August 19, 2022
Design Principle of High Pressure Jet Grouting Wall Protection Technology
In view of the leakage and collapse problems in the drilling of complex strata, especially in the drilling of multi-layer complex strata and deep complex strata, referring to the principle of high-pressure rotary jet grouting reinforcement of foundation, the high-pressure rotary jet grouting technology is introduced into the drilling of complex strata, and the conventional cement slurry perfusion method is changed to improve the effectiveness of cement slurry in the drilling of complex strata.
Structural Features of High-Pressure Rotary Drilling Tools
The drilling tool consists of jet grouting body, nozzle, steel ball, drill bit, etc.
The nozzle is the key component of the rotary jet drilling tool, which converts the pressure energy of high-pressure liquid flow into kinetic energy. Its structure directly determines the size of jet flow energy and directly affects the radius of the consolidation body, that is, directly affects the plugging effect of wall protection.
Under the condition of high pressure and high speed, the jet from the nozzle has great energy per unit of time.
The influence of nozzle cross-sectional area on a jet is obvious. When the cone angle θ is 13 ° ~ 14 °, the flow loss is the smallest and the flow rate of the nozzle is larger. The nozzle diameter should be 3 ~ 5 mm.
Nozzle with M16 external thread buckle, screw into the jet body in time, according to different formation needs, convenient adjustment nozzle diameter.
2. Jet Grouting Body
The outer diameter of the jet is 65 mm, the inner diameter is 34 mm, and the length is 260 mm. Four M16 spiral holes are machined to connect the nozzles. The number of nozzles can be easily adjusted according to the needs of different formations.
3. Drilling Bit
It is a conical cemented carbide bit with three cemented carbides in the front and two through holes in the bottom, which is convenient to sweep holes when drilling under resistance. 32 mm conical surface in the drill bit, when high-pressure jet construction, put steel ball sealing.
The Formula of High-Pressure Rotary Jet Cement Slurry
Formula without flowing water
When there is no flowing water in the target layer, considering the time-consuming of the high-pressure rotary jet process and the performance of cement slurry, the cement slurry formula is water cement ratio 0.5 ( ash: cement 96 % + bentonite 4 % ), water reducing agent 1 %, water glass 2 % ~ 3 %. Bentonite mainly increases slurry workability and rheology, bentonite needs pre-hydration
Properties of the cement slurry: fluidity 190 ~ 210 mm, water separation rate 2 % ~ 4 %, initial setting time 4.5 h, final setting time 6.5 h.
Formulations with flowing water
When the target layer has flowing water, the SJP cement slurry can be used. The cement slurry has the characteristics of small initial consistency and little consistency increase with time. When the slurry begins to lose fluidity, the consistency has a sudden change at the time point. The formula is cement, water, and SJP additives. SJP additives include three kinds of additives. Additive 1 is a cellulose organic material, which is used to break the isolation state of cement particles by hydration products so that it can quickly participate in the reaction and generate dense cement between cement particles. Additive No. 2 calcium silicate early strength agent and No. 3 amide stabilizer are mainly used to control the reaction speed and degree of cement hydration. With different dosages of the three additives, the pumpable period of cement slurry can be adjusted in the range of 5 ~ 50 min. The initial setting of the cement slurry is 2 ~ 3 h, and the final setting is 2 ~ 3 h after the initial setting. The water evolution rate of cement slurry during consolidation is small, and the later strength is 10 % higher than that of pure cement slurry.