开口桩与闭口桩承载力时效的试验研究

FIELD TEST ON TIME EFFECT OF BEARING CAPACITY ON END-OPEN PILE AND END-CLOSED PILE

为研究软土中开口桩与闭口桩承载力差异及承载力随时间增长问题,共完成了36组模型桩的原位静压沉桩试验,开口桩与闭口桩各18组,试验持续时间长达72d。在试验条件下,发现闭口桩与开口桩的承载力最小时效系数分别为2.4和3.6。桩直径越小,承载力增加幅度越大,承载力时效系数也越大。开口桩与闭口桩承载力随时间增加而增大,沉桩后休止72d,开口桩与闭口桩承载力达到稳定值,此后承载力增加不再明显。开口桩初始极限承载力小于闭口桩初始极限承载力,仅为闭口桩的60%～70%,沉桩后休止72d,开口桩与闭口桩稳定时效承载力的大小几乎相同。开口桩的土塞长度随桩径的增大而增加,其承载力时效系数约为闭口桩的1.4～1.6倍。

To research the differences of bearing capacity and the time-related setup of both end-open pile and end-closed pile in soft clay, field test of in-situ static pressures of 36 piles have been carried out within 72 days. Under such circumstances, the test results show that the minimum time effect coefficient of end-closed pile is 2.4 while end-open pile 3.6. Besides, the smaller the pile diameter is, the greater positive range and coefficient bearing capacity are. The bearing capacity increases with time, reaching steady value after 72 days＇ intermission but showing no distinctive raise later on. The original capacity of end-open pile is 60% - 70% of end-closed one but with the same bearing capacity after intermission of 72 days. The soil length of end-open pile increases with the increase of pile diameter with time effect coefficient 1.4 - 1.6 times against that of the end-closed pile.