| Against the background of the high liquid limit soil abandonment improvement in the fourth section of the first contract section of Liyu Expressway in Guangxi,this paper focuses on the high liquid limit soil improvement method in conformity with the requirements of subgrade filling standards.Indoor geotechnical tests are used to determine the engineering classification of abandoned soil,mechanical properties of tunnel slag,compactness and California bearing ratio(CBR)of specimens with different improvement methods.Given economy and the characteristics of construction,a suitable method is put forward for the improvement of high liquid limit soil of Liyu Expressway in Guangxi,and with numerical simulation,the construction parameters of subgrade layered filling are obtained according to the settlement stabilization duration and the construction progress.The research contents and results of this paper are as follows:(1)Interior experiments are made about how to improve the high liquid limit soil by physical and chemical methods.The tests showed that the spoil was a high-liquid-limit soil of medium compressibility.The compaction curve of high liquid limit soil failed to coincide with the peak value of California bearing ratio(CBR)curve,and the corresponding water content difference between them was 5.89%,indicating that high liquid limit soil possessed water stability.Meanwhile,when the water content was high,the increased compaction work could not improve the compaction of the high liquid limit soil.And the tunnel slag with low content made no difference to the California Load Ratio(CBR)of the modified specimens.The CBR value of the modified specimen would not show a significant change until the content of cave slag reached over 65%.Therefore,the CBR value of the modified specimen would increase exponentially as the amount of slag in the tunnel grew.When quicklime was used for chemical improvement,the high liquid limit soil would agglomerate,resulting in slow growth of specimen strength and inconvenience for on-site construction.(2)FLAC3D simulation is adopted to analyze the settlement law of layered filling of high liquid limit soil improved by tunnel slag Based on the creep theory,viscoplastic and elastoplastic constitutive models were used for different layers of fillers to figure out how the number and the location of the tunnel slag layer would influence the subgrade filling process and long-term post-construction settlement and deformation.In addition,the influence of seepage on subgrade settlement was taken into consideration due to the high water content of high liquid limit soil.According to the construction progress of the roadbed and the time for the settlement to stabilize,the thickness of the on-site construction layer was settled to be 0.5 m of the tunnel slag layer and 1.0 m of the high liquid limit soil layer.(3)This paper proposes the technical parameters and construction process of layered filling high liquid limit soil subgrade.In light of the compaction degree of subgrade,porosity bending value,the construction parameters of different layers of subgrade and the combination way of compaction machines were specified.On the basis of the monitoring data of the subgrade in the field test,comparisons and analysis were made about the simulation curve of subgrade settlement and the difference of the monitoring data of the field section monitoring points.The fact that the settlement of creep curve based on seepage was higher than that of creep curve and in-situ monitoring curve meant it was necessary to consider the influence of seepage action for high liquid limit soil subgrade.And high liquid limit soil was able to meet the filling requirements of subgrade below 6m with excellent mechanical properties. |
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