23-141-SC_141_Archer_Drive_Tieback_Addendum.pdf
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- Attached to
- EWP Project 5228 - 141 Archer Dr.
- Solicitation number
- IFB No. PW-0124
- Issued by
- Santa Cruz County, San Francisco City, California
About this file
This document is an addendum to a geotechnical engineering report by Butano Geotechnical Engineering, Inc. for a project located at 141 Archer Drive in Santa Cruz, California. The addendum provides specific recommendations for grouted tiebacks to be used in a retaining wall mitigation project, focusing on technical design criteria for anchoring into sandstone bedrock. The recommendations include using small diameter grouted anchors (3 to 8 inches in diameter), spacing tiebacks no closer than 5 feet on-center, and utilizing a working shaft skin friction of 1,000 psf within the bonded zone of the sandstone.
The document specifies technical details for anchor installation, including an unbonded length assumption in the soil overlying sandstone until 15 feet of vertical cover is achieved, with a minimum unbonded length of 10 feet. Additionally, the report recommends pull-testing procedures, suggesting that one half of the anchors should be tested to 110 percent of the design load, with full testing required if any anchors fail. The addendum is part of a broader project to address retaining wall mitigation, with the geotechnical recommendations serving as a critical component of the structural design and stabilization strategy.
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B U T A N O G E O T EC H N I C A L E N G I N E E R I N G , I N C .
404 WESTRIDGE DRIVE, WATSONVILLE, CALIFORNIA 95076
PHONE: 831.724.2612
WWW.BUTANOGEOTECH.COM
July 14, 2023 Project No. 23-141-SC
Scott Winton 141 Archer Drive Santa Cruz, California 95060
SUBJECT: ADDENDUM RECOMMENDATIONS – GROUTED TIEBACKS
Proposed Retaining Wall Mitigation 141 Archer Drive Santa Cruz, California
REFERENCE: Butano Geotechnical Engineering, Geotechnical Investigation –
Design Phase, 141 Archer Drive, Santa Cruz, California, Project No.
23-141-SC, June 1, 2023
At your request we are providing addendum recommendations for the referenced report.
Specifically, we are providing recommendations for grouted tiebacks.
1.1 Tiebacks – Grouted
The retaining wall may be designed utilizing grouted tiebacks embedded into the sandstone.
The following criteria should be used when designing small diameter grouted anchors (3 to 8 inches in diameter) into the sandstone.
Tiebacks will anchor into the bedrock and should be spaced no closer than 5 feet on-center.
A working shaft skin friction of 1,000 psf may be used in the sandstone within the bonded zone. The unbonded length should be assumed in the soil overlying the sandstone and until 15 feet of vertical cover is achieved based on an installation angle of 15 degrees. The minimum unbonded length is 10 feet.
Addendum Recommendations July 14, 2023 141 Archer Drive Project No. 23-141-SC Santa Cruz, California Page 2
Anchor capacity is dependent on tendon strength and bonded length.
One half of the anchors should be pull-tested to 110 percent of the design load. If any anchors fail, then all other anchors should be pull-tested.
It is a pleasure being associated with you on this project. If you have any questions or if we may be of further assistance, please do not hesitate to contact our office.
Sincerely, BUTANO GEOTECHNICAL ENGINEERING, INC.
Greg Bloom, PE, GE Principal Engineer
File details come from the government source that posted it. Updated .