HomeMy WebLinkAboutBLD1991-00121 Geo Tech 04r 02;91 OS: 17 t s.206" 452 8498 NI I• ,: .._...,...; -.,6-SOC. 16 002
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?1,• - 7 NORTHWESTERN TERRITORIES INC.
'1,, — Enoirvrs a i„,;-ine Sunreyr,rs 111 Plonners
Construction CoordirtatiOn St Materials resting
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3ANK STABILIZATION AAD ADTINC REINFORCEMENT
AT BUILDING SITE
IN PORT LUDLO , WASHINGTON
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04.•02 91 09: 17 V200 452 849S NTI`--,"I.`3RR ASSOC. C1003
BANK .STABILIZATION AND FOOTING REINFORCEMENT
• AT BUILDING bill
- IN PORTLO , ASHINGT N
GENERAL
On March 29, 1991, a geotechnical inspection and evaluation was made at a
residential. building site located at 49 Highland Drive in the Port KAidlow
-- -- development area near the Golf Course in Section 16, Township 28 North, - Range
1 East, W. i., Jefferson County, Washington. As shown in the accompanying
PhotogLaphs, foundation footing forms tiad already been erected for the pro-
posed residence. Some concern has been expressed by the County Building
Inspector that the unstable -bank which closely borders the back wall of the
house (shown in photographs), may cause future problems from slides, particu-
larly during heavy rainfall. •
Point of contact at the building site was Fans Vadder, the home building
contractor. The-owner -or this property is Rocco Azza_rito_
PROPERTY SITE DESCRIPTION
From Highland Drive, the building site is level for some 60 feet to the toe of
a bank which .is about 25 feet fn height and slopes at en inclination of some
50'. in order to maximize the space required for horse construction, one of
the house footings had to be constructed right up to the- toe of this present-
ly unstable le bank.
The country rock in this area is a heavy basaltic formation which outcrops at
or within three to four feet from ground surface at this particular crone ty.
(Note the bedrock outcrop in the upper left portion ot• the PtiotogL pf5 near
the top of bank) . The thin three to four feet mantle of overlying soil con-
sists of silt and sand with -about eighteen inches of topsoil within the upper
root zone.
CONCLUSIONS AND. RECOI NDAT ON. S
No retaining wail., is required along the bank toe adjacent to the back
house footing. However-, for long ter:: stability it: will be necessary to
strip away .the unstable soil and loose slabs of weathered rock all ailing
the bank face adjacent to and overlapping the house footing about tan
-- feet on each side. This can be readily accomplished by a bac:khoe which
will soon encounter firm bedrock within a few feet of the ground surface
along the- bank face. Once the backhoe meets refusal, this bank should
become and-remain generally stable in future years.
2. During the process of bank scaling, two trees will have their roots
undermined _ and therefore pose a threat to the home if they are not
04 '029I 09: 18 Tr206 452 8498 NTT-(L R1i ASSOC. Z004
• removed. These two vulnerable trees were pointed out to the contractor
during the site visit.
3. To accomplish the above recommended.-band stabilization most efficiently
by mechanical_ backhoe, it will be necessary to remove-most of the exist-
ing footing-forms. This may be advantageous since a somewhat larger and
more heavily reinforced house footing than those observed at the site is
recommended here due to the possibility of differential settlement.
Such a possibility exists since portions of the tooting are placed
alternately upon relatively softer soil and then on much firmer bedrock.
To bridge across any such variations in around support, it is suggested
that the house footings -be modified in tee following manner:
a. Increase the footing width to 16 inches and. depth to 8 inches.
b. Increase the horizontal rebars in the footing to three #47s.
c. Place two #4 horizontal bars in the footing wall and place all
corresponding vertical #4 bars at two feet on centers.
4. As an alternative to the foregoing strengthening scheme for the house
footing, all of the footings could be excavated down to uniform bedrock,
and the existing lessor strength footing design ;,':ould then be retained.
STANDARD ,DISCLOSURE- STAT .
This report is based on a .visual inspection of the existing site conditions
and/or facility_ No scientific measurements, tests or calculations were
performed. The findings and report are limited to the nnrhal standard of care
of the industry for an investigation without benefit of scientific data and..
Calculations. Unlce; construction flans are rcwicwed .,no the construction
work is inspected by_the nq.ineer, no warrenty is made by the Engineer con-
- cawing conformity of the-construction of the conclusions ons Mild ecommend: rrsne
of this report.
Norman A. Dixon, FRG
engineering
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