Section 362.1810. Deep foundations.

 

(1)   Downdrag. This is a department rule in addition to the requirements in IBC section 1803.5.5: Investigations and reports for deep foundations shall include analysis of whether downdrag is anticipated. Where downdrag is anticipated, the report shall include a determination of the position of the deep foundation's neutral plane, an estimate of the soil settlement at the neutral plane, and a determination of the maximum load at the neutral plane.

(2)   Determination of allowable loads. Substitute the following wording for the requirements in IBC section 1810.3.3:

(a) The allowable axial and lateral loads on deep foundations shall be determined by an approved formula, load tests or static analysis.

(b) The factor of safety to be used for deep foundation design shall depend on the extent of field testing performed to verify capacity.

(c) If the ultimate capacity is assessed solely by static analysis, a minimum factor of safety of 3.0 shall be applied to the ultimate capacity to determine allowable load capacity.

(d) If only static analysis and dynamic field testing are performed, a minimum factor of safety of 2.5 shall be applied to the ultimate capacity to determine allowable load capacity.

(e)

1. If one or more static load tests are performed, in addition to a static analysis, a minimum factor of safety of 2.0 shall be applied to the ultimate capacity to determine allowable load capacity, except as provided in subd. 2.

2. A minimum factor of safety of 1.5 may be used for structures in occupancy category I, provided all of the following conditions are met:

a. The deep foundations are required only to control settlement.

b. The deep foundations are not required to prevent a bearing capacity failure.

c. A static load test, a static analysis and dynamic field testing have been performed.

(3)   Driving criteria. This is a department rule in addition to the requirements in IBC section 1810.3.3.1.1: Driving criteria for deep foundations shall be submitted prior to installing the foundations, if requested by the building official.

(4)   Approved formulas. This is a department informational note to be used under IBC section 1810.3.3.1.1:

Note: The Department has approved the following two dynamic driving formulas, when used within the parameters prescribed below.

1. Washington State Department of Transportation formula:
Rn = 6.6 F eff WH ln(10 N )

Where:

R n is the ultimate axial compression capacity in kips.

F eff is an efficiency factor based on hammer and pile type.

W is the hammer weight in kips.

H is the drop height of the hammer in feet.

N is the average penetration resistance at the end of driving, in blows per inch.

Acceptable F e ff values are:

0.55 for all pile types driven with an air or steam hammer.

0.37 for open-ended diesel hammers for concrete and timber piles.

0.47 for open-ended diesel hammers for steel piles.

0.35 for closed-ended diesel hammers for all pile types.

2. Corrected FHWA-Modified Gates Equation:
R u = [(1.75)(( e E r ) 0.5 ) (log(10 N b ))-100] ( F o ) ( F s ) ( F p ) ( F h )

Where:

R u is the ultimate axial compression capacity in kips.

e is the hammer efficiency.

E r is the hammer energy in foot-pounds.

N b is the final penetration resistance in blows per inch.

F o is an overall correction factor.

F s is a correction factor for soil type.

F p is a correction factor for pile type.

F h is a correction factor for hammer type.

Acceptable hammer-efficiency values are:

0.75 for drop hammers.

0.85 for other hammers, or an efficiency recommended by the hammer manufacturer.

Acceptable correction factors are:

Overall F o : 0.94.

Soil F s : 1.00 for mixed soil profile.

0.87 for sandy soil profile.

1.20 for clayey soil profile.

Pile F p : 1.00 for closed-ended pipe.

1.02 for open-ended pipe.

0.80 for H-Section piles.

Hammer F h : 1.00 for open-ended diesel.

0.84 for closed-ended diesel.

1.16 for air or steam single-acting.

1.01 for air or steam double-acting.

1.00 for hydraulic.

If at least 1 static load test is performed to field-check the penetration resistance criteria calculated by the above dynamic formulas, a minimum safety factor of 2.5 must be applied to the ultimate axial compression capacity calculated by the dynamic formula to determine the allowable pile load. If only dynamic testing (including signal matching) is performed to field-check the penetration resistance criteria determined by the dynamic formula, a minimum safety factor of 2.75 must be applied to the ultimate axial compression capacity calculated by the dynamic formula to determine the allowable pile load. If no field testing is performed to check the penetration resistance criteria calculated by the dynamic formula, a minimum safety factor of 3.0 must be applied to the ultimate axial compression capacity calculated by the dynamic formula to determine the allowable pile load.

The above formulas are predicated on the following three conditions: (1) static load testing and/or dynamic testing being performed on pile(s) driven in uniform site soil conditions, (2) test pile(s) being driven with the same hammer and cushion used for installation of production piles, and (3) test pile(s) being of the same type and section used for production piles. If any of the three conditions is not met, additional field testing is required. With static load testing and/or dynamic testing, penetration resistance criteria calculated by the dynamic formula must be modified as appropriate based on the results of the field testing. A site must be defined as a project site, or a portion of it, where subsurface conditions can be characterized as geologically similar in terms of subsurface stratigraphy, including the sequence, thickness, geologic history, engineering properties and groundwater aspects.

(5)   Factor of safety for uplift. The exception in IBC section 1810.3.3.1.5 is not included as part of this code.

(6)   Helical piles. This is a department informational note to be used under IBC section 1810.3.3.1.9:

Note: See sub. (2) for factors of safety that supersede the criteria in this section. For example, under sub. (2) (c) , (d) and (e) , this factor may be 3, 2.5 or 1.5, respectively.

(7)   Deep foundations in subsiding areas. Substitute the following wording for the requirements in IBC section 1810.3.4:

(a) Where deep foundations are installed through subsiding fills or other subsiding strata and derive support from underlying firmer materials, consideration shall be given to the downward drag load that may be imposed on the deep foundations by the subsiding upper strata.

(b) Where the influence of subsiding fills is considered as imposing loads on the deep foundation, the allowable stresses specified in this chapter are permitted to be increased where satisfactory substantiating data are submitted.

(c) The position of the deep foundation's neutral plane shall be determined, and the settlement of the soil at the level of the neutral plane shall be estimated. The maximum load in the deep foundation, which occurs at the neutral plane, shall be determined.

(8)   Design cracking moment. Substitute the following equation for IBC equation 18-11: j M n = 3( f' c ) 0.5 ( S m ).

(9)   Driven timber piles. Substitute the following wording for the requirements in IBC section 1810.4.1.5: Any sudden decrease in driving resistance of an end-supported timber pile shall be investigated with regard to the possibility of damage. If the sudden decrease in driving resistance cannot be correlated to load-bearing data, the pile shall be removed for inspection or rejected, or shall be assigned a reduced capacity commensurate with the loss of end-bearing in lieu of removing or rejecting the pile.

CR 00-179 : cr. Register December 2001 No. 552 , eff. 7-1-02; CR 04-016 : am. (3) (e), cr. (6) Register December 2004 No. 588 , eff. 1-1-05; CR 06-120 : renum. Comm 62.1807 to be Comm 62.1808 and am. (1), (2), (3) (intro.), (4) (intro.), (5) (intro.) and (a) and (6) Register February 2008 No. 626 , eff. 3-1-08; CR 10-103 : (title), (1), (2), (7) renum. from Comm 62.1808, (title), (2), (3), (5) and am., (9) renum. from Comm 62.1809 and am.; cr. (3) to (6), (8) Register August 2011 No. 668 , eff. 9-1-11.