Drilled Shaft Calculation

Job Name:

Shaft 1-2-3 : Drilled Shaft Design Program (Version 4.3)

Job Location:

University of South Florida

Engineer:

Danny Winters (Revised: 02/14/2012)

Shaft Diameter 1:

3

ft

Displacement Criteria:

1

in

Shaft Diameter 2:

ft

Dead Load Factor:

1.25

Shaft Diameter 3:

ft

End Bearing Influence Zone:

3

diameters

Cut-off / Scour Elevation:

0

ft

Pressure Limit:

750

psi

Shaft Capacity Design Methods

Side Shear Analysis Method

End Bearing Analysis Method

Clay:

Silt:

Sand:

Limestone:

Alpha Method AASHTO

Most Conservative AASHTO (Clay Method)

O'Neill and Hassan (1994) Reese and O'Neill (1988)

Boring Number:

Ground Surface Elevation:

ft

Water Table Elevation:

ft

Elevation

Depth

SPT-N

Soil Type

Rock Coring Information

(ft)

(ft)

(psi)

(psi)

Rock Coring Information

User Defined

Recovery

%

(TSF)

Nomenclature

%R = percent recovery of rock coring (%)

 =

 =

=

D = diameter of drilled shaft (FT) =

= diameter of the tip of a drilled shaft (FT) = angle of internal friction of soil (DEG) = nominal unit shear resistance (TSF)

 = unit weight (pcf)

GPI = Grout Pressure Index (DIM)

k = empirical bearing capacity coefficient (DIM)

K = load transfer factor

N =

= bearing capacity factor (DIM) = corrected SPT blow count =

=

= undrained shear strength (TSF) TCM = Tip Capacity Multiplier (DIM)

= vertical effective stress (TSF) adhesion factor applied to S_u (DIM)

coefficient relating the vertical stress and the unit skin friction of a drilled shaft (DIM)

m

SPT N corrected coefficient relating the vertical stress and the unit skin friction of a drilled shaft (DIM)

D_b depth of embedment of drilled shaft into a bearing stratum (FT)

D_p

f

f_s, q_s

average (uncorrected) Standard Penetration Test blow count, SPT N (Blows/FT)

N_c N_corr

q_s average splitting tensile strength of the rock core (TSF)

q_u average unconfined compressive strength of the rock core (TSF)

S_u

Procedures Commentary SECURITY NOTE:

General Worksheet

Enter Boring Log Information

Up to three shaft diameters can be analyzed. Microsoft XP users must set Security Level in

Macro Security to Medium. This is done in Tools - Options - Macro Security - Security Level.

Enter Job Name Job Name must be entered before analysis is run.

Enter Job Location Job Location is optional.

Enter Engineer Engineer is optional.

The Boring Log worksheet can be displayed by clicking the Boring Log button or clicking on the

Boring Log sheet tab at the bottom of Excel (see

Procedures & Commentary for Boring Log

Worksheet below).

Select Working Units English or Metric units can be selected for entering raw data. The worksheet will convert from English units to Metric units and vice versa. The analysis will automatically use English units for the calculations.

Enter Shaft Diameter(s)

Enter Displacement Criteria Displacement Criteria defines the mobilized end

bearing and side shear in either cohesionless or cohesive soils as a function of a Tip Capacity Multiplier (TCM) and Side Shear Multipliers (SSM), respectively, based on Reese and O'Neill 1988 (see Figures 1 through 4). TCM upper limits (ungrouted shafts) are set at 1.0 for both cohesive and cohesionless soils. SSM upper limit for cohesionless soils is set at 1.0 and linearly extrapolated for cohesive soils beyond 2%. Silt is dependent on the analysis method selected (sand or clay). End bearing in limestone is dependent on the unconfined compressive strength and percent recovery. Side shear for limestone is set at 1.0 for all %D displacements.

Figure 1 - Normalized Load Transfer in End Bearing Versus Settlement in Cohesionless Soils for Drilled Shafts (after Reese and O'Neill 1988)

Figure 2 - Normalized Load Transfer in End Bearing Versus Settlement in Cohesive Soils for Drilled Shafts (after Reese and O'Neill 1988)

Figure 3 - Normalized Load Transfer in Side Resistance Versus Settlement in Cohesionless Soils for Drilled Shafts (after Reese and O'Neill 1988)

Figure 4 - Normalized Load Transfer in Side Resistance Versus Settlement in Cohesive Soils for Drilled Shafts (after Reese and O'Neill 1988)

Enter Dead Load Factor Dead Load Factor is used to subtract the weight of

the shaft from the mobilized capacity. The default value reflects the AASHTO LRFD Bridge Design Specifications (Interim 2003).

Enter End Bearing Influence Zone The End Bearing Influence Zone defines the depth below the tip of the shaft that contributes to the end bearing capacity by finding the minimum q_p from the soils down to the depth defined by this parameter.

