广东地区大直径超长钻孔灌注桩荷载传递特性试验研究

通过广东软土地区大直径超长钻孔灌注桩大吨位静载试验,分析该地区大直径超长钻孔灌注桩承载特性及荷载传递机制,为该地区大直径超长桩的理论研究和工程应用提供宝贵的参考数据。实测结果研究表明:试桩的Q-s曲线呈缓变型,桩端承载力分担总荷载比例均低于15%,表现为摩擦桩特性;随桩顶荷载增加,桩土相对位移沿桩身的递增幅度呈先增大后减小的趋势,淤泥质粉质黏土和淤泥达到极限侧摩阻力所需的桩土相对位移分别为17和6 mm,砂土达到极限侧摩阻力所需桩土相对位移为22~27 mm,桩身上部土层侧摩阻力发生不同程度的软化;桩身上部粉质黏土的桩土相对位移为18~23 mm,在桩土总的相对位移达40 mm时,下部粉质黏土层侧摩阻力达到极限值的87%以上,桩土相对位移继续增大时,侧阻增加趋势较为平缓,并逐渐接近于极限值;风化砂岩侧摩阻力随桩土相对位移的增加而增大,极限荷载下侧摩阻力未完全发挥;桩端阻力随着桩端沉降量的增加呈加工硬化型。

EXPERIMENTAL RESEARCH ON BEARING CHARACTERISTIC OF LARGE-DIAMETER AND SUPER-LONG BORED PILE IN GUANGDONG AREA

Based on the large tonnage static load tests of 2 large-diameter and super-long bored piles in Guangdong soft soil area，bearing characteristics and transport mechanism of load are studied in this paper，and the measured results obtained from the tests provide precious data for theoretical research of large-diameter and super-long bored piles in Guangdong area. The results show that load-movement curves of the piles vary gradually. The test piles show the characteristics of friction piles because sharing ratios of pile tip bearing capacity are fewer than 15%. With the increase of pile top load，the increasing rate of relative displacement of piles and soil at certain pile body first increase and then decrease. The ultimate pile-soil relative displacements for completely mobilizing the shaft resistance are found to be about 17mm and 6mm separately in muddy silt clay and silt，22 to 27mm in sand，18mm to 23 in upside silty clay layers of pile. Shaft resistance of upside soil of pile is softened inordinately. The shaft resistance in downside silty clay layers of pile is about more than 87% of ultimate shaft resistance while pile-soil relative displacement is 40mm and increasing rate of the shaft resistance is gently as the relative displacement continues. With the increasing of pile-soil relative displacement，the shaft resistances of weathering sandstone is developing and not fully play finally. Pile side resistance increase as hardening type along with the increasing of pile tip settlement.