Abstract: Based on a foundation pit project of Qingdao Metro, field tests of the micro-steel pipe pile supporting structure were carried out by placing resistance-type strain gauges symmetrically on the outer wall of the micro-steel pipe pile and earth pressure boxes on the pile facing the earth. The pile bending moment and pile side earth pressure data of three parts such as soil layer, soil-rock interface and rock layer were collected respectively. The evolution characteristics of pile side pressure and pile bending moment at soil-rock interface during excavation of foundation pit were analyzed, and the variation law of pile side pressure and pile bending moment of the inner row micro-steel pipe pile changing with the excavation depth of foundation pit in the quaternary soil layer, soil-rock interface and rock layer was studied. The results show that with the increase of foundation pit excavation depth, the soil pressure values on pile side in soil layer and rock layer show a trend of first decreasing and then increasing, then decreasing and then increasing, and then continuously increasing. The soil pressure on the pile side at the soil-rock interface shows a trend of wavy increase, and the increase is large, which belongs to the weak point of the soil layer stress. The prestressed anchor (cable) support can effectively coordinate the internal force of the pile body and limit the occurrence of large deformation of the pile body, so as to avoid the growth of the bending moment of the pile. The bending moment value of the micro-steel pipe pile near the soil-rock joint surface is small and the growth is slow. The soil pressure on the pile side is greatly influenced by the spatiotemporal effect of excavation of the foundation pit.

Key words: tunnel engineering; foundation engineering; soil-rock interface; earth pressure; pile bending moment; micro-steel pipe pile; time-space effect

摘要： 依托青岛地铁某基坑工程，在微型钢管桩外壁对称布置电阻式应变片，在桩身迎土面布置土压力盒，开展了微型钢管桩支护结构的现场试验，分别采集土层中、土岩分界面以及岩层中3个部位桩身弯矩与桩侧土压力数据；分析了基坑开挖过程中土岩界面桩侧土压力及桩身弯矩的演化特性；研究了第四系土层中、土岩分界面及岩层中内排微型钢管桩桩侧土压力与桩身弯矩随基坑开挖深度的变化规律。研究表明：随基坑开挖深度的增加，土层中、岩层中桩侧土压力值均呈现先减小后增大，再减小又增大，随后持续增大的变化趋势；土岩分界面处桩侧土压力呈波状递增变化，且增幅较大，属于岩土层受力的薄弱点；预应力锚杆(索)支护能够有效协调桩身内力并限制桩身产生大变形，避免了桩身弯矩的增长；位于土岩结合面附近微型钢管桩弯矩数值较小且增长较缓；桩侧土压力受基坑开挖的时空效应影响较大。

关键词: 隧道工程；地基基础工程；土岩分界面；土压力；桩身弯矩；微型钢管桩；时空效应