These are used when column loads are extremely large, the topsoils are weak, and the soils that have a good strength and compressibility characteristics are in a reasonable depth below ground level. If Df /B 1, the foundations are called deep foundations such as piles, drilled piers/caissons, well foundations, large-diameter piers, pile raft systems.ĭeep foundations are much like shallow foundations except the load coming from columns or superstructure is transferred into the soil vertically. Deep Foundations.Ī typical deep foundation is shown as per the above figure (b). These are used when the natural soil at the site has a reasonable safe bearing capacity, acceptable compressibility, and the column loads are not very high.Īlso, read: Test for Compressive Strength of Brick | Water Absorption | Dimensions Test 2. Shallow foundations are thus used to spread the load/pressure coming from the column or superstructure (That is several times the safe bearing pressure of supporting soil) horizontally so it is transmitted at a level that the soil can safely support. In general, the foundation of building foundations of bridges and buildings might be divided into two major categories as below.Īlso, read: Piling for Foundation | Use of Pile Foundation | Characteristics of Pile Foundation 1.
When determining which foundation is the most economical (foundation), the engineer should consider the superstructure load, the subsoil conditions, as well as the desirable tolerable settlement. What Is the Minimum Depth of Raft Foundation?Ī raft foundation, also called a raft foundation, is essentially a continuous slab resting on the soil that extends over the entire footprint of the building, thereby supporting the building and transferring its weight to the ground.Raft Foundation: Common Types of Raft Foundations Raft Foundation: Trapezoidal Combined Foundation Raft Foundation: Rectangular Combined Foundation If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it. I like to debate structural engineering theory - a lot.
A shear wall or a beefy fixed base moment frame might be stiff enough to offset some rotation whereas a simple gravity column probably would not. If the supported structure and its connection to the footing were stiff enough to be adversely affected by small footing rotations, that same supported structure would probably be stiff enough to help resist that footing rotation. There's kind of a catch 22 at play with the supported structure. But then, eccentric footings are a pretty regular occurrence and we're rarely bothered by the degree of tilt in those instances. The linearly varying soil stress certainly does imply tilt. You don't think the extra footing on a single side could resist settlement greater on that side and cause the whole thing to begin to tilt? RE: Bearing Pressure Under Eccentrically Loaded Footings labeattie (Structural) I'll often combine this with Once2006's recommendation to extract the maximum benefit from a seemingly unhelpful footing extension.Īs a matter of principle, I don't for a second believe that adding more footing actually makes the situation worse out there in the wild. As such, it often makes more sense to compare your allowable bearing pressure to something closer to the average bearing stress rather than the peak. You care how much the supported structure settles. And you don't care how much the footing edge settles. Most shallow foundation allowable stresses are determined based on settlement concerns rather than true failure. A useful trick is to recognize that, in many cases, you can exceed your allowable stress at the edge of the footing.