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CONTENTS
Volume 33, Number 1, April10 2023
 

Abstract
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Key Words
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Address
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Abstract
The unconfined compression strength (UCS) of soils is commonly used either before or during the construction of geo-structures. In the pre-design stage, UCS as a mechanical property is obtained through a laboratory test that requires cumbersome procedures and high costs from in-situ sampling and sample preparation. As an alternative way, the empirical model established from limited testing cases is used to economically estimate the UCS. However, many parameters affecting the 1D soil compression response hinder employing the traditional statistical analysis. In this study, gene expression programming (GEP) is adopted to develop a prediction model of UCS with common affecting soil properties. A total of 79 undisturbed soil samples are collected, of which 54 samples are utilized for the generation of a predictive model and 25 samples are used to validate the proposed model. Experimental studies are conducted to measure the unconfined compression strength and basic soil index properties. A performance assessment of the prediction model is carried out using statistical checks including the correlation coefficient (R), the root mean square error (RMSE), the mean absolute error (MAE), the relatively squared error (RSE), and external criteria checks. The prediction model has achieved excellent accuracy with values of R, RMSE, MAE, and RSE of 0.98, 10.01, 7.94, and 0.03, respectively for the training data and 0.92, 19.82, 14.56, and 0.15, respectively for the testing data. From the sensitivity analysis and parametric study, the liquid limit and fine content are found to be the most sensitive parameters whereas the sand content is the least critical parameter.

Key Words
gene expression programming; external criteria; parametric study; sensitivity analysis; statistical check; unconfined compression strength

Address
Muhammad Naqeeb Nawaz and Song-Hun Chong: Department of Civil Engineering, Sunchon National University, 255, Jungang-ro, Sunchon-si, Jeollanam-do, 57922, Korea
uhammad Muneeb Nawaz and Waqas Hassan: NUST Institute of Civil Engineering, National University of Sciences and Technology, Islamabad 44000, Pakistan
Safeer Haider: Department of Civil, Environmental and Architectural Engineering, University of Padua, Italy
Jin-Seop Kim: Radioactive Waste Disposal Research Division, Korea Atomic Energy Research Institute, Daejeon 34057, Korea

Abstract
This study explores a new energy partitioning approach to determine the fracture toughness of 3-D printed pristine/recycled high density polyethylene (HDPE) blends employing the essential work of fracture (EWF) concept. The traditional EWF approach conducts a uniaxial tensile test with double-edge notched tensile (DENT) specimens and measures the total energy defined by the area under a load-displacement curve until failure. The approach assumes that the entire total energy contributes to the fracture process only. This assumption is generally true for extruded polymers that fracture occurs in a material body. In contrast to the traditional extrusion manufacturing process, the current 3-D printing technique employs fused deposition modeling (FDM) that produces layer-by-layer structured specimens. This type of specimen tends to include separation energy even after the complete failure of specimens when the fracture test is conducted. The separation is not relevant to the fracture process, and the raw experimental data are likely to possess random variation or noise during fracture testing. Therefore, the current EWF approach may not be suitable for the fracture characterization of 3-D printed specimens. This paper proposed a new energy partitioning approach to exclude the irrelevant energy of the specimens caused by their intrinsic structural issues. The approach determined the energy partitioning location based on experimental data and observations. Results prove that the new approach provided more consistent results with a higher coefficient of correlation.

Key Words
3D printing; energy partitioning method; essential work of fracture (EWF); fracture toughness; fused deposition modeling (FDM); high-density polyethylene (HDPE); recycled plastics

Address
Sukjoon Na, Ahmet Oruc, Claire Fulks, Travis Adams and Sungmin Youn: Department of Civil Engineering, Marshall University, One John Marshall Drive, Huntington, WV 25755, USA
Sanghoon Lee: Department of Computer Sciences and Electrical Engineering, Marshall University, One John Marshall Drive, Huntington, WV 25755, USA
Dal Hyung Kim: Department of Mechanical Engineering, Kennesaw State University, 1000 Chastain Road, Kennesaw, GA 30144, USA

Abstract
A series of experiments were performed to evaluate the effects of activated carbon on the compressive strength and air content of Portland Cement Concrete (PCC). Activated carbon/PCC composites were prepared by mixing concrete components with commercial activated carbon granules with weight fractions of 0, 0.5%, 1%, and 2% to cement. All PCC specimens were then tested for compressive strength on 7, 14, 21, and 28 days. The experimental results showed that adding 0.5% of activated carbon increased the compressive strength significantly over the curing periods compared to the normal PCC without activated carbon. For the specimens has 0.5% activated carbon, the 7, 14, 21, and 28-day compressive strengths increased by 28.7%, 22.2%, 26.8%, and 22.9%, respectively. However, adding excessive amounts of more than 1% activated carbon had a minimal effect on the compressive strength or even decreased it, which agrees with other studies. Regarding the air contents of the mixtures, adding activated carbon decreased the air content from 3.6% to around 1.5%. The surface morphologies of fine aggregates and activated carbon particles were compared using a novel image processing technique. The results indicated that the surface of activated carbon significantly differs from that of aggregates.

