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Home My WebLink AboutCDP 2019-0002; HILLSIDE RESIDENCE; PRELIMINARY GEOTECHNICAL INVESTIGATION; 2018-04-09Geotechnical Exploration, Inc. SOIL AND FOUNDATION ENGINEERING • GROUNDWATER • ENGINEERING GEOLOGY 09 April 2018 Jessie Smith c/o Kapono Corporation 29550 Cole Grade Road Valley Center, CA 92082 Subject: Preliminary Geotechnical Investigation Smith Residential Lot South of 4240 Hillside Drive Carlsbad, California Dear Mr. Smith: Job No. 18-11842 CITY OF C11,•. ,. , , c .. ) PLANNlNG DIVl~ION At the request of your contractor, a representative of Geotechnlcal Exploration, Inc. has visited the subject site and performed an evaluation of the soil conditions in the area of the proposed new residence. It is our understanding that the site is being developed to receive a new single-family residence, a driveway and associated improvements which will utilize retaining walls, continuous footings and slab on grade. As part of our investigation, we observed and evaluated the soil conditions at four locations within the proposed new building areas. We understand that the new residential structure would be built on the eastern half of the lot. In addition, we reviewed a conceptual grading plan showing proposed cut and fill slopes and the proposed building pad. The building pad is going to be located on a vacant lot on the east side of Hillside Drive at a lower elevation than the street. It is our opinion that the final grading plans should be prepared in accordance with the recommendations included in this report. 7420 TRADE STREET• SAN DIEGO, CA. 921219 (858) 549-7222 • FAX: (858) 549-1604 e EMAIL: geotech@gei-sd.com Smith Residential Lot Carlsbad, California Job No. 18-11842 Page 2 The field work, conducted on March 26, 2018, consisted of excavating and logging four exploratory test pits in the location of the proposed new residence, driveway and improvements. The excavations revealed that the building site Is underlain by approximately 1.5 to 6 feet of loose to medium dense, silty/clayey sand fill soil over medium dense to dense, silty sand formational materials. The on-site soils are considered to have a low expansion potential with an Expansion Index of less than 50. Based upon our observation, probing of the on-site soils and laboratory test results, it is our opinion that the new foundations and slab on grade for the residence can be founded in properly compacted fill or the existing forma'tional materials. The loose to medium dense fill soil in the proposed building pad and driveway area should be removed and properly compacted as part of site preparation for the new retaining walls, foundations and slab areas. All fill should be compacted to at least 90 percent of Maximum Dry Density. The Maximum Dry Density of the soil has been determined per ASTM D1557-12. 1. It is our opinion that properly compacted fill or the medium dense to dense formational materials will provide adequate bearing strength for the proposed new foundations. New footings placed In properly compacted fill or the existing medium dense to dense formational soils can be designed for an allowable soil bearing capacity of 2,500 pounds per square foot (psf). We do recommend that the proposed footings and slabs contain at least a nominal amount of reinforcing steel to reduce the separation of cracks should they occur. The allowable soil bearing capacity may be increased one-third for structural design including seismic or wind loads. Also, the static allowable soil bearing capacity may be increased by 800 psf for each additional foot of embedment over 1.5 feet in depth, and 500 psf for each additional foot over Smith Residential Lot Carlsbad, California Job No. 18-11842 Page 3 1 foot in width, up to a maximum of 4,000 psf for static loading. The allowable soil bearing capacity may be increased one third when subjected to seismic loading. 