| In this paper,depended on the red sandstone subgrade construction technology of Jiangxi Dong chang freeway Project,the research objects are the intense weathered red sandstone subgrade filler along the nearby line and different dosage of lime and cement improved soil.Through a large number of laboratory tests,a series of studies on variation laws of bearing capacity of subgrade soil under the condition of non soaking and soaking,drying and watering cycle and water-load coupling were carried and variation laws of bearing capacity of red sandstone and its improved soil under the action of soaking and drying and watering cycles were obtained.The main contents and conclusions of this paper are as followed.(1)The basic mechanical properties of red sandstone,lime and cement improved soil were tested and the influencing factors of bearing capacity of red sandstone subgrade were studied.The results show that the effect of water,adulterating agent and degree of compaction on the bearing capacity of red sandstone subgrade was very large,the water had a strong degradation effect on the strength of the plain soil,the strength was almost zero after soaking in water,and the water stability of plain soil was poor.(2)The variation laws of unconfined compressive strength of plain soil and lime and cement improved soil with different degrees of compaction under drying and watering cycle were studied:The unconfined compressive strength of the plain soil gradually decreased under drying and watering cycle,and then tended to be stable,what’s more,decreased mostly after the first drying and watering cycle.For the 5%and 7%dosage of cement improved soil and lime soil,with the increase of cycle times,the 28d unconfined compressive strength decreased first and then increased and then decreased,and the compressive strength had a rebound in fourth drying and watering cycle.The variation law of strength of the 3%dosage of the cement improved soil under the dry wet cycle was the same as that of the plain soil and the water stability was poor.(3)The 7d unconfined compressive strength tests were carried out under the condition of soaking water,different soaking time and acid and alkali water,and the effects of soaking and non soaking,different soaking time and pH value on unconfined compressive strength were analyzed:After soaking in the short time for one hour,the intensity of soil water decreased rapidly.With the increase of soaking time,the strength decreased slowly and tended to be stable;for more than 5%dosage of cement improved soil and lime improved soil,after soaking in a short period for one hour,the intensity decreased in a certain.With the increase of soaking time,unconfined compressive strength decreased slowly,and the strength increased after soaking for four days.For the 3%dosage of cement improved soil,the variation law of strength with time was the same as that of the plain soil.The acid and alkali water had certain influence on the soil and cement and lime improved soil,but the effect was not very large.With the increase of pH value,the unconfined compressive strength of plain soil and the 7%dosage of lime improved soil gradually increased,and the unconfined compressive strength of the 7%dosage of the cement improved soil increased in a whole with the increase of pH value,but there was a slight fluctuation in the middle.(4)The compressive properties of plain soil and cement and lime improved soil were studied under the condition of soaking and drying and wetting cycles:①After soaking in the short period of one hour,the compression modulus of the plain soil decreased rapidly and the compression coefficient increased rapidly.With the increase of soaking time,the compression modulus decreased slowly,the compression coefficient increased slowly,and finally tended to be stable.The dosage of 5%and 7%cement modified soil and lime improved soil had similar rule with the extension of soaking time.After soaking in the short period within one hour,the compressive modulus decreased greatly.With the extension of soaking time,the compression modulus decreased slowly,and the compression modulus after soaking for four days had a certain degree of rebound.Its compressibility has improved.With the increase of soaking time,the compressive properties of the 3%dosage of cement improved soil was the same as that of the plain soil.②Under the condition of drying and watering cycle,the compression modulus of plain soil decreased greatly,and the attenuation was the most after the first cycle and tended to be stable;For the 5%and 7%dosage of the cement improved soil and lime improved soil,the compression modulus decreased greatly after one cycle,and then decreased slowly.After 4 cycles,compressive modulus increased to a certain extent,and then decreased.(5)Considering the effects of soaking time,drying and watering cycles on strength and compression of plain soil and lime and cement improved soil,the concepts of weighted average unconfined compressive strength,weighted average compressive modulus,strength loss coefficient and compression modulus loss coefficient were introduced,in order to evaluate the loss of strength and compression under soaking and drying and watering cycle. |
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