Question

A 5m wide and 10m long rectangular foundation is built on a site where the soil profile consists of 3m of gravel and 4m of clay overlying rigid impermeable rock as shown in Figure 8. The foundation carries a surcharge loading of q=65 kN/m2 Initially the water table is 1 m below the surface of the gravel. The water table rises to the surface of the gravel slowly over a period of time and the surface loading induces an increase of total stress at point O. The preconsolidation pressure at O is 130 kN/m2. The properties of clay are shown in Table 4. The gravel has: r21.5 kN/m':, 18 kN/m Determine: The effective stress increase, Ao', at the center of the clay layer (Refer to the relevant chart at the 1. end of the exam paper) The effective stress at point O at the initial stage. 2. The effective stress at point O at the finally stage. 3. 4 The settlement of the soil system (Assume the gravel is incompressibility) Table 5: Properties of clay Void ratio 0.75 P Specific gravity G 2.65 Over consolidation ratio OCR 4.25 Compression index 0.35 Co Re-compression index 0.032 Ca Saturated unit weight kN/m 19.06 Ysat E A 10m PLAN q 65 kN/m Gravel Gravel Clay Impermeable rock ELEVATION Figure 8 The following may be useful in the calculation: if C logio 1+e Н, if c н, logio AS O 1+e otherwise Н, Ce elogio logio H.+ 1+e 1+e 2m1m

Answer 1

Aurcharge loadgs m3 KN/m2 21.5 KN/m3 }8 KNI M Y dry 16KN/m3 /30 far graul Aat far clay e GS Ce aat O35 0.03 2 19.D6 OCR 75 Ri65 4.25 (i1 Imcrear in aph dtu 8 x I +21.SX 2 + 2 x19.D6 t65 16412 21.25X3E 2 X I9.06+ 65 $:1.Enm 166.8 275 KN/mA A imital stus kN/m2 164.12 in )aptir is in natur table t6687 Autlement ef clay layir Licemprasaible clay thum Ls H 4m Hx Ce nomatly AH lag/L66.87 164.12 4X 0.35 4-75 6.77 mm