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黑棉土是一种特殊的强膨胀土,为避免其胀缩导致的基础和结构损坏,需研究其力学特性及桩基承载特性。首先通过室内试验测定黑棉土的有荷膨胀特性、侧限压缩特性和剪切特性。试验结果表明,当上覆压力由0k Pa增加到300k Pa时,土体的有荷膨胀率从36.6%减小至3.3%;含水率增大时,土体平均侧限压缩模量和抗剪强度均减小;含水率为52.0%的黑棉土在较大剪切位移(6mm)时的黏聚力较峰值强度下的黏聚力下降70%。之后通过离心机试验比较不同含水率的黑棉土地基中单桩的承载特性发现,相比含水率为23.0%的黑棉土地基,含水率为52.0%的黑棉土地基中单桩的刚度和承载力均明显降低,桩端阻力的下降尤为明显。建议在工程桩基设计中,湿化下黑棉土的摩阻力宜采用大剪切位移下土体抗剪强度。
Black cotton soil is a kind of special strong expansive soil. In order to avoid the foundation and structural damage caused by its swelling and shrinking, its mechanical properties and the bearing characteristics of pile foundation should be studied. First of all, by indoor test measured black cotton soil has a load expansion characteristics, lateral compression and shear characteristics. The experimental results show that when the overpressure increases from 0k Pa to 300k Pa, the load expansion of soil reduces from 36.6% to 3.3%. When the moisture content increases, the average lateral compressive modulus of soil and shear strength The cohesive strength of black cotton with moisture content of 52.0% at the greater shear displacement (6mm) decreased by 70% compared with the peak strength. After comparing the bearing properties of single pile in black cotton soil with different moisture contents by centrifuge test, it was found that the stiffness of single pile in black cotton soil with moisture content of 52.0% was higher than that of black cotton soil with moisture content of 23.0% And bearing capacity are significantly reduced, the drop of pile end resistance is particularly evident. It is suggested that in the design of engineering pile foundation, the frictional resistance of black cotton soil under wetting should adopt the shear strength of soil under large shear displacement.