HomeMy WebLinkAboutCT 73-18; RANCHO DEL PONDEROSA UNIT 2; SLOPE STABILITY ANALYSIS; 1975-06-11Ponderosa Homes, Incorporated
Project No. 72-25~
June 11, 1975' •
P.age 2 ••
Based on the previouslj established fill soil parameters and the Janbu
method of analysis, it is our opinion that the proposed fill slope ~il1
have an adequate indicated factor of safety against deep-seated slope
failure under static conditions, if constructed in accordance with plans
and specifications. Calculations are.attached to support this conclusion.
All slo'pes should be planted, drained and properly maintained in order .to,
help co~trol erosion and surface sloughing.
Our review of the preliminary report indicates that the fill slope in
Unit 3 will be constructed in an area partially underlain py the Del
Mar formation which is composed of alternating layers of claystone,
siltstone and sandstone. Our experience indicates that relatively soft
clay seams and sometimes groundwater problems are associated with this
unit. It is therefore recommended that-the toe of the fill slope be
keyed' completely through the overburden alluvial and soil mantle into
formational soils and that the key-be examined by an engineering geologist
of our firm. If adverse geologic condHions or adverse water conditions'
are present in the key, additional key depth or width and possibly subsurface
drai.ns may be required. These recommendations can be given at the time
of construction in an addendum report.
If you have any questions concerning our additional ·slope stability
analysis, please contact the project engineer assigned to this project,
Mr. Richard P. While of our firm.
WOODWARD-CLYDE CONSULTANTS
LJL/RPW/jr
Attachments
'(2) Ponderosa Homes; Inc.
(4) Rick Engjneeri~g Company
Attn: Norm Arndt
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Project No. 72-253 e·, ••
Assumptions:
(1) Maximufu height of slopes~
(2) Maximum slope inclination,
(3) Unit· weight of soil, .
(4) "Apparent angle of internal friction,
(5) Apparent cohesion,
(6) No seepage forces.
References:
. . . '.' .
H = 67
2.2 :1, :: :
y = 125" pcf
~ = 30°
C =. 300 psf·
·(1) Janbu, N., IIStabi.lity Analysis of Slopes with Dimens.ionless
Parameters ll , Harvard Soil Mechanics Series No. 46, 1954 •
. (2) Janbu, ~., IIDimensionless Parameters for Homogeneous Earth
·Sl opes./I, JS~1FD, No. SM6, Novem.ber, 1967.·
Analysis: .
Safety Factor, F.S. = N c cf . rH .. Where Ncf is the stability No.
for 51 opes wi th both c and ~ •.
r H tan p
c
= 125 x 67 x .577 = 16.1
30.0
From Figure 10 of Reference 2
47 x 300 _ F.S. = 125 x 67 -1.69
N = 47 cf