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CONTENTS
Volume 26, Number 1, July10 2021
 


Abstract
This paper presents a simplified analytical approach for evaluating the load-displacement response of single tapered pile and pile groups under static axial compressive loads. The response of the tapered pile shaft is considered elastically in the initial stage, whereas the increase in stresses due to slippage along the pile-soil interface is obtained from a developed undrained cylindrical cavity expansion solution based on the K0-based anisotropic modified Cam-clay (K0-AMCC) model. An effective iterative computer program is developed to calculate the load-displacement behaviour of a single tapered pile. Regarding the response analysis of tapered pile groups, a finite-difference method is employed to calculate the interaction between tapered pile shaft, and the linear elastic model to simulate the interaction developed at the pile base. A reduction coefficient is introduced into the analysis of pile shaft interaction to clarify the reinforcing effect between tapered piles. Therefore, the settlement calculation methods of pile groups are proposed for different pile cap stiffness. The calculation methods of single tapered pile and pile groups are validated using two 3D Finite Element (FE) programs, and the comparison results show that reasonable predictions can be made using the method proposed in this paper. Parametric studies are conducted to investigate the effects of taper angle, soil anisotropy, pile spacing, and pile number on the load-displacement behaviour of single tapered pile and tapered pile groups.

Key Words
cylindrical cavity expansion; K0-AMCC model; load-displacement behaviour; single tapered pile; tapered pile groups

Address
Yunong Li:Key Laboratory of Green Construction and Intelligent Maintenance for Civil Engineering of Hebei Province, Yanshan University, Qinhuangdao, Hebei Province, People's Republic of China

Wei Li: School of Civil Engineering & Mechanics, Yanshan University, Qinhuangdao, Hebei Province, People's Republic of China

Abstract
This paper summarizes the results of small-scale laboratory modelling of pile behavior under lateral loading, considering the parameters such as short or long, single or group, spacing and rigidity or flexibility of piles. The head of piles was fixedly connected to the cap. In addition, the PIV method has been used to examine the effect of the mentioned parameters on the failure mechanism and pile-soil interaction more accurately. The results show that the short piles have a rigid movement, the displacement of the surrounding soil has occurred along the total length of the pile and the piles rotate around a point but the long piles have a flexible movement at the part of the pile length. It seems that the group effect be more obvious for long piles than short piles. Also, the effective depth of total soil displacement vectors around the trail pile is more than the lead one in long pile group, while this depth for trail pile is less than the lead pile in short pile group. Due to the sharper angles of total displacement vectors around the trail pile, the intensity of soil shear strains around the trail pile is greater than the lead pile.

Key Words
deflection and rotation point; laterally loaded piles; physical modelling; pile group; pile-soil interaction

Address
Aysan Poorjafar nd Hooshang Katebi: Faculty of Civil Engineering, Department of Geotechnical Engineering, University of Tabriz, Tabriz, 5166616471, Iran

Mahzad Esmaeili-Falak: Department of Civil Engineering, Tehran North Branch, Islamic Azad University, Tehran, 1468763785, Iran

Abstract
Although the development and utilization of X-section cast-in-place concrete (XCC) pile have been reported for some time, the long-term effects of XCC piling in fine-grained soil, in particular the set-up effects, have received little attention. This paper reports a coupled effective analysis of XCC piling using the dual-stage Eulerian-Lagrangian (DSEL) technique. The pile installation and subsequent soil consolidation was explicitly and consecutively modelled. The generation of excess pore pressure and alteration of stress states during the pile installation were explored. The distribution and magnitude of effective normal stress at pile/soil interface, in particular its evolution with time, were investigated. The influence of set-up effects on the XCC pile shaft resistance was assessed and quantified. It was found out, although the shaft resistances of both XCC and circular pile develops substantially with time, the consolidation in the wake of XCC pile installation can bring in more capacity enhancements and therefore practical benefits. The ultimate shaft resistance of XCC pile is 45% higher than that of the circular pile of the same cross-sectional area. Additionally, practical advice was given on how to optimize of the cross-sectional shape of XCC piles to take full advantage of set-up effects and achieve economical designs.

