Soft Soil Improvement is an in-situ technique to stabilise soft soil. Recently (1999), a research project at the Soil Mechanics Laboratory of the Ghent University (Department of Civil Engineering) was set up in order to evaluate the influence of the amount and type of grout injected in the soil at high pressures. A test site in Antwerp, called "Zandwinningsput" was chosen. Laboratory tests and model tests were carried out in order to evaluate the influence of grout content under well-controlled conditions. Field tests (CPT and SCPT) were executed in order to evaluate the extent of the improved zone, the variation of the strength characteristics around the injection point and the influence of execution parameters such as pressure, injected grout-volume and penetration speed.
Soft soil is mainly characterised by large deformations, low strength and high water content. Moreover, soft soils (like dredged fines) are often contaminated by heavy metals or by human activity. Soft Soil Improvement is an in situ technique developed and patented within the DEME (Dredging, Environmental Marine Engineering) Group. It was primarily designed for soil stabilisation in relation with dredging activities. But other applications like immobilisation of heavy metals or other contaminants in the soft soil have been investigated.
The mixing unit prepares the grout mixture to be injected. According to the required object, different type of agents can be used, such as cement, bentonite, fly ashes, line polymers, etc. A high-pressure pump sends the prepared mixture at pressures up to 400 bars to the injection unit. The computerised unit controls and registers all injection parameters: injection time, operational depth of the mixing blade, torque for the rotation of the mixing blade, down/up speed, rotational speed and the flow of the injected mixture.
