• 산업기술연구
• /
• 제21권A호
• /
• pp.317-327
• /
• 2001

For soils with high void ratios, the inverse method of utilizing results obtained from centrifuge model test was used to find the constitutive relation of effective stress - void ratio - permeability whereas conventional oedometer test and constant rate of strain consolidation test were also used to fine its relation at ranges of relatively low void ratio. Results of column test about settlement of interface and pore pressure and distribution with time were compared with numerically estimated values to confirm such a constitutive relation as obtained from the inverse method. Consolidational settlement in dredged and reclaimed ground, where the consolidation was in progress, was predicted by using the numerical technique implemented with the finite strain consolidation theory.

• Geomechanics and Engineering
• /
• 제30권2호
• /
• pp.169-185
• /
• 2022

The urbanization and increasing rate of population demands effective means of transportation system (basement and tunnels) as well as high-rise building (resting on piled foundation) for accommodation. Therefore, it unavoidable to construct basements (i.e., excavation) nearby piled foundation. Since the basement excavation inevitably induces soil movement and stress changes in the ground, it may cause differential settlements to nearby piled raft foundation. To understand settlement and load transfer mechanism in the piled raft due to excavation-induced stress release, numerical parametric studies are carried out in this study. The effects of excavation depths (i.e., formation level) relative to piled raft were investigated by simulating the excavation near the pile shaft (i.e., H_e/L_p=0.67), next to (H_e/L_p=1.00) and below the pile toe (H_e/L_p=1.33). In addition, effects of sand density and raft fixity condition were investigated. The computed results have revealed that the induced settlement, tilting, pile lateral movement and load transfer mechanism in the piled raft depends upon the embedded depth of the diaphragm wall. Additional settlement of the piled raft due to excavation can be account for apparent loss of load carrying capacity of the piled raft (ALPC). The highest apparent loss of piled raft capacity ALPC (on the account of induced piled raft settlement) of 50% was calculated in in case of H_e/L_p = 1.33. Furthermore, the induced settlement decreased with increasing the relative density from 30% to 90%. On the contrary, the tilting of the raft increases in denser ground. The larger bending moment and lateral force was induced at the piled heads in fixed and pinned raft condition.

• 한국지반신소재학회논문집
• /
• 제7권3호
• /
• pp.25-30
• /
• 2008

본 논문에서는 순환골재 다공질 콘크리트말뚝(RAPP)공법에 대한 실내모형실험의 결과를 바탕으로 RAPP로 개량된 복합지반의 침하 및 압밀 거동 특성을 분석하였다. 이를 위하여 실내모형실험에서 관측된 복합지반의 침하량과 무보강 지반의 침하량을 비교하여 복합지반의 침하저감효과를 분석하였으며 복합지반의 압밀도를 산정하여 RAPP공법으로 인한 압밀촉진효과를 검토 하였다. RAPP공법으로 인한 복합지반의 침하저감효과는 상재하중증분이 증가할수록 감소하였으나 전반적으로 SCP공법에 의한 효과보다 크게 나타났으며 압밀촉진효과는 SCP공법과 유사하게 나타났다.

• 한국지반신소재학회논문집
• /
• 제8권4호
• /
• pp.9-17
• /
• 2009

본 연구는 폐기물 매립지에서 폐기물의 분해 등으로 인해 부등침하가 발생할 경우 SRSL(Self Recovering Sustainable Liner)를 활용한 매립지 최종복토층의 안정성에 미치는 영향을 확인해보는 것을 목적으로 한다. FLAC(Fast Lagrangian Analysis of Continua) 2D 프로그램을 이용하여 폐기물 분해 양상을 빈칸(blank)으로 설정한 후 수치해석을 수행하였으며, 기본 물성치시험 및 문헌조사 등을 통해 각 층에 대한 구성성분의 변수를 산정하였다. 이전 현장투수시험 등을 통해 얻어진 파괴 시 안전균열폭(6mm)을 바탕으로 부등침하 발생 시 부등침하의 폭, 깊이, 개수별 매립지 최종복토층의 침하량을 산정하여 부등침하에 대한 구조적 안정성을 검토하였다. 해석결과, 깊이에 따른 영향은 없으며, 침하갯수가 증가할수록 오히려 매립지 최종복토층에 인장력을 발휘하여 안정성 확보를 유리하게 하며, 부등침하의 폭이 전체길이에 24.5% 이내일 경우 안정성에는 문제가 없는 것을 확인하였다.

• Geomechanics and Engineering
• /
• 제6권2호
• /
• pp.173-194
• /
• 2014

Laboratory and field data showed that deep mixed (DM) columns accelerated the rate of consolidation of the soft foundations. Most analyses of consolidation of DM column-improved foundations so far have been based on the elastic theory. In reality, the DM columns may yield due to the stress concentration from the soft soil and its limited strength. The influence of column yielding on the degree of consolidation of the soft foundation improved by DM columns has not been well investigated. A three-dimensional mechanically and hydraulically-coupled numerical method was adopted in this study to investigate the degree of consolidation of the DM column foundation considering column yielding. A unit cell model was used, in which the soil was modeled as a linearly elastic material. For a comparison purpose, the DM column was modeled as an elastic or elastic-plastic material. This study examined the aspects of stress transfer, settlement, and degree of consolidation of the foundations without or with the consideration of the yielding of the DM column. A parametric study was conducted to investigate the influence of the column yielding on the stress concentration ratio, settlement, and average degree of consolidation of the DM column foundation. The stress concentration ratio increased and then decreased to reach a constant value with the increase of the column modulus and time. A simplified method was proposed to calculate the maximum stress concentration ratios under undrained and drained conditions considering the column yielding. The simplified method based on a composite foundation concept could conservatively estimate the consolidation settlement. An increase of the column modulus, area replacement ratio, and/or column permeability increased the rate of consolidation.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2006년도 춘계 학술발표회 논문집
• /
• pp.838-845
• /
• 2006

