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CONTENTS
Volume 19, Number 1, September20 2019
 

Abstract
Shallow failures occur frequently in both engineered and natural slopes in expansive soils. Rainfall infiltration is the most predominant triggering factor that contributes to slope failures in both expansive soils and clayey soils. However, slope failures in expansive soils have some distinct characteristics in comparison to slopes in conventional clayey soils. They typically undergo shallow failures with gentle sliding retrogression characteristics. The shallow sliding mass near the slope surface is typically in a state of unsaturated condition and will exhibit significant volume changes with increasing water content during rainfall periods. Many other properties or characteristics change such as the shear strength, matric suction including stress distribution change with respect to depth and time. All these parameters have a significant contribution to the expansive soil slopes instability and are difficult to take into consideration in slope stability analysis using traditional slope stability analysis methods based on principles of saturated soil mechanics. In this paper, commercial software VADOSE/W that can account for climatic factors is used to predict variation of matric suction with respect to time for an expansive soil cut slope in China, which is reported in the literature. The variation of factor of safety with respect to time for this slope is computed using SLOPE/W by taking account of shear strength reduction associated with loss of matric suction extending state-of-the art understanding of the mechanics of unsaturated soils.

Key Words
expansive soils; slope stability; unsaturated soils mechanics; case study

Address
Shunchao Qi and Jia-wen Zhou: State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University, Chengdu, Sichuan 610065, PR China

Sai K. Vanapalli: Department of Civil Engineering, University of Ottawa, Ottawa, ON, K1N 6N5, Canada

Xing-guo Yang and Gong-da Lu: College of Water Resource and Hydropower, Sichuan University, Chengdu, Sichuan 610065, PR China

Abstract
The use of electrokinetic dissipation method to study the fluid flow law in micro-pores is of great significance to reservoir rock microfluidics. In this paper, the micro-capillary theory was combined with the coupling model of the seepage field and the current field under the excitation of the harmonic signal, and the coupling theory of the electrokinetic effect under the first-order approximation condition was derived. The dissipation equation of electrokinetic dissipation and viscous resistance dissipation and its solution were established by using Green\'s function method. The physical and mathematical models for the electrokinetic dissipation of reservoir rocks were constructed. The microscopic mechanism of the electrokinetic dissipation of reservoir rock were theoretically clarified. The influencing factors of the electrokinetic dissipation frequency of the reservoir rock were analyzed quantitatively. The results show that the electrokinetic effect transforms the fluid flow profile in the pores of the reservoir from parabolic to wavy; under low-frequency conditions, the apparent viscosity coefficient is greater that one and is basically unchanged. The apparent viscosity coefficient gradually approaches 1 as the frequency increases further. The viscous resistance dissipation is two orders of magnitude higher than the electrokinetic effect dissipation. When the concentration of the electrolyte exceeds 0.1mol/L, the electrokinetic dissipation can be neglected, while for the electrolyte solution (<10-2M) in low concentration, the electrokinetic dissipation is very significant and cannot be ignored.

Key Words
electrokinetic dissipation; viscous resistance dissipation; viscosity coefficient

Address
Xiaoqian Zhang, Qifei Wang, Chengwu Li, Xiaoqi Sun, Zheng Yan and Yao Nie: College of Emergency Management & Safety Engineering, China University of Mining & Technology, Beijing, 100083, China

