Abstract：Research purposes:The permeability critical standard is important for the assessment of grouting quality of karst subgrade． The two key problems were studied thought doing the model test and making theoretical analyses． One was whether there was a critical fissure that could not bring about the underground erosion collapse or not． The other one was if there was such a critical fissure，what was the characteristic value of the permeability of the critical fissure．
Research conclusions:The study results showed that the width of the critical fissure was the key factor for the collapse of covered karst due to the subgrade erosion，the soil property，the compactness and critical hydraulic gradient of the cover，and the collapse width of the critical fissure of the covered karst subgrade was about 2 ～ 4 mm． For the dissoluble rocks subgrade with development of erosion fissure，while the fissure width was less than or equal to 3 mm，or the permeability of karst subgrade was less than or equal to 47Lu，the covered karst subgrade would not collapse under the natural condition．Therefore，it is recommended that the 47Lu should be regarded as the permeability critical standard for grouting quality of karst subgrade．
Peng Hui．Study on The Effect of Grouting In Karst Subgrade Detection By Water Pressure Test Method In Coverage Karst Collapse［D］．Chengdu: Southwest Jiaotong University，2012．
2012, Vol. 29 
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