Criterion of vehicle stability in floodwaters based on theoretical and experimental studies

Vehicles parking on streets or roads can cause various hazards to people and property when they are swept away by urban floods. It is therefore appropriate to investigate the criterion of vehicle stability for such flood conditions, especially for different scenarios and where the criterion of vehicle stability is usually represented by the incipient velocity for the vehicle. In the current study, different forces acting on a partially submerged vehicle are outlined, together with the corresponding expressions of these forces, and a mechanics-based formula of incipient velocity is given for partially submerged vehicles under different orientation angles. About 200 runs of flume experiments were conducted to obtain the conditions of water depth and corresponding velocity at the threshold of vehicle instability for three orientation angles, using two types of die-cast model vehicles at two model scales. Experimental data obtained from the large-scale model vehicles were then used to determine two parameters in the derived formula. Finally, incipient velocities for three vehicle orientation angles were estimated using two different approaches, including predictions using the scale ratios from the small-scale model vehicles and computations based on derived formula using the prototype vehicle parameters. These critical conditions for the prototype conditions, based on the scale ratios, compared well with the calculations obtained using the derived formula, which guaranteed the predicative accuracy of the formula. In addition, the effect of different ground slopes on the vehicle incipient motion was also investigated, using similar experiments and based on the theory of similarity, which indicated that the incipient velocity for a small passenger vehicle on a ground slope of 1:50 was about 25 % lower than the value on a flat ground for an incoming depth of 0.25 m.