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CONTENTS
Volume 34, Number 2, July25 2023
 

Abstract
By conducting three-dimensional simulation with consideration of small-strain characteristics of soil stiffness, the effects of excavation geometry and tunnel cover to diameter ratio on deformation mechanisms of an existing tunnel located either at a side of basement or directly underneath the basement were systematically studied. Field measurements were used to verify the numerical model and model parameters. For basement excavated at a side of an existing tunnel, the maximum settlement and horizontal displacement of the tunnel are always observed at the tunnel springline closer to basement and tunnel crown, respectively, regardless of basement geometry. By increasing basement length and width by five times, the maximum movements of tunnel located at the side of basement and directly underneath the basement increase by 450% and 186%, respectively. Obviously, tunnel movements are more sensitive to basement length rather than basement width. For basement excavated at a side of an existing tunnel, tunnel movements at basement centerline become stable when basement length reaches 10 He (i.e., final excavation depth). Moreover, tunnel heaves due to overlying basement excavation become stable when the normalized basement length (L/He) is larger than 8.0. As tunnel cover to diameter ratio varies from 2.5 to 3.0, the maximum heave and tensile strain of tunnel due to overlying basement excavation decrease by up to 41.0% and 44.5%, respectively. If basement length is less than 8 He, the assumption of plane strain condition of basement-tunnel interaction grossly overestimates tunnel movements, and ignores tensile strain of tunnel along its longitudinal direction. Thus, three-dimensional numerical analyses are required to obtain a reasonable estimation of tunnel responses due to adjacent and overlying basement excavations in clay.

Key Words
basement excavation; basement length; basement width; three-dimensional deformation; tunnel

Address
Wanchun Chen, Lixian Tang, Haijun Zhao,Shuang Dong and Jie Liu: China Construction Eight Engineering Division Rail Transit Construction Co., L.T.D., Nanjing, 210046 China
Qian Yin: Nanjing Metro, Nanjing, 210018, China
Zhaohan Zhu: School of Electrical Engineering, Southwest Jiaotong University, Chengdu, 611756, China
Xiaodong Ni: Key Laboratory of Ministry of Education for Geomechanics and Embankment Engineering, Hohai University, Nanjing, 210024, China

Abstract
To improve the understanding of infiltration characteristic of modified slurry and the support efficiency of filter cake in silty sand strata, the slurry infiltration (SI) and filter cake formation (FCF) were investigated in a laboratory apparatus. The water discharge and the excess pore pressure at different depths of silty sand strata were measured during SI. The relationship between permeability coefficient/thickness ratio of filter cake (kc/L) and effective slurry pressure conversion rate of filter cake (n) were analyzed. Moreover, the SI and FCF process as well as the modification mechanism of CMC (carboxymethyl cellulose) were clarified. The experimental results indicate the formation of only external filter cake in the silty sand strata. The slurry particles obtain thicker water membrane after being modified by CMC, which blocks partial water path in filter cake and decreases the water discharge significantly. The silty sand excavated from tunnel face also contributes to the water discharge reduction. The kc of the external filter cake ranges from 3.83X10-8 cm/s to 7.44X10-8 cm/s. The n of the external filter cake is over 96%, which decreases with increasing kc/L. A silty sand content within 10% is suggested during construction to ensure the uniformity of the filter cake.

Key Words
filter cake formation; modified slurry; river-crossing tunnel; slurry infiltration; stability of tunnel face

Address
Sai Zhang, Jianwen Ding, Ning Jiao, Shuai Sun and Jinyu Liu: Department of Underground Engineering, Southeast University,
NO.2 Southeast University Road, Jiangning District, Nanjing, China

Abstract
Red-bed soft rock is a common stratum and it is necessary to evaluate the mechanical properties and bearing capacity of red-bed soft rock mass affected by different environmental effects. This paper presents a complete procedure for evaluating the bearing capacity of red-bed soft rock by means of geophysical exploration and in-situ rock mechanics tests. Firstly, the thickness of surface loosened rock mass of red-bed soft rock was determined using geophysical prospecting method. Then, three environmental effects, including natural weathering effect, dry-wet cycling effect and concrete sealing effect, were considered. After each effect lasted for three months, in-situ rock mass mechanical tests were conducted. The test results show that the mechanical properties of rock mass considering the sealing effect of concrete were maintained. After considering the natural weathering effect, the mechanical parameters decrease to a certain extent. After considering the effect of dry-wet cycling, the decreases of mechanical parameters are the most significant. The test results confirm that the red-bed soft rock dam foundation rock mass will be significantly affected by various environmental effects. Therefore, combined with the mechanical test results, some useful implementations are proposed for the construction of a red-bed soft rock dam foundation.

