While there are many factors at play, a common rule of thumb for foundation depth is to go as deep as the width of the foundation wall. For instance, if your foundation wall is 8 inches wide, a depth of 8 inches is a starting point.
Structural Most building codes require the foundation to be at least 12 inches (~300 mm) below the ground surface to protect from undermining by surface erosion. Provided the engineering considerations of bearing capacity, sliding, and overturning are met, the minimal code embedment is usually satisfactory.
The depth of a foundation depends on several factors, such as the type of soil, the type of structure, the design loads, the groundwater level, the seismic risk, and the environmental conditions.
Foundations shall extend not less than 12 inches below finished grade and in no case less than the frost line depth. b. Footing sizes are based on soil with an allowable soil pressure of 2,000 pounds per square foot.
In chalk soils, foundation depths can be as little 500-750mm, but no less than 450mm to protect against frost action. In sand and clay soils, the depth of foundations should be no less than 900mm deep and BS8103 recommends a depth of not less than 1.0m.
For every 2 feet of adjustment to the width of the house, add or subtract 2 inches of footing width and 1 inch of footing thickness (but not less than 6 inches thick).
Footings shall be a minimum of 8 inches by 24 inches (203 mm by 610 mm) for houses two and one-half stories and less. The footings for a three-story building shall be 10 inches by 24 inches (254 mm by 610 mm).
The minimum depth of footings below the surface of undisturbed soil, compacted fill material or controlled low strength material (CLSM) shall be 12 inches (305 mm).
As per Cl. 7.2, IS:1904, All foundations shall extend to a depth of at least 50 cm below the natural ground level. The minimum depth of footing on sandy soil is 0.8 - 1 m, for rocky soil, it is 0.05 - 0.5 m and for clayey soil, it is 0.9 - 1.6 m.
It can be calculated by dividing the foundation load by the contact area between the foundation and the soil. For example, if a strip foundation has a width of 1 m and a length of 10 m, the contact area is 10 m2. If the foundation load per unit length is 170 kN/m, the foundation stress is 17 kPa.
The critical depth is defined as the depth below which the shaft resistance of driven piles does not change; above this depth, the shaft resistance increases with depth reaching to its maximum value at the critical depth.
Explanation: Rankine's formula provides the guidance on the minimum depth of foundation based on bearing capacity of the soil. Where, Df = minimum depth of foundation, qu= ultimate bearing capacity of the soil, γ = density of soil, = angle of repose or internal friction of soil.
The footing is what's actually in contact with the ground, while the foundation is the structure that transfers the load to the earth. A simple way to visualize the difference when comparing it to the human body would be to view the footing as the actual feet of the legs and the foundation being the legs themselves.
The frost-line depth is established by the authority having jurisdiction based on field experience and must be listed along with other design criteria in Table R301. 2(1). Exterior foundations must extend below the frost line and a minimum of 12 inches (305 mm) below undisturbed soil.
Still, we recommend that the depth of the footing extends to a minimum of 12 inches after you've hit undisturbed soil. It also must extend at least 12 inches below the frost line (the depth to which the ground freezes in winter).
To determine the size of the footing, a simple formula is used: Structural Load (lbs) / Soil Capacity (psf) = Footing Surface Area Required (sq. ft.)
A minimum of 12”inches deep for all footings and the width will be determined by the amount of stories, 12” inches for a single story, 15” inches for a two story and 23” inches for a three story. This is based on a soil bearing capacity of 1500(psf).
Footing thickness - 8 to 12 inches. Footing depth - varies based on frost line and soil strength (some footings can be shallow, while other must be deep)
For slab the rule of thumb is as follows. For a 10 foot span of slab 10X12/24 = 5 inches thick. For a 12 foot span of slab 12X12/24 = 6 inches thick and so on and so on. For depth of a Concrete beam 1 inch per foot of span eg: 20 foot span = 20 inches of depth or 1 ft 8 inches.
Generally 1.5m should be the depth of foundation. But do consider what our other quorans have replied to this. Safe bearing capacity, Water table and many other factors should be considered before you decide upon this.
Residential Buildings: Typically, houses and smaller residential buildings require shallower foundations. In most cases, a foundation depth of 900mm to 1200mm (approximately 3 to 4 feet) is sufficient.
Loam soil is a balanced mixture of sand, silt, and clay, offering several advantages for foundation support and stability. Drainage: Loam soil provides excellent drainage capabilities, allowing excess water to move away from the foundation.