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 Fiqure 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: 21.5 kN/m'; Yary 18 kN/m Determine: The effective stress increase, Aa', at the center of the clay layer (Refer to the relevant chart at the 1. end of the exam paper). 2 The effective stress at point O at the initial stage. The effective stress at point O at the finally stage 3. The settlement of the soil system (Assume the gravel is incompressibility) 4. Table 5: Properties of clay Void ratio 0.75 Specific gravity Ga 2.65 Over consolidation ratio OCR 4.25 Compression index 0.35 Cc Re-compression index 0.032 Saturated unit weight 19.06 kN/m Ysat 10m PLAN 2 q=65 kN/m Gravel Gravel Clay Impermeable rock o ELEVATION Figure 8 Wt mm

Answer 1

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