Soil damage
Water table:
• When soil is saturated, the line above is water table
• Parallels earth surface
• Varies with seasonal fluctuations
• Precipitation, on ground surface
• In practice: water table to be below foundation to avoid damage [hydro static/ capillary action]
• Water to be drained away “from building”
• Drainage tiles: 6″ below lowest floor slab
• Open joists to be covered with wire mesh then coarse gravel or stone back fill
• Slab on grade with no hydrostatic pressure is on gravel fill (6″-8″), water not drawn by capillary
• Sealant are used in all connections
Water table:
Boundary between aeration (zone) & saturation zone
Increased moisture content in bearing soils effects:
Chance in volume and reduction in bearing capacity
“not” increase in cohesion, or decrease in compatibility
Sudden loss of shearing resistance in cohesion less soil
Liquefaction
“Not” plasticity, collapsing soil, or expansive soil
Unstable differential settlement: building failures due to unstable subsoil that causes differential settlement of foundation:
Based on large beds of clay contained in gravel
“not” stratified rocks, small boulders in gravel, or deep layer of dry sand and gravel
Erosion: Removal of vegetarian from site causes erosion
“not” pollution, disorientation, defoliation
To reduce potential vertical movement due to expansive clay:
• Over excavate below footing grade & fill with compacted gravel,
• Extend footings & foundations to a depth of consistent ground moisure
• Drain surface water away from foundation
• Control roof water run off
“Not”: Water proof foundation to reduce filtration plant trees near building to stabilize ground
Settlement: As wp (weight) of buildings increase, soil under footing compresses, reduce void volume then bldg settles. Even bedrock has to be verified slight even settlement is okay.. Differential settlement creates cracks/ failures continuous survey of site as construction occurs is required settlement continuous with time due to void, moisture, movements
Earth movement: Great with easy subsoil, clay swells (wet) & shrinks moisture content @ surface with clay creates each movements @ 5′ earth movement is great. Serious issues if footings are different. Adjacent excavations affect clay moisture content this causes settlement or slippage @ sub surface clay slope surface + raw or moisture moves earth mass evidence: Structure with tilt or rows or sloping power poles
Cubic yard: Units measuring cuts & soils is volume “not” square yard (area), acres (area_, tonnage (weight)
Balancing cut & fill is for site grading
“not” Sediment control, land reclamation, footing excavation
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