HomeMy WebLinkAboutRS_Geotechnical_Response_Secondary_Review_180814.pdfTERRA ASSOCIATES, Inc.
Consultants in Geotechnical Engineering, Geology
and
Environmental Earth Sciences
August 14, 2018
Project No. T-7677
Mr. Kyle Lublin
Pulte Homes of Washington, Inc.
3535 Factoria Blvd SE, Suite 110
Bellevue, Washington 98006
Subject: Response to Comments
Forest Terrace
2611 Union Avenue NE
Renton, Washington
Reference: 1. Geotechnical Report, Vandermay, 2611 Union Avenue NE, Renton, Washington,
Project No. T-7677, prepared by Terra Associates, Inc., dated July 19, 2017
2. Protected Slope Analysis, Forest Terrace, 2611 Union Avenue NE, Renton, Washington,
Project No. T-7677, prepared by Terra Associates, Inc., dated June 14, 2018,
revised June 18, 2018
3. Geotechnical Engineering Review, Forest Terrace, Renton, Washington,
File No. 0693-082-00, prepared by GeoEngineers, dated August 7, 2018
Dear Mr. Lublin:
We have reviewed comments received from the City of Renton regarding geotechnical recommendations
contained in the referenced design reports. The comments are summarized in the referenced letter to the City of
Renton from GeoEngineers. The following is our response to the comments in the order listed in their letter.
Comment]
As recommended, we have reviewed the Washington State Department of Transportation Geotechnical Design
Manual (WSDOT GDM) and have revised our analysis to follow the recommendations in Chapter 7. Based on
our review of Chapter 6, it appears that the seismic analysis is not necessary for this slope. As such, we have
removed the seismic portion of our analysis.
12220 113th Avenue NE, Ste. 130, Kirkland, Washington 98034
Phone (425) 821-7777 • Fax (425) 821-4334
Mr. Kyle Lublin
August 14, 2018
Comment 2
We have prepared a figure that shows the details of the proposed cut rockeries for the Forest Terrace project.
The figure shows the proposed height, minimum width, batter, drainage, and embedment of the rockeries. The
figure is attached to this response letter.
Comment 3
Based on our review of Chapter 6 of the WSDOT GDM, a seismic analysis is not required for this slope.
Therefore, we have revised our analysis to follow the WSDOT GDM and have removed the seismic portion
from our slope stability results.
Comment 4
We have been retained by Pulte Homes of Washington, Inc. to observe construction. We will pay careful
attention to the cut rockeries to ensure the soil conditions are as expected. If soil conditions vary from what was
observed in the test pits, we will work with Pulte to ensure the rockeries and the slope meet the requirements of
the approved plans.
Comment 5
We have revised the slope stability analysis and have included the additional potential failure surfaces as
requested. The results of the analysis indicate the slope remains stable in the post construction condition. We
would note that one result shows a factor of safety of 1.22; however, this failure surface is through the face of
the rockery only and does not include the overall slope. We have included this analysis to show the necessity of
moving the limits of the analysis around to gain useful failure surfaces that include the overall slope, as well as
the rockeries. The additional results are attached to this letter.
Comment 6
We acknowledge that the advance outwash soils will be susceptible to erosion and we will work with Pulte and
the contractor to ensure all necessary measures are taken onsite to ensure long term slope stability.
Comment 7
The embedment for the rockeries is shown on the attached rockery detail and will be a minimum of 1.5 feet
below the adjacent grade. The embedment was not modeled because we are not relying on the embedment for
overall stability; we are only relying on the embedment to protect the foundation of the rockery from being
undermined.
Comment 8
As shown on the attached figure, the rockeries will be constructed with a 1:6 (Horizontal: Vertical) batter.
Project No. T-7677
Page No. 2
Mr. Kyle Lublin
August 14, 2018
Comment 9
We have included a filter fabric to be placed between the cut slope and the 12 inch drainage column that will be
constructed behind the rockeries. This should be sufficient to prevent soil migration from the sand outwasb to
the drainage column.
We trust the information presented is sufficient for your current needs. If you have any questions or require
additional information, please call.
Sincerely MAno 14 S
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Carolyn 4?66 Cta
Project E 6jSTR'�eeckerny
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Enclosed: Figu Details
Slide Output
Project No. T-7677
Page No. 3
2(MAX)
1�
1' COMPACTED STRUCTURAL FILL
ABOVE DRAIN COLUMN (TYP.)
4' MAX6 V CRUSHED ROCK FILTER MATERIAL,
BETWEEN 2 AND 4 INCH SIZE WITH
LESS THAN 2% FINES WIDE DRAIN
COLUMN (TYP.)
5' MAX.
2(MAX) H/3
1.5'
(MIN.)
V MIN.
