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CONTENTS
Volume 20, Number 2, January25 2020
 

Abstract
The construction of combined pile-raft foundations is considered as the main option in designing foundations in high-rise buildings, especially in soils close to the ground surface which do not have sufficient bearing capacity to withstand building loads. This paper deals with the geotechnical report of the Northern Fereshteh area of Tabriz, Iran, and compares the characteristics of the single pile foundation with the two foundations of pile group and geogrid. Besides, we investigate the effects of five principal parameters including pile diameter and length, the number of geogrid layers, the depth of groundwater level, and pore water pressure on vertical consolidation settlement and pore water pressure changes over a year. This study assessed the mechanism of the failure of the soil under the foundation using numerical analysis as well. Numerical analysis was performed using the two-dimensional finite element PLAXIS software. The results of fifty-four models indicate that the diameter of the pile tip, either as a pile group or as a single pile, did not have a significant effect on the reduction of the consolidation settlement in the soil in the Northern Fereshteh Street region. The optimum length for the pile in the Northern Fereshteh area is 12 meters, which is economically feasible. In addition, the construction of four-layered ten-meter-long geogrids at intervals of 1 meter beneath the deep foundation had a significant preventive impact on the consolidation settlement in clayey soils.

Key Words
consolidation settlement; deep foundation; geogrid; pile; pile group; PLAXIS

Address
Mahdi Shariati: 1.) Division of Computational Mathematics and Engineering, Institute for Computational Science,
Ton Duc Thang University, Ho Chi Minh City 758307, Vietnam
2.) Faculty of Civil Engineering, Ton Duc Thang University, Ho Chi Minh City 758307, Vietnam

Sadaf Mahmoudi Azar: Department of Civil Engineering, Tabriz Branch, Islamic Azad University, Tabriz, Iran

Mohammad-Ali Arjomand: Faculty of Civil Engineering, Shahid Rajaee Teacher Training University, Tehran, Iran

Hesam Salmani Tehrani: School of Civil Engineering, College of Engineering, University of Tehran, Tehran, Iran

Mojtaba Daei: Faculty of Civil Engineering, University of Tabriz, Tabriz, Iran

Maryam Safa: Institute of Research and Development, Duy Tan University, Da Nang 550000, Vietnam


Abstract
The dynamic response of crossing tunnels under heavy-haul train loads is still not fully understood. In this study, based on the case of a high-speed tunnel underneath an existing heavy-haul railway tunnel, a model experiment was performed to research the dynamic response characteristics of crossing tunnels. It is found that the under-crossing changes the dynamic response of the existing tunnel and surrounding rock. The acceleration response of the existing tunnel enhances, and the dynamic stress of rock mass between crossing tunnels decreases after the excavation. Both tunneling and the excitation of heavy-haul train loads stretch the tunnel base, and the maximum tensile strain is 18.35 µe in this model test. Then, the measured results were validated by numerical simulation. Also, a parametric study was performed to discuss the influence of the relative position between crossing tunnels and the advanced support on the dynamic behavior of the existing tunnel, where an amplifying coefficient of tunnel vibration was introduced to describe the change in acceleration due to tunneling. These results reveal the dynamic amplifying phenomenon of the existing tunnel during the new tunnel construction, which can be referred in the dynamic design of crossing tunnels.

Key Words
crossing tunnels; heavy-haul train loads; dynamic response; model experiment; numerical simulation

Address
Jie Dong, Shuai Zhong and Hai-long Wang: College of Civil Engineering, Hebei University of Architecture, Zhangjiakou 075000, Hebei, People\'s Republic of China

Zhi-hui Wu: School of Civil Engineering, Chongqing University, Chongqing 400045, People\'s Republic of China

Abstract
Rock damage is the main cause of accidents in underground engineering. It is difficult to predict rock damage accurately by using only one parameter. In this study, a rock failure prediction model was established by using stress, energy, and damage. The prediction level was divided into three levels according to the ratio of the damage threshold stress to the peak stress. A classification predicting model was established, including the stress, energy, damage and AE impact rate using Bayesian method. Results show that the model is good practicability and effectiveness in predicting the degree of rock failure. On the basis of this, a multi-parameter classification predicting deterioration model of rock failure was established. The results provide a new idea for classifying and predicting rockburst.

