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HomeMy WebLinkAbout; Terramar Unit 1 Lot 10; Soils Report; 1986-08-22.- : i f “I ,, * ‘.& - - .- ENGINEERING GEOLOGIC EVALUATION OF DEVELOPMENT FEASIBILITY, PLANNED NEW DWELLING, VACANT LOT ON SHORE DRIVE, CARLSBAD, CALIFORNIA FOR - - ,.:..‘. - ,;‘. - ! ENGINEERING DEPT. LIBRARY City of Carlsbad 2075 Las Palmas Drive CarlsbaQ CA92009-4859 - - - i \: -----.A--LA-A-----I-. Sirkei Index Map , - :. - -. ‘.. ‘. 20’ “69’ - Topoqr-aphii Index Map , - . > - william R. munson associates consunlrg engirleefing Qedqirtr r August 22, 1986 Coastal Commission Application No. 6-86-443 - Mr. Hal Heers 1802 Parliament Leucadia,, CA 92024 - SUBJECT: 8 Engineering Geologic Evaluation of Development Fbasibility, Planned New Dwelling, Vacant Lot on Shore Drive, Carlsbad, California - Leual Description: Lot ,lO; Terramar Unit #l, Map No. 2696 'portion tit H, Map NO. 823: A.P.#210-06-10 : - Gentlemen: Pursuant to the request and authorization of Mr. Lee Riley, your governmental advocate, .-the undersigned conducted a limited i ! 1 -' -~ examination of the subject property and proximity during August 1986. The purpose of the field work and study was to provide the basis for evaluating the feasibility of constructing a planned new dwelling at the site, from an engineering geologic standpoint. ‘- - 32302 comb copistrono . suite 207 . son juon copistrono . 92675 . p,o, box 857 l (714) W-~QOT . : - Mr. Hal Heers -2- Reportedly, the work and this report were prompted by a desire to preliminarily document exposed and apparent attendant geotechnical conditions for project submittal to the California Coastal Commission. - - - - - This report summarizes the findings of the limited examination and study, and presents relevant conclusions and recommendations for decision-making in this matter. SCOPE The field work comprised'visual examination of the lot terrain and attendant appurtenances, and 'the exposed terrain and structures on contiguous properties. Moreover, the integrity of the attendant near-surface soils was evaluated by random probing with a hand-held narrow steel shaft (a device used for that purpose); and relevantterrain configurations were measured by a hand level/inclinometer. Due to a gunited bluff face, the identification and classification of the concealed earth materials was made several hundred feet southerly where bedrock and overiying unconsolidated terrace deposits are'exposea in the bluff. _ . . The field work and preparation of this report were augmented by the writer's knowledge and understanding of local geologic conditions and associated physical impacts imposed thereon by residential hillside development: and review of the following technical documents: - - ’ I Mr. Hal Heers - -3- 1. - L - - 2. 3. 4. 5. :. C.M. Engineering Associates, 3 July 1986, Plot Plan for Heer Residence at 19-scale (W.O. 06-84-14) V'.... 'Frdnk.. Gonzales and Associates Architects, 30 June ., -. 1986, Building Plans,.-Including Foundation Plan, Floor Plan, Section,--~ Rbof Plan and Elevations (7-sheets) - --,.~~ .'. ,-' Jpb-No. 2054. Weber, Harold F., 1963, Geology and Mineral Resources of Ban Diego County, California, County Report 3 of the California Division of Mines and Geology. Young, J.M. and Berry, R-W., April 1981, Tertiary Lithostratigraphic Variations, Banta Margarita River to Agua Hedionda Lagoon, Paper in Geologic Investigations of the Coastal Plain, San Diego, California prepared for the 1981 San Diego Association of Geologists Field Trip (Pages 33-51). : Lajoie, K.R., et al, November 1979, Quaternary Marine Shorelines 'aad Coastal Deformation, San Diego to Santa Barbara, California, Paper Prepared for the 1979 Geologaical Society of American Annual Meeting. The scope, of the examination and study did not include subsurface exploration (i.e., backhoe tr'enches or drilled I _, borings), nor soil engineering field/laboratory testing and . analysis. - - - - Mr. Hal Heers Accordingly, the field work conducted is classified surficial, whereby evaluation was limited to surface and very near-surface conditions, apparent and obvious to the writer, and interpretations made therefrom based on published (i.e., documented) geologic/topographic conditions. Evaluation of subsurface conditions, and conclusions made therefrom, which were not reflected at the ground surface or by available documented geologic relationships, are beyond the scope of the field examination and study, and this report. Such information would have to be secured from a comprehensive subsurface geotechnical, investigation in the+form of exploratory drilled .,.