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CONTENTS
Volume 19, Number 2, October10 2019
 

Abstract
In this paper, simulation tests were conducted with similar materials to study the distribution of residual voids in longwall goaf. Short-time step loading was used to simulate the obvious deformation period in the later stage of arch breeding. Long-time constant loading was used to simulate the rheological stage of the arch forming. The results show that the irregular caving zone is the key area of old goaf for the subsidence control. The evolution process of the stress arch and fracture arch in stope can be divided into two stages: arch breeding stage and arch forming stage. In the arch breeding stage, broken rocks are initially caved and accumulated in the goaf, followed by the step deformation. Arch forming stage is the rheological deformation period of broken rocks. In addition, under the certain loads, the broken rock mass undergoes single sliding deformation and composite crushing deformation. The void of broken rock mass decreases gradually in short-time step loading stage. Under the water lubrication, a secondary sliding deformation occurs, leading to the acceleration of the broken rock mass deformation. Based on above research, the concept of equivalent height of residual voids was proposed, and whose calculation equations were developed. Finally, the conceptual model was verified by the field measurement data.

Key Words
longwall old goaf; residual voids; broken rock compression test; equivalent height of residual voids

Address
Changxiang Wang, Ning Jiang,Xizhen Sun, Buchu Zhang and Yao Lu: 1.) College of Mining and Safety Engineering, Shandong University of Science and Technology, Qingdao 266590, China
2.)State Key Laboratory of Mining Disaster Prevention and Control Co-Founded by Shandong Province and the Ministry of Science and Technology, Qingdao 266590, China

Baotang Shen: 1.)College of Mining and Safety Engineering, Shandong University of Science and Technology, Qingdao 266590, China
2.)State Key Laboratory of Mining Disaster Prevention and Control Co-Founded by Shandong Province
and the Ministry of Science and Technology, Qingdao 266590, China
3.)The Commonwealth Scientific and Industrial Research Organisation (CSIRO), PO Box 883, Kenmore, Queensland 4069, Australia

Yangyang Li: 1.)College of Mining and Safety Engineering, Shandong University of Science and Technology, Qingdao 266590, China
2.)State Key Laboratory of Mining Disaster Prevention and Control Co-Founded by Shandong Province
and the Ministry of Science and Technology, Qingdao 266590, China
3.)State Key Laboratory of Water Resource Protection and Utilization in Coal Mining, Beijing, China

Abstract
The long-term settlement characteristics for the cast-in-place bored pile in the deep-thick soft soil are investigated by post-grouting field tests. Six cast-in-place bored engineering piles and three cast-in-place bored test piles are installed to study the long-term settlement characteristics. Three post-grouting methods (i.e., post-tip-grouting, post-side-grouting, and tip and side post-grouting) are designed and carried out by field tests. Results of the local test show that decreased settlements for the post-side-grouted pile, the post-tip-grouted pile and the tip and side post-grouted pile are 22.2%~25.8%, 30.10%~35.98% and 32.40%~35.50%, respectively, compared with non-grouted piles. The side friction resistance for non-grouted piles, post-side-grouted pile, post-tip-grouted pile and the tip and side post-grouted pile undertakes 89.6~91.3%, 94.6%, 92.4%~93.0%, 95.7% of the total loading, respectively. At last, the parameters back analysis method and numerical calculation are adopted to predict the long-term settlement characteristics of the cast-in-place bored pile in the deep-thick soft soil. Determined Bulk modulus (K) and a creep parameter (Ks) are used for the back analysis of the long-term settlement of the post-grouted pile. The settlement difference between the back analysis and the measurement data is about 1.11%-7.41%. Long-term settlement of the post-grouted piles are predicted by the back analysis method, and the predicted results show that the settlement of the post-grouted pile are less than 6 mm and will be stable in 30 days.

