9.1.1 Numerical Modeling of Hydroplaning using Assumed Hydroplaning Tire Profile
9.1.1.3 Hydroplaning on Pavement with Transverse or Longitudinal Pavement Grooving
of the simulation results has been made against the past experimental data. It has been shown that the friction factors derived by the proposed simulation model agree with the experimentally measured data for both transverse and longitudinal pavement grooving.
The effects of pavement grooving dimensions on hydroplaning for both the transverse and longitudinal pavement grooving are studied. It is noted that in general, a larger groove width, a larger groove depth and a smaller center-to-center groove spacing would result in a larger hydroplaning speed and a higher friction coefficient at incipient hydroplaning for both transverse and longitudinal pavement grooving. It is also found that groove width is an important factor in reducing hydroplaning occurrences and a primary factor in groove design.
Groove depth is the next important factor followed by groove spacing. However, as the range of spacing adopted in practice is typically much larger than that for the groove width or depth, varying the groove spacing could be a more convenient measure in combating hydroplaning.
It is observed that transverse pavement grooving consistently gives a higher hydroplaning speed and friction coefficient at incipient hydroplaning as compared to longitudinal pavement grooving of the same groove design. However, it does not mean that longitudinal pavement grooving is not effective in hydroplaning prevention. It is found that certain longitudinal groove design would allow a noticeable improvement in traction control while others may not. The research also reconciles the conflicting arguments in past literature on whether longitudinal pavement grooving can improve skid number and hydroplaning potential. Through the use of numerical simulations, it is found that the conclusions in past experimental research were actually dependent on the groove dimensions used in the respective study. This shows that the use of the numerical hydroplaning simulation model is an effective and efficient way to analyze different pavement groove designs in hydroplaning analysis.
The design of pavement grooving has so far been based on experience and has been largely empirical in nature. Currently, most agencies provide guidelines on recommended groove dimensions. However these guidelines could not offer pavement engineers information such as the safety factor or safety margin against hydroplaning, resulting in a lack of understanding of the effectiveness of the designed groove dimensions against hydroplaning.
Since hydroplaning is a major safety consideration for pavement grooving design, it is of practical interest and desirable for pavement engineers or designers to be aware of the safety implications of a design. With the capability of the numerical simulation model to model hydroplaning on pavement surfaces with pavement grooving, the research is now capable of performing a rational study on the design and evaluation of transverse and longitudinal pavement grooving based on the hydroplaning consideration.
The concept of hydroplaning risk is introduced and is used as a mean to quantify the effectiveness of the pavement grooving against hydroplaning (for evaluation purpose) or as a safety margin (for design purpose). An evaluation procedure to determine the hydroplaning risk of a given transverse and longitudinal pavement grooving design has been developed to allow pavement engineers to evaluate the effectiveness of the existing pavement grooves in combating hydroplaning. A trial-and-error design procedure is developed to allow pavement engineers to select appropriate transverse or longitudinal groove dimensions based on a selected level of hydroplaning risk. The trial-and-error procedure is time-consuming and can yield more than one possible groove design that can satisfy the required hydroplaning risk level. Hence the use of hydroplaning risk tables in the design of transverse or longitudinal groove dimensions is advocated. A hydroplaning risk table would offer the designer flexibility in selecting a desirable design from the pool of feasible designs by incorporating other practical considerations.
Structure-Interaction
The hydroplaning simulation model developed in the first stage of this research have so far been able to describe hydroplaning on plane pavement surfaces with and without microtexture, and on pavement surface with longitudinal and transverse pavement grooving.
However, this model has a major limitation: the need to have an assumed tire deformation profile at incipient hydroplaning. The requirement of prior knowledge of the tire deformation profile has made the scope of potential applications of the model rather restrictive. For example, the developed model could not provide solutions to issues concerning the effect of water-film thickness, loading conditions on the predicted hydroplaning speed and more importantly, the modeling of wet-pavement skid resistance. Hence the second stage of the research focuses on the relaxation of the assumption of the input tire deformation profile by considering the full tire-fluid-pavement interaction problem. The key research findings are summarized as follows.