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CONTENTS
Volume 39, Number 3, November10 2024
 

Abstract
In recent years, the increasingly frequent extreme weather conditions in Yellow River Alluvial Plain (YRAP) like heavy rains and drought have resulted in significant Ground Water Level (GWL) fluctuations. After long-distance transportation by Yellow River, the silt in this area gains characteristics of high particle roundness and poor grain gradation, which makes it sensitive to the changes of water content. Consequently, upon GWL fluctuations, the bearing behaviors of Rigid Pile Composite Foundation (RPCF) gradually deteriorate and result in additional settlement. In order to investigate the changing disciplines and inherent mechanisms of the RPCF bearing behaviors upon GWL fluctuations, a large-scale model test was performed and presented. The experimental results suggest that RPCF settlement experiences a sudden increase in the first GWL fluctuation cycle and then gradually stabilizes in the following cycles. Such phenomenon could be attributed to the soil structure rearrangement induced by matric suction reduction in the GWL rise process and growth of effective stress in the GWL drop process. Further, considering the soil stiffness deterioration in the GWL rise process, the traditional composite modulus method for RPCF settlement estimation was modified to extend its application in unsaturated YRAP. The changing disciplines, mechanisms and estimation method presented can facilitate practicing engineers to gain a more comprehensive understanding on the bearing behaviors of RPCF in YRAP upon GWL fluctuations.

Key Words
bearing capacity; ground water level fluctuation; matric suction; rigid pile composite foundation; Yellow River alluvial plain

Address
Yunlong Liu, Chongxuan Yuan, Lei Wang and Sihua Zhang: Zhengzhou University, Zhengzhou, Henan, 450066, China

Abstract
This study investigates the control effect of isolation piles on ground settlement resulting from foundation pit excavation. Based on the three-stage analysis method, first, the Kerr three-parameter foundation model is introduced, and the deflection differential equation is derived to solve the horizontal displacement of the diaphragm wall. Then, based on the horizontal displacement of the diaphragm wall, the boundary element method is used to calculate the additional stress at the boundary of the foundation pit, and the horizontal additional displacement and additional stress of the soil free field at the position of the isolation pile are obtained using the Mindlin solution. Subsequently, soil free field additional stress is applied to the pile foundation, and the shielding effect of group piles is also considered. Based on the Kerr three-parameter foundation model, the deflection differential equation of the pile foundation under the influence of horizontally oriented additional stress is established to solve the horizontal displacement of the isolated piles. Finally, the boundary element method is used again to invert the additional stress caused by the horizontal displacement of the isolation pile, and the surface settlement after the isolation pile is calculated in combination with the Mindlin vertical displacement solution. The spatial finite element model is established and compared with the theoretical calculation results to prove the rationality of the theory. The influence of basic construction parameters is analyzed theoretically, and it is found that the surface settlement is reduced by 30.9% compared with no isolation pile. Of the selected parameters in this paper, the effects of the isolation pile's controlled diameter, spacing, and elastic modulus, the thickness and elastic modulus of the diaphragm wall on the surface settlement are 4.9 mm, 3.1 mm, 3.3 mm, 3 mm, 1.7 mm, respectively, which are 45.4%, 28.7%, 30.6%, 27.8%, 15.7% of the standard working conditions, respectively. This shows that optimization of the isolation pile parameters has the best effect on surface settlement, optimization of the diaphragm wall parameters has the poor effect.

Key Words
boundary element method; foundation engineering; isolated piles; Kerr three-parameter foundation model; spatial finite element model; surface settlement control

Address
Kunpeng Li and Shihai Chen: College of Civil Engineering, Huaqiao University ,668 Jimei Avenue, Jimei District, Xiamen City, Fujian, China
Peng Zhao and Rupeng Pei: Xiamen Construction Engineering Co., Ltd. Of China Railway First Group., Xiamen, Fujian, China

Abstract
The shear strength (SS) of soil is a critical parameter utilized in the design of civil engineering projects. The SS parameters, including cohesion (c) and friction angle (o), can be determined through methods conducted either in the field or within a laboratory environment. However, the traditional method for determining SS parameters are not only costly but also time-consuming. Recently, the application of machine learning (ML) in geotechnical problems has received increasing attention. In order to select an appropriate ML model and assess the effect of physical properties on the SS of soil. This research endeavors to predict critical SS parameters of soil through the application of five machine learning (ML) models, integrating easily-available physical soil index, including specific gravity (G), saturation degree (Sr), liquid limit (LL), silt content (SC), and clay content (CC). The used ML techniques include Extreme Gradient Boosting (XGBoost), Random Forest (RF), Multilayer Perceptron (MLP), Support Vector Machine (SVM), and Convolutional Neural Network (CNN). A range of metrics, encompassing the root mean square error (RMSE), mean absolute error (MAE), and determination coefficient (R) were used to measure the predictive efficacy of the employed models as well as compare the performance of the used ML models. The values of R2 range from 0.769 to 0.987 indicate that all ML models exhibit excellent predictive capabilities for estimating SS parameters, in which the XGBoost, and CNN techniques show outperforming results compared to the other models. The study uses decision tree feature importance (DTFI) and coefficient feature importance (CFI) techniques to investigate how various physical properties impact the predictive capabilities of the model and indicates that both G and LL have a substantial impact on the predictive accuracy of cohesion and friction angle.

