The URL can be used to link to this page

Home My WebLink AboutCT 02-28; La Costa Condominiums; Slope Stability Analysis and related reports; 2005-11-07Leighton and Associates, Inc. A LEIGHTON GROUP COMPANY TRANSMITTAL To:Kwan So 2683 Costebelle Drive La Jolla, California 92037 Date: July 18, 2006 Project No. 980161-003 Transmitted: X Mail/UPS Courier Pick Up Overnight The Following: Draft Report Final Report Extra Report Proposal X Other For: X Your Use X As Requested Subject: Documents Relative to the Geotechnical Services Leighton and Associates provided during the period of the February 28 and November 27. 2005 (i.e. the time period covered by the Outstanding Invoices dated November 17. 2005 and December 12. 2005 LEIGHTON AND ASSOCIATES, INC. Bv: Randy Wagner 3934 Murphy Canyon Road, Suite B205 • San Diego, CA 92123^425 858.292.8030 « Fax 858.292.0771 • www.leightongeo.com Leighton and Associates, Inc. A LEIGHTON GROUP COMPANY January 18,2005 Project No. 980161-002 To: CALSO, LLC 3529-2B Cannon Road, Suite 519 Oceanside, California 92056 Attention: Mr. Ken Cablay Subject: Remedial Grading Procedures Relative to the Existing Landslides and North-Facing Hillside, La Costa Condominiums, Lot 185 of La Costa South Unit 1, Carlsbad Tract No. 02-28, Carlsbad, California References: Leighton and associates, 2002, Updated Preliminary Geotechnical Report, Lot 185, La Costa Avenue South Unit 1, Carlsbad, California, Project No. 980161-002, dated October 30,2002 O'Day Consultants, 2004, Grading and Erosion Control Plans for La Costa Condominiums, Carlsbad Tract No. 02-28, Drawing No. 422-4A, 8 Sheets, Dated November 5, 2004 , 2005, Buttressing and Replacement Fill Plan for La Costa Condominiums, 1 Sheet, dated December 23, 2004, revised January 3, 2005 ,m Introduction This report provides our recommended remedial grading procedures that should be followed during the grading and construction of the southern side of the La Costa Condominiums project (Lot 185 of La Costa South Unit 1, Carlsbad Tract No. 02-28) located in Carlsbad, California. At the request of the City of Carlsbad, theses procedures were prepared in order to minimize any potential slope instability conditions that might impact the existing residences present on the ridgeline above the La Costa Condominiums project during the construction of the recommended buttresses and replacement fill. The recommendations concerning the grading and construction of the project have been provided in the Updated Preliminary Geotechnical Report for the project (Leighton, 2002). 3934 Murphy Canyon Road, Suite B205 • San Diego, CA 92123-4425 858.292.8030 • Fax 858.292.0771 • www.leightongeo.com * 980161-003 "*• m The recommendations are still considered valid and should be followed unless superseded by recommendations in this report or recommendations made during the grading of the site.TO M Background m m Based on the results of our prior preliminary investigation of the site (Leighton, 2002), the north-facing hillside along the southern side of the site has a number of potential slope ** instability conditions that warrant special design and construction considerations. These * conditions include: 1) adverse geologic conditions such as existing landslides, clayseams and fracture zones, out-of-slope bedding, etc.; 2) fill and cut slopes constructed at slope inclinations of 1.5:1 (horizontal to vertical) that are steeper than current