Horizontal U-Tube Road Heating System using Tunnel Ground Heat

Abstract

A temperature controlled pavement has a significant requirement for preventing road from freezing, and for avoiding winter traffic accidents at specific places. For example, a slip accident at tunnel mouth frequently occurs in winter and causes serious danger for human life and a heavy traffic jam. A Horizontal U-Tube (HUT) road heating system was introduced in order to prevent traffic accidents associated with a road freezing at the west side mouth of Nanaori-Toge tunnel, Aizu-bange, Fukushima Prefecture in Japan. A group of Horizontal U-tubes were buried at a depth of 1.2 m in the ground of the central part of the tunnel. The ground heat extracted by the HUT is injected into the anti-freezing pavement blocks made of concrete at the tunnel mouth through a heat injection pipe mounted in each block. Extensive field experiments have been carried out to investigate the pavement surface temperature, extracted ground heat and micro-meteorological characteristics inside and outside the tunnel. This paper presents the field experimental results at Nanaori-Toge tunnel regarding road anti-freezing and ground heat extraction performance of the HUT system. Even when air temperature was 4 °C lower than the freezing point, the anti-freezing pavement connected with the HUT could keep positive. It is concluded that the HUT road heating system using shallow ground heat in the tunnel is effective in preventing the road surface freezing at tunnel mouth.