2 Foundation LoadsA foundation supports a number of different kinds of loads:Dead Load – of the building which is the sum of the weights of the frame, the floors, roof, and walls.Live Load – which is the sum of the weights of the people in the building, the furnishings and equipment they use, and snow, ice and water on the roof
3 Foundation LoadsWind Loads – which can apply lateral downward and uplift loads to a foundationHorizontal pressures – of earth and water against sub building wallsHorizontal thrusts – from arches, rigid frames, domes, and vaultsBuoyant uplift force – from underground water, identical to the force that cause a boat to floatEarthquake forces – horizontal and vertical forces caused by the motion of the ground relative to the building.
4 Satisfactory Foundation A satisfactory foundation for a building must meet three general requirements.The foundation including the underlying soil and rock must be safe against a structural failure that could result in collapse.During the life of the building, the foundation must not settle by an amount that could damage the structure or impair its function.The foundation must be feasible both technically and economically and practical to build without adverse effects to surrounding property
5 Foundation Settlement All foundations settle to some extent as the soil adjust around and beneath them because of the loadNo settlement (unnoticeable)Uniform settlementDifferential settlement
6 Soil Classified for Engineering Purposes Rock – continuous mass of solid mineral materialSoil – general term referring to earth materialBoulder – two hands to pick upCobble – one hand to pick up
7 Soil Classified for Engineering Purposes Course Gravel Soilsgravel – can be lifted with thumb and forefingersand – can be seem but cannot be pick up .25 in in.Fine gravel soilsSilt – equal dimension range in size from .002 in inClay – play shape and smaller then in.
8 Cohessive vs. Frictional Clay Soils – cohesive – retain a measurable shear resistance in the absence of confining forcesSand and Silt soils – fictional or cohessiveless – the shear resistance is directly proportional to the confining force pushing particles together.
9 Other IssuesPeat and other organic soils are not suitable for the support of buildings foundationsWater passes readily through clean gravels and sans, slowly through very fine silts and sands, and almost not at all through many clays.An excellent way to keep a basement dry is to surround it with a thick layer of clean gravel or crushed stone. Water passing through the soil toward the building cannot reach the basement without first falling to the bottom of the gravel layer.
10 Subsurface Exploration and Soil Testing Prior to designing a foundation for any building larger than a single family house, it is necessary to determine the soil and water conditions beneath the soil and water conditions beneath the site.Test pits are useful when foundation is not expected to extend deeper than about 8 ft. Test water level and soil contentsBoring machines use on deeper soil test.