Key Words
rock failure; multi-parameter; acoustic emission; Bayesian; classified predicting

Address
Chunlai Wang, Changfeng Li, Zeng Chen, Zefeng Liao and Feng Shi: School of Energy and Mining Engineering, China University of Mining and Technology Beijing, 100083, Beijing, China

Guangming Zhao:School of Energy and Safety Engineering, Anhui University of Science and Technology, 232001, Huainan, Anhui, China

Weijian Yu: School of Resource and Environment and Safety Engineering, Hunan University of Science and Technology, 411201, Hunan Xiangtan, China

Abstract
In the design of geotechnical structures, engineers choose either peak or critical state friction angles. Unfortunately, this selection is based on engineer\'s preference for economy or safety and lacks the assessment of the expected level of deformation. To fill this gap in the design process, this study proposes a strain based empirical method. Proposed method is founded on the experimentally supported assumption that higher dilatancy angles result in more brittle soil response. Using numerous triaxial test data on ten different soils, an empirical design chart is developed that allows the estimation of shear strain at failure based on soil\'s peak dilatancy angle and mean grain diameter. Developed empirical chart is verified by conducting a small scale retaining wall physical model test. Finally, a design methodology is proposed that makes the selection of design friction angle in structured way possible based on the serviceability limits of the proposed structure.

Key Words
angle of dilation; friction angle; model test; particle image velocimetry; coarse grained soils

Address
Emirhan Sancak and Ozer Cinicioglu: Department of Civil Engineering, Faculty of Engineering, Bogazici University, 34342, Istanbul, Turkey

Abstract
Evaluation of earthquake impacts in settlements with a high risk of earthquake occurrence is important for the determination of site-specific dynamic soil parameters and earthquake-resistant structural planning. In this study, dynamic soil properties of Karliova (Bingol) city center, located near to the intersection point of the North Anatolian Fault Zone and the East Anatolian Fault Zone and therefore having a high earthquake risk, were investigated by one-dimensional equivalent linear site response analysis. From ground response analyses, peak ground acceleration, predominant site period, 0.2-sec and 1-sec spectral accelerations and soil amplification maps of the study area were obtained for both near-field and far-field earthquake effects. The average acceleration spectrum obtained from analysis, for a near-field earthquake scenario, was found to exceed the design spectra of the Turkish Earthquake Code and Eurocode 8. Yet, the average acceleration spectrum was found to remain below the respective design spectra of the two codes for the far-field earthquake scenario. According to both near- and far-field earthquake scenarios in the study area, the low-rise buildings with low modal vibration durations are expected to be exposed to high spectral acceleration values and high-rise buildings with high modal vibration durations will be exposed to lower spectral accelerations. While high amplification ratios are observed in the north of the study area for the near-distance earthquake scenario, high amplification ratios are observed in the south of the study area for the long-distance earthquake scenario.

Key Words
site response analysis; far-field effect; near- field effect; local soil conditions; Karl

Address
Yetis Bulent Sonmezer: Department of Civil Engineering, Faculty of Engineering, Kirikkale University, 71450 Kirikkale, Turkey

Murat Celiker: 9th Regional Directorate, General Directorate of State Hydraulic Works, 23200 Elazig, Turkey

Abstract
A novel approach for predicting lateral displacement caused by pile installation in anisotropic clay is presented, on the basis of the cylindrical and spherical cavities expansion theory. The K0-based modified Cam-clay (K0-MCC) model is adopted for the K0-consolidated clay and the process of pile installation is taken as the cavity expansion problem in undrained condition. The radial displacement of plastic region is obtained by combining the cavity wall boundary and the elastic-plastic (EP) boundary conditions. The predicted equations of lateral displacement during single pile and multi-pile installation are proposed, and the hydraulic fracture problem in the vicinity of the pile tip is investigated. The comparison between the lateral displacement obtained from the presented approach and the measured data from Chai et al. (2005) is carried out and shows a good agreement. It is suggested that the presented approach is a useful tool for the design of soft subsoil improvement resulting from the pile installation.