Key Words
activated carbon; compressive strength; Portland cement concrete composite; scanning electron microscopy

Address
Sungmin Youn, Andrew Ball, Claire Fulks and Sukjoon Na: Department of Civil Engineering, Marshall University, 1 John Marshall Dr, Huntington, WV, USA
Sanghoon Lee: Department of Computer Sciences and Electrical Engineering, Marshall University, 1 John Marshall Dr, Huntington, WV, USA

Abstract
Xanthan gum and starch compound biopolymer (XS), an environmentally friendly soil-binding material produced from natural resources, has been suggested as a slope protection material to enhance soil strength and erosion resistance. Insufficient wet strength and the consequent durability concerns remain, despite XS biopolymer-soil treatment showing high strength and erosion resistance in the dried state, even with a small dosage of soil mass. These concerns need to be solved to improve the field applicability and post-stability of this treatment. This study explored the utilization of an alkaline-based cation crosslinking method using calcium hydroxide and sodium hydroxide to induce non-thermal gelation, resulting in the enhancement of the wet strength and durability of biopolymer-treated soil. Laboratory experiments were conducted to assess the unconfined compressive strength and cyclic wetting-drying durability performance of the treated soil using a selected recipe based on a preliminary gel formation test. The results demonstrated that the uniformity of the gel structure and gelling time varied depending on the ratio of crosslinkers to biopolymer; consequently, the strength of the soil was affected. Subsequently, site soil treated with the recipe, which showed the best performance in indoor assessment, was implemented on the field slope at the bridge abutment via compaction and pressurized spraying methods to assess feasibility in field implementation. Moreover, the variation in surface soil hardness was monitored periodically for one year. Both slopes implemented by the two construction methods showed sufficient stability against detachment and scouring, with a higher soil hardness index than the natural slope for a year.

Key Words
biopolymer; calcium hydroxide; crosslinking; field application; slope protection; sodium hydroxide; soil hardness

Address
Minhyeong Lee: Disposal Performance Demonstration Research Division, Korea Atomic Energy Research Institute,
111 Daedeok-daero 989beon-gil, Yuseong-gu, Daejeon 34057, Republic of Korea
Ilhan Chang: Department of Civil Systems Engineering, Ajou University, 206 World cup-ro, Yeongtong-gu, Suwon, 16499,
Gyeonggi-do, Republic of Korea
Seok-Jun Kang, Dong-Hyuk Lee and Gye-Chun Cho: Department of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology,
291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea

Abstract
Cementitious materials such as Ordinary Portland Cement (OPC), fly ash, lime, and bitumen have been employed for soil improvement over the years. However, due to the environmental concerns associated with the use of OPC, substituting OPC with calcium sulfoaluminate (CSA) cement offers good potential for ground improvement because it is more eco-friendly. Although earlier research has investigated the stabilizing effects of CSA cement-treated sand, no attempt has been made to examine soil behavior under high confining pressure. As a result, this study aimed to investigate the shear strength and mechanical behavior of CSA cement-treated sand using a consolidated drained (CD) triaxial test with high confining pressure. The microstructure of the examined sand samples was investigated using scanning electron microscopy. This study used sand with CSA cement contents of 3%, 5%, and 7% and confining pressures of 0.5, 1.0, and 1.5 MPa. It revealed that the confining pressures and CSA cement content significantly affected the stress-strain and volumetric change behavior of CSA cement-treated sand at high confining pressures.

