How does the RJP method work?
The basic principle of RJP method is the same as the other high pressure jet grouting drilling rig. A jetting fluid is pumped through the jet grouting nozzle at high pressure. This produces a high-energy "cutting jet" which erodes the soil from its natural position and mixes it with the binder suspension. By rotating and simultaneously retracting the jet grouting drill string, the cutting jet describes a tightly-spaced helix in the soil, resulting in a column-shaped space filled with binder suspension and soil. The binder causes this mixture to set and solidify, as a result of which load-bearing jet grouting columns are formed.
While the reinforcement mechanism is actually different. This method creates an improved cylindrical structure with a radius of 2000 to 3500 mm in the ground by rotating and pulling up a converging-type split two-stage jet system that injects ultra high-pressure water (aqua jet) and air, as well as ultra-high pressure hardening material (abrasive jet) and air from a monitor attached to the tip of a multi-pipe rod assembly.
Effectiveness of RJP method
RJP method can install grout columns with the diameter ranging from 3.1-4.6m at the depth from 14-10m in silty sand layer and silty clay layer. The former has fine content of 48%; the latter has the SPT-N value ranging from 5-10.
The fine content of the in-situ soil has a significant influence on the unconfined compressive strength of RJP grout column. For example, when the fine content of the grout column located in the silty sand layer is as high as 48%, the unconfined compressive strength is almost different from the grout column located in silty clay layer (fine content=80%). To increse the strength of grout columns in silty sand layers, the water-cement ratio of grout needs to be reduced.
Due to the large diameter of RJP grout column, the number of inclines jet grouting piles can be minimized and the quality of overlapping grout columns can be improved when grouting is carried out in complicated subsoil condition or limited space.