PE-11-Plastic Settlement

PE-11-Plastic Settlement - 11 -Plastic Settlement...

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11 -Plastic Settlement (Consolidation) *01: Pore pressure in a compressible stratum. *02: Total settlement of a single clay layer. *03: Using Boussinesq to find the stress in a clay. *04: Surface loads with different units. *05: Find the pre-consolidation and the index C c . *06: Final voids ratio after consolidation. *07: Settlement due to a lowered WT. *08: Find the over-consolidation ratio (OCR). *09: Find the coefficient of consolidation C v . *10: Time rate of consolidation. *11: Use of the time factor. *12: Degree of consolidation. *13: Laboratory versus field time rates. *14: Different degrees of consolidation. *15: Depth of excavation for minimal settlement. *16: Lead time required for consolidation. *17: Settlement of a canal levee. *18: Differential settlement of a levee. *19: Settlement of a bridge pier. *20: Method to estimate the coefficient of consolidation. *21: Apparent optimum moisture content. Symbols for Plastic Settlement e Voids ratio. E S Soil elastic modulus. C C Compression index. G S Specific gravity of the solids of a soil. OCR Over consolidation ratio. H Depth of zone influence. DH c Plastic settlement (also called primary consolidation). DH total Total settlement of a structure. DH s Second consolidation settlement. Dp Increasing pressure on the surface. u Pore water pressure. P e Pre-consolidation pressure of a specimen. γ SAT Saturated unit weight of the soil. γ W Unit weight of water. U Degree of consolidation. 250
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*Plastic Settlement–01: Porewater pressure in a compressible soil. (Revision: Oct.-08) a. How high will the water rise in the piezometer immediately after the application of the surface load of 3 ksf? b. What is the degree of consolidation from the 3 ksf at point A, when h =15 ft.? c. Find h when the degree of consolidation at A is 60%. p = 3 ksf 252
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Solution: a) Assume a uniform increase of the initial excess pore water pressure throughout the 10-foot thickness of the clay layer: 2 0 3,000 The pore water pressure is 3 48. ,000 / 62 1 .4 w w p uph l b f t h feet γ =∆ = = = = = b) The degree of consolidation at A is U A (%) when h = 15 feet: 0 (15 )(62.4 ) %1 1 0 01 6 100 (48.1 )(62.4 9% ) A A uf t p c f U t p c f ⎛⎞ =− = ⎜⎟ ⎝⎠ c) When U A = 60 %, what is the value of h ? () ( ) 0 0.6 1 1 3,000 10 . 63 , 0 0 0 1 , 2 0 0 1,200 .2 64 9 . 1 2 AA A A A w uu U up s s f f psf psf u fee h pc t f ==− =− = == = 253
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*Plastic Settlement-02: Total settlement of a single layer. (Revision: Aug-08) A new building is planned upon the site shown below. Assume that the clay solids have a specific gravity of 2.67. Find the primary consolidation settlement if the clay is normally consolidated. p = 1 ksf 8 feet 7 feet 17 feet Clay w = 34%, LL = 50%, γ sat = 120 pcf Sand γ = 110 pcf, γ sat = 115 pcf Water Table Solution: () 0.009( 10) 0.009(50 0.36 1 0.34 2.67 0.91 , −− = −= == = = = =+ + c ss o d sand dry sat w w mid Skempton formula for the C LL Se wG but S e The stress of the clay at its mid stratum before the building was built is pH H H γγ γ 10 (0.11 )(8 ) (0.115 0.0624) (7 ) (0.120 (8.5 ) 1.74 , 17 12 (0.36) 1 log 1 1 7.6 + = +∆ + ∆= = = ++ clay o co oo kcf ft p ksf The consolidation settlement is H i Cp p H ep nches 254
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*Plastic Settlement-03: Boussinesq to reduce the stress with depth.
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PE-11-Plastic Settlement - 11 -Plastic Settlement...

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