Key Words
calcium sulfoaluminate; consolidated drained triaxial test; high pressure; shear strength; volume change

Address
James Innocent Ocheme, Sakiru Olarewaju Olagunju, Ruslan Khamitov,Alfrendo Satyanaga, Jong Kim and Sung-Woo Moon: Department of Civil and Environmental Engineering, Nazarbayev University, Nur Sultan, 010000, Kazakhstan

Abstract
Rock disturbance caused by blasting and stress relaxation is commonly observed during excavation. As the distance from the source of disturbance increases, the degree of disturbance decreases, and rock at a large depth does not experience disturbance. However, in stability analyses, a single value of disturbance is often applied to the entire rock mass, which leads to underestimated results. In this study, this modeling mistake is addressed by considering realistically varying rock disturbance. The safety of infinite slopes in a disturbed rock mass with a strength governed by the Hoek–Brown failure criterion is investigated based on the kinematic approach of limit analysis. The maximum disturbance is assigned to the outermost slope face because it is directly exposed to blasting damage and dilation, and the disturbance progressively decays with distance in the rock mass. The safety analysis results indicate that the assumption of uniform disturbance in the entire rock mass leads to underestimation of the rock strength and safety on infinite rock slopes. A critical slip surface appears to be within the disturbed rock layer as well as the interface between the disturbed upper rock and undisturbed lower rock.

Key Words
Hoek–Brown failure criterion; infinite slope; limit analysis; rock disturbance; rock slope stability

Address
Dowon Park: Department of Civil Engineering, University of Seoul,163 Seoulsiripdae-ro, Dongdaemun-gu, Seoul 02504, Republic of Korea

Abstract
Recycled concrete aggregate (RCA) is widely used as a construction material in road construction, concrete structures, embankments, etc. However, it has been reported that calcite (CaCO3) precipitation from RCA can be a cause of clogging when used in drainage applications. An accelerated calcite precipitation (ACP) procedure has been devised to evaluate the long-term geochemical performance of RCA in subsurface drainage systems. While the ACP procedure was useful for the French Drain application, there remained opportunities for improvement. In this study, key factors that control the formation of calcite precipitation were quantitatively evaluated, and the results were used to improve the current prototype ACP method. A laboratory parametric study was carried out by investigating the effects of reaction temperature and time on the formation of calcite precipitation of RCA, with determining an optimum reaction temperature and time which maximizes calcite precipitation. The improved ACP procedure was then applied to RCA samples that were graded for Type I Underdrain application, to compare the calcite precipitation. Two key findings are (1) that calcite precipitation can be maximized with the optimum heating temperature (75C) and time (17 hours), and (2) the potential for calcite precipitation from RCA is not as significant as for limestone. With the improved ACP procedure, the total amount of calcite precipitation from RCAs within the life cycle of a drain system can be determined when RCAs from different sources are used as pipe backfill materials in a drain system.

Key Words
calcite precipitation; clogging; french drain; recycled concrete aggregate (RCA)

Address
Boo Hyun Nam: Department of Civil Engineering, Kyung Hee University, Republic of Korea
Jinwoo An: School of Engineering, University of Mount Union, Alliance, Ohio, U.S.A.
Toni Curate: Department of Civil, Environmental, and Construction Engineering, University of Central Florida, Orlando, Florida, U.S.A.

Abstract
This study aims to establish the correlations between variables related to a slope during rainfall and factor of safety (FOS) and displacement using a coupling analysis method that is designed to consider both in rainfall conditions. With the recent development of measurement technologies, the approach of using the measurement data in the field has become easier. Particularly, they have been obtained in tests to determine the real-time safety and movement of a slope; however, a specific method has not been finalized. In addition, collected measurement data for recognizing the FOS and displacement in real-time with a specific relevance is difficult, and risks of uncertainty, such as in soil parameters and time, exist. In this study, the correlations between various slope-related variables (i.e., rainfall intensity, rainfall duration, angle of the slope, and mechanical properties including strength parameters of selected three types of soil; loamy sand, silt loam, sand) and the FOS and displacement are analyzed in order of seepage analysis, slope stability analysis and slope displacement analysis. Moreover, the methodology of coupling analysis is verified and a fundamental understanding of the factors that need to be considered in real-time observations is gained. The results show that the contributions of the abovementioned variables vary according to the soil type. Thus, the tendency of the displacement also differs by the soil type and variables but not same tendency with FOS. The friction angle and cohesion are negative while the rainfall duration and rainfall intensity are positive with the displacement. This suggests that understanding their correlations is necessary to determine the safety of a slope in real-time using displacement data. Additionally, databases considering rainfall conditions and a wide range of soil characteristics, including hydraulic and mechanical parameters, should be accumulated.

