HomeMy WebLinkAboutCT 02-28; LA COSTA CONDOMINIUMS; LANDSIDE STABILIZATION; 2007-04-16American GeotechnicaUnc
SOIL, FOUNDATION AND GEOLOGIC STUDIES
April 16,2007 F.N. 23080.02
wth Revisions
DRAINAGE REPORT
HYDROLOGY AND HYDRAULICS CALCULATIONS
BANICH, POWERS, CALSO
LANDSLIDE STABILIZATION
2416 SACADA CIRCLE, CARLSBAD
RECEIVED
JUL 0 3 2007
ENGINEERING
DEPARTMENT
Prepared by
AMERICAN GEOTECHNICAL
22725 Old Canal Road, Yorba Linda, Califomia 92887
Tel: (714)685-3900
22725 Old Canal Road, Yorba Linda, CA 92887 • (714) 685-3900 • FAX (714) 685-3909
5600 Spring Mountain Road, Suite 201, Las Vegas, NV 89146 • (702) 562-5046 • FAX (702) 562-2457
5764 Pacific Center Blvd., Suite 112, San Diego, CA 92121 • (858) 450-4040 • FAX (858) 457-0814 - '^ ,
712 Fifth Street, Suite #B, Davis, CA 95616 • (530) 758-2088 • FAX (530) 758-3288 •••' ^
\
FN 23080 02 llAmencan Geotechnical, Inc.
April 16, 2007
Page 1
BRIEF NARRATIVE
As requested,we are providing a brief narrative regarding the existing and proposed conditions. A more
detailed description is included in the report issued by American Geotechnical on March 27, 2007,
entitled "Landslide Stabilization Recommendations" which contains plans for remediation. The existing
drainage (prior to failure) was very poor. Lots at the top-of-slope directed drainage over the descending
slope that had concentrated flow during periods of heavy rainfall. Additionally, no maintenance had been
provided over the years for mid slope drainage. The slope failure occurred in February 2005, during a
period of record-breaking rainfall in southem Califomia. The effects of the rainfall and subsequent mnoff
raised the groundwater level and also created seepage parallel to the slope face reducing the shear strength
of the slide materials which resulted in the observed failure.
The proposed plan addresses any surface drainage concems and provides a high strength reinforced slope
re-build that will enhance the slopes ability to resist future failures. The new proposed repair creates a
stronger slope with appropriate drainage provisions, substantially improved from the existing condition.
;:onstrucl anergy cJissipci.^i
100 lb t rock ; See detail) i •1^ f
-0
Aocro.x Scale '' =:'}'
R^^Pai ft
Explanatior
A'
215-'
Appfo<ina!e Lccation of Cross Section
Appro.<;rr,3te Location cf Finisn Concour
Approximate Location of Tieback Wail Systein
Appro:<imate Location of Proposed Key E.xcavation 1
Approximate Location of Surface Dram
Appro:<;mate Location of Slope .Access Road-cut
For Leighton Large Diamieter Boring (1998;
Estimated Location cf Origina! Slope Access
Road-cut By Leighton
FL = Flowline "a) bottom elev. ot v-ditch
Note. On the comp'etton of grading apply permanent non-irrigated
landscaping using hydromulch spray with a seed mix consisting
of the foilowing:
Mulhenbergia ngens (Deer Grass) 2 lbs. per acre
Leymus triticcides (Beardle Wildryej. 10 lbs. per acre
Festuca rubra Moiate' (Red Fountain Grass). 8 lbs. per a'. -
Deschampsia eiongata (Slender Hairgrass) 5 lbs. per acre
Vulpia microstachys (Small Fesvue). 5 lbs per acre
£.u^TI-3'0RK QUANTITIES
IMPORT ••-
EXPOR- ^
=E.V4ECIJL,.
