Application Research On Bidirectional Mixing Dry Jet Mixing Columns To Improve Lian-Yan Railway Soft Soil

Lianyungang to Yancheng railway lines is the main traffic trunk lines between cities of northern jiangsu of jiangsu province, and is an important part of jiangsu coastal railway channel. This railway passes through lianyungang coastal soft soil area, and the soft soil features high compressibility, low permeability, poor bearing capacity, and long settlement stability time, etc. In this study, based on project of composite foundation method and treatment of high water content soft soil foundation technology research, which was researched combined by China Railway Survey and Design Institute of Five and Southeast University, application research on the bidirectional mixing dry jet column composite foundation to railway soft soil treatment was conducted.Through the laboratory, field test and theoretical analysis, the quality of bidirectional mixing dry jet column, load-bearing characteristics and deformation characteristics were researched. The feasibility and superiority of reinforcing soft soil foundation by bidirectional mixing dry jet column technology in railway engineering were verified. The main work and achievements are as follows:(1) This study improved the construction machinery and construction technology of bidirectional mixingdry jet column technique. This study developed successfully the bidirectional mixing dry jet column automatic control system at the front desk and dust removal equipment, and upgrading the air compressor equipment, which improved bidirectional mixing dry jet column construction efficiency, automatic control technology, environmental protection and quality monitoring. Injection of right amount of water on the column head at the end of the mixing column construction effectively solves the poor column body quality issue above ground water table.(2) Based on the geological conditions of Guanyun railway section, different foundation reinforcement scheme is given. The bidirectional mixing dry jet column technology was suggested accorrding to the bearing capacity, settlement and economy of the ground. At last, a detailed design and check scheme was presented.(3) The bidirectional mixing of dry jet column core quality is observed. By cement-soil strength test for core samples and single column load test, the advantages and disadvantages of the bidirectional mixing technology and the conventional mixing technology were compared, which indicated the superiority of the bidirectional mixing technology. Through single column load test, the load transfer law of bidirectional mixing dry jet column was discussed, which was verified further by numerical simulation method. Compared with conventional mixing dry jet column, the bidirectional mixing dry jet column load transfer depth is larger, the effective reinforcement depth increased significantly.(4) Through the PLAXIS finite element simulation, the paper analyzes the settlement of ground improved by the bidirectional mixing dry jet column reinforcement during embankment filling stage and railway operation stages. Bidirectional mixing dry jet column reinforcement technology meet the requirements of high speed railway, which further verified the feasibility of bidirectional mixing technology applied in the railway construction.