~ .~ ~, borings and/or excavated trenches. ': Within the limitations of the subject field examination, the following attendant features and conditions were recorded and/or evaluated: ; 0 Composition/geometry and integrity of exposed earth materials at the surface and in the near-surface. 0 Man-made alternations of the terrain. 0 Evidence, if any, of'prior ground instability. 0 Conditions conducive to site stability/instability. 0 Engineering properties of earth materials, including expansivity, based upon visual examination. - - Mr. Hal Heers -5- . - PRINCIPALS - 0 Owner: Dennis & Carol Troish 6830 Van Buren Blvd. Riverside, Calif. 92509 (714) 685-7481 - - - - -’ - - - - - 0 Architect: Paul Thoryk Thoryk Incorporated 1202 Morena Blvd. Suite 400 San Diego, Calif.:. 92110 (619) 275-5612 0 'Civil Engineer/Surveyor: CM Engineering Assoc. 550 West Vista Way Melrose Center Vista, CA 9'2083 (619) 758-3689 0 Governmental Agencies: California Coastal Commission/City of Carlsbad ENCLOSURES 0 Figure 1 - Geologic/Topographic Index Map . . . 0 Figure 2 - Site" Plan/Geotechnical Map 0 Figure 3 - Schematic Geologic Section A-A' 0 Figure 4 - Major Earthquakes and Recent Active Faults in the San Diego Region... - - , .’ - - - - - - .- - - Mr. Hal Heers -6- GITE DESCRIPTION The seaside property is rectangular in shape, and fronts on the westerly side of Shore Drive off of Carlsbad Boulevard in the incorporated city of Carlsbad. The overall dimensions are 60-feet wide by [+/-I 150-feet deep to the mean high tide line. It backs westerly onto the base of moderately high sea cliff terrain and a racky beach beyond. The northerly and southerly adjacent properties, which have approximately the same elevation as the subject site, are developed with long established single family dwellings. Terrain The seaward margin of the property is marked by a [+/-I 29-foot high bluff face that is everywhere concealed by a gunite blanket that, reportedly, was applied about 1972. Apparently, the gunite constructionwas'hecessitated to protect the bluff from wave action, and to a'rrest on-going landward erosion and gradual reduction of the building site. Moreover, as viewed from the property, the gunite bluff protection extends monolithically many hundreds of feet northerly.and southerly of the site. The configuration of the gunited bluff, from top to bottom, comprises a [+/-I 14-foot high l/4:1 to 1:l precipitous cliff that toes out at an irregular seaward sloping natural bench, which terminates as a [+/-I 6-foot high near-vertical face above the rocky beach. - - Mr. Hal Heers - -7- - - - - - -’ - - -- - The existing 60-foot wide by [+/-I 95-foot deep lot pad is relatively level' to very slightly inclined in a southwest to seaward direction. The average pad elevation is [+/-I 39.5-feet above sea level, which is approximately the street elevation. The terrain between the elevated lot pad and the bluff comprises a relatively uniform [+/-I 3:l (i.e. 18- to 20-degree) natural slope. Veoetation The earthen surface supports a sparse to moderate growth of thick-bladed ice plant, a few shrubs'at the southerly margin of the lotpad, and an aloe-type plant at the northerly margin. Improvements 0 A chainlink"fence, located 40-feet from the street, extends across the width and along the boundary of the property. 0 A masonry garden wall on the southerly property line between the chainlink fence and the street. _ . . ‘0 The aforementioned 'gunite protection blanket on the bluff. Although the details of construction of the gunite blanket are unknown to the undersigned, the condition of the gunite suggests that reinforcement steel (or equal) was used and, possibly, the system was anchored by rock bolts and/or earth anchors. - - Mr. Hal Heere -8- - - .