HomeMy WebLinkAboutF_Grant Avenue_Geotechnical Letter.pdf
Cobalt Geosciences, LLC
P.O. Box 82243
Kenmore, Washington 98028
Date: June 27, 2019 Project: 1600 Grant Avenue S. Job No.: 2019-162
Contractor: Gary Location: Renton Weather: Sun 60
Observations:
At your request and authorization, Cobalt Geosciences, LLC was on site to evaluate the shallow
soil conditions in the area of the proposed detention vault. We have reviewed a geotechnical
report prepared by Nelson Geotechnical dated June 10, 2005 as well as our previous geotechnical
letters for the project.
Based on the civil engineering plans, the proposed detention vault will require excavations of 17 to
23 feet below grade as part of construction. Near the southwestern corner of the vault,
excavations of about 20 feet will be required and the lateral distance to the curbline along Grant
Avenue S. is approximately 20 feet. We understand that the contractor will place a single block
height ecology block wall along the back of the curb and embedded about 12 inches below the top
of curb. Additionally, a fence, lights, and Jersey barrier should be placed along the curbline
during construction.
The soils observed in the existing vault area sidewalls consist of 6 to 8 feet of medium dense silty-
sands with gravels. These soils include native glacial till and undocumented fill along the south
end of the vault area. Dense to very dense glacial till is situated below the weathered soils and fill
materials.
It appears feasible to excavate a series of benches or continuous slope from the area near the
roadway and ecology block wall downward to the base of the vault excavation. We recommend a
minimum 2 feet wide level bench in front of the single-block height ecology block wall. From that
point, a series of benches 4 feet wide and 4 feet tall or a continuous 1H:1V slope may extend down
until dense to very dense glacial till is encountered (and verified by the geotechnical engineer).
Temporary excavations in the unweathered glacial till may extend downward as a continuous
slope at 3/4H:1V to the bottom of the vault. These excavations must be verified in the field as safe
by the geotechnical engineer during the construction work and periodically until the vault has
been backfilled. All slopes must be covered with clear visqueen when active work is not taking
place. The geotechnical engineer must be notified daily when work will take place below these
slope areas so that they may verify stability prior to personnel entering the excavation.
If during the excavation process down to the bottom of vault elevations; it is determined that
there is inadequate lateral space to create a safe temporary excavation at the angles discussed
above, it will be necessary to either re-grade the slope system, extending the top of the excavation
into the shoulder of the roadway or in a worse-case scenario, install a short soldier pile wall at the
base of the excavation. Figure 1 shows the excavation recommendations. We have attached the
results of a slope stability analysis for static, temporary conditions. We have utilized typical soil
parameters for glacial till soils along with loads associated with traffic on the roadway.
There is a very slight chance of soil movement and nearly no chance of roadway settlement. We
recommend daily visits by the geotechnical engineer or representative from the time period
June 27, 2019
Page 2 of 2 Reference: Grant Place
between excavation work and until backfill is within 6 feet of the finish grade. Additionally, we
recommend that the project surveyor install a series of pins or monuments between the curb and
south drive lane and on the level bench just south of the ecology block (near the curb). Similar
points should be installed every 20 feet along the detention vault excavation where the steeper
excavations are required (about 40 feet laterally along Grant). Survey data should be provided
within 24 hours of data acquisition.
Sincerely,
Cobalt Geosciences, LLC
Phil Haberman, PE, LG, LEG
Principal
PH/sc
2063311097; phil@cobaltgeo.com
6/26/2020
6/26/2020
6/26/2020
*** GEOSTASE(R) ***
** GEOSTASE(R) (c)Copyright by Garry H. Gregory, Ph.D., P.E.,D.GE **
** Current Version 4.30.24-Double Precision, August 2018 **
(All Rights Reserved-Unauthorized Use Prohibited)
*********************************************************************************
SLOPE STABILITY ANALYSIS SOFTWARE
Simplified Bishop, Simplified Janbu, or General Equilibrium (GE) Options.
