Techno Press
Tp_Editing System.E (TES.E)
Login Search


gae
 
CONTENTS
Volume 21, Number 3, May10 2020
 

Abstract
Non-destructive exploration using elastic waves has been widely used to characterize rock mass properties. Wave propagation in jointed rock masses is significantly governed by the characteristics and orientation of discontinuities. The relationship between spatial heterogeneity (i.e., joint spacing) and wavelength for elastic waves propagating through jointed rock masses have been investigated previously. Discontinuous rock masses can be considered as an equivalent continuum material when the wavelength of the propagating elastic wave exceeds the spatial heterogeneity. However, it is unclear how stress-dependent long-wavelength elastic waves propagate through a repetitive rock-joint system with multiple joints. A preliminary numerical simulation was performed in in this study to investigate long-wavelength elastic wave propagation in regularly jointed rock masses using the three-dimensional distinct element code program. First, experimental studies using the quasi-static resonant column (QSRC) testing device are performed on regularly jointed disc column specimens for three different materials (acetal, aluminum, and gneiss). The P- and S-wave velocities of the specimens are obtained under various normal stress levels. The normal and shear joint stiffness are calculated from the experimental results using an equivalent continuum model and used as input parameters for numerical analysis. The spatial and temporal sizes are carefully selected to guarantee a stable numerical simulation. Based on the calibrated jointed rock model, the numerical and experimental results are compared.

Key Words
rock mass; elastic wave velocity; quasi-static resonant column test; joint stiffness; DEM simulation

Address
Song-Hun Chong: Department of Civil Engineering, Sunchon National University 255 Jungang-ro, Sunchon, Jeollanam-do 57922, Republic of Korea

Ji-Won Kim and Gye-Chun Cho: Department of Civil and Environmental Engineering, KAIST, 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea

Ki-Il Song: Department of Civil Engineering, Inha University, 100 Inha-ro, Michuhol-gu, Incheon 22212, Republic of Korea


Abstract
The process of evaporation from free water surface was simulated in a large scale environmental chamber under various controlled atmospheric conditions and also was modelled by a new mass transfer model. Six evaporation tests were conducted with increasing wind speed and air temperature in the environmental chamber, and hence the effect of atmosphere parameters on the evaporation process and the corresponding response of water were investigated. Furthermore, based on the experiment results, seven general types of mass transfer models were evaluated firstly, and then a new model consisted of wind speed function and air relative humidity function was proposed and validated. The results show that the free water evaporation is mainly affected by the atmospheric parameters and the evaporation rate increases with the increasing air temperature and wind speed. Both the air and soil temperatures are affected by the energy transformation during water evaporation. The new model can satisfactorily describe the evaporation process from free water surface under different atmospheric conditions.

Key Words
free water surface; evaporation rate; mass transfer model; environmental chamber

Address
Wei-Kang Song and Yibo Chen: School of Civil Engineering, Zhengzhou University, 100 Science Avenue, Zhengzhou, China

Abstract
The shear strength of unsaturated soils, a research hotspot in geotechnical engineering, has great guiding significance for geotechnical engineering design. Although kinds of calculation models for the shear strength of unsaturated soil have been put forward by predecessors, there is still need for new models to extensively consider the nonlinear variation of shear strength, particularly for the nonlinear effect of the net normal stress on the shear strength of unsaturated soil. Here, the shear strength of unsaturated soils is explored to study the nonlinear effects of net normal stress with the introduction of a general nonlinear Mohr-Coulomb (M-C) strength criterion, and the relationship between the matric suction (or suction stress) and degree of saturation (DOS) constructed by the soil-water characteristics curve (SWCC) of van Genuchten is also applied for unsaturated soil. Then, two calculation models (i.e., an envelope shell model and an effective stress model) are established for the shear strength of unsaturated soils under the nonlinear strength theory. In these two models, the curve of the shear strength of unsaturated soils versus the net normal stress exhibits a tendency to gently. Moreover, the proposed formulas have flexibility and convenience with five parameters (for the effective stress model) or six parameters (for the envelope shell model), which are from the M-C strength parameters of the saturated soil and fitting parameters of SWCC of van Genuchten. Thereafter, by comparison with the classical theory of the shear strength of unsaturated soils from some actual cases, the rationality and accuracy of the present models were verified.

Key Words
shear strength of unsaturated soil; soil-water characteristic curve (SWCC); suction stress; envelope shell model; effective stress model

Address
Dongping Deng, Shasha Wen, Kuan Lu and Liang Li: School of Civil Engineering, Central South University, Changsha 410075, China

Abstract
The synthetic rock mass (SRM) were used to investigate the influence of specimen size on the mechanical properties of jointed rock mass. The SRM were established based on parallel bond model (PBM) and smooth joint model (SJM) and the scaled rock specimens were sampled in two SRMs considering three sampling locations. The research results show that the smaller the initial fracture density is, the greater the uniaxial compressive strength (UCS), elastic modulus (E) is when compared with the same sampling location. The mechanical properties of rock specimens obtained by different sampling methods in different SRMs have different scale effects. The strength of rock specimens with more new cracks is not necessarily less than that of rock specimens with fewer new cracks and the failure of rock is caused by the formation of macro-fracture surface.