Key Words
dam foundation; geophysical prospecting; in-situ mechanical testing; natural weathering; dry-wet cycling; red-bed soft rock

Address
Liming Zhou, Yujie Li, Fagang Wang and Yang Liu: Key Laboratory of Geotechnical Mechanics and Engineering of Ministry of Water Resources,
Changjiang River Scientific Research Institute, Wuhan, Hubei 430010, China

Abstract
Aiming at the grouting treatment of water inflow in karst conduits, a visualized experiment system for conduit-type grouting blocking was developed. Through the improved water supply system and grouting system, and the optimized multi-source information monitoring system, the real-time observation of diffusion and deposition of slurry, and the data acquisition of pressure and velocity during the whole process of grouting were realized, which breaks through the problem that the monitoring element is easy to fail due to slurry adhesion in conventional test system. Based on the grouting experiments in static and flowing water, the diffusion and deposition behavior of the quick-setting slurry under different working conditions were analyzed. The temporal and spatial variation behavior of the pressure and velocity were studied, and the blocking mechanism of the grouting were further revealed. The results showed that: (1) Under the flowing water condition, the counter-flow diffusion distance of slurry was negatively correlated with the flow water velocity and the volume ratio of cement and sodium silicate (C-S ratio), and positively correlated with the grouting volume. The slurry deposition thickness was negatively correlated with the flowing water velocity, and positively correlated with the grouting volume and C-S ratio. (2) The pressure increased slowly before blocking of the flowing water and rapidly after blocking in karst conduits. (3) With the continuous progress of grouting, the flowing water velocity decreased slowly first, then significantly, and finally tended to be stable. According to the research results, some engineering recommendations were put forward for the grouting treatment of the conduit-type water inflow disaster, which has been successfully applied in the treatment project of the China Resources Cement (Pingnan) Limestone Mine. This study provided some guidance and reference for the parameter optimization of grouting for the treatment projects of water inflow in karst conduits.

Key Words
blocking mechanism; grouting in flowing water; limestone mine; water inflow

Address
Zehua Bu and Zhenhao Xu: Geotechnical and Structural Engineering Research Center, Shandong University, Jinan, Shandong 250-061, China;
School of Qilu Transportation, Shandong University, Jinan, Shandong 250061, China
Dongdong Pan, Haiyan Li, Jie Liu and Zhaofeng Li: Geotechnical and Structural Engineering Research Center, Shandong University, Jinan, Shandong 250-061, China

Abstract
In order to prevent environmental pollution, initiatives to increase the sustainability of resources are supported by society. However, the performance of recycled materials does not generally match that of natural materials. This study looks into the use of geogrid to improve various types of recycled aggregates. For this purpose, five different recycled aggregates were created by recycling wastes from the construction industry. Besides, direct shear tests (DS tests) were carried out on these recycled aggregates to determine their shear strengths. Following that, a triaxial geogrid was placed in the recycled aggregates to provide reinforcement, and the DS tests were conducted on the reinforced recycled aggregates. The results of the tests were also compared to those of tests performed on natural aggregates (NA). In conclusion, it was found that the recycled aggregates have lower shear strengths than the NA. Nonetheless, when reinforced with geogrid, the shear strength of the recycled concrete aggregates (RCA) and construction and demolition wastes (CDW) exceeded that of the NA. Furthermore, the geogrid reinforcement increased the shear strength of the recycled crushed bricks (CB), though not to the level of the NA.