standards allow * without some type of additional stabilization; 3) seepage zones and surface drainage from the residential lots on the ridgeline that is directed down the hillside (instead of toward the street); and 4) the close proximity of the existing residential structures on the ridgeline to * the anticipated backcut needed to construct the buttresses and replacement fill. Since a number of potential slope instability conditions are present, remedial grading recommendations to stabilize the slope have been presented in the Updated Preliminary Geotechnical Report for the project (Leighton, 2002). This report provides more specific procedures that should be followed during the grading operations.•m at m Remedial Grading Procedures The following procedures are guidelines that should be implemented during the grading of the site. 1) Survey Staking of the Buttress and Replacement Fill Backcut and Property Boundary In order to place the recommended slope inclinometers behind the top of the proposed buttress and replacement fill key backcut and install the slope survey monuments along the property boundary; the backcut/limits of grading should be staked by the project civil engineer/surveyor. 2) Slope Inclinometer and Survey Monument Installation •• Prior to any of the remedial grading operations, the three recommended slope inclinometers and the slope survey monuments should be installed. The approximate ,„ locations of the slope inclinometers and slope survey monuments are presented on the attached Remedial Grading Map (Plate 1). •m In order to install the slope inclinometers, access roads and drill pads will need to be m constructed. Based on the staking of the top of the buttress and replacement backcut location and/or property lines, the optimal location of the slope inclinometers C^B be "• determined prior to construction of the access road and relatively level -2-Leighton 980161-003 slope inclinometers are anticipated to be on the order of 60 to 90 feet in depth. The slope inclinometers, which are special grooved pipes that a measuring instrument can be lowered into, need to be backfilled with a lean sand/cement slurry. In addition, two sets of initial readings need to be performed prior to any grading or removals next to the inclinometers. For planning purposes, installation of the three slope inclinometers, placement of the slurry backfill and the two initial readings should take approximately 5 working days to complete. Once the slope inclinometers are installed, they should be read on a weekly basis prior to the excavation of the backcut in the general vicinity of the inclinometer. The frequency of the readings should be increased to a daily basis (at a minimum) once the backcut is started. The daily readings should be continued until the buttress or replacement fill soils are placed to the top of the backcut. We anticipate that our filed staff geologist will perform the slope inclinometer monitoring and that the findings can be determined in the field to minimize any delays. We also recommend the placement of surface survey monuments above the proposed buttress and replacement fill key backcut along the property boundary as another method of monitoring any slope instability conditions. The survey monuments can simply be metal pins or short pieces of rebar pounded into the ground. The monuments should be surveyed on a periodic basis with more frequent readings performed when grading is ongoing near the monuments. The survey readings should be given to the geotechnical consultant as soon as possible after the readings are taken. 