I. Project Overview

Main technical indicators of this project

1. The foundation design grade of this project is Grade A. Moderately weathered argillaceous siltstone is the bearing stratum, and the concrete cover thickness of the pile body should be ≥50mm.

2. The pile end of the compressive pile should penetrate into the bearing stratum not less than 1D, and the pile end of the uplift pile should penetrate into the bearing stratum not less than 2D.

3. After the pile hole drilling enters the bedrock, clear the hole and take samples in sections every 500 mm drilled; analyze the samples and prepare for final hole acceptance.

4. After the pile hole is formed, the sediment at the bottom of the hole must be removed. After hole cleaning, the sediment thickness must not exceed 50mm, and underwater concrete should be poured immediately.

5. The concrete strength grade of the cast-in-place piles in this project is C35 underwater concrete, with a slump of 180-220mm.

6. Quantity (1) Support piles: 337; (2) Engineering piles: Building 1: 101, Building 2: 86, Building 3: 91, Building 4: 79, Building 5: 126, Building 6: 10, Building 2: basement 216; total: 711.

II. Reverse Circulation Equipment

Reverse circulation process principle: Mud flows from the mud pit into the drill hole and mixes with drill cuttings. Under the suction of the vacuum pump, the mixture enters the slag inlet of the drill bit, passes through the inner cavity of the drill pipe and the slurry discharge control valve, and is discharged into the sediment pool. The mud is recycled after sedimentation.

Reverse circulation: Mud naturally flows or is pumped into the hole from outside the pipe, and then is sucked up to the surface together with soil slag.

III. Process Flow of Reverse Circulation Bored Cast-in-Place Pile

(I) Pile Position Setting Out

IV. Key Points of Quality Control

(I) Pile Position Control

(II) Pile Verticality Control

(III) Pile Length Control

(IV) Control of Pile Penetration Depth into Rock

(V) Control of Sediment Thickness at Pile Bottom

(VI) Pile Integrity Control

(VII) Pile Top Elevation Control

(VIII) Quality Requirements

V. Key Points of Safety Control

(I) Mud Pit Protection

1. Conduct safety training and technical briefings for construction technicians and workers before construction.

2. After the drilling machine is in place, conduct a comprehensive inspection of the drilling rig and supporting equipment. The drilling rig must be installed stably and firmly; the drill frame should be equipped with diagonal bracing or guy ropes.

3. The quality and safety department, together with electricians, shall regularly inspect the cables used by the drilling rig. Joints must be firmly bound to ensure they are waterproof and leak-free. When moving the drilling rig, cables must not be squeezed.

4. When the drill bit is lifted near the bottom edge of the casing, reduce speed and lift smoothly to prevent collision with the casing and hooking the bottom edge of the casing.

5. For casings that have been buried but not yet drilled, or for completed piles where the casing has not been removed, install a top cover or lay a safety net for shielding.

6. Lifting operations shall be under the unified command of a designated person. Riggers participating in lifting must master the safety requirements of the operation, and other personnel shall have clear division of labor.

7. Strictly inspect the reliability and safety of all components of the lifting equipment before lifting operations.

8. In case of power failure or other special circumstances during operation, lower the heavy object to the ground; it must not be suspended in the air.

VI. Work Content of Pile Foundation Construction Workers

1. Identify pile positions: determine the pile number of the newly opened hole based on the set-out pile points and the laid steel rails.

2. Determine the pile diameter, pile top elevation, rail surface elevation, hanger bar length, empty pouring height, etc. according to the drawings, as shown below.

3. Confirm the placement of the machine position and the piling sequence, and handle emergencies (skip piling positions, analyze situations after concrete cannot be poured, etc.).

4. Identify rock samples, confirm whether rock has been entered, final hole, and whether there are interlayers.‍