Study On Structural Stability And Application Of Cold Resistant Layer Subgrade In Seasonal Frozen Region

Freezing damage is very common on roads in seasonally frozen regions and frost heaving and thawing settlement of subgrade is one of the most typical freezing damage,which seriously affects the service life of roads in seasonally frozen regions and increases the cost of road maintenance.How to improve the service performance of road in seasonal frozen region and reduce frost heaving and thawing settlement disease of subgrade in seasonal frozen region has become a practical problem to be solved urgently.Under the action of negative temperature gradient in winter,the water in the subgrade migrates to the top surface of the subgrade and freezes into ice under the action of negative temperature.The change of water from liquid to solid causes the volume to increase and compresses the surrounding structure,thus forming the phenomenon of frost heaving.In spring,with the rise of temperature,the frozen soil melts gradually to form a saturated layer,which causes the void between the roadbed and the cushion.Under the action of driving load,the water in the saturated layer and the subgrade filler are extruded out of the road structure,leading to grouting.The frost heaving and thawing settlement problem seriously affects the stability of subgrade.At present,the commonly used disposal measures include improving the soil quality of subgrade,heat preservation method,and improving the structure of subgrade and pavement,etc.These methods can improve the frost heaving and thawing settlement of subgrade to a certain extent.Further research is needed to realize green,environmentfriendly and efficient temperature isolation methods by combining regional advantages.With the continuous development of oil shale resources,a large number of oil shale waste residues have accumulated into mountains,posing a threat to the surrounding ecological environment.In recent years,national macro-control and environmental protection have restricted the exploitation of river stone,and the sand and stone materials used for road construction are increasingly scarce.It is urgent to find new road construction materials to replace sand and stone materials to relieve the shortage situation.Based on the National Natural Science Foundation of China(51578263)and the Science and Technology Project of Jilin Province Transportation Department(2017ZDGC-6),aiming at the problem of frost damage of subgrade in seasonal frozen region,from the point of view of improving subgrade stability,this paper puts forward a method of using cold resistance layer subgrade to solve the problem of frost heaving and thawing settlement of subgrade in seasonal frozen region,which realizes the reuse of waste oil shale waste residue and alleviates the current situation of shortage of sand and gravel materials.Among them,the cold resistance layer subgrade is extruded polystyrene foam plate(XPS plate),oil shale waste residue and fly ash modified silty soil.The material selection,structure design and performance test of cold resistance layer subgrade were carried out by combining theoretical analysis,indoor and outdoor test and numerical simulation.This paper analyzes the water-temperature distribution and dynamic response law of the subgrade with cold resistance layer under the environment condition of seasonal freezing zone,and successfully applies the cold resistance layer to the real project.The practical application effect of cold-resistant layer subgrade was evaluated by in-situ loading test,and the numerical simulation method was used to supplement and improve the evaluation of practical engineering application effect of cold-resistant layer subgrade,which provided reference for the application of cold-resistant layer structure in seasonally frozen subgrade.The main research contents of this paper are as follows:(1)Based on the analysis of the heat flow distribution in the road environment,in order to reduce the heat exchange between the surface heat flow and the subgrade and improve the frost resistance stability of the subgrade filling,the cold resistance layer subgrade form using XPS plate and modified soil was proposed.The basic performance parameters of the XPS plate and the modified soil were determined by experiments,and the structure of the XPS plate was calculated according to the thermal resistance equivalence principle.The modified soil is oil shale waste residue and fly ash modified silty clay,which is a new type of subgrade filling with outstanding frost resistance and stability,excellent road performance and the ability to realize the reuse of waste resources.(2)The indoor and outdoor cold-resistance tests of the cold-resistance layer subgrade were carried out,and the cold-resistance performance of the cold-resistance layer subgrade was evaluated by comparative analysis.The indoor test realizes the precise control of freezing conditions through one-way freeze-thaw test system and evaluates the cold resistance characteristics of the subgrade with cold resistance layer.Based on the indoor test,the outdoor model test was carried out to further explore the cold resistance performance of the cold resistance layer subgrade in the natural environment,which could provide data reference for the actual engineering application.(3)To evaluate the dynamic response characteristics of the cold-resistant subgrade,the dynamic response tests were carried out.The dynamic response test of outdoor modified soil was carried out to explore the dynamic stress variation rule of the modified soil under natural freeze-thaw environment,so as to provide data support for solving the problem of frost heaving and thawing settlement from the perspective of dynamic response.Indoor dynamic response test of cold-resistant layer subgrade was conducted to explore the dynamic response rule of cold-resistant layer subgrade under different load conditions and evaluate the dynamic stability of cold-resistant layer subgrade.(4)On the basis of the research on the characteristics of cold resistance and dynamic response of the cold resistance layer subgrade,the engineering application research of the cold resistance layer subgrade is carried out to realize the transformation of the research results to the engineering.The construction technology and economic benefit of cold resistance layer subgrade in engineering are studied,and the engineering feasibility of cold resistance layer roadbed is evaluated.Sensors are placed in the real project,and the performance parameters of the cold-resistant subgrade is evaluated by collecting the temperature data of different freezing periods and the dynamic response data of in-situ loading tests.(5)The ABAQUS finite element model of actual engineering was established to calculate the temperature field and dynamic field respectively.By analyzing the annual temperature distribution law of engineering and the distribution law of dynamic stress and displacement under dynamic load,the application effect of cold resistance layer subgrade in engineering is fully displayed.This chapter is a supplement to the evaluation of engineering application effect of cold resistance layer subgrade.