软弱地层钢管桩嵌岩深度及侧阻力特性

对于软弱岩层中的打入桩,目前尚无公认的方法评估桩侧阻力。针对巴拿马Amador邮轮码头航站楼嵌岩钢管桩基础,开展了9组桩基动力测试,采用波动方程分析方法获取桩侧阻力。研究了地层中桩侧阻力分布规律、岩层中桩侧阻力与单轴抗压强度的关系。得出如下结论:1)侧阻力分布曲线均呈抛物线形式,可以明显区分出软黏土、粉质砂土、强风化岩、中风化岩4个地层。将曲线跌落后的部分定义为嵌岩段,据此得到桩A-4嵌岩深度为6 m、其他桩嵌岩深度为4 m,均满足设计最小嵌岩深度3 m的要求。2)岩层桩侧阻力-抗压强度(UCS)曲线均呈指数分布,而非线性分布。3)软弱岩层中,侧阻力起主导作用。同一UCS值,泥质粉砂岩中桩侧阻力明显大于玄武岩。4)随着UCS增大,岩体的自稳能力逐渐增强,摩擦系数逐渐转变为影响侧阻力的主导因素。UCS增大到一定数值后,桩侧阻力趋于稳定。5)获得了岩层桩侧阻力-抗压强度关系式,为估算场地岩层中桩侧阻力提供了依据。

Rock socketed depth and lateral resistance characteristics of steel pipe in soft rock

For driven piles in the soft rock stratum,there is currently no accepted method to evaluate the side resistance.For the rock socketed steel pipe pile foundation of Panama Amador cruise terminal,nine groups of dynamic tests of pile foundation have been carried out,and the side resistance of pile has been obtained by wave equation analysis method.The distribution law of pile side resistance in stratum and the relationship between pile side resistance and uniaxial compressive strength in rock stratum has been studied.The conclusions are as follows:1)The distribution curve of side resistance is in parabola form,and four strata can be distinguished obviously,which are soft clay,silty sand,strongly weathered rock,and moderately weathered rock.The part after the curve falls is defined as the rock socketed section.Based on this,the rock-socking depth of pile A-4 is 6 m,and the rock-socking depth of other piles is 4m,which meets the design minimum rock-socking depth of 3m.2)The pile side resistance compressive strength(UCS)curve of rock stratum is exponential distribution,and non-linear distribution.3)In the soft rock stratum,the side resistance plays a leading role.With the same UCS value,the pile side resistance in argillaceous siltstone is obviously larger than basalt.4)With the increase of UCS,the self-stability of rock mass gradually enhances,and the friction coefficient gradually changes into the dominant factor affecting the side resistance.After UCS increases to a certain value,the pile side resistance tends to be stable.5)The relationship between pile side resistance and compressive strength in the rock stratum is obtained,which can provide a basis for estimating pile side resistance in the rock stratum.