In-Depth Notes on Preliminary Work in Construction

Objective of Preliminary Work

  • Understand importance of preliminary work in construction.
  • Learn activities involved in site preparation:
    • Site clearance, grading, leveling.
    • Importance of securing the construction site.
  • Identify temporary facilities:
    • Site offices, storage areas, worker facilities.
  • Types of temporary structures:
    • Scaffolding, shoring, formwork, and their roles in construction.

Introduction to Preliminary Work

  • Definition: Preliminary work ensures smooth and safe workflow before actual construction.
  • Includes:
    • Site preparation.
    • Establishment of temporary facilities.
    • Implementation of temporary works.
  • Groundwater Control: Key focus area to prevent water-related issues that affect structural integrity and efficiency.

Main Components Covered

  • Site Preparation: Goals include:
    • Clearing and grading.
    • Establishing temporary facilities.
    • Implementing temporary work structures.
    • Groundwater control.

Purpose of Site Preparation

  • Clearing and Grading:
    • Remove vegetation, debris, and obstacles (rocks/old structures).
    • Level ground for proper foundation support.
  • Soil Testing and Stabilization:
    • Determine bearing capacity, moisture content; stabilize soil if needed.
  • Access and Drainage:
    • Set up routes for vehicles, drainage to prevent flooding.
  • Marking Boundaries and Layout:
    • Define site boundaries, ensure construction matches design plans.
  • Utility Setup:
    • Prepare for utilities like water, electricity, sewage connections.

Key Preliminary Activities

  • Site Clearance:
    • Remove trees, debris, and existing structures.
  • Surveying:
    • Boundary marking; employing professional survey equipment to define construction points.
  • Access Roads:
    • Construct temporary or permanent roads for material and machinery transport.
  • Fencing and Security:
    • Install barriers to secure sites and prevent unauthorized access.

Temporary Facilities

  • Definitions: Structures/services for the duration of construction projects.
  • Types of Temporary Facilities:
    • Site Office: Portable units for management staff.
    • Storage Area: Spaces for materials, equipment.
    • Worker Facilities: Restrooms, canteens, resting zones.
    • Power & Water Supply: Respective secure sources for operations.

Temporary Works

Scaffolding
  • Platforms for safe access to high construction areas.
Shoring
  • Purpose: Stabilizes buildings, trenches, and excavations.
    • Two types particularly useful:
    • Raking Shoring: Inclined members supporting walls.
    • Dead Shoring: Vertical supports for load-bearing during modifications.
Trench Shoring
  • Prevents soil collapse; utilizes hydraulic, timber, or sheet piling methods.
Pile Shoring
  • Steel/concrete piles driven to enhance stability in weak soil conditions.

Groundwater Control

  • Definition: Techniques to manage groundwater to avert complications in construction.
  • Importance:
    • Prevents soil instability and structural damage.
    • Enhances safety and efficiency in excavation work.
Methods of Groundwater Control:

  1. Dewatering

    • Creates dry work environment by lowering groundwater levels.
    • Types:
      • Wellpoint System: Efficient for shallow excavations, uses vacuum pumps.
      • Deep Well System: Suitable for large excavations with high groundwater flow.
      • Educator Wells: For deeper sites with low permeability.

  2. Cutoff Barriers: Prevent water from entering excavation:

    • Sheet Piling: Watertight walls blocking lateral water movement.
    • Slurry Walls: Bentonitic cement filling to create impermeable walls.
    • Grouting: Injecting materials to seal soil and rocks.

  3. Drainage Systems: Redirect groundwater away without lowering the water table.

    • French Drains: Trenches with pipes capture excess groundwater.
    • Subsurface Drainage: Below-ground systems to manage excess water.
    • Interceptor Drains: Prevent water reaching excavation.

  4. Artificial Ground Freezing (AGF): Creates a barrier by freezing groundwater using liquid nitrogen.

  5. Electro-Osmotic Treatment: Uses electrical currents to control water flow in soils.