Who analyze the dynamic relationship between a building site’s unique characteristics and the given specifications of a particular structure.
Builders have long understood the fundamental importance of a well-laid foundation. Some Egyptian, Greek, and Roman columns still stand after thousands of years, mainly because their builders knew that the sub-structure of a building is in some ways more important than the super-structure.
The Gospel of Matthew includes the parable of The Wise and Foolish Builders: “And the rains came down, the streams rose, and the winds blew and beat against that house, yet it did not fall, because it had its foundation upon the rock.”
Foundation engineers focus on the substructure; that portion of a building that rests on the surrounding soil to support the load of the superstructure and protect it from the elements.
Foundation engineering may be involved in designing construction plans for a building substructure, or they may be called upon to consult on a foundation repair, developing remedies for foundation issues found or suspected beneath an existing building.
Foundation Design: Site, Soil, and Structure
The Site. Before designing a foundation repair plan, the foundation engineer begins by studying the basic site survey. The lot may be level, low-lying, on a hillside, in a flood zone or near a body of water. Each of these are elements that must be factored into the design of an effective foundation. A poorly drained site will require techniques that move the rainwater away from the house. A hillside site may require planning to convey a neighbor’s water across the property to street drains or rural ditching.
The Soil. Before a new house or subdivision is built, a geotechnical survey may find that the soil under the new building is clay, sand, or rock, infirm or lose strata, helping the builder determine factors such as load-bearing, water retention and the prospect of soil expansion or subsidence. In North Texas, expansive clay soil is common, requiring specific techniques to avoid foundation damage from the swelling and shrinking of the soil which can be caused by alternating periods of rain and drought.
The Structure. The building design is a complete system of walls, beams, and joists which work together to support the whole.
Based on the site, soil and structure, an appropriate deep or shallow sub-structure will be built, which may include footings, pilings, piers or different types of concrete slab, with the primary design objective of transferring the building load to the ground, while avoiding any future negative effects of unusual topography, soil instability or harsh local weather.
Common Foundations: Slabs, Piers, and Pilings
Most modern homes use a slab-on-grade foundation, where concrete is poured directly onto a prepared surface. Depending on the characteristics of the soil and the structure, the slab may be a supported slab, which rests on the same footing as the building walls; a monolithic slab, which incorporates the slab and footing in the same concrete pour; or a floating slab, which touches the footing at an expansion joint. Sometimes the slab and footing are reinforced with steel rods to prevent cracking, and the slab may be poured on a base of gravel, to facilitate drainage.
Some homes are built with piers built of concrete. Piers raise the floor joists of the structure above the ground, leaving a crawl space. In coastal areas, the builder may raise the structure even higher above the ground on pilings, allowing floodwaters or storm surge to pass under the building without damaging the structure or contents.
Foundation Maintenance: How Foundation Engineers Prevent Costly Foundation Problems
Issues. As a building begins to age, the foundation can be threatened by changes such as soil movement, water intrusion, or a seismic event. Initial effects may be minor, such as a door that sticks or a crack in wall plaster. However, if left uncorrected, minor issues can lead to major structural problems.
Inspection. The best way to protect any building is to treat minor foundation issues as a warning sign – and call for a foundation inspection. Cracks in a pier and beam foundation or cracks in brick, mortar, tile, or sheetrock may only be signs of normal settling, but only a professional foundation engineer can make that determination.
Reporting. The work product of an engineer’s inspection is the professional inspection report. The foundation engineer’s report has many uses when an authoritative finding is required. A home buyer may wish to be assured that a floor crack can be permanently repaired. A home seller may need to show that a wall crack is not a sign of a more serious problem.
Corrective Action. When a foundation problem is determined to be a significant threat to the integrity of the structure, a foundation engineer is best qualified to advise the homeowner or contractor on a detailed repair plan.
Repair plan. The foundation engineer draws up a foundation repair plan based on the inspection and subsequent analysis. The plan can then be executed by a qualified contractor. The foundation engineer may also be called to approve completed work done by a contractor for city permitting procedures.
Maintenance. A good foundation engineer’s report provides the basis for an effective maintenance plan. The foundation engineer should also recommend improvements such as lot drainage or modest repairs which can prevent a minor issue from becoming a major problem.
Monitoring. After repairs or maintenance issues have been addressed, the foundation engineer’s report will continue to serve as a guide for the homeowner or contractor, to follow up and monitor whether a slab repair or a new drainage system has been effective.