(Spencer, Morgenstern-Price, USACE, and Lowe & Karafiath)
Including Pier/Pile, Planar Reinf, Nail, Tieback, Line Loads
Applied Forces, Fiber-Reinforced Soil (FRS), Distributed Loads
Nonlinear Undrained Shear Strength, Curved Strength Envelope,
Anisotropic Strengths, Water Surfaces, 3-Stage Rapid Drawdown
2- or 3-Stage Pseudo-Static & Simplified Newmark Seismic Analyses.
*********************************************************************************
Analysis Date: 6/ 27/ 2019
Analysis Time:
Analysis By: Cobalt Geosciences, LLC
Input File Name: C:\Users\Phil\Desktop\Arlington Geostase\GRANT
TEMPO.gsd
Output File Name: C:\Users\Phil\Desktop\Arlington Geostase\GRANT
TEMPO.OUT
Unit System: English
PROJECT: Grant Place
DESCRIPTION: 1600 Grant, Renton
BOUNDARY DATA
6 Surface Boundaries
7 Total Boundaries
Boundary X - 1 Y - 1 X - 2 Y - 2 Soil Type
No. (ft) (ft) (ft) (ft) Below Bnd
1 0.000 50.000 20.000 50.000 1
2 20.000 50.000 25.000 50.000 1
3 25.000 50.000 29.000 50.000 1
4 29.000 50.000 37.000 42.000 1
5 37.000 42.000 47.000 27.000 2
6 47.000 27.000 67.000 27.000 2
7 0.000 42.000 37.000 42.000 2
User Specified X-Origin = 0.000(ft)
User Specified Y-Origin = 0.000(ft)
MOHR-COULOMB SOIL PARAMETERS
2 Type(s) of Soil Defined
Soil Number Moist Saturated Cohesion Friction Pore Pressure Water
Water
and Unit Wt. Unit Wt. Intercept Angle Pressure Constant Surface
Option
Description (pcf) (pcf) (psf) (deg) Ratio(ru) (psf) No.
1 Weathered Till 115.0 125.0 0.00 34.00 0.000 0.0 1
0
2 Glacial Till 120.0 130.0 100.00 38.00 0.000 0.0 1
0
WATER SURFACE DATA
1 Water Surface(s) Defined
Unit Weight of Water = 64.000 (pcf)
Water Surface No. 1 Specified by 4 Coordinate Points
Pore Pressure Inclination Factor = 0.50
Point X-Water Y-Water
No. (ft) (ft)
1 0.00 58.00
2 96.00 30.00
3 120.00 20.00
4 155.00 20.00
WATER SURFACE DATA HAS BEEN SUPPRESSED
SEISMIC (EARTHQUAKE) DATA
Specified Peak Ground Acceleration Coefficient (PGA) = 0.000(g)
Default Velocity = 0.000(ft) per second
Specified Horizontal Earthquake Coefficient (kh) = -.2800(g)
Specified Vertical Earthquake Coefficient (kv) = 0.000(g)
(NOTE:Input Velocity = 0.0 will result in default Peak
Velocity = 2 times(PGA) times 2.5 fps or 0.762 mps)
Specified Seismic Pore-Pressure Factor = 0.000
Horizontal Seismic Force is Applied at Center of Gravity of Slices
EARTHQUAKE DATA HAS BEEN SUPPRESSED
LINELOADS OR POINT LOADS
2 Lineload(s) Specified
Lineload X-Pos Y-Pos Force Spacing Inclination
No. (ft) (ft) (lbs) (ft) (deg)
1 2.00 50.00 400.0 2.0 90.00
2 22.00 50.00 400.0 1.0 90.00
METHOD A Selected: LINELOAD capacity subtracted from Driving Forces/Moments.
NOTE - An Equivalent Line Force Is Calculated For Each Row Of Lineloads
Assuming A Uniform Distribution Of force Horizontally Between
Individual Point Loads (if applicable).
TRIAL FAILURE SURFACE DATA
Circular Trial Failure Surfaces Have Been Generated Using A Random Procedure.
