해안 연약지반의 심층혼합처리공법(DCM) 시공사례 연구

Abstract

최근들어 연약지반이 분포한 해안지역을 따라 항만개발이 활발히 진행되면서 연약지반처리공법중 잔류침하 가능성이 없고, 장비의 진입이 용이하며 공사비가 상대적으로 저렴한 심층혼합처리공법(DCM)의 적용이 증가하고 있는 추세이다. 본 연구는 심층혼합처리공법의 현장적용시 발생할 수 있는 시공상의 문제점을 사전에 파악하고, 대상지반에 적합한 시방배합비를 제시하여 고품질, 고효율의 경제적인 시공이 되고자 한다. 대상지반의 불교란 시료를 채취하여 실내시험을 실시한 결과 원지반의 특성은 통일분류법상 CH의 연약지반으로 분류되며, 배합시험에서는 상대적으로 장기강도 발현이 좋은 고로 슬래그 시멘트를 사용하고, 대상지반의 최적 배합비를 도출한 결과 설계 단위시멘트량 보다 30㎏f/㎥ 작은 것으로 확인되었다. 사용수는 담수보다 해수의 강도가 조금 높게 나타났으며, 개량체의 일축압축강도는 물-시멘트비가 높아짐에 따라 강도는 낮게 나타났고, 단위시멘트량과 재령이 높아짐에 따라 강도는 증가하는 경향을 보였다. 연구결과 심층혼합처리공법(DCM)의 현장적용시 실내배합시험을 선행하여 대상지반에 적합한 사용재료의 선정 및 최적 배합비를 도출하여야할 것으로 사료된다.; Lately, as the costal areas with the soft ground distributed much have been vigorously developed, the DCM (Deep Cement Mixing Method) has been applied more frequently, because of no residual settlement, easy access of equipments and relatively low construction cost. The purpose of this study was to address the problems of the DCM on the spots and thereby, suggest a mixing ratio specification adequate to the coastal soft ground to ensure a high-quality and high-efficient economic construction. For this purpose, the test pieces not agitated were sampled from the subject costal soft ground to be tested at the lab. As a result, it was found that the subject coastal ground could be classified into the CH soft ground according to the Unified Soil Classification System in terms of its properties. When the blast-furnace slag cement characterized by a relatively good long-term strength development was used and thereby, an optimal mixing ratio was calculated for the subject ground, it was found that the actual amount of unit cement would be smaller by 30㎏f/㎥ than the designed one. On the other hand, the strength was a little higher when the sea water was used than when the fresh water was used. In addition, the higher the ratio of water to cement was, the unconfined compression strength was lower, and the strength was proportional to amount of unit cement and its aging. All in all, it is conceived that when the DCM is applied on the spot, it will be necessary to conduct a lab test for the mixing ratio and thereby, select the materials appropriate to the subject costal ground and determine an optimal mixing ratio.