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CONTENTS
Volume 36, Number 6, March25 2024
 

Abstract
In the implementation of most civil structures, especially underground, deep excavations with a vertical slope are required. Using flexible retaining walls is applied as one of the ways to stabilize vertical holes. Therefore, it is necessary to know the parameters affecting the performance of such walls in reducing their horizontal movement. In this research, by building a suitable laboratory model, the parameters of the amount of flexibility, the embedment depth of the wall, the type and number of tieback in the wall were investigated for 42 static laboratory models. The purpose of this research is to study the flexible retaining wall with helical tieback compared to simple tieback at different heights, which shows the best performance in terms of reducing horizontal displacement in proportion to increasing or decreasing flexibility. On the other hand, one of the parameters affecting the flexibility of the wall, which is its bending stiffness, was extracted by numerical software outputs and studied on the results such as relative flexibility, stiffness, safety and numerical stability of the wall.The results of this study show that among the parameters, in the first place, the effect of the type of tieback is inhibited and in the second place, the ratio of thickness to wall height is known as the most important parameter. the best performance for walls with the helical tiebacks in reducing their horizontal displacement can be economically, flexibly and stability assigned to a wall that tiebacks is in the range of H2t⁄ to H4t⁄ and its flexibility ratio is 2/3.

Key Words
flexible; helical tieback; simple tieback

Address
Majid Khanjani, Seyed Hamid Lajevardi,Seyed Mohammad Mirhosseini and Ehsanollah Zeighami: Department of Civil Engineering, Arak Branch, Islamic Azad University, Arak, Iran
Hamid Reza Saba: Department of Civil Engineering, Arak Branch, Islamic Azad University, Arak, Iran;
Department of Civil Engineering, Tafresh University, Tafresh, Iran

Abstract
Piled raft foundation has become widely used in the recent years because it can increase bearing capacity of foundation with control settlement. The design for a piled raft in terms vertical load and lateral load need to understands contribution load behavior to raft and pile in piled raft foundation system. The load-bearing behavior of the piled raft, especially concerning lateral loads, is highly complex and challenge to analyze. The complex mechanism of piled rafts can be clarified by using three dimensional (3-D) Finite Element Method (FEM). Therefore, this paper focuses on free-standing head pile group, on-ground piled raft, and embedded raft for the piled raft foundation systems. The lateral resistant of piled raft foundation was investigated in terms of relationship between vertical load, lateral load and displacement, as well as the lateral load sharing of the raft. The results show that both vertical load and raft position significantly impact the lateral load capacity of the piled raft, especially when the vertical load increases and the raft embeds into the soil. On the same condition of vertical settlement and lateral displacement, piled raft experiences a substantial demonstrates a higher capacity for lateral load sharing compared to the on-ground raft. Ultimately, regarding design considerations, the piled raft can reliably support lateral loads while exhibiting behavior within the elastic range, in which it is safe to use.

Key Words
embedded raft; finite element analysis; lateral load sharing of raft; pile group; piled raft

Address
Sommart Swasdi: Department of Civil Engineering and Environment, Faculty of Engineering,
Prince of Songkla University, Songkhla 90110, Thailand
Tanan Chub-Uppakarn: Department of Civil Engineering and Environment, Faculty of Engineering,
Prince of Songkla University, Songkhla 90110, Thailand;
Southern Natural Disaster Research Center, Prince of Songkla University, Songkhla 90110, Thailand
Thanakorn Chompoorat and Worathep Sae-Long: Department of Civil Engineering, School of Engineering, University of Phayao, Phayao 56000, Thailand