Key Words
lateral displacement; pile installation; anisotropic clay; cavity expansion; modified Cam-clay model

Address
Chao Li and Jin-feng Zou: School of Civil Engineering, Central South University, Hunan 410075, China

Lin Li: Department of Geotechnical Engineering, Tongji University, Shanghai 200092, China

Abstract
In recent years, the stability, safety and comfort of trains has received increased attention. The mechanical characteristics and differential settlement of the foundation are the main problems studied in high-speed railway research. The mechanical characteristics and differential settlement of the foundation are greatly affected by the ground treatment. Additionally, the effects of train load and earthquakes have a great impact. The dynamic action of the train will increase the vibration acceleration of the foundation and increase the cumulative deformation, and the earthquake action will affect the stability of the substructure. Earthquakes have an important practical significance for the dynamic analysis of the railway operation stage; therefore, considering the impact of earthquakes on the railway substructure stability has engineering significance. In this paper, finite element model of the CFG (Cement Fly-ash Gravel) pile + cement-soil compacted pile about composite foundation is established, and manual numerical incentive method is selected as the simulation principle. The mechanical characteristics and differential settlement of CFG pile + cement-soil compacted pile about composite foundation under train load are studied. The results show: under the train load, the neutral point of the side friction about CFG pile is located at nearly 7/8 of the pile length; the vertical dynamic stress-time history curves of the cement-soil compacted pile, CFG pile and soil between piles are all regular serrated shape, the vertical dynamic stress of CFG pile changes greatly, but the vertical dynamic stress of cement-soil compacted pile and soil between piles does not change much; the vertical displacement of CFG pile, cement-soil compacted pile and soil between piles change very little.

Key Words
composite foundation; train load; mechanical characteristics; differential settlement

Address
Xuansheng Cheng, Gongning Liu, Lijun Gong: 1.) Key Laboratory of Disaster Prevention and Mitigation in Civil Engineering of Gansu Province, Lanzhou University of Technology, No. 287, Langongping Road, Qilihe District, Lanzhou, Gansu province, China
2.) Western Engineering Research Center of Disaster Mitigation in Civil Engineering of Ministry of Education, Lanzhou University of Technology, No. 287, Langongping Road, Qilihe District, Lanzhou, Gansu province, China

Xinhai Zhou: Western Engineering Research Center of Disaster Mitigation in Civil Engineering of Ministry of Education, Lanzhou University of Technology, No. 287, Langongping Road, Qilihe District, Lanzhou, Gansu province, China

Baozhen Shi: China Railway 21st Bureau Group Sixth Engineering Co., LTD., No. 921, Beibinhe west road, Anning District, Lanzhou, Gansu province, China

Abstract
The enzyme-induced carbonate precipitation (EICP) method has been investigated to improve the hydro-mechanical properties of natural soil deposits. This study was conducted to explore the stiffness evolution during various stress scenarios. First, the optimal concentration of urea, CaCl2, and urease for the maximum efficiency of calcite precipitation was identified. The results show that the optimal recipe is 0.5 g/L and 0.9 g/L of urease for 0.5 M CaCl2 and 1 M CaCl2 solutions with a urea-CaCl2 molar ratio of 1.5. The shear stiffness of EICP-treated sands remains constant up to debonding stresses, and further loading induces the reduction of S-wave velocity. It was also found that the debonding stress at which stiffness loss occurs depends on the void ratio, not on cementation solution. Repeated loading-unloading deteriorates the bonding quality, thereby reducing the debonding stress. Scanning electron microscopy and X-ray images reveal that higher concentrations of CaCl2 solution facilitate heterogeneous nucleation to form larger CaCO3 nodules and 11-12 % of CaCO3 forms at the inter-particle contact as the main contributor to the evolution of shear stiffness.

Key Words
enzyme; CaCO3; debonding; shear stiffness; stress relaxation; X-ray CT

Address
Jun Young Song: Korea Polar Research Institute, Incheon 21990, Republic of Korea

Youngjong Sim: Land and Housing Institute, Korea Land and Housing Corporation, Daejeon 34047, Republic of Korea

Sun Yeom: Korea Institute of Civil Engineering and Building Technology, Gyeonggi-Do 10223, Republic of Korea

Jaewon Jang: Department of Civil and Environmental Engineering, Hanyang University, Seoul 04763, Republic of Korea

Tae Sup Yun: Department of Civil and Environmental Engineering, Yonsei University, Seoul 03722, Republic of Korea


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