软基上埋式箱涵土压力的离心模型试验研究

Experimental Research of Centrifuge Model of Soil Pressure on Positive-buried Box Culvert on Soft Foundation

为考察软基上埋式箱涵受力特性,通过离心模型试验,研究了其竖向和侧向土压力、土压力系数随填土高度变化的规律及周围填土位移场的变化情况。试验结果表明,使用桩基的箱涵与两侧路堤产生了显著的差异沉降,并在涵洞处形成了驼峰;内外土柱差异沉降在路堤中形成了拱脚位于涵顶两侧的上凸压力拱,并使拱脚处竖向土压力集中,且竖向土压力系数随路堤填筑呈开口向下的抛物线分布,在某一涵顶路堤高度下达最大值;同时,随涵顶路堤填筑,涵洞侧向土压力和侧向土压力系数增加,由于涵侧路堤以沉降为主的位移模式与挡土墙后填土不同,涵洞侧向土压力小于现行规范值。软基上路堤、涵洞和地基的协同作用分析表明,传统的强涵基、弱地基的设计理念将使涵顶竖向土压力集中,并导致结构失效。为降低涵洞结构破坏风险,建议采用轻质填料填筑涵顶、涵洞反开挖施工和结构设计考虑涵顶竖向土压力集中等措施。

In order to investigate the force characteristics of the positive-buried box culvert on soft foundation, the regularities of the vertical and lateral soil pressures and the coefficients of soil pressure varying with the depth of fill, and the variation of fill displacement field around the culvert are studied using the centrifuge model tests. The test results show that （ 1 ） there is an obvious differential settlement between the culvert and the adjacent embankment and a hump distribution occurred at the culvert because of the pile foundation of the culvert; （2） the upwardly convex pressure arch whose arch springing located at 2 sides of the culvert top appears in the embankment and makes the vertical soil pressure of the arch springing concentrated due to the differential settlement between the inner and outer soil columns, the coefficient of the vertical soil presents a downwards parabola with the construction of embankment, which arrives the maximum when the fill height on the culvert top reaches a certain value ; （2） the lateral soil pressure and the coefficient of lateral soil pressure increase with the construction of embankment, the lateral soil pressure on the culvert is less than the value in the current specification because the settlement displacement mode of the embankment adjacent the culvert is different from that of the backfill of the retaining wall. The analysis of the synergistic effect of embankment, culvert and foundation shows that the traditional design concept of a strong foundation under the culvert and a weak foundation under the adjacent embankment will make the vertical soil pressure on the culvert top concentrated and lead to the culvert structure failure. In order to reduce the culvert structure failure risk, it is suggested to construct the embankment above the culvert with light filling, to construct the culvert with the reverse excavation method and to consider the vertical soil pressure concentration during the culvert structure design.