This Master Thesis treats the issue of dealing with water in road constructions. The report consists of two articles and a part consisting of appendices.
The first article is a litterature review presenting relevant topics and issues when considering water affecting the unbound layers in road constructions. Initially, the litterature review focuses on how the climate is changing in regard of increased precipitation levels and expectations to the future scenarios. A focus of how the water enters and thereby affects the strength of the construction are considered. Several laboratory and field test results found in the litterature, made in order to understand the effects of water to the strength of the unbound layers, are represented and it is discussed which effects are to be considered, when road constructions are exposed to high amounts of water.
The main focus is on the bearing capacity (E-moduli) of the unbound layers. This is due to its importance when modelling the residual life of the construction. The Mathematical Modelling Of Pavement Performance (MMOPP) approaches the climatic effects when modelling the residual life by considering a reduction in E-values due to temperature changes. No considerations are made with regard to inundation caused by heavy rainfalls.
The second article represents a series of field tests performed at Aalborg University. The test series aims at investigating one cycle of rising/lowering a water table within a road construction at controlled steps allowing to correlate E-values and water table. The water table was determined with a sounding device at positions coincedent with E-values.
It is examined how the E-values are affected and to see if any permanent reduction is observed. The tests were performed on 30 cm of subbase sand and 20 cm of base gravel standard road construction materials on top of a limestone subgrade. E-values were determined by using the non-destructive Prima 100 light weight deflectometer. Test field was constructed with drainage pipes allowing inlet/outlet of water to be determined at controlled steps.
The reduction in E-values of the unbound layers will affect the maximum allowable stresses, according to the dansih guideline for designing road constructions leading to an accelerated deterioration if precautions are not made. One way of compensating for bearing capacity reduction, due to a water table inside the unbound layers, could be to increase the thickness of the upper layer reducing the stresses on the lower unbound layer affected by water.
Main results of the field tests series:
- E-values of unbound layers reduces linearly to ≈60% of its origin due to complete saturation when the water table reaches the surface level.
- The same linear trend was observed for both the reducing and the recovering of E-values when construction was later drained.
- A bearing capacity 'loss' of approximately 5-10% was observed when water table was lowered and hence raised for one cycle.
On the basis of the results it is suggested that:
- Future events of extreme precipitation should be considered when designing and maintaining road constructions.
- This could be implemented by increasing the upper layer's thickness on road locations vulnerable to inundation.
- Setting up some simple modelling of water tables for standard cross sections estimating the water table inside the construction at any given time during an extreme event, could be used to estimate the time span of bearing capacity loss and thereby determine the time horizon for road closure or narrowing.