A developer has bought a piece of land with the objective to develop a touristic complex comprising several buildings. The site is close to a river and a beach, and the soil profile consists of 9 m of soft alluvial clay overlying some dense sand. A preliminary geotechnical analysis has revealed that high settlements should be expected because of the soft clay and, given that the project is not urgent, a preloading strategy has been recommended to reduce the settlement. The preloading consists of placing 3m of fill (bulk unit weight of 15kN/m3 , saturation degree of about 70%) over an area of 200m per 200m (see Figure 1). The fill includes a draining layer to facilitate drainage at the soil surface (not showed in the Figure). The preload is used to consolidate the clay until the project starts. After 8 years, some fill will be removed, to restore the initial surface level, and buildings will be erected on the site (see Figure 2). This assignment focuses on one 40m per 100m building locating in the centre of the site, exerting a uniform pressure of 20kPa on the soil (see Figure 1).

Additional information about the project are:

Water table is at the ground surface.

Oedometer tests on the alluvial clay returned a coefficient of compression of 0.6, a coefficient of rebound of 0.05 and a coefficient of consolidation of 2.7 m2 /y.

The in-situ void ratio was estimated to vary with depth (z) as eo(z)=1.5-0.04*z, for 0 z 9m

Geotechnical investigations conducted prior to any construction activity on site revealed that the clay is normally consolidated.

You can neglect the settlement of the sand.

The saturated unit weight of the clay is 15.3kN/m

a. Compute the settlement at the end of primary consolidation under the centre of the building on the initial profile before any preloading is applied to the soil. The maximum tolerable settlement is 100mm, is the building settlement within the tolerance?

b. Given the value of expected building settlement, it is decided to preload the soil with some fill (see details above) before erecting the building. Compute the settlement at the end of primary consolidation under the centre of the preloading fill (noted sf).

Could you answer question above for me? and show me the steps. Thank you for help.

(1) Fill 200m Clay Site 40m Sand (2) 100m 200m Fill Clay A Sand Preload area (3) Building Clay A Sand Not to scale. Figure 1: plane view of the site showing the Figure 2: preloading sequence: (1): footprint of the preloaded area and of the building. preloading fill is placed on the soil surface; Note that part of the preloading fill is removed (2): in the course of years, the soil settles before erecting the building. under the pressure of the fill; (3): after some time, the excess fill is removed so that the site is back at its initial elevation. (sf. settlement of fill at point A). In a 4th stage (not showed on figure), the building is erected. (1) Fill 200m Clay Site 40m Sand (2) 100m 200m Fill Clay A Sand Preload area (3) Building Clay A Sand Not to scale. Figure 1: plane view of the site showing the Figure 2: preloading sequence: (1): footprint of the preloaded area and of the building. preloading fill is placed on the soil surface; Note that part of the preloading fill is removed (2): in the course of years, the soil settles before erecting the building. under the pressure of the fill; (3): after some time, the excess fill is removed so that the site is back at its initial elevation. (sf. settlement of fill at point A). In a 4th stage (not showed on figure), the building is erected