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Volume 32, Number 3, February10 2023

Through qualitative analysis and quantitative analysis, the contradictory conclusions about the stability of the settled goaf with two-layer coal seams subject to building load were obtained. Therefore, it is necessary to combine the additional stress method and numerical simulation to further analyze the foundation stability. Through borehole analysis and empirical formula analogy, the height of water-conducting fracture zone in No.4 coal and No.9 coal were obtained, providing the calculation range of water-conducting fracture zone for numerical simulation. To ensure the accuracy of the elastic modulus of broken gangue, the stress-strain curve were obtained by broken gangue compression test in dried state of No.4 coal seam and in soaking state of No.9 coal seam. To ensure the rationality of the numerical simulation results, the actual measured subsidence data were retrieved by numerical simulation. FISH language was used to analyze the maximum building load on the surface and determine the influence depth of building load on the foundation. The critical building load was 0.16 MPa of No.4 settled goaf and was 1.6 MPa of No.9 settled goaf. The additional stress affected the water-conducting fracture zone obviously, resulted in the subsidence of water-conducting fracture zone was greater than that of bending subsidence zone. In this paper, the additional stress method was analyzed by numerical simulation method, which can provide a new analysis method for the treatment and utilization of the settled goaf.

Key Words
ad-ditional stress method; building loads; crushing gangue compression test; foundation stability; settled goaf with two-layer coal seams

Yao Lu and Ning Jiang: State Key Laboratory of Mining Disaster Prevention and Control Co-Founded by Shandong Province and the Ministry of Science and Technology, Shandong University of Science and Technology, Qingdao 266590, China
Changxiang Wang and Meng Zhang: College of Safety Science and Engineering, Anhui University of Science and Technology, Huainan 232000, China
Dezhi Kong: Wenzhou Medical University, Wenzhou 325000, China
Haiyang Pan: State Key Laboratory of Mining Disaster Prevention and Control Co-Founded by Shandong Province and the Ministry of Science and Technology, Shandong University of Science and Technology, Qingdao 266590, China;
General Institute of Exploration and Research of China National Administration of Coal Geology, Beijing 10039, China

One of the main parameters that affect the design of suction caisson-supported offshore structures is uplift behavior. Pull-out of suction caissons is profoundly utilized as the offshore wind turbine foundations accompany by a tensile resistance that is a function of a complex interaction between the caisson dimensions, geometry, wall roughness, soil type, load history, pull-out rate, and many other parameters. In this paper, a parametric study using a 3-D finite element model (FEM) of a single offshore suction caisson (SOSC) surrounded by saturated soil is performed to examine the effect of some key factors on the tensile resistance of the suction bucket foundation. Among the aforementioned parameters, caisson geometry and uplift loading as well as the difference between the tensile resistance and suction pressure on the behavior of the soil-foundation system including tensile capacity are investigated. For this purpose, a full model including 3-D suction caisson, soil, and soil-structure interaction (SSI) is developed in Abaqus based on the u-p formulation accounting for soil displacement (u) and pore pressure, P.The dynamic responses of foundations are compared and validated with the known results from the literature. The paper has focused on the effect of geometry change of 3-D SOSC to present the soil-structure interaction and the tensile capacity. Different 3-D caisson models such as triangular, pentagonal, hexagonal, and octagonal are employed. It is observed that regardless of the caisson geometry, by increasing the uplift loading rate, the tensile resistance increases. More specifically, it is found that the resistance to pull-out of the cylinder is higher than the other geometries and this geometry is the optimum one for designing caissons.

Key Words
3-D finite element analysis; suction caisson; tensile capacity; u-p formulation

Azam Arefi, Pooria Ahad and Mohammad Silani: Department of Mechanical Engineering, Isfahan University of Technology, Isfahan, 84156-83111, Iran
Mehdi Bayat: Department of Civil Engineering, Aalborg University, Aalborg, Denmark;
Current address: Svanehoj Danmark A/S, Fabriksparken 6, 9230 Svenstrup J, Denmark

Settlement estimation in cohesion materials is a crucial topic to tackle because of the complexity of the cohesion soil texture, which could be solved roughly by substituted solutions. The goal of this research was to implement recently developed machine learning features as effective methods to predict settlement (𝑆m) of shallow foundations over cohesion soil properties. These models include hybridized support vector regression (𝑆𝑉𝑅), random forests (𝑅𝐹), and coot optimization algorithm (𝐶𝑂𝑀), and black widow optimization algorithm (𝐵𝑊𝑂𝐴). The results indicate that all created systems accurately simulated the 𝑆𝑚, with an 𝑅2 of better than 0.979 and 0.9765 for the train and test data phases, respectively. This indicates extraordinary efficiency and a good correlation between the experimental and simulated 𝑆𝑚. The model's results outperformed those of 𝐴𝑁𝐹𝐼𝑆−𝑃𝑆𝑂, and 𝐶𝑂𝑀−𝑅𝐹 findings were much outstanding to those of the literature. By analyzing established designs utilizing different analysis aspects, such as various error criteria, Taylor diagrams, uncertainty analyses, and error distribution, it was feasible to arrive at the final result that the recommended 𝐶𝑂𝑀−𝑅𝐹 was the outperformed approach in the forecasting process of 𝑆m of shallow foundation, while other techniques were also reliable.

