Soil Nails and Shotcrete Facing Used to Stop Sloughing on a 1:1 Slope Caused by Excessive
Rainfall
December, 2006
Aljoya House at Mercer Island, Mercer Island, WA
Helical Anchors as Soil Nails to Anchor a Shotcrete Retaining Wall
Helical Pile Installation Contractor:
General Contractor:
Geotechnical Engineers:
T-OZ Construction Co. - Lakebay, WA
WG Clark Construction Co. - Mercer Island, WA
Associated Earth Sciences, Inc. - Kirkland, WA
Helical Anchor Specifications:
(14) 1.5” dia, SS5 Chance Anchors, with 8”, 10”, 12” Helicies; 20 KIPS Allowable Tension Load, Galvanized
Lawton silt at point of entry, moist to very moist, slightly fractured to non-fractured, with increased plasticity with increasing depth 14 blowcount to 24 blowcount at anticipated anchor TIP elev; 30 ft embedment depth
Helical Pile Manufacturer:
AB Chance - Centralia, MO
Project Overview
Continuous very heavy rains caused sloughing of the soils above an existing soldier
pile wall. A 1:1 cut had been created from the adjacent property line to the solider
pile wall, and the slope was failing. There was significant concern about the impact
on the adjacent office building if the sloughing was allowed to continue unchecked.
The forecast for continued rainfall led to the urgency for the construction of a
soil nail and shotcrete facing to stabilize the slope. Helical screw anchors were
chosen for this project because of the ability to install them with small, hand-portable
equipment, the lack of spoils, the immediate verifiability of the anchor capacities
and the ability to immediately apply shotcrete after anchor installation.
Two crews were mobilized to work off man-lifts to install the anchors to depths ranging
from 32 to 38 lineal feet with torques up to 4,600 ft. Lbs. The anchors were installed
in two rows, 7 to a row with one verification load test performed on an anchor in
each row. Although the sloughing had created a bench to work from at some of the
anchor locations along the top row, the sloughing created a dangerous slope along
the lower row thus requiring crews on the slope to be roped and tethered at all times
to anchors installed in the foundation of the adjacent building.
Specialists in Foundation Piering
and Underpinning Systems