(See Commentary below)

Soil Parameters

Figure 3 - Soil Unit Weight - Standard Penetration Test (SPT - N) Relationships

Enter Cut-off / Scour Elevation Default Cut-off / Scour Elevation is Ground

Elevation. Cut-off / Scour Elevation below Ground Elevation will negate that soil in the

effective stress calculations.

Enter Grout Pressure Limit The Grout Pressure Limit is based on the grouting mechanism capacity (default = 750 psi).

Select Analysis Methods for Side Shear and End Bearing

Click Calculate Shaft Capacities Calculate Shaft Capacities will calculate shaft

capacities based on the boring log. The grouted tip capacity will then be analyzed based on the applied grout pressure (Mullins, et al., 2001).

Click Reset Workbook (optional) Reset Workbook will clear all sheets including the Boring Log worksheet.

100 105 110 115 120 125 130 135 0 10 20 30 40 50 60 70 80 SPT N U ni t W ei gh t (p cf ) Clay Silt Sand

Clay

Silt

Sand

Limestone

S_u = 125 * N psf (Kulhawy and Mayne, 1990), where N is the standard penetration test number. S_u = 125 * N psf (Kulhawy and Mayne, 1990), where N is the standard penetration test number. (See Table 1 for  values)

Table 1 - Values for  based on SPT - N values

q_u, q_s, and percent recovery are defined by the user in the Boring Log worksheet.

Side Shear Analysis Methods Clay AASHTO Table 10.8.3.3.1-1 Alpha Method User Defined Silt O'Neill and Hassan (1994)

Alpha Method

Most Conservative

(See AASHTO section 10.8.3.3.1) f_s =  * S_u, where S_u is the mean undrained shear strength (TSF) and  is the adhesion factor (DIM) (see AASHTO Table 10.8.3.3.1-1). The calculations account for the top five feet which is noncontributing.

fs is defined by the user in the Boring Log worksheet (TSF). The side shear defined by the user is for that specific elevation and derived from load testing results. If load testing results are not available, then another method should be selected.

Also known as the Modified Beta Method. If SPT N < 15 then

m = SPT N / 15 *  (Reese and O'Neill, 1988).

(See AASHTO section 10.8.3.3.1) f_s =  * S_u, where S_u is the mean undrained shear strength (TSF) and  is the adhesion factor (DIM) (see AASHTO Table 10.8.3.3.1-1). The calculations account for the top five feet which is noncontributing.

Most Conservative method will run through the

calculations for each analysis method and use the most conservative value.

User Defined fs is defined by the user in the Boring Log worksheet (TSF). The side shear defined by the user is for that specific elevation and derived from load testing results. If load testing results are not available, then another method should be selected.

Sand

AASHTO Table 10.8.3.4.2-1

O'Neill and Hassan (1994)

Reese and O'Neill (1988) (See AASHTO Table 10.8.3.4.2-1)

Reese and Wright (1977) (See AASHTO Table 10.8.3.4.2-1)

Quiros and Reese (1977) (See AASHTO Table 10.8.3.4.2-1)

Meyerhof (1976) (See AASHTO Table 10.8.3.4.2-1)

Also known as the Modified Beta Method. If SPT N < 15 then

Touma and Reese (1975) (See AASHTO Table 10.8.3.4.2-1)

Most Conservative

User Defined

Limestone McVay and Townsend (1990)

User Defined

End Bearing Analysis Methods

Clay

Silt

Reese and O'Neill (1988) (See AASHTO Table 10.8.3.4.3-1)**

Most Conservative method will run through the

calculations for each analysis method and use the most conservative value.

fs is defined by the user in the Boring Log worksheet (TSF). The side shear defined by the user is for that specific elevation and derived from load testing results. If load testing results are not available, then another method should be selected.

fs = 1/2 * qu1/2 _{* qs}1/2 _{* %R}

where: qu is the unconfined compressive strength of the rock (TSF), qs is the splitting tensile strength of the rock (TSF), and %R is the percent recovery.

AASHTO (Limestone) (See AASHTO section 10.8.3.5 (C10.8.3.5-4 & C10.8.3.5-5)) For q_u <= 20 TSF, f_s = 0.15 * q_u and for q_u > 20 TSF, f_s = 0.67 * q_u0.5_{, where q}

u is the

unconfined compressive strength of the rock (TSF).

fs is defined by the user in the Boring Log worksheet (TSF). The side shear defined by the user is for that specific elevation and derived from load testing results. If load testing results are not available, then another method should be selected.

AASHTO (Clay) (See AASHTO section 10.8.3.3.2) q_p = N_c * S_u <= 40.0 TSF, where N_c = 6 [ 1 + 0.2 ( Z / D ) ] <= 9, D is the diameter of drilled shaft (FT), Z is the penetration of shaft (FT), S_u is the undrained shear strength (TSF). Also known as Reese & O'Neill 1987.

AASHTO (Clay) (See AASHTO section 10.8.3.3.2) q_p = N_c * S_u <= 40.0 TSF, where N_c = 6 [ 1 + 0.2 ( Z / D ) ] <= 9, D is the diameter of drilled shaft (FT), Z is the penetration of shaft (FT), S_u is the undrained shear strength (TSF).