Key Words
forecasting; optimization algorithms; random forests; settlement; shallow foundation; support vector regression

Yi Han and Ye Wang: School of Architecture, Anhui Science and Technology University, Bengbu, Anhui, 233100, China
Xingliang Jiang: CCCC Water Transportation Consultants Co., Ltd., Beijing 100007, China
Hui Wang: Department of Civil Engineering, Tongji University, Shanghai 200092, China

To ensure the safety of underground infrastructures, ground can sometimes be first treated by cement slurry and then stabilized using artificial ground freezing (AGF) technique before excavation. The hydration heat produced by cement slurry increases the soil temperature before freezing and results in an extension of the active freezing time (AFT), especially when the Metro Jet System (MJS) treatment is adopted due to a high cement-soil ratio. In this paper, by taking advantage of an on-going project, a case study was performed to evaluate the influence of MJS and AGF on the ground temperature variation through on-site measurement and numerical simulation. Both on-site measurement and simulation results reveal that MJS resulted in a significant increase in the soil temperature after treatment. The ground temperature gradually decreases and then stabilized after completion of MJS. The initiation of AGF resulted in a quick decrease in ground temperature. The ground temperature then slowly decreased and stabilized at later freezing. A slight difference in ground temperature exists between the on-site measurements and simulation results due to limitations of numerical simulation. For the AGF system, numerical simulation is still strongly recommended because it is proven to be cost-effective for predicting the ground temperature variation with reasonable accuracy.

Key Words
active freezing time; artificial ground freezing; hydration heat; metro jet system; numerical simulation

Jiling Zhao, Ping Yang and Lin Li: College of Civil Engineering, Nanjing Forestry University, Nanjing 210037, Jiangsu, China
Junqing Feng: East China Construction Co., Ltd of China Railway No.3 Group. Nanjing, 211106, Jiangsu, China
Zipeng Zhou: Nanjing Institute of Surveying, Mapping & Geotechnical Investigation, Co., Ltd. Nanjing 210019, Jiangsu, China

Ground fissures have a huge effect on the integrity of surface structures. In high-intensity ground fissure regions, however, land resource would be wasted and city building and economic development would be limited if the area avoiding principle was used. In view of this challenge, to reveal the seismic response and seismic failure characteristics of ground fissure sites, a shaking table test on model soil based on a 1:15 scale experiment was carried out. In the test, the spatial distribution characteristics of acceleration response and Arias intensity were obtained for a site exposed to earthquakes with different characteristics. Furthermore, the failure characteristics and damage evolution of the model soil were analyzed. The test results indicated that, with the increase in the earthquake acceleration magnitude, the crack width of the ground fissure enlarged from 0 to 5 mm. The soil of the hanging wall was characterized by earlier cracking and a higher abundance of secondary fissures at 45. Under strong earthquakes, the model soil, especially the soil near the ground fissure, was severely damaged and exhibited reduced stiffness. As a result, its natural frequency also decreased from 11.41 Hz to 8.05 Hz, whereas the damping ratio increased from 4.8% to 9.1%. Due to the existence of ground fissure, the acceleration was amplified to nearly 0.476 m/s2, as high as 2.38 times of the input acceleration magnitude. The maximum of acceleration and Arias intensity appeared at the fissure zone, which decreased from the main fissure toward both sides, showing hanging wall effects. The seismic intensity, duration and frequency spectrum all had certain effects on the seismic response of the ground fissure site, but their influence degrees were different. The seismic response of the site induced by the seismic wave that had richer low-frequency components and longer duration was larger. The discrepancies of seismic response between the hanging wall and the footwall declined obviously when the magnitude of the earthquake acceleration increased. The research results will be propitious to enhancing the utilizing ratio of the limited landing resource, alleviation of property damages and casualties, and provide a good engineering application foreground.

Key Words
ground fissure; seismic failure characteristics; seismic response; shaking table test; soil damage

Chao Zhang, Xuzhi Nie, Yuekui Pang and Youjun Xu: School of Civil Engineering, Inner Mongolia University of Science & Technology, Baotou 014010, China;
Academician Workstation of Mine Safety and Underground Engineering, Inner Mongolia University Science and Technology,Baotou 014010, China
Zhongming Xiong: School of Civil Engineering, Xi'an University of Architecture & Technology, Xi'an 710055, China
Xiaolu Yuan: School of Materials and Metallurgy, Inner Mongolia University of Science & Technology, Baotou 014010, China
Yan Zhuge: School of Natural & Built Environments, University of South Australia, Adelaide, 5108, Australia

