Construction Technology of High-Pressure Jet Grouting Pile

Construction Technology of High-Pressure Jet Grouting Pile

High-pressure jet grouting pile construction technology was first proposed in Japan in the 1970s, it is based on hydrostatic grouting, the introduction of hydraulic coal mining technology, and the development of the use of jets to cut and stir the ground, changing the structure and composition of the original stratum, while filling cement slurry or composite slurry to form a solidified body, in order to achieve the purpose of strengthening the foundation and anti-seepage water.

Application Scope

1. It is less affected by the soil layer, soil particle size, soil density, hardening agent viscosity, and hardening time of hardening agent, and can be widely used in various soil layers such as silt, muddy soil, clay soil, silty clay, ( sub-clay ), silty soil ( sub-sand ), sand, loess and plain fill or even gravel soil in artificial fill.

2. Can be used as both existing buildings and new building foundation reinforcement, can also be used as foundation seepage; it can be used as temporary measures in construction ( such as deep foundation pit sidewall retaining or water retaining, waterproof curtain, etc. ), can also be used as foundation reinforcement and anti-seepage treatment of permanent buildings.

3. When used to treat peat soil or groundwater with erosion, the groundwater flow rate is too large and has gushed water foundation engineering, its applicability should be determined by test.

Process Principles and Design Requirements

1. Reinforcement Principle
The high-pressure jet grouting method uses the drilling rig to drill the grouting pipe with the nozzle into the predetermined position of the soil layer and makes the slurry or water and ( air ) become 20 ~ 40 MPa high-pressure jet from the nozzle, punching, disturbing and damaging the soil. At the same time, the drill pipe gradually increases at a certain speed, and the slurry is forced to mix with the soil particles. After the slurry is solidified, a cylindrical consolidation body ( i.e. rotary jet pile ) is formed in the soil to achieve the purpose of strengthening the foundation or water sealing and seepage prevention.

According to different injection methods, injection grouting can be divided into single pipe method, double pipe method, and triple pipe method.

Single pipe method: single layer injection tube, only injection cement slurry.

Double pipe method: also known as the slurry gas injection method, is the use of double grouting pipe at the same time the high-pressure cement slurry and air two kinds of medium jet transverse jet ejection, impact damage soil. Under the combined action of the high-pressure slurry and the airflow around the outer ring, the energy of the damaged soil increases significantly, and finally, a large consolidation body is formed in the soil.

The triple pipe method is a kind of slurry, water, and air injection method, which uses triple grouting pipes conveying water, air, and slurry respectively. A cylindrical airflow is surrounded by high-pressure water generated by high-pressure generating devices such as high-pressure pumps, and high-pressure water jet flow and air coaxial jet flow are carried out to cut the soil, forming a large gap. Then the cement slurry is injected into the cut and broken foundation at low pressure by the slurry pump. The nozzle is rotated and lifted so that the cement slurry and soil are mixed, solidified in the soil, and a large consolidation body is formed. The solidifying diameter can reach 2 m.
 

The reinforcement radius of the jet grouting method is related to many factors, including jet pressure P, lifting speed S, shear strength τ of reinforced soil, nozzle diameter d, and slurry consistency B. The reinforcement range is proportional to the jet pressure P and nozzle diameter d, and inversely proportional to the lifting speed S, soil shear strength τ, and slurry consistency B. The solidifying strength is related to the cement content and soil quality in unit solidifying.

Pile-forming Mechanism

The piling mechanism of high-pressure jet grouting includes the following five functions :

(1) High-pressure jet cutting destroys soil action. The jet flow pressure destroys the soil in the form of the pulse so that the soil has holes and the soil cracks expand.

(2) Mixed stirring. During the rotary lifting process, the drill pipe forms a gap at the back of the jet. Under the jet pressure, it forces the soil particles to move in the opposite direction ( i. e., the direction with small resistance ) to the nozzle and mixes with the slurry to form a new structure.

(3) Lifting replacement effect (triple tube method). When the soil is cut by a high-speed water jet, a part of the cut soil particles are discharged from the ground due to the introduction of compressed gas. The void left after the discharge of soil particles is supplemented by cement slurry.

(4) Filling and seepage consolidation. High-pressure cement slurry can quickly fill the gap between the punched groove and soil particles, consolidate by water evolution, and also penetrate into a certain thickness of the sand layer to form a consolidation body.

(5)Compaction effect. In the process of cutting a broken soil layer by high-pressure jet flow, there is residual pressure at the edge of the broken part, which can produce a certain compaction effect on the soil layer, so that the compressive strength of the edge part of the rotary jet pile is higher than that of the central part.