi-level strut systems, accidental strut failure is possible. Once a single strut fails, it is possible for the loads carried from the previous failed strut to be transferred to the adjacent struts and therefore cause one or more struts to fail. Consequently, progressive collapse may occur and cause the whole excavation system to fail. One of the reasons for the Nicoll Highway Collapse was attributed to the failure of the struts and walers. Consequently, for the design of braced excavation systems in Singapore, one of the requirements by the building authorities is to perform one-strut failure analyses, in order to ensure that there is no progressive collapse when one strut was damaged due to a construction accident. Therefore, plane strain 2D and three-dimensional (3D) finite element analyses of one-strut failure of the braced excavation system were carried out in this study to investigate the effects of one-strut failure on the adjacent struts.

Key Words
three-dimensional; braced excavation; one-strut failure; load transfer percentage; load increase percentage; finite element

Address
Wengang Zhang: 1.) National Joint Engineering Research Center of Geohazards Prevention in the Reservoir Areas, 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, 430072, China

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

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

Fan Zhang: IIIBIT-Sydney, Federation University, NSW 2000, Australia


Abstract
The objective of this paper is to present abacuses obtained from a parametric study of deep-lined tunnels using a numerical finite element model. This numerical model was implemented in software GEOMEC91, which is a two-dimensional axisymmetric model that considers the progress of excavation and the placing of the lining through the activation and deactivation of elements. It is adopted a step of excavation constant (1/3 of radius), constant velocity and circular cross section along the tunnel axis. It is used for rock mass a viscoplastic constitutive law with von-Mises criterion of viscoplasticity without hardening whose deformation rate over time is given by the Bingham model. The lining uses a linear elastic constitutive law. In total are 1716 analysis presented in 60 abacuses that show the value of ultimate convergence (Ueq) due to tunneling speed. In addition, it is shown an example of the use of the abacuses to determine the ultimate convergence (Ueq) of the tunnel and pressure (Peq) on the lining.

Key Words
tunnels; finite element method; long-term analysis; elastic lining; soil-structure interaction

Address
Felipe P. M. Quevedo and Denise Bernaud: Department of Civil Engineering Federal University of Rio Grande do Sul, 99 Osvaldo Aranha, Porto Alegre, Rio Grande do Sul, Brazil

Abstract
In this study, a relationship between small-strain shear modulus (Gmax) and overconsolidation ratio (OCR) based on shear wave velocity (VS) measurement was established to identify the stress history of centrifuge model ground. A centrifuge test was conducted in various centrifugal acceleration levels including loading and unloading sequences to cause various stress histories on centrifuge model ground. The VS and vertical effective stress were measured at each level of acceleration. Then, a sensitivity analysis was conducted using testing data to ensure the suitability of OCR function for the tested cohesionless soils and found that OCR can be estimated based on VS measurements irrespective of normally-consolidated or overconsolidated loading conditions. Finally, the developed Gmax-OCR relationship was applied to centrifuge models constructed and tested under various induced stress-history conditions. Through a series of tests, it was concluded that the induced stress history on centrifuge model by compaction, g-level variation, and past overburden load can be analysed quantitatively, and it is convinced that the OCR evaluation technique will contribute to better interpret the centrifuge test results.

Key Words
overconsolidation ratio (OCR); shear wave velocity (VS); centrifuge tests

Address
Hyung Ik Cho and Chang Guk Sun: Earthquake Research Center, Korea Institute of Geoscience and Mineral Resources,
124 Gwahak-ro, Yuseong-gu, Daejeon 34132, Republic of Korea

Jae Hyun Kim: Department of Infrastructure Safety Research, Korea Institute of Civil Engineering and Building Technology, 283 Goyangdae-ro, Goyang-si, Gyeonggi-do 10223, Republic of Korea

Dong Soo Kim: Department of Civil Engineering, Korean Advanced Institute of Science and Technology,
291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea

