Some researchers have proposed or optimized a number of devices that can mainly be divided into two types: varying head and constant head. Studies on the laboratory testing method for the anisotropic effect of permeability are limited, mainly because there is currently no experimental equipment or test method available to measure the permeability of porous asphalt mixtures in different directions. To be precise, the water flow inside the pavement is susceptible to horizontal permeability rather than vertical permeability because the pavement is a two-dimensional surface with a thickness of 4РІР‚вЂњ6РІР‚вЂ°cm. It is no surprise that permeability anisotropy has been the key to evaluating pavement drainage. Past experience has shown that a large amount of flow occurred in the horizontal direction in coarse superpave mixes with thick lifts, whereas fine mixes with thin lifts tended to have more of a vertical flow. Researches have been carried out to investigate the permeability of porous asphalt mixtures.

Generally, the void ratio of porous asphalt pavement is more than 18% and is even as high as 23% or 25% to ensure drainage.

Therefore, the depiction of permeability evaluation influenced by clogging is a facing challenge and it is worthwhile devoting much effort to this. There is not enough literature that evaluates permeability and the effect of clogging. The pavement tended to be impermeable when the pores of pavement become clogged and it performs as an ordinary dense-graded asphalt pavement, so the advantages of good performance on drainage are no longer comprehended. The clogging characteristic of the porous asphalt pavement is a common problem owing to deposition of sediments on the pavement surface, the storm water, and vehicles. During the service life of permeable pavements, there are many factors that cause the early decline in drainage, including the decrease in voids caused by clogging. A durable and sustainable drainage capability offers economic and social benefits in an environmentally friendly manner. In addition, permeable pavements continue to represent an excellent form of source control for both surface runoff and pollutants. The rapid removal of excess water is vital to ensure good soil and material behavior in layered pavement systems. The main function of porous asphalt mixtures is to eliminate pavement flooding. Porous asphalt mixtures play an essential role in permeable pavements as the material that is affected by moisture. Permeable pavements have recently received great attention for improving driving safety because of their good drainage performance. Under the action of clogging and driving load, a reasonable thickness of the upper layer and a drainage evaluation should be considered to improve road safety. In addition, the peak value of pore water pressure is also affected by the upper-layer height of the pavement. Moreover, the pore water pressure increased due to the reduction in voids and a high level of clogging. To avoid surface ponding, the drainage capacity coefficient (DCC) can be used to evaluate the maximum drainage capacity (MDC) influenced by clogging. The results indicate that the internally retained water should not be ignored because the semiconnected voids were filled with water rapidly at the beginning of permeability tests. The variation in pore water pressure was simulated by considering the decrease in voids and the increase in clogging grains. Then, finite element models for asphalt pavements with hydromechanical coupling were proposed based on porous media theory and BiotРІР‚в„ўs theory. To preliminarily reveal the decrease in permeability caused by clogging of permeable asphalt pavement, an innovative device was proposed to evaluate the anisotropy of permeability influenced by clogging, and the maximum drainage capacity without surface ponding can be obtained when the supplied water was controlled. The purpose of this paper is to report on the drainage of porous asphalt pavement evaluation method suited for use in analyzing clogging effect.

Porous asphalt texture