Study On Suitability For Soil Cavity Inside The Subgrade In Karst Area For Its Reconnaissance And Measures

The soil cavity in Karst area is a special karst phenomena,it has many characteristics such as in bedding shallowly,developing quickly,distributing densely and resulting in ground subsiding,which bring a great damage to the construction of the subgrade and maintenance of highway.And the stability of subgrade is threaten seriously.Find effective swift prospecting method and remedial measures imperative .So it is more important practical purpose and theoretical significance to Study on suitability for soil cavity inside the subgrade in Karst area for its reconnaissance and measures.A case study on the highway of Guilin-Yangshuo.The article analyzes the conditions of formation,the main influential factors and the distributed regulation of soil cavity in Karst area. The geologic environmental suitability of the shallow soil cavity inside the subgrade in Karst area have been researched with geophysics measurement technologies.Treating measures of soil cavity in the different conditions have been presented.From the research,the following achievements have been achieved.Analyzing the conditions of formation ,the mainly factors affecting and the mechanism of Karst collapse of the soil cavity in Karst area,we can present superposition modes during the course of a rain and sum up the distributed regulation of soil cavity in Karst area.With geophysical measurement technologies,the suitability of the shallow soil cavities (h<10m,d<3m)are researched.The results show:The highdensity resistivity method does not suit for prospecting shallow soil cavities because this method is only sensitive to the uniform conductor of low resistance in the high resistance.The shallow seismic reflection method does not suit the prospecting shallow soil cavities because seismic wave field is quite complicate.The shallow reflex wave is not gained and it cannot be distinguished within the depth of 10m.The Ground Penetrating Radar suits the prospecting shallow soil cavities owing to its high speed sample and high distinguishing ability and it can define the configuration and spatial location of the shallow soil cavities.By using the engineering practical experience and the physical model test of Karst collapse,remediation measures and their suitableness together with their techno—economical aspects are presented according to their categories. Excavation and backfill are suitble for the shallow soil cavities underground the depth of 1～2m.Heavy pounding and seepage-proof surface sealment are suitable for the soil cavities underground of the depth of 2m～3m and above groundwater level;Grouting is suitable for the soil cavities (depth>5m,width>2m)that locate fluctuation of groundwater level about bedrock surface ; The thesis presents the excavate-inverted filter and geotechnical fabric to the soil cavities underground of the depth of 2m～5m and above fluctuation of groundwater level.By using the engineering practice,this method not only prevents the soil loss form the rockbed but also operates surface water seepage and keeps the balance of water environment in Karst area.Crossing structures are suitable for the soil cavities that are dense and large scale or the grikes and lapie are very deep.