1000 Trial Surfaces Have Been Generated.
1000 Surfaces Generated at Increments of 0.2402(in) Equally Spaced Within the
Start Range
Along The Specified Surface Between X = 0.00(ft)
and X = 20.00(ft)
Each Surface Enters within a Range Between X = 39.00(ft)
and X = 60.00(ft)
Unless XCLUDE Lines Were Specified, The Minimum Elevation
To Which A Surface Extends Is Y = 0.00(ft)
Specified Maximum Radius = 5000.000(ft)
5.000(ft) Line Segments Were Used For Each Trial Failure Surface.
The Spencer Method Was Selected for FS Analysis.
Selected fx function = Constant (1.0)
SELECTED CONVERGENCE PARAMETERS FOR SPENCER METHOD:
Initial estimate of FS = 1.500
FS tolerance = 0.000001000
Initial estimate of theta(deg) = 15.00
Theta tolerance(radians) = 0.0001000
Minimum theta(deg) = -45.00 ; Maximum theta(deg) = 45.00
Theta convergence Step Factor = 5000.00
Maximum number of iterations = 50
Allowable negative side force = -1000.0(lbs)
Maximum force imbalance = 100.000000(lbs)
Maximum moment imbalance = 100.000000 (ft/lbs)
Selected Lambda Coefficient = 1.00
Specified Tension Crack Water Depth Factor = 0.000
Total Number of Trial Surfaces Attempted = 1000
WARNING! The Factor of Safety Calculation for one or More Trial Surfaces
Did Not Converge in 50 Iterations.
Number of Trial Surfaces with Non-Converged FS = 461
Number of Trial Surfaces With Valid FS = 539
Percentage of Trial Surfaces With Non-Converged and/or
Non-Valid FS Solutions of the Total Attempted = 46.1 %
Statistical Data On All Valid FS Values:
FS Max = 3.949 FS Min = 1.517 FS Ave = 2.236
Standard Deviation = 0.439 Coefficient of Variation = 19.62 %
Critical Surface is Sequence Number 535 of Those Analyzed.
*****BEGINNING OF DETAILED GEOSTASE OUTPUT FOR CRITICAL SURFACE FROM A
SEARCH*****
BACK-CALCULATED CIRCULAR SURFACE PARAMETERS:
Circle Center At X = 857.436744(ft) ; Y = 1624.705094(ft); and Radius =
1784.692358(ft)
Circular Trial Failure Surface Generated With 6 Coordinate Points
Point X-Coord. Y-Coord.
No. (ft) (ft)
1 17.538 50.000
2 21.953 47.653
3 26.374 45.319
4 30.802 42.997
5 35.237 40.687
6 39.264 38.603
LINE LOAD FORCE(S) DISTRIBUTED TO ADJACENT SLICES:
Slice No. H-Force V-Force
2 0.000 156.202
3 0.000 243.798
Force Distribution Factor = 0.500
Sum of the Lineload Forces = 600.00(lbs)
Iter. Theta FS FS
No. (deg) (Moment) (Force)
(fx=1.0) Lambda Delta FS
1 -15.0000 1.397042 1.516231 -0.268 0.1191890E+00
2 -19.9500 1.564362 1.517297 -0.363 0.4706517E-01
3 -18.5480 1.429439 1.516990 -0.336 0.8755032E-01
4 -19.4599 1.474328 1.517189 -0.353 0.4286094E-01
5 -20.3342 2.123034 1.517382 -0.371 0.6056523E+00
6 -19.5177 1.480084 1.517202 -0.354 0.3711747E-01
7 -19.5648 1.485330 1.517212 -0.355 0.3188224E-01
8 -19.8518 1.534745 1.517275 -0.361 0.1746999E-01
9 -19.7502 1.512691 1.517253 -0.359 0.4562339E-02
10 -19.7712 1.516724 1.517258 -0.359 0.5336489E-03
11 -19.7740 1.517276 1.517258 -0.360 0.1755442E-04
12 -19.7739 1.517258 1.517258 -0.360 0.1598607E-06
Factor Of Safety For The Preceding Specified Surface = 1.517
Theta (fx = 1.0) = -19.77 Deg Lambda = -0.360
The Spencer Method Has Been Selected For FS Analysis.