Key Words
cohesion; deep learning; ensemble learning; feature importance; friction angle; support vector machine

Address
Ba-Quang-Vinh Nguyen: School of Civil Engineering and Management, International University, Ho Chi Minh City, Vietnam;
Vietnam National University, Ho Chi Minh city, Vietnam
Yun-Tae Kim: Ocean Engineering Department, Pukyong National University, Busan, Korea

Abstract
In this study, free and forced vibration behaviour of viscoelastic porous functionally graded (VPFG) plates resting on elastic foundations are investigated. Differential equations are obtained via higher order shear deformation theory. Equations of motion are obtained through energy formulations and Hamilton's principle. Navier's method based on double Fourier series is employed for the solution. Damping effect is implemented into the analysis by means of Kelvin and linear standard viscoelastic models. Viscoelastic material properties are used instead of elastic properties by means of the correspondence principle. Displacements of the plates are determined in Laplace domain and transformed into time domain by using Durbin's Modified Inverse Laplace transform method. The proposed algorithm's accuracy is validated through free and damped vibration analyses on VPFG plate, with results compared to existing studies in the literature. The study examines the influence of viscoelastic damping parameters, porosity volume fraction indexes, foundation characteristics, porosity distribution patterns and material property variations on the damped forced vibration response.

Key Words
forced vibration; free vibration; linear viscoelastic models; porous functionally graded plates

Address
Ömer Faruk Çapar, Mehmet Bugra Ozbey and Yavuz Cetin Cuma: Department of Civil Engineering, Adana Alparslan Turkes Science and Technology University, Türkiye
Mehmet Halil Çalim: Department of Civil Engineering, Cukurova University, Adana, Türkiye

Abstract
Seepage flow through complex foundations is one of the main factors causing dam failure. To foresee this problem, seepage modeling and analysis are usually performed. This study investigated seepage behavior as affected by complex, foliated, rock foundations in an earth dam. The PLAXIS 3-D LE software was used to analyze seepage problems for steady state flow. The normal high-water level (NHWL) with anisotropic permeability was considered in the models. The anisotropic permeability of foliated rocks was determined according to the angle of inclination. The flow characteristics along the dam axis could be divided into five zones, with three zones for the middle parts (MD1, MD2 and MD3) and one zones for each of the two abutments (LA and RA). The quantities of flow (water transmissibility) upstream to downstream (QX) on each zone highly depended on the geological structures. Although the average seepage transmissibility values of the residual soil and phyllite were almost equal for every zone. The values in the anticline areas were higher than for the syncline areas, especially for the middle zones. The flow tended to transfer from residual soil into phyllite rock in the anticline area. The transmissibility ratio of anticline to syncline was more than 2 times for both the residual soil and phyllite. The finger drain and river channel attracted substantial flow in the longitudinal (QY) and vertical (QZ) directions. However, the verification of the field piezometric versus the modeling heads showed the possibility of blockage of the finger drain.

Key Words
3-D modeling; complex foundations; earth dam; field monitoring; seepage

Address
Truong Q. Nhu, Nipawan Kunsuwan, Warakorn Mairaing,
Bunpoat Kunsuwan and Thawatchai Chalermpornchai: Department of Civil Engineering, Faculty of Engineering at Kamphaeng Saen, Kasetsart University,
Kamphaeng Saen, Nakhon Pathom, Thailand

Abstract
In large-scale engineering construction, there are many cases of highly concealed adverse geological phenomena (HCAGP) at certain scale that are not revealed until excavation. It is crucial to ascertain their geological characteristics and rapidly formulate treatment since they often have enormous negative impacts on the project. However, conventional exploration and evaluation methods are not suitable for HCAGP due to the long acquisition time and strict requirements. Therefore, this paper proposes a dynamic-tracking investigation and evaluation method (DTIEM), which carries out a series of fast and effective techniques, including down-the-hole (DTH) drilling, cross-inclined holes, seismic tomography and P-wave velocity (VP) tests, for preliminary data of HCAGP. Then, an initial treatment plan is proposed to guide the construction. Subsequently, the initial data of the HCAGP are tracked and revised until the end of construction. This method was applied to a deep groove at a hydropower station, which was exposed when the excavation of dam section 11. The results show that by using the DTIEM, the preliminary engineering characteristics of the deep groove were obtained quickly. The rock mass quality of the top deep groove was grade III2 with 9.82 GPa, the middle part was grade III1 with 15.07 GPa, and the bottom part was grade II with 19.68 GPa. The quality of rock mass gradually increases with the increase of depth. From the numerical simulation, the maximum additional displacement is about 20 mm at the dam crest, 4 ~ 7 mm at the dam heel, and 2 ~ 5 mm at the dam toe. The numerical simulation and monitoring results show that the stress and strain of the dam and foundation are within a safe range in each stage. Thus, the proposed method is feasible.

