HomeMy WebLinkAboutDrilled Shaft Foundation AddendumI~ Yeh and Associates, Inc.
C ons ulting Engineers & Scienti s ts
January 21, 2014
Mr. Ryan Miller
Hunter Ridge Energy Services, LLC
143 Diamond Avenue
Parachute, CO 81635
Project No. 213-086
Subject: Addendum, Drilled Shaft Foundation, Divide Road Water Facility in Garfield County ,
Co lorado
Dear Mr. Miller,
Yeh and Associates prepared a Geotechnical Investigation for the Divide Road Water Facility in
Garfield County, Colorado under Project No . 213-086, dated June 10, 2013. We were
requested to provide deep foundation recommendations as an alternative foundation for the
Booster Pump House. We understand test hole TH-20 is located near the proposed structure.
We recommend drilled piers bottomed in bedrock be used to support the structure . Based on
the results of our subsurface investigation, recommendations for drilled shafts are presented
below.
1. For Allowable Stress Design (ASD) criteria, drilled shafts embedded in the hard
bedrock may be designed for an allowable end bearing pressure of 40 ksf and a skin
friction of 4 ksf for the portion of drilled shaft in bedrock .
2. Drilled shafts should penetrate a minimum of 5 feet into unweathered bedrock or 3
times the shaft diameter, whichever is greater. We anticipate shaft lengths on the
order of 30 feet. We recommend a minimum shaft diameter of 16 inches . In
addition, length to diameter ratios should not exceed 30 : 1.
3. Bedrock may be very hard at various elevations and vary in consistency from shale
to sandstone. The contractor should mobilize equipment of sufficient size and
operating condition to achieve the required design bedrock penetration .
4. The upper 3 feet of drilled shaft shou ld be neglected for lateral load resistance
ca lculation . For lateral loading analysis using LPILE program , the parameters from
the table below may be used .
Friction Horizontal Effective
Material Soll Angle,+ Cohesion, c Modulus of Unit
Model (psf) Subgrade C50 Welght,y (d eg) Reac tion, kh (pcl) (p cO
Fill Reese 26 200 125 Sa nd ----
Clay St iff Clay --500 500 0 .005 120
Weathered Stiff Clay 1000 100 0.010 12 5 Bedrock --
Bed ro ck Sti ff Clay --10000 2000 0.004 135
2000 C l ay S t reet , S u i t e 200 , De n ve r , CO 802 1 1 , (303 ) 78 1 -9590 , F ax (303) 78 1 -9583
1 525 B l ake Ave nu e , G l enwoo d S pr ings , CO 8 1 60 1 , (970) 384-1 500 , F ax (970) 384 -1 50 1
570 T urn er Dri ve , S u ite D , Du rango , C O 8 1 303 , (970) 382 -9590, F ax (970) 382 -9583
Divide Road Water Facility Project No. 213-086
5. The minimum spacing requirements between drilled shafts should be three
diameters from center to center. Groups of piers will also require appropriate
reductions of the lateral capacities based on "shadowing" and other group effects.
For lateral loading, recommended P multipliers should comply with AASHTO Table
10.7.2.4-1 to account for lateral group effects.
6. A representative of the soils engineer should observe drilled shaft installation
operations on a full-time basis.
If you have questions or need additional information, please call us at 970-384-1500.
Sincerely,
YEH AND ASSOCIATES, INC.
Richard D. Johnson, P.E.
Project Manager ,
Page 2 of2