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CONTENTS
Volume 18, Number 6, August30 2019
 

Abstract
In order to study the effect of stress and water pressure on the permeability of fractured rock mass under three-dimensional stress conditions, a single fracture triaxial stress-seepage coupling model was established; By using the stress-seepage coupling true triaxial test system, large-scale rock specimens were taken as the research object to carry out the coupling test of stress and seepage, the fitting formula of permeability coefficient was obtained. The influence of three-dimensional stress and water pressure on the permeability coefficient of fractured rock mass was discussed. The results show that the three-dimensional stress and water pressure have a significant effect on the fracture permeability coefficient, showing a negative exponential relationship. Under certain water pressure conditions, the permeability coefficient decreases with the increase of the three-dimensional stress, and the normal principal stress plays a dominant role in the permeability. Under certain stress conditions, the permeability coefficient increases when the water pressure increases. Further analysis shows that when the gob floor rock mass is changed from high stress to unloading state, the seepage characteristics of the cracked channels will be evidently strengthened.

Key Words
single fractured rock mass; stress-seepage coupling; true triaxial test system; floor water-inrush

Address
Wenbin Sun,Liming Yin and Junming Zhang: College of Mining and Safety Engineering, Shandong University of Science and Technology,Qingdao 266590, People\'s Republic of China

Yanchao Xue: 1.)College of Mining and Safety Engineering, Shandong University of Science and Technology,
Qingdao 266590, People\'s Republic of China
2.) School of Resources & Civil Engineering, Northeastern University, Shenyang 110819, People\'s Republic of China



Abstract
The groundwater level (GWL) is an important subsoil condition for the design of foundation. GWL tends to fluctuate often with seasonal variation, which may cause unexpected, additional settlements with some reductions in the safety margin of foundation. In this study, the effects of fluctuating GWL on the load carrying and settlement behavior of footing were investigated and quantified. A series of model load tests were conducted for various GWL and soil conditions using a hydraulically-controlled chamber system. Changes in load level and rising and falling GWL fluctuation cycle were considered in the tests. Settlements during GWL rise were greater than those during GWL fall. The depth of the GWL influence zone (dw,inf) varied in the range of 0.3 to 1.5 times footing width and became shallower as GWL continued to fluctuate. Design equations for estimating GWL-induced settlements for footings were proposed. The GWL fluctuation cycle, load level and soil density were considered in the proposed method. Changes in settlement and factor of safety with GWL fluctuation were discussed.

Key Words
groundwater level; groundwater fluctuation; footings; settlement; factor of safety

Address
Donggyu Park: Dongah Construction Industrial, 85, Gwangnaru-ro 56-gil, Gwangjin-gu, Seoul 05116, Republic of Korea, School of Civil and Environmental Engineering, Yonsei University, Seoul, Republic of Korea

Incheol Kim, Garam Kim and Junhwan Lee: School of Civil and Environmental Engineering, Yonsei University, 50, Yonsei-ro, Seodaemun-gu, Seoul 03722, Republic of Korea

Abstract
In-situ leaching could be one of the promising mining methods to extract the minerals from deep fractured rock mass. Constrained by the low permeability at depth, however, the performance does not meet the expectation. In fact, the rock mass permeability mainly depends on the pre-existing natural fractures and therefore play a crucial role in in-situ leaching performance. More importantly, fractures have various characteristics, such as aperture, persistence, and density, which have diverse contributions to the promising method. Hence, it is necessary to study the variation of fluid rate versus fracture parameters to enhance in-situ leaching performance. Firstly, the subsurface fractures from the depth of 1500m to 2500m were mapped using the discrete fracture network (DFN) in this paper, and then the numerical model was calibrated at a particular case. On this basis, the fluid flow through fractured rock mass with various fracture characteristics was analyzed. The simulation results showed that with the increase of Fisher\' K value, which determine the fracture orientation, the flow rate firstly decreased and then increased. Subsequently, as another critical factor affecting the fluid flow in natural fractures, the fracture transmissivity has a direct relationship with the flow rate. Sensitive study shows that natural fracture characteristics play a critical role in in-situ leaching performance.

Key Words
in-situ leaching; rock mass permeability; natural fracture; DFN; fracture characteristics

Address
Wen-li Yao and Zhen Yang: Key Laboratory of Deep Coal Resource Mining, Ministry of Education, School of Mines, China University of Mining and Technology, Xuzhou, 221116, China

Sharifzadeh Mostafa and Chris Aldrich: Department of Mining and Metallurgical Engineering, Western Australian School Mines, Curtin University, Kalgoorlie, 6430, Australia

Ericson Ericson: Faculty of Science and Engineering, Department of Mining and Metallurgical Engineering,
Western Australian School Mines, Curtin University, Kalgoorlie, 6430, Australia

Guang Xu : Department of Mining Engineering, Missouri University of Science and Technology, Rolla, MO. 65409, U.S.A.


