排水粉喷桩加固软土地基桩周土体强度变化规律

Strength change feature of surrounding soil in the vicinity of DJM columns in ground improved by DJM-PVD combined method

排水粉喷桩(2D工法)是同时采用粉喷桩和塑料排水板加固软土地基的一种新工法。在某高速公路中进行了排水粉喷桩加固软土地基的现场试验段施工,分别采用静力触探试验、十字板剪切试验等方法测定加固前及其加固后不同龄期的粉喷桩桩周土强度,得到了施工后桩间土强度变化的规律。测试结果表明采用粉喷桩联合排水板法加固后,桩周土强度有一个先降低后提高的过程,28天龄期时恢复到原状土强度,随着龄期的增长桩周土强度可以进一步增加。最后对桩周土强度的变化机理进行了初步探讨。

A remarkable combined method of the dry jet mixing with prefabricated vertical drains （DJM-PVD combined method） is innovated and successfully practiced in a highway project on very soft clay in Jiangsu Province,China. The strength change feature of surrounding soil in the vicinity of a DJM column is investigated. The field results of cone penetration and vane shear tests indicated that the strength of surrounding soil decreases in a short period after the installation of DJM due to the destruction of soil. As time passing,the shear strength of surrounding soil increases due to excessive pore pressure dissipation. At 28 days of elapsed time after installation,the strength of surrounding clay exceeds that of the intact clay before installation. With the increasing of elapsed time,the strength of surrounding soil would increase continually. The dissipation of excessive pore pressure and soil fracturing are two basic factors involved in the strength increases in surrounding soil.