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CONTENTS
Volume 38, Number 2, July25 2024
 

Abstract
The drilling angle of the well is an important factor that can affect the sand production process and make its destructive effects more severe or weaker. This study investigated the effect of different well angles on sand production for the Asmari Formation, located in one of the oil fields southwest of Iran. For this purpose, a finite difference model was developed for three types of vertical (90), inclined (45), and horizontal (0) wells with casing and perforations in the direction of minimum and maximum horizontal stresses, then coupled with fluid flow. Here, finite element meshing was used, because the geometry of the model is so complex and the implementation of finite difference meshes is impossible or very difficult for such models. Using a combined FDM-FEM model with fluid flow, the sand production process in three different modes with different flow rates for the Asmari sandstone was investigated in this study. The results of numerical models show that the intensity of sand production is directly related to the in-situ stress state of the oil field and well drilling angle. Since the stress regime in the studied oil field is normal, the highest amount of produced sand was in inclined wells (especially wells drilled in the direction of minimum horizontal stress) and the lowest amount of sand production was related to vertical wellbore. Also, the Initiation time of sand production in inclined wells was much shorter than in other wellbores.

Key Words
numerical modeling; perforation; sand production; sanding initiation; sanding rate; well inclination angle

Address
Nemat Nemati and Kaveh Ahangari: Department of Mining Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran
Kamran Goshtasbi: Department of Mining Engineering, Faculty of Engineering, Tarbiat Modares University, Tehran, Iran
Reza Shirinabadi: Department of Petroleum and Mining Engineering, South Tehran Branch, Islamic Azad University, Tehran, Iran;
Research Center for Modeling and Optimization in Science and Engineering, South Tehran Branch,
Islamic Azad University, Tehran, Iran

Abstract
In paste backfill mining, cemented coal gangue–fly ash backfill (CGFB) can effectively utilize coal-based solid waste, such as gangue, to control surface subsidence. However, given the pressurized water accumulation environment in goafs, CGFB is subject to coupling effects from water pressure and chloride ions. Therefore, studying the influence of pressurized water on the chlorine salt erosion of CGFB to ensure green mining safety is important. In this study, CGFB samples were soaked in a chloride salt solution at different pressures (0, 0.5, 1.5, and 3.0 MPa) to investigate the chloride ion transport characteristics, hydration products, micromorphology, pore characteristics, and mechanical properties of CGFB. Water pressure was found to promote chloride ion transfer to the CGFB interior and the material hydration reaction; enhance the internal CGFB pore structure, penetration depth, and chloride ion content; and fill the pores between the material to reduce its porosity. Furthermore, the CGFB peak uniaxial compression strain gradually decreased with increasing soaking pressure, whereas the uniaxial compressive strength first increased and then decreased. The resulting effects on the stability of the CGFB solid-phase hydration products can change the overall CGFB mechanical properties. These findings are significant for further improving the adaptability of CGFB for coal mine engineering.

Key Words
chloride ion transport; coal gangue–fly ash backfill; fracture morphology; pore analysis; water pressure

Address
Dawei Yin, Zhibin Lu, Zongxu Li and Xuelong Li: State Key Laboratory of Mine Disaster Prevention and Control,
Shandong University of Science and Technology, Qingdao 266590, China
Chun Wang: Henan Polytechnic University, JiaoZuo 454000, China
Hao Hu: State Key Laboratory of Mining Response and Disaster Prevention and Control in Deep Coal Mines,
Anhui University of Science and Technology, Huainan 232001, China