3) Excavation of the Buttress and Replacement Fill Although the slope stability analysis performed during the prior geotechnical studies did not indicate the need to construct the buttress and replacement fill keys in sections, we recommend that the buttress and replacement fill key backcut be done in four sections in order to minimize the potential impacts to the residences along the ridgeline. The approximate location of the sections is presented on the attached Remedial Grading Map (Plate 1). The sections should be excavated from west to east (i.e. Section A first and Section D last). An access road for the construction equipment may be graded along the top of the backcut; but any excavation for the access road should be limited to a maximum height of 10 feet or less. Access roads/ramps into and out of adjacent sections should be made as steep as possible in order to limit the amount of removals in the adjacent section. Based on our professional experience, the access road/ramps can be excavated at inclinations on the order of 3:1 to 4:1 (horizontal to vertical). Once the excavations for the buttress and replacement fill keys is commenced, the excavation and construction should be performed as quick as possible to minimize leaving any exposed backcut open for any length of time, hi general, exposed backcut heights more than 1/2 the total height of the backcut should not be left open over any weekend. Excavations within 10 feet of the basal rupture surface of the landslides or clayseams or fills less than 10 feet higher than the rupture surface or clayseam should not be left overnight. Geologic observations or the results of the slope inclinotnrffa- or -3-Leighton 980161-003 slope survey monitoring programs during the grading operations may dictate recommendations that may be different than the preceding recommendations. Any necessary supplies (such as gravel, filter fabric and subdrain pipe) should be ordered and delivered to the site prior to when it's needed in order to minimize time delays. We also recommend that periodically during the day, a representative of the grading contractor and the geotechnical consultant visually observe the back cut and the area above it for indications of slope movement. Any indications of movement should be communicated to the project team so that steps to determine the severity or remediate the conditions can be made. 4) Potential Slope Instability Issues Purina Construction If during the excavation of the buttresses and replacement fill keys, indications of significant slope movement are observed based on visual observations or results of the slope inclinometers or slope survey monuments, steps should be taken immediately to evaluate the condition. The actual mitigation should be based on the existing geologic conditions and the status of the grading operations. Additional geologic mapping or a subsurface investigation may be needed to determine the extent of the instability conditions. Geotechnical analysis (including additional slope stability calculations) may also be needed to evaluate the conditions and provide corrective measures. Measures such as excavating the lower portion of the buttress and replacement fill keys in small sections (i.e. on the