Monday, December 10, 2012


Following is a step-by-step procedure for designing a continuous foundation on a granular soil reinforced with metallic strips.

Step 1. Establish the following parameters

a. Foundation
- Net load per unit length, Q
- Depth, Df
- Factor of safety, FS, against bearing capacity failure on unreinforced soil
- Allowable settlement, Se

b. Soil
- Unit weight, '
- Friction angle, %
- Modulus of elasticity, Es
- Poisson’s ratio, µs

c. Reinforcement ties
- Width, w
- Soil-tie friction angle, Φµ
- Factor of safety against tie pullout, FSP
- Factor of safety against tie break, FSB

Step 2. Assume values of B, u, h, and number of reinforcement layers N.
Note that the depth of reinforcement,  d, from the bottom of the foundation

Step 3. Assume a value of LDR = wn

Step 4. Determine the allowable bearing capacity, q'all  , on unreinforced sand, or

Step 5. Determine the allowable bearing capacity, q'all   , based on allowable settlement. From Eq. (5.41),

The magnitude of I7 for continuous foundations can be taken to be approximately 2 for this calculation.

Step 6. The smaller of the two allowable bearing capacities (that is, q'all  or q''all  ) is equal to qo.

Step 7. Calculate qR (load per unit area of the foundation on reinforced soil) as

Step 8. Calculate T for all layers of reinforcement using Eq. (7.1). 

Step 9. Calculate the magnitude of FP /T for each layer to see if FP /T >=  FSP.

If FP /T < FSP , the length of reinforcing strips may have to be increased by substituting X´ (>X) in Eq. (7.5) so that FP /T is equal toFSP


Step 10. Use Eq. (7.2) to obtain the thickness of the reinforcement strips.

Step 11. If the design is unsatisfactory, repeat Steps 2 through 10.

TABLE 2.1   Terzaghi’s Bearing Capacity Factors—Eqs. (2.32), (2.33), and (2.34)


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