Study on compaction effect and horizontal stress of collapsible loess foundation treated by rammed-expanded compaction pile

Abstract

In order to study the change of compaction effect and horizontal stress along the depth of collapsibility loess highway subgrade treated by rammed-expanded lime-soil compaction piles with different pile diameters and pile spacing, the compaction coefficient, horizontal stress, over-consolidation ratio, cone tip resistance and side-wall resistance around the pile were analyzed. The results show that the compaction coefficient, collapsibility coefficient, horizontal stress, consolidation degree, cone tip resistance and side-wall resistance of soil between piles can be significantly increased in the range of treatment depth, and then the bearing capacity of the foundation is mentioned. When the pile spacing increases from 1.0 m to 1.2 m and 1.5 m, the average soil compaction coefficient between piles increases by 1.37% and 4.11%, and the average collapsibility coefficient increases by 1.75 and 2.79 times, respectively. When the pile spacing is 1.0 m, 1.2 m and 1.5 m, the average horizontal stress ratio corresponding to the 400 mm pile diameter is 3.23, 2.47 and 1.92, the over-consolidation ratio is 11.58, 6.64 and 3.94, respectively, the average cone tip resistance increases by 2.54 times, 1.92 times and 1.31 times, respectively, and the side-wall resistance increases 3.07 times, 2.35 times and 1.47 times, respectively. The average horizontal stress ratio corresponding to the pile diameter of 450 mm is 3.52, 2.74 and 2.21, the over-consolidation ratio is 13.80, 8.26 and 5.27, respectively, the average cone tip resistance increases by 2.77 times, 2.03 times and 1.39 times, and the side-wall resistance increases by 3.40 times, 2.59 times and 1.66 times, respectively. The influence of pile spacing on the soil parameters above is greater than that of pile diameter. In practical engineering, it is recommended to treat collapsible loess foundation with rammed-expanded lime-soil compaction pile with pile spacing≤1.2 m.

Keywords

collapsible loess foundation / rammed-expanded lime-soil compaction pile / soil between piles / compaction coefficient / horizontal stress