A wide embankment is to be constructed on a flood plain. The site investigation has revealed a layer of very soft lightly over-consolidated clay between 4.0 m and 8.0 m below the base of the embankment. It is anticipated that excess pore pressures generated in this layer of soil during construction may adversely affect the stability of the embankment, and prior to construction, piezometers are to be located at the centre of this layer. Laboratory tests indicated that a depth of 6m of vertical effective stress, =80, the over-consolidation ratio, OCR is 1.50 (=,), the in-situ earth pressure coefficient, K0 = 1.0 and the in-situ specific volume, =1.714. When the sample of the clay was 1-D normally consolidated, the earth pressure coefficient was found to be 0.65. The results also indicate that the soil may be modelled using MCC with the following materials: = 0.25 = 0.045 = = 2.733 M = 1.02 Assume negligible dissipation occurs during construction and that at the piezometer location the changes in vertical and horizontal total stresses as a result of a change Q in the vertical stress at the surface are given as follows: By an elastic distribution: = 0.90Q h = 0.40Q Prior to yield and following yield: = 0.90Q h = 0.70Q (a) Show that the apparent pre-consolidation pressure at a depth of 6 m prior to construction is approximately 110 kPa and that the measured in-situ specific volume is consistent with that predicted by the Modified Cam Clay model (b) A piezometer is located on the centre-line of the embankment at a depth of 6 m. Predict the excess pore pressure, u, that would be recorded by this piezometer if the soil at this location: (i) Yields (ii) Reaches critical state (c) If the bulk unit weight of the fill material forming the embankment is to be 20 kN/m3, what would be the height of the embankment when the soil at the piezometer if the soil at the piezometer location: (i) Yields (ii) Reaches critical state

a a A wide embankment is to be constructed on a flood plain. The site investigation has revealed a layer of very soft lightly over-consolidated clay between 4.0 m and 8.0 m below the base of the embankment. It is anticipated that excess pore pressures generated in this layer of soil during construction may adversely affect the stability of the embankment, and prior to construction, piezometers are to be located at the centre of this layer. Laboratory tests indicated that a depth of 6m of vertical effective stress, o' = 80kPa, the over-consolidation ratio, OCR is 1.50 (OCR oymax 02/01), the in-situ earth pressure coefficient, Ko = 1.0 and the in-situ specific volume, v=1.714. When the sample of the clay was 1-D normally consolidated, the earth pressure coefficient was found to be 0.65. The results also indicate that the soil may be modelled using MCC with the following materials: 1 = 0.25 K = 0.045 Vx = 2.875 r=2.733 M=1.02 Assume negligible dissipation occurs during construction and that at the piezometer location the changes in vertical and horizontal total stresses as a result of a change Q in the vertical stress at the surface are given as follows: 801 = 0.408Q By an elastic distribution: 8v = 0.908Q Prior to yield and following yield: Soy = 0.908Q 801 = 0.708Q (a) Show that the apparent pre-consolidation pressure at a depth of 6 m prior to construction is approximately 110 kPa and that the measured in-situ specific volume is consistent with that predicted by the Modified Cam Clay model (b) A piezometer is located on the centre-line of the embankment at a depth of 6 m. Predict the excess pore pressure, ou, that would be recorded by this piezometer if the soil at this location: (i) Yields (ii) Reaches critical state (C) If the bulk unit weight of the fill material forming the embankment is to be 20 kN/m?, what would be the height of the embankment when the soil at the piezometer if the soil at the piezometer location: (i) Yields (ii) Reaches critical state a a A wide embankment is to be constructed on a flood plain. The site investigation has revealed a layer of very soft lightly over-consolidated clay between 4.0 m and 8.0 m below the base of the embankment. It is anticipated that excess pore pressures generated in this layer of soil during construction may adversely affect the stability of the embankment, and prior to construction, piezometers are to be located at the centre of this layer. Laboratory tests indicated that a depth of 6m of vertical effective stress, o' = 80kPa, the over-consolidation ratio, OCR is 1.50 (OCR oymax 02/01), the in-situ earth pressure coefficient, Ko = 1.0 and the in-situ specific volume, v=1.714. When the sample of the clay was 1-D normally consolidated, the earth pressure coefficient was found to be 0.65. The results also indicate that the soil may be modelled using MCC with the following materials: 1 = 0.25 K = 0.045 Vx = 2.875 r=2.733 M=1.02 Assume negligible dissipation occurs during construction and that at the piezometer location the changes in vertical and horizontal total stresses as a result of a change Q in the vertical stress at the surface are given as follows: 801 = 0.408Q By an elastic distribution: 8v = 0.908Q Prior to yield and following yield: Soy = 0.908Q 801 = 0.708Q (a) Show that the apparent pre-consolidation pressure at a depth of 6 m prior to construction is approximately 110 kPa and that the measured in-situ specific volume is consistent with that predicted by the Modified Cam Clay model (b) A piezometer is located on the centre-line of the embankment at a depth of 6 m. Predict the excess pore pressure, ou, that would be recorded by this piezometer if the soil at this location: (i) Yields (ii) Reaches critical state (C) If the bulk unit weight of the fill material forming the embankment is to be 20 kN/m?, what would be the height of the embankment when the soil at the piezometer if the soil at the piezometer location: (i) Yields (ii) Reaches critical state