Abstract
In this study, various countermeasures used to mitigate tunnel deformations due to nearby multi-propped basement excavation in soft clay are explored by three-dimensional numerical analyses. Field measurements are used to calibrate the numerical model and model parameters. Since concrete slabs can constrain soil and retaining wall movements, tunnel movements reach the maximum value when soils are excavated to the formation level of basement. Deformation shapes of an existing tunnel due to adjacent basement excavation are greatly affected by relative position between tunnel and basement. When the tunnel is located above or far below the formation level of basement, it elongates downward-toward or upward-toward the basement, respectively. It is found that tunnel movements concentrate in a triangular zone with a width of 2 He (i.e., final excavation depth) and a depth of 1 D (i.e., tunnel diameter) above or 1 D below the formation level of basement. By increasing retaining wall thickness from 0.4 m to 0.9 m, tunnel movements decrease by up to 56.7%. Moreover, tunnel movements are reduced by up to 80.7% and 61.3%, respectively, when the entire depth and width of soil within basement are reinforced. Installation of isolation wall can greatly reduce tunnel movements due to adjacent basement excavation, especially for tunnel with a shallow burial depth. The effectiveness of isolation wall to reduce tunnel movement is negligible unless the wall reaches the level of tunnel invert.

Key Words
countermeasures; isolation wall; jet grouting; multi-propped basement; tunnel

Address
Jinhuo Zheng and Minglong Shen: Fujian Provincial Institute of Architectural Design And Research Co.,Ltd., Fuzhou 350001, China
Shifang Tu:China Railway 16th Bureau Group 3rd Corporation Limited, Zhejiang Huzhou, 313000, China
Zhibo Chen: Department of Geotechnical and Geological Engineering, Zijin School of Geology and Mining,
Fuzhou University, Fuzhou 350116, China
Xiaodong Ni: Key Laboratory of Ministry of Education for Geomechanics and Embankment Engineering,
Hohai University, Nanjing, 210024, China

Abstract
The contact pressure between the surrounding rock and the support is an important indicator of the surrounding rock pressure. There has been a bottleneck in the prediction of contact loads between surrounding rock and primary support in deep-buried mountain tunnels. The main reason is that a reliable method wasn't existed to quantify the contact loads. This study had been taken into account the flexible support role of the primary support, and the fitting curve of surrounding rock deformation for dynamic tunnel construction was proposed. New formulas for the calculation of contact loads between surrounding rock and primary support were obtained by inversion. Comparative analysis of the calculation results with numerical simulation verified the reliability of the calculation method in this study. It can be seen from the analyses that the contact load between surrounding rock and primary support increases, remains unchanged and decreases during acceleration, uniform velocity and deceleration, respectively, and the deformation of the surrounding rock in the acceleration and deceleration stages cannot completely converted into contact loads. The contact loads between surrounding rock and primary support of medium-strength and weak surrounding rock tunnels are generally within 150 kPa and 1 MPa, respectively. For tunnels with weak surrounding rock, advanced support can be installed to reduce the unique release coefficient 0 and the value of the constant D, with the purpose of reducing the contact loads between surrounding rock and primary support. Changes in support parameters have a small effect on the contact loads between surrounding rock and primary support, but increase or decrease the safety factor, resulting in a waste of resources or a situation that threatens the safety of the support. The results of this research provide guidance for the prediction of contact loads between surrounding rock and primary support for dynamic tunnel construction.

Key Words
contact load; fitted curve; flexible support; inversion; mountain tunnel

Address
Jian Zhou and Yunliang Cui,Department of Civil Engineering, Hangzhou City University, Hangzhou 310015, China;
Key Laboratory of Safe Construction and Intelligent Maintenance for Urban Shield Tunnels of Zhejiang Province,
Hangzhou City University, Hangzhou 310015, China
inan Yang, Mingjie Ma and Luheng Li: The Key Laboratory of Road and Traffic Engineering, Ministry of Education, Tongji University, Shanghai 201804, China

