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Foundation Settlement By Kamal Tawfiq, Ph.D., P.E. Fall 2008

Foundation Settlement By Kamal Tawfiq, Ph.D., P.E. Fall 2008. Foundation Settlement :. Total Foundation Settlement = Elastic Settlement + Consolidation Settlement S total = S e + S c. {. Foundation Type (Rigid; Flexible)

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Foundation Settlement By Kamal Tawfiq, Ph.D., P.E. Fall 2008

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  1. Foundation Settlement By Kamal Tawfiq, Ph.D., P.E. Fall 2008

  2. Foundation Settlement: Total Foundation Settlement = Elastic Settlement + Consolidation Settlement Stotal = Se + Sc { Foundation Type (Rigid; Flexible) Elastic Settlement or Immediate Settlement depends on Settlement Location (Center or Corner) { Theory of Elasticity Elastic Settlement Time Depended Elastic Settlement (Schmertman & Hartman Method (1978) Elastic settlement occurs in sandy, silty, and clayey soils. By: Kamal Tawfiq, Ph.D., P.E.

  3. Water Table (W.T.) Expulsion of the water Water Voids Solids By: Kamal Tawfiq, Ph.D., P.E. Consolidation Settlement (Time Dependent Settlement) * Consolidation settlement occurs in cohesive soils due to the expulsion of the water from the voids. * Because of the soil permeability the rate of settlement may varied from soil to another. * Also the variation in the rate of consolidation settlement depends on the boundary conditions. SConsolidation = Sprimary + Ssecondary Primary Consolidation Volume change is due to reduction in pore water pressure Secondary Consolidation Volume change is due to the rearrangement of the soil particles (No pore water pressure change, Δu = 0, occurs after the primary consolidation)

  4. Elastic Settlement 2 Se = Bqo (1 - μs) α (corner of the flexible foundation) 2 Es 2 Se = Bqo (1 - μs) α (center of the flexible foundation) Es Where α = 1/π [ ln ( √1 + m2 + m / √1 + m2 - m ) + m*ln ( √1 + m2 + 1 / √1 + m2 - 1 ) m = B/L B = width of foundation L = length of foundation By: Kamal Tawfiq, Ph.D., P.E.

  5. 3.0 2.5 α αav αr 2.0 α, αav, αr 1.5 For circular foundation α = 1 αav = 0.85 αr = 0.88 1.0 3.0 1 2 3 4 5 6 7 8 9 10 L / B Values of α, αav, and αr By: Kamal Tawfiq, Ph.D., P.E.

  6. Elastic Settlement Using the Strain Influence Factor: [Schmertman & Hartman Method (1978)] The variation of the strain influence factor with depth below the foundation is shown in Figure 1. Note that, for square or circular foundations, Iz = 0.1 at z = 0 Iz = 0.5 at z = 0.5B Iz = 0 at z = 2B Similarly, for foundations with L/B ≥ 10 Iz = 0.2 at z = 0 Iz = 0.5 at z = B Iz = 0 at z = 4B Se = C1 C2 ( q - q) ∑ (Iz / Es ) Δz where Is = strain influence factor C1 = a correction factor for the depth of foundation embedment = 1 - 0.5 [q / (q - q)] C2 = a correction factor to account for creep in soil = 1 + 0.2 log (time in years /0.1) q = stress at the level of the foundation q = overburden pressure = γ Df Example: B x L q Df Iz q = γ Df Es ΔZ1 ΔZ2 Is3 ΔZ3 Es3 Average Is Average Es ΔZ4 Depth, z

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