Key Words
effective normal stress; large deformation finite element analysis; set-up effect; shaft resistance; XCC pile

Address
Fei Liu, Jiangtao Yi, Junjie Dong and Hang Zhou: School of Civil Engineering, Chongqing University, No.83 Shabei Street, Chongqing, 400045, China

Abstract
In this study, a rock tunnel subjected to blast load is modeled mathematically. For this purpose, a cylindrical shell element is used and the motion equations are derived by energy method and Hamilton's principle. In the inner surface of tunnel, different blast holes are considered and its force in radial direction is coupled by motion equations. The structural damping of the structure is assumed by Kelvin-Voigt model. Hoek-Brown failure criterion is utilized for explosion damage analysis of the tunnel. The motion equations are solved numerically by differential quadrature method (DQM). The effect of different parameters such as depth of tunnel, number and diameter of blast holes, type of stone, geological strength index (GSI) and density of stone, type and mass of explosive material are studied on the damage factor of Hoek-Brown criterion. Numerical results show that with increasing the density of explosive material, number and diameter of blast holes, the thickness of damage is increased in the tunnel. In addition, the depth of damage is decreased with increasing strength, GSI, density of rock and depth of tunnel.

Key Words
blasting; GSI; Hoek-Brown failure criterion tunnel; mathematical modelling; numerical method

Address
Farhad Chinaei and Kaveh Ahangari:Department of Mining Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran

Reza Shirinabadi: Department of Petroleum and Mining Engineering, South Tehran Branch, Islamic Azad University, Tehran, Iran

Abstract
To determine ground stress behavior under the special condition of a regenerated roof, we established a model of elastic rectangular cantilever thin plates. Moreover, the critical conditions for bending and fracturing the regenerated roof during mining were analysed. Meanwhile, by applying continua FLAC-3D numerical simulation, this research simulated changes in the stress and strain on a regenerated roof during mining and proposed prevention and control methods for dynamic disasters. The results show that: (1) the thinner the regenerated roof, the larger the tensile stress on the roof based on analysis using the theoretical model. Furthermore, the longer the advance distance during mining, the greater the tensile stress on the regenerated roof. (2) By analysing simulation results, during the fracturing of the regenerated roof, roof displacement firstly suddenly increases and then gradually decreases to be stable. Floor-heave-induced displacement presents a divergent state, that is, increases outwards in an elliptical manner. (3) For control of the regenerated roof, monitoring on activities of the roof should be strengthened and stress should be relieved timeously. Moreover, effective support methods should be taken to prevent development of hazards on working faces and roadways caused by the widespread behavior of the roof.

Key Words
elastic rectangular cantilever thin plate; ground stress behavior; numerical simulation; regenerated roof; roof control

Address
Xuelong Li: 1.) State Key Laboratory of Mining Disaster Prevention and Control,
Shandong University of Science and Technology, Qingdao, 266590, Shandong, China
2.) State Key Laboratory of Coal Resources and Safe Mining, China University of Mining and Technology, Xuzhou, 221116, Jiangsu, China
3.)College of Energy and Mining Engineering, Shandong University of Science and Technology, Qingdao, 266590, Shandong, China
4.)State Key Laboratory of Coal Mine Disaster Dynamics and Control, College of Resource and Safety Engineering, Chongqing University, Chongqing 400030, China

Shaojie Chen: 1.)State Key Laboratory of Mining Disaster Prevention and Control, Shandong University of Science and Technology, Qingdao, 266590, Shandong, China
2.) College of Energy and Mining Engineering, Shandong University of Science and Technology, Qingdao, 266590, Shandong, China

Qiming Zhang: State Key Laboratory of Coal Resources and Safe Mining, China University of Mining and Technology, Xuzhou, 221116, Jiangsu, China

Xin Gao and Fan Feng: State Key Laboratory of Mining Disaster Prevention and Control, Shandong University of Science and Technology, Qingdao, 266590, Shandong, China