2. The proposed footings should have a minimum depth of 18 inches and a width of at least 12 inches, founded in the medium dense to dense formational material or properly compacted fill. A minimum of steel for continuous footings should include at least two No. 4 bars continuous, with two bars 3 inches from the bottom of the footing. 3. Site-specific seismic design criteria to calculate the base shear needed for the design of the residential structure are presented in the following table. The design criteria was obtained from the California Building Code (CBC) 2016 edition, and is based on the distance to the closest active fault and soil profile classification. 4. The proposed structure should be designed in accordance with Section 1613 of the 2016 CBC, which incorporates by reference the ASCE 7-10 for seismic design and the following parameters should be utilized. We have determined the mapped spectral acceleration values for the site based on a latitude of 33.1514 degrees and longitude of 117.3273 degrees, utilizing a program titled "Design Maps and Tools," provided by the USGS, which provides a solution for ASCE 7-10 (Section 1613 of the 2016 CBC) utilizing digitized files for the Spectral Acceleration maps. In addition, we have assigned a Site Classification of D. The response parameters for design are presented in the following table. The design spectrum acceleration vs. Period Tis attached. Smith Residential Lot Carlsbad, California TABLE I Job No. 18-11842 Page 4 Happed s_pectraf Acceleration Values and Design Parameters 1.127 1.049 1.568 1.182 0.788 5. The liquefaction of saturated sands during earthquakes can be a major cause of damage to buildings. Liquefaction is the process by which soils are transformed into a viscous fluid that will flow as a liquid when unconfined. It occurs primarily in loose, saturated sands and silts when they are sufficiently shaken by an earthquake. On this site, the risk of liquefaction of foundation materials due to seismic shaking is considered to be remote due to the relatively shallow, medium dense to dense nature of the formational material and the lack of a shallow static groundwater surface under the site. No soil liquefaction or soil strength loss is anticipated to occur due to a seismic event. 6. Any new concrete slabs on-grade (on properly compacted fill or dense formational soils) should be a minimum of 4 inches actual thickness and be reinforced with at least No. 3 steel bars on 18-inch centers, in both directions, placed at mid-height in the slab. The interior slab should be underlain by a 15-mil vapor barrier (15-mil StegoWrap) placed directly on properly compacted subgrade. The sand base may be waived. We recommend that isolation joints and sawcuts be incorporated to at least one-fourth the thickness of the slab in any slab designs. The joints and cuts, if properly placed, should reduce the potential for and help control floor slab cracking. In no case, however, should control joints be spaced farther than 20 feet apart, or the width of the slab. Control joints should be placed within Smith Residential Lot Carlsbad, California Job No. 18-11842 Page 5 12 hours after concrete placement as soon as concrete sets and no raveling of aggregate occurs. Slabs spanning any existing loose soils and supported by perimeter deepened foundations should be designed as structural slabs. 