Selected fx function = Constant (1.0)
SELECTED CONVERGENCE PARAMETERS FOR ANALYSIS METHOD:
Initial estimate of FS = 1.500
FS tolerance = 0.000001000
Initial estimate of theta(deg) = 15.00
Theta tolerance(radians) = 0.0001000
Minimum theta(deg) = -45.00 ; Maximum theta(deg) = 45.00
Theta convergence Step Factor = 5000.00
Maximum number of iterations = 50
Maximum force imbalance = 100.000000(lbs)
Maximum moment imbalance(if Applicable) = 100.000000 (ft/lbs)
Selected Lambda Coefficient = 1.00
Tension Crack Water Force = 0.00(lbs)
Specified Tension Crack Water Depth Factor = 0.000
Depth of Tension Crack (zo) at Side of First Slice = 0.000(ft)
Depth of Water in Tension Crack = 0.000(ft)
Theoretical Tension Crack Depth = 3.135(ft)
NOTE: In Table 1 following, when a tension crack with water is present on the
first slice (right facing slope) or on the last slice (left facing slope), the
"side force" in the tension crack is set equal to the water pressure resultant.
*** Table 1 - Line of Thrust(if applicable) and Slice Force Data ***
Slice X Y Side Force fx Force Angle Vert.
Shear
No. Coord. Coord. h/H (lbs) (Deg)
Force(lbs)
1 17.54 50.00 0.000 0.00 1.000 0.00 0.0
2 20.00 49.35 0.500 13.52 1.000 -19.77 -4.6
3 21.95 48.02 0.158 54.85 1.000 -19.77 -18.6
4 25.00 42.33 0.000- 149.36 1.000 -19.77 -50.5
5 26.37 42.71 0.000- 197.20 1.000 -19.77 -66.7
6 29.00 42.62 0.000- 306.24 1.000 -19.77 -103.6
7 30.80 42.21 0.000- 384.70 1.000 -19.77 -130.1
8 32.72 41.62 0.000- 451.90 1.000 -19.77 -152.9
9 35.24 40.60 0.000- 280.49 1.000 -19.77 -94.9
10 37.00 40.00 0.103 158.05 1.000 -19.77 -53.5
NOTE: A value of 0.000- for h/H indicates that the line of thrust is at or below
the lower boundary of the sliding mass. A value of 1.000+ for h/H indicates that
the line of thrust is at or above the upper boundary of the sliding mass.
***Table 2 - Geometry Data on the 10 Slices***
Slice Width Height X-Cntr Y-Cntr-Base Y-Cntr-Top Alpha Beta Base Length
No. (ft) (ft) (ft) (ft) (ft) (deg) (deg) (ft)
1 2.46 0.65 18.77 49.35 50.00 -27.99 0.00 2.79
2 1.95 1.83 20.98 48.17 50.00 -27.99 0.00 2.21
3 3.05 3.15 23.48 46.85 50.00 -27.83 0.00 3.45
4 1.37 4.32 25.69 45.68 50.00 -27.83 0.00 1.55
5 2.63 5.37 27.69 44.63 50.00 -27.67 0.00 2.97
6 1.80 5.63 29.90 43.47 49.10 -27.67 -45.00 2.03
7 1.91 4.74 31.76 42.50 47.24 -27.51 -45.00 2.16
8 2.52 3.68 33.98 41.34 45.02 -27.51 -45.00 2.84
9 1.76 2.65 36.12 40.23 42.88 -27.35 -45.00 1.99
10 2.26 1.11 38.13 39.19 40.30 -27.35 -56.31 2.55
***Table 2A - Coordinates of Slice Points Defining the Slip Surface***
Point X-Pt Y-Pt
No. (ft) (ft)
1 17.537538 50.000000
2 20.000000 48.691026
3 21.952528 47.653118