Abstract
Civil engineering structures such as gravity concrete dams, arch dams, pressure tunnels, foundations of high-rise buildings and bridges are generally founded on rock. Design and performance of these structures are highly dependent on the deformation modulus of the rock mass so that expected deformations and/or differential settlements stay within the tolerable limits of the structures. In situ deformation modulus measurements of rock masses are generally performed by using the borehole dilatometer and plate loading tests in Turkey. The diameter of plate loading test device is 30-35 cm. Tests are performed in small unlined tunnels excavated in different elevations of dam abutments. The deformations upon loading are measured on the loading plate in the plate loading tests. It is not possible to exclude the effect of excavation disturbed zone since deformations are not measured with these devices. Large diameter plate test system may have multiple level extensometers set in drill holes opened perpendicular to loading plates. Reading from these extensometers may be utilized to exclude the effect of disturbed zone close to surface together with stress distribution estimated by using elastic theory. There are several field test methods for determining deformation modulus and each method has its own shortcomings. The optimum methodology to correlate plate loading test results with corresponding in-situ deformation modulus values is to back-calculate deformation modulus by using settlements measurements during the construction of dam body. In this paper, Deriner Arch Dam settlements measured during the construction are used to back calculate deformation modulus. It is found that in situ deformation modulus is about two times higher than the average value determined by plate loading tests. This finding will have important effects on the depth of foundation excavations, concrete layers to fortify structure foundations and the amount of consolidation grouting

Key Words
deformation modulus; excavation disturbed zone; plate loading test

Address
Davut Yilmaz: Department of Civil Engineering, Ankara Y

Abstract
With the development of city construction, the situations of foundation pit excavations adjacent to an existing structure occur more frequently. A series of centrifuge model tests and numerical analyses considering actual excavation process were performed to study the deformation and earth pressure of retaining wall, deformation characteristics of retained soil with various limited soil widths. The horizontal displacement and bending moment of the retaining wall decrease with decreasing limited soil width while the rate of the decrease increases with decreasing limited soil width. The horizontal displacement of the retained soil decreases with decreasing limited soil width while the settlement of the retained soil increases with increasing limited soil width. The deformation zone is almost triangular for unlimited condition and trapezoidal for limited condition. As the limited soil width decreases, the deformation zone shrinks and the inclination of deformation zone increases. The lateral earth pressure on the retaining wall shows two-segment distribution and decreases with decreasing limited soil width. The vertical earth pressure shows non-uniform distribution along width and decreases with decreasing limited soil width due to increasing arching effect. The critical width is much smaller than excavation influence width. This may be explained by the fact that only the deformation of soil within critical width will influence the soil near the wall.

Key Words
centrifuge model test; earth pressure; foundation pit excavation; limited soil width; numerical analysis; retaining wall

Address
Hongliu Jin and Ga Zhang: State Key Laboratory of Hydroscience and Engineering, Tsinghua University, Beijing 100084, PR China

Yusheng Yang:China Institute of Water Resources and Hydropower Research, Beijing 100084, PR China

Abstract
This research presents dynamic response analysis of a porous functionally graded (FG) nanobeam under a moving point load. The nanobeam formulation has been established with the use of a higher-order refined beam model and nonlocal strain gradient theory (NSGT) including two scale factors named nonlocal and strain gradient factors. The porous FG material has been modeled via modified power-law functions which contain porosity volume according to even or uneven porosity dispersions. Moreover, graded nonlocality has been considered in order to provide a better modeling of size effects for FG nano-size structures. The governing equations of the nanobeam have been discretized with the use of differential quadrature method (DQM) and inverse Laplace transform approach has been utilized to calculate the dynamic deflections. The main findings of the present research indicate the influences of nonlocal strain gradient factors, moving load speed, pore amount, porosity distribution and elastic medium on dynamic deflection of FG nanobeams.

Key Words
dynamic response; thermal load; moving load; porosity; strain gradient

Address
Kareem Mohsen Raheef, Ridha A. Ahmed, Adil Abed Nayeeif, Raad M. Fenjan and Nadhim M. Faleh: College of Engineering, Mustansiriah University, P.O. Box 46049, Bab-Muadum, Baghdad 10001, Iraq



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