科研之友
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摘要
Many underground excavation failures are caused by severe water inflow due to the piping through the opening in the diaphragm wall. The opening can be created by slurry pocket or air pocket during concrete placement by tremie method. This type of defect in diaphragm wall can be detected by sonic logging to show the condition of trench wall and by measuring actual concrete dosage during placing. The same detecting method can be used in two very rare case histories where just-completed primary panels in very soft and thick clay deposit were overturned from the adjacent tremie concreting secondary panel during cold winter. The abnormal increasing concrete dosage and the smooth trench wall profile of secondary panel from sonic logging identify the occurrence of this incident. The causes to trigger this incident include (1) panel size, (2) weather condition, (3) tremie concreting speed of secondary panel, (4) initial and final setting times of concrete in trench, (5) roughness of trench wall, etc. Since the temperature for the two case histories is very low during tremie concreting, the initial setting time of concrete in secondary panel, given by equivalent age maturity function, is much longer than the time to place the concrete in secondary panel. To clarify the failure mechanism, the force-equilibrium analysis of inclined primary panel is conducted taking into account the driving force induced by the concrete pressure in the unset secondary panel and the resistant force given by the adhesion between inclined primary panel and soft clayey soil. It can be concluded from this investigation that the concrete in the secondary panel due to lower concrete curing temperature still remains unset or in plastic form and this will generate much larger driving force to push the adjacent just-completed primary panel to tilt. The measures to prevent similar incidents from happening are also suggested in this paper.
- 出版日期2016-5
