The Research Of High-speed Rail Subgrade Filler Improvement Experiment In Loess Area

In order to boost the economic development in western China, our country set off a new upsurge of high-speed railway construction in northwest area. High-speed rail can greatly improve the transportation capacity and promote the economic growth in western China, it can have great significance for the coordinated development of the Eastern and Western regional economies. For the rapidity of trains on high-speed railway,it should guarantee the stability and safety when the trains is driving. The railway subgrade needs higher-quality and the subgrade fill has direct relationship with the quality of the railroad bed. Loess is widely distributed in the northwest China and the high quality filler of orailway roadbed is very scarce, if the high-speed rail are made of high quality packing. it will greatly improve the cost of the engineering construction if the high-speed rail is using high quality packing. Therefore,it can save resources and reduce the construction cost as to assure the mproved loess meet the requirements of high-speed railway embankment and it plays a promoting role in the construction of high-speed railway in loess region.Lime and cement are traditional improved materials, the early strength of lime improved loess is not high as well as the water resistance is poor, the cost of cement loess is higher. In order to save resources and reduce cost, use slag powder and fgd gypsum to improve loess.Generally, the effect of several improved materials are incorporated into the loess than single modified material is incorporated into the loess. This paper first proposed to use slag powder,fgd gypsum and lime three materials combined to improve loess, which slag powder is10%,20%, lime is5%,8%,10%, gypsum is 3%,6%,9%, through different contents to improve loess. It would solve the problem of lime loess which the water resistance is poor and the early strength is low. And to ensure the strength can achieve the strength of cement loess,improved materials can repla-cement, which can reduce costs.This paper studies the loess of Lanzhou hinge project about Baoji-Lanzhou High-speed Rail, using undisturbed loess and remodeled loess and improved loess with slag powder,fgd gypsum and lime to conduct a series of laboratory experiment, including liquid and plastic limit test, compression test, collapsible test, triaxial shear test, unconfined compressive strength test and water immersion test. Establish ballastless subgrade model by Midas / GTS software for numerical simulation analysis,and study the engineering properties of undisturbed loess, remodeled loess and improved loess loess. This paper achieve some some valuable results by experiments and numerical simulation analysis.(1)High speed railway design specifications(TB10621-2009) requires the 7d compressive strength of High-speed railway subgrade bed underfill should reach 550 kPa in cold regions.The results showed that unmodified loess can not as roadbed filler to be used directly in thehigh-speed railway roadbed project.(2)The laboratory experimental results of the improved loess(No.1-9), which slag powder20%, lime5%,8%,10%, gypsum3%,6%,9%. Compared with the remodeled loess,liquid and plastic limit have a relatively large increase, plasticity index has some decreases.The cohesive force and friction angle have greatly improvement, so the shear strength is high.The Collapsible get eliminated, compression coefficient is less than 0.1MPa, improved loess are low compressible soil. 7d unconfined compressive strength is far greater than 0.55 MPa,and the compressive strength is increased with time increasing, the maximal compressive strength of 28 d reaches 4.72 MPa. After the improved loess of 28 d soaking 24 h, the greatest strength is 2.93 MPa, with high water resistance, can meet the requirements of high-speed railway subgrade.(3)The laboratory experimental results of the improved loess(No.10-18),which slag powder20%, lime 5%, 8%, 10%, gypsum 3%, 6%, 9%. The cohesive force and friction angle can increase, but compared with improved loess(No.1-9), they have some decline, such changes show that reduce slag powder can affect the shear strength of improved loess. 7d unconfined compressive strength is more than 0.55 MPa, can meet the requirements of high-speed railway subgrade. After the improved loess of 28 d soaking 24 h, the greatest strength is 1.64 MPa, softening coefficient is smaller than the improved loess(No.1-9),indicating that water resistance is poorer than the loess of 20% slag powder. Comprehensive analysis the mechanical properties of No.1-18 improved loess, No.6(20% slag powder,10%lime,6%gypsum) is the best.(4)Study the improved loess subgrade of different proportions and establish ballastless subgrade model by Midas/GTS software for numerical simulation analysis, which the settlement of railway embankment in weight and upper static loads. The results show that the maximum settlements of improved loess subgrade with different proportions are less than15 mm, which can meet high-speed railway ballastless subgrade requires less than 15 mm.Numerical simulation verify the slag powder, gypsum and lime incorporated into the loess can reduce the settlement, to provide a scientific evidence for design of high-speed railway subgrade.