236 Step 1: Determine Idealized Soil Profile and Geotechnical Design Parameters The first step consists of the determination of an idealized soil profile based on the results of the subsurface investigation program. Presenting a detailed evaluation of the subsurface investigation program goes beyond the scope of this manual, and therefore is not presented in detail herein. Figure B shows the assumed idealized soil profile. The assumed geotechnical design parameters are summarized in Table B.
Table B Interpreted soil parameters. Layer Nob bSoil Type Model Depth* (ft) Φ (deg) Su (psf) γ' (pcf) ks** (pci) ε50** (-) 1 Sand (Reese)
1.5 - 15 30
-
115 90
-
2 Sand (Reese)
15 - 30 30
-
52.6 60
-
3 Soft Clay
30 - 40
-
300 47.6
-
0.02 4 Sand (Reese)
40 - 50 30
-
57.6 80
-
* Depth is
measure from the top of pile ** Refer to Chapter 3 for discussion on estimating soil parameters The top of pile is 1.5 feet above the ground surface, and groundwater is located 13.5 feet below the ground surface (15 feet below top of pile. Step 2: Obtain Preliminary Structural Design The lateral response of the pile depends on the stiffness
properties of the pile itself, as well as on the subsurface soil conditions. A preliminary structural design (drilled shaft diameter, number
of size of reinforcement, etc) needs to be established before computing deflections, bending moment and shear diagrams. For this example, the following preliminary structural design is selected Drilled shaft diameter = 54 inches Concrete Compressive Strength = 4,000 psi
•
20 #10 single bars (Fy = 60 ksi) Concrete cover to edge of bar distance = 3 inches No permanent steel casing Drilled Shaft Length = 45 feet (5 feet embedment into Layer No. 4)
•
#3 bars for Ties Step 3: Determine Factored Loads The actual and detailed determination of the factored loads is beyond the scope of this example.
In general, at minimum, factored loads for Strength and Service Limit States should be determined and analyzed.
As applicable, other Limit States such as Extreme I (earthquake) should also be considered. For simplicity, this example will only analyze Strength and Service Limit States. The Strength factored loads are used to assess the structural
integrity of the pile, while the Service factored loads are used to estimate the lateral deflection profile of the pile.
237 Table B presents the factored loads used in this example. All loads are applied at the top of the pile.
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