PUNNING DKPARTMENT APPROVAL
, _^ oat: / /
PLAXNING OrBECTOR
'AS BUILT'
CITY OF CARLSB AT-
S2FAI?. .= LAN'S FOR:
Construct energy dissipatsr
'00 !b T rock (See detail;
Fcr 1 ,5 ri 1V portion of tne slope dace
, geogrid ;S/"teen 3F35)'P beb/veer-'tl
j layers at a 24" vertical spacing
See cross secb'cn ^ - ,A -'or details
Explanation
--215
Appro.^imate Lccatior of Cross Section
Approximate Locatior of Finish Contour
.Approximate Location of Tieback Wali System
Approximate Location of Proposed Key E.:<cavafion
Approximate Location of Surface Drain
Approximate Location of Slope Access Road-cut
For Leighton Large Diamiete-" Bonng ' 1998'
Estimated Location cf Onginal Slope Access
Poad-cut By Leighton
FL = Flow'ine 'B boctomi eiev c' v-ditch
Note. On the completion of grading apply permanent non-irrigated
landscaping using hydromulch spray with a seed m,ix consisting
of the following:
Mulhenbergia ngens (Deer Grass), 2 ibs. per acre
Leymus triticcides (Beardle Wildrye). 10 lbs per acre
Festuca rubr.a Moiate' (Red Fountain Grass). 8 lbs. pe acre
Deschamips'a elcngafa (Slender Hairgrass) 5 !bs pe^ acre
Vulpia miicrostachys (Small Fesvue). 5 Ibs per acre
•-;MPC<'T
PUNNING DEPABTMENT APPROVAL
s;i7= om-. / ''
'AS BUILT'
CITY OF CARLSBAD'i>^^
WM American Geotechnical
SOIL, FOUNDATION AND GEOLOGIC STUDIES
22725 OLD CANAL. ROAD • VORBA LINDA, CA 92887 • (800) 275-4436 • FAX (714) 685-3909
BY: Al^ FILE NO,: 22.o80.o2
DATK: PROJECT:. SHEET:. / / 3
DESCRimON:, H ix> I o ^) y / I-l.y I- tx'.j.' iL."^ G a 1 c
f-li To-lis. I aVif-n. SciMCtrf VJ-^ V cV.Ac,!-
Cl CM „
^ / 5^-^ ^lv<^ L
1= 6-5^ 'Vu
Co poe i
n = , P, q 1 -n ^
•1 American Geotechnical
son., FOUNDATION AND GEOLOGIC STUDIES
22725 OLD CANAL ROAD • YORBA LINDA, CA 92887 • (800) 275-4436 • FAX (714) 685-3909
BY: ^^-^ Fll,F.NO.: l^oRO.'^'Z
DATE;___O!±i:0^j!kL- PRO.IF.rT: SAU SCH /F^'^ ^/ CAi.--i.O ,SHF.FT: / 3
\ ^ yd \ o Cj y /l4yci m -'l,ci g-^lc. DESCRIPTION:.
C Q, piy~c ' ^^'^ c 0»^ ••^ t:''. o." i- :
Ho=; olcpe OrciOv 'i-.Li-ii.. ftl- Vifcjart 2 .
p. 2.15 f I'
2{ 1.5') 7v •
0= o-G\3
Q, , r LiL^l M'2'2.s)( G.S^/^C 05)^= cf^ yy2 \if^^s
•1 American Geotechnical
SOIL, FOUNDATION AND GEOLOGIC STUDIES
22725 OLD CANAL ROAD • YORBA LINDA, CA 92887 • (800) 275-4436 • FAX (714) 685-3909
BY: _.Alh:^! FILENO,:_^i£8£>^
DATE: __Oiti£li!L2. I'ROJECT: BjC^J |6H /I^I^Eg^ /CAL^o SHEE7:
DESCRIPTION: ^\^'ptct^^ / V^X'Q^ MI \CA CAl^
Ike. -»c j/civ,-iV-^ frli-i uo.-i i'C Ctrnrni,.'. o'e,o' /" N l*J R rip fop s'll-o.q 'f'-r rifcuvjcn'-
p;peS( HEC!i|. , c l.a.p-lc'- lo ) ••
5 ^ c
F'ycr. T;.b!« lO.i J^HUlf^ ( fltCI^ , AUpW |o) :
Apr.- Cr.M^ \ c^pr,^ end) = V L ^ 3,( IT^59f+ f V(l-)
•3 , , ^'
Directions for ^^lication:
(1} From precipitation maps delBmiine 6 hr and 24 hr amounls
for the selected frequency. Tliese maps are Included in the
County Hydrology MarmeS (10.50. and 100 yr maps included
in tfie Design and Procedure Manual).