Key Words
down-the-hole (DTH); dynamic-tracking investigation and evaluation method (DTIEM); highly concealed adverse geological phenomena (HCAGP); P-wave velocity

Address
Yihan Du: School of Architecture and Civil Engineering, Anhui Polytechnic University, Wuhu 241000, China;
College of Environment and Civil Engineering, Chengdu University of Technology, Chengdu 610059, China;
Engineering Research Center of Anhui Green Building and Digital Construction,
Anhui Polytechnic University, Wuhu 241000, China
Wei Han: School of Architecture and Civil Engineering, Anhui Polytechnic University, Wuhu 241000, China;
Engineering Research Center of Anhui Green Building and Digital Construction,
Anhui Polytechnic University, Wuhu 241000, China
Dexin Nie, Yufeng Wei and Mo Zhang: College of Environment and Civil Engineering, Chengdu University of Technology, Chengdu 610059, China

Abstract
Pile foundations are frequently subjected to dynamic loads, necessitating a thorough investigation of cyclic shear characteristics at pile-soil interfaces. To investigate the influence of soil moisture content and concrete surface roughness on the cyclic shear characteristics of interfaces, a series of cyclic shear tests were conducted using a large-scale indoor direct shear apparatus. The effects of three normal stresses (100, 200, and 300 kPa), four moisture content levels (14%, 19%, 24%, and 29%), and five concrete surface joint roughness coefficients (0.4, 5.8, 9.5, 12.8, and 16.7) on interface shear stress and volumetric strain behavior of residual soil were analyzed. Numerical simulations were employed to analyze the microstructural changes in particles. The results show that the water content has a significant effect on the interface stress-displacement curve. It shows a cyclic hardening type at low water content and a cyclic softening type at high water content. There is a critical roughness on the concrete surface. After exceeding this value, the shear strength of the interface is no longer improved. The number of force chains in the soil increases with the increase of the number of cycles and roughness. The increase of the number of particles in the force chain leads to the increase of the instability of the force chain structure. Therefore, most of the force chains are composed of three particles. The main direction of the normal and tangential contact force anisotropy is closely related to the shear direction. The main direction will deflect with the shear direction, and the deflection angle is about 35.

Key Words
direct shear test; moisture content; numerical simulation; roughness; soil-structure interface

Address
Feiyu Liu: School of Mechanics and Engineering Sciences, Shanghai University, Shanghai 200444, China;
School of Civil Engineering and Architecture, East China Jiaotong University, Nanchang 330013, China;
Zhejiang Huadong Geotechnical Investigation and Design Institute Co., Ltd., Hangzhou, Zhejiang 310030, China
Kechao Ma:School of Mechanics and Engineering Sciences, Shanghai University, Shanghai 200444, China
Wei Yu: Zhejiang Huadong Geotechnical Investigation and Design Institute Co., Ltd., Hangzhou, Zhejiang 310030, China

Abstract
Sand liquefaction caused by earthquakes is one of the serious threats to underground stations. The change in groundwater level may have a great influence on the seismic behavior of underground stations buried in sand foundations. In this paper, a 3D numerical model for the soil-structure interaction system was established by applying the fully nonlinear finite difference program FLAC3D. The impact of different groundwater levels on the seismic behavior of underground stations was explored in numerical analyses. The fluid-solid coupling and different seismic intensities were taken into consideration in the model. The numerical results demonstrate that the decrease of groundwater level significantly restrains the uplift of the underground station and the liquefaction of the site. The dynamic soil pressure around the sidewall under a higher water table is larger than that under a low water table. Under the earthquake, the ground peak acceleration increases as the groundwater level decreases. For the station structure, the decrease of groundwater level is unfavorable to the shear resistance of the middle columns. However, the effect of different groundwater levels on the axial stress of the middle columns is relatively small. The research results can be used as a reference for the seismic design of subway stations shallowly buried in the sand foundation with different groundwater levels.

Key Words
groundwater level; sand liquefaction; seismic response; soil-structure interaction; subway station

Address
Min-Zhe Xu, Zhen-Dong Cui and Li Yuan: State Key Laboratory of Intelligent Construction and Healthy Operation & Maintenance of Deep Underground Engineering, School of Mechanics and Civil Engineering, China University of Mining and Technology, Xuzhou, Jiangsu, 221116, P.R. China

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