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CONTENTS
Volume 14, Number 2, February10 2018
 

Abstract
Coal samples with different joints morphology were subjected to uniaxial compression experiments, cracks evolution was recorded by Nikon D5300 and acoustic emission (AE) energy signals were collected by AEwin Test for Express-8.0. During loading process, coal samples deformed elastically with no obvious cracks changes, then they expanded gradually along the trace of the original cracks, accompanied by the formation of secondary cracks, and eventually produced a large-scale fracture. It was more interesting that the failure mode of samples were all shear shape, whatever the original cracks morphology was. With cracks and damage evolution, AE energy radiated regularly. At the early loading stage, micro damage and small scale fracture events only induced a few AE events with less energy, while large scale fracture leaded to a number of AE events with more energy at the later stage. Based on the multifractal theory, the multifractal spectrum could explain AE energy signals frequency responses and the causes of AE events with load. Multifractal spectrum width (∆a), could reflect the differences between the large and small AE energy signals. And another parameter (∆f ) could reflect the relationship between the frequency of the least and greatest signals in the AE energy time series. This research is helpful for us to understand cracks evolution and AE energy signals causes.

Key Words
cracks evolution; multifractal; acoustic emission; load; coal

Address
Xiangguo Kong, Enyuan Wang, Xiaofei Liu, Dexing Li and Quanlin Liu: 1.) Key Laboratory of Gas and Fire Control for Coal Mines, China University of Mining and Technology, Xu Zhou, Jiangsu 221116, China

2.) State Key Laboratory of Coal Resources and Safe Mining, China University of Mining and Technology, Xu Zhou, Jiangsu 221116, China

3.) School of Safety Engineering, China University of Mining and Technology, Xu Zhou, Jiangsu 221116, China


Xueqiu He: 1.)School of Safety Engineering, China University of Mining and Technology, Xu Zhou, Jiangsu 221116, China

2.) College of Civil and Resource Engineering, University of Science and Technology Beijing, Beijing 100083, China


Abstract
This paper presents a set of results of plate load tests that imposed incremental cyclic loading to a sandy soil bed containing multiple layers of granulated rubber-soil mixture (RSM) at large model scale. Loading and unloading cycles were applied with amplitudes incrementally increasing from 140 to 700 kPa in five steps. A thickness of the RSM layer of approximately 0.4 times the footing diameter was found to deliver the minimum total and residual settlements, irrespective of the level of applied cyclic load. Both the total and residual settlements decrease with increase in the number of RSM layers, regardless of the level of applied cyclic load, but the rate of reduction in both settlements reduces with increase in the number of RSM layers. When the thickness of the RSM layer is smaller, or larger, settlements increase and, at large thicknesses may even exceed those of untreated soil. Layers of the RSM reduced the vertical stress transferred through the foundation depth by distributing the load over a wider area. With the inclusion of RSM layers, the coefficient of elastic uniform compression decreases by a factor of around 3-4. A softer response was obtained when more RSM layers were included beneath the footing damping capacity improves appreciably when the sand bed incorporates RSM layers. Numerical modeling using \"FLAC-3D\" confirms that multiple RSM layers will improve the performance of a foundation under heavy loading.

Key Words
cyclic loading; multiple RSM layers; residual and resilient settlements; coefficient of elastic uniform compression (CEUC); numerical analysis

Address
S.N. Moghaddas Tafreshi and N. Joz Darabi: Department of Civil Engineering, K.N. Toosi University of Technology, Valiasr St., Mirdamad Cr., Tehran, Iran

A.R. Dawson: Nottingham Transportation Engineering Centre, University of Nottingham, Nottingham, U.K.

Abstract
The preparation of repeatable and uniformly reconstituted soil specimens up to the specified conditions is an essential requirement for the laboratory tests. In this study for large samples replication, the simultaneous usage of the traveling pluviation and curtain raining technique is used to develop a new method, called the curtain travelling pluviator (CTP). This simple and cost effective system is based on the air pluviation approach, whilst reducing the sample production time, can reproduce uniform samples with relative densities ranging from 25% to 96%. In order to investigate the resulting suitability and uniformity from the proposed method, a series of tests is performed. The effect of curtain traveling velocity, curtain width, drop height, and flow rate on the parameters of the sample is thoroughly investigated. Increase in the curtain velocity and drop height leads to the increase in relative density for the sand specimen. Increase in curtain width typically resulted in the reduction of relative density. Test results reveal that the terminal drop height for the sand specimen in this study is more than 500 mm. Relative density contour lines are presented that can be utilized in optimizing the drop height and curtain width parameters. Sample uniformity in the vertical and horizontal orientation is investigated through the sampling containers. Increasing relative density tends to result in the higher sample repeatability and uniformity.

