土层及钻机差异对灌注桩孔径变化规律的影响

Research on Effect of Different Soil layer Character and Drilling Machine on Variation of Diameter of Cavities of Cast-in-place Bored Piles

在成孔质量的各影响因素中,土层性质及成孔机具对孔径变化的影响最为显著。文章基于砂土和粘性土自身性质的差异,以及常规钻机和旋挖钻机施工特性,结合工程现场成孔实测数据,通过对不同土层条件下孔径变化趋势的统计和分析,总结出孔径变化规律。结果表明:孔径沿深度分布大致呈缩小趋势,浅部土层性质不稳,孔径变化剧烈,易受各种因素影响而产生扩孔;常规钻机护壁性能好,成孔孔径随时间变化小,相对稳定,而旋挖钻机护壁性能差,尤其在砂土中易形成缩孔;粘性土自身性质稳定,缩孔效应不明显。砂土层的粘聚力甚小,更易出现松弛,导致土体侧向位移;在砂层土采用常规钻机优势明显。在常州土层中采用旋挖钻机施工,若含有大范围砂层,建议在一清后4.5h内灌注混凝土。

Soil layer character and drilling machine play the most important role among the factors which affect the quality of cavity formation. This paper makes statistics of and analyzes the trend of variation of diameter of cavities in different soil layer so as to summarize the rule and mechanism of variation of diameter of cavities by making use of measured data about diameter of cavities in engineering site. The results indicate as follows ： the diameter of cavities decreases with depth increase, and the diameter of cavities in shallow soil layer change fiercely for its＇ quality unstable, which will make diameter of cavities expand for the disturb of soil layer due to effect of many factors; General drilling machines have good performance in shaft wall protection by drilling mud, so the diameter of cavities retains little variation with time, whereas rotary drilling machines have bad performance in shaft wall protection by drilling mud, especially in sand where they will make contractive cavities. The quality of cohesive soil is stable so that the cavities contraction is not obvious. Meanwhile, cohesive forces C of sand is little, which will produce relaxation to induce lateral displacement;General drilling machines has obvious advantages in sand, and it is advised that concrete showld be casted into cavities within 4.5h after first purging of cavities if it has a large amount of sand in Changzhou ＇ s soil layer in the condition of using rotary drilling machines.