Abstract
Use of cement in stabilizing the sulfate-bearing clay soils forms ettringite/ thaumasite in the presence of moisture leads to excessive swelling and causes damages to structures built on them. The development and use of non-traditional stabilisers such as alkali activated ground granulated blast-furnace slag (AGGBS) and enzyme for soil stabilisation is recommended because of its lower cost and the non detrimental effects on the environment. The objective of the study is to investigate the effectiveness of AGGBS and enzyme on improving the volume change properties of sulfate bearing soil as compared to ordinary Portland cement (OPC). The soil for present study has been collected from Tilda, Chhattisgarh, India and 5000 ppm of sodium sulfate has been added. Various dosages of the selected stabilizers have been used and the effect on plasticity index, differential swell index and swelling pressure has been evaluated. XRD, SEM and EDX were also done on the untreated and treated soil for identifying the mineralogical and microstructural changes. The tests results show that the AGGBS and enzyme treated soil reduces swelling and plasticity characteristics whereas OPC treated soil shows an increase in swelling behaviour. It is observed that the swell pressure of the OPC-treated sulfate bearing soil became 1.5 times higher than that of the OPC treated non-sulfate soil.

Key Words
soil stabilization; alkali activated ground granulated blast-furnace slag; OPC; enzyme; differential free swell; swell pressure

Address
Ansu Thomas, R. K. Tripathi and L. K. Yadu: Department of Civil Engineering, National Institute of Technology Raipur, Chhattisgargh, India

Abstract
The present research deals with the deformation in transversely isotropic thin circular thermoelastic rotating plate due to time-harmonic sources. Frequency effect in the presence of rotation and two temperature is studied under thermally insulated as well as isothermal boundaries. The Hankel transform technique is used to find a solution to the problem. The displacement components, stress components, and conductive temperature distribution with the radial distance are computed in the transformed domain and further calculated in the physical domain using numerical inversion techniques. Some specific cases are also figured out from the current research.

Key Words
transversely isotropic; thin circular plate; Hankel transform; time harmonic sources

Address
Parveen Lata and Iqbal Kaur: Department of Basic and Applied Science, Punjabi University, Patiala, India

Abstract
The main objective of this study is to evaluate and compare the efficiency of ordinary Portland cement (OPC) in enhancing the unconfined compressive strength of soft soil alone and soft soil mixed with recycled tiles. The recycled tiles have been used to treat soft soil in a previous research by Al-Bared et al. (2019) and the results showed significant improvement, but the improved strength value was for samples treated with low cement content (2%). Hence, OPC is added alone in this research in various proportions and together with the optimum value of recycled tiles in order to investigate the improvement in the strength. The results of the compaction tests of the soft soil treated with recycled tiles and 2, 4, and 6% OPC revealed an increment in the maximum dry density and a decrement in the optimum moisture content. The optimum value of OPC was found to be 6%, at which the strength was the highest for both samples treated with OPC alone and samples treated with OPC and 20% recycled tiles. Under similar curing time, the strength of samples treated with recycled tiles and OPC was higher than the treated soil with the same percentage of OPC alone. The stress-strain curves showed ductile plastic behaviour for the untreated soft clay and brittle behaviour for almost all treated samples with OPC alone and OPC with recycled tiles. The microstructural tests indicated the formation of new cementitious products that were responsible for the improvement of the strength, such as calcium aluminium silicate hydrate. This research promotes recycled tiles as a green stabiliser for soil stabilisation capable of reducing the amount of OPC required for ground improvement. The replacement of OPC with recycled tiles resulted in higher strength compared to the control mix and this achievement may results in reducing both OPC in soil stabilisation and the disposal of recycled tiles into landfills.

Key Words
environmental-friendly; soil stabilisation; recycled tiles; OPC replacement; chemical testing

Address
Mohammed A. M. Al-Bared, Indra S. H. Harahap, Zahiraniza Mustaffa and Montasir O. A. Ali: Department of Civil and Environmental Engineering, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 32610, Malaysia

Aminaton Marto: Malaysia-Japan International Institute of Technology, Universiti Teknologi Malaysia (UTM) Kuala Lumpur, 54100 Kulala Lumpur, Malaysia

Seyed Vahid Alavi Nezhad Khalil Abad: Department of Civil Engineering, Birjand University of Technology, Birjand, Iran