7. The active earth pressure (to be utilized in the design of cantilever, non- restrained walls) should be based on an Equivalent Fluid Weight of 38 pounds per cubic foot (for level backfill only) if on-site soils are used. Additional loads applied within the potential failure block should be added to the active soil earth pressure by multiplying the vertical surcharge load by a 0.31 lateral earth pressure coefficient. For unrestrained walls with sloping 2: 1 backfill and low expansive soil, we recommend an equivalent fluid pressure of 52 pcf. For restrained wall conditions with level backfill, we recommend an equivalent fluid weight of 56 pcf and 76 pcf when supporting 2: 1 sloping backfill. Surcharge loads may be converted to lateral pressures by multiplying by a factor of 0.47. Should seismic soil increment be required, the unrestrained walls with level backfill should be designed for an additional pressure of 14 pcf, in addition to the regular static loading, with zero pressure at the top and the maximum pressure at the bottom of the wall. 8. The passive earth pressure of the encountered formational soils and/or properly compacted fill to be used for design of shallow foundations and footings to resist the lateral forces, should be based on an Equivalent Fluid Weight of 275 pcf. This passive earth pressure is valid for design only if the ground adjacent to the foundation structure is essentially level for a distance of at least three times the total depth of the foundation and is properly compacted or dense natural soil. An allowable Coefficient of Friction of 0.40 Smith Residential Lot Carlsbad, California Job No. 18-11842 Page 6 times the dead load may be used between the bearing soils and concrete foundations, walls or floor slabs. 9. Adequate measures should be taken to properly finish-grade the site after the new structure and other improvements are in place. Drainage waters from this site and adjacent properties should be directed away from perimeter foundations, floor slabs, footings and slope tops, and onto the natural drainage direction for this area or into properly designed and approved drainage facilities. Proper subsurface and surface drainage will help minimize the potential for waters to seek the level of the bearing soils under the foundations, footings, and floor slabs. Failure to observe this recommendation could result in undermining, differential settlement of the building foundation or other improvements on the site, or moisture-related problems. It is not within the scope of our services to provide quality control oversight for surface or subsurface drainage construction or retaining wall sealing and base of wall drain construction. It is the responsibility of the contractor and/or their retained construction inspection service provider to provide proper surface and subsurface drainage. 