Dry And Wet State Discrimination And The Application Of Water/Snow Accumulation Model On The Road Surface Of Jiangsu Expressway In Winter

With the development of social economy, the development of modern transportation grows rapidly. The transportation has become an important lifeline of the national economic development and social life. Adverse weathers pose a serious threat to production and living. Precipitation is a key factor which changes the pavement condition and affects the safety of transportation. The influence of rainfall process on traffic mainly concentrates on the visibility of front road and the skid-resistant performance of the pavement. Therefore, the research about the change of the pavement conditions during the precipitation events is very important.In order to ascertain the process of road water (or snow) accumulation, the change of road surface dry-wet conditions and the influence of meteorological factors on them, in this paper, a series of the observed data on the process of precipitation at Jintan Experimental Base was used as the input data of the Sass model which is modified for the quantitative calculation of the water and snow accumulation on the road surface of Jiangsu expressway by changing some physical parameters. This model is used to simulate the road surface water (snow) accumulation for two rainfall processes and a snowfall process in this paper. Based on the classification of the simulation results and the comparisons between the classification data, the records of automatic instruments and the artificial observations, the accuracy of the model in the simulations of road surface dry-wet conditions is verified and the influence of the meteorological factors on the road surface water (snow) accumulation is discussed. The results of the research show that: (1) The influence of meteorological factors on the road surface water (snow) accumulation is reflected on the direct impact of rainfall (snowfall) in the road surface water (snow) accumulation, however, the other meteorological factors have relative indirect impacts on the road condition through the effects of evaporation. (2) The modified Sass model is applicable to the simulation of road surface dry-wet condition with a high accuracy. It can be popularized and applied to the real-time monitoring and forecasting of road surface condition on an expressway. (3) In the process of water drainage on the road surface, the difference between the contribution rate of runoff and the contribution rate of evaporation is great in different periods. In terms of total quantity, the runoff played a main role on drainage. (4) There is a hysteresis of model output. On the one hand, it is related to the delay of the real-time data retrieved from meteorological instrument observation. On the other hand, our research presumes the road with no infiltration surface, which is different from the actual road. It leads to the difference between water and drainage process of simulation and actual road condition.To explore the accuracy of forecasting the state of the road, the data of GFS (Global Forecasting System) for 0.5°×0.5° on the reanalyzed and forecasting field and WRF (Weather Research and Forecasting model) for Version 3.7.1, a mesoscale numerical model is adopted for the simulations and diagnostic analysis of a rain event from January 13th to 14th in 2015. In this paper, the impact of patterns on the simulation results is analyzed as well. To take the advantage of WRF mode on the mesoscale numerical simulation, the impact on the simulation results for the different land surface parameterization schemes is mainly discussed. The coupled land surface parameterization schemes were the SLAB scheme, RUC scheme, NOAH scheme. (1) The WRF model has a good performance on forecasting precipitation cell, precipitation distribution and accumulated precipitation. (2) Due to the limited capacity that the resolution used in the experiment for simulating local small scale system. Because of the model’s problems and the different land surface parameterization schemes, the time of precipitation appearance in the simulation delays. (3)The simulation results of temperature (air and surface temperature) of three schemes are very close to the observed values. It indicates that the model has an advantage in simulating temperature, especially the pavement temperature. (4) Using the WRF model to simulate this precipitation process, and utilize the model output to calculate road state by model of road surface water (snow) accumulation, and the result of model values and the actual values are largely consistent. The results show that it is able to forecast pavement condition and provide reliable information for the state of road surface in traffic. (5) In general, NOAH is better than other two schemes.