Geo_Report-8730_Main St.pdf�F^
t-)* lip,
Geotechnical Report
8730 Main St.
Edmonds, WA
o w�N
fl"
�+
a +
Report Date: 5/19/2016
Dear Client,
As requested, we have conducted a geotechnical soil investigation to the standards of
the City of Edmonds regarding the construction of a secondary structure at 8730 Main St,
Edmonds. We performed a field investigation of the site as well as a thorough grain size analysis
utilizing USDA methodology and classification.
We have concluded, based on our observations, the drainage design for the proposed
structure should be created using an infiltration rate of 2 inches per hour. The short-term
infiltration rate of the soils onsite (sand) is 8 inches per hour and the City of Edmonds
recommends a correction factor of 4.
We trust the information provided in this report is sufficient for your current needs. If
you have any questions, please contact us.
Regards,
Cash M. Carr PE
Geotechnical Engineering Study
Regarding: Proposed additional structure
Introduction
This report presents the results of our grain size analysis and geotechnical report for the
proposed structure at 8730 Main St, Edmonds. This report is intended to address the need for
drainage capability tailored to the soils located beneath and surrounding the addition.
Site Description
The site of the additional structure is located in the backyard of the residence and is
accessible via driveway. A 4 ft. retaining wall follows the southwestern corner of the yard.
SITE MAP
southerntWhite cross marks'ocation of test pit (9ft north of property
western property line;I
Site Geology
According to the Washington State Department of Natural Resources, the sediment at
this location is Quaternary Vashon till (Qvt) and Quaternary Vashon advance outwash (Qva).
Both are comprised of unsorted, unlithified clays, silts, sands, and gravels deposited during the
Vashon Stade of the Fraser Glaciation. Distinctive features include well developed stratification
and local iron oxide staining. The Department of Natural Resources classifies this location as
having 'very low to low' liquefaction susceptibility and a seismic site class C to D with a seismic
design code D1.
Risks
While every effort has been made to define and quantify geologic risk to this site,
unknowns may exist beyond the reasonable scope of investigation.
Recommendations
We recommend an estimated design infiltration rate of 2 inches per hour as suggested
by the Edmonds Stormwater Code Supplement for soils that fall under the USDA classification
of 'sand.' This utilizes the short-term infiltration rate of 8 inches per hour for this soil type while
allowing for a correction factor of 4 (Figure 6).
Limitations
Recommendations included in this report are based on our understanding of the
proposed additions/repairs/construction activities as the specified location, our on-site
observations, and our test results. Conditions within the site may vary with location and it is
possible they may not be reflected in this report due to testing limitations. Should any
construction plans or site conditions change after initial exploration, please notify us
immediately so we can adjust our findings and/or plan of action accordingly.
Recommendations are made with the expectation that adequate compliance with
construction code and county regulation will be employed during construction activities. Land
use and site conditions may change over time and will require further research if additional
planning or construction is deemed necessary. We assume no responsibility for
misinterpretation or misuse of the recommendations included in this report. This report is
intended solely as geotechnical information about subsurface condition on the site and does
not include environmental hazard assessment at this time.
This report is intended to address drainage requirements particular to this site based on
our observations and test results. Because we have developed recommendations and testing
with this in mind, this report is not valid for any further purpose. We recommend that we be
consulted if additional scope is needed.
Soil Log
SOIL
DEPTH LAYER TRACES
F1"' USCS OF: COLOR NOTES:
MI
0.25 Silty Gravel Glacial till, lenses of severe oxidation, abundant
Sand organics, occasional charcoal, slightly damp, clasts
1,
0.5
(SM) ranging from 0.5-15cm
0.75.
el
�.... ...
5 Silty yGravel
.Grav� Grey'f-' oxidized, occasional lenses of darker sand likely
1.5 Sand 0row caused by organic decomposition
175 (SM)
j
2
2.25
2.5
2.75 r ;
3
-...325- ......
_ OfGradual increase in fines
3.5
3.75
4 SiltyGravel G. 'e y Higher clay content nearing 46", grey in color
4.25_ Sand
---m .e_.,_.....° 4.5 (SM)
4.75...
