Research On The Bearing Characteristics And Influence Factors Of The Saturated Loess Under The Railway Embankment Reinforced By The Cement-soil Mixing Pile

Saturated loess is a regional special soil evolved by the loess. In recent years, scholars in our country are mainly concentrated in reforming collapsible loess foundation, which has also made a lot of research results, but less concerned with saturated loess foundation encountered in the construction of the railway and other projects. the saturation of saturated loess is so large that the collapsibility of loess has disappeared, the state of soil is molliplast or plastic flow, the bearing capacity of soil is low, the compression amount is larger, line and subgrade of railway built on it will have great settlement and uneven settlement, therefore, it is essential to study foundation reinforcement technology special for saturated loess. Soil-cement mixing pile composite ground is widely used to reinforce in all kinds of soft foundation, for its convenience, no environmental pollution and remarkable economic benefit in the process of construction. While no matter the reinforcement mechanism or the method of design and calculation of the cement-soil mixing pile have some drawbacks, which is need to be further study and discussed. This paper used the cutting ring method,the shallow plate load test, the single pile static load test and the load test of single pile composition foundation,based on soil-cement mixing piles sited in zhongchuan railway,(DK48 + 430 — DK49 + 030)segment, and analyzed the data obtained from field measurement, to study the following issues:(1) Two-ash content is an important factor to the load-bearing characteristics of cement-soil mixing pile composite foundation. In the range of 16%~20%, as the increase of two-ash content, the bearing capacity of cement-soil mixing pile composite foundation increases gradually, the bearing capacity of cement-soil mixing pile whose two-ash content is 20% is better than that whose two-ash content is 16%.(2) Reinforced by the method of cement-soil mixing, the bearing capacity improved from 91.3kPa to 164 kPa,the saturated loess foundation in test section has dramatically improved mechanical properties of the foundation, higher strength of soil and increase coefficient of 1.7 of the bearing capacity of foundation;(3) The pile-soil stress ratio scope reinforced by the cement-soil mixing pile whose two-ash content is 16% in rigidity loading plate is from 4.0 to 6.0.(4) By FLAC3 D,pile lateral friction and axial force have been analyzed: With the increase of the depth, the degree of pile lateral friction play is more and more obvious; When the top load is small, axial force is small and not attenuating obviously with the increase of depth. As load increasing, axial force increases and attenuates obviously with the increase of depth.(5)By FLAC3 D,when the two-ash content is in the range of 12%~20%, as the increase of two-ash content, the bearing capacity of cement-soil mixing pile composite foundation increases, which is consistent with the measured conclusion(6) Based on the work mechanism of piles and soil, the pile soil interaction model is established. Then using FLAC 3D as numerical simulation software, combining with the actual engineering situation, to simulate the single pile and single pile composite foundation, the results is in agreement with the field test results, which further verifies the accuracy of field loading test, and has certain guiding significance for engineering practice.