- Moreover, it was apparently constructed with a subdrain facility for the collection and disposition of migrating groundwater, as indicated by an exposed [+/-I 3-inch diameter outlet drainpipe that extends through the gunite near the base of the bluff. DRAINAGE Lot drainage comprises sheet flow runoff of incident rainfall that is received on the gunited bluff and directed to the beach, below. Drainage from the east is intercepted by Shore Drive and conducted elsewhere to a storm drainlfacility; whereas, runoff on the southerly- and northerly-adjacent lots drain to the bluff substantially within their property boundaries. + PLANNED DEVELOPMENT/CONSTRUCTION According to the Reference 2 building plans, the site is to be '; ,~ i..b ,?* developed by constructing a [+/-I 4400-square foot 2-story : dwelling (as viewed from the seaward side) with a j-car garage. ? ;' .r,- ,a The garage floor is to be [+/-I l-inch below the street level. I I_ i: The main floor of the dwelling', which is to be at approximately' !"' street level, will include two bedrooms, two bathrooms, a living room, dining room, kitchen, study and laundry room. The lower level will be a basement, the floor of which will be 9- to .- lo-feet below- existing grade. A distinguishing feature of the is that the dominant gable roof is to be 27.5-feet high .’ ~ - I - - - .- ,s - -. if! \ Ii T 7 !I ~ Y b - - Mr. Hal Heers -9- relative to the front yard grade to accomodate a 2-story high front room and master bedroom at the seaward end. Moreover, the design Will create a maximum 16-foot high attic above most of the garage and dwelling. The set-back of the rear building line from the top of the 3:l earthen seaward elope will be minimum 12-feet. The only appurtenance shown on the plans is a 6-foot deep wooden deck cantilevered off the seaward end of the building to provide access from the living room and master bedroom, However, other improvements will undoubtedly include a con.crete driveway, concrete flatwork, garden walls, and'rear yard retaining walls. The foundation system will include a maximum lo-foot high retaining wall to form the back wall and side walls of the basement. Accordinglyi"'the retaining wall is to provide support for the peripheral lo'ads of the superimposed upper floor and roof: whereas, poets supported by pad footings will support the interior and westerly (i.e. seaward) wall loads. Moreover, the foundation system for the garage, study and front entry will _ / consist of conventional continuous footings, two pad footings and a grade 'beam footing across the garage openings. There will also be a pad footing to support the canopy over the front entry L walkway. - - . Mr. Hal Heers -10" . \ The ground floor system will consist of concrete slab-on-grade. NOTE: The Reference 2 plane did not include retaining wall, foundation or floor slab details. Apparently, earthwork grading will be limited to an estimated maximum [+/-I 10.5-foot deep excavation to form the basement and basement-level rear yard. Moreover, the rear yard excavation will undoubtedly be a lldaylight" cut at the seaward-facing elope. The plans do not include a grading plan; nor do they show perimeter rear yard retaining walls that will probably be required to support the construction cute below the side yards and along the southerly and northerly property lines. / All excavated earth materials will be exported from the site. - GEOLOGIC SETTING ; : Regionally, the property is situated on the coast plain at the seaward margin of .the foothills of the Santa Ana Mountains, which comprises a part of the Peninsular Range Province. Locally, the underlying Santiago formation bedrock of ~ ,. Eocene age is capped by Quaternary marine terrace deposits. GEOMORPHOLOGY The near-level to gently seaward eloping surface of the building site is a substantially natural platform that is widespread in the coastal plain of the Carlsbad-Oceanside area of northwest San Diego County. There, it is generally [+/-I 40-feet above sea level. - II ,. .’ Mr. Hal Heers - -ll- - ,- - The feature comprises the remnant of a"late Pleistocene marine terrace and superimposed ancient beach deposits that emerged from the ocean 85 to 120 thousand years ago. The sandy beach sediments, termed marine terrace deposits, were formed on a trancated bedrock platform (i.e. marine terrace) cut by wave action 'at a,time when sea level was roughly 20- to 4%feet below the present ocean level (i.e. during Pleistocene Ice Ages when global glaciation caused a corresponding lowering of sea level). - The process of the ensuing emergence to the present terrac~e level has been tectonic (i.e. by mountain building forces) at a - continuing very gradual rate. Although imperceptible, the rate of movement is measureable by sophisticated equipment over a period of many months or years. - - GEOTECHNICAL CONDITIONS Earth Materials 0 Fill - None - - 0 Marine Terrace DSDOSitS (symbol -Qmt) - The gently dipping wave-cut marine terrace platform (i.e. bedrock) is capped by an estimated 25- to 30-foot , ,. thick prism of-pale yellowish brown slightly silty to silty, very fine to medium grained sand. These ancient beach sediments are dense, very friable to weakly cemented (imparted by iron oxide and natural salt compounds), non-expansive, very permeable, and very erosive. - t - Mr. Hal Heers -12- - 0 Bedrock (symbol - Ts) - The underlying Santiago formation bedrock forms the lowermost [+/-I 12- to - - - - - - - - - - 15-feet of the bluff. It consists of crudely stratified dark gray-brown clayey siltstone that is very stiff to hard, and exhibits moderate to high expansivity. Moreover, the fine grained bedrock is generally impermeable and relatively erosion resistant. By contrast, the bluff comprises a near-vertical rise above the sandy-gravelly beach and a seaward-inclined ledge, above -- both of which are comprised of bedrock: and a variably-inclined precipitous erosional cliff face in the sandy marine terrace deposits. Of course, the features are concealed by the gunite blanket. "" The circa 1972 gunite blanket appeared to be substantially in place as orignally constructed. The only evidence of marked distress were a vertical crack at the face of the gunited vertical rise above the beach, and some curvilinear cracks on the inclined ledge. They are attributed to toppling of the bedrock along a joint fracture, and to expansivity pressures, respectively. Notwithstanding, the gunite face also exhibits several minor hairline cracks. . - .- - ’ Mr. Hal Heers . - - - - - - - - - - - Geolouic Structure Based on outcrops in the general area, available published data, and interpretation of site conditions, the following determinations are made: 0 The marine terrace sands are very crudely to indistinctly stratified, with low angle seaward dips. 0 The Santiago bedrock strata dip 3- to &degrees seaward (i.e. westerly), and are cut by a system of high angle (i.e. near-vertical) joint fractures that strike roughly north'south and east-west, respectively. Groundwater Groundwater seepage in ocean bluffs is commonplac,e in the coastal margin of Southern California. Typically, water derived from incident rainfall and irrigation 'percolates downward through the relatively permeable granular terrace deposits until reaching the relatively impermeable wave-cut surface of the bedrock. The groundwater then, migrates seaward at the top of the bedrock until it **daylights8V as seepage in the bluff. Although not evident at the site or proximity due to the gunite blanket, the above described relationships are believed to exist. - - _ - - - - - ,- - - - - - - - - Mr. Hal Fleers -14- BLUFF/SLOPE STABILITY The attendant terrain exhibits no evidence of landsliding, or inclination thereof. Moreover, there is no evidence of significant downslope creep movement in the earthen surface or in superimposed structures. A cursory examination of structures on the contiguous properties likewise revealed no evidence of