超固结膨胀土地基桩网结构路基承载特性现场试验研究

Field Test Study on Bearing Characteristics of Geogrid-reinforced and Pile-supported Embankment in Over-consolidated Expansive Soil

以膨胀土区云桂客运专线CFG桩网结构路基为工程背景,开展全尺寸现场路基填筑试验,对比分析3种不同桩长和2种不同桩间距CFG桩网结构路基的桩土沉降、桩土应力比、格栅拉力以及地基反力的演变规律。研究结果表明:随着荷载的增加,土拱效应会经历初级土拱-完整土拱-增强土拱的演变过程,土拱效应的增强与地基的超固结特性和静置期间的应力重分布有关,二次填筑过程中长桩(S3、S4)的土拱系数曲线经历了从摩擦型桩到端承式桩的转变,这种现象对于短桩(S2)并不明显。桩的承载效率E随着桩长的增加而增大,最终稳定值约为80%;在填筑初期会产生较大的瞬时地基反力,从而导致桩间土强度折减效应的波动,其随着土拱效应的产生迅速减小并趋于稳定,S1~S4的稳定值分别为0.81、0.56、0.46、0.31。格栅应变主要发生在填筑初期,第一次填筑过程中的应变主要由桩土差异沉降导致,第二次填筑过程中的应变主要由复合地基整体沉降导致。最后通过对比分析7种不同土拱理论计算结果,发现同时考虑地基反力并引入土拱塑性系数α和等效土压力系数β能够更好地预测该地区拱的发展过程,现有理论方法均无法直接预测土拱的增强效应。研究成果可为类似地区高速铁路桩网结构的结构设计和变形控制提供参考。

In this paper, based on the CFG geogrid-reinforced and pile-supported embankment of the Kunming-Nanning high-speed railway in the expansive soil area, a full-scale field filling test was carried out. The evolution characteristics of soil settlement, pile-soil stress ratio, geogrid strain, and foundation reaction force of CFG pile network structure subgrade with 3 types of different pile lengths and 2 types of different pile spacing embankment were monitored and analyzed. The results show that as the load increases, the soil arching effect will undergo the evolution process of primary soil arching-complete soil arching-reinforced soil arching. This soil arching effect is related to the over-consolidation characteristics and stress redistribution of the foundation. The secondary filling process will cause the soil arch coefficient curve of the long piles(S3 and S4) to change from friction piles to end-bearing piles, while this phenomenon is not obvious for short piles(S2). The loading efficiency Eof the pile increases with the pile length, Efinally tends to be a stable value of about 80%. In the initial stage of filling, a large instantaneous foundation reaction force will be generated, which will cause the strength reduction effect of the soil between the piles to fluctuate. With the generation of the soil arching effect, it will rapidly decrease and become stable. The stable values are 0.81, 0.56, 0.46, and 0.31, respectively. The strain of the geogrid mainly occurs in the initial stage of filling, which is mainly caused by the differential settlement of the pile and soil during the filling process, and the strain in the second filling process is small, mainly caused by the overall settlement of the composite foundation. Finally, by comparing and analyzing 7 different types of soil arch calculation theories, it is found that considering the influence of foundation reaction force, the soil arch plastic coefficient α and equivalent earth pressure coefficient β can better predict the development process of soil arch in this area. But the existing theoretical methods can not directly predict the enhanced effect of the soil arch. The research results can provide a reference for the structural design and deformation control of high-speed pile-net structure in similar areas.