模型實驗에 의한 실트地盤의 側方流動에 관한 硏究

Abstract

본 연구에서는 모형재하실험용 재하장치를 제작하고, 재하하중을 0.05kg/cm2씩 증가시켜 가면서 측방유동에 관련된 모형재하실험을 각각 실시하였다. 모형재하실험에 필요한 시료는 연약한 실트지반에 대하여 함수량을 일정하게 증가시키면서 조성하였고, 또한 연약한 실트지반에 오염물질과 모래를 일정한 비율로 혼합하여 조성하였다. 모형재하실험을 통하여 침하량, 측방변위량, 융기량 등의 소성변형값을 실측하여, 유한요소해석 프로그램(MIDAS/GTS)을 이용하여 구한 수치해석 결과를 비교하고, 기존 이론식과 비교․분석한 결과 다음과 같은 결론을 얻었다. 연약한 실트지반과 오염된 실트지반 및 모래섞인 실트지반은 전단강도의 증가에 따라 전단강도의 실측값과 계산값이 서로 비슷한 증가경향을 보여 계산식에 대한 신뢰가 확인되었다. 재하조건에 따른 변위량 분포에서 함수량과 오염물질이 증가할수록 최대침하량은 재하판 중앙에서 발생하였으며, 최대측방변위량의 발생위치는 깊이 방향으로 하강하면서 확대되는 경향을 보였다. 침하량 2.5cm, 측방변위량 1.5cm, 융기량 1.0cm의 일반적인 관리기준값이 극한하중시의 허용변위량에 상당히 접근하고 있어 일반적인 관리기준값의 타당함을 나타내고 있다. 그러나 오염된 실트지반은 관리기준값이 극한하중시의 허용변위량보다 다소 작게 나타나 허용변위량 산정에 유의할 필요가 있다고 사료된다. MLo, MLp, MLs 지반의 실측치 한계하중값은 4.14cu, 3.06cu, 4.20s로 산정되었으며, 수치해석의 한계하중값은 3.87cu, 2.52cu, 3.43s로 산정되어 MLS 지반의 한계하중값은 가장 크게 나타났다. 이는 연약한 실트지반에 모래가 함유되어 지반이 점차 안정화되는 것으로 사료된다. 수치해석에 의한 한계하중값은 실측치의 한계하중값보다 작게 산정되어 수치해석 결과가 다소 안전측인 것으로 판단된다. MLo, MLp, MLs 지반의 실측치 극한하중값은 9.53cu, 5.94cu, 9.78s로 산정되었으며, 수치해석의 극한하중값은 8.77cu, 4.88cu, 7.40s로 산정되었다. MLP 지반은 오염물질의 증가로 인하여 지반의 소성화가 급진적으로 촉진되어 지반의 지지력이 저하됨을 알 수 있다. MLS 지반은 모래가 함유되어 지반이 점차 안정화되는 것으로 사료되고, 수치해석에 의한 극한하중값은 실측치의 극한하중값보다 작게 산정되어 수치해석 결과가 다소 안전측인 것으로 판단된다. MLo, MLp, MLs 지반의 극한하중 작용시의 최대측방유동압(Pmax)은 Matsui․Hong의 제안식에서 구한 값과 비슷한 경향을 나타내었으며, 지표면에서의 측방유동압은 Pmax/3 정도로 Poulos의 분포형과 같이 나타났다. 최대측방유동압이 발생하는 깊이는 실측치는 0.33H～0.38H에서 발생하였으며, 수치해석은 0.25H～0.33H 깊이에서 발생하여 수치해석의 최대측방유동압이 발생하는 위치가 지표면측으로 상승하여 나타났다. MLo, MLp, MLs 지반에 대한 극한하중은 기존의 관리도에서 얻어진 극한하중과 상당히 유사한 값을 나타내므로 기존 관리도의 실제 적용에 무리가 없음을 알 수 있다. 그러나 모래섞인 실트지반은 松尾․川村의 (Sv-(Ym/Sv) 관리도에서 결정된 극한하중이 하중-침하량(q-Sv) 관계에서 얻은 극한하중보다 약간 작은 값을 나타내고 있어 다소 안전측인 것으로 판단된다.|This study made the loading unit for the model test and conducted the model loading test related to lateral flow as increasing load by 0.05kg/cm2. Sample for the model test was prepared with constant increase of the amount of contained water on soft soil and pollutants and sand were mixed and prepared by constant ratio on silt soil. As a result of measuring settlement, lateral displacement, heaving and plastic deformation values through model test, comparing the results of numerical analysis obtained from using finite element analysis program(MIDAS/GTS) and comparing to and analyzing the prior theoretical equations, the following conclusions were obtained. As it was found that soft silt soil, polluted silt soil, and silt soil mixed with sand showed similar trend in measured and estimated values according to the increase of shear strength, reliability of estimated values was confirmed. Settlement in distribution of displacement based on loading condition was extended as the amount of contained water and pollutants increased, the maximum settlement was occurred at the center of the loading platform, and the maximum lateral displacement descended toward the depth and showed trend to extend. The maximum heaving position was occurred nearby the center, and the displacement was larger in numerical analysis than in measured value. As general management standard values of 2.5cm of settlement, 1.5cm of lateral displacement and 1.0cm of heaving approached permissible displacement under ultimate surcharge, it showed validity of general management standard values. But, management standard values of polluted silt soils were smaller than permissible displacement under ultimate surcharge and it was considered that it is necessary to pay attention to estimate permissible displacement. Critical surcharges of measured value of MLo, MLP and MLS soils were estimated as 4.14cu, 3.06cu, and 4.20s, also those of numerical analysis were estimated as 3.87cu, 2.52cu, and 3.43s. The critical surcharge of MLS soils showed as the largest value. It was judged that it became gradually stable result that soft silt soils contain the sand. That means critical surcharges by the numerical analysis showed smaller value than the critical surcharge of measure value and it was judged that the numerical analysis was more stable. Also ultimate surcharges of measured value of MLo, MLP and MLS soils were estimated as 9.53cu, 5.94cu, and 9.78s, also those of numerical analysis were estimated as 8.77cu, 4.88cu, and 7.40s. MLP soils fostered plasticity of soil rapid due to increase of pollutants, and it caused that the bearing surcharge was lower. It was judged that it became gradually stable result that MLS soils contain the sand. Ultimate surcharges by the numerical analysis showed smaller value than the ultimate surcharge of measured value and it was judged that the numerical analysis was more stable. Maximum lateral flow pressure(Pmax) under the ultimate surcharge of MLo, MLP and MLS soils showed similar trend to values obtained in formula suggestion by Matsui․Hong and lateral flow pressure on surface was Pmax/3 and it was the same as Poulos's distribution type. The depth of maximum lateral flow pressure was found at 0.33H～0.38H of measured value and 0.25H～0.33H of numerical analysis, and the maximum lateral flow pressure position by numerical analysis was rising toward surface. And the depth of maximum later flow pressure at MLo, MLP and MLS was rising toward surface compared to that of complex type and Poulos. Since the ultimate surcharge of MLo, MLP and MLS soils showed considerably similar values to that of existing management, it was found that existing management method can be applied to practice. But, silt soils mixed with the sand showed that ultimate surcharge from Matsuo․Kawamura (Sv-(Ym/Sv) management had smaller values than from relations with surcharge-settlement(q-Sv) and it was more stable.