Foundation Types in Construction

Foundations and Retaining Walls

• Foundations transmit building loads to the underlying soil.
• Foundation type selection depends on ground conditions, water level, site environment (nearby buildings), and structure type.
• Foundations need to transfer loads safely to undisturbed soil and provide sufficient structural safety.
• Construction requires minimal resources, minimal cost, and time-efficient techniques.
• Geotechnical investigation can optimize foundation design, costing 0.5%-5% of the project but significantly saving money.

Introduction to Foundations

• Foundations support the structure's weight and transmit load to the soil or rock.
• Knowledge of geology, soil mechanics, rock mechanics, and structural engineering is applied.
• Foundations are often expensive and complex to repair. Poor design or construction can lead to building demolition.
• Mistakes can occur due to construction or geotechnical errors.

Before Excavation

• Subsurface exploration is essential.
• Previous developments (buildings) and geological maps need to be considered.
• Exploration targets soil/rock strata, engineering properties, and groundwater levels.

Bore Holes

• Bore holes are used for subsurface exploration to understand soil/rock conditions.

Core Logging

• Core logging is a process that collects soil and rock samples from bore holes.

Types of Foundations

• Shallow foundations (e.g., spread footings, strip footings, combined footings, slab on grade, mat foundation).
• Deep foundations (e.g., piles, piers, caissons, raft foundations, basement foundations).

Shallow Foundations

• Pad footings support single column loads in the footing center.
• Strip footings are long, reinforced concrete members supporting load-bearing walls consistently.
• Combined footings are rectangular/trapezoidal reinforced concrete members supporting multiple columns.
• Slab on grade is a continuous reinforced concrete foundation.
• Mat/Raft foundations are large, thick concrete structures supporting the entire structure.

Types of Deep Foundations

• Piles can be driven into the ground using wood, steel or precast concrete.
• Piers are similar to piles but have larger diameters.
• Caissons are large piers that act as watertight structures for construction work.

Bored Pile Construction

• Augured and CFA (Continuous Flight Auger) methods are common.

Pile Caps and Spread Footings

• Proper detailing of pile caps is crucial.

Numerical Methods

• Used to study the load-deformation responses of piles.
• Charts are used to evaluate pile settlement based on soil and pile geometry/stiffness parameters.

Pile Function

• Piles transfer loads from the bridge to the foundations.
• Pile loads are pre-calculated during the bridge design process.

Pile Resistance

• Pile resistance results from friction along the pile sides and bearing on the bottom of the pile.
• Driven piles are used where driving allows for achieving the required resistance or reaching rock.
• Cast-in-place piles are used in situations with proximity to rock or where vibration from the driven piles is undesirable.

Driven Steel H-Piles

• Suitable for rural applications, but careful consideration is needed given the limitations imposed by driving stresses and conflicting views on strength.

Trench-box Excavation Shoring Systems

• Suitable for shallow and stable excavations where water is not an issue.
• Prefabricated walls and connected braces are used.

Sheet Piling and Excavation

• Thin steel sheets are used as continuous barriers and retaining walls for excavation and construction purposes.

Sheet Pile Excavation Shoring Systems

• The system uses steel or vinyl sheet piles when groundwater is an issue. Installation can only be used in areas where it doesn't damage adjacent structures.

Sheetpile Walls

• Temporary shoring and retention of deep soil, often above and below the water table.
• Often connected by multiple anchors or bracing/struts.
• Relatively low cost and can be reused.

Soldier Pile Walls

• Used for vertical excavations in stiff clay or weak rock.
• Often feature bored concrete piles or piers with infill shotcrete panels.
• Can potentially have "tie-back" ground anchors to aid in restraint.
• Relatively low cost, and can often be set to integrate into rock.

Contiguous Pile Walls

• Used to reinforce earth retention in dry soil situations.
• Formed from bored or CFA piles, often placed in such a way that they are close to each other.
• Minimal shotcrete is required.

Secant Pile Walls

• Used for watertight basement foundations in soil below the water table..
• Formed by CFA piles.
• Can be hard-soft or hard-hard piles (primary/secondary, reinforced/unreinforced).

Diaphragm Walls

• Permanent retaining wall typically placed below the water table.
• Stiff retention system, fewer anchors usually needed.
• Can be installed into rock, for cut-off purposes.
• Ideal for depths greater than 30m, with good verticality control.

Types of Retaining Walls

• Gravity – rely on weight for stability
• Embedded – mobilize surrounding earth pressures to resist loads
• Categories of retaining walls, such as gravity walls, gabion walls, crib walls, and cantilevered walls are presented.
• Buttress walls, reinforced earth walls, and bridge abutments are additional types explained.

Abutments in Bridges

• Form the connection between the bridge deck and the approach roads.
• Support vertical and horizontal loads from the superstructure.

Different soil types and their properties are presented, as well as typical design sections and failure modes for specific structures.