4 25.000000 46.044104
5 26.374077 45.318614
6 29.000000 43.941564
7 30.802148 42.996507
8 32.715420 42.000000
9 35.236708 40.686814
10 37.000000 39.774694
11 39.264442 38.603337
***Table 3 - Force and Pore Pressure Data On The 10 Slices (Excluding Reinforcement)***
Ubeta Ubeta Ualpha Earthquake
Force Stress Force Pore Force Distributed
Slice Weight Top Top Bot Pressure Hor Ver Load
No. (lbs) (lbs) (psf) (lbs) (psf) (lbs) (lbs) (lbs)
1 185.3 0.0 0.0 0.0 0.0 0.0 0.0 0.00
2 410.4 0.0 0.0 0.0 0.0 0.0 0.0 0.00
3 1104.4 0.0 0.0 0.0 0.0 0.0 0.0 0.00
4 682.4 0.0 0.0 0.0 0.0 0.0 0.0 0.00
5 1621.6 0.0 0.0 0.0 0.0 0.0 0.0 0.00
6 1166.8 0.0 0.0 0.0 0.0 0.0 0.0 0.00
7 1043.6 0.0 0.0 0.0 0.0 0.0 0.0 0.00
8 1075.4 0.0 0.0 0.0 0.0 0.0 0.0 0.00
9 553.1 0.0 0.0 0.0 0.0 0.0 0.0 0.00
10 302.3 0.0 0.0 0.0 0.0 0.0 0.0 0.00
***Table 3A - Center of Pressure of Water Loads On the 10 Slices***
Only Applicable Slices Listed
Slice X-Ubeta Y-Ubeta Ubeta-Moment
No. (ft) (ft) (ft/lbs)
***Table 3B - Center of Pressure of Distributed Loads On the 10 Slices***
Only Applicable Slices Listed
Slice X-Dload Y-Dload Dist-Load Dload-Moment
No. (ft) (ft) (lbs) (ft/lbs)
TOTAL WEIGHT OF SLIDING MASS = 8145.54(lbs)
EFFECTIVE WEIGHT OF SLIDING MASS = 8145.54(lbs)
TOTAL AREA OF SLIDING MASS = 70.51(ft2)
***TABLE 4 - SOIL STRENGTH & SOIL OPTIONS DATA ON THE 10 SLICES***
Slice Soil Cohesion Phi(Deg) Options
No. Type (psf)
1 1 0.00 34.00
2 1 0.00 34.00
3 1 0.00 34.00
4 1 0.00 34.00
5 1 0.00 34.00
6 1 0.00 34.00
7 1 0.00 34.00
8 2 100.00 38.00
9 2 100.00 38.00
10 2 100.00 38.00
SOIL OPTIONS: A = ANISOTROPIC, C = CURVED STRENGTH ENVELOPE (TANGENT PHI & C),
F = FIBER-REINFORCED SOIL (FRS), N = NONLINEAR UNDRAINED SHEAR STRENGTH,
R = RAPID DRAWDOWN OR RAPID LOADING (SEISMIC) SHEAR STRENGTH
NOTE: Phi and C in Table 4 are modified values based on specified
Soil Options (if any).
***TABLE 5 - Total Base Stress Data on the 10 Slices***
Slice Alpha X-Coord. Base Total Total Total
No. (deg) Slice Cntr Leng. Normal Stress Vert. Stress Normal/Vert.
* (ft) (ft) (psf) (psf) Stress Ratio
1 -27.99 18.77 2.79 59.38 75.27 0.789
2 -27.99 20.98 2.21 228.95 210.21 1.089
3 -27.83 23.48 3.45 349.81 362.41 0.965
4 -27.83 25.69 1.55 392.69 496.64 0.791
5 -27.67 27.69 2.97 489.40 617.54 0.792
6 -27.67 29.90 2.03 513.09 647.44 0.792
7 -27.51 31.76 2.16 433.24 545.44 0.794
8 -27.51 33.98 2.84 327.41 426.54 0.768
9 -27.35 36.12 1.99 239.34 313.70 0.763
10 -27.35 38.13 2.55 97.16 133.52 0.728
***TABLE 5A - Total Base Force Data on the 10 Slices***
Slice Alpha X-Coord. Base Total Total Total
No. (deg) Slice Cntr Leng. Normal Force Vert. Force Normal/Vert.