distress. Accordingly, the apparent stable condition is attributed to the coarse grained, dense and massive characteristics of the thick sequence of terrace deposits. DONNSLOPE CREEP PHENOMENA . / The attendant terrace deposits are subject to downslope movement within the outermost few feet of the slope face. Moreover, the margin of the'building pad nearest the slope is also subject to movement. The natural phenomena affects nearly all sloping terrain to some degree, is most dramatic in fine grained (clayey) soils, and affects granular soils least. It is tenned'downslope creep, and the affected zone below the slope face and pad margin is termed . . the creep zone. By definition, downslope creep is the imperceptibly slow downslope movement of surface and near-surface earth materials under the perpetual force of gravity. The rate and magnitude of downslope creep is a function of slope height, slope inclination, soil density, expansivity and ground moisture. 6 Mr. Hal Heers - -15- .I SEISMICITY/FAULTING There are no active or potentially active faults that are known to transect the property. The nearest known location of major - faulting is the fault zone [+/-I 3-miles offshore, which is associated with the Rose Canyon Fault. The Rose Canyon Fault, which has been classified potentially active to possibly active (i.e. it is controversial), may be linked with the active Newport-Inglewood Structural Zone that parallels the coastline. The magnitude 6.3 Long Beach earthquake was caused by a sudden strain release along this structural zone of faulting. Accordingly, a magnitude 6.0 and'6.5 earthquake may occur - along the fault system within the economic life of the structure (iye., 50 to 100 years). Of course, there are numerous other faults in the Southern California region that;have the potential for generating strong ground shaking at the site. Accordingly, the planned - ~- - - - - - construction should incorporate standard aseismic design ., considerations to mitigate the effect of ground shaking induced by a moderate earthquake along a nearby fault (i.e., ,. -,. Newport-Inglewood, Rose Canyon, and Whittier-Elsinore), or by a major or great earthquake generated along a distant fault (i.e., San Andreas'or San Jacinto). * - Mr. Hal Heers -16- - - - - CONCLUSIONS 1. Based on the limited investigation and study described heretof,ore, it is the opinion of the undersigned that the planned construction and associated grading for a new dwelling and appurtenances at the subject property is feasible from an engineering geologic standpoint, subject to'the recommendations rendered hereinafter. ' 2. The attendant terrain exhibits no deleterious geologic conditions that would preclude implementing the planned residential development, provided foundations bear suitably in competent natural ground foruniform support, and the planned seaward disposition of site drainage be implemented to minimize or preclude slope erosion. 3. Attendant' subgrade earth materials at the building site exhibit soil expansivity potential in the range of low to nil (i.e. marine terrace deposit sands). 4. The circa 1972 protective g-unite blanket on the bluff face has affectively arrested bluff regression, which is an otherwise active process along the Oceanside-Carlsbad coastline. Moreover, except for a few open cracks, the 1 ,. gunite system has "survived the test of time (i.e. 14+ years) during which it has been battered by numerous assaults by a storm whipped ocean. 5. In the absence of evidence to the contrary (in the form of marked distress), the gunite blanket is inferred to have a functional eubdrain system to effectively collect and - - - 1 Mr. 6. 7. 8. 9. 