(2) Adjust 8 hr predpitatton (if necefwary) so that it is withtn
the range of 45% to 65% of the 24 hr precipitation (not
applicaple to Desert).
(3) Plot 6 hr precipitation on the right side of the chart.
(4) Draw a <ine through the point parallel lo tne plotted lines.
(5) This line is the intensity-duration curve for the location
being analyzed.
Application Form:
(a) Selected frequency \QCi year
2. 5 in.. P 2^ 4-.5
(c) Adjusted = 2 -5 m.
•P24
mm,
(e) i = C S'l in./hr.
Note: This chart replaces the iFttenslly-Duration-Frequency
curves used since 1965,
2.5
i 3.65.5.271
Z.12J3.18i4.af'
iJK 12.53:3.37'
3.5
I
4.5 _5J
i
6.53;
8.30]
"4.Z\
6.3617.42;
^353'3,771 1.06 i1.8a;2.1S
6it3 '.i2* ijBS.
o w : 1.03'1 38'
ceo''o.so: 1.19'
SM io«); 1.06'
o:4V]o.«ifo.a2'
q^]o.5iio.6s'
jo.44j6:E9
1W| 0.28 .039(0.58
052 ]0.Mi0,«3l
0,1!l_l0_.ffl!038;
0.17 IQ35lo,33
2,69
2.07'
'1.72
i.A-)
"l,3i
J.OZ
O:B5
0.73 om
0.54
'0:47
2.'49'2,90;
2,07 2.11 i
1.79'2.09'
1.59 i.86
Jl.23j.43:
1.02 1:19 j
!0.88i 1.63 [
:p:78:aS1'
To.B5:0,7ei
•'asoto.5B
1054
5,4«
4,31'
3.73
332
2.76
2.39
2,12
i.83
1,3S
JM6
1.04
OS?
075
6.67
11.86I_I3.I7'
SJ54 liaeoi
_ ^-^' ^
^5.e4'j6.49 •
•^irss ij5.39;'
iSol 4.67 '
H.49^ 1S.S1
11 Tea'12.72
9L27 rio.11
3.73
3:10
2.69
2.38
1.84
1.53
4,15
3.45
2.98
2.5S
2.(W
1.70
1.32 11.17
_ 1.-18 2JJ1_
6.38 I J OB
0,86 i_0j4
0,75' i 0.B4"
7.13^
5:13
5.13
'4.56
3.79
3.28
2:92
2,25
1.87
1.62
•ijp"
1.03"
7.70
'S.46"
SCO
4.98
4:16
3^56
3.1'8
2.4S
2.04
1.76
1.57
1.30'
1.13
0.92 100
F I G U R R
Intensity-Ouration Design Chart - Tsmptate
raAmerican Geotechnical, Inc.
APPENDIX A
Supporting Documents
San Diego County Hydrology Manual
Date: June 2003
Section:
Page:
3
6 of 26
Table 3-1
RUNOFF COEFFICIENTS FOR URBAN AREAS
Land Use Runoff Coefficient "C"
Soil Type
NRCS Elements County Elements % IMPER. A B C D
Undisturbed Natural Terrain (Natural) Permanent Open Space 0* 0.20 0.25 0.30 0.35
Low Density Residential (LDR) Residential, 1.0 DU/A or less 10 0.27 0.32 0.36 0.41
Low Density Residential (LDR) Residential, 2.0 DU/A or less 20 0.34 0.38 0.42 0.46
Low Density Residential (LDR) Residential, 2.9 DU/A or less 25 0.38 0.41 0.45 0.49
Medium Density Residential (MDR) Residential, 4.3 DU/A or less 30 0.41 0.45 0.48 0.52
Medium Density Residential (MDR) Residential, 7.3 DU/A or less 40 0.48 0.51 0.54 0.57
Medium Density Residential (MDR) Residential, 10.9 DU/A or less 45 0.52 0.54 0.57 0.60
Medium Density Residential (MDR) Residential, 14.5 DU/A or less 50 0.55 0.58 0.60 0.63
High Density Residential (HDR) Residential, 24.0 DU/A or less 65 0.66 0.67 0.69 0.71
High Density Residential (HDR) Residential, 43.0 DU/A or less 80 0.76 0.77 0.78 0.79
Commercial/Industrial (N. Com) Neighborhood Commercial 80 0.76 0.77 0.78 0.79
Commercial/Industrial (G. Com) General Commercial 85 0.80 0.80 0.81 0.82
Commercial/Industrial (O.P. Com) Office Professional/Commercial 90 0.83 0.84 0.84 0.85
Commercial/Industrial (Limited I.) Limited Industrial 90 0.83 0.84 0.84 0.85
Commercial/Industrial (General L) General Industrial 95 0.87 0.87 0.87 0.87
*The values associated with 0% impervious may be used for direct calculation of the runoff coefficient as described in Section 3.1.2 (representing the pervious runoff
coefficient, Cp, for the soil type), or for areas that will remain undisturbed in perpetuity. Justification must be given that the area will remain natural forever (e.g., the area
is located in Cleveland National Forest).