10. Due to the possible build-up of groundwater (derived primarily from rainfall and irrigation), excess moisture is a common problem in below-grade structures or behind retaining walls that may be planned. These problems are generally in the form of water seepage through walls, mineral staining, mildew growth and high humidity. In order to minimize the potential for moisture-related problems to develop, proper cross ventilation and water- proofing must be provided for below-ground areas, In crawl spaces, and the Smith Residential Lot Carlsbad, California Job No. 18-11842 Page 7 backfill side of all structure retaining walls must be adequately waterproofed and drained. Proper subdrains and free-draining backwall material (such as gravel or geocomposite drains such as Miradrain 6000 or equivalent) should be installed behind all retaining walls on the subject project in addition to wall waterproofing. Geotechnical Exploration, Inc. will assume no liability for damage to structures that is attributable to poor drainage. 11. Planter areas and planter boxes should be sloped to drain away from the foundations, footings, and floor slabs. Planter boxes should be constructed with a closed bottom and a subsurface drain, installed in gravel, with the direction of subsurface and surface flow away from the foundations, footings, and floor slabs, to an adequate drainage facility. The finish grade around the addition should drain away from the perimeter walls to help reduce or prevent water accumulation. Exterior slabs or rigid improvements should also be built on properly compacted soils and be provided with concrete shrinkage reinforcement and adequately spaced joints. Geotechnical Exploration, Inc. recommends that we be asked to verify the actual soil conditions revealed in footing excavations prior to form and steel reinforcement placement. In addition, any new fills or loose soils should be properly compacted under the observations and testing of our firm. Smith Residential Lot Carlsbad, California Job No. 18-11842 Page 8 Should you have any questions regarding this matter, please contact our office. Reference to our Job No. 18-11842 will help to expedite a response to your inquiries. Respectfully submitted, eiser Senior Project Geologist Jaime A. Cerros, P.E. R.C.E. 34422/G.E. 2007 Senior Geotechnical Engineer at VICINITY MAP Thomas Bros Guide San Diego County pg l l06-G6 Smith Residence Va cant Lot South of 4240 Hillside Drive Carlsbad, CA. Figure No. I Job No. 18-11842 A N NO SCALE (approximate) REFEREN<:€: Thi, Pft:APNl wet~from-,e,dung W'ldlll9dTOPVIEWTOPOGR.l/'H'fdrawfngf,lffMdedbythe cliMIMdfram~ ffeld,w,co,vwlaancepw1omM,dt,yGEI. 14-118-42-p.a/ p r , ----,--7 ~HP.1 I I I HILLSIDE DRIVE 115' 105' 94' LEGEND ~ HP.3 Approximate l ocation of Exploratory Handpit Assumed Property Boundary NOTE:Thl1 PlotF'lanilootlOt:.UMab-legllll ~-Loc«tionNWldd.,_.iorlaeteapp-oxlmsi. . .A.ctualprop91tydl~1andlocdontolutlltlN maybaol:r.a!nec:lftommeApprowdBulld.,gPl-orttw·Aa-BtAll"GradlngPlana. PLOT PLAN Smith Residence Vacant Lot South of 4240 Hillside Drive Carlsbad, CA. Figure No. II Job No. 18-11842 ..-....e.i. Geotechnlcal &I Exploration, Inc. April 20J8 ; IS Cl ..J ~ 'EQUIPMENT DIMENSION & TYPE OF EXCAVATION Hand Tools 3' X 3' X 4' Handpit SURFACE ELEVATION GROUNDWATER/ SEEPAGE DEPTH ± 115' Mean Sea Level Not Encountered FIELD DESCRIPTION AND CLASSIFICATION --' w1-------------------~--1 g ~ DESCRIPTION AND REMARKS <n ::r: t w Cl ! ! (Grain size, Density, Moisture, Color) ~ -1 1 -M· -~ ;. - -... 2 -~--,. - 3 - - - - - 5 - - - - SILTY SAND , fine-to medium-grained, with roots and rock fragments. Loose to medium dense. Dry. Dark brown. FILL {Qaf) SIL TY SAND , fine-to medium-grained; moderately cemented. Medium dense to dense. Dry to damp. Light gray. OLD PARALIC DEPOSITS {Qop 24) Bottom@4' cj <n ::i SM SM DATE LOGGED 'I 3-26-18 LOGGED BY JKH -:,!! 0 ~'5' ~ ~'6' ~ c:i ~ ~ cf t w o.e, :::!!:~ 0 Cl. d~ wa:: ~~ :.-~q + _J (..) i=' ::, i=' ~?: Cl) UJ(f.) :z 0 :::'z --'W :::5 Cf.) :'.'5ci5 ~Cf.) -Cl) u5~ < Cf.) n.:,:: o..