A railway embankment is to be built on a profile of soft clay in an estuarine environment of NSW.

The ground surface is at elevation +2m AHD (AHD: Australian Height Datum) and the top surface

of the embankment should be at elevation +4m AHD. The initial design put forward by a

geotechnical engineer is a 2m high embankment, 7m crest to crest, with 2H:1V batter slopes. The

bulk density of the embankment is estimated to be 1.78 t/m³. The soil profile consists of 50 m of

soft clay overlying some dense sand. Some soil specimens were collected and tested returning the

following values: m = 2.5 MPa ¹, Poisson's ratio of 0.3, Gs=2.65, c, = 14m²/y. The objective of

this assignment is to compute the settlement under the centreline of the embankment using different

assumptions and models and evaluate the different results. Plane strain conditions can be assumed.

1- Under the centreline, what are the deformation conditions (i.e. 1D, 2D, 3D)?

2- Plot the increase of vertical stress and horizontal stresses under the centreline of the

embankment, due to the embankment. Plot stresses from the surface to 50m, in 1 m

increment. The plot should look like sin r plots of tutorial solutions. For this question,

produce all steps of calculation at a depth of 5m and plot the rest of the stress values.

3- Assuming 1D conditions (i.e. no lateral deformation, no stress dissipation), compute the

primary consolidation settlement under the centreline. Discretise the soil into sub-layers if

you deem it necessary. Comment your result.

4- Using the SB method, compute the primary consolidation settlement of the embankment

under the centreline for:

a. No discretization of soil profile:

b. Discretization of the soil profile into 2 sub-layers of thickness

c. Discretization of the soil profile into 5 sub-layers of thickness

d. Discretization of the soil profile into 10 sub-layers of thickness

e. Discretization of the soil profile into 20 sub-layers of thickness

For each discretised profile, compute the stress at the appropriate depth(s).

5- Compute the primary consolidation settlement of the embankment under the centreline

following the method of the lecture notes, i.e. 1D in the confinement triangle + the SB

method outside.

6- Conclude on your findings in terms of the effect of discretization on the settlement value,

choice of model, effect of assumptions made, magnitude of settlement.

7- Using the result of question 5, compute and plot the evolution of primary consolidation

settlement in time from t=1year to t90, in 5 years increment in between (1, 5, 10, 15 etc...).

END OF THE ASSIGNMENT