1 i
4' MAX 6 DENSE NATIVE SOILS (TYP.)
WRAP DRAINAGE COLUMN IN MIRAFI 140N
FILTER FABRIC OR EQUIVALENT (TYP.)
(MIN.)
COMPETENT NATIVE SOIL TO BE /I- KEYWAY -1
VERIFIED BY GEOTECHNICAL J
ENGINEER 4" MINIMUM DIAMETER
KEYWAY SHOULD BE SLOPED DRAIN PIPE SURROUNDED BY
DOWN TOWARDS THE FACE CLEAN WASHED 3/4" DRAIN
BEING PROTECTED POINT OF DISCHARGE (TYP.)
NOT TO SCALE
ROCKERY NOTES:
1. ROCKERY CONSTRUCTION SHALL BE COMPLETED
IN ACCORDANCE WITH THE ASSOCIATION OF
ROCKERY (ARC) CONTRACTORS GUIDELINES.
2. ROCK USED MUST MEET THE REQUIREMENTS
FOR ROCK QUALITY SPECIFIED IN SECTIONS 9-13.7(1)
OF THE WSDOT STANDARDS SPECIFICATIONS (2004).
3. ALL CAP ROCKS MUST BE SECURE AND NOT ABLE
TO BE DISLODGED BY HAND.
SLIDE OUTPUT
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8/13/2018 192942156.htm
Slide Analysis Information
Roadway
Project Summary
File Name: Roadway.slmd
Slide Modeler Version: 8.016
Project Title: Forest Terrace
Analysis: Post Construction - Various Limits
Author: C. Decker
Company: Terra Associates, Inc.
Date Created: 6/8/2018, 3:14:01 PM
Currently Open Scenarios
Group Name
Scenario Name
Global Minimum
Compute Time
Post Construction
Master Scenario
Bishop Simplified: 1.224330
00h:00m:01.488s
Janbu Simplified: 1.274310
Upper Slope Condition
Master Scenario
Bishop Simplified: 1.387200
00h:00m:00.876s
Janbu Simplified: 1.326200
oMaster
Scenario
Bishop Simplified: 1.392110
00h:00m:00.933s
Post Construction -Slope Limits
Janbu Simplified: 1.339530
General Settings
Units of Measurement: Imperial Units
Time Units: days
Permeability Units: feet/second
Data Output: Standard
Failure Direction: Right to Left
Analysis Options
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All Open Scenarios
Slices Type: Vertical
Analysis Methods Used
Bishop simplified
Janbu simplified
Number of slices:
50
Tolerance:
0.005
Maximum number of iterations:
75
Check malpha < 0.2:
Yes
Create Interslice boundaries at intersections
Yes
with water tables and piezos:
None
Initial trial value of FS:
1
Steffensen Iteration:
Yes
Groundwater Analysis
All Open Scenarios
Groundwater Method:
Water Surfaces
Pore Fluid Unit Weight [lbs/ft3]:
62.4
Use negative pore pressure cutoff:
Yes
Maximum negative pore pressure [psf]:
0
Advanced Groundwater Method:
None
Random Numbers
All Open Scenarios
Pseudo -random Seed: 10116
Random Number Generation Method: Park and Miller v.3
Surface Options
192942156.htm
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8/13/2018
All Open Scenarios
Advance Outwash
Surface Type:
Circular
Search Method: Auto Refine Search
Divisions along slope:
20
Circles per division:
10
Number of iterations:
10
Divisions to use in next iteration:
50%
Composite Surfaces:
Disabled
Minimum Elevation:
Not Defined
Minimum Depth:
Not Defined
Minimum Area:
Not Defined
Minimum Weight:
Not Defined
Seismic Loading
All Open Scenarios
Advanced seismic analysis: No
Staged pseudostatic analysis: No
Materials
192942156.htm
Property
Advance Outwash
New Structural Fill
Rockery Rocks
Color
Ll
r il
Strength Type
Mohr -Coulomb
Mohr -Coulomb
Mohr -Coulomb
Unit Weight [lbs/ft3]
120
125
125
Cohesion [psf]
0
0
75
Friction Angle [°]
38
34
45
Water Surface
Assigned per scenario
Assigned per scenario
Assigned per scenario
Ru Value
0
0
0
Materials In Use
Material Master Scenario 0 Master Scenario 0 Master Scenario
Advance Outwash❑
New Structural Fill ❑
Rockery Rocks ❑
Global Minimums
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8/13/2018 192942156.htm
Post Construction 0 Upper Slope Condition 0 Post Construction - Slope Limits a
Method: bishop simplified Method: bishop simplified Method: bishop simplified
FS
1.224330
FS
1.387200
FS
1.392110
Center:
72.466,
Center:
47.479,
Center:
61.599,
Right Slip Surface
96.348
Endpoint:
144.965
Left Slope
