PE-10-Elastic-Settlement

PE-10-Elastic-Settlement - 10 - Elastic Settlement *01:...

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10 - Elastic Settlement *01: Elastic settlement of a truck tire. *02: Schmertmann’s methods for a spread footing. *03: Schmertmann’s methods for a deep footing. *04: The 2:1 method. *05: The Boussinesq versus Westergaard methods. *06: Differential settlement. *07: The elastic strain versus Schmertmann methods. *08: Multilayered Schmertmann. *09: Elastic settlement of a mat foundation. Symbols for Elastic Settlement N Raw value of the STP (obtained in the field). q o Contact pressure. C 1 Embedment coefficient. C 2 Creep correction factor. E S Soil elastic modulus. E eq Equivalent modulus. D(D e ) Differential settlement between adjacent foundation. D H i Elastic settlement. I Influence factor. I Z Simplifying influence factor. e Strain at mid stratum. γ Unit weight of the soil. v Poisson’s ratio. M T Transverse moment. 230
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*Elastic Settlement-01: Settlement (rutting) of a truck tire. (Revision: Aug-08) You are required to move a 60-ton truck-mounted crane onto your construction site. The front wheels carry 20% of the load on tires inflated with 55 psi air pressure. Calculate the possible rutting depth to your temporary jobsite road built from an in- situ compacted medium sand. A surface SPT shows an N = 12 and the tire’s bearing area is roughly square. Estimate the depth of the rutting. Solution: Each front tire has a square bearing area of BxB such that: 2 2 2 o tire's load (0.5)(20%)(120,000 ) 218 14.8 tire pressure q (55 / ) lb B in B inches lb in == = = A rough estimate of the soil’s elastic modulus is E s = 14 N = 14(12) = 168 ksf . Since the sand is compacted, it is a dense sand, and the I z = ε is averaged to 0.3 throughout its depth to 2B = 2(14.8 inches) ~ 30 inches. Since the crane loads are on the surface and only for a few days, C 1 = C 2 = 1. Therefore, for the single layer of soil, the rutting is, 2 12 22 2 0.30 144 (1)(1)(55 )( )(30 ) 168 / 1,0 0. . 0 2 0 4 ⎛⎞ ∆= = × ⎜⎟ ⎝⎠ o s lb in k CC q dz in E in k ft ft l inches of rutt b ing ε 232
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*Elastic Settlement-02: Schmertmann method used for granular soils. (Revision: Aug-08) Estimate the settlement of a square footing placed on a fine, medium dense sand, embedded 4 ft below the ground surface, for long-term use. Use the Schmertmann method. Assume 14 s E N where E s is in ksf ; used for fine medium sands. Layer z E s I z = ε (in) (ksf) 1 42 140 0.30 0.090 2 60 210 0.46 0.130 3 66 168 0.16 0.061 = 0.281 s z E z I () 22 12 1 200 The contact pressure on the soil is, 4 (0.120 ) 3.60 49 The coefficients for the Schmertmann method are : 0.48 Depth factor 1.0 0.5 1.0 0.5 0.93 3.60 Cree of f o Qk q D ft kcf ksf Bf t CandC D C q γ =− = = ⎛⎞ =− = ⎜⎟ ⎝⎠ 2 2 0 p factor 1.35 . The Schmertmann formula for the elasti 1. c settlement is, (0.93)(1.35)(3. 2 60)(0.28 ) 7 1 B o C for a five year period CCq z E inches ε = ∴∆= ∆ = = 233
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*Elastic Settlement-03: Schmertmann method used for a deeper footings.
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This note was uploaded on 09/11/2011 for the course CEG 4011 taught by Professor Staff during the Summer '10 term at FIU.

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PE-10-Elastic-Settlement - 10 - Elastic Settlement *01:...

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