Recently construction work in Korea, demands of favorable condition ground had been increased with industrialization acceleration and economic growth. However, because of limited land space, it was so hard to ensure favorable condition grounds that construction work proceeds until soft ground area on plans of road, railroad and industrial complex. In this case, soft ground improvement was required such as a stone column method. Stone column method, making a compaction pile using crushed stone, is a soft ground improvement method. However, stone column method is difficult to apply to the ground which is not mobilized enough lateral confine pressure because no bulging failure resistance. Hence, in present study, evaluates the stone columns reinforced by geogrid for settlement reduction and wide range of application of stone columns. Triaxial compression tests were conducted for evaluation which is about behavior characteristics of stone column on replacement rate. Then, 3-dimensional numerical analysis were conducted for application of stone column reinforced by geogrid as evaluate behavior characteristics and settlement reduction effect of stone column reinforced by geogrid on reinforcing depth change of geogrid.

• Geomechanics and Engineering
• /
• 제32권4호
• /
• pp.387-396
• /
• 2023

Ground subsidence, which is a current concern that affects piled raft foundations, has occurred at a high rate in Ho Chi Minh City, Viet Nam, due primarily to groundwater pumping for water supply. In this study, the groundwater level (GWL) change affect on a piled raft foundation was investigated based on the three-dimensional finite element method (3D-FEM) using the PLAXIS 3D software. The GWL change due to global groundwater pumping and dewatering were simulated in PLAXIS 3D based on the GWL reduction and consolidation. Settlement and the pile axial force of the piled raft foundation in Ho Chi Minh subsoil were investigated based on the actual design and the proposed optimal case. The actual design used the piled foundation concept, while the optimal case applied a pile spacing of 6D using a piled raft concept to reduce the number of piles, with little increased settlement. The results indicated that the settlement increased with the GWL reduction, caused by groundwater pumping and dewatering. The subsidence started to affect the piled raft foundation 2.5 years after construction for the actual design and after 3.4 years for the optimal case due to global groundwater pumping. The pile's axial force, which was affected by negative skin friction, increased during that time.

• Geomechanics and Engineering
• /
• 제6권5호
• /
• pp.419-436
• /
• 2014

Soil improvement by preloading with PVD in combination with vacuum is helpful when a considerable load is required to meet the desired rate of settlement in a relative short time. To facilitate the vacuum propagation, vertical drains are usually employed in conjunction. This ground improvement method is more and more applied in the Mekong delta of Vietnam to meet the needs of fast infrastructure development. This paper reports on a pilot test that was carried out to investigate the effect of ground improvement by vacuum and PVD on the rate of consolidation at the site of Saigon International Terminals Vietnam (SITV) in Ba Ria-Vung Tau Province, Viet Nam. Three main aspects of the test will be presented, and namely, instrumentation and field monitoring program, calculation of consolidation settlement and back-analysis of soil properties to see the difference before and after ground improvement.

• 한국지반신소재학회논문집
• /
• 제19권4호
• /
• pp.85-93
• /
• 2020

본 연구에서는 오염된 지반의 정화 시에 발생되는 침하량 계측에 대한 VMS의 적용성을 평가하기 위하여, 오염지반의 침하에 대한 실내실험을 수행하였다. 즉, 수치사진측량기법을 기반으로 개발된 3D-Visual Monitoring System(VMS)와 기존 계측장비인 토탈스테이션을 이용하여, 오염지반 침하에 대한 계측결과를 비교하였다. 실험결과, 중금속으로 오염된 지반의 침하량은 친수성 필터가 적용된 실험조건에서 많이 발생하였다. 계측결과를 바탕으로 VMS의 오차범위를 산정한 결과, 최소 및 최대 오차범위는 각각 ±0.36mm와 ±0.87mm 산정되었고, VMS의 오차량은 모든 실험조건에서 오차범위를 만족하는 것으로 확인되었다. VMS의 평균오차율을 산정한 결과, 소수성 필터조건에 비하여 친수성 필터 조건에서 낮은 평균오차율을 보였다. 이를 바탕으로 오염된 지반의 침하량 계측에 있어서 VMS의 적용이 가능한 것으로 평가되었다.

• 한국지반공학회논문집
• /
• 제26권9호
• /
• pp.15-24
• /
• 2010

압밀침하량과 속도에 영향을 미치는 압밀층 두께와 심도가 위치마다 상이하므로 압밀침하와 속도는 공간적 평가방법 이용하여 분석되어야 한다. 또한, 확률론적 방법을 이용하여 공간적인 압밀침하 및 속도 추정결과의 불확실성을 평가 할 수 있다. 본 논문에서는 압밀침하와 속도를 공간적으로 평가하기 위하여 크리깅기법으로 추정한 공간적인 지층분포를 이용하였다. 또한, 지반정수의 통계량과 확률분포형을 이용하여 압밀침하 및 속도의 불확실성을 평가하였다. 이 결과와 이용하여 압밀시간을 단축하기 위해 연직배수공법을 적용해야 하는 면적과 최종 설계지반표고를 맞추기 위해 추가성토를 수행해야 하는 면적을 분석하였으며, 이러한 분석결과는 지반정수들의 변동성에 큰 영향을 받는 것으로 나타났다. 본 논문에서 제시한 분석절차와 방법은 지반공학적 설계의 의사결정과정에 사용될 수 있었다.