Key Words
direct shear test; granular soils; recycled aggregate-geogrid interaction; recycled materials; sustainability

Address
Bahadir Ok, Huseyin Colakoglu and Umud Dagli: Department of Civil Engineering, Alparslan Turkes Science and Technology University,
Balcali Neighborhood, Çatalan Street No:201/1 01250 Saricam, Adana, Turkey

Abstract
Intensive rainfall during the summer season in Korea has triggered numerous devastating landslides outside of downtown in mountainous areas. The 2D slope stability analysis that is generally used for cut slopes and embankments is inadequate to model slope failure in mountainous areas. This paper presents a new 3D slope stability formulation using the global sliding vector in the limit equilibrium method, and it uses an ellipsoidal slip surface for static and quasi-static analyses. The slip surface's flexibility of the ellipsoid shape gives a lower FS than the spherical failure shape in the Fellenius, Bishop, and Janbu's simplified methods. The increasing sub-columns of each column tend to increase the FS and converge to a steady value. The symmetrical geometric conditions of the convex turning corners do not indicate symmetrical failure of the surface in 3D analysis. Pseudo-static analysis shows that the horizontal seismic force decreases the FS and increases the mass volume at the critical failure state. The stability index takes the FS and corresponding sliding mass into consideration to assess the potential risk of slope failure in complex mountainous terrain. It is a valuable parameter for selecting a vulnerable area and evaluating the overall risk of slope failure.

Key Words
ellipsoidal slip surface; global sliding vector; limit equilibrium method; three-dimensional slope stability analysis

Address
Hosung Shin: Department of Civil and Environmental Engineering, University of Ulsan,
Daehak-ro 93, Nam-Gu, Ulsan 44610, Republic of Kiorea

Abstract
Rate-dependent mechanical response of sand, subjected to loading of medium to high strain rate range, is of interest for several civilian and military applications. Such rate-dependent response can vary significantly based on the initial density state of the sand, applied confining pressure, considered strain rate range, drainage condition and sand morphology. A numerical study has been carried out employing a recently proposed visco-plastic constitutive model to explore the rate-dependent mechanical behaviour of Toyoura sand under drained triaxial loading condition. The model parameters have been calibrated using the experimental data on Toyoura sand available in published literature. Under strain rates higher than a reference strain rate, the simulation results are found to be in good agreement with the experimentally observed characteristic shearing behaviour of sand, which includes increased shear strength, pronounced post-peak softening and suppressed compression. The rate-dependent response, subjected to intermediate strain rate range, has further been assessed in terms of enhancement of peak shear strength and peak friction angle over varying initial density and confining pressure. The simulation results indicate that the rate-induced strength increase is highest for the dense state and such strength enhancements remain nearly independent of the applied confinement level.

Key Words
drained triaxial shearing; numerical modelling; rate-dependent response; strain rate effect; Toyoura sand; visco-plastic constitutive model

Address
Mousumi Mukherjee and Siddharth Pathak: School of Civil and Environmental Engineering, Indian Institute of Technology Mandi, Mandi-175075, H.P., India

Abstract
In this study, a series of three-dimensional numerical analyses were carried out to investigate the penetration performance of a dynamically installed Hall anchor. The advanced coupled Eulerian-Lagrangian (CEL) technique was adopted to accurately simulate the large soil deformation during the vertical penetration of a Hall anchor. In total, 52 numerical analyses were conducted to investigate the relationship between anchor penetration depth and the initial kinematic energy. Moreover, a sensitivity analysis was performed to investigate the effects of soil shear strength and soil type on the penetration mechanism of a drop anchor under self-weight. There is a monotonic increase in the penetration depth with an increasing anchor weight when the topsoil of the riverbed is not subjected to erosion. On the other hand, all the computed depths significantly increase when soil erosion is taken into consideration. This is mainly due to an enhanced initial kinematic energy from an increased dropping depth. Both depths increase exponentially with the initial kinematic energy. An enhanced shear strength can potentially increase the side resistance and end-bearing pressure around a drop anchor, thus significantly reducing the downward penetration of a hall anchor. Design charts are developed to directly estimate penetration depth and associated plastic zone due to dynamically installed anchor at arbitrary soil shear strength and anchor kinematic energy.

Key Words
design chart; Hall anchor; kinematic energy; penetration mechanism; undrained shear strength

Address
Haijun Zhao, Jiawei Che, Wanchun Chen, Dongli Guo, Haiyang Hu and Shuang Dong: China Construction Eight Engineering Division Rail Transit Construction Co., L.T.D., Nanjing, 210046, China
Zhaohan Zhu: School of Electrical Engineering, Southwest Jiaotong University, Chengdu, 611756, China
Qian Yin: Nanjing Metro, Nanjing, 210018, China

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