* (ft) (ft) (lbs) (lbs) Force Ratio
1 -27.99 18.77 2.79 165.59 185.34 0.893
2 -27.99 20.98 2.21 506.26 410.44 1.233
3 -27.83 23.48 3.45 1205.50 1104.43 1.092
4 -27.83 25.69 1.55 610.18 682.43 0.894
5 -27.67 27.69 2.97 1451.11 1621.61 0.895
6 -27.67 29.90 2.03 1044.10 1166.78 0.895
7 -27.51 31.76 2.16 934.61 1043.58 0.896
8 -27.51 33.98 2.84 930.74 1075.44 0.865
9 -27.35 36.12 1.99 475.16 553.14 0.859
10 -27.35 38.13 2.55 247.70 302.34 0.819
***TABLE 6 - Effective and Base Shear Stress Data on the 10 Slices***
Slice Alpha X-Coord. Base Effective Available Mobilized
No. (deg) Slice Cntr Leng. Normal Stress Shear Strength Shear Stress
* (ft) (ft) (psf) (psf) (psf)
1 -27.99 18.77 2.79 59.38 40.05 26.40
2 -27.99 20.98 2.21 228.95 154.43 101.78
3 -27.83 23.48 3.45 349.81 235.95 155.51
4 -27.83 25.69 1.55 392.69 264.88 174.57
5 -27.67 27.69 2.97 489.40 330.10 217.57
6 -27.67 29.90 2.03 513.09 346.08 228.10
7 -27.51 31.76 2.16 433.24 292.23 192.60
8 -27.51 33.98 2.84 327.41 355.80 234.50
9 -27.35 36.12 1.99 239.34 287.00 189.15
10 -27.35 38.13 2.55 97.16 175.91 115.94
***TABLE 6A - Effective and Base Shear Force Data on the 10 Slices***
Slice Alpha X-Coord. Base Effective Available Mobilized
No. (deg) Slice Cntr Leng. Normal Force Shear Force Shear Force
* (ft) (ft) (lbs) (lbs) (lbs)
1 -27.99 18.77 2.79 165.59 111.69 73.61
2 -27.99 20.98 2.21 506.26 341.48 225.06
3 -27.83 23.48 3.45 1205.50 813.12 535.92
4 -27.83 25.69 1.55 610.18 411.57 271.26
5 -27.67 27.69 2.97 1451.11 978.78 645.10
6 -27.67 29.90 2.03 1044.10 704.25 464.16
7 -27.51 31.76 2.16 934.61 630.40 415.49
8 -27.51 33.98 2.84 930.74 1011.45 666.63
9 -27.35 36.12 1.99 475.16 569.76 375.52
10 -27.35 38.13 2.55 247.70 448.47 295.58
Average Effective Normal Stress = 308.5810(psf)
Average Available Shear Strength = 245.4067(psf)
Total Length of Failure Surface = 24.5347(ft)
****TABLE 7 - SLICE REINFORCEMENT DATA****
***Lineload Slice Force Data on the 10 Slices (Only Applicable Slices
Listed)***
Slice Horiz Force Vert Force Result Force Inclin(deg) Moment@Base Cntr
No. (lbs) (lbs) (lbs) (ft/lbs)
1 0.0 200.0 -200.0 90.00 0.350987E+03
2 0.0 400.0 -400.0 90.00 0.590506E+03
SUM OF MOMENTS = -0.216998E-04 (ft/lbs);Imbalance (Fraction of Total Weight) = -
0.2664009E-08
SUM OF FORCES = -.152455E-06 (lbs);Imbalance (Fraction of Total Weight) = -
0.1871643E-10
Sum of Available Shear Forces = 6020.98(lbs)
Sum of Mobilized Shear Forces = 3968.33(lbs)
FS Balance Check: FS = 1.517258
**** END OF GEOSTASE OUTPUT ****