-o..z I--i~ zo ~ z o::i ::i:C..l ,O •w o..O ~~ 0 ....10 cJis ~::;. ~o 0::i: w (..) a,(..) a,,..__....__....._....._ __________________ _,__....__...._ _ ___. _ ___. __ _.__....__ _ __.. _ __.. _ _, w Cl a'. C) :x: !:: ::. "' ~ 9 2 0 ~ g Q. ~ \... ~ IZI [II ■ 0 ~ PERCHED WATER TABLE BULK BAG SAMPLE IN-PLACE SAMPLE MODIFIED CALIFORNIA SAMPLE NUCLEAR FIELD DENSITY TEST STANDARD PENETRATION TEST JOB NAME Smith Residence SITE LOCATION Vacant Lot -South of 4240 Hillside Dr., Carlsbad, CA JOB NUMBER REVIEWED BY LDR/JAC LOG No. 18-11842 flii:i-·-HP-1 FIGURE NUMBER ~•oration, Inc. Illa ffe-~ .. i t:; (!) ii' ~ ;r EQUIPMENT DIMENSION & TYPE OF EXCAVATION DATE LOGGED Hand Tools, Hand Auger 3' X 3' X 7' Handpitl Auger Hole 3-26-18 SURFACE ELEVATION GROUNDWATER/ SEEPAGE DEPTH ± 105' Mean Sea Level Not Encountered ~ Q) g _, w ::i::: 0 _, Ii: m a.. ::i: ~ w >-0 (./) (./) 1 2 3 4 5 6 7 8 FIELD DESCRIPTION AND CLASSIFICATION DESCRIPTION AND REMARKS (Grain size, Density, Moisture, Color) SILTY SAND . fine-to medium-grained, with some roots. Loose to medium dense. Damp. Red-brown. FILL (Qaf) -becomes dark red-brown with white sandstone fragments. Hand auger from 3'-7'. -24% passing #200 sieve. SILTY SAND, fine-to medium-grained; moderately cemented. Medium dense to dense. Damp. Light gray and red-brown. OLD PARALIC DEPOSITS (Qop 24) Bottom @7' uj <.i uj ::j SM SM LOGGED BY JKH ~ ii::= ~'[ ~ e__. oe e__. ci w ::;; ~ WO:: ~~ :::.-r::t:i U:::> :::iF :::, /:: :st-:s ci5 ::;;-_::;; ~ (./) _(./) ~o °t-5!! a..z ~ ~ i~ ~~ •w ~~ ~Cl 9.2 98.0 80 11.5 123.3 'I ~ C ci ~ 0-+_ d <n wen ~ ~ s: 'z -'W a.. ::i::: a.. 0 o:::i ~~ _,o ~ (.) mu <n= fil.___...,___,.__.__ __________________ ...,__,.___,.__ _ __._ _ __._ __ ...,__..._ _ __,_ _ __,_ _ _. (!) ii'. (!) :i: t: ~ ~ (!) g z 0 ~ 0 ;r ~ \.. .Y [gJ III ■ [II ~ PERCHED WATER TABLE BULK BAG SAMPLE IN-PLACE SAMPLE MODIFIED CALIFORNIA SAMPLE NUCLEAR FIELD DENSITY TEST STANDARD PENETRATION TEST JOB NAME Smith Residence SITE LOCATION Vacant Lot -South of 4240 Hillside Dr., Carlsbad, CA JOB NUMBER REVIEWED BY LDR/JAC LOG No. 18-11842. 4~,,---HP-2 FIGURE NUMBER Exploration, Inc. lllb ~ ~ § 6 Cl ...J Q. 1iS 'EQUIPMENT DIMENSION & TYPE OF EXCAVATION Hand Tools 3' X 3' X 3' Handpit SURFACE ELEVATION GROUNDWATER/ SEEPAGE DEPTH ± 94' Mean Sea Level Not Encountered ! :x: 1-fh 0 2 - - - 3 - - - - 4 - - - 5 - - - FIELD DESCRIPTION AND CLASSIFICATION DESCRIPTION AND REMARKS (Grain size, Density, Moisture, Color) SILTY SAND, fine-to medium-grained, with some roots. Loose to medium dense. Damp. Dark brown. FILL (Qaf) SIL TY SAND , fine-to medium-grained; moderately well cemented. Dense. Damp. Red-brown. OLD PARAUC DEPOSITS (Qop 2-4) Bottom@ 3' cr.i c.j cr.i :;j SM SM DATE LOGGED -.... 3-26-18 LOGGED BY JKH ~ 0 ~ ~'u ~ ~'ff ~ ~ ,..: ci w 0 .e, ::d~ 0 c.. c:i o_ :::;;-t ~ WCX: ~~ ~f ~q _J wen (.)~ => ~ ·o I--'W ::s ci5 -:a: ~ (/) :!;:Z ::Stn ~Cf.> -en ~15 "-I c,.5 o..z ~~ i~ 0.. z o=> ~~ •w ~c ~8 _,o ~:a; ~o me.> w= fil...._ _ _._ _ _,__.,__ __________________ _._ _ _.__ _ _.