千枚岩上覆钙质砂层大直径钢管桩沉降特性分析

Settlement characteristic of large-diameter steel pipe pile in weathered phyllite overlying calcareous sand

将高应变拟合分析的荷载-沉降(Q-S)曲线与静载试验直接测得的Q-S曲线进行对比分析,可获得千枚岩上覆钙质砂层大直径钢管桩的沉降特性。分析结果表明:当大直径钢管桩穿过较薄的钙质砂层且进入较硬的强风化千枚岩层足够深度时,Q-S特性表现为端承型桩,桩顶沉降主要由桩身压缩引起,残余沉降小;当大直径钢管桩穿过深厚钙质砂层且桩端支承于偏软的强风化千枚岩层时,Q-S特性表现为摩擦型桩,无论高应变还是静载试验,均能充分发挥土阻力,达到极限荷载时沉降急剧增大,累计总沉降量和残余沉降大;千枚岩层上覆钙质砂层的厚度对大直径钢管桩承载力影响微小,大直径钢管桩的极限承载力主要取决于穿过钙质砂层后进入千枚岩层的深度以及千枚岩持力层强弱。

Based on a contrastive analysis of simulated load-settlement curve from high strain dynamic test and measured load-settlement curve from static load test,we can obtain the settlement characteristic of large-diameter steel pipe pile in weathered phyllite overlying calcareous sand.The analysis results show that when the pile penetrates through a thin layer of calcareous sand and goes deep enough in the highly weathered hard phyllite,the settlement under the applied load is mainly caused by compression of the pile and the residual settlement is small.Both the high strain dynamic test and static load test are difficult to mobilize the soil resistance sufficiently.On the contrary,the settlement of pile under the ultimate pile load is large and residual settlement is also large when the pile penetrates through deep calcareous sand and just bears in the highly weathered soft phyllite.Soil resistance can be given full play in both high strain and static load tests.According to the analysis results,the thickness of calcareous sand has little effect on the ultimate bearing capacity of steel test pipe pile which mainly depends on the embedded length of highly weathered phyllite and strength of bearing stratum.