Abstract
A modified model combining Kriging and Monte Carlo method (MC) is proposed for probabilistic estimation of tunnel face stability in this paper. In the model, a novel uniform design is adopted to train the Kriging, instead of the existing active learning function. It has advantage of avoiding addition of new training points iteratively, and greatly saves the computational time in model training. The kinematic approach of limit analysis is employed to define the deterministic computational model of face failure, in which the Hoek-Brown failure criterion is introduced to account for the nonlinear behaviors of rock mass. The trained Kriging is used as a surrogate model to perform MC with dramatic reduction of calls to actual limit state function. The parameters in Hoek-Brown failure criterion are considered as random variables in the analysis. The failure probability is estimated by direct MC to test the accuracy and efficiency of the proposed probabilistic model. The influences of uncertainty level, correlation relationship and distribution type of random variables are further discussed using the proposed approach. In summary, the probabilistic model is an accurate and economical alternative to perform probabilistic stability analysis of tunnel face excavated in spatially random Hoek- Brown media.

Key Words
probabilistic model; tunnel face stability; Hoek-Brown criterion; kriging; uniform design

Address
T.Z. Li: 1.)Department of Civil and Architecture Engineering, Changzhou Institute of Technology, Jiangsu, China
2.)School of Civil Engineering, Central South University, Hunan 410075, China

X.L. Yang: School of Civil Engineering, Central South University, Hunan 410075, China


Abstract
The present paper seeks to investigate propagation and reflection of waves at free surfaces of homogeneous, anisotropic and rotating micropolar fibre-reinforced medium with voids. It has been observed that, in particular when P-wave is incident on the free surface, there exist four coupled reflected plane waves traveling in the medium; quasi-longitudinal displacement (qLD) wave, quasi-transverse displacement (qTD) wave, quasi-transverse microrotational wave and a wave due to voids. Normal mode Analysis usually called harmonic solution method is adopted in concomitant with Snell\'s laws and appropriate boundary conditions in determination of solution to the micropolar fibre reinforced modelled problem. Amplitude ratios which correspond to reflected waves in vertical and horizontal components are presented analytically. Also, the Reflection Coefficients are presented using numerical simulated results in graphical form for a particular chosen material by the help of Mathematica software. We observed that the micropolar fibre-reinforced, voids and rotational parameters have various degrees of effects to the modulation, propagation and reflection of waves in the medium. The study would have impact to micropolar fibre-reinforecd rotational-acoustic machination fields and future works about behavior of seismic waves.

Key Words
rotation; micropolar; reflection; fibre-reinforced; voids; P-waves; reflection coefficients

Address
Augustine Igwebuike Anya and Aftab Khan: Department of Mathematics, COMSATS University Islamabad, ParkRoad Chak Shahzad, Islamabad, 44000 Pakistan

Abstract
Lightweight concrete (LWC) provides an attractive alternative to conventional piles by improving the durability of deep foundations. In this paper, the drivability of cylindrical and tapered piles made of lightweight and common concrete (CC) under hammer impacts was investigated by performing field tests and numerical analysis. The different concrete mixtures were considered to compare the mechanical properties of light aggregate which replaced instead of the natural aggregate. Driving tests were also conducted on different piles to determine how the pile material and geometric configurations affect driving performance. The results indicated that the tapering shape has an appropriate effect on the drivability of piles and although lower driving stresses are induced in the LWC tapered pile, their final penetration rate was more than that of CC cylindrical pile under hammer impact. Also by analyzing wave propagation in the different rods, it was concluded that the LWC piles with greater velocity than others had better performance in pile driving phenomena. Furthermore, LWC piles can be driven more easily into the ground than cylindrical concrete piles sometimes up to 50% lower hammer impacts and results in important energy saving.

Key Words
pile driving; lightweight concrete (LWC); tapered pile; field testing; signal matching; finite difference method

Address
Omid Tavasoli: Department of Civil Engineering, East Tehran Branch, Islamic Azad University, Tehran, Iran

Mahmoud Ghazavi: Department of Civil Engineering, K. N. Toosi University of Technology, Tehran, Iran

Abstract
Estimation of representative elementary volume (REV) of jointed rock masses is critical to predict the mechanical behavior of field-scale rock masses. The REV of jointed rock masses at site is strongly influenced by stress state. The paper proposed a method to systematically studied the influence of confining stress on the REV of jointed rock masses with various strengths (weak, medium and strong), which were sourced from the water inlet slope of Xiaowan Hydropower Station, China. A finite element method considering material heterogeneity was employed, a series of two-dimensional (2D) models was established based on the Monte-Carlo method and a lot of biaxial compressive tests were conducted. Numerical results showed that the REV of jointed rock masses presented a step-like reduction as the normalized confining stress increased. Confining stress weakened the size effect of jointed rock masses, indicating that the REV determined under uniaxial compression test can be reasonably taken as the REV of jointed rock masses under complexed in-situ stress environment.

