Research On Utility Tunnel Foundation Treated By Compaction Piles And Post-work Immersion Test In The Self-weight Collapsible Loess Area With Large Thickness

In order to determine the reasonable treatment range of utility tunnel foundation in self-weight collapsible loess with large thickness;to revel the regularity of the compacting impact on foundation varying with treatment depth;to research the infiltration law and settlement characteristics of utility tunnel natural foundation and composite foundation after immersion;and to have a further discussion about loess collapsibility based on independent ph ysical property.The experiment of foundation treated by different depth of lime soil(pure soil)compaction piles,and in-situ immersion test with TDR moisture meter and layered settlement instrument embedded in utility tunnel natural foundation and tre ated compaction foundation,both were conducted on the ground of collapsible loess with large thickness(>38m).The results show that:(1)In the range of pile length,the impact on soil between piles grows with depth increases;compacting impact on each test unit improves as the pile length increases,the impact between piles affected by soil layer reduces gradually,and the impact in the range of pile length tend to be stable.(2)Vertical penetration is faster than radial in composite foundation,which is related to that compaction plies foundation soil is horizontal encrypted.(3)On condition that taking effective waterproof measures,the reasonable treatment depth should be controlled in the scope of 9-12 m,at utility tunnel or other similar light construction and structure in collapsible loess area with large thickness.(4)During immersion,any point in saturated zone in natural foundation and treated foundation,there are 4 states: unsaturated,conduct unsaturated,transient unsaturated and saturated,and its change curve of volume moisture content shows obvious stages,which is closely related to the infiltration law of water.(5)The movement of moist fronts is not entirely evolutionary,it mainly goes down at the beginnin g of immersion;as time goes on,it goes downward and oblique upward simultaneously.(6)When water goes oblique downward to infiltrate,it doesn't maintain a certain angle,both infiltration angles change from small to big over time,and the angle of comp action piles foundation decreases as treatment depth increases.(7)Impermeability of composite foundation enhanced as treatment depth.(8)Collapse at each soil layer in natural foundation doesn't happen at the same time;the immersion settlement of compaction piles foundation decreases as treatment depth.(9)By making analysis,achieved the relationship between self-weight collapsibility coefficient,water content ratio and void ratio of this natural foundation before and after treatment in Lanzhou New District,to predict the coefficient of self-weight collapsibility through a small amount of physical property indicators of loess,so that saving a lot test costs and time for evaluating collapsibility of natural foundation and judging treatment effect in the region,which is of certain practical value in engineering in collapsible loess area.