砂性土层中静压桩的荷载传递和承载力研究

LOAD TRANSFER AND BEARING CAPACITY OF PILES JACKED INTO SANDY DEPOSITS

通过对某砂性土场地内一组H型钢长桩的原位试验,分别以2倍和2.5倍的单桩承载力设计值进行压桩,同时,以一根类似土层中的锤击桩作为对比试验,并沿桩身安装频振型应变计考察桩在载荷试验过程中的荷载传递性状。试验结果显示:静压桩的荷载传递性状表现为端承摩擦桩,而锤击桩的荷载传递性状则表现为摩擦端承桩。以最终贯入度收桩的锤击桩,其桩端深度大于以超载预压法收桩的静压桩。静压桩的极限承载力与其曾经历的最大压桩力紧密关联。当静压桩的最大压桩力达2.5倍的单桩承载力设计值时,虽然其桩端较锤击桩而言置于较浅并较软的土层上,但极限承载力并不小于锤击桩。原因在于,较高的压桩力可能降低了桩在高荷载条件下的蠕变沉降,从而增加了桩的极限承载能力。

It is reported a series of tests on three long H-piles installed into sandy deposits. Two of the piles was installed by a 900t jacking machine in accordance with a pre-creep termination criterion. The other pile was installed by hydraulic hammer in accordance with the requirement of final sets. Vibrating wire strain gauges were installed along the piles to investigate the load-transfer characteristics during load tests. The test results show that the jacked piles behave as friction piles while the driven pile is much more end-bearing. The driven pile was founded on deeper and stiffer soil stratum than the jacked piles. However, its ultimate bearing capacity is not higher than the jacked pile that ever experienced jacking load as large as 2.5 times of the working load. The bearing capacities of the jacked piles are highly related to the level of jacking load applied during installation. The pre-creep termination criterion takes great effect on reducing the creep settlements of the jacked piles during load tests, hence increasing their bearing capacities.