Characterising the failure pattern of a station box of Taipei Rapid Transit System (TRTS) and its rehabilitation

The case history where flooding due to the leakage through the openings in diaphragm wall accompanied by piping in excavation bottom severely affected the construction of a station box of Taipei Rapid Transit System (TRTS) is presented. The emergency grouting adjacent to but outside the diaphragm wall was conducted following the leakage. However, injection pressure due to slow setting time of grout not only aggravated the piping but also caused the side effect deflecting the diaphragm wall toward excavation area. The severe piping quickly washed the soil into station box and the differential settling of buildings above along with propagating surface cracks forced the use of water emplacing in station to ease the piping and further ground loss; meanwhile, seal grouting and void filling grouting were undertaken to facilitate the rehabilitation of foundation construction through which the station box was opened subsequently. Based on analyzed interactive behaviour between water emplacing or injection pressure and wall deflection or brace load, the diaphragm wall and bracing system would not have functioned normally during grouting if water had not been introduced in the station. The cause of opening in the diaphragm wall is triggered by the abnormal concrete placement which can be avoided through the suggested procedure of examination. The paper discusses the insights into a review of instrument records and provides the lessons learned.