Characteristics Research On Settlement Of Dynamic Consolidation Foundation Of Unsaturated Soil

Along with the fast development of our country’s economy, we have constructed a great number of high-speed railways and passenger special lines to solve the problem that the original railway system is of inadequate transport capacity and low efficiency. As an important part of high-speed railway construction, railway foundation settlement plays important roles in the development of high-speed railways. Focusing on the construction process of the Qingdao-Jinan passenger special line, this paper takes a dynamic compaction test section of Qingzhou straightened section from this special line as the research subject. Through series of research methods, such as standard indoor and outdoor consolidation tests, centrifuge model tests, numerical simulation and field settlement observations and etc., this paper mainly focuses on the settlement deformation characteristics of dynamic compaction foundation and the treatment effect of dynamic compaction. Major discoveries are summarized as follows:1. Through analysis and comparison between the test results of centrifuge model of untreated and dynamic compaction sections, it can be found that dynamic compaction can reduce the amount of foundation settlement during the filling period. The deformation of affected area of the ground was decreased sharply, after dynamic compaction, which indicates the obvious effects of the dynamic compaction;2. Through series of field tests including plate load test and static cone penetration test, this paper tests the foundation engineering geological characteristics and basic physical-mechanical characteristics of unsaturated soil of the dynamic compaction section, from which the bearing capacity, compression modulus and other geotechnical physical dynamic parameters of the soils are determined. The results of field tests displayed:after dynamic compaction, the bearing capacity can be improved about2times and compression modulus can be improved about1.6times;3. Through field settlement observation, the settlement and deformation laws of dynamic compaction foundation are investigated. By comparing field settlement observation results of the dynamic compaction section with that of a natural foundation section, it is concluded that dynamic compaction can effectively eliminate differential settlement and improve the constraining force and non-deformability of the foundation. The effect of dynamic compaction is very obvious;4. Through the analysis of consolidation theory of unsaturated soil, it is found that after dynamic compaction the penetration coefficient change of the foundation soil was mainly related to void ratio and the change of water content. The paper also deduced the expressions of penetration coefficients for unsecured silt and silty clay after dynamic compaction;5. Numerical analysis the value of center stress on the bottom of subgrade was between γH and average stress, and the stress increase as the increase of width height ratio. Numerical analysis also shows that attached stresses along the center profile of subgrade decayed faster in the upper ground than the deeper section;6. By comparing the results of field settlement observation and various settlement forecasting methods, it can be found that in the process of steady filling, hyperbolic model can reflect the settlement-time relation of the dynamic compaction foundation more accurately.