T.R.c.M공법의 시공성 확보를 위한 지반보강공법에 관한 연구

Abstract

연구대상지역이 지하상가 및 주거 밀집지역, 기존 지하철, 많은 교통량 등을 가지고 있는 전형적인 도심지구간이기 때문에 기존 시설의 안전성을 확보하고, 작업구역 내 사용자들의 편익을 최대한 보장할 수 있는 T.R.c.M공법을 적용하고자 하였다. 그러나 연구대상지역이 한강에 인접해 있고, 투수계수가 큰 충적층의 연약한 지반조건을 가지고 있어 T.R.c.M공법을 시공하기 위해서는 지하수위 저감 대책이 필요한 실정이다. 본 연구에서는 T.R.c.M 도달기지#1의 시공성을 확보하기 위한 지하수위 저감 대책으로 Deep Well공법을 적용하는데 있어서의 적용성을 검토하였고, Deep Well공법의 적용에도 불구하고 추진방향의 지하수위가 목표 저하량에 미치지 못하였다고 판단되어, 수평선단그라우팅에 대한 적용성을 검토하게 되었다. 이에 따른 T.R.c.M공법의 수직벽체 시공에 있어서 트렌치굴착에 따른 그라우팅 적용성 검토가 수행되었다. 또한 계측분석을 통해 시공 안전성을 판단하였다. 적용성 검토 결과, Deep Well공법 시공 시 양수로 인한 최대지하수위 저하량이 작업구 굴착저면(G.L(-)11.3m)보다 상부에 위치하여 지하수 유출이 예상되었고, 배수로 인한 지하수위 변화 영향반경(R)을 산정한 결과 28.92m로 예상되었다. 또한, 지하수위 저하에 따라 발생할 수 있는 인접구조물의 침하량은 C point에 인접한 지점에서 예상되는 침하량이 11.94mm로서 건축구조물 기준 침하량 1 inch를 만족하는 것으로 예상되었다. 수평선단그라우팅 시공 시 주입범위는 터널의 상부 1.32m범위와 ±(π/4+φ/4)의 각도로 둘러싸인 부분, 주입률은 λ≤45로 예상되었다. T.R.c.M 트렌치 시공성 확보를 위해 전면 차수그라우팅 또는 방사형 중복 부분그라우팅을 실시하여 차수 및 지반보강을 하는 것이 바람직하다고 판단되었다. 수치해석(PLAXIS)을 통한 지표침하량의 결과와 현장계측을 통해 얻어진 수렴치가 0.007m로 비슷한 결과가 예상되었으며, 이는 현장 기준치인 1 inch의 80%인 20.32mm이내이기 때문에 안전한 것으로 판단되었다.; The area for study is a typical downtown area, which has underground shopping centers and densely residential area, existing subway, a lot of traffic etc.. Therefore, T.R.c.M(Tubular Roof construction Method) was applied, which is able to secure the safety of existing facilities and convenience of users in building site. However, the measure to reducing level of ground water is required to construct with T.R.c.M in the area for study because the area for study has soft ground condition of alluvium, which is adjacent to Han river. In this study, we reviewed the availability to apply deep well method for the measure to reducing level of ground water to secure the constructability of T.R.c.M arrival base #1. Despite the application of deep well method, it was judged that the level of ground water in the progress direction was not reached to the objective drop so the availability of horizontal end grouting was reviewed. Accordingly, the review of availability of grouting by trench excavation for vertical wall construction in T.R.c.M. We also judged the safety of construction through measurement analysis. As a result of reviewing the availability, the outflow of ground water was expected because the drop of maximum level of ground water by water pumping under construction by deep well method was located at upper place than excavation bottom(G.L(-)11.3m), and the effect radius of changing the level of drainage was expected to 28.92m. Furthermore, settlement of nearing structure that may occur due to the drop of the level of ground water was expected to meet 1 inch of basic settlement in building structure because the settlement which was expected at the place adjacent to C point was 11.94mm. It was expected that the range of injection under construction of horizontal end grouting was the range of 1.32m at upper part of tunnel and the part surrounded by the angle of ±(π/4+Φ/4), and the expected injection ratio was �運�45. It was judged that making water proof and ground reinforcement by executing waterproof grouting or radial shape duplicated partial grouting was desirable to secure the availability of construction by T.R.c.M. Convergent value obtained from the result of earth surface settlement by numerical analysis(PLAXIS) and site measurement was 0.007m, which was similar to our expectation, and it was considered to be safe because it was within the range of 20.32mm, 80% of 1 inch that was site basic value.