Abstract
Dispersion occurs when clay soil disperses under specific conditions and is rapidly washed away. While there are numerous methods for rectifying it, they are neither cost nor time-effective. The current study used metakaolin and zeolite to improve heavily dispersive clay soil either separately or in combination at 0%, 2%, 4%, 6%, and 8% of the soil weight. After 7 days of curing, the samples were tested to determine the extent of change in the dispersion potential, as well as the improvement of the geotechnical properties of the soil. The results indicated that the addition of 2% zeolite with 6% to 8% metakaolin decreased the dispersion potential considerably. Double hydrometry test findings revealed that the dispersion potential decreased by almost 70% and entered the non-dispersive group; the crumb test also revealed this. Atterberg limits testing indicated a decrease in the plasticity index which reduced the flexibility of the samples. The greatest decrease in PI (67.5%) was achieved with the addition of 8% zeolite plus 8% metakaolin to the soil. The results of density tests revealed that a decrease in the optimal moisture content increased the maximum dry density of soil. This increase in density was a response to the high reactivity of metakaolin with calcium hydroxide and the formation of calcium hydroxide hydrate gel. This eventually caused an increase in the unconfined compressive strength, the greatest increase in strength of about 1.8-fold was observed with a combination of 2% zeolite and 6% metakaolin compared to the unmodified sample.

Key Words
crumb test; dispersive clay soil; double hydrometry test; metakaolin; soil stabilization; zeolite

Address
hmadreza Soltanian, Amirali Zad, Maryam Yazdi and Amin Tohidi: Department of Civil Engineering, Faculty of Civil and Earth Resources Engineering, Islamic Azad University,
Central Tehran Branch, Tehran, Iran

Abstract
The joint probability distribution of uncertain geomechanical parameters of geotechnical strata is a crucial aspect in constructing the reliability functional function for roof structures. However, due to the limited number of on-site exploration and test data samples, it is challenging to conduct a scientifically reliable analysis of roof geotechnical strata. This study proposes a Copula method based on small sample exploration and test data to construct the intensity characteristics of roof geotechnical strata. Firstly, the theory of multidimensional copula is systematically introduced, especially the construction of four-dimensional Gaussian copula. Secondly, data from measurements of 176 groups of geomechanical parameters of roof geotechnical strata in 31 coal mines in China are collected. The goodness of fit and simulation error of the four-dimensional Gaussian Copula constructed using the Pearson method, Kendall method, and Spearman methods are analyzed. Finally, the fitting effects of positive and negative correlation coefficients under different copula functions are discussed respectively. The results demonstrate that the established multidimensional Gaussian Copula joint distribution model can scientifically represent the uncertainty of geomechanical parameters in roof geotechnical strata. It provides an important theoretical basis for the study of reliability functional functions for roof structures. Different construction methods for multidimensional Gaussian Copula yield varying simulation effects. The Kendall method exhibits the best fit in constructing correlations of geotechnical parameters. For the bivariate Copula fitting ability of uncertain parameters in roof geotechnical strata, when the correlation is strong, Gaussian Copula demonstrates the best fit, and other Copula functions also show remarkable fitting ability in the region of fixed correlation parameters. The research results can offer valuable reference for the stability analysis of roof geotechnical engineering.

Key Words
coal seam roof; Gaussian copula; joint probability distribution; small sample; uncertain mechanical parameters

Address
Jiazeng Cao and Tao Wang:1State Key Laboratory for Geomechanics and Deep Underground Engineering, School of Mechanics and Civil Engineering,
China University of Mining and Technology, Xuzhou, Jiangsu, 221116, China;
National Key Laboratory of Petroleum Resources and Engineering, China University of Petroleum, Beijing 102249, China;
Key Laboratory of Geohazard Prevention of Hilly Mountains, Ministry of Natural Resources,
Fujian Key Laboratory of Geohazard Prevention, Fuzhou, Fujian 350002, China;
Technology Innovation Center for Mine Geological Environment Restoration in the Alpine and Arid Regions,
MNR, Lanzhou, Gansu, 730000, China
Mao Sheng: National Key Laboratory of Petroleum Resources and Engineering, China University of Petroleum, Beijing 102249, China
Yingying Huang: Key Laboratory of Geohazard Prevention of Hilly Mountains, Ministry of Natural Resources,
Fujian Key Laboratory of Geohazard Prevention, Fuzhou, Fujian 350002, China
Guoqing Zhou: State Key Laboratory for Geomechanics and Deep Underground Engineering, School of Mechanics and Civil Engineering,
China University of Mining and Technology, Xuzhou, Jiangsu, 221116, China

