Principles of Foundation Engineering
9th Edition
ISBN: 9780357684832
Author: Das
Publisher: Cengage Learning US
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Chapter 9, Problem 9.4P
To determine
Find the expected settlement beneath the center of the foundation.
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In the following example, a rectangular foundation must be designed whose B/L ratio must be equal to 0.5.The ultimate allowable load Qadm that must be transmitted to the ground is 520 KN, using a safety factor of 2.0. Designing with Meyerhoff theory, assume that the soil undergoes a general shear failure process. For this problem, propose values of B and L that meet the B/L ratio until Qadm is found to be equal to 520 kN.
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3.12 For a strip foundation, the width is 1.2m, buried depth is 1.2m, the
standard value of the load applied on the foundation F=155KN/m, the
soil layer is distributed as follows: from the ground to the depth of 1.2m is
the land fill, =18KN/m³; the depth in the range of 1.2~1.8m is silty clay,
fak=155kPa, E,=8.1Mpa, y=19KN/m³; below the depth of 1.8m is the
mucky clay, fak=102kPa, E,=2.7Mpa. Try to check the base pressure and
the bearing capacity of the weak sub-layer.
Ground
F=155KN/m
OLand fill 18KN/m³
1.2m
O Silty clay
La-155kPa;E-8.1Mpa;y-19KN/m³
-0, 1.0
O Mucky clay
-0, H1.0
Sak-102kPa;E,-2.7Mpa
1.2m
A foundation (Figure 1) transmits a stress of 100 kPa on the surface of a soil deposit.
a. Evaluate increases of vertical stresses points A, B, and C at the depth of 2m and Sm (2
points)
b. At what depth is the increase in vertical stress below A less than 10% of the surface
stress?
6 m
+2 m-
A
2 m
-4 m-
Figure 1: Plan of foundation
Chapter 9 Solutions
Principles of Foundation Engineering
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- A rectangular foundation (8x6 ft) carrying an axial load of 350 Kips is constructed on the soil profile shown below. Determine: a) The total stress, effective stress, and pore water pressure at the top, middle, and bottom of the clay layer (Normally Consolidated) after a very long time b) The final consolidation settlement of the clay layer caused by construction of the foundation (Use the weighted average method) c) The settlement of the clay layer after 2 years d) The degree of consolidation at the middle of clay layer after 4 years e) How long it takes for the clay layer to reach 95% degree of consolidation? 350 kips 5 ft 8 ft dry sand Ya-110 Pef 15 ft Yuu-115 Pef 30 ft Your-119 Pef 6 ft GWT sand NC Clay C-0.32;C-0.06 C.-4.5x10 cm²/sec Coarse sandarrow_forwardRefer to Figure 5.12. For a rectangular foundation on layered sand, given:●● B = 4 ft, L = 6 ft, H = 2 ft, Df = 3 ft●● γ1 = 98 lb/ft3, Φ'1 = 30º, c'1 = 0●● γ2 = 108 lb/ft3, Φ'2 = 38º, c'2 = 0Using a factor of safety of 4, determine the gross allowable load the foundation can carry.arrow_forwardProblem II. The initial principal stresses at a certain depth in a clay soil are 100 kPa on the horizontal plane and 50 kPa on the vertical plane. Construction of a surface foundation induces additional stresses consisting of a vertical stress of 45 kPa, a lateral stress of 20 kPa, and a counterclockwise (with respect to the horizontal plane) shear stress of 40 kPa. a. Plot Mohr's circle (1) for the initial state of the soil and (2) after construction of the foundation. b. Determine the change in magnitude of the principal stresses. C. the change in maximum shear stress d. the change in orientation of the principal stress plane resulting from the construction of the foundation.arrow_forward
- For a strip foundation, the width is 1.2m, buried depth is 1.2m, the standard value of the load applied on the foundation Fx=155kN/m, the soil layer is distributed as follows: from the ground to the depth of 1.2m is the land fill, y=18kN/m°; the depth in the range of 1.2-1.8m is silty clay, fak=155kPa, E,=8.1 Mpa, y=19KN/mº; below the depth of 1.8m is the mucky clay, fax=102kPa, E=2.7Mpa. Try to check the base pressure and the bearing capacity of the weak sub-layer.arrow_forwardQ3c. The soil profile at a new construction site for a shallow foundation is shown in Figure Q3. Prior to construction, a uniformly distributed load of 120 kN/m² is applied to the surface of the soil. By using C, equal to 0.133C. Sand Y = 14 kN/m? 3m Ground water table 3m Ysat = 18 kN/m Sand Ysat = 19 kN/m? Void ratio e = 0.8 3m Clay LL = 40 Sand Figure Q3 (i) Calculate the settlement of the clay layer caused by primary consolidation if the clay is normally consolidated. (ii) Calculate the settlement of the clay layer caused by primary consolidation if the preconsolidation pressure (o'.) = 170 kN/m².arrow_forwardA