Research On Filling Technology Of Red Sandstone Highway Roadbed

A large volume of soft rock areas is distributed across the country.However,due to poor engineering properties,soft rock is usually not suitable for filling works directly.After modification,soft rock can be used for filling works,to save a huge investment,avoid a large number of spoils,and meet the purpose of environmental protection.In the thesis,taking Huaihua-Zhijiang Highway Project as an example,the red sandstone filler in soft red sandstone areas passed across by Huaihua-Zhijiang Highway is tested and studied.Through many laboratory and field tests,the applicability of red sandstone to roadbed filling and the results of cement modified red sandstone,as well as the construction technologies of red sandstone for roadbed filling are systematically studied.Main conclusions are obtained as follows:(1)The test and study results of lithology of red sandstone show that based on the weathering degree of red sandstone,its disintegration performance varies but its strength will drop sharply with the effects of water.Through the comparison between the surface vibration compaction test and compaction test of weathered soil of red sandstone,it can be found that the maximum dry density among compaction parameters is almost irrelevant to the test method.Consequently,the surface vibration compaction method can be replaced with the compaction test to determine compaction parameters.(2)Through the comparison between the effects of lime and cement modified red sandstone filler,it can be found that cement can greatly improve the bearing capacity and water stability of the filler while the lime modified filler does not work well.Therefore,cement is determined to be as the additive to modify red sandstone filler.(3)For the modified soil of red sandstone,the unconfined compressive strength is taken as the design index,which can better evaluate the water stability of the filler.The test and study results show that when the cement content is above 4%,the wetting-drying test results of unconfined compressive strength meet the strength requirements and the cement content to modify red sandstone is determined to be 5%.(4)For the detection by portable falling weight deflectometer(PFWD),its impact load stress range is consistent with the actual dynamic stress of the roadbed,and it can be used directly to detect the roadbed quality.Detection value by PFWD,compactness,and the deflection value measured by Benkelman beam test are highly related.Therefore,PFWD can replace the two values to detect the roadbed quality.The detection test results show at Evd≥54.6MPa,the roadbed compactness and deflection value meet the roadbed acceptance requirements.Therefore,it is proposed that the detection control index of red sandstone roadbed shall meet the case with Evd≥55MPa.(5)Based on the construction of test sections,the construction processes and technologies of red sandstone modified soil for roadbed filling are proposed and such key construction technology points as rock breaking and cement mixing uniformity are summarized.