__ _ ___._ _ ___._ ______ ..._ _ __._ _ __._ _ _, CJ ii'. Cl :I: t: :le VJ ~ ~ CJ g z 0 ~ g ~ ..... y [8J [II ■ 0 ~ PERCHED WATER TABLE BULK BAG SAMPLE IN-PLACE SAMPLE MODIFIED CALIFORNIA SAMPLE NUCLEAR FIELD DENSITY TEST STANDARD PENETRATION TEST JOB NAME Smith Residence SITE LOCATION Vacant Lot -South of 4240 Hillside Dr., Carlsbad, CA JOB NUMBER REVIEWED BY LDR/JAC LOG No. 18-11842 ;1--~ HP-3 FIGURE NUMBER Expforatlon, Inc. Ille ~ ., "' ~ .., b (!) ~ r EQUIPMENT DIMENSION & lYPE OF EXCAVATION Hand Tools 3' X3' X4' Handpit SURFACE ELEVATION GROUNDWATER/ SEEPAGE DEPTH ± 105' Mean Sea Level Not Encountered 'iii' ~ I l-a. w 0 - - 4- - 5 - - - FIELD DESCRIPTION AND CLASSIFICATION -' w g ~ DESCRIPTION AND REMARKS ~ ~ ( Grain size, Density, Moisture, Color) SIL TY SAND , fine-to medium-grained, with some roots and rock fragments. Loose to medium dense. Damp. Dark brown. FILL (Qaf) -becomes red-brown. en u en :::;j SM SIL TY SAND , fine-to medium-grained; SM moderately well cemented. Medium dense to dense. Damp. Red-brown. OLD PARAUC DEPOSITS (Qop 2..J Bottom@4' DATE LOGGED " 3-26-18 LOGGED BY JKH ~ ~'[ ~= C C 0 g_ c:i ~ ci w 0~ ~~ :!:~ + ' 0-WO: ~~ :::,~ ~q __j WCI) (.) i=? ~U) :::, i= :lo--:::. ~ 0 ;::Si: -'W ~!!l :11i Cl) _Cl) Cl)-Cl) a. I a.Z ~o i~ zo z o=> ;:!;:(.) •O •w ~~ X 0 -'o <CZ ~:lo ~o o::. w u a:io en= o,...__...,__..__,__ __________________ ...,__..___.....__ ....... _ ....... __ ...__.,__ _ __.._ _ __.._ _ _,, w (!) ii'. (!) E i3) i \... y_ [8J II] ■ 0 ~ PERCHED WATER TABLE BULK BAG SAMPLE IN-PLACE SAMPLE MODIFIED CALIFORNIA SAMPLE NUCLEAR FIELD DENSITY TEST STANDARD PENETRATION TEST JOB NAME Smith Residence SITE LOCATION Vacant Lot -South of 4240 Hillside Dr., Car1sbad, CA JOB NUMBER REVIEWED BY LDR/JAC LOG No. 18-11842 ;,,•·*-HP-4 FIGURE NUMBER Exploration, Inc. llld -§ ~ "' j ti t!) i ... w t!) n' t!) ~ :i! rn j 0 oc t!) " ~ w + z 0 i= ~ 8 'u 0. ~- ci5 z w 0 >-a:: 0 135 130 125 120 115 110 105 100 95 90 85 80 75 0 5 41i-4ji ~ i \ ' \ ' \ \ ' \ \ \ \ \ \ \ ' \ \ \ \ \ Source of Material HP-2@3.0' ~~ I\ I/ \ Description of Material SILTY SAND {SM}1 Red-brown ~ I 1 \ ' , I\ \ Test Method ASTM D1557 Method A • \ I\ \ I\ \ \ \ ~ \ \ \ TEST RESULTS \ 1 \ \ Maximum Dry Density 123.2 PCF ' '\ ' -- \ I\ Optimum Water Content -----11.&. % \ \ \ \ \ \ ~ Expansion Index (El) -- " \ \ \ I\ ' \ \ \ ~ ' \ ' \ \ I\ \ \ '-Curves of 100% Saturation \ ' for Specific Gravity Equal to: \ I\ I\. \ \ 2.80 ' I\ ' \ II. \. 2.70 I\ ' \. II. \. '\ 2.60 ' '\ \. II\. I\. I\. \ II. ' I\. ' \. '\ '\ ,, \. ' \. ' \. " \ I\. I"-'\ , .... '\ I'°'\ .... l's. ' .... II. ' ' II. '-'\,. .... II. ' "-'I \.. "' l'-..1 10 15 20 25 30 35 40 45 WATER CONTENT, % Geotechnlcal MOISTURE-DENSITY RELATIONSHIP Exploratlon, Inc. Figure Number: IV Job Name: Smith Residence Site Location: Vacant Lot -South of 4240 Hillside Dr., Ca Is ba< Job Number: 18-11842 EUSGS Design Maps Summary Report User-Specified Input Report Title South of 4240 Hillside Drive, Carlsbad, CA Thu April 5, 2018 18:25:46 UTC Building Code Reference Document ASCE 7-10 Standard (which utilizes USGS hazard data available in 2008) Site Coordinates 33.1514°N, 117.3273°W Site Soil Classification Site Class D -"Stiff Soil" Risk Category I/II/III USGS-Provided Output S5 = 1.127 g S1 = 0.432 g SMS = 1.182 g SM1 = 0.678 g Sos= 0.788 g S01 = 0.452 g For information on how the SS and 51 values above have been calculated from probabilistic (risk-targeted) and deterministic ground motions in the direction of maximum horizontal response, please return to the application and select the "2009 NEHRP" building code reference document. l\.lCEa Response Sped rum Paiod., T {$ft) o,_..a C•.Y.• ,9 VAH ~ 1_1,.l,1 For PGAM, TL, CRs• and CR1 values, please view the detailed re12ort. Des.lgn Response Spectrum (t[I) 0.3.J ('"'J (lh I 1.•lf• ) 1)_1 I.:> I I ..VJ 11.I.• l Bi :!J.,.1 Although this information is a product of the U.S. Geological Survey, we provide no warranty, expressed or implied, as to the accuracy of the data contained therein. This tool is not a substitute for technical subject-matter knowledge.