INTD 306: Foundation Systems

Foundation Systems

• A foundation system supports the building's load, transfers it to solid ground, and prevents excessive settlement or differential settlement.
• It also repels water accumulation, anchors the building to the ground, and keeps the basement dry and healthy.

Soil Classification

• Soil is classified into four groups: Sands and gravels, clays, silts, and solid rock, which has the highest bearing capacity.
• Soil type and bearing capacity (Kg/cm2) are determined through subsurface exploration and testing.

Subsurface Exploration Methods

• Borings and test pits are common exploration methods.
• Core borings involve removing soil samples at regular intervals, recording the type of material, depth, moisture content, and density.
• A minimum of four borings are taken, one near each corner of the proposed building.

Soil Treatment

• Drainage: Sloping the ground away from the building and installing a footing drain to minimize water-related problems.
• Fill: Removing unsuitable soil and replacing it with compacted new material (soil, sand, gravel, or other material).
• Compaction: Compacting existing soil to provide a suitable base for construction.

Concrete Joints

• Settlement joints (2 cm thick, filled with elastic materials) are used when: • Parts of a building are not equal in terms of dead load (D.L) and live load (L.L). • Soil is not homogeneous. • Site level changes as a building will be constructed on different foundation levels.
• Expansion joints are used for large construction areas, weather conditions, concrete equipment issues, and limited manpower.
• Concrete casting joints are used for the same reasons as expansion joints but have the disadvantage of creating weak points in the structure.

Location and Excavation

• Before excavating, determine subsoil conditions through test borings.
• Footings should extend through to undisturbed soil.
• Use a batter board to locate and retain the building's outline.
• Check local codes for minimum setback (building regulations).
• Mark the location of the outer walls of a building and assure square corners.

Plinth

• A plinth is a basic building element that distributes the load of columns evenly over the foundation.
• The plinth height is between 300mm to 450mm from ground level.
• A damp proof membrane (polyethylene sheet) prevents moisture transmission and concrete from gaining moisture through capillary action.

Foundation Systems Classification

• Foundations can be categorized into two broad divisions:
  1. Shallow Foundation/Spread footings (< 1.0 m)
  2. Deep Foundation/ Pile or caisson (> 2.0 m)

Shallow Foundation/Spread Footings

• A. Wall footing/strip: placed under a continuous foundation wall supporting a bearing wall.
• B. Isolated Pad/Independent: supports one column.
• C. Combined footings: support two or more columns in situations where columns are spaced close together.
• D. Mat or raft: used when soil bearing is low or loads are heavy in relation to soil pressures.

Deep Foundation/Pile or Caisson

• Used when soil is unsuitable for spread footings.
• Piles transmit building loads through unsuitable soil to more secure soil.
• Drilled piers are formed by drilling out a hole and filling it with concrete.
• Piles are usually placed in groups or in a line under a bearing wall.
• Pile foundation is used where good soil is at a higher depth (10 or 15 m) or soil has low bearing capacity.

Excavation Steps

• Step 1: Excavation involves removing earth to prepare the site for footings, foundations, and pipes for site drainage.
• Step 2: Forms are constructed on undisturbed soil at the bottom of the excavation.
• Rebar (reinforcing steel rods) is embedded into concrete.

This quiz covers the basics of foundation systems in building construction, including their role in supporting building weight and transferring it to solid ground.