5 5' final depth of excavated test pit
No water table or sign of�..��_.__._�.......e....m_wm ...-m.............._
* g seasonal high water were encountered at the test pit
**A secondary test pit was examined in order to confirm findings
Grain Size Analysis Results
Table 1a. Grain size analysis of 0-1"
depth
Diameter (mm) Weight (g)
% Weight
% Passing
4.75 0 ...............................................45...............i,�......4.�...___
0.0100
..
2.000 87
45.5
.n 0�� _...��__..���._._�_..._...
..841 17
8.9
45.5
0.425 32
16.8
28.8
.47
10.47
18.3
.0.250.w20 -_
0.180
_ .
4.19
14.1
0.150 _...- _8
5
2.62
11.5
.. 0.002 7
3.66..__�_..�_.
2.6
_.......... _ w.
0.001 5
2.62
0.0
Total; 191
M
V
,° (J
10 or[
M
Grain Size Distribution 0-12" Sample
1,100 UO ROL 10"Cli
Grain Size (mml
Figure la. Grain size distribution of sample at 0-12" depth.
Table 1b. Normalized fines percentages for sample at 0-12" depth
Soil Type Diameter (mm) Percent Passing Normalized %
...........
Sand 2.0054.5 88.5
...... . . ..... ....... . . .. . . . . .... .......... --- — ------ . ........... .... .. I
. ,.-,,.
Silt 0.05 6.3 6.7
. 4
. ..... . . ............ .... ...... —,
Clav 0.002 2.6 .8
100% "ad 0 40 70 00 60 40 30
-4dgnwn P"tsk swW
Figure 1b. Results from grain size analysis for sample at 0-12" depth on USDA Textu9l£ »:.
taken from ESCS Appen«:2t<:-ig. . White star denotes determined classification (sand). I
Table 2a. Grain size analysis of 12-24" depth
Diameter (mm)
. ............
Weight (g) -
% Weight
-------
% Passing
4.75
0
0.0
100
2.000
88
49.4
50.6
0.841
158.4
42.1.
0.425
.
33
. ........... . . .
18.5 .
23.6
. . . ...... . . .......... . . . .........
0.250
20
---
11.24
- . ..... . .....
12.36
0' -- no
5
2.81
9.55
04
2.25
7.30
— - ------ — -----
0.050
8
4.49 ...... .
2.81
...................
0.002
2
1.12
1.69
0.001
3
1. 69
0.00
..Total.,......
otaI
. . ..............
M
M
10
'*0
SO
40
30
20
Grain Size Distribution 12-24" Sample
Grain 5411c Inw)
Figure 2a. Grain size distribution of sample at 12-24" depth,
Table 2b. Normalized fines percentages for sample at 12-24" depth
Soil Type -mmDiameter (mm) Percent Passing Normalized
%
Sand _2_00..-. ...... . . ..... ... ....... .......
..........
50.6 94.4
Silt 0.052.8 2.2
Clay 0.002 1.7 3.3
-40*AMW POVIC*00 O&W
Figure 2b. Results from grain size analysis for sample at 12-24" depth on USDA Textural
Triangle, taken from ESCS Appendix C pg. 68. White star denotes determined classification
(sand).
Table 3a. Grain
...........��......����....��...........���.
size analysis
_._.
of 24-36" depth
........................me.-...._
Diameter
(mm)
Weight (g)
% Weight % Passing ......
—
4.75...........
.......
0
0.0 100.0
2.000
43
25.7 '' 74.3
0.841_
18
10.8 63.5
..
_.._ ......................._.._
0.425
63
37.7 25.7
. 0.250
�...�..._.. ...� 24
14.37 11.38
...
...................................... 0.180
5._��....
_..�......w.......-,
2.99..��
8.38.,..
0.150
4
2.40 5.99
..
0.050
3.
�..-...
1.804.19
0.002
...� _.
4
. .. . . �19
2.40 1.80
0.001
...Total,
3
1.80 0.00
�...��...
�_,.._.,....,_...167...,........_....._....._......--....�..�.��.
70,0
M
i
M
1,00, 010 0 01 1 1
Grain SWe ImO
Figure 3a. Grain size distribution of sample at 24-36" depth.
Table 3b. Normalized fines percentages for sample at 24-36" depth
. . . . ......... ........ ....