order of 25 to 50 foot wide sections); enlarging the buttress and replacement fill keys; or providing alternative slope stabilization may be warranted. If you have any questions regarding our report, please contact this office. We appreciate this opportunity to be of service. Respectfully submitted, LEIGHTON AND ASSOCIATES, INC. Randall K. Wagner, CEG 1612 Senior Associate Attachment: Plate 1 - Remedial Grading Map Distribution: (3) Addressee (4) O'Day Consultants, Attention: Mr. John Strohminger -4-Leighton Leighton and Associates, Inc. A LEIGHTON GROUP COMPANY To: Attention: Subject: March 30, 2005 Project No. 980161-003 CALSO, LLC C/o Lighthouse Ventures, LLC 3529-2B Cannon Road, Suite 519 Oceanside, California 92056 Mr. Gregg Linhoff Conclusions Regarding Existing Significant Geotechnical Issues of the La Costa Condominiums Project, Lot 185 of La Costa South Unit 1, Carlsbad Tract No. 02- 28, Carlsbad, California Based on the sensitive issues of the existing north-facing hillside (along the south side of the property) and other portions of the site of the proposed La Costa Condominiums project (Carlsbad Tract No. 02-28), remediation of the site from a geotechnical standpoint will be significant in cost and scope. The sensitive issues of the hillside include both ancient and recent landslides and instability issues related to old manufactured fills placed on the steep slope during the prior development of the adjacent property. Issues on the other portions of the site include removal of potentially unstable and compressible old fill soils and manufactured slopes. In order to develop the property, relatively large buttresses and stability fills will need to be constructed and significant removals will need to be performed. During the construction, temporary backcuts will need to be excavated in a phased operation and will need to be monitored to evaluate potential slope movement that may impact the existing properties on the hillside above the project. The recent landslide activity on the slope underscores the fact that the scope and costs to mitigate the existing conditions of the slope, both natural and manufactured, will greatly exceed prior expectations. If you have any questions regarding our report, please contact this office. We appreciate this opportunity to be of service. Respectfully submitted, LEIGHTON AND ASSOCIATES, INC. K. Wagner, C 1612 Distribution: (3) Addressee 3934 Murphy Canyon Road, Suite B205 « San Diego, CA 92123-4425 858.292.8030 • Fax 858.292.0771 • www.leightongeo.com Leighton and Associates, Inc. A LEIGHTON GROUP COMPANY TRANSMITTAL To:City of Carlsbad Risk Management 1635 Faraday Avenue Carlsbad, California 92008-7314 Attention: Ms. Janet Jones Transmitted: X Mail/UPS Courier Pick Up Cal Overnight The Following: Draft Report X Final Report Extra Report Proposal Other Date: May 2, 2005 Project No. 980161-003 For: X Your Use X As Requested Subject: Preliminary Geotechnical Investigation. Lot 185. La Costa Avenue South Unit 1. Carlsbad. California. Project No. 4980161-001. dated September 24. 