Sand

AASHTO Table 10.8.3.4.3-1

Reese and O'Neill (1988) (See AASHTO Table 10.8.3.4.3-1)**

Reese and Wright (1977) (See AASHTO Table 10.8.3.4.3-1)**

Meyerhof (1976) (See AASHTO Table 10.8.3.4.3-1)**

Touma and Reese (1975) (See AASHTO Table 10.8.3.4.3-1)**

Limestone FHWA (1998)

Grouted End Bearing Analysis Grout Pressure Index (GPI)

**(See AASHTO section 10.8.3.4.3) For diameters greater than 4.17 FT, qp is reduced as follows: q_pr = 4.17 / D_p * q_p, where D_p is the tip diameter of the drilled shaft (FT).

End Bearing, q_p = 2.5 * q_u * %Recovery <= 40.0 TSF, where q_u is the unconfined compressive strength of the rock (TSF).

Grout Pressure Index is a non-dimensional ratio of the applied grout pressure to the predicted ungrouted end bearing at 5%D.

Tip Capacity Multiplier (TCM)

Figure 4 - Tip Capacity Multiplier for determining the grouted end bearing capacity in cohesionless soils. Tip Capacity Multiplier at %D is equal to the grouted capacity at %D divided by the ultimate calculated end bearing. The grouted capacity was determined from load test data (Mullins, et al., 2005, Mullins and Winters, 2004, and Mullins, et al. 2001).

Grouted End Bearing Capacity, q_grouted The grouted end bearing capacity for cohesionless soils is the calculated ultimate end bearing times the TCM (determined from Figure 4). The grouted end bearing capacity for cohesive soils is the ultimate calculated end bearing.

Boring Log Worksheet

Figure 4 - Example Boring Log Entry

Select Working Units English or Metric units can be selected for entered raw data. The worksheet will convert from English units to Metric units and vice versa. The analysis will automatically use English units for the calculations. User Defined values must be entered in the units of TSF. Values in the User

Defined column will not be converted to SI units.

Enter Boring Name Boring Name is used in the graphs for

identification.

Enter Ground Surface Elevation Ground Surface Elevation is the starting elevation

of the soil boring.

Enter Water Table Elevation Water Table Elevation is the elevation of the water

table for that soil boring.

Click Unprotect Worksheet (Optional) Unprotect Worksheet button will unlock the entire

worksheet. Protecting the worksheet will aid in data entry by allowing the user to Tab to the next entry.

Click Access Rock Coring Information (Optional) The Access Rock Coring Information button will allow the user to enter data for rock coring information (if applicable).

Enter Soil Boring Information

Soil Types Soil Type 1: Plastic Clays

Soil Type 2: Clay, Silt, Sand Mix, Silts and Marls Soil Type 3: Clean Sands

Soil Type 4: Soft Limestone, Very Shelly Sands Soil Type 5: Void (No Capacity)

Figure 5 - Detailed Soil Types Form

Soil Boring Information includes Depth, SPT N, Soil Type (see Soil Types Commentary), and Rock Coring Information (Compressive Strength, Splitting Tensile Strength, and Percent Recovery) (if applicable).

Click Soil Type Details button will show a detailed soil type form (Figure 3).

Click Update Boring Log Updating the boring log will calculate Elevations and Soil Parameters.

Capacity Worksheet(s)

Capacity Plot(s)

Figure 6 - Detailed Shaft Capacity & Grout Pressure Plot

NOTE: It should be noted that all calculations are performed at the bottom of layers, not the middle of layers. This will calculate conservative values and differ from the users hand calculations. To mitigate this effect, make layer thicknesses small < 2ft (0.6m).

Ungrouted and grouted capacities will be placed in a worksheet designated for each diameter (Diam 1,

Diam 2, and Diam 3). The following will be

included in each worksheet: Job Name, Shaft Diameter, Boring Number, Elevation, Ultimate Side Shear, Ultimate End Bearing, Ultimate Shaft Capacity (Ungrouted), Mobilized Shaft Capacity (Ungrouted and Grouted), and Grout Pressure.

The Mobilized Shaft Capacity (Ungrouted and Grouted) and Grout Pressure will be graphed versus Elevation (Diam1 Plot, Diam2 Plot, and

Diam3 Plot). An example plot (Figure 6) shows

load improvement, length improvement, required grout pressure for improvement, and graph details. -80 -60 -40 -20 0 20 40 60 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 Capacity (tons)

El

ev

ati

on

(f

t)

800 Grout Pressure (psi)

Ele

vati

on

(ft)

Tarragona St & CSX RR

Ungrouted Capacity @ 1.00 in Disp Grouted Capacity @ 1.00 in Disp Grout Pressure 3 ft Diameter, Boring TH 3 Soil Cutoff (Zero Capacity) Shaft Length Improvement Load Improvement

Grout Pressure Required for Improvement Project I.D.

Shaft Size & Boring I.D.

Grout Pressure Limit (Equipment / Construction Limitations)

Patents

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