Cement injection method for reinforcing soil, using lances and piezometric tubes for recirculating excess water in grout

摘要

Grout is injected into the soil using lances (5) and excess water in the grout is removed via piezometric tubes (9) driven into the soil, so that it can be recirculated and used for mixing with fresh grout components. The lances and piezometric tubes are removed from a central excavation region (31) kept dry using a drainage pump (25), which is temporarily removed to monitor the water table (30) around this region. A method for reinforcing soil by injecting cement with additives comprises the following steps : (i) a row of lances with a perforated periphery are introduced into the soil at a variable angle of 0-45 degrees relative to the vertical, so that the outer lances have the largest angle and the central lances have the smallest angle, in order to cover an area of 0.5 x 0.5 m and 1 x 1 m ; (ii) a row of piezometric tubes are introduced vertically into the soil, the number of these tubes being equal to ca. 5 % of the number of lances ; (iii) grout is pre-injected through a row of holes (20) in the lances, at a pressure of 2-6 atmospheres, the grout having been prepared in a mixing device (3) belonging to a system with an injection pump (2) and compressor (1), and the grout also being circulated inside the injection needles (6) movably mounted inside the lances and ending in plugs ; (iv) the lances and piezometric tubes are removed from a central excavation region, which is then excavated whilst being kept dry using a drainage pump ; (v) the water table in the area around the central excavation region periphery is monitored by temporarily removing the drainage pump ; and (vi) repeated injections are made, followed by a repeat of step (v), until the desired water table is reached. The grout comprises 1-5 g/l aluminium sulphate, 1-5 g/l barium sulphate, 1-5 g/l magnesium sulphate and 0-10 g/l Portland cement with a high calcium carbonate content, the latter being absent if the soil has a sufficient calcium content. The grout components are added to the mixing device via a dosing valve which is connected to a water storage vessel (4) and which is used to collect excess water present in the grout via the piezometric tubes, which have recirculation pressure gauges (22) and thermometers (23) at their top ends. Injection penetration and reactivity can be regulated so that water recovery is 30-50 % and the temperature increase is kept at 60-80 degrees C.