Engineering Application Research Of Lime Soil Of Back Filling Behind Abutment At Changsha-Zhuzhou Freeway

With the bridges and culverts structure in the expressway construction increasing,the quality of the back filling behind abutment has a direct connection with the service performance and service life of the freeway. If the quality of the back filling behind abutment is bad,it will bringing about many problems, for example: serious destroy to the road surface of back filled region; rutting and cracking will appear on the junction of the approach slab and bridge-head; the transverse Crack and differential 6settlement will appear on the road surface's junction of integral abutment and Subgrade; the rutting will appear in the pavement surface of the approach slab; the transverse Crack will appear in the pavement surface of integral back filled region and so on. therefore, a study on the material and stability backfill on the back filling behind abutmen is carried out, which has important and practical significance for guaranteeing the quality of freeway construction as well as accelerating the speed of construction.At present, to handle the unfavorable influences brought about by the back towards fixup, the following measures can be taken, for example: back towards foundation treatment; better quality fixup material being adopted and appropriate construction technology being used.Combined with the engineering entity of CHANGSGA to ZHUZHOU highway, this thesis takes material selection into consideration and select lime soil for studying.By analyzing the action mechanism and influencing factors of the limestone soil, it is found that currently the main disadvantages of limestone soil are:(1)The method for determining the optimum water content is deficient;(2)The method for determining the dose of lime is deficient;(3)Lacking in detection indexes.This subject studies on the above three disadvantages, combined with the AK0+640 culvert engineering entity of CHANGSGA to ZHUZHOU expressway and Huang Hua airport interchange.As for the first one, on the basis of the optimum water content from initial compaction test, the water content is increased by 2.5% to each group of lime dosage, to carry out comparison tests and then to determine the optimum water content which is most favorable to form strength of limestone. As for the second, this subject use four indexes——unconfined compressive strength, CBR, expansive capacity of CBR and compression coefficient——to determine the dose of lime comprehensively.In order to ensure the quality of the projects of back filling behind abutment, this subject tests the change or variation of dry density of lime soil, unconfined compressive strength, elastic modulus, direct shearing test, in condition of different age. The results of strength index tests indicate that: the strength increasing of limestone soil mainly concentrated in a month at the very beginning, while change becomes relatively slower later on.In order to preliminarily verify the effect of the back filling behind abutment with limestone soil, this paper applied ANSYS software to numerically simulate the post-construction settlement of subgrade after back filling behind abutment.At last, in order to ensure the quality of backfilling subgrade and verify the ultimate effect of backfilling with limestone soil, this subject put forward a set of quality control methods and did deflection test and settlement observation on backfilling subgrade, against a series of possible problems that may arise from the back filling behind abutment of CHANGSHA to ZHUZHOU freeway AK0+640 entity engineering. The results show that: when backfilling behind abutment is done with limestone soil, the backfilling parts are of better bearing capacity and can match the performance requirements very well. Comparing with eolian sand, cohesive soil and gravel, limestone soil improves the general bearing capacity greatly and represent better mechanical ability.