Key Words
traveling pluviation; curtain raining; sand specimen preparation; relative density; uniformity

Address
Majid Kazemi and Jafar B. Bolouri: Department of Civil Engineering, Ferdowsi University of Mashhad, Mashhad, Iran

Abstract
In this paper, the creep behavior of bolted rock was analyzed by using the unconfined creep tests and the numerical results. Based on the test results, the Bolted Burgers creep model (B-B model) was proposed to clarify the creep mechanism of rock mass due to rock bolts. As to the simulation of the creep behaviour of bolted rock, a new user-defined incremental iterative format of the B-B model was established and the open-source FLAC3D code was written by using the object-oriented language (C++). To check the reliability of the present B-B creep constitutive model program, a numerical model of a tunnel with buried depth of 1000 m was established to analyze the creep response of the tunnel with the B-B model support, the non-support and the bolt element support. The simulation results show that the present B-B model is consistent with the calculated results of the inherent bolt element in FLAC3D, and the convergence deformation can be more effectively controlled when the proposed B-B model is used in the FLAC3D software. The big advantage of the present B-B creep model secondarily developed in the FLAC3D software is the high computational efficiency.

Key Words
bolted rock; creep test; Bolted Burgers model; FLAC3D secondary development

Address
Tong-Bin Zhao, Yu-Bao Zhang and Yun-Liang Tan: 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, Shandong 266590, PR China

Qian-Qing Zhang:Geotechnical and Structural Engineering Research Center, Shandong University, Jinan, Shandong 250061, PR China

Abstract
Annually, the global production of construction aggregates reaches over 40 billion tons, making aggregates the largest mining sector by volume and value. Currently, the aggregate industry is shifting from sand to hard rock as a result of legislation limiting the extraction of natural sands and gravels. A major implication of this change in the aggregate industry is the need for understanding rock fragmentation and energy absorption to produce more cost-effective aggregates. In this paper, we focused on incorporating dynamic rock and soil mechanics to understand the effects of loading rate and water saturation on the rock fragmentation and energy absorption of three different sandstones (Red, Berea and Buff) with different pore sizes. Rock core samples were prepared in accordance to the ASTM standards for compressive strength testing. Saturated and dry samples were subsequently prepared and fragmented via fast and dynamic compressive strength tests. The particle size distributions of the resulting fragments were subsequently analyzed using mechanical gradation tests. Our results indicate that the rock fragment size generally decreased with increasing loading rate and water content. In addition, the fragment sizes in the larger pore size sample (Buff sandstone) were relatively smaller those in the smaller pore size sample (Red sandstone). Notably, energy absorption decreased with increased loading rate, water content and rock pore size. These results support the conclusion that rock fragment size is positively correlated with the energy absorption of rocks. In addition, the rock fragment size increases as the energy absorption increases. Thus, our data provide insightful information for improving cost-effective aggregate production methods.

Key Words
rock fragmentation sizes; dynamic and fast loading rates; hydration effect; porosity; energy absorption; split Hopkinson pressure bar (SHPB)

Address
Eunhye Kim: Department of Mining Engineering, Colorado School of Mines, 1610 Illinois Street, Golden CO 80401, U.S.A.