10. - Hal Heers - ' / -17- dispose of migrating groundwater along the interface between the clayey siltstone bedrock and the overlying marine terrace sands. Surf icial sandy terrace deposits on and near a descending slope are prone to minor downslope creep movement. The planned excavations should encounter only sandy terrace deposits. Accordingly, they may .be made utilizing conventional excavation equipment. Groundwater should not be problematic to the planned construction, or to the continued stability of the bluff, provided the inferred subdrain system does actually exist, and it continues to function in+an efficient manner. Being located in Southern California, the site is subject to strong ground shaking by nearby or distant earthquakes. However, 'the performance of structures built in compliance with current Uniform Building Code criteria and founded in firm ground, such as occurs within the underlying subgrade earth materials,,, has generally proven to be satisfactory under conditions of earthquake-induced ground shaking. Local mapped faults and inferred fault traces are deemed inactive in the classical sense, and not problematic from 1 . . the standpoint of" earthquake induced ground rupture or shaking. BECOHMENDATIONS 5 1. A subsurface geotechnical investigation of the site should L be conducted prior to finalization of foundation and 8 grading plans. The purpose, of course, is to verify the _~ _,.. ..,~ -. ? preliminary findings described heretofore, and to provide .- (" - - the basis for specific reccmmendations including: Foundation design criteria, structural set-backs, site drainage, grading specifications, and in-construction inspections. 2. All foundations for structures should be founded in competent/dense terrace sand, which is generally 6- to 12-inches below the surface. 3. All structures on or near sloping terrain (i.e. ocean slope and bluff) should have a minimum embedment in dense terrace sand to a depth determined by a minimum lo-foot horizontal edge distance, measured from the bottom outside of the footing to the face of the slope. 4. Pursuant to Table 29-B of the Uniform Building code, the following'criteria are deemed applicable for foundations in the bedrock: 0 Allowable foundation pressure - 2000 Ibs/sguare foot 0 Coefficient of friction - 0.35 0 Lateral bearing - 200 Ibs/sguare foot/foot of depth 5. Unless otherwise recommended by a qualified Soil Engineer, the basement retaining wall system should be designed to resist a surcharge equivalent to a level sloping backfill (i.e., 30 pounds per cubic foot equivalent fluid pressure) per the following appropriate Los Angeles City Building Code section. The retaining wall system should be equipped with an effective subdrain system to effectively preclude the build-up of hydrostatic (i.e. porewater) pressures behind the wall). _- .- - .~ . ‘ Mr. Hal Heers - -18- I I I , 1 ! I I I / , I I / I. 1 SEC. 911309- REIA~NING WALLS (I, De.lcn. Retntntng walls rba,, be deskned to reslat the later- .I prrrwre 01 the rc,mtned materla, delermlned In accordance vltb rccrpted englneerlng prlnclpler The adl chrmcttrlttlu and design crlterla ncee33~y for such m dc1rrmlnrUc.n shall be obldned from a speeln, 1oundaUon In- mtlgstien perlormed by an agency acceptable ,o the De- partnvnt. The Departmtnt shall approve such ehcmcterlstiw ,x”d erltrrla only rfter rccelvlng II wrltten oplnlon from the In- vestlga:ion agency togelhtr wltb tuhs(nntlatlng cvlde”ce. ESCEPT,ON: FrrcsC.ndlng Wdk WMCA or* “Of over is, (11 hdghl m baaelncnt Wdb lahkh horn .pona Of IS’ m IUS bdtarsn anpporw may bs ddgned ,I ocoordancs with Sub- rrction .lbJ of this Seelion. 140 DIV. 23 fee. ¶1.2309 ICmU TABLE NO. 23-E surrun slope 61 BAlIbmd MM.e*ld* ,,“,I% to “STL LEVRL 9 to * : :: : 1 1.3 , 1% to 1 Rqulralent ““d,b-;;&t .; ;; pi to 1 ii * Where the surhce slow of tbc ret.laed .ath varle,, th. d&g,, mlop ah-11 be obtatned by canatcttng a Ilae Imm the top of the aall to the hlghcat point on the alope, whose lb-&, .m rlthl” the horlzonta, dhtanes fro,” t,,. .ten, cqua, to the stem helsht of Lbe “al,. 01) Arblby D&g” Method. Wrll# rblch ntaln dnlncd e.rtb and come wlthln the llmlts 01 the exceptton to Subsntlon f., ol this mcctton may be deslgned for a” lssumed earth pressure cqu,. ..knt to thlt exerted by a fluid relghtng not 1-s than ah”,.” k, TabIt 23-E. A vatilc~l component equat to one-third of the her,. mnW force Ed obt&,ed “my be auummd at the plane oI app,,c.