Study On The Improvement Of Expansive Soil Subgrade Of Mengzi Highway Engineering

In the last few decades,with the improvement of engineering construction technology,more and more countries are faced with the problem of expansion soil in the process of construction.The actual project Mengzi Expressway(Yangji segment)involved in this paper are entirely expansive soil.Expansive soil was a multi-slot and remarkable expansion soil.In the engineering field,expansive soil was often identified as invisible geological disasters on account of its typical characteristics of water swelling and dehydration shrinkage.In the high grade highway subgrade engineering,expansive soil had serious damage to the engineering structure,and it often produced long-term deformation damage for the highway.To solve this problem,this paper selected the expansive soil improved by lime,and combined with indoor compaction test,CBR test and swell shrink test to make study on the effectiveness of the improved expansive soil solution for lime,and the main conclusions of this thesis are as follows:(1)In the compaction test,with the moisture content increased from 17.2% to26.1%,the corresponded dry density was increased first and then decreased with the parabolic variation,which was from the 1.57g/cm3 increased to 1.65 g / cm3,then gradually reduced to 1.57 g / cm3,and the optimum water content was 21.3%,the corresponded maximum dry density was 1.65 g / cm3.(2)In CBR test,the change relationship between unit pressure and quantity of penetration of these three test group(1-3)are basically the same when each layer compaction was 30 times,that's to say,with the gradual increase of the pressure units,the penetration quantity was also increased gradually,and the increasing trend was gradually accelerated.When the penetration quantity of these three test groups is2.5mm,the corresponded unit pressure was 532 kPa,566kPa,538 kPa respectively,and the corresponded CBR value was 7.6%,8.1% and 7.7%;When the penetration quantity is 5mm,the corresponded unit pressure was 709 kPa,763kPa,750 Pa respectively,and the corresponded CBR value was 6.8%,7.3%,7.1%.The change relationship between unit pressure and quantity of penetration of these three test group(4-6)are basically the same when each layer compaction was 50 times,that's to say,with the gradual increase of the pressure units,the penetration quantity was also increased gradually,and the increasing trend was gradually accelerated.When the penetration quantity of these three test groups is 2.5mm,the corresponded unit pressure was 733 kPa,733kPa and738 kPa respectively,and the corresponded CBR value was 10.5%?10.5% and 10.5%;When the penetration quantity is 5mm,the corresponded unit pressure was1079 kPa,1066kPa and 1074 Pa respectively,and the corresponded CBR value was10.3%,10.2% and 10.2%.The change relationship between unit pressure and quantity of penetration of these three test group(7-9)are basically the same when each layer compaction was 50 times,that's to say,with the gradual increase of the pressure units,the penetration quantity was also increased gradually,and the increasing trend was gradually accelerated.When the penetration quantity of these three test groups is2.5mm,the corresponded unit pressure was 829 kPa,808kPa and 816 kPa respectively,and the corresponded CBR value was 11.8%,11.5% and 11.7%;When the penetration quantity is 5mm,the corresponded unit pressure was 1129 kPa,1130kPa and 1132 Pa respectively,and the corresponded CBR value was 10.8%,10.8% and 10.8%.(3)In CBR test,with the hit times increase of each layer of soil,the soil dry density was also increased gradually as well as the corresponded CBR value of I=2.5mm and I=5mm.The penetration quantity for 2.5mm corresponded to the CBR value was always greater than the penetration quantity for 5mm corresponded to the CBR value,but with different penetration conditions of CBR,its value just had little difference;And with the increase of dry density,the Increasing trend of the value of CBR was basically consistent with three different corresponded penetration,when the strike frequency were 50 and 98,the CBR values satisfied the subgrade filling requirements.(4)In the expansion and contraction test,the corresponded expansion amount of each layer was very low,and the corresponded expansion amount is less than 4%,when the tamping number of each layer is changed from 30,50 to 98.With the increase of the number of compaction,the corresponded sample soil's dry density was also increased gradually,and the volume expansion after the specimen soaked also showed increasing trend and changed increasing linearly.