Diameter Percent
Soil Type (mm) Passing Normalized %
Sand 2.00 74.3 94.4
Silt 0.05 4.2 3.2
Clay 0.002 1.8 2.4
G, 010
11giZE'au"I
-44ION"M Patcoolt W&W
Figure 3b. Results from grain size analysis for sample at 24-36" depth on USDA Textural
Triangle, taken from ESCS Appendix C pg. 68. White star denotes determined classification
(sand).
Table 4a. Grain
size analysis
of 36-48" depth
Diameter......_....._.........�._......_...._.__.
M) ... ... ....
Weight (g)
%Weight
% Passing
4.75
0
0.0
100.0
2.000
------------..g....1...._.._
...... 61
26.2
. . .... ... . . . . . .......
73.8
........... -
0.4
19
8.2
65.7
0.425
49
21.0
44.6
0.250
58
24.8919.74
_. .....
....
0.180
12
5.15
-
14.59
0.150
9
3 .8-6
10.73
0.050
7
3.00
7.73
0.002
8
3.43
4.29
0 .001
1 0
.29
0.00
Total:
233
1, CIG "',
M
M
Grain Size Imm)
Figure 4a. Grain size distribution of sample at 36-48" depth,
Table 4b. Normalized fines percentages for sample at 36-48" depth
Soil Type Diameter (
............. .... . . .....
mm) Percent Passing Normalized
Sand %
2.00 73.8 893
Silt
0.05 7.7 4.7
Clay 0.002 4.3 5.8
Textural Triangle U.S.D.A,.
40"
mom
P"Mat Oww
Figure 4b. Results from grain size analysis for sample at 36-48" depth on USDA Textijral
Triangle, taken from ESCS Appendix C pg. 68. White star denotes determined classification
(sand).
Table 5a. Grain size analysis of 48-60" depth
Diameter
(mm)
Weight (g)
%Weight % Passing
4.75
0
0.0 100.0
1—
............ .
2.000
65
26.6 73.4
0.841
18
7.4 66.0
0.425
57
23.4 42.6
0.250
50
20.49 22.13
. ...... ......... . ...... ...
0.180
. .....
18
7.38 14.75
0.150
7
2.87 11.89
.......
0.050
9
3.69 8.20
0.002
135.33
2.87
0.001
.. . .........
0.00
Total:
244
—2.87-
IC[ fl
0 10 L", () I ! I 1.. ^:i
Gr'ain S�Ze ('MMI
Figure 5a. Grain size distribution of sample at 48-60" depth.
Table 5b. Normalized fines pt
Soil Type Diameter (mm
Sand 2.00
Silt 0.05
Clav 0.002
_ntages for samp
Percent Passing
73.4
8.2
2.9
e at 48-60" depth
Normalized %
88.8
7.3
. .... . . . ......... . ---
3.9
. I IWIS 4M
Figure 5b. Results from grain size analysis for sample at 48-60" depth on USDA Textural
Triangle, taken from ESCS Appendix C pg. 68. White star denotes determined classification
(sand).
Table C�t; Recommended InGtra five Rates Based on USDA Soil Textural l lassi cadoon
Figure 6. Recommended infiltration rates based on USDA Soil Textural Classification, taken from
ECSC Appendix C pg. 67. Based on the results of our grain size analysis we recommend an
estimated design infiltration rate of 2 inches per hour.
EAtar¢` at Design
*Shur°t-I'vrrtt
t.'°o�rr°artitmn
(Long-term) Infiltrakion
iraffitrution Rate
Factor
Rate
(irr.,4'hr)
CF
(iujhr)
t k.a:rn iaand,� n vcisand gnAvehya bald (,a c: 20
2
1 �
9P%, tuml bolil ^w.1;i I'Md Vs n"4' tana6R ul lx'w:
10 10 sr�c^),"0
a
4
I.oarnv Sand
4
0.5
sw9taw,F`n L9a44 i8,
�
....._. 0,25 »..
(Ecology
N)05),
5),
Figure 6. Recommended infiltration rates based on USDA Soil Textural Classification, taken from
ECSC Appendix C pg. 67. Based on the results of our grain size analysis we recommend an
estimated design infiltration rate of 2 inches per hour.