High Pressure Jet Grouting
High pressure jet grouting (HPJG) is a well-established and versatile ground improvement technique used in geotechnical engineering and foundation engineering projects. It is routinely used to reinforce and stabilize the soil, to improve its permeability characteristics, and to strengthen the foundations of existing structures. HPJG is a method of injecting grout into the substrate at high pressure, which breaks the soil up into small particles and forms a grout column or “soil-cement” column.
High pressure jet grouting is typically used in applications where there are very weak or highly weathered soils, and where access for conventional grouting is difficult or impossible. It is commonly employed for the stabilisation of slopes, embankments and fills, as well as for the construction of foundation piles in areas where conventional drilling of piling slurry is not possible. It is also used to reinforce shallow excavation walls, create curtain walls and improve the strength of shallow foundations.
In terms of the overall HPJG process, the injection systems are extremely powerful and enable precise control of the grout pressure, gelation time and flow rate. The grout enters the ground at high pressure, and aerates and emulsifies the soils in a process known as “Jetting”. This process also displaces the soil and reduces the pore water pressure in the surrounding area, allowing for the quick formation of a grout column or “soil-cement” column, thereby providing rapid reinforcement and stabilisation of the soil.
The water-cement ratio of the grout should be carefully selected to get the desired characteristics. The grout should be of optimal viscosity and gel time before it is delivered at high pressures into the ground. The rheology of the grout also needs to be properly adjusted at each depth to ensure proper soil/cement interaction between the grout and the soil, ensuring that the soil strength characteristics are sufficiently improved for a stable, safe and cost effective project.
The procedure for jet grouting involves the penetration of a jetting nozzle which is connected to a high-pressure pump by a reinforced high-pressure hose. The grout is injected at high pressure into the soil, pulverizing and mixing with the soil particles to form a cemented column. The diameter of the jetting nozzle and the pressure at which the grout is injected is adjusted to account for the type of soil and the desired properties of the soil-cement column.
The jet grouting method has the capability to construct a soil-cement columns to depths of 10 metres below the surface, and the soil-cement columns can efficiently be placed in any soil, independent of the grain size. In addition, the strength characteristics of the soil-cement columns can be varied depending on the desired application.
In conclusion, high pressure jet grouting is a well-established and versatile ground improvement technique that can be used to improve several soil types in areas of difficult access. The process of injecting the grout at high pressures into the soil and forming soil-cement columns provides rapid reinforcement and stabilisation of the soil, improving its strength characteristics and reducing pore water pressure. This technique can also be used to construct foundation piles of up to 10 metres in depth, effectively improving the soil on the site.
