Mechanical Behavior Of Fully Weathered Red Mudstone And Lime Treated Red Mudstone

Based on Sichuan’s 14th Five-Year Plan and the outline of the 2035 Vision,a modern integrated transport system will be built.The province is planning to build a number of railway lines with Chengdu as the centre.However,it is difficult to guarantee the use of high quality subgrade filling for the entire railway line near Chengdu Plain.And it is of great importance for the construction of railways around Chengdu if the red mudstone spoil from the tunnel caverns and road graben excavations along the outer ring of Chengdu can be used as subgrade filling.Based on this,a study on the mechanical properties of the fully weathered red mudstone and its improved filler was carried out.In this paper,a series of basic physico-mechanical tests were carried out to investigate the basic physico-mechanical properties of the fine-grained fillings of the fully weathered red-layered mudstone in Tianfu New District,Chengdu.On this basis,static triaxial tests were carried out to investigate the effects of confining pressure,water content,compaction degree,curing age and lime mixing ratio on the fine-grained fill of the fully weathered red mudstone.Dynamic triaxial tests on the saturated red mudstone filling were carried out,and the main research contents and results are as follows.（1）The fully weathered red mudstone fine-grained filling group is C₃,when the compaction degree is K95,the optimal water content state to meet the requirements of the subgrade filling of high-speed railway,but the strength and stiffness significantly reduced after encountering water.it is still recommended to use the fully weathered red mudstone improved filling to fill the subgrade.（2）A hyperbolic model for predicting the stiffness of red mudstone and its modified filling under low confining pressure considering dry density,water content,lime content and stiffness decay coefficient p.The model could provide some reference basis for the design of red mudstone and its modified filling for railway subgrades.（3）The fully weathered red mudstone saturated filling was progressively damaged in the process of cyclic loading,and did not have the Compression characteristics of the coarse-grained filling in railway subgrades.Its accumulated deformation could be specifically classified into three types:plastic stable（Range A）,plastic creep（Range B）and incremental damage（Range C）,and two methods which were respectively critical dynamic stress method and cumulative strain rate method,were proposed to classify the stability limits of the red mudstone fine-grained filling.The dynamic stress ratio under the stability limit of the saturated red mudstone filling was found to show an exponential decay with the increase of the confining pressure,and the bearing capacity of the red mudstone subgrade filling was overestimated when the static strength index was used to design it.（4）The softening characteristics of the red mudstone filling in water were significantly suppressed by the addition of lime.The 4%lime modified specimens can also meet the strength requirements of the filler in the surface layer of the subgrade bed after immediate maintenance for 1 day,but the improvement of the strength and stiffness of the red mudstone saturated specimens by lime has a certain limit.