Key Words
post-grouting local test; long-term settlement; deep-thick soft soil; cast-in-place bored pile; back analysis method

Address
Jin-Feng Zou, Tao Yang and Dong-ping Deng: School of Civil Engineering, Central South University, No.22, Shaoshan South Road,Central South University Railway Campus, Changsha, Hunan Province, People\'s Republic of China


Abstract
Available methods to determine the ultimate bearing capacity of shallow foundations may not be accurate enough owing to the complicated failure mechanism and diversity of the underlying soils. Accordingly, applying new methods of artificial intelligence can improve the prediction of the ultimate bearing capacity. The M5\' model tree and the genetic programming are two robust artificial intelligence methods used for prediction purposes. The model tree is able to categorize the data and present linear models while genetic programming can give nonlinear models. In this study, a combination of these methods, called the M5\'-GP approach, is employed to predict the ultimate bearing capacity of the shallow foundations, so that the advantages of both methods are exploited, simultaneously. Factors governing the bearing capacity of the shallow foundations, including width of the foundation (B), embedment depth of the foundation (D), length of the foundation (L), effective unit weight of the soil (gamma) and internal friction angle of the soil (phi) are considered for modeling. To develop the new model, experimental data of large and small-scale tests were collected from the literature. Evaluation of the new model by statistical indices reveals its better performance in contrast to both traditional and recent approaches. Moreover, sensitivity analysis of the proposed model indicates the significance of various predictors. Additionally, it is inferred that the new model compares favorably with different models presented by various researchers based on a comprehensive ranking system.

Key Words
artificial intelligence; M5\'-GP hybrid model; ultimate bearing capacity; shallow foundation; granular soil

Address
Rouhollah Khorrami and Ali Derakhshani: Department of Civil Engineering, Faculty of Engineering, Shahed University, Tehran, Iran

Abstract
A novel theoretical solution is presented for created (zero initial radius) cavity expansion problem based on Cam-Clay model and considers the effect of initial anisotropic in-situ stress and drained conditions. Here the strain of this theoretical solution is small deformation in elastic region and large deformation in plastic region. The works for cylindrical and spherical cavities expanding in drained condition from zero initial radius are investigated. Most of the conventional solutions were based on the isotropic and undrained condition, however, the initial stress state of natural soil mass is anisotropy by soil deposition history, and drained cavity expansion calculation is closer to actual engineering in permeable soil mass. Finally, the parametric study is presented in order to the engineering significance of this work.

Key Words
theoretical solution; created cavity expansion problem; cam-clay model; initial anisotropic in-situ stress; drained condition; large deformation

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

Abstract
A case study of monitoring and analysis of surface settlement induced by tunneling of Tabriz metro line 2 (TML2) is presented in this paper. The TML2 single tunnel has been excavated using earth pressure balanced TBM with a cutting-wheel diameter of 9.49 m since 2015. Presented measurements of surface settlements, were collected during the construction of western part of the project (between west depot and S02 station) where the tunnel was being excavated in sand and silt, below the water table and at an average axis depth of about 16 m. Settlement readings were back-analyzed using Gaussian formula, both in longitudinal and transversal directions, in order to estimate volume loss and settlement trough width factor. In addition to settlements, face support and tail grouting pressures were monitored, providing a comprehensive description of the EPB performance. Using the gap model, volume loss prediction was carried out. Also, COB empirical method for determination of the face pressure was employed in order to compare with field monitored data. Likewise, FE simulation was used in various sections employing the code Simulia ABAQUS, to investigate the efficiency of numerical modelling for the estimating of the tunneling induced-surface settlements under such a geotechnical condition. In this regard, the main aspects of a mechanized excavation were simulated. For the studied sections, numerical simulation is not capable of reproducing the high values of in-situ-measured surface settlements, applying Mohr-Coulomb constitutive law for soil. Based on results, for the mentioned case study, the range of estimated volume loss mostly varies from 0.2% to 0.7%, having an average value of 0.45%.

Key Words
TBM-EPB; mechanized tunneling; settlements; face pressure; grouting; empirical methods; COB; FEM

Address
Amir H. Rezaei: Department of Civil Engineering, Azarbaijan Shahid Madani University, PO Box: 5375171379, Tabriz, Iran

Mojtaba Shirzehhagh: Department of Civil Engineering, Tarbiat Modares University, PO Box 14115-175, Tehran, Iran

Mohammad R. Baghban Golpasand: Department of Civil Engineering, Seraj Institute of Higher Education, PO Box 5137894797, Tabriz, Iran

