Experimental Study Of The Dynamic Properties Of Swamp Turfy Soil Under Cyclic Loading

Turfy soil is a special type of soil widely spread in the northeast of China,the Qinghai-Tibet Plateau,Sichuan and northwest Yunnan.It is a product of plant residues that have been formed through long-term geological action and complex biochemical processes with the development of bogs,and the development environment is usually characterised by low-lying terrain,abundant precipitation,a high groundwater table and the growth of water-loving plants.Due to its special environment and complex development process,it incorporates a large number of organic matter,incompletely decomposed plant roots,grass and wood fibres,and has a high moisture content,high organic matter content,large porosity and low strength properties.At present,the rapid development of line construction in the eastern part of Jilin,such as the Dunbai highspeed railway and the Heda Expressway,some sections of which inevitably pass through the distribution area of the turfy soil,the special characteristics of the low strength and high compressibility of the turfy soil may bring certain safety hazards to the normal operation of the motorway and high-speed railway.This paper investigates the stress-strain pattern and dynamic deformation characteristics of turfy soils under cyclic loading by means of the GDS dynamic triaxial test method in the area of Dunhua City,eastern Jilin Province,to provide a reference basis for the maintenance of existing highways and the design and construction of new routes in the future.The main research work and conclusions are as follows:(1)The basic physicochemical property indexes of the turfy soils in the study area were determined by conventional indoor physical tests,and the particle analysis of the turfy soils was carried out to analyse the depth distribution pattern of the basic properties of the turfy soils and to provide reference for the scheme design of the dynamic triaxial tests.(2)An indoor dynamic triaxial test was designed to investigate the stress-strain relationship,dynamic modulus of elasticity and dynamic damping ratio of the turfy soil under different consolidation conditions and different horizontal dynamic loads by applying dynamic loads in multiple stages.It was found that the consolidation pressure,organic matter content,vibration frequency and number of vibrations had certain influence on the dynamic characteristics of the turfy soil.The organic matter content and consolidation pressure change the internal structure and pore space of the soil,while the frequency and number of vibrations affect the force state of the soil,thus influencing the degree of soil deformation,load resistance and energy dissipation.(3)The effects of different stress levels and organic matter contents on the cumulative strain and cumulative dynamic pore pressure and the evolution of the hysteresis curves of turfy soils under long-term cyclic loading were investigated.The analysis of the reasons for the pattern reveals that the stress level and organic matter content of the turfy soil affect its structure,thus influencing the deformability and permeability of the soil,and therefore the cumulative strain and dynamic pore pressure show a certain regularity with the variation of the influencing factors.(4)A variety of empirical models of cumulative strain were used for the prediction of cumulative strain in turfy soils under cyclic loading.By fitting the data obtained from the indoor dynamic triaxial tests and adding the influencing factors such as surrounding pressure,organic matter content and initial partial stress to the parameters of the empirical model,an empirical model that can predict the cumulative strain of the turfy soil under long-term cyclic loading was obtained.The part of the test data that was not involved in the fitting was selected and compared with the model prediction results for verification,and the overall agreement was good.