Research on Freeze-thaw Collapse of Cutting and Bridge Transition Section Embankment Slope in Seasonal Frozen Area
|School||Harbin Institute of Technology|
|Keywords||freeze thawing collapse horizontal drainpipe heat preservation board arch skeleton geogrid slope stability|
The collapse mechanism of seasonally frozen slope is relatively complex, and itlacks systematical investigation and in-site data. Periodic action of frost heave andthaw settlement of slope soil make the slope collapse periodically in seasonallyfrozen area, which always causes not only a great economic loss but also high safetytrouble for traffic project.Based on sufficient research on the treatment measures of slope collapseseasonally frozen region in domestic and oversea, it is discovered that the mostimportant factors to cause the stability of cutting slope are temperature, groundwaterrecharge, migration quantity and heat and mass quantity of slope. On the basis ofthese factors, two control methods are adopted in this paper. One method consists ofhorizontal drainpipe, heat preservation board, and arch skeleton comprehensivetechnical measure to prevent cutting slope from collapsing. The other method isbidirectional geogrid to promote the stability of embankment slope in road-bridgetransition section.In this paper, there are two freeze-thaw circles in-site monitoring on horizontaldisplacement field, moisture field, groundwater level, temperature field, heat andmass transfer field in cutting slope in testing section; and on temperature field ofslope, geogrid overburden pressure, horizontal deformation and strain of geogrid inroad-bridge transition section. In addition, this paper systemically studies the slope-stability-promoted engineering effect of the comprehensive technical measureswhich consists of horizontal drainpipe, arch skeleton and heat preservation board inseasonally frozen region, as well as the reinforcing effect mechanism of geogrid andthe control effect of lateral deformation of embankment slope in road-bridgetransition section in frozen and thawed time. Moreover, this paper also systemicallyresearches the effectiveness of geogrid in promoting the safety factor ofembankment slope.Through two freeze-thaw circles in-site monitoring and theoretical calculations,the following conclusions can be concluded:1. Technical measures of horizontal drainpipe can dramatically decreasegroundwater level, slope soil moisture capacity and in frozen time the quantity ofslope soil moisture migration.2. Comprehensive technical measures can effectively reduce the horizontaldisplacement. Slope without comprehensive technical measures usually collapsesafter the first freezing-thaw circle, but the slope with comprehensive technicalmeasures is still stabile after two freezing-thaw circle. 3. Heat preservation board can significantly decreased the max frozen depth ofcutting slope in seasonal frozen soil region. It also can delay the freezing time andreduce heat and mass quantity of slope.4. Arch skeleton can effectively protect cutting slope. Compared to the cuttingslope without arch skeleton, the shallow crevasses of cutting slope, which had beenprocessed by arch skeleton, were reduced dramatically in length, square and depth.5. Geogrid can effectively control lateral deformations of embankment slopesection and enhance safety factor of embankment slope in road-bridge transitionsection. Besides, due to the effect of heat and mass transfer, value of horizontaldeformation and strain of geogrid in frozen time are both larger than the value inthawed time.In the horizontal drainpipe, arch skeleton and heat preservation boardcomprehensive technical measures, the groundwater will be drained out throughmulti-layered drainpipe technology. All those are important for the slope stability.The heat preservation board can reduce the frozen depth of the bottom of slope andthe freezing-thaw extent of slope, so it can protect freezing-thaw from collapse.Arch skeleton is beneficial for the slope soil. Geogrid can effectively inhibit lateraldeformations and increase safety factor of embankment slope in road-bridgetransition section through additional anti-sliding moment.Comprehensive technical measures introduced in this paper were successfullyapplied in cutting slope management engineering of Harbin-Dalian High-speed RailProject, and a significant economic benefit has been achieved.