Abstract
Open-pit (OP) and underground (UG) mining are usually used to exploit shallow and deep ore deposits, respectively. When mine deposit starts from shallow subsurface and extends to a great depth, sequential use of OP and UG mining is an efficient and economical way to maintain mining productivity. However, a transition from OP to UG mining could induce significant rock movements that cause the slope instability of the open pit. Based on Yanqianshan Iron Mine, which was in the transition from OP to UG mining, a large-scale two-dimensional (2D) model test was built according to the similar theory. Thereafter, the UG mining was carried out to mimic the process of transition from OP to UG mining to disclose the triggered rock movement as well as to assess the associated slope instability. By jointly using three-dimensional (3D) laser scanning, distributed fiber optics, and digital photogrammetry measurement, the deformations, movements and strains of the rock slope during mining were monitored. The obtained data showed that the transition from OP to UG mining led to significant slope movements and deformations that can trigger catastrophic slope failure. The progressive movement of the slope could be divided into three stages: onset of micro-fracture, propagation of tensile cracks, and the overturning and/or sliding of slopes. The failure mode depended on the orientation of structural joints of the rock mass as well as the formation of tension cracks. This study also proved that these non-contact monitoring technologies were valid methods to acquire the interior strain and external deformation with high precision.

Key Words
open-pit mining; underground mining; similar theory; 3D laser scanning technology; distributed optic fiber; slope failure

Address
Bin Zhang, Hanxun Wang and Nengxiong Xu: School of Engineering and Technology, China University of Geosciences (Beijing),29 Xueyuan Road, Haidian District, Beijing 100083, China

Jie Huang: Department of Civil and Environmental Engineering, The University of Texas at San Antonio,1 UTSA Circle, San Antonio, Texas, 78249, U.S.A.


Abstract
Based on the effective stress principle, a new formula for shear strength of unsaturated soil is derived under the general nonlinear Mohr-Coulomb (M-C) strength criterion to improve the classical strength criterion of unsaturated soil. Meanwhile, the simple irrigation model under steady seepage is adopted to obtain the distribution of the matrix suction or the degree of saturation (DOS) above the groundwater table in the slope. Then, combined with the improved strength criterion of unsaturated soil and the simple irrigation model under steady seepage, the limit equilibrium (LE) solutions for the unsaturated slope stability are established according to the global LE conditions of the entire sliding body with assumption of the stresses on the slip surface. Compared to the classical strength criterion of unsaturated soil, not only the cohesion soil but also the internal friction angle is affected by the matric suction or the DOS in the improved strength criterion. Moreover, the internal friction angle related to the matric suction has the nonlinear characteristics, particularly for a small of the matric suction. Thereafter, the feasibility of the present method is verified by comparison and analysis on some slope examples. Furthermore, stability charts are also drawn to quickly analyze the unsaturated slope stability.

Key Words
unsaturated slope; DOS; nonlinear M-C strength criterion; LE analysis; stability charts

Address
Dong-ping Deng,Kuan Lu and Liang Li: School of Civil Engineering, Central South University, Changsha 410075, China

Abstract
A frozen fringe plays a key role in frost heave development in soils. Previous studies have focused on the physical and mechanical properties of the frozen fringe, such as overall hydraulic conductivity, water content and pore pressure. It has been proposed that the thickness of the frozen fringe controls frost heave behavior, but this effect has not been thoroughly evaluated. This study used a temperature-controllable cell to investigate the impact of frozen fringe thickness on the characteristics of frost heave. A series of laboratory tests was performed with various temperature boundary conditions and specimen heights, revealing that: (1) the amount and rate of development of frost heave are dependent on the frozen fringe thickness; (2) the thicker the frozen fringe, the thinner the resulting ice lens; and (3) care must be taken when using the frost heave ratio to characterize frost heave and evaluate frost susceptibility because the frost heave ratio is not a normalized factor but a specimen height-dependent factor.

Key Words
laboratory analysis; frost heave; frozen fringe; frost heave amount; frost heave rate; frost heave ratio; specimen height

Address
Hyun Woo Jin, Jangguen Lee and Byun Hyun Ryu: Department of Extreme Environmental Research Center, KICT, 283, Goyang-daero, Ilsanseo-gu, Goyang-si, Gyeonggi-do, Republic of Korea

Yunsup Shin: Department of Offshore Energy and Offshore Geotechnics, NGI, Norway

Young-Eun Jang: Department of Urban and Environmental Engineering, UNIST, Republic of Korea


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