Abstract
To improve the utilization rate of phosphate tailings (PTs) and widen the sources of subgrade filler, the PTs is employed to modify clay, forming a PTs modified clay, applied in the subgrade. Accordingly, the environmental friendliness of PTs was investigated. Subsequently, an optimal proportion was determined through compaction and California Bearing Ratio (CBR) experiments. Afterward, the stability of mixture with the optimal proportion was further evaluated through the water stability and dry-wet stability experiments. Finally, via the gradation and microstructure experiments, the strength mechanism of PTs modified clay was analyzed. The results show that the PTs were classified in the non-hazardous solid wastes, belonging to Class A building materials. With the increase of PTs content and the decrease of clay content, the optimum water content and the swelling degree gradually decrease, while the maximum dry density and CBR first increase and then decrease, reaching their peak value at 50% PTs content, which is the optimal proportion. The resilient modulus of PTs modified clay at the optimal proportion reaches 110.2 MPa. The water stability coefficient becomes stable after soaking for 4 days, while the dry-wet stability coefficient decreases with the increase of cycles and tends to be stable after 8 cycles. Under the long-term action, the dry-wet change has a greater adverse impact than continuous soaking. The analysis demonstrates that the better strength mainly comes from the skeleton role of PTs and the cementation of clay. The systematic laboratory test results and economic analysis collectively provide data evidence for the advantages of PTs modified clay as a subgrade filler.

Key Words
clay; economic efficiency; environment-friendly; mechanical property; mechanism; phosphate tailings

Address
Xiaoqing Zhao, Zhongling Zong and Jiawei Li: School of Civil and Ocean Engineering, Jiangsu Ocean University, Jiangsu 222005, China;
Marine Resources Development Institute of Jiangsu (Lianyungang), Jiangsu 222005, China;
Jiangsu Ocean Engineering Research Center for Intelligent Infrastructure Construction, Jiangsu 222005, China
Tianfeng Yang, Teng Liang and Zeyu Shen: School of Civil and Ocean Engineering, Jiangsu Ocean University, Jiangsu 222005, China
Gui Zhao: College of civil and transportation engineering, Hohai University, Jiangsu 210098, China

Abstract
In the traditional slope stability analysis, ignoring the spatial variability of slope soil will lead to inaccurate analysis. In this paper, the K-L series expansion method is adopted to simulate random field of soil strength parameters. Based on Random Limit Equilibrium Method (RLEM), the influence of variation coefficient and fluctuation range on reliability of soil slope supported by micro-pile is investigated. The results show that the fluctuation ranges and the variation coefficients significantly influence the failure probability of soil slope supported by micro-pile. With the increase of fluctuation range of soil strength parameters, the mean safety factor of the slope increases slightly. The failure probability of the soil slope increases with the increase of fluctuation range when the mean safety factor of the slope is greater than 1. The failure probability of the slope increases by nearly 8.5% when the fluctuation range is increased from sv=2 m to sv =8 m. With the increase of the variation coefficient of soil strength parameters, the mean safety factor of the slope decreases slightly, and the probability of failure of soil slope increases accordingly. The failure probability of the slope increases by nearly 31% when the variation coefficient increases from COrc=0.2, COro=0.05 to COrc=0.5, COro=0.2.

Key Words
micro-pile; spatial variability; monte-carlo method; random limit equilibrium method (RLEM); soil slope

Address
Yuke Wang, Haiwei Shang and Xiang Yu: School of Water Conservancy and Transportation, Zhengzhou University, Zhengzhou, 450001, China;
Henan Key Laboratory of Grain and oil storage facility and safety, Henan University of Technology, Zhengzhou, 450001, China
Yukuai Wan: School of Civil and Hydraulic Engineering, Ningxia University, Yinchuan, 750021, China

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