1999 LEIGHTON AND ASSOCIATES, INC. By: Randy Wagner 3934 Murphy Canyon Road, Suite B205 • San Diego, CA 92123-4425 858.292.8030 • Fax 858.292.0771 • www.leightongeo.com 4 Leighton and Associates, Inc. A LEIGHTON GROUP COMPANY TRANSMITTAL To:Kwan So 2683 Costebelle La Jolla, California 92037 Date: July 18, 2005 Project No. 980161-004 Transmitted: X Mail/UPS Courier Pick Up Overnight The Following: Draft Report Final Report 2 Extra Report Proposal Other For: X X Your Use As Requested Subject: Preliminary Geotechnical Investigation Report for the La Costa Condos. dated September 24.1999 LEIGHTON AND ASSOCIATES, INC. By: Randy Wagner 3934 Murphy Canyon Road, Suite B205 • San Diego, CA 92123-4425 858.292.8030 • Fax 858.292.0771 • www.leightongeo.com La Costa Condos (October 26, 2005) *" 1) Existing Conditions • Global Stability M Shear Pins Tie-Backs » Offsite Easement Issue m • Surficial Stability (Offsite) • Temporary Back-Cut Stability (E-E1, B-B', K-K1, & possibly A-A1) *" Shear pins * Tie-Backs Grading Buttress in Sections " 2) Unknowns • Natural Hillside on East Side (M1) • Continuous Clayseam.** 3) Additional Subsurface Investigation • Large-Diameter Borings 4) Other Alternatives „ • Larger Buttress • Raising Grades La Costa Avenue Condominiums Carlsbad, California Slope Stability Analysis Project #980161-004 Date: 11/07/05 co "oCD O Q)C\J O^ s O coto 2ow a S a E /? CO Q) co oQ £ Q. O 0)2> CO.c oo Too If) II coCO o "o CO LL •3 5155! =s~^ - So 'c o £ .SODOQ. Q. La Costa Avenue Condominiums Carlsbad, California Slope Stability Analysis Project #980161-004 Date: 11/02/05 < < O Q.to 10 o <• - £03 ^- i- Q. C/J </> C t- (/)., OJ O » T3 2 a) E > W W (T>ffl -S02^5, ^c/>Q. Q. || O fll<D OCM k-, O . IIwco S3o z uuCO oo CMeg CDCO »IO T- O w O '•G<D O CO O <Dt: =Q- u.ro c v>Q. OCDCM E>CO I to COO IO) rou. H *f 0 z UJ CO >- </>a o CM ii a> 5s co CNJCMin ccC/3 %co CN =*S_•° o o>*S8 co eo co * ^C T- v> O • •0) '^= <Do °^5 CDQ. ca Qi 0) CO O CD CL O 0) E? ICO o00 com caco ^- O o o -*-»o03LL, jsj COCO ® in-o ^ in « (0 os?ra f3 CO .— 5 o•§ * f S .1= J= ™tr c o r: .£< DO Q. O. CD cb U V -.»." 3 < —> «ir> c 2§O 7! £?•£ -Q Sjo «r ^-! « 2 oj E > w<n (ft to -5 "inO O z CO ^ O CDCM iS QJ O ^Ql[f^^ CO CO LO roCO CD 'O z UJto Oc*- r- Nc o £ .«>Z> O D. Q.oC\Jv- 0. . o*•* T~*m ^^ CS S .S oJ5 'c "o '£.r \ -^t i \ f\*tCDC_J(J§h C %•SS *e -g ^O ^1 • • •—IA- o> c -rll!«I« 'c o £ .2Q DO Q. Q. Cg t5o> _N ^S_=£ O Q) XJ CVJ O u_ c\i £ "-^ Q. C T- (/) (1) LJ *3 0) 0 2 too o O fl) </) OJ^- r= CO C Q- U 1 < CD CN LO £00 CD"b u_o wLL ' CM O UJ UJ UJ co "o0)(f) N =£8 u.-Q o o CO T- Q. «- 03 -^= 0) T3 £ « E > oo > =ro ci < wex oi^ o II ^o =O)^ (5 »JC 0)e -su oCO (O IT) f03 0) —O 0TOiL W D O CL Q. UJ UJ oa S' _N t/) og O 08 o CD c. w .2 CO mO ^ " TJTJ ® 0)«?-S £ > o10 oj CO 03 ^ 8" <D W ro _J Q. E .j < HIoz $Q g.H- 2' OLU CO ._NCO^ IT)*8*.Q CM OO T S£ ®0 — T— Q.co w c T- co,„ 0) O 0) -DCD CO roD•n W ffi MS JS E E > cosi^wj o 0) "w raOJ t- .— 03 C -J Q. U. —I < CDO10CD»*—CDCO COu_ u. gi c i§ : ottr^ O»- OPi,>.—m o«:'DOIXQ. uocSaiil 028we o £ .¥Q O O 0. a U OJ CO La Costa Avenue Condominiums Carlsbad, California Slope Stability Analysis Project #980161-004 Date: 10/18/05 ^HH:^ Leighton and Associates A GTG Company GEOTECHNICAL CONSULTANTS (L - Iff- / 7"^ ^ ' -— / 3934 Murphy Canyon Road, #8205, San Diego, CA 92123-4425 (858) 292-8030 • FAX (858) 292-0771 • www.leightongeo.com Q) CM m "D j^ O (n ~*«x ^"^ *-~C -Q CNJ 0} Fn°m^ c9-0 ^ ™ £CQ 9 co o Q. III!!ii«ii f|S|*O t 'T' CO ~i.n i= *- —M ^ <D co <oIcSiiJS^ c ToQ. mn 0)8ou_ c Q_ ro0) JC CO •aQ. O LO II 03 ro f CO om T— 1" "roCO>*—o §rou_ CDCDC 0 0 Q) CO oo ro to•7-5vjEOX)o>CommentsProposNCOc\ii__bCDCD File NameSection00caCOCNJCD "roQ 0) (13 CO ro Q.0 Analysis MethodB"wQ.LOiou_ c b, ro0) CO "Bo.Surcharge = 150CON.CD foCO H—o 3orau. I .'