mat foundation, 15 m x 15 m, is made of reinforced concrete and to be supported by a three-layer soil profile, as shown. The mat is 1 m thick, and the average stress on the surface of the slab assessed from the structural engineering analysis is 75 kPa. (Unit weight of concrete = 23.58 kN/m^3) The 5-m thick sand layer immediately below the mat foundation has been compacted to standard Proctor specifications, most likely to optimum moisture content, which is why its moist density is given. (A) Determine the pre-construction effective stress at Point A (bottom of the clay layer). This is the in situ effective stress (overburden pressure) measured from the ground surface prior to the placement of the mat foundation. (B) Determine the vertical stress increase induced by the mat foundation at Point A using the “Influence Chart,” commonly referred to as the “Spider Web.” (C) Determine the vertical stress increase induced by the mat foundation at Point A using the “Stress Isobars.” (D)…arrow_forward
- Consider a continuous foundation of width B = 1.4 m on a sand deposit with c = 0, = 38, and = 17.5 kN/m3. The foundation is subjected to an eccentrically inclined load (see Figure 6.33). Given: load eccentricity e = 0.15 m, Df = 1 m, and load inclination = 18. Estimate the failure load Qu(ei) per unit length of the foundation a. for a partially compensated type of loading [Eq. (6.89)] b. for a reinforced type of loading [Eq. (6.90)]arrow_forwardSolve Problem 7.8 using Eq. (7.29). Ignore the post-construction settlement. 7.8 Solve Problem 7.4 with Eq. (7.20). Ignore the correction factor for creep. For the unit weight of soil, use γ = 115 lb/ft3. 7.4 Figure 7.3 shows a foundation of 10 ft × 6.25 ft resting on a sand deposit. The net load per unit area at the level of the foundation, qo, is 3000 lb/ft2. For the sand, μs = 0.3, Es = 3200 lb/in.2, Df = 2.5 ft, and H = 32 ft. Assume that the foundation is rigid and determine the elastic settlement the foundation would undergo. Use Eqs. (7.4) and (7.12).arrow_forwardA 8 m layer of sand, of saturated unit weight 22 kN/m3, overlies a 6 m layer of clay, of saturated unit weight 27 kN/m3. A foundation carrying 1200 KN load is to be founded on the soil layer. If the clay is normally consolidated and the increase in effective pressure due to the foundation load at the center of clay is 27 kN/m2, Soil parameters are Cc = 0.25, eo = 1.0. Assume required data •Draw the soil profile diagram in detail, mentioning all the soil properties with the foundation details. •Calculate the consolidation settlement at the center of the clay layer.arrow_forward
- The initial principal stresses at a certain depth in a clay soil are 200 kPa on the horizontal plane and 100 kPa on the vertical plane. Construction of a surface foundation induces additional stresses consisting of a vertical stress of 45 kPa, a lateral (horizontal) stress of 20 kPa, and a counterclockwise (with respect to the horizontal plane) shear stress of 40 kPa. Plot Mohr's circle (1) for the initial state of the soil and (2) after construction of the foundation. Determine (a) the change in magnitude of the principal stress, (b) the change in maximum shear stress, and (c) the change in orientation of the principal stress plane resulting from the construction of the foundation.arrow_forward2 ft 2 ft 24 ft 24 ft 24 ft Problem 4 B D E F G | 3 ft DL=100 kip DL=180 kip LL = 60 kịp LL = 120 kip DL=190 kip DL=110 ki • The plan of a mat foundation with column loads is shown in Figure 2. Use the rigid method to calculate the soil pressures at point A, B, C, D, E, F, G, H, , J, K, L, M and N. The size of the mat is 76 ft x 96 ft, all columns are 24 in x 24 in in section, and qlnet = 1.5 kip/ft². Verify that the soil pressures are less than the net allowable bearing capacity. LL = 120 kip LL = 70 ki 30 ft DL=180 kip DL=400 kip DL=200 kip LL = 250 kip LL = 120 kip DL=360 kip LL = 120 kip LL = 200 kip ex 30 ft DL-190 kip DL=500 kip LL = 130'kip LL = 240 kip DL=T10 kip DL=200 kip LL =300 kip LL =120 kip 30 ft DL=180 kip DL=120 kip LL =120 kip L =70 kip x' 3 ft IDL=120 kip DL=180 kip ILL =70 kip LL =120 kip J Figure 2: Plan of a Mat Foundation M L K Harrow_forwardA vertical column load, P = 600 kN, is applied to a rigid square concrete foundation. The foundation rests at a depth Df= 0.75 m on a uniform dense sand with the following properties: average modulus of elasticity, Es = 20,600 kN/m², and Poisson's ratio, µs = 0.3. Calculate the required foundation dimensions if the allowable settlement under the center of the foundation is 25mm. 600 kN Foundation 0.75 m Вхв Soil Hs = 0.3 E, = 20, 600 kN/m² 5.0 m Rockarrow_forward
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