Rock masses often contain natural fractures of varying sizes, and the size of the natural fractures may affect the propagation of hydraulic fractures. We conduct a series of triaxial hydraulic fracturing tests to investigate the effect of the pre-existing fracture size a on hydraulic fracture propagation. Experimental results show that the pre-existing fracture size impacts hydraulic fracture propagation. As the pre-existing fracture size increases, the hydraulic fracture propagates towards the pre-existing fracture tips, evidenced by the decreased distance between the final hydraulic fracture and the pre-existing fracture tips. Furthermore, the attracting effect of pre-existing fracture tips increases when the distance between the wellbore and the pre-existing fracture is short (L/D=2 or 4 in this study). With increased distance between the wellbore and the pre-existing fracture (L/D=6 in this study), the hydraulic fracture propagates to the middle of the pre-existing fracture rather than the tips, as the attracting effect of the pre-existing fracture diminishes.

Key Words
elastic strain energy density; fracture propagation; fracture propagation path; hydraulic fracturing; pre-existing fracture size

Bo Zhang: School of Civil Engineering, Shandong University, Jinan, Shandong 250061, PR China;
Structural Laboratory, Shandong Institute of Transportation Science, Jinan, Shandong 250014, PR China
Yao Li and n Songa: School of Civil Engineering, Shandong University, Jinan, Shandong 250061, PR China
Xue Y. Yang: Shandong Urban Construction Vocational College, Jinan, Shandong 250014, PR China
Shu C. Li: Research Center of Geotechnical and Structural Engineering, Shandong University, Jinan, Shandong 250061, PR China
Chao Wei: Research Center of Geotechnical and Structural Engineering, Shandong University, Jinan, Shandong 250061, PR China;
State Key Laboratory for Geomechanics and Deep Underground Engineering, China University of Mining and Technology,
Xuzhou, Jiangsu 221116, China

For structures with underground basement walls, the soil-structure-interaction between the side soil and the walls affects the response of the system. There is interest in quantifying the relationship between the lateral earth pressure and the wall displacement using p-y curves. To date, passive p-y curves in available limited studies were assumed elastic-perfectly plastic. In reality, the relationship between earth pressure and wall displacement is complex. This paper focuses on studying the development of passive p-y curves behind rigid walls supporting granular soils. The study aims at identifying the different components of the passive p-y relationship and proposing a rigorous non-linear p-y model in place of simplified elastic-plastic models. The results of the study show that (1) the p-y relationship that models the stress-displacement response behind a rigid basement wall is highly non-linear, (2) passive p-y curves are affected by the height of the wall, relative density, and depth below the ground surface, and (3) passive p-y curves can be expressed using a truncated hyperbolic model that is defined by a limit state passive pressure that is determined using available logarithmic spiral methods and an initial slope that is expressed using a depth-dependent soil stiffness model.

Key Words
passive pressure; plaxis; p-y curves; rigid walls; soil-structure interaction

Imad Elchiti, George Saad and Shadi S. Najjar: Department of Civil and Environmental Engineering, American University of Beirut,
P.O. Box 11-0236 Riad El-Solh 1107-2020, Lebanon

With the development of infrastructure, there is a critical shortage of filling materials all over the word. However, a large amount of silt accumulated in the lower reaches of the Yellow River is treated as waste every year, which will cause environmental pollution and waste of resources. Microbial induced calcium carbonate precipitation (MICP) technology, with the advantage of efficient, economical and environmentally friendly protection, is selected to solidify the abandoned Yellow River silt with poor mechanical properties into high-quality filling material in this paper. Based on unconfined compressive strength (UCS) test, determination of calcium carbonate (CaCO3) content and scanning electron microscope (SEM) test, the effects of cementation solution concentration, treatment times and relative density on the solidification effect were studied. The results show that the loose silt particles can be effectively solidified together into filling material with excellent mechanical properties through MICP technology. The concentration of cementation solution have a significant impact on the solidification effect, and the reasonable concentration of cementation solution is 1.5 mol/L. With the increase of treatment times, the pores in the soil are filled with CaCO3, and the UCS of the specimens after 10 times of treatment can reach 2.5 MPa with a relatively high CaCO3 content of 26%. With the improvement of treatment degree, the influence of relative density on the UCS increases gradually. Microscopic analysis revealed that after MICP reinforcement, CaCO3 adhered to the surface of soil particles and cemented with each other to form a dense structure.

Key Words
calcium carbonate content; filling material; MICP; unconfined compressive strength; Yellow River silt

Yuke Wang, Rui Jiang and Gan Wang: College of Water conservancy Science and Engineering, Zhengzhou University, Zhengzhou, 450001, China;
National Local Joint Engineering Laboratory of Major Infrastructure Testing and Rehabilitation Technology,
Zhengzhou 450001, China
Collaborative Innovation Center of Water Conservancy and Transportation Infrastructure Safety Protection,
Henan Province, Zhengzhou, 450001, China
Meiju Jiao: College of Water conservancy Science and Engineering, Zhengzhou University, Zhengzhou, 450001, China

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