Failures of Concrete Slit Drains Caused by Negative Effect of their Erroneous Integration Into Surrounding Multi-Layer Road Systems

Concrete slit drains (also known as slot drains – see fig. 1,2) are being used for the draining of highways and roads, as well as for large handling and parking areas. Recently, this system of drainage has become increasingly applied, which does, however, bring with it an increased incidence of failures. The study concentrates on the failures of concrete slit drains, caused by the negative effect of their erroneous integration into surrounding multi-layer road systems. It starts with a theoretical analysis of the problem, i.e. the negative influence of thermal expansivity of surrounding concrete slabs on slit drains, the impact of their shrinkage, and the co-action of these factors. In addition, it presents a computer numerical analysis of a concrete slit drain loaded by the pressure of adjacent concrete slabs exposed to temperature effects and shrinkage. The most frequent stresses are modelled and the relevant results introduced. Furthermore, the authors introduce a real case from construction practice illustrating extensive damage to concrete slit drains, followed by the relevant computer simulation. From the computer simulation and lab tests it follows that the failures of concrete slit drains can be easily caused by deformations of the concrete slabs constituting the surrounding multi-layer road system. Thermally-induced expansions and contractions, as well as concrete shrinkage, produce, in non-dilating connection, stress in the link between the multi-layer road system and the lateral walls of the slit drains. The slit drains are highly sensitive even to a very small malfunction of the expansion joints (e.g. clogging of the slit by solid materials), or their bad installation. It is apparent that failures (cracks) in the slits arise even by the slight compression of a slit drain (to the order of tenths of a millimetre). The analysis presented shows the necessity for a careful installation of expansion joints during the placement of the slit drains into the surrounding multi-layer system, which could otherwise induce horizontal pressures on the drains. The study is concluded by recommendations for designers.