Exercícios - Capítulo 16 - Soil Mechanics - Lambe

with elevation is not a straight line At the far right is plotted the difference between total stress and pore water pressure It was obtained merely by subtracting the pore water pressure from the total stress since the pore water pressure at all points is negative the numerical value of the pore pressure was added to that of the total stress Also shown is the plot of σ S100 uw ie the effective stress as defined by Eq 1616 with uw 0 and σm σ100 At some height in a column of fine sands such as that in Example 163 the pore water ceases to be continuous When the pore water is not continuous the pore water pressure is no longer a unique function of height above the phreatic line Water could be trapped in voids far above the phreatic line and could still exist at positive pressure As can be seen from Example 163 there is considerable difference between the values of σ uw and σ S100 uw above elevation 40 The stress σ S100 uw is probably closer to the stress that best correlates with soil behavior than is σ uw 166 SUMMARY OF MAIN POINTS 1 The effective stress is a Saturated soil b Partially saturated soil σ σ uw aw ua uw 2 For geostatic stresses and static pore water a σ h γi Δzi b by assuming σm 0 c σ h K0 σ v 3 In granular soils the effective stress is approximately the contact stress multiplied by the ratio of contact area to total area PROBLEMS 161 For the Thames Estuary clay in Fig 710 make a plot of σv ua and uw versus elevation for a depth of 40 ft Compare your plot of σv with that given in Fig 710 162 Refer to the subsoil profile for South Bank in Fig 78 Which would be the larger value of σv at a depth of 140 ft a σv computed for static pore pressure b σv computed for the pore pressure indicated by the standpipe in Fig 78 What is the magnitude of the difference between the two values of σv 163 The water table in Example 161 rises 2 m the tide comes in while the soil surface elevation remains constant Compute the values of σv σh σv at element 4 164 The contact area ratio in the sand under the center of the tank at elevation 5 m in Example 162 is 01 Discuss the likelihood of sand particle crushing following the filling of the tank with water 165 The height of soil column in Fig 164a is 20 m The soil fine sand has the following properties e 0473 constant with depth G 269 Sw 100 an 005 For the fully drained condition line A compute for point a uw ua σv σh Hint The air pressure is atmospheric Assume geostatic stresses 166 Refer to Fig 516b Compute the effective stress for an interparticle spacing of 40 A The spacing is held constant while salt is added to water around the particles Does the effective stress increase or decrease Explain 163 σv γt x z 205 x 5 σv 103 kPa U γw x d 98 x 4 392 σv σv U 103 392 σv 638 kPa σh Ko σv σh 04 x 638 σh 2552 kPa 164 Δσv γw x h 98 kNm3 x 10 98 kPa σv γt x z 1766 x 5 883 kPa U γw x 9 98 x 9 882 σv σv U 01 kPa σv final 98 01 981 kPa σparticle σv Anec 981 0001 981 MPa Se σresistência 981 MPa da areia então pode ocorrer esmagamento