DU/A = dwelling units per acre
NRCS = National Resources Conservation Service
3-6
HANDBOOK OF
CIVIL ENGINEERING
CALCULATIONS
Tyler G. Hicks, RE., Editor
International Engineering Associates
Member: American Society of Mechanical Engineers
Institute of Electrical and Electronics Engineers
United States Naval Institute
McGRAW-HiLL
l\lew Yorit San Francisco Wasliington, D.C. Aucicland Bogota
Caracas Lisbon London IWadrid IWexico City IMilan
•Montreal New Delhi San Juan Singapore
Sydney Tokyo Toronto
I
|:M. WATER SYSTEM DESIGN
Ba/f-fu// sewer
(sewer.
Ute Ihalf-full sewer, or 2(7.75) = 15.50 ftVs ({\AA%
5.50/1.55 = 10 million gal/day (438.1 L/^i
es are sized on the basis of being tiill of hqui^ f
B = inlet elevation, ft above the site datum- JB-'
Pipe length between inlet and outlet, ft Substi!
' in/in).
Is often used for sizing sewer pipe,-, in thij^^
that is a function of the pipe roughness- Jt-t
ter, ft;S = pipe slope, ft/ft. Table 14 lists
Riewer design, the value n = 0.013 for piper's
, umerous charts have been designed to siin<.>
pical chart designed specifically for sewei?, te left, and project through the slope ratio of
rate and slope scales, read the next larger^ t
m). When using this chart, always read the
I fluid flow velocity as 5 ft/s (1.5 mis) on the ;
Tor a sewer flowing}?^//. -l I
I ianning Formula
vith some
I
jointed and
unplaned
I
I
0.040
0.030
0.020
0.017
0.015
0.013*
0.012
0.010
0.009
|GO:g-2 83
90-^-2,55
80 4-2.27
•70-f-1,98
60-i-l 70
50-1-1.42
*:
40-1- 113
30
20'
•0,85
0.57
I" 10-=-0.28 ~
' 9-]-0,25 I
8-1-0,23 °
7-3-0,198
6-=-0,170
5-1-0.14
O.ll
3-E-0.08
2--0,06
0.028
305-
254-
203-
152-
WATER-SUPPLY AND STORM-WATER SYSTEM DESIGN
0.0001
00002
0.0003
00004
0.0005
0.0006
0.0007
[0.0008
0.001
0.002
0003
0004
0.005
0006 2
-10.007 S
-|0008 „
001 I
0.02
0.03
0.04
0.05
0.06
0.07
008
2438 -96
2286-90
2134-84
1981 -78
1829-72
1676-66
1524 -60
1372-54
1219-48
1067-42
914-36
838-33
762-30
686-27
610-24
E c
533-21 Z-0) V a> E o 457-CO •6 XJ
a a 381 -15 °^
1°
^0
0,2
03
04
0,5
0,6
07
0,8
IO
7.27
Q6-|2
0,9-
12-
e 1-5-
1,8-
2 I
8 2 4-E
2 7-i9
3 0-g
3,4
FIGURE 12. Nomogram for solving the Manning formula for circular pipes flowing fiill and
n = 0.013.
lapter 10 - HEC 14 - Hydraulics - Engineering - FHWA Page 13 of i:
Two feasible options have been identified. First, a 2.3-ft-deep, 23-ft-long pool, with an 11.5-ft-apron
using Ogg = 0.5 ft. Second, a 1.4-ft-deep, 18-ft-long pool, with a 6-ft-apron using Dgp = 0.83 ft. The
choice between these two options will likely depend on the available space and the cost of riprap.
