Sub-surface Drainage System Design And Application Technology In Freeway Asphalt Pavements

The analysis on some highway drainage status and drainage facilities'setting shows that after a period of using time, all kinds of diseases are inevitably to emerge in the high-type highway pavement, especially the water damage, which is the main natural factors. Many kinds of diseases such as subgrade depression, water scouring, slide, mudding, asphalt pavement raveling, stripping, map cracking and cement concrete pavement pumping, faulting, fracture are to do with the erosion of surface and underground water to some extent. Water intensifies the damage of subgrade and pavement structure, accelerates the deterioration of pavement serviceability, which shorten their service life. Therefore, whether the road drainage is unobstructed affects pavement operational performance and service life, which becomes an important factor.Installation of pavement structure subsurface drainage system can rapidly discharge the water over accumulated in the pavement structure outside of the subgrade and pavement structure. It is advantageous in improving pavement operational performance and enhancing its service life.Based on some studies at home and abroad, with analysis on water damage in pavement, design method of subsurface drainage system is discussed in this paper, and the major technical performance indexes is introduced too. Through much theoretical analysis of laboratory experiments, mechanism properties and composition design method of porous cement-treated macadam is obtained. With the pavement construction of Long-Da freeway in Shenzhen, the design and study of subsurface drainage system has been carried out in detail, and the design process of subsurface drainage system is obtained. Connected with cross section patterns of freeway, the design method of drainable base course system and edge drainage system which meet to request are given too. The aggregate grading and mixture ratio of porous cement-treated macadam are obtained based on accurate survey on material properties and lots of laboratory experiments. After the construction of experiment road, a summary of mixing, spreading, roller compaction and maintenance process about subsurface drainage system is made, and the analysis on the cost of construction about drainable base course is also carried. According to the test of coefficient of permeability, porosity and strength of compression about local test samples and core samples, the paper concludes that main performance index of subsurface drainage system has achieved the design anticipated effect.Operating Long-Da freeway for three years, the test results and road condition of it show that setting subsurface drainage system can improve the drainage performance, which is a valid method to solve the water damage in pavements, in rainy regions of south China.