Abstract
The piled raft foundations are subjected to lateral loading under the action of wind and earthquake loads. Their bearing behavior and flexural responses under these loadings are of prime concern for researchers and practitioners. The insufficient experimental studies on piled rafts subjected to lateral loading lead to a limited understanding of this foundation system. Lateral load sharing between pile and raft in a laterally loaded piled raft is scarce in literature. In the present study, lateral load–displacement, load sharing, bending moment distribution, and raft inclinations of the piled raft foundations have been discussed through an instrumented scaled down model test in 1 g condition. The contribution of raft in a laterally loaded piled raft has been evaluated from the responses of pile group and piled raft foundations attributing a variety of influential system parameters such as pile spacing, slenderness ratio, group area ratio, and raft embedment. The study shows that the raft contributes 28–49% to the overall lateral capacity of the piled raft foundation. The results show that the front pile experiences 20–66% higher bending moments in comparison to the back pile under different conditions in the pile group and piled raft. The piles in the piled raft exhibit lower bending moments in the range of 45–50% as compared to piles in the pile group. The raft inclination in the piled raft is 30–70% less as compared to the pile group foundation. The lateral load–displacement and bending moment distribution in piles of the single pile, pile group, and piled raft has been presented to compare their bearing behavior and flexural responses subjected to lateral loading conditions. This study provides substantial technical aid for the understanding of piled rafts in onshore and offshore structures to withstand lateral loadings, such as those induced by wind and earthquake loads.

Key Words
bending moment; lateral load; load sharing; raft inclination; pile group; piled raft

Address
Dinesh Kumar Malviya and Manojit Samanta: Academy of Scientific & Innovative Research (AcSIR), Ghaziabad, Uttar Pradesh – 201002 India
Geotechnical & Geohazards Group, CSIR-Central Building Research Institute Roorkee, Uttarakhand – 247667 India

Abstract
This paper describes the general trends of the stress-strain behavior of Korean weathered soil prior to failure and behavior at failure under triaxial loading. The isotropically consolidated samples were tested in a testing device under monotonic undrained loading. Relative density, effective mean pressure and fine content were the factors varied in the experimental investigation. The test results were analyzed and their behaviors were interpreted within the framework of plasticity constitutive model for a weathered Korean silty sand. Possible physical bases for the proposed forms are discussed. Validation of the applied model using the laboratory results is also given.

Key Words
constitutive model; monotonic undrained loading; silty sand; triaxial testing; weathered soil

Address
Sangseom Jeong and Junyoung Ko. Sumin Song: School of Civil and Environmental Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Republic of Korea
Junyoung Ko: Department of Civil Engineering, Chungnam National University, 99 Daehak-ro, Yuseong-gu, Daejeon 34134, Republic of Korea
Jaehong Kim: Department of Civil Engineering, Dongshin University, 67 Dongshindae-gil, Naju-si, 58245, Republic of Korea

Abstract
Liquefaction phenomenon refers to a phenomenon in which excess pore water pressure occurs when a dynamic load such as an earthquake is rapidly applied to a loose sandy soil ground where the ground is saturated, and the ground loses effective stress and becomes liquid. The laboratory repetition test for liquefaction evaluation can be performed through a repeated triaxial compression test and a repeated shear test. In this regard, this study attempted to evaluate the effects of the relative density of sand on the liquefaction resistance strength according to particle size distribution using repeated triaxial compression tests, and additional experimental verification using numerical analysis was conducted to overcome the limitations of experimental equipment. As a result of the experiment, it was confirmed that the liquefaction resistance strength increased as the relative density increased regardless of the classification of soil, and the liquefaction resistance strength of the SP sample close to SW was quite high. As a result of numerical analysis, it was confirmed that the liquefaction resistance strength increased as the confining pressure increased under the same relative density, and the liquefaction resistance strength did not decrease below a certain limit even though the confining pressure was significantly reduced at a relatively low relative density. This is judged to be due to a change in confining pressure according to the depth of the ground. As a result of analyzing the liquefaction resistance strength according to the frequency range, it was confirmed that there was no significant difference from the laboratory experiment results in the basic range of 0.1 to 1.0 Hz.