Step 5. Forthe design discharge, determine if TW/y^ ^.75
TW/y^ = 2.0/2.7 = 0.74, which satisfies TW/y^ <0.75. No additional riprap needed.
10.2 Riprap Aprgn
The most commonly used device for outlet protection, primarily for culverts 1500 mm (60 in) or smaller, is a
riprap apron. An example schematic of an apron taken from the Federal Lands Division of the Federal
Highway Administration is shown in Figure 10.4.
Figure 10.4. Placed Riprap at Culverts (Central Federal Lands Highway Division)
mrti
I, tmin^liii hK t
Internum lM«iJK nm
ll 11 (OEM
A. V
tf wtrm -mf
w #
wt
LA
aay£HT WTH STAHOMD
£10 SECTJCW
I
cuLvm wtTMon STAMOMO em xaoK
nWTSCTNt *Pfim AT CULirE/fT OUTIST
^'Tiiiiiitiiu—
piicco niMuip
AT CULVERTS
They are constructed of riprap or grouted riprap at a zero grade for a distance that is often related to the
outlet pipe diameter. These aprons do not dissipate significant energy except through increased roughness
for a short distance. However, they do serve to spread the flow helping to transition to the natural drainage
way or to sheet flow where no natural drainage way exists. However, if they are too short, or otherwise
ineffective, they simply move the location of potential erosion downstream. The key design elements of the
riprap apron are the riprap size as well as the length, width, and depth of the apron.
Several relationships have been proposed for riprap sizing for culvert aprons and several of these are
discussed in greater detail In Appendix D. The independent variables in these relationships include one or
more ofthe following variables: outlet velocity, rock specific gravity, pipe dimension (e.g. diameter), outlet
Froude number, and tailwater. The following equation (Fletcher and Grace, 1972) is recommended for
circular culverts:
D,o =0.2D Q
(10.4)1
215 TW
where,
DgQ = riprap size, m (ft)
Q = design discharge, mVs (ftVs)
D = culvert diameter (circular), m (ft)
TW = tailwater depth, m (ft)
g = acceleration due to gravity, 9.81 m/s^ (32.2 ft/s^)
Tailwater depth for Equation 10.4 should be limited to between 0.4D and 1 .OD. If tailwater is unknown, use
0.4D.
Whenever the flow is supercritical in the culvert, the culvert diameter is adjusted as follows:
2
where,
ittp ://www. fhwa.dot.gov/engineering/hydraulics/pubs/06086/hec 14ch 10.cfin
(10.5)
7/2/200'
apter 10 - HEC 14 - Hydraulics - Engineering - FHWA
D' = adjusted culvert rise, m (ft)
y^ = normal (supercritical) depth in the culvert, m (ft)
Equation 10.4 assumes that the rock specific gravity is 2.65. If the actual specific gravity differs significantly
from this value, the DJQ should be adjusted inversely to specific gravity.
The designer should calculate Dgg using Equation 10.4 and compare with available riprap classes. A project
or design standard can be developed such as the example from the Federal Highway Administration Federal
Lands Highway Division (FHWA, 2003) shown in Table 10.1 (first two columns). The class of riprap to be
specified is that which has a Dgg greater than or equal to the required size. For projects with several riprap
aprons, it is often cost effective to use fewer riprap classes to simplify acquiring and installing the riprap at
multiple locations. In such a case, the designer must evaluate the tradeoffs between over sizing riprap at
some locations in order to reduce the number of classes required on a project.
Table 10.1. Example Riprap Classes and Apron Dimensions
Class •go (mm) DgoOn) Apron Length' Apron Depth
1 125 5 4D 3.5Dgo
2 150 6 4D 3.3D50
3 250 10 5D 2-4Dgo
4 350 14 6D 2-2Dgo
5 500 20 7D 2.0D50
6 550 22 8D 2OD50
'D is the culvert rise.
The apron dimensions must also be specified. Table 10.1 provides guidance on the apron length and depth.