Adriana Garcia and Hossein Changani: Department of Mining Engineering, University of Utah, Salt Lake City UT 84102, U.S.A

Abstract
The present study investigates the soil-structure interaction (SSI) effects on the seismic performance of smart base-isolated structures. The adopted control algorithm for tuning the control force plays a key role in successful implementation of such structures; however, in most studied carried out in the literature, these algorithms are designed without considering the SSI effect. Considering the SSI effects, a linear quadratic regulator (LQR) controller is employed to seismic control of a smart base-isolated structure. A particle swarm optimization (PSO) algorithm is used to tune the gain matrix of the controller in both cases without and with SSI effects. In order to conduct a parametric study, three types of soil, three well-known earthquakes and a vast range of period of the superstructure are considered for assessment the SSI effects on seismic control process of the smart-base isolated structure. The adopted controller is able to make a significant reduction in base displacement. However, any attempt to decrease the maximum base displacement results in slight increasing in superstructure accelerations. The maximum and RMS base displacements of the smart base-isolated structures in the case of considering SSI effects are more than the corresponding responses in the case of ignoring SSI effects. Overall, it is also observed that the maximum and RMS base displacements of the structure are increased by increasing the natural period of the superstructure. Furthermore, it can be concluded that the maximum and RMS superstructure accelerations are significant influenced by the frequency content of earthquake excitations and the natural frequency of the superstructure. The results show that the design of the controller is very influenced by the SSI effects. In addition, the simulation results demonstrate that the ignoring the SSI effect provides an unfavorable control system, which may lead to decline in the seismic performance of the smart-base isolated structure including the SSI effects.

Key Words
base isolation; soil-structure interaction; smart base-isolated structures; LQR controller; particle swarm optimization algorithm

Address
Saeed Shourestani, Fazlollah Soltani and Mojtaba Ghasemi: Department of Civil and Surveying Engineering, Graduate University of Advanced Technology, Kerman, Iran

Sadegh Etedali: Department of Civil Engineering, Birjand University of Technology, Birjand, Iran

Abstract
Sand Compaction Piles (SCPs) are constructed by feeding and compacting sand into soft clay ground. Sand piles have been installed with irregular cross-sectional shapes, and mixtures of both sand and clay, which violate the design requirement of circular shape according to the replacement area ratio due to various factors, including side flow pressure. Therefore, design assumptions cannot be satisfied according to the conditions of the ground and construction and the replacement area ratio. Two case histories were collected, examined, and interpreted in order to study the effect of the shape of SCPs. The effects of the distortion of SCP shape and the mixture of sand and clay were studied with the results of large direct shear tests. The design internal friction angle was secured with the irregular cross-sectional sand piles regardless of the replacement area ratio. The design internal friction angle was secured regardless of mixed condition when the mixture of sand and clay was higher than the replacement area ratio of 65%. Therefore, systematic construction management is recommended with a replacement area ratio below 65%.

Key Words
sand compaction pile (SCP); replacement area ratio; composite soil; mixed soil; large scale direct shear test

Address
Jeonggeun Kwon and Changyoung Kim: Research Institute of Industrial Technology, Pusan National University, 2 Busandaehak-ro 63beon-gil (40 Jangjeon-dong),
Geumjeong-gu, Busan, Republic of Korea

Jong-Chul Im and Jae-won Yoo: Department of Civil Engineering, Pusan National University 2 Busandaehak-ro 63beon-gil (40 Jangjeon-dong), Geumjeong-gu, Busan, Republic of Korea

Abstract
Water inrush through the destruction of water resisting rock mass structure was divided into direct water inrush, key block water inrush and splitting water inrush. In the direct water inrush, the Reynolds numbers has a significant effect on the distribution of the water flow and vortex occurred in the large Reynolds numbers. The permeability coefficient of the fracture is much larger than the rock, and the difference is between 104 and 107 times. The traditional theory and methods are not considering the effect of inertia force. In the position of the cross fracture, the distribution of water flow can only be linearly distributed according to the fracture opening degree. With the increase of Reynolds number, the relationship between water flow distribution and fracture opening is studied by Semtex.