Key Words
numerical simulation; confining stress; scale effect; representative elementary volume; jointed rock masses

Address
Na Wu, Zhengzhao Liang, Yingchun Li, Xikun Qian and Bin Gong: State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, 116024, China

Abstract
Time-domain commercial codes are widely used to evaluate the seismic behavior of tunnels. Those tools offer a good insight into the performance and the failure mechanism of tunnels under earthquake loading. Viscous damping is generally employed in the dynamic analysis to consider damping at very small strains in some cases, and the Rayleigh damping is commonly used one. Many procedures to obtain the damping parameters have been proposed but they are seldom discussed. This paper illustrates the influence of the Rayleigh damping formulation on the tunnel visco-elastic behavior under earthquake. Four Rayleigh damping determination procedures and three soil shear velocity profiles are accounted for. The results show significant differences in the free-field and in the tunnel response caused by different procedures. The difference is somewhat decreased when the soil site fundamental frequency is increased. The conventional method which consists of using solely the first soil natural mode to determine the viscous damping parameters may lead to an unsafe seismic design of the tunnel. In general, using five times site fundamental frequency to obtain the damping formulation can provide relatively conservative results.

Key Words
tunnel; seismic response; Rayleigh damping; small strain

Address
Qiangqiang Sun and Jingshan Bo: Institute of Disaster Prevention, Sanhe, China

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


Abstract
The IB-SEM numerical method combines the spectral/hp element method and the rigid immersed boundary method. This method avoids the problems of low computational efficiency and errors that are caused by the re-division of the grid when the solids move. Based on the Fourier transformation and the 3D immersed boundary method, the 3D IB-SEM system was established. Then, using the open MPI and the Hamilton HPC service, the computational efficiency was increased substantially. The flows around a cylinder and a sphere were simulated by the system. The surface of the cylinder generates vortices with alternating shedding, and these vortices result in a periodic force acting on the surface of the cylinder. When the shedding vortices enter the flow field behind the cylinder, a recirculation zone is formed. Finally, the three-dimensional pore flow was successfully investigated.

Key Words
Fourier transformation; 3D immersed boundary method; the 3D IB-SEM system; open MPI

Address
Jing Wang, Shucai Li, Liping Li, Peng Lin and Xingzhi Ba: 1.) School of Qilu Transportation, Shandong University, Jinan 250061, China
2.) Research Center of Geotechnical and Structural Engineering, Shandong University, Jinan 250061, China

Shuguang Song: 1.) Research Center of Geotechnical and Structural Engineering, Shandong University, Jinan 250061, China
2.) School of Transportation Engineering, Shandong Jianzhu University, Jinan 250101, China


Abstract
Seismic vulnerability assessment is a useful tool for rational safety analysis and planning of large and complex structural systems; it can deal with the effects of uncertainties on the performance of significant structural systems. In this study, an efficient dynamic reliability approach, probability density evolution methodology (PDEM), is proposed for seismic vulnerability analysis of earth dams. The PDEM provides the failure probability of different limit states for various levels of ground motion intensity as well as the mean value, standard deviation and probability density function of the performance metric of the earth dam. Combining the seismic reliability with three different performance levels related to the displacement of the earth dam, the seismic fragility curves are constructed without them being limited to a specific functional form. Furthermore, considering the seismic fragility analysis is a significant procedure in the seismic probabilistic risk assessment of structures, the seismic vulnerability results obtained by the dynamic reliability approach are combined with the results of probabilistic seismic hazard and seismic loss analysis to present and address the PDEM-based seismic probabilistic risk assessment framework by a simulated case study of an earth dam.

Key Words
earth dams; randomness of ground motion; seismic vulnerability; dynamic reliability; seismic risk

Address
Hongqiang Hu: Department of Geotechnical Engineering, College of Civil Engineering, Tongji University, Shanghai 200092, China

Yu Huang: 1.)Department of Geotechnical Engineering, College of Civil Engineering, Tongji University, Shanghai 200092, China
2.) Key Laboratory of Geotechnical and Underground Engineering of the Ministry of Education, Tongji University, Shanghai 200092, China

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