# Handout14 - How long Wait until U = 20-2 xloo = 90 => T y...

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· Surcharge/Preload Example (Assume Sufficient Material is Available and Surcharging is Cost Effective) Detennine: How long a preload or surcharge would be required so that the final settlement under a wide loaded area with Acr of 2000 psf is < 2 inches? 1. Find clay properties: Clay => Undisturbed Sample 20 ft => Sample Depth: 10ft into clay "(sat = 120 pcf => Laboratory Test -7 eo = 1.14, C c = 0.50, O"~ax = 1600 psf, 2 Cy = 0.05 ft /day 2. Calculate Suit (use 1 layer for simplicity) At mid-depth in clay: O"~ = 8 (125) + lO (120) - lO rw = 1576 psf O"~ =: O"~ax => NC clay for Acr = 2000 psf S = 20(12) (0.50) 10 3576 = 20 in. ult 1+1.14 g1576 3. Try preload to Acr = 2000 pst. Let all but 2 in. of settlement occur. Then unload and build -
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Unformatted text preview: How long? Wait until U = 20-2 xloo = 90% => T y = 0.848 20 (0.05)t Ty = 2 => t = 1696 days = 4.7 yrs (10) < 4. But 4.7 yrs is too long. Assume that sufficient fill material is available to' create a surcharge , with Acr = 3500 psf. Then O"~ = 1576 psf and 0"( = 5076 psf. Therefore, Suit for surcharge = 28.5 in. Wait until S = 18 in. has occurred => U :;;;.-!.!. .xlOO = 63% Time (yrs) 28.5 S (in.) 5 10 15 18 20 25 30 1 2 3 4 5 6 ifU = 63% => Ty = 0.32 T H2 t = y dr = 640 days = 1.75 yrs ...much better! C y Scheme: a. surcharge with a fill, Acr = 3500psf b. wait 1.75 yrs, get 18 in. settlement c. remove surcharge d. build e. get = 2 in. settlement during building life...
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