Scheme Module

Details & Technical Key Points

Problems Solved & Advantages

1. Equipment Selection

Adopt crawler-type single-tube high-pressure jet grouting rig (such as: XL-50). The crawler chassis enables self-propelled movement, adapts to muddy and rough terrain in the foundation pit, and allows fast relocation.

Solves equipment handling difficulties in narrow foundation pits and improves positioning efficiency.

2. Process Parameters (Single-Tube Method)

Design pile diameter: 600 mm

Jet pressure: 20–30 MPa

Lifting speed: 20–26 cm/min

Rotating speed: 20–25 r/min

Cement slurry: P.O 42.5 Portland cement, water-cement ratio 1.0, slurry density ≈ 1.49

Parametric construction ensures pile diameter and strength meet design requirements.

3. Construction Process

① Site leveling & slurry discharge trench: Clear obstacles, excavate slurry ditches and sedimentation tanks to collect returned slurry and prevent pollution.

② Survey & positioning: Total station setting out, marked with bamboo sticks + lime; pile position error ≤ 5 cm.

③ Rig positioning: Crawler travels to hole position, adjusted horizontally; verticality deviation < 1.5%.

④ Drilling & pipe insertion: Integrated drilling and pipe insertion; assisted sinking to design depth with 0.5–1.0 MPa low-pressure water jet to avoid nozzle clogging.

⑤ Slurry preparation: Mix cement slurry strictly at water-cement ratio 1.0, mixing time ≥ 2 minutes, filtered through 0.8 mm screen.

⑥ Jet grouting lifting: After reaching design depth, spray at the bottom for 30 seconds, then lift while spraying at set pressure (≈20 MPa), lifting speed (≈26 cm/min), and rotating speed up to pile top.

⑦ Pile head treatment: Slow lifting within 1 m of pile top to ensure compaction.

⑧ Cleaning & relocation: Clean pipelines, crawler moves to next pile position.

Standardized process ensures construction continuity and pile quality, reducing the risk of broken piles.

4. Quality Control

①Test piles: Conduct at least 3 process test piles before formal construction to verify and optimize parameters.

②Process monitoring: Record pressure, flow rate, and lifting speed in real time; grout return controlled at 10%–25%.

③Lapping treatment: When resuming after interruption, lapping length ≥ 1.0 m; interval between adjacent piles ≥ 48 hours.

④Pile inspection: Core drilling after 28 days to test strength and integrity; unconfined compressive strength generally ≥ 3.0 MPa.

Ensures continuous and uniform piles, meeting mechanical requirements for water stop or reinforcement.

5. Secant Pile Application

For water-stop curtains, use secant arrangement between jet grouting piles and bored piles, or between jet grouting piles. For example: 600 mm diameter jet grouting piles with 100 mm secant width to form a continuous soil-cement wall, effectively blocking groundwater seepage inside and outside the pit.

Solves water-stop challenges in water-rich strata during foundation pit excavation and protects the surrounding environment.