Stabilisation of estuarine silt with lime and/or cement

The tidal barrage situated at the mouth of the river Rance, near Saint Malo (France) has led to a considerable silting upstream of the barrage. The deposited material is fine estuarine silt which is frequently dredged to maintain navigable channels; the use of this material is only possible after stabilisation. This study evaluates the possible use of this material as a sub-base for lightly trafficked local roads; therefore the stabilisation has to achieve the required geotechnical characteristics. Physico-chemical characterisation of the silt was carried out using SEM with XRD. The estuarine deposit comprises clay, silt and sand; the characteristics of this material result from its mineral composition and its high organic content. Stabilisation tests were carried out with various mixtures of quicklime, Portland cement and a mixture of both. The results of the tests show an increase in the unconfined compressive strength and the CBR value with both lime and cement treatments. The characteristics of the deposit with lime–cement mixes were superior to those obtained with lime only and cement only treatments. Finally it is concluded that the estuarine silt has the potential to be stabilised to a standard suitable for use as a road sub-base; however further testing is required before proceeding to field trials.