Study On The Red Sandstone Roadbed Improved Soil Consolidation Settlement Characteristic In Dongchang Expressway

The red sandstone soil is widely distributed in our country,mianly appearing as red and weathering from the Mesozoic Cenozoic clastic sedimentary rock.It is a kind of special material,with particle breakage,easy weathering,strong hydrophilicity and mineral composition diversity.With the increase of China's highway construction.it draws many difficulties when encountering constructions in red sandstone regions.Using red sandstone as roadbed filler can save a great deal of project investment and reduce the quantity of the abandoned party,so as to protect the regional environment,it has remarkable social and economic benefits.It will produce a series of subgrade problems when directly using the red sandstone without any treatment,such as pavement bulge and mud pumping,subsidence,cracking,slope and erosion,roadbed uneven settlement and bearing capacity of diseases.The commonly used methods of soil improvement are physical and chemical methods,which can meet the design requirements after the improvement of chemical methods.In this paper,using lime and cement as additives,relying on the red sandstone roadbed construction technology projectof Jiangxi Dongchang Highway,using lime and cement to modify red sandstone.The consolidation settlement characteristics of red sandstone modified filler is analyzed,the main content and the research conclusions of this paper are as follows:(1)The basic physical and mechanical parameters of strong weathered red sandstone soil and modified soil with different ratios were obtained by indoor SEM tests,XRD tests,screening tests,limit moisture content tests and compaction tests.(2)By analyzing direct shear test results,the improvedred sandstone soil performs betterat strength than before,improved cement modified soil performs better than improvedlime modified soil;For improvedlime and cement soil,the internal friction angledid not change obviously with the increase of blending ratio,but the cohesion has been greatly improved;the improved mechanism is mainly rely on increasing cohesion to improve soil strength.7%-ratio-improvedlime and cement soil hits the maximum of shear strength.Unconfined compressive strength test results show that the degree of compaction has a great influence on unconfined compressive strength.(3)In this paper,the consolidation test of red sandstone packing under different loading modes is carried out by using traditional consolidation test instrument.1)Through the standard one-dimensional consolidation test,the relationship curve between the void ratio and the axial stress is obtained.With the increase of the load,the axial strain rate and the deformation of the soil were decreased with the increase of the load and the axial strain,and the effect of the 7%-ratio-improvedlime and cement soilwas the best.2)Through the consolidation test with loading ratio at 0.5 and 3,it is found that the loading ratio has a certain influence on the improvement of the red sandstone.And under the condition of high loading ratio,the soil mass is compressed,the settlement is fast,and the settlement is increased.With the increase of time,the porosity ratio and axial strain rate are decreased.3)Through preloading 400kPa and 800kpa consolidation test,it is found that the surcharge preloading has accelerated settlement to the soil,the greater the overload pressure,the better the compaction effect of soil is,the smaller the settlement deformation gets.4)This paper used the finite element software Flac3D to analyze numerical simulation of the improved red sandstone subgrade settlement deformation,to simulate the situations of improved red sandstone filling in roadbed and embankment,the effects of different ratioson improved soil is concluded.The results showed that:7%-ratio-improved lime and cement soil reaches minimum on settlement,which after improved soil filling roadbed,comparing to the settlement of to grain soilfilling subgrade,settlement of 7%-ratio-improved limesoilis reduced by 32.45%,settlement of 7%-ratio-improved cement soilis reduced by 32.80%;after improved soil filling lower embankment comparing to the settlement of to grain soilfilling subgrade,settlement of 7%-ratio-improved limesoilis reduced by 34.66%,settlement of 7%-ratio-improved cement soilis reduced by 34.98%.(5)The numerical analysis shows that the subgrade settlement of the improved soil fillinglower embankment is smaller than improved soil filling roadbed;comparing to the roadbed filled with with 0.8-meter-thick improved red sandstone soil filler,the effect of lowerembankment filled with 0.8-meter-thick improved red sandstone soil filler are better at roadbed stability.