Abstract
The brine leakage is a tough problem in artificial freezing engineering. This paper takes the common soft clay in Wujiang District as the study object, and calcium chloride solutions with six salinity levels were considered. The \'classic\' cooling curve method was employed to measure the freezing point of specimens after freeze-thaw. Results indicate that four characteristic stages can be observed including supercooling, abrupt transition, equilibrium and continual freezing, strongly dependent on the variation of unfrozen water content. Two characteristic points were found from the cooling curves, i.e., freezing point and initial crystallization temperature. A critical value for the former exists at which the increment lowers. The higher the saline content approximately linearly, lower the freezing point. In the initial five cycles, the freezing point increases and then stabilizes. Besides, the degree of supercooling was calculated and its correlations with water, salt and freeze-thaw cycles were noted. Finally, an empirical equation was proposed for the relationship of freezing point and three main factors, i.e., water content, saline content and freeze-thaw cycles. Comparison of calculated and measured data proves that it is reliable and may provide guidance for the design and numerical analysis in frozen soil engineering.

Key Words
freezing point; freeze and thaw; frozen soils; salinity; supercooling degree

Address
Songhe Wang, Qinze Wang and Fengyin Liu: Institute of Geotechnical Engineering, Xi\'an University of Technology, Xi

Abstract
This paper presents an investigation on the properties of two types of cement kiln dust (CKD)-stabilized dredged sediments, silt and clay with a comparison to hydrated lime stabilization. Unconfined compressive strength (UCS) and California bearing ratio (CBR) tests were conducted to examine the optimal stabilizer content and classify the type of highway material. A strength development model of treated dredged sediments was performed. The influences of various stabilizer types and sediment types on UCS were interpreted with the aid of microstructural observations, including X-ray diffraction and scanning electron microscopy analysis. The results of the tests revealed that 6% of lime by dry weight can be suggested as optimal content for the improvement of clay and silt as selected materials. For CKD-stabilized sediment as soil cement subbase material, the use of 8% CKD was suggested as optimal content for clay, whereas 6% CKD was recommended for silt; the overall CBR value agreed with the UCS test. The reaction products calcium silicate hydrate and ettringite are the controlling mechanisms for the mechanical performance of CKD-stabilized sediments, whereas calcium aluminate hydrate is the control for lime-stabilized sediments. These results will contribute to the use of CKD as a sustainable and novel stabilizer for lime in highway material applications.

Key Words
cement kiln dust; dredged sediment; pavement materials; stabilization; strength

Address
Naphol Yoobanpot, Pitthaya Jamsawang and Krissakorn Krairan: Soil Engineering Research Center, Department of Civil Engineering, King Mongkut

Abstract
To explore the influence of coal thickness on the mechanical behavior and the failure characteristics of rock-coal-rock (RCR) mass, the experimental investigation of uniaxial compressive tests was conducted first and then a systematic numerical simulation by particle flow code (PFC2D) was performed to deeply analyze the failure mechanical behavior of RCR specimens with different coal thicknesses in conventional compression tests. The overall elastic modulus and peak stress of RCR specimens lie between the rock and the coal. Inter-particle properties were calibrated to match the physical sample strength and the stiffness response. Numerical simulation results show that the deformation and strength behaviors of RCR specimens depend not only on the coal thickness, but also on the confining pressure. Under low confining pressures, the overall failure mechanism of RCR specimen is the serious damage of coal section when the coal thickness is smaller than 30 mm, but it is shear failure of coal section when the coal thickness is larger than 30 mm. Whereas under high confining pressures, obvious shear bands exist in both the coal section and the rock section when the coal thickness is larger than 30 mm, but when the coal thickness is smaller than 30mm, the failure mechanism is serious damage of coal section and shear failure of rock section.

Key Words
rock mechanics; RCR combined body; particle flow; confining pressure; failure; mechanical behavior

Address
Wei-Yao Guo, Yun-Liang Tan, Feng-Hai Yu, Tong-Bin Zhao, Shan-Chao Hu, Dong-Mei Huang: 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 266590, China
2.) National Demonstration Center for Experimental Mining Engineering Education, Shandong University of Science and Technology,Qingdao 266590, China

Zhe Qin: National Demonstration Center for Experimental Mining Engineering Education, Shandong University of Science and Technology,Qingdao 266590, China



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