Abstract
Crack instability propagation during coal and rock mass failure is the main reason for electromagnetic radiation (EMR) generation. However, original cracks on coal and rock mass are hard to study, making it complex to reveal EMR laws and mechanisms. In this paper, we prefabricated cracks of different inclinations in coal and rock samples as the analogues of the native cracks, carried out uniaxial compression experiments using these coal and rock samples, explored, the effects of the prefabricated cracks on EMR laws, and verified these laws by measuring the surface potential signals. The results show that prefabricated cracks are the main factor leading to the failure of coal and rock samples. When the inclination between the prefabricated crack and axial stress is smaller, the wing cracks occur first from the two tips of the prefabricated crack and expand to shear cracks or coplanar secondary cracks whose advance directions are coplanar or nearly coplanar with the prefabricated crack\'s direction. The sample failure is mainly due to the composited tensile and shear destructions of the wing cracks. When the inclination becomes bigger, the wing cracks appear at the early stage, extend to the direction of the maximum principal stress, and eventually run through both ends of the sample, resulting in the sample\'s tensile failure. The effect of prefabricated cracks of different inclinations on electromagnetic (EM) signals is different. For samples with prefabricated cracks of smaller inclination, EMR is mainly generated due to the variable motion of free charges generated due to crushing, friction, and slippage between the crack walls. For samples with larger inclination, EMR is generated due to friction and slippage in between the crack walls as well as the charge separation caused by tensile extension at the cracks\' tips before sample failure. These conclusions are further verified by the surface potential distribution during the loading process.

Key Words
coal and rock; prefabricated crack; failure mode; electromagnetic radiation; surface potential

Address
Dazhao Song,Liming Qiu and Sida Wang: School of Civil and Resource Engineering, University of Science and Technology Beijing, Beijing 100083, China

Qiuju You: Beijing Research Center of Urban Systems Engineering, Beijing 100035, China

Enyuan Wang and Zhonghui Li: School of Safety Engineering, China University of Mining and Technology, Xuzhou 221116, China

Xiaoyan Song: College of Applied Science and Technology, China University of Mining and Technology, Xuzhou 221116,

Abstract
Yieldable steel ribs have been widely applied in tunnels excavated in rheological rocks. For further understanding the influence of yieldable steel ribs on supporting effect, mechanical behavior of tunnels supported by them in rheological rocks is investigated in this paper. Taking into account the deformation characteristic of yieldable steel ribs, their deformation is divided into three stages. In order to modify the stiffness of yieldable steel ribs in different deformation stages, two stiffness correction factors are introduced in the latter two stages. Viscoelastic analytical solutions for the displacement and pressure in the rock-support interface in each deformation stage are obtained. The reliability of the theoretical analysis is verified by use of numerical simulation. It could be concluded that yieldable steel ribs are able to reduce pressure acting on them without becoming damaged through accommodating the rock deformation. The influence of stiffness correction factor in yielding deformation stage on pressure and displacement could be neglected with it remaining at a low level. Furthermore, there is a linearly descending relationship of pressure with yielding displacement in linear viscoelastic rocks.

Key Words
tunnel; viscoelasticity; yieldable steel ribs; analytical solution; support parameters

Address
Kui Wu, Zhushan Shao, Su Qin and Nannan Zhao: School of Civil Engineering, Xi\'an University of Architecture & Technology, Xi\'an 710055, China

Abstract
Massive investments are going on to promote and build transportation infrastructure all across the globe with the challenges being more than budgetary. Sandy soils which are predominant in coastal and border areas in India have typical characteristics. The shear strength of such soil is very low which makes it difficult for any kind of geotechnical construction and hence soil stabilization needs to be carried out for such soil conditions. The use of geocells is one of the most economical methods of soil improvement which is used to increase strength and stiffness and reduce the liquefaction potential of the soil. The use of geocells in stabilizing desert sand and results from a series of plate load test on unreinforced soil and geocell reinforced homogenous sand beds are presented in the present study. It also compares the field results using various load class vehicles like heavy load military vehicles on geocell reinforced soils with the experimental results and comes out with the fact that the proposed technique increases the strength and stiffness of sandy soil considerably and provides a solution for preventing settlement and subsidence.

