Professional Construction Guide: Cement Deep Mixing Pile Waterproof Curtain Technique

Technical Requirements for Construction

1. The case project’s waterproof curtain utilizes cement deep mixing piles with a triple-head Ø850@600 cross-section configuration. The construction method employs the “two-jet, two-mix” technique with overlapping sleeve joint connections.

2. Construction requires:

   • Triple-head mixing equipment

   • P.O42.5 ordinary Portland cement

   • Water-cement ratio of 1.5

   • Cement content of 20%

   • 28-day unconfined compressive strength ≥0.8MPa

3. Pile construction specifications:

   • Dual-direction grout injection (upward and downward mixing)

   • Uniform cement-soil mixture required

   • Standard mixing speed: 1m/min (reduced in silty soil layer③)

   • Repeat mixing speed: 1.0-2.0m/min

   • Additional grout injection at the pile bottom section

   • Water immersion is prohibited during sinking

4. Pre-construction requirements:

   • Underground obstacle detection is mandatory

   • Obstacle removal and backfilling with plain soil (no rocks or waste)

   • Proper equipment selection (especially power units and mixing tools)

   • Site leveling and layered compaction before construction

5. Construction continuity:

   • No 24-hour cold joints permitted

   • Cold joints require reinforcement marking

   • Joints exceeding 24 hours need jet grouting reinforcement

6. Tolerance standards:

   • Pile position deviation ≤30mm

   • Diameter variation ≤2%

   • Bottom elevation deviation ≤+50mm

   • Verticality deviation ≤1/300

7. Quality control measures:

   • First batch (minimum 3 piles) requires supervisor monitoring

   • Monitoring parameters: cement dosage, grout ratio (specific gravity method), pumping duration, mixing times, length, and verticality control

8. Compliance standards:

   • Technical Code for Soil-cement Mixing Wall (JGJ/T199-2010)

   • Relevant acceptance specifications

Construction Process Flow

Key Process Points

1. Site Preparation

   • Leveling and surface obstacle removal

   • Backfilling with compacted plain soil

   •  50-ton crane capacity foundation is required

2. Survey Layout

   • Coordinate benchmark positioning

   • Permanent/temporary marker installation

   • Survey verification and approval

3. Trench Excavation

   • 0.8m³ excavator for perimeter trenching

   • Continuous obstacle removal

   • Proper spoil management

4. Positioning Steel Placement

   • Vertical trenches: 200×200 steel (2.5m length)

   • Parallel trenches: 300×300 steel (8-20m length)

   • Secure welding connections

   • Special H-beam placement at corners

5. Pile Positioning

   • 1200mm center spacing for Ø850 piles

   • H-beam surface marking with red paint

6. Equipment Setup

   • Stabilization and alignment verification

   • Plumb bob verticality control

   • <5cm positioning tolerance

Mixing Speed and Grout Control

1. Operational parameters:

   • Sinking speed ≤1m/min

   • Lifting speed ≤2m/min

   • Bottom section extended mixing

   • Comprehensive recording system

2. Grout preparation:

   • On-site mixing platform

   • Adjacent 100㎡ cement storage

   • P.O42.5 cement with a 1.5 water-cement ratio

   • 1.5-2.5MPa injection pressure

   • 28-day strength ≥0.8MPa

Construction Sequence Methods

Method 1: Skip-trench Double-hole Full Mixing

• Standard connection approach

• Construction sequence: 1－2－3－4－5

Method 2: Single-Side Compression Connection

• For corner sections or construction breaks

• Shadow areas indicate overlap drilling

• Suitable for N-value <50 soils

• Ensures continuous waterproofing

Critical Challenges and Solutions

Cold Joints

• Causes: Power/water interruption, operational delays

• Solution:

  • Plain pile reinforcement at the joint exterior

  • Timely remediation (<24h vs >24h protocols)

  • Special drilling precautions for remedial piles

Water Seepage

• Continuous monitoring during excavation

• Remediation methods:

  1. Drainage Pipe Method

     • Seepage point pipe installation

     • Rapid-setting waterproof mortar encapsulation

     • Post-curing pipe sealing

  2. Dual-fluid Grouting

     • Chemical grout preparation

     • Parallel pumping system (Y-connector)

     • Flow/pressure control to prevent leakage

Quality Assurance Protocol

Inspection Procedures

1. Material Verification

   • Certified mill test reports

   • On-site testing (including expired/damp cement check)

2. Precision Survey

   • Dedicated survey team

   • <5cm position tolerance

   • <±5cm depth control

   • <1/200 verticality

   • 5cm design margin compliance

3. Grout Quality

   • Continuous mixing (minimum 30s)

   • Specific gravity monitoring

   • Backup pump system readiness

Quality Control Measures

1. Site Optimization

   • Minimized equipment relocation

   • Continuous operation planning

2. Trench Specifications

   • Dimensional control for equipment access

3. Verticality Assurance

   • Track-mounted triple-axis rigs

   • Dual theodolite monitoring (90° configuration)

   • Real-time drill pipe observation

4. Mixing Integrity

   • Speed control for complete soil fracturing

   • Continuous grout monitoring

   • 1.0m remedial mixing for pipe blockages

   • 10-20s delay before resuming to prevent pile fractures

This professional construction guide provides comprehensive technical specifications for cement deep mixing pile waterproof curtain implementation, ensuring compliance with international engineering standards and quality assurance protocols. The detailed methodology covers all critical aspects from material preparation to quality verification, with special attention to challenging scenarios and their technical solutions.