Key Words
liquefaction; numerical analysis; poorly graded soil; relative density; repeated triaxial test; well graded soil

Address
Hyeok Seoa and Daehyeon Kim: Department of Civil Engineering,Chosun Univercity, 309 Pilmundaero, Don-gu, Gwangju, Republic of Korea

Abstract
This paper presents a geomechanical framework for designing and optimizing layout patterns of cutterheads for rock Tunnel Boring Machines (TBMs), aiming to enhance their engineering performance. By examining the forces and moments exerted by rock, the study addresses geometric constraints associated with cutter boxes in key regions of the cutterhead, including the center, face, and gage areas, as well as the three-dimensional effects of cutterhead curvature on the geometric constraints of the back of the cutter boxes in the gage area. Novel formulas are proposed for determining the center points of cutter boxes and calculating both the minimum angular spacing and distance spacing between consecutive cutter boxes along a spiral path. The paper outlines an optimized layout design process for four cutterhead configurations: random, random paired, radial, and double spiral designs. Examples are provided to illustrate the results of applying these designs. The findings underscore the efficacy of the proposed methods in achieving a uniform and symmetrical distribution of cutters and buckets on the cutterhead surface. This approach effectively eliminates boundary overlap and minimizes unbalanced forces and moments. From a geomechanical standpoint, this framework offers a robust strategy for enhancing the performance and reliability of TBM cutterheads in rock tunneling operations.

Key Words
bucket; cutter box; cutterhead; hard rock; layout design; optimization; overlap; TBM

Address
Ebrahim Farrokh: Amirkabir University of Technology (Tehran Polytechnic), Hafez Ave., Tehran, Iran

Abstract
One of the issues with clayey soils, particularly those with significant quantities of organic matter, is the creep settling problem. Clay soils can be strengthened using a variety of techniques, one of which is the use of stone columns. Prior research involved foundation loading when the soil beds were ready and confined in one-dimensional consolidation chambers. In this study, a particular methodology is used to get around the model's frictional resistance issue. Initially, specimens were prepared via static compaction, and they were then re-consolidated inside a sizable triaxial cell while under isotropic pressure. With this configuration, the confining pressure can be adjusted, the pore water pressure beneath the foundation can be measured, and the spacemen's lateral border may be freely moved. This paper's important conclusions include the observation that secondary settlement declines with area replacement ratio. Because of the composite ground's increasing stiffness, the length to diameter ratio (l/d) and the stone column to sample height ratio (Hc/Hs) both increase. The degree of improvement varies from 12.4 to 55% according to area replacement ratio and (l/d) ratio.

Key Words
creep improvement factor; ground improvement; organic soil; secondary settlement; stone column

Address
Kumail R. Al-Khafaji, Mohammed Y. Fattah and Makki K. Al-Recaby: Department of Civil Engineering, University of Technology, Baghdad, Iraq

Abstract
Permafrost refers to the condition where the ground is frozen. It is crucial to review and evaluate the ground;s characteristics before construction. In this study, electrical resistivity surveying is chosen as the investigative technique to apply and illustrate the results on the state of permafrost ground and to summarize its applicability. Field experiments are conducted in the Yeoncheon area of South Korea, which has a freezing index of 522.6C days. The target area is categorized into two ground conditions: the first where the original ground freezes, and the second involves excavating the original ground up to a depth of 3 meters, backfilling it, and then artificially injecting fluid. Thus, frozen ground conditions are simulated under both natural and artificial circumstances. Electrical resistivity surveys are performed under both above-freezing and sub-zero temperature conditions, with the experiments conducted at sub-zero temperatures revealing relatively more high-resistivity zones due to the temperature conditions. In this area, the distribution of soil moisture content is also investigated using the Time Domain Reflectometry (TDR) technique. It is observed that the ground into which water is artificially injected had a relatively higher moisture content, although the difference is minor. Finally, a 3D map of the target ground is constructed based on the measured electrical resistivity values, and through this, the distribution of porosity, a crucial design parameter, is also depicted. This research demonstrates that the electrical resistivity technique can effectively evaluate the state of frozen and unfrozen ground and further suggests that it can detailed extract the characteristics of the target ground.

Key Words
3D map; electrical resistivity; frozen ground; porosity; time domain reflectometry

Address
Dae-Hong Min and Hyung-Koo Yoon:Department of Construction and Disaster Prevention Engineering, Daejeon University, Daejeon 34520, Republic of Korea

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