Key Words
synthetic rock mass; scale effect; mechanical properties; failure mode

Address
Xiao Wang, Wei Yuan and Yatao Yan: School of Civil Engineering, Southeast University, Nanjing 210096, China

Xue Zhang: College of Mining and Safety Engineering, Shandong University of Science and Technology, Qingdao 266590, China

Abstract
In this study, numerical analyses were conducted to investigate the load transfer mechanisms and dynamic responses between the vertical shaft and the surrounding soil using a dynamic analysis method and a pseudo-static method (called response displacement method, RDM). Numerical solutions were verified against data from the literature. A series of parametric studies was performed with three different transient motions and various surrounding soils. The results showed that the soil stratigraphy and excitation motions significantly influenced the dynamic behavior of the vertical shaft. Maximum values of the shear force and bending moment occurred near an interface between the soil layers. In addition, deformations and load distributions of the vertical shaft were highly influenced by the amplified seismic waves on the vertical shaft constructed in multi-layered soils. Throughout the comparison results between the dynamic analysis method and the RDM, the results from the dynamic analyses showed good agreement with those from the RDM calculated by a double-cosine method.

Key Words
vertical shaft; underground structure; multi-layered soil; seismic design; dynamic analysis; response displacement method (RDM)

Address
Yongmin Kim: School of Civil and Environmental Engineering, Nanyang Technological University,50 Nanyang Avenue, Singapore 639798, Singapore

Hyunsung Lim: Department of Infrastructure Safety Research, Korea Institute of Civil Engineering and Building Technology
283 Goyangdae-ro, Ilsanseo-gu, Goyang-si, Gyeonggi-do 10223, Republic of Korea

Sangseom Jeong: Department of Civil and Environmental Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Republic of Korea

Abstract
The permeation grouting is a commonly used technique to improve the engineering geology condition of the soft ground. It is of great significance to predict the permeation range of the grout so as to ensure the effects of grouting. This paper conducts a theoretical analysis of jet-grouting effects in ground improvement and rotary grouting pile installation by utilizing deformation-permeation coupled poroelastic solutions based on Biot\'s s theory and Laplace-Fourier integral transform technique. The exponential function and the intermittent trigonometric function are chosen to represent time-dependent grouting pressure usually encountered in ground improvement and rotary grouting pile installation process, respectively. The results, including the radial displacement, the hoop stress, the excess pore fluid pressure, the radial discharge, and the permeation radius of grout, are presented for different grouting time, radial positions and grouting lengths. Parametric study is conducted to explore the effects of variation of the exponent in the exponential grouting pressure-time relationship on grouting-induced responses. It is expected that the proposed solutions can be used to estimate the permeation range of grouting in ground improvement and rotary grouting pile installation.

Key Words
poroelastic; coupled permeation and deformation; ground improvement; rotary grouting pile; grouting pressure

Address
You Wang and Jingpei Li: Department of Civil Engineering, Tongji University, Shanghai 200092, China

Lin Li: Department of Civil and Environmental Engineering, Louisiana State University, LA 70803, U.S.A.

De\'an Sun: Department of Civil Engineering, Shanghai University, Shanghai 200444, China

Abstract
Estimating the damage induced by an explosion around a blast hole has always been a challenging issue in geotechnical engineering. It is difficult to determine an exact dimension for damage zone since many parameters are involved in the formation of failures, and there are some uncertainties lying in these parameters. Thus, the present study adopted a probabilistic approach towards this problem. First, a reliability model of the problem was established and the failure probability of induced damage was calculated. Then, the corresponding exceedance risk curve was developed indicating the relation between the failure probability and the cracked zone radius. The obtained risk curve indicated that the failure probability drops dramatically by increasing the cracked zone radius so that the probability of exceedance for any crack length greater than 4.5 m is less than 5%. Moreover, the effect of each parameter involved in the probability of failure, including blast hole radius, explosive density, detonation velocity, and tensile strength of the rock, was evaluated by using a sensitivity analysis. Finally, the impact of the decoupling ratio on the reduction of failures was investigated and the location of its maximum influence was demonstrated around the blast point.

Key Words
failure probability; cracked zone radius; Monte Carlo method; reliability analysis; exceedance risk curve

Address
Mahdi Shadabfar: Department of Civil Engineering, Sharif University of Technology, Azadi Avenue, Tehran, Iran

Hongwei Huang: Department of Geotechnical Engineering, Tongji University, No. 1239, Siping Road, Shanghai, China

uan Wang and Chenglong Wu: Department of Geotechnical Engineering, Hohai University, No. 1, Xikang Road, Nanjing, China

Abstract
In the process of mining closely spaced coal seams, the problem of roadway arrangement in lower coal seams has long been a concern. By means of mechanical model calculation and numerical simulation postprocessing, the distribution of the stress deviator below the floor of a goaf and the evolution of the stress deviator in the vertical and horizontal directions are studied under the influence of horizontal stress. The results of this theoretical study and numerical simulation show that the stress deviator decreases exponentially with increasing depth from the floor below the coal side. With the increase in the horizontal stress coefficient

Key Words
closely spaced coal seams; roadway layout; stress deviator; horizontal stress

Address
Zhaolong Li, Renliang Shan,Honghu Yuan and Yonghui Wei: School of Mechanics and Civil Engineering, China University of Mining & Technology (Beijing), Beijing 100083, China

Chunhe Wang: 1.) School of Mechanics and Civil Engineering, China University of Mining & Technology (Beijing), Beijing 100083, China
2.) China Construction Communications Engineering Group Corporation Limited, Beijing 100161, China


Techno-Press: Publishers of international journals and conference proceedings.       Copyright © 2020 Techno-Press
P.O. Box 33, Yuseong, Daejeon 34186 Korea, Tel: +82-42-828-7996, Fax : +82-2-736-6801, Email: info@techno-press.com