.*.•.*.. • . • . • . LU LU d> Nw eg in ~ o 8 I^W t5 is ^ §«•§ i CD CL o O) *- *- (0 "I 2 "o — °i_ 03 ^Z3 O f(/) CO U. H* LU s J. .'•' ' ^ t < - N . • •• •;• •. • '• •. • v *.'v•• •/• •. • *- •:• v- *• •:•??• *.•. •. • •. • ^ • • < • *. • • W$M: .0og m UJ j^ 0 ^ ?§ Q. Z ^c^E'•g m B w<D C T- CO(/) (/) O - • . . 0) '-3 <D T3 jl«lU _. 0) ^ 2 2 Q) E > W .8855'$. P&0to-co CO ^- =: CO 5_J Q. U 1 < **—{/)Q. O £ 0.1 »cli-S^lElr;C C O £< DO Q.W?Piezometric LiXi0 *~V «-C r\j CDO L_ O cSo 3ra •§ 21 g aJ2 1> c "o £ .aO W 3D Q. Q.^S «C',-; o c< «(> -J ~m— £ SJ wfc o £ .2 E *~ §IDU Q- Q- o ~ ^>/ 8> « 2 o>,' .25S0"/ w ^ o £(0«..a LU UJ cg t30> 10 C\j C 'CL T3 0> LL1 o ,_ S8 ^Q. C.o -2 "S <n ^f °- II § 8c <n c/>O O Q)E 11 0) CO CD nsCO 3- II ^ ro ® £ ro i- =a> co —TO JQ-LIIJ< CO o03 UJ UJ LU•z. § O 01 LU CO (133d) NOI1VA313 UJ LJJ Co 't5o w ^W T3§2 o 3"S(0 COo oO Q- JSiG _N W) Q. &lt> -* O •° CM CD [UCQ £ OO Q. C v- COO - . . .+3 CD "o $§£coQ^ LLI 111 CO to 03 — CD Cu i <; COn Q- 0) Oo m -i- r- OO ,. CD LU II .. c CD = ?fV If! CO CO CO LVA313 c0)oOiffyJS o c o £ .»O </) D O 0. 0."- S" c ~!111*15 •= -C " N'•e c o c .2< 13 U Q. Q. • N LLJ UJ 0 'o0) CO Cflw20aw !n E-E1 finished w pin10/23/2005en Proposed Gradeg "oCD CO 0) COz V il . . BCOQ -aCD CO CO •»-•wCO SpencerAnalysis Method"to Q.Surcharge = 15CQ. 1^: ID CD 0 2Ou_ c Q. IMroo> CO 0 CD T — 1) ®sCO in x — £,0) COco *<—o 1 03 LL CN c 'o. UJ LJJ g*-»oCD CO toCOo6 CO•+-'toIPK1_J osed GradesQ. 2a, to'cu= UJ LLJ C.g t>0) CO <li 03•^ to LE moo CN CO CN O•r— 0)*-»TOQ T30) OS{/> . CO05 Q. O^rtoin /sis Method:MM*TO C < **—toQ. O1Cr- 1! 0) L? CO Oi_ Z5CO c coD.'jx: IDCD 0 2O U- c Q_ U. fTTtU(D^: CO O-8 tt45ipol2?f"iJ5 c o £ ,5>O D O Q. Q- JSJ CO cf"o. Cg "o0) to so ea0 c</) O(U -*3TJ Oco Q) O^o E W COi.z o ID <N CD CO g Ci SO OL OJ C — CO_J Q- U 1 CD T3 to o Q £ •ojCD -2 «'SCO J, "coc (/>Q. LO II CD8ou_ c Q. CD CO^rCO "wQ. O LO T~II CD E? CO o 13 CO ooo II : T~ , . CD moco 5 CO CO 0*^o 03 LL 10 c 'o. O CDco 2O JO'o co 0•o 2O -aCDV)oCL 2 CL 'o iZ tooo C! CL CO O CN .C o .52T- CO CD -o To oQ £, Q) «1to 5to c • • • • • • • -^H• • t • • * • "^2 • •*•*••••• •••••t ^»••••••»"t t t • id * • < >• • • • • JQ • •• • • • j..»-»• • t • •"~ L • '• •• ••••••• • • • • • •• • • • • 9 • • ••••••• •••••*• • • * • « • »• • • . .•» . » CO CO CO •» La Costa Avenue Condominiums Carlsbad, California Slope Stability Analysis Project #980161-004 Date: 10/17/05 - 5 sg < T- O i_ c ^ og 0 Q -7; CD $^ O Q- "i w -4-* r«55 ro o .i?O il Q) Q -n CD CDS 0 E >W W CD ,5 O COCM 0)O) ro fcifS ro en C) \— >% IroCO rou_ o UJ 8 8 ST— 1— U33d)NOllVA313 , < -N m * -I I -§|f 8 s (/>i 5-aJw J, O QJ W TO>• = « sQ_ U I < OTCL OCD 04 0) S>co" 00CO 05CO oTO LL. O UJ g-So S* S 3= 2 y^ 2> c ~16 •" .3 i- 2•o 5 S ^ o«= — £ N§C e £ .?I3O a Q."§ !Itiol^5S°o>.— £ ' • N^5 'c o Z 9a DO Q.CL 0) c o n 9QDOQ. 0.l333'^OUVA3T3 S 8 S - Q • •.'•:•'••'"•?•:•' • 21". * • . * — S</> ow o Ig Q.o ® o < o 2w c T- CQ •o ™ "SO i- (J)CD CO ro O ^> «• a! LE J (Oex oCD CM II CD ^3 CO cn ,2CO oasLL P S U 2 UJ § JN V) ?i".i|=•tt O O o£$ ^42^ -2 g Eco £ co O C 7°llO u_ CD -<2T- QQ <D T)IS oQ £'5s2 «-22w|, ^g Q. OLT) II OO5 ro | CO • --f »*•*•• ••••J»^w**»»oo /• «•••*•* • ' f f * , « • » •r. ...w... ...—& 00 »« ,.» '?"i O) § CO CD 0)x: CO I CO£_=?H. Q co-8 0) O CO CD Q £O 3 co-o a ^ O CD CD -^& oJ E > w o-g ^S c< CO CNJin CD CO o Ct5 CO CN -5 c o £ .!»O rs O CL 0. o D R^»o 01 UJ UJ cot>(D CO w^fi.