Key Words
water inrush; Reynolds numbers; permeability coefficient; cross fracture; the distribution of water flow

Address
Jing Wang, Shu-Cai Li and Cheng-Lu Gao: Geotechnical and Structural Engineering Research Center, Shandong University, Jinan 250061, Shandong, China

Li-Ping Li: 1.) Geotechnical and Structural Engineering Research Center, Shandong University, Jinan 250061, Shandong, China

2.) State Key Lab of Subtropical Building Science, South China University Of Technology, Guangzhou 510005, Guangdong, China


Abstract
Many laboratory experiments on crack propagation under uniaxial loading and biaxial loading have been conducted in the past using transparent materials such as resin, polymethyl methacrylate (PMMA), etc. However, propagation behaviors of three-dimensional (3D) cracks in rock or rock-like materials under tri-axial loading are often considerably different. In this study, a series of true tri-axial loading tests on the rock-like material with two semi-ellipse pre-existing cracks were performed in laboratory to investigate the acoustic emission (AE) characteristics and propagation characteristics of 3D crack groups influenced by intermediate principal stress. Compared with previous experiments under uniaxial loading and biaxial loading, the tests under true tri-axial loading showed that shear cracks, anti-wing cracks and secondary cracks were the main failure mechanisms, and the initiation and propagation of tensile cracks were limited. Shear cracks propagated in the direction parallel to pre-existing crack plane. With the increase of intermediate principal stress, the critical stress of crack initiation increased gradually, and secondary shear cracks may no longer coalesce in the rock bridge. Crack aperture decreased with the increase of intermediate principal stress, and the failure is dominated by shear fracturing. There are two stages of fracture development: stable propagation stage and unstable failure stage. The AE events occurred in a zone parallel to pre-existing crack plane, and the AE zone increased gradually with the increase of intermediate principal stress, eventually forming obvious shear rupture planes. This shows that shear cracks initiated and propagated in the pre-existing crack direction, forming a shear rupture plane inside the specimens. The paths of fracturing inside the specimens were observed using the Computerized Tomography (CT) scanning and reconstruction.

Key Words
three-dimensional crack; true tri-axial loading; intermediate principal stress; propagation; acoustic emission; CT scan and reconstruction

Address
Xi Z. Sun: College of Mining and Safety Engineering, Shandong University of Science and Technology, 579 Qianwangang Road, Huangdao District, Qingdao, Shandong Province, 266590, China

B. Shen: 1.) College of Mining and Safety Engineering, Shandong University of Science and Technology, 579 Qianwangang Road, Huangdao District, Qingdao, Shandong Province, 266590, China

2.) Commonwealth Scientific and Industrial Research Organization (CSIRO) Energy, P.O. Box 883, Kenmore, Brisbane QLD 4069, Australia

Bao L. Zhang: 1.) College of Mining and Safety Engineering, Shandong University of Science and Technology, 579 Qianwangang Road, Huangdao District, Qingdao, Shandong Province, 266590, China

2.) School of Architecture and Civil Engineering, Liaocheng University, NO.1 Hunan Road, Dongchangfu District, Liaocheng, Shandong Province, 252059, China





Abstract
Reliable estimation of compressive as well as tensile in-situ stresses is critical in the design and analysis of underground structures and openings in rocks. Kaiser effect technique, which uses acoustic emission from rock specimens under cyclic load, is well established for the estimation of in-situ compressive stresses. This paper investigates the Kaiser effect on marble specimens under cyclic uniaxial compressive as well as cyclic uniaxial tensile conditions. The tensile behavior was studied by means of Brazilian tests. Each specimen was tested by applying the load in four loading cycles having magnitudes of 40%, 60%, 80% and 100% of the peak stress. The experimental results confirm the presence of Kaiser effect in marble specimens under both compressive and tensile loading conditions. Kaiser effect was found to be more dominant in the first two loading cycles and started disappearing as the applied stress approached the peak stress, where felicity effect became dominant instead. This behavior was observed to be consistent under both compressive and tensile loading conditions and can be applied for the estimation of in-situ rock stresses as a function of peak rock stress. At a micromechanical level, Kaiser effect is evident when the pre-existing stress is smaller than the crack damage stress and ambiguous when pre-existing stress exceeds the crack damage stress. Upon reaching the crack damage stress, the cracks begin to propagate and coalesce in an unstable manner. Hence acoustic emission observations through Kaiser effect analysis can help to estimate the crack damage stresses reliably thereby improving the efficiency of design parameters.

Key Words
acoustic emission (AE); Kaiser effect; marble; cyclic uniaxial compressive test; cyclic Brazilian test

Address
Yulong Chen: Department of Hydraulic Engineering, Tsinghua University, China

Muhammad Irfan: Civil Engineering Department, University of Engineering and Technology Lahore, Pakistan

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