Key Words
geosynthetic applications; soil-geosynthetic interaction; unpaved roads; geocell, field results; settlement

Address
Anand Kumar, Akshay P. Singh and Kaustav Chatterjee: Department of Civil Engineering, Indian Institute of Technology Roorkee, Roorkee 247667, India

Abstract
Renewed interest in the long-term pile foundations has been driven by the increase in offshore wind turbine installation to generate renewable energy. A monopile subjected to repetitive loads experiences an evolution of displacements, pile rotation, and stress redistribution along the embedded portion of the pile. However, it is not fully understood how the embedded pile interacts with the surrounding soil elements based on different pile geometries. This study investigates the long-term soil response around offshore monopiles using finite element method. The semi-empirical numerical approach is adopted to account for the fundamental features of volumetric strain (terminal void ratio) and shear strain (shakedown and ratcheting), the strain accumulation rate, and stress obliquity. The model is tested with different strain boundary conditions and stress obliquity by relaxing four model parameters. The parametric study includes pile diameter, embedded length, and moment arm distance from the surface. Numerical results indicate that different pile geometries produce a distinct evolution of lateral displacement and stress. In particular, the repetitive lateral load increases the global lateral load resistance. Further analysis provides insight into the propagation of the shear localization from the pile tip to the ground surface.

Key Words
long-term monopile foundation; semi-empirical numerical scheme; terminal void ratio; shakedown; displacement evolution; soil densification

Address
Song-Hun Chong: Department of Civil Engineering, Sunchon National University, Republic of Korea

Ho-Sung Shin: Department of Civil and Environmental Engineering, University of Ulsan, Republic of Korea

Gye-Chun Cho: epartment of Civil and Environmental Engineering, Korean Advanced Institute for Science and Technology, Republic of Korea

Abstract
Anomalies and/or fractured grounds not detected by the surface geophysical and geological survey performed during design stage may cause significant problems during tunnel excavation. Many studies on prediction methods of the ground condition ahead of the tunnel face have been conducted and applied in tunneling construction sites, such as tunnel seismic profiling and probe drilling. However, most such applications have focused on the drill and blast tunneling method. Few studies have been conducted for mechanized tunneling because of the limitation in the available space to perform prediction tests. This study aims to predict the ground condition ahead of the tunnel face in TBM tunneling by using an electrical resistivity tomography survey. It compared the characteristics of each electrode array and performed an investigation on in-situ tunnel boring machine TBM construction site environments. Numerical simulations for each electrode array were performed, to determine the proper electrode array to predict anomalies ahead of the tunnel face. The results showed that the modified dipole–dipole array is, compared to other arrays, the best for predicting the location and condition of an anomaly. As the borehole becomes longer, the measured data increase accordingly. Therefore, longer boreholes allow a more accurate prediction of the location and status of anomalies and complex grounds.

Key Words
electrical resistivity tomography; electrode array; prediction of anomaly; tunnel boring machine; tunnel face

Address
Kang-Hyun Lee: esearch Institute, Korea Expressway Corporation, 208-96, Dongbu-daero 922beon-gil, Hwaseong-si, Gyeonggi-do, 18489 Korea

Jin-Ho Park and In-Mo Lee: School of Civil, Environmental and Architectural Engineering, Korea University, 145 Anam-ro, Seongbuk-gu, Seoul, 02841, Korea

Jeongjun Park: Korea Railroad Research Institute, 176, Cheoldobangmulgwan-ro, Uiwang-si, Gyeonggi-do, 16105, Korea

Seok-Won Lee: Department of Civil and Environmental Engineering, Konkuk University, 120 Neungdong-ro, Gwangjin-gu, Seoul 05029, Korea


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