   Chapter 17, Problem 17.14P Principles of Geotechnical Enginee...

9th Edition
Braja M. Das + 1 other
ISBN: 9781305970939

Solutions

Chapter
Section Principles of Geotechnical Enginee...

9th Edition
Braja M. Das + 1 other
ISBN: 9781305970939
Textbook Problem

Refer to the footing in Problem 17.12 and Figure 17.17. a. Estimate the average friction angle, ϕ′, within the 2B zone. Assume the average dry unit weight of the soil within this zone to be 17 kN/m3. b. Estimate the average elastic modulus of the 2B zone for settlement calculation. Use Eq. (17.33) 17.12 The cone penetration resistance (qc) and sleeve-frictional resistance (fc) obtained during a subsoil exploration program are shown in Figure 1717 A square footing (B = 1.5 m) is to be constructed at a depth of 1 m. Estimate the type of soil within a distance of 2B below the footing. Use the Robertson et al. correlation chart (Figure 17.13) (a)

To determine

Find the average friction angle ϕ.

Explanation

Given information:

The average dry unit weight is 17kN/m3.

The width of footing B is 1.5m.

The atmospheric pressure (pa) is 100kN/m2.

Calculation:

Find the distance 2B of the footing as follows:

Substitute 1.5m for B.

2B=2×1.52B=3m

Therefore, the Cone penetration resistance and sleeve friction area averaged up to 3m footing.(depth of 4m from the surface).

Refer Figure 17.17 in the textbook.

Take the value of (qc) and sleeve friction (fc) resistance using figure 17.17 as shown in Table 1.

 Depth (m) qc(kN/m2) (fc)kN/m2 1 4,200 90 2 3,500 70 3 4,500 50 4 4,800 100

Table 1

Find the effective overburden pressure (σo) at depth of 1m using the relation:

σo=depth×γd (1)

Substitute 17kN/m3 for γd and 1m for depth in Equation (1).

σo=17×1=17kN/m2

Find the effective overburden pressure (σo) at depth of 2m using the relation:

σo=depth×γd (2)

Substitute 17kN/m3 for γd and 2m for depth in Equation (2)

(b)

To determine

Find the average elastic modulus of the 2B zone for settlement with various depth.

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