Crack Of Highway Pavement And Low Temperature Crack Resistance Of Isolation Layer In Sichuan Tibetan Zone

Highway in Sichuan Tibetan zone?in Ganzi and Aba?is the critical corridor for the inland to enter Tibet.It has great significance in political and economic to promote the economic and social developing rapidly along the highway.As there are many pavement diseases in this area and the main failure mode is low temperature cracking,it is of great practical significance to analyze and study the low temperature crack resistance of asphalt concrete and pavement structure under the unique climatic conditions in this area.Asphalt concrete is a viscoelastic material in a large temperature range.The temperature stress caused by temperature falling can be dissipated by stress relaxation.However,in the lower temperature range,the asphalt concrete tends to be elastic.If the temperature falls rapidly or the surface material with poor relaxation performance,the thermal stress will accumulate and ultimately lead to low temperature cracking.In addition,the reflective crack will shrink and propagate repeatedly under the influence of cyclic temperature,and stress concentration will occur at the crack tip,which will eventually lead to fatigue cracking of the surface layer.Based on the above theory,in this paper,typical temperature field of pavement structure,low temperature crack resistance and fatigue performance of single-graded isolation layer,influence of homogeneous degree on crack propagation behavior,crack resistance of isolation layer of full section pavement structure and crack propagation of reflective crack under extreme climate conditions in Tibetan zone were studied in detail,and the main contents of this paper are as follows:1.Through collecting and analyzing the meteorological data of about 13 typical stations Tibetan area?in Sichuan province?in recent thirty years,combining with the investigation of pavement performance and pavement distress,and core sampling of G213?S450?S217,the paper deeply analyzed the pavement damage mechanism and influenced factors in Tibetan area.2.Through measuring typical cyclic temperature in Tibetan area and combining ABAQUS finite element software,the typical temperature field of pavement structure in Tibetan area in winter,summer and corresponding extreme conditions are analyzed,and the temperature state and characteristics of each structure layer are clarified,the effects of different meteorological parameters on temperature field are compared,which provides a basis or a guide temperature for the subsequent research.3.In this paper,BBR,DSR and LAS?Linear Amplitude Sweep?tests were conducted to analyze the creep and fatigue properties of single-graded isolation layer at low temperature,and the correlation analysis of low-temperature evaluation index(modified low temperature grading index:?35?T_c?index based on stiffness modulus principal curve:S_S-t?energy index:W _ls?7?t?8??relaxation time:??composite flexibility:J?index parameter based on black space:G&R,etc.)was carried out to choose the the most suitable indirect evaluation indexes of low temperature crack and fatigue resistance of single-graded isolation layer structure in Tibetan area.The high temperature performance of single-graded isolation layer was verified by using strain recovery rate?R?and non-recoverable creep compliance(J_nr)combined with multiple stress repeated creep recovery test.Meanwhile,the paper combining OT?Overlay Test?test and four-point bending fatigue test using isolation layer specimens to analyze the crack and fatigue resistance performance of single-graded isolation layer structure,and the direct evaluation index of low temperature crack and fatigue resistance of isolation layer were chosen.4.In the numerical analysis of crack propagation based on homogeneous degree,the criterion of‘basic element'was introduced into the division of non-uniform material elements,and the mechanical parameters such as elastic modulus,Poisson's ratio and other strength parameters are randomly assigned according to Weibull distribution,so as to characterize the randomness and non-uniformity of the distribution of material defects,meanwhile,asphalt concrete beam bending test and Marshall splitting test,the influence of homogeneous degree on crack propagation behavior and the stress distribution were systematically analyzed,which are helpful to understand the cracking and failure mechanism of asphalt concrete,and could also provide some reference for subsequent design and research.5.Reflective crack growth models of full section asphalt pavement structure under extreme temperature field were established with ABAQUS finite element software?Including initial defects?,then based on saturated hysteresis energy,the effect of isolation layer on crack resistance of asphalt pavement structure is analyzed with different thickness conditions of isolation layer as an example.At the same time,the crack resistance of isolation layer,the crack initiation and propagation life,propagation path and propagation law of reflection crack were analyzed based on different isolation layer parameters,different temperature drop amplitude and non-uniform settlement equation,in addition,the crack damage characteristics of pavement structure in Sichuan Tibetan was studied in depth.