- Uen of Vie lores The depth 01 tbe retaIned. earth ahall be the rartleal dlatanc. below the ground 8urface measured at the rlll lace for ,tem de. str” or mewred .t the hec, of tbs lootIny for overtumlng and .Ihlh~. te) Snrebmrm Any ruperlmposcd lcadl~, UEC t rctalncd a.t’th. ehrll be eonmldcmd ,a wrcharpa and pmvtde B 1~ I” the daknn. Unllomly dlstrlbuted loada may b, wmldercd u l qu,vr,. lent nddcd dr”tb ol rct.lncd earth. Sunhugs loading due o eon- Unuaus or Isolated lootings #ha,, be detsrmlned by the fc.i,or,ny t”Ormu!aa or by in rqulvalcnt method appmved by the Superlnten- daat ol BulldIng. Resmnnt rAten Pmcc 03 Pb’ Yt=- x’+ b’ krtlon of L&em1 Reaulturt ,,==:: [(;:+t..-‘;‘) - (;)I ’ . WhelW R = Renultant latenl force meuurcd I” pounds prr loot r! -I, width . P = Reaultnnt surcharge load 01 conUnu”us or Isolated loot- Inga meraured ln pounda per loot ol length panllc, to the WUlL x = Dhtancs OK resultant lond from back lace 01 wall mm- awed In le& h = Depth below point 01 .pp,,e.“on of surcharge loadlng to X top or wall roootlag rnrar”md In rcct E d = Depth of lateral reruNant b&w point 01 appllcatlon 01 mmharga loadlntt menawed In feet. z (tan-1 ;) = The angle In ndlan, whose ~tmgent ts eWm1 $ u1 0 to .!! . x Sec. 912309 fCei3Ll - 211 DIV. 23 149 Lcmdn ~pplled Wllhla a horizontal distance equal to the wall stem belghf mauumd Irom.the back lace of tbe wall. ah.,, be eorutdered u “,rch.rga, For Lolhted lootla~ barlag . xldth pvrlet to the rllt Icu ,han tbre. iset. -It” may be rsdueed to I,8 the ufculrted due. l’tm results& lmtsnl force -R” shall be swumed to ba rnlform 1,~ tha 1s”~ ot fooUng par&s, to th. wall. md to dlmt”t,h unt- lormly to Vera at the dtatanca 2” beyond the ends of the foe”“~. VirUca, p-m due to rxchargs applied to the top et the ‘wa,l footing tray be eo”sldersd to spread unllormly wlthln the lbnlta ol the .tem lad plane. maklng M .“gle ol 4Y rttb the rclt,saL (d) Beulng Ramwe md Overtumlng. % a mulmlnn “tucil on I”“eatl,catlon. The resultant of vcrtlen~ lands #hall pnss through the ml~dle onr.hlrd ol (e) Rlctlon and Lmtent 8oU Rarswu +ii ctdnln~ wdlr rhmll be reatralned abrlnlt ulldlnr b lrletto” of the b-e .‘wl”st the earth. by lateml reslixt.nco of t K e ml,. or by. comblnallan of the two. Allownble frlctloa and Iateml sol1 values ahall not exceed thana illlowed In Dlvlslon 28 01 thts ArtI& except .s provided by . ,pec,a, foundatton lnrestl~~tlon. When usea. keys Bhkll be umnncd to lower the plw~c 01 ltie- tlonnl reststnnee and the depth of lateral baarlng to the level al the bottom of the ksy. Lateral bearlng pressures shall be ummcd to act on a vetttcal pllns laatsd at tba toe of the looting. (g) Spccl~l CondlUonr whenever. In the oplnlan of tbhc Super- tntendent of Bulldtng. the adequwey of tbba fcundsttc” m.ter,a, to @upport I wall 16 questlonable. m “““,“a, aweb. s eondltto” exlslr. or rheoever the mtalned earth Is so stratllle T or of such a character u to Invllldata ““mm, destrcn assumpttons. he may requlro n specla, foundatton lnvestlgatlon before approvtng .“y permlt lor such . “al,. -_ .,.A- .I 1 =: I Mr. Hal Heers -- - 6. - 7. 8. 9. - - - - 10. 11. 12. - -2o- Structures should be designed in accordance with applicable earthquake standards contained in Chapter 23 of the Uniform Building Code. Unless otherwise recommended by a qualified Soil Engineer based on chemical testing, Type II cemente should be used in concrete for all construction. The dwelling should be equipped with a roof gutter-downspout system to minimize ground saturation and nuisance water. Bulk and/or fine grading of the lot shall conform to the City of Carlsbad grading requirements. All site and roof drainge received should be collected and conducted to Shore Drive or to the beach in a nonerosive manner. Moreover, surface water.should not be allowed to pond on earthen areas (including planters), and no lot pad runoff or drainpipe discharge should be allowed on the unprotected sandy slope below the building site. All slope and pad ~irrigation should be applied at minimal rates to maintain health and growth. Automatic sprinklers are not recommended. Mo,reover, slope planting should ~ ,. consist of drought tolerant, deep rooted and light weight species. All earthwork utility trench backfill and retaining wall backfill, should be placed in a compacted manner in accordance with recommendations, testing, observation and - . Mr. 13. 