Key Words
displacement; factor of safety; rainfall; seepage; slope stability

Address
Jeong-Yeon Yu, Jong-Won Woo, Kyung-Nam Kang and Ki-Il Song: Department of Civil Engineering, Inha University, 100 Inha-ro, Michuhol-gu, Incheon 22212, Republic of Korea

Abstract
To test the effect of various pile tip shape series of model scale loading tests were carried out on test piles with special pile tips. Special pile tips were made using the 3D printer and were attached to the bottom end of the test pile for loading tests. The pile tips were made to have 30, 45, 60 inclined tips, as well as a rounded tip. The main objective of the test was to observe the effect of various pile tip shapes on settlement and penetrability of the pile. Moreover, a numerical model simulating the pile loading test carried out in this study was established and verified based on the loading test results. From this, the stress concentration around the pile tip was investigated. This will allow us to analyze the decrease of stress concentration around the pile tip which is the main cause of the pile tip damage during pile installation. However, modifying the pile tip shape will eventually increase the settlement of the pile. By estimating the degree of increase in pile settlement, the viability and the efficiency of the pile shape modification was judged. In addition, case studies on the effect of different pile tip shape and ground conditions on pile settlement and stress dispersion was conducted.

Key Words
3D printing; driven pile; load-settlement curve; pile damage (integrity); pile drivability; pile tip bearing

Address
Jaehong Kim: Department of Civil and Environmental Engineering, Dongshin University, Naju 58245, Korea
Junyoung Ko: Department of Civil Engineering, Chungnam National University, Daejeon 34134, Korea
Dohyun Kim: Department of Civil and Environmental Engineering, Hanbat National University, Daejeon 34158, Korea

Abstract
When a submerged floating tunnel is connected to the ground, there is a risk of stress concentration at the shore connection owing to the displacement imbalance caused by low confinement pressures in water and high confinement pressures in the ground. Here, the effects of the boundary condition and stiffness of the joints installed at the shore connection on the behaviors of a submerged floating tunnel and its shore connection were analyzed using a numerical method. The analysis results obtained with fixed and ground boundaries were similar due to the high stiffness of the ground boundary. However, the stability of the shore connection was found to be improved with the ground boundary as a small displacement was allowed at the boundary. The effect of the joint stiffness was evaluated by investigating the dynamic behavior of the submerged floating tunnel, the magnitude of the load acting on the bored tunnel, and the stress distribution at the shore connection. A lower joint stiffness was found to correspond to more effective relief of the stress concentration at the shore connection. However, it was confirmed that joints with low stiffness also increase the submerged floating tunnel displacement and decrease the frequency of the dynamic behavior, causing a risk of increased resonance when wave loads with low frequency are applied. Therefore, it is necessary to derive the optimal joint stiffness that can achieve both stress concentration relief and resonance prevention during the design of shore connections to secure their dynamic stability.

Key Words
ground boundary; flexible joint; numerical method; shore connection; submerged floating tunnel

Address
Seok-Jun Kang, Jun-Beom An, Dong-Hyuk Lee and Gye-Chun Cho: Department of Civil and Environmental Engineering, Korean Advanced Institute for Science and Technology
291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea
Minhyeong Lee: Disposal Performance Demonstration Research Division, Korea Atomic Energy Research Institute,
111 Daedeok-daero 989Beon-gil, Yuseong-gu, Daejeon, Republic of Korea

Abstract
Coastal and offshore structures such as ports and offshore wind farms will often need to be built on fine-grained sediments. Geotechnical properties associated with sediment compressibility are key parameters for marine construction designs especially on soft grounds, which involve clay-mineral dominated fines that can consolidate and settle significantly in response to engineered and environmental loads. We conduct liquid limit tests and 1D consolidation tests with fine-grained soils (silica silt, mica, kaolin and bentonite) and biogenic soils (diatom). The pore fluids for the liquid limit tests include deionized water and a series of brines with NaCl salt concentrations of 0.001 m, 0.01 m, 0.1 m, 0.6 m and 2.0 m, and the pore fluids for the consolidation tests deionized water, 0.01 m, 0.6 m, 2 m. The salt concentrations help the liquid limits of kaolin and bentonite decrease, but those of diatom slightly increase. The silica silt and mica show minimal changes in liquid limit due to salt concentrations. Accordingly, compression indices of soils follow the trend of the liquid limit as the liquid limit determined the initial void ratio of the consolidation test. Diatoms are more likely to be broken than clastic sediments during to loading, and diatom-rich sediment is therefore generally more compressible than clastic-rich sediment.

Key Words
fine-grained soils; electrical forces; liquid limit; pore-fluid chemistry; soil classification

Address
Junbong Jang and Handikajati Kusuma Marjadi: Department of ICT Integrated Safe Ocean Smart Cities Engineering, Dong-A University, Busan 49315, South Korea

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