湿陷性黄土场地竖向承载灌注桩浸水试验研究
张 磊1,2, 罗少锋1,2, 鲁 洁1,2

(1. 西安建筑科技大学 土木工程学院,陕西 西安 710055; 2. 西安建筑科技大学 陕西省岩土与地下空间工程重点实验室,陕西 西安 710055)

桩基础; 湿陷性黄土; 浸水试验; 竖向荷载; 侧摩阻力

Immersion tests on vertically loaded cast-in-place piles in collapsible loess
ZHANG Lei1,2, LUO Shaofeng1,2, LU Jie1,2

(1. School of Civil Engineering, Xi'an Univ. of Arch. & Tech., Xi'an 710055, China; 2.Shaanxi Key Laboratory of Geotechnical and Underground Space Engineering, Xi'an Univ of Arch & Tech., Xi'an 710055, China)

pile foundations; collapsible loess; immersion test; vertical loads; skin friction

DOI: 10.15986j.1006-7930.2019.04.010

备注

为研究自重湿陷性黄土场地中钻孔灌注桩的竖向承载性状,开展了3根试桩在天然、先加载后浸水和预浸水3种工况下的静载荷试验.试验结果表明,桩顶沉降随桩顶荷载的增加而增大,桩侧摩阻力随桩土相对位移的增加而增大,某些深度处桩侧摩阻力在达到峰值后甚至减小.桩顶荷载传至桩底后桩端反力随桩顶荷载的增加而增大,其变化速率逐渐增大.在本试验小试坑浸水及场地地层条件下,桩顶未施加荷载时桩侧未产生负摩阻力; 桩顶维持4 000 kN荷载不变时桩周土体浸水湿陷,桩侧正摩阻力减小,桩顶沉降增大,但也未在桩侧产生负摩阻力.桩周土体浸水软化,其所能提供的最大侧摩阻力减小.

Field tests were conducted to investigate vertical bearing behaviors of the cast-in-place pile in collapsible loess site under natural, post-soaked and pre-soaked conditions. Test results show that the settlement at pile top increases when the vertical load applied at pile top increases. The skin friction increase with the increase of the relative displacement between pile and soil, while at some depths, they even decrease after reaching their peaks. The pile tip resistance increases with the increase of the vertical load after the applied load was transferred to pile tip, and the changing rate increases gradually. On conditions of the relatively small soaking pit and the stratum of the test site, there is no occurrence of the negative skin friction during soaking with no vertical load applied at pile top. When maintaining a 4 000 kN load at pile top, after soaking the loess around pile collapses, the positive skin friction decreases, and the settlement at pile top increases, while the negative skin friction does not occur. The loess was softened after soaking, leading to the decrease of the maximum skin friction provided by it.