Study On The Detection And Influence Factors Of Transverse Cracks In The Water-Stable Layer Of Expressway Subgrade

Transverse crack is one of the main damage types of subgrade cement stabilized macadam base(referred to as subgrade water stable layer),and it is also the most common crack.It is widely distributed and greatly shortens the service life and performance of the road.Especially in the large temperature difference cold and arid areas such as northwest and northeast China,the problem of transverse cracking of subgrade and pavement is more serious,but there are few studies on the cracking of water stable layer of expressway subgrade in this area.Zhangbian Expressway,namely Zhangye-Biandukou Expressway,is an important part of the G6 Beijing-Tibet Expressway connecting line.It is located in a high-altitude cold and arid area.The temperature difference between day and night and season in the area is large,which is more likely to lead to the cracking of the water-stable base In the form of reflective cracks,it is manifested in the surface layer of highway asphalt,which seriously affects the highway capacity and service life.Based on Zhangbian Expressway,this paper studies the transverse cracking of water-stable base.In order to find out the development characteristics of transverse cracks in subgrade water-stable layer in alpine region,find a suitable detection method for transverse cracks in water-stable layer,and determine the influencing factors and thresholds of transverse cracks in water-stable base,this paper mainly studies the following contents.(1)The integrity and quality of water-stable layer core samples of large thickness paving and layered paving subgrade were compared.(2)The transverse cracks of subgrade water-stable layer are measured,photographed,digitized,statistically and fractally analyzed.The basic characteristics of transverse cracks of subgrade water-stable layer,such as nature,scale,shape and development degree,are quantitatively studied.At the same time,the differences of transverse crack development characteristics of subgrade water-stable layer in different geographical environments(terrain height difference,temperature,etc.)are compared,and the differences of transverse crack development characteristics between large thickness paving and layered paving are compared.(3)Infrared thermal imaging technology is used to detect the cracks in the water-stable layer.The detected images are processed by self-programming to obtain the contour map of crack temperature.(4)Combined with the actual situation of on-site construction,through laboratory tests,the effects of different cement content,water content,gradation and maintenance methods on promoting early strength,moisturizing,heat preservation,water saving and inhibiting micro-cracks of subgrade water-stable layer are studied,which provides theoretical support for optimizing the curing process of subgrade water-stable layer.Through the above research,the following research results are obtained.(1)The integrity of subgrade water stable layer with large thickness paving process is obviously better than that of layered paving.(2)The development of cracks has a significant correlation with the paving process and altitude.The higher the altitude is,the more cracks are developed,and the thicker the paving layer is,the more cracks are developed.(3)Through the thermal infrared and detection of transverse cracks,the crack boundary of the water stable layer can be clearly determined,and the micro cracks at the end of the cracks and the potential damage areas around the cracks that cannot be monitored by the naked eye or ordinary optical imaging can also be detected.(4)Under the influence of a single factor,the compressive strength of the water stable layer increases with the increase of cement content or water content,but as the influencing factors continue to increase,the compressive strength growth rate slows down;the strength of the water stable layer specimen is generally high when using geotextile maintenance,and the strength is the lowest without any maintenance condition.With the increase of the proportion of large particles,the strength of the water stable layer sample decreases slightly.At the same time,when the cement content is less than 4.6 %,the moisture content is less than 4.3 %,and the maximum particle size content is more than 32.1 %,the compressive strength of the water stabilized layer does not meet the construction requirements when one of the conditions is met.