Research On Calculating Settlement Of Subgrade Of Unsaturated And Soft Soil

The settlement of subgrade of highway is the result of the force that contains the static load of the embankment and dynamic load of the traffic. Especially when the subgrade is composed of unsaturated and soft soil, the settlement of subgrade will be large and the time required for consolidation is long. Up to now, there is still no complete calculating method to calculate the settlement of subgrade. Most of problems about settlement of subgrade were calculated by using the classical consolidation theory of saturated soil. However, in most cases subgrade soil is unsaturated, the calculated results of settlement of subgrade will engender great of error.Therefore, we need to study on mechanism of settlement of subgrade about soft soil in-depth, and get a calculating method about unsaturated and soft soil through analysis of test datas and theoretical formulas. It has not only theoretical significance, but also has important practical significance. In view of this, the main contents and results of this paper are summarized as follows:(1)According to summarizing and analyzing the consolidation theory of unsaturated soil at home and abroad, I found that the most representative consolidation theory of unsaturated soil was proposed by Professor Chen Zhenghan, College of Logistics Engineering. But this theory applies only to general situations. In order to simulate the special properties of soft soil, I put the nonlinear and viscoelastic model as the constitutive model of soft soil and put it into the consolidation theory proposed by Chen Zhenghan. So, I derived an consolidation-creep coupling equation about unsaturated and soft soil.(2)Collecting several groups of data about settlement test of subgrade about soft soil, analysing the parameters of soil, determining the reasonable ranges of computational parameters, monitoring of all test results are summarized, and analysing the developing trend of settlement of soft soil with the time.(3)Selecting the parameters of soft soil in subgrade of K59+710 section of N0.06 contract period of Wu Ying highway(from Wuhan to Yingshan), calculating the settlement of subgrade by the consolidation-creep coupling equation and the numerical simulation software PLAXIS, and getting the results about the theory and the numerical simulation.(4)According to comparing the calculated results with the previous theoretical results and the experimental results, I find that three conclusions are generally consistent, and the results of theoretical calculation can reflect the creep characteristics of soft soil in the long-term. So, I can consider that my theory is reasonable.