124.794
Radius:
18.656
Radius:
73.183
Radius:
49.219
Left Slip Surface
88.000,
Left Slip Surface
77.000,
Left Slip Surface
77.000,
Endpoint:
86.016
Endpoint:
78.000
Endpoint:
78.047
Right Slip Surface
90.009,
Right Slip Surface
99.998,
Right Slip Surface
99.991,
Endpoint:
90.000
Endpoint:
93.999
Endpoint:
93.995
Left Slope
88.000
Left Slope
77.000
Left Slope
77.000
Intercept:
90.000
Intercept:
82.000
Intercept:
82.000
Right Slope
90.009
Right Slope
99.998
Right Slope
99.991
Intercept:
90.000
Intercept:
93.999
Intercept:
93.995
Resisting Moment:
10937.2
Resisting Moment:
412138 lb-
Resisting Moment:
323243 I b -
Ib -ft
ft
ft
Driving Moment:
8933.19
Driving Moment:
297100 Ib-
Driving Moment:
232195 lb -
Ib -ft
ft
ft
Total Slice Area:
4.40107
Total Slice Area:
61.2975 ft2
Total Slice Area:
73.4564 ft2
ft2
Surface Horizontal
22.9978 ft
Surface Horizontal
22.991 ft
Surface Horizontal
2.00925 ft
Width:
Width:
Width:
Surface Average
2.66537 ft
Surface Average
3.19501 ft
Surface Average
2.19041 ft
Height:
Height:
Height:
Method: janbu simplified
FS
1.274310
Center:
72.466,
96.348
Radius:
18.656
Left Slip Surface
88.000,
Endpoint:
86.016
Right Slip Surface
90.009,
Endpoint:
90.000
Left Slope
88.000
Intercept:
90.000
Right Slope
90.009
Intercept:
90.000
Resisting Horizontal
289.197 lb
Force:
Driving Horizontal
226.943 Ib
Force:
Total Slice Area: 4.40107
ft2
Surface Horizontal 2.00925 ft
Width:
Surface Average 2.19041 ft
Height:
Method: janbu simplified
FS
1.326200
Center:
75.776,
97.626
Radius:
20.063
Left Slip Surface
71.615,
Endpoint:
78.000
Right Slip Surface
94.857,
Endpoint:
91.429
Resisting Horizontal
5868.21 Ib
Force:
82.000
Driving Horizontal
4424.841b
Force:
93.367
Total Slice Area: 83.0335
ft2
Surface Horizontal 23.2418 ft
Width:
Surface Average 3.5726 ft
Height:
Method: janbu simplified
FS
1.339530
Center:
66.167,
116.382
Radius:
39.879
Left Slip Surface
77.000,
Endpoint:
78.003
Right Slip Surface
98.734,
Endpoint:
93.367
Left Slope
77.000
Intercept:
82.000
Right Slope
98.734
Intercept:
93.367
Resisting Horizontal
5518.91 Ib
Force:
Driving Horizontal
4120.03 Ib
Force:
Total Slice Area:
73.9007 ft2
Surface Horizontal
21.7337 ft
Width:
Surface Average
3.40028 ft
Height:
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Valid/Invalid Surfaces
Post Construction 0
Method: bishop simplified
Number of Valid Surfaces: 11357
Number of Invalid Surfaces: 22
Error Codes:
Error Code -112 reported for
22 surfaces
Method: janbu simplified
Number of Valid Surfaces: 11264
Number of Invalid Surfaces: 115
Error Codes:
Error Code -108 reported for
115 surfaces
192942156.htm
Upper Slope Condition 0
Method: bishop simplified
Number of Valid 5984
Surfaces:
Number of Invalid 0
Surfaces:
Method: janbu simplified
Number of Valid 5984
Surfaces:
Number of Invalid 0
Surfaces:
Post Construction - Slope Limits 0
Method: bishop simplified
Number of Valid Surfaces: 6819
Number of Invalid Surfaces: 24
Error Codes:
Error Code -112 reported for
24 surfaces
Method: janbu simplified
Number of Valid Surfaces: 6842
Number of Invalid Surfaces: 1
Error Codes:
Error Code -108 reported for 1
surface
Error Codes
The following errors were encountered during the computation:
-108 = Total driving moment or total driving force < 0.1. This is to limit the calculation of extremely high safety factors if the
driving force is very small (0.1 is an arbitrary number).
-112 = The coefficient M -Alpha = cos(alpha)(1+tan(alpha)tan(phi)/F) < 0.2 for the final iteration of the safety factor calculation.
This screens out some slip surfaces which may not be valid in the context of the analysis, in particular, deep seated slip
surfaces with many high negative base angle slices in the passive zone.
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