£§ UJ UJ I CD Q. O « CQ w E 10 (O ~«)C O. U -- 1 < (fl Q. O ^ b u ® 0) s O) T~ ro "ix: <uIs </> CO COCO ro CO COu. •*•">',» • 113 -s1cDOO »/>•O CM:= X? •-SS-151^'•£ c o £< r> o o.a0)c_lowoIQ.ao0I8oS , . o||l|>>_ .~ 5<3 (8 5<3\\T—ftt)C_J0o|•• NQ. i£H_8.ow• -c o ji .5DO Q. Q. LLJ LLJ Cg o V) N CNJ 10 .y: ° •Q CM Q) cW O0) '4= 0Q. CO 05 C/5 Q. Q) =_ CO ">•c *— ~ .C _ NO 05 D (J OL O.ao>c-Jyj=0><n?^S~-~ ^ eg:= £ •U- O) csil^S1 •! € £ .8< D O Q. Q..y Iog"o§0o~ «u. j: ••"fS,tt0).««O) " .a o> p|i|?Sra c o £ ®to D O o. Q. -• - LJJ UJ cg "oCDCO co CO &• J^4 CO Q. 5 10 =H§-Q ogill f^ UJ§c •«- 0)oc <DQ. CO 0)COoQ. O $%coQ v^,uen JCLlZa 03 O 2 o g>^- (0 »•5 ^§ s (O CO CD CO O CO CO % .33d1 SOU*.'313 LU UJ co 'o CO _N55ciE o UJ *= UJ cco O 0) '^3 "O O0) 05 O « •^ CO 2o ro Q ^Eco ro o _o) D_ i~ Q. o U .. Q) = m »-C Q> i— CO V) C/5 UJ UJ o ro moo Co 00 </> C T- CQ « I '1 w IO c S Q ±? 10COm 03 C/)03 ® E > w §S^<55'« ^&^co^ S.3a:!z.3< o o COLL 0)tr€ c o £ .9Q- Q-oCM co'IDC §. .^.:.85 'So o |<"£ 8*- §>..~ .C • • M«S 'c 75 j~ .$O DO 0. a O -C •LL 0) c Q)co•-c o !c «DOQ. Q. O 111 1/5 u. co i- O^ O i_i CM 0)-^Pr o |J- *~ m U- O 0. CO C T- CO Q) O <W "O "S "S ro 2 w T-, 0) 5 ^.2 CD £ > co«? « to ^ •«o o O CO 0 CO~ CO CDCN (0 o "o CD <D CM .« £ .•_: Ntr c o jc .??Z> O Q. Q. o 96 cg "o0 i_ m'PSC3^J cg"-*-»o B.2CO ro pQ £, 0) m V c ^*j 0 C ^ C/3 CO <0 CD ™ -(fl <3 §-? «>-s *£ IO O'§".0 I> a) r~- o— !; <N Nc o •£ .2r> u OL o_tt0)o cEIts o£g .yLL 0> c -5*— O O r~<S > '55 _ ED 'c o jr .SJQ D O O. O_ OJ (£> CD CO O CD 9o z $ Q R.t- z'o LU Ig 9 5S.o o d o c i •"- cO fr\ ^ 0) '-g *-* O Q. 0) o ^ W w ^ o oj ^ fN O ' ' ^ 5^E^?W W 03 ™ '55O O z </) ^, O <D ^* *"OJ >?- ^= CD 5—I Q- U 1 < en CD CDcr>CD m(f) Qo(0 O O LU '..333. NO .V-3-3 N CO CN 9CD o ir> O L- i|o o. w . 0) *3 Q> E > ro ro . =._i a. u — i < O)CD• II zo. •O 03 CL Oo II O CD CD O o II CD CDC 2 X: '01 I-•-»w >>.COo o'a.o "ow < .0o !S -: 2 ' ^Uu <O O) f~ «ii!!«f» o c o r. .2Q to O O Q- Q. § 03CO o o 6 LJ NC oo. Q.m w c T-_ 0) O Q>2 ffi E > CA881^1, " &^ To w3o:E5^ LOCO03 o oroLL ULUC/3 • . JSjen inW o^ <N c5"o T ^1 Q)<D — O CLCO </> C T- COO 2 o Q £/jOco-olu -o CD g ^& 0) E > coeo CO CD *5 't/i0 O Z W j>* O Q) ^O CDCD t. r= CD 9_i DL u i < 10LOO03C/) COU. OLU CO 8, <DC_Jo^J£3£IX .Sn>EbULIOQ0CDS,5>0)cr>oQIDC°</)0)(—0o CT)t>J!cCL 31O)C_loSll>i0)CL t! f 8 \.^ > • • • ' -. «uj 5< • • --* «-_—k>? • • • » '£ I 0) C i- CD T-co w o .. .. s ZQ»-o LU CO (133d) NOI1VA313 cO ±4 <»10 T- O ^ O u_ •Qg3 ~> O Q. C T- (/) o<1>CO to O «lll82^o (/) CO 03 . •• '_ 03 Q.- ^^ -2 CD ^ — m C .^ _J Q- UL Jj < U- Z CO OCD OCM O00 • 3j 1 3' • c - h- g '"0 "> O QL CD C •«- CO W K .2 « - -n Q>-2 « E > _ O Q) o ro CO u. .— CO C_J Q- U __ 1 < 10 in eg 2ro CO 20ra z 1133d) NOI1VA313 3 8P* <N CM ID ^ O -0 04 0) C.o "•*—»o 0) CO CO ct/> OOJ '4= 03 <?? O 0- (/)</>o o 0) W (ACL O Q) 03 boo '-J o a? w J5co jt- n= co ci a. u i < 03 C/) O "oCO 8• Q) If) CNJ ^V* o •5§ Sd ^ o ..!, *~ -C*o-<2C •«- 03 13 O roQ £ Q. O LD oCO II ' T, w I S 8 | (5o & / j CjL ^t "••* ""^« P ® 52 {SCD ^- = co 9_j CL u—i < g> - 03r* <j) O 3 CO 03O COin ooCO 5o (/) *~ IO v; O— O-° CM .o "o0> Q) •*- O O- g^S"co OQ £ -Q £ Q> «=*S <D E > wi t/i m ro *r^ <~> g-O) to roOJ C. £ CD C_i Q- U 1 < Q. O " 0) ooo 03 CO g) T- O _S> 2rs " CO CO 2o COu_ '»331 •* ,; •^ ^>;_ o "o c3cots0 O-a c •o ® s75 Q CL £ m w w co ,-Ao o z (/)1(3 Q--*- *-O (y w03 ^- r= 03_J Q- U I - Q. OID O) 03 I CD Ooo _ LO 03 03t—O Iccu_ E I 6 c o £ .9>ODOO.Q. ••' -.1 Leighton and Associates, Inc. A LEIGHTON GROUP COMPANY December 22,2005 Project No. 980161-003 To: CALSO, LLC 2683 Costebelle Drive La Jolla, California 92037 Attention: Mr. Kwan So Subject: Status of Geotechnical Evaluation/Slope Stability Analysis Relative to the Existing Landslides and North-Facing Hillside, La Costa Condominiums, Lot 185 of La Costa South Unit 1, Carlsbad Tract No. 02-28, Carlsbad, California In accordance with the request of Mr. Gregg Linhoff of Lighthouse Ventures, this letter presents the status of our geotechnical evaluation/slope stability analysis relative to the existing landslides and north-facing hillside at the La Costa Condominiums located in Carlsbad, California. Due to the recent surficial failures/landslides that have occurred on the north-facing slope, we have preformed an additional slope stability analysis of the hillside on the southern side of the property. Based on the results of the revised slope stability analysis, portions of the slope did not have the minimum required factor-of-safety of 1.5 based on the existing geologic conditions, previous laboratory test results, and the current proposed grades. Additional analysis indicated mat in order to obtain the minimum factor-of-safety, two rows of shear pins would be required if the proposed design remained unchanged. We understand that the construction of the shear phis may not be economically feasible and other alternatives may need to be undertaken. In order to eliminate the need for the shear pins, additional slope stability analysis was performed to determine how much fill would be needed if a buttress was placed in front of the existing slope. Figure 1 presents the approximate location of the required buttress. As indicated on Figure 1, the size of the buttress would extend across the entire southeastern most building complex, a portion of the building complex to the west, and the driveway in front of the buildings. The required size of the buttress is such, that a significant revision of the site development plans would be needed in order to construct the buttress. 3934 Murphy Canyon Road, Suite B205 • San Diego, CA 92123-4425 858.292.8030 • Fax 858.292.0771 • www.leightongeo.com 980161-003 The need for the shear phis and the relatively large buttress fill is due hi part to the soil strength parameters that have been used in the slope stability analysis. Some of the soil strength parameters (especially the clayseam values) may be able to be revised based on additional subsurface investigation of the actual geologic conditions. We are currently preparing a scope of work and cost estimate to perform an additional slope investigation. The scope of work will include the excavation of 2 to 3 additional borings, in-situ soil strength testing, and revised slope stability analysis. The intent of the additional investigation would be to be able to utilize higher strength parameters and increase the factor-of-safety of the slope without having to install shear phis or significantly enlarge the buttress. If you have any questions regarding our report, please contact this office. We appreciate this opportunity to be of service. Respectfully submitted, LEIGHTON AND ASSOCIATES, INC. Randall K. Wagner, CEG1612 Senior Associate Geologist Attachment: Figure 1- Required Buttress Distribution: (1) Addressee (1) Lighthouse Ventures Attention: Mr. Gregg Linhoff -2- 4 Leighton