This class covers all specialist geotechnical works that improve ground strength, stability, permeability, or prepare the foundation ground before and during construction.
While Class B (Ground Investigation) is about understanding soil conditions, Class C is about improving or altering soil and rock conditions to make them suitable for construction.
1. Purpose of Class C
- To include specialist ground treatment and support methods.
- To ensure proper measurement rules for complex geotechnical works.
- To separate these works from normal excavation, piling, and earthworks (covered in other CESMM classes).
2. Main Subdivisions of Class C (as per CESMM4)
C1. Ground Treatment (Stabilisation/Improvement)
- Grouting (cement, chemical, polyurethane).
- Pressure grouting, compaction grouting, jet grouting.
- Soil Stabilisation by lime, cement, fly ash.
- Vibro-compaction / Vibro-replacement (Stone Columns).
- Dynamic compaction (dropping heavy weights).
- Permeation grouting to reduce permeability.
- Measurement Unit: m³ of treated soil, or Linear metre (m) of grout holes/columns.
C2. Groundwater Control (Specialist Dewatering)
- Wellpoint systems.
- Deep wells with pumps.
- Cut-off walls (slurry walls, diaphragm walls, sheet piles for groundwater exclusion).
- Recharge wells to control drawdown.
- Measurement Unit: m of well installed, or per system Lump Sum (LS).
C3. Ground Reinforcement (Anchors, Nails, Micropiles)
- Soil nailing (steel bars drilled & grouted into soil).
- Ground anchors (prestressed or passive).
- Micropiles (small-diameter piles, <300 mm).
- Rock bolts and dowels.
- Measurement Unit: Linear metre (m) of installation, or Each (No.).
C4. Ground Freezing / Ground Heating
- Artificial ground freezing for tunnelling, shaft sinking, and deep excavations.
- Ground heating (rare, used in special projects like permafrost protection).
- Measurement Unit: Lump Sum (LS) or per treated length.
C5. Specialist Excavation Support
- Diaphragm walls (slurry trench, reinforced concrete).
- Secant pile walls.
- Contiguous bored pile walls.
- Soil mixing walls.
- Measurement Unit: m² of wall constructed, or m³ of soil replaced.
C6. Instrumentation and Monitoring (Specialist)
- Instruments for monitoring soil and structure performance:
- Inclinometers (slope/retaining wall monitoring).
- Settlement plates.
- Strain gauges, load cells.
- Piezometers (hydraulic/electrical).
- Measurement Unit: Each (No.) or Lump Sum (LS) for complete monitoring package.
3. Measurement Rules (CESMM4 Guidance for Class C)
- Items must state the process clearly (e.g., “Jet grouting 1 m diameter columns to 15 m depth”).
- Dimensions (diameter, depth, spacing) should be clearly specified.
- Ancillary works (pumping, spoil disposal, casing, flushing, consumables) are deemed included unless specified separately.
- Temporary works (like trial grouting, performance tests) must be described if required.
- Monitoring is measured separately.
4. Example BOQ for Class C
| Item No. | Description | Unit | Quantity | Rate | Amount |
|---|---|---|---|---|---|
| C1.1 | Jet grouting 1.0 m dia columns, 12 m depth | m | 300 | … | … |
| C1.2 | Soil stabilisation by lime/cement, 1.5 m depth | m² | 1200 | … | … |
| C2.1 | Installation of wellpoint dewatering system | m | 150 | … | … |
| C2.2 | Deep wells (300 mm dia) with submersible pump | No. | 6 | … | … |
| C3.1 | Soil nails, 25 mm dia bars, 10 m long | m | 500 | … | … |
| C3.2 | Rock anchors, 32 mm dia, tensioned, 20 m length | No. | 40 | … | … |
| C4.1 | Ground freezing system for shaft (30 m depth) | LS | 1 | … | … |
| C5.1 | Diaphragm wall 600 mm thick, 20 m depth | m² | 800 | … | … |
| C6.1 | Inclinometers installed in boreholes | No. | 4 | … | … |
| C6.2 | Settlement plates for embankment monitoring | No. | 10 | … | … |
5. Practical Example
👉 Suppose you are constructing a metro tunnel in soft ground:
- You need diaphragm walls (C5) for retaining the station box.
- Before tunnelling, you install jet grouting (C1) to stabilise weak soils.
- Wellpoint dewatering (C2) controls groundwater inflow.
- Ground anchors (C3) support temporary retaining walls.
- In difficult zones, ground freezing (C4) is adopted.
- During all this, instruments (C6) monitor settlement and wall deflections.
✅ In short:
Class C (Geotechnical & Specialist Processes) in CESMM4 provides a structured way to measure ground improvement, dewatering, reinforcement, support systems, and monitoring instruments. It ensures these complex activities are itemized and priced transparently in BOQ.
