The Effect of Soil Types on the Design and Choice of Foundations
Construction and building highly depend on the type and quality of soil beneath them to be put. If the soil under various buildings moves to either side, then the building is in danger of developing cracks, be weak and even fall. Therefore, there is a need for developers of any building to study and have enough information about the soil conditions at a site ought to be used so that they can design an appropriate structure. In most cases, the soil conditions are believed to be a certain category and footings. In designing the structures, foundations are developed with a safety margin to account for various soil conditions within the sensible limits. However many soils in different sites are a combination of various categories meaning that soil profile of a site can change from one side to another and down into the soil.
Engineers have the obligation of carrying out soil investigations to determine which type of foundation to set up at a given site. The major investigations carried out are subsurface and surface investigations.
The investigations involve examination of subsoil conditions by soil engineers. Most commonly, the number and location of borings are dependent on the type of structure and the conditions of the site. Under uniform and normal soil conditions, borings are usually spaced 100-150` apart. However in situations where soil conditions are not uniform, and soil footings are spaced closely, the borings should be spaced 50` apart to ensure safety. To enhance reliability, the borings must reach the firm strata and extend 20 feet more into the bearable soil. The borings usually provide crucial information involving type, depth, moisture content, and ground water level of a particular site.
These investigations are carried out with the intent of to determine the presence; of high water table, trouble and soils, rocks close to the surface, fills, and evidence of subsidence. Once the surface investigations have been carried out, buildings that are close to each other require existing and earth foundations, presence of water is an indication of a high water table thereby requiring waterproofing types of foundation, and a level terrain is an indication of an easy site to work with among others. With the recommendations of surface investigation, it is explicit that the foundation of buildings highly depends on the soil condition and more particularly the types of soils.
The soil mechanics engineers developed a simple system for aiding engineers in determining the properties of any given soils. The unified system is usually based on the identification of soil by analyzing their plasticity and textural characteristics and further grouping them by their respective behaviors. Soils tend to exist in mixtures that contain varying proportions of a variety of sizes of particles whereby each of them highly contribute to the entire mixture.
According to soil mechanics engineers, there are three groups of soils namely; coarse-grained, fine-grained and highly organic.
Coarse grained soils are soils that contain relatively large particles. They are composed of sands or gravels that are constituted of a variety of particles. They are further divided into, sands, gravelly soils, and sandy soils. A coarse-grained group of soils contain a good bearing value making them suitable for the establishment of foundations when well confined and drained.
They are referred to as slits and clays. The fine-grained group of soils is dived by their plasticity features (L, H). They are made up of smaller slit and clay particles. Fine-grained soils are suitable for foundations after various compactions.
Highly organic soils are soils that are very compressible thereby being unsuitable for any construction. In most cases, they are made up of grass, leaves and branch particles. Examples of highly organic soils are; humus, peat, and swamp soil. They can be easily identified by their color, odor and texture. Highly organic soils contain a high moisture content.
From the above discussion, it is clear that foundations are determined by the types of soils in a given site. For instance, a simple spreading footing that highly dependent on the magnitude of the weight carried is ideal for most fine-grained soils. In cases where the soils are poor and the structures to be put are relatively heavier, then there is a need for engineers to seek alternative methods. Moreover, pile foundations sometimes can also work in sites with fine cohesive clay and slit soils. There are three types of foundations namely; spread footings, drilled piers, and mat foundations.
They are mostly used light load buildings and in sites with strong, shallow soils. The footings are meant to deliver the building’s load to the soil. Spread footings are ideal for low-rise buildings of about three to four stories.
Drilled piers foundations are suitable for expansive soils and with low and medium building loads. The piers are designed to deliver the load weight to the stronger capacity soil located far below the ground.
They are suitable for low-load buildings on expansive or very weak soils. They are in most cases made of post-tensioned concrete that allows the structures to float on the weak soils.
The soil conditions of any given site are very crucial regarding the type of foundation that should be put in such a place. Therefore, engineers should consider various soil conditions like soil plasticity through various investigations before deciding which foundation to lay on any given site. Putting the right foundation in the right location will increase the safety of people in that surrounding.
“SOIL INVESTIGATION AND FOUNDATION TYPES.” The Constructor. N.p., n.d. Web. 10 Oct. 2015.