14. - 15. - - - - 16. Hal Heere -21- approval of a qualified Soil Engineer. Alternately, retaining wall and utility trench backfill may consist of washed concrete sand, pea gravel, or equal self-compacting select earth materials. Retaining wall design6 and specifications should include an adequate subdrainage system and self-compacting backfill such as pea gravel, or clean native earth materials mechanically compacted under the observation and testing of a gualified Soil Engineer. Moreover, the back side of retaining walls should be effectively waterproofed. To prevent the influx of surface runoff into the granular backfill, the upper 12-inches of exterior retaining wall backfill should consist of on-site cohesive soil compacted to a firm'and unyielding condition. The open crack6 in the gunite blanket should be caulked and maintained to minlmize moisture from reaching the expansive bedrock and, thu's to minimize future cracking. Significant modification of the plans and specifications should be reviewed and approved by the project Engineering Geologist upon formulation,.to determine compatibility with ._ ,~.. , I, attendant geotechnical conditions, and to provide additional recommendations deemed necessary under the circumstances. To verify adequate excavation depth6 for foundations, the project Engineering Geologist should be notified at least 40 hours in advance of the excavation to provide timely inspection. - Mr. Hal Heers - -22- CLOSURE The undersigned Engineering Geologist warrants, that the work performed in the preparation of this limited report was done in accordance with generally accepted principles and practice in the field of engineering geology. This warranty is in lieu of all other warranties, either expressed or implied. - .- -~ This report was prepared to aid those endeavoring to expedite develoment planning of the site, and,to enhance future design engineering and construction. The .findings and recommendations are based on' information and data secured from field reconnaissance mapping, the project plans, available geotechnical data, and:,inter@retations made therefrom. -. Condition6 may be encountered during grading and/or construction that may differ with those presented herein. Thus, the Engineering Geologist should be requested to provide inspection -_- ,..._ ,.~ 1 . . of all excavations. - - - - - I Mr. Hal Heers \ -23- - .I - Should you have any questions regarding this report, or if I may be of further service, please contact me at your convenience. - - ,’ / :j’ - ,, 1,. C.E.G. 866 - - - m/61m Enclosures Distribution: '(1) Addressee (2) California Coastal Commission (1) Lee'Riley. - - - - - p,~clF/i omaw I 0 I ,~,LEGEND Km 8 J Faults Alluvial Deposits El T tm Son Moteo Formotion (Pliocene) 0 _ ,. El Qmt Marine Terrace Son Onofre Formotion Deposits (Miocene) Ponds or Lagoons Sontiogo Formation (Eocene) 0 Outcrop, i0c0tion Topoaraphic/GeoIocric Index Map Scale :. 1 ” z&3,115 ~ Source: Figure 1 -,. - .- - - .- - ..~ - .- - - ‘- \> /I, I t 75% . L’JT II dtrhrvsr crack ~~m;t; - b@. h&*1+ . - c-- SlTE PLAN/GEOTECHNI CAL MAP Scale: Reference: ~~-*, 1” = 20’ FIGURE 2 I / I I I I I I I I I I / . _ . . .- e... . . . . ..-. . ..-. . . . . . . . . . . . . . . . - - .-.. _. . . . . - . . . . . . . . .- n c SCHEMATIC GEOLOGIC SECTION A-A’ c ii SEE ENCUX6D -mlrVa +~lOrz(~ OF term m6f+’ w - - - - - ‘y?! r, >. “-1’9 ‘.... 3 +:. 9 . .:.,. ::..:.. l y..,‘:... .; ‘i .*. . . . . . c, -.. -- j IIU ,:a :t.. w -.- T\ -.A .>& -‘,I,‘:,. (,i) . . MAJOR EARTHOUA’KES- t-‘RECENT .ACTlVE FAULTS IN THE ~SAN DIE& RE&ON, ‘CALIF. Earthquakes of magnitude 6 and greater in the San Diego region. Solid circles show epicenters with year of earthquake and magnitude or maximum intensity. Open circles with question marks indicate poorly known epicenters. .- - - - FIGURE 4