Apron length is given as a function of the culvert rise and the riprap size. Apron depth ranges from 3.5DgQ for
the smallest riprap to a limit of 2.0DgQ for the larger riprap sizes. The final dimension, width, may be
determined using the 1:3 flare shown in Figure 10.4 and should conform to the dimensions of the
downstream channel. A filter blanket should also be provided as described In HEC 11 (Brown and Clyde,
1989),
For tailwater conditions above the acceptable range for Equation 10.4 (TW> 1.0D), Figure 10.3 should be
used to determine the velocity downstream ofthe culvert. The guidance in Section 10.3 may be used for
sizing the riprap. The apron length is determined based on the allowable velocity and the location at which it
occurs based on Figure 10.3.
Over their service life, riprap aprons experience a wide variety of flow and tailwater conditions. In addition,
the relations summarized in Table 10.1 do not fully account for the many variables in culvert design. To
ensure continued satisfactory operation, maintenance personnel should inspect them after major flood
events. If repeated severe damage occurs, the location may be a candidate for extending the apron or
another type of energy dissipator.
Design Example: Riprap Apron (SI)
Design a riprap apron for the following CMP installation. Available riprap classes are provided in Table 10.1.
Given:
Q = 2.33 mVs
D = 1.5m
TW = 0.5m
Solution
Step 1. Calculate Dgp from Equation 10.4. First verify that tailwater is within range.
TW/D = 0.5/1.5 = 0.33. This is less than 0.4D, therefore,
use TW = 0.4D = 0.4(1.5) = 0.6 m
•50=0,20 Q ( D
TW
= 0,2(1,5) 2.33 0,13 m
step 2. Determine riprap class. From Table 10.1, riprap class 2 (Dgg = 0.15 m) is required.
ttp://www.fhwa.dot.gov/engineering/hydraulics/pubs/06086/hecl4chl0.cfrn
Page 14 of 1;
7/2/200'
apter 10 - HEC 14 - Hydraulics - Engineering - FHWA
step 3. Estimate apron dimensions.
From Table 10.1 for riprap class 2,
Length, L = 4D = 4(1.5) = 6m
Depth = 3.3D5Q = 3.3 (0.15) = 0.50 m
Width (at apron end) = 3D + (2/3)L = 3(1.5) + (2/3)(6) = .8.5 m
Design Example: Riprap Apron (CU)
Design a riprap apron for the following CMP installation. Available riprap classes are provided in Table 10.1.
Given:
Q = 85 ftVs
D = 5.0 ft
TW = 1.6 ft
Solution
Step 1. Calculate Dgg from Equation 10.4. First verify that tailwater is within range.
TW/D = 1.6/5.0 = 0.32. This is less than 0.4D, therefore,
Page 15 of 1!
=0,2D
= 0.4(5)=
f Q 1
2.0 ft
'^f D ]
ITWJ = 0,2 (5.0) 85 —1 = 0,43 ft = 5.2in 2.0 .^12(5.0)'^
step 2. Determine riprap class. From Table 10.1, riprap class 2 (Dgg = 6 in) is required.
Step 3. Estimate apron dimensions.
From Table 10.1 for riprap class 2,
Length, L = 4D = 4(5) = 20 ft
Depth = 3.3DgQ = 3.3 (6) = 1.65 ft
Width (at apron end) = 3D + (2/3)L = 3(5) ••- (2/3)(20) = 28.3 ft
10.3 Riprap Aprons After Energy Dissipators
Some energy dissipators provide exit conditions, velocity and depth, near critical. This flow condition rapidly
adjusts to the downstream or natural channel regime; however, critical velocity may be sufficient to cause
erosion problems requiring protection adjacent to the energy dissipator. Equation 10.6 provides the riprap
size recommended for use downstream of energy dissipators. This relationship is from Searcy (1967) and is
the same equation used in HEC 11 (Brown and Clyde, 1989) for riprap protection around bridge piers.
2 \ (10.6)
D.= 3 0,692
1
V
2g
is
where,
DgQ = median rock size, m (ft)
V = velocity at the exit of the dissipator, m/s (ft/s)
S = riprap specific gravity
The length of protection can be judged based on the magnitude ofthe exit velocity compared with the natural
channel velocity. The greater this difference, the longer will be the length required for the exit flow to adjust to
the natural channel condition. A filter blanket should also be provided as described in HEC 11 (Brown and
Clyde, 1989).
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ttp://www.fhwa.dot.gov/engineering/hydrauUcs/pubs/06086/hecl4chl0.cfm 7/2/200'