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Home My WebLink About; Meadowlark Reclamation Facility; Soils Report; 1981-03-24. Soil Mechanics l 6eology l FoyRdation Engineering 9295 Chesopeake Dr., Suite E . Son Diego. California 92123 . (714) 56&7827 - GEOLOGIC h SOILS ENGINEERING INVESTIGATION PROPOSED IMPROVEMENTS SAN MARCOS COUNTY WATER DISTRICT MEADOWLARK RECLAMATION FACILITY - CITY OF CARLSBAD, CALIFORNIA FOR - CM ENGINEERING ASSOICATES W.O. 196-SD - MARCH 24, 1981 l ..~ . - - ENGINEERING DEPT. LIBRARY City of Carlsbad 2075 Las Palmas Drive Carlsbad CA92009-4859 Los An#eh office: c?1317aw158 . Omnge county OJpx I7l4J 547-%Jos - c,M Engineering Associates . W.O. 196-SD March 1981 : ’ - ’ - - - - - - I - - - - - - _ .e.- TABLE OF CONTENTS INTRODUCTION ................................................ 1 SITE CONDITIONS......................................; ...... 2 PROPOSED IMPROVBMENTS ....................................... 4 SITE INVESTIGATION .......................................... 4 GEOTECHNICAL CONDITIONS ..................................... 6 EARTH MATERIALS .......................................... 6 BEDROCK ............................................... 6 ALLWIUM .......................... . ................... 7 FILL .................................................. 7 GROUNDWATER ........................................... 7 CONCLUSIONS ................................................. 8 GENERAL .................................................. 8 BEDROCK EXCAVATION ....................................... 8 GROUNDWATER .............................................. 9 SLOPE DESIGN .............................................. 9 FLOOD'CONTROL ..................... ..; .................... 9 SEDIMENTATION TANK CONSTRUCTION .......................... 10 NEW BUILDING CONSTRUCTION ................................ 11 RECOMMENDATIONS ............................................. 12 HARD ROCK GRADING........................................1 2 FLOOD CONTROL-WALL CONSTRUCTION .......................... 12 BERM ..................................................... 13 BUILDING AND TANK CONSTRUCTION ........................... 13 GroSofIr, Inc. - *;M Engineering L * ., ' W.O. 196-SD March 1981 _ TABLE OF CONTENTS (CONTINUED) d-c GRADING ................................................. 14 INSPECTIONS ............................................. 14 - INVESTIGATION LIMITATIONS .................................. 15 - ENCLOSURES Exploration Map - Geologic Cross Sections A-A' & Test Pit Logs B-B' f - - - - GcoSoilr, Inc. - - - - - - - . - .- -- -. -. - Soil Mechanics l Geology l Foundation Engineering _- 9295 Chesapeake Dr., Suite E . San Diego. California 92123 l (714) 5607827 : March 24, 1981 W.O. 196-SD CM Engineering Associates 550 West Vista Way Melrose Center Vista, California 92083 Attention: Mr. Vincent DePalma Subject: Geologic h Soils Engineering Investigation Proposed Improvements San Marcos County Water District Meadowlark Reclamation Facility City of Carlsbad, California. Gentlemen.& GeoSoils, Incorporated has recently completed a geologic and soils engineering investigation of the subject property. The purpose of. this.invest-iqation was to evaluate site qeotechnical conditions relative to proposed improvements of the existing Meadowlark Reclamation Facility. We understand that the proposed enlargement of the facility will include the development of level pad areas for future building sites and the construction of a retaining wall (or earth and rock berm) adjacent to the San Marcos Canyon for the purpose of flood control. h Angeles ofiiw: (21317e3-31sB . Onlnp GwmY office: VI41 547-8703 - ., CM Engineering Associates * '. - Page 2 W.O. 196-SD March 24, 1981 - _ -. Our investigation is intended to evaluate geologic and soils engineering condit.ons of the property and their effect on the .- - proposed construction. Existing facilities and planned improvements are shown on the Exploration Map attached as Plate 1. The map is based on a. 50 scale topographic base map prepared by Rick Engineering Company. - SITE CONDITIONS The existing treatment facility is situated at the head of San Marcos Canyon west of Ranch0 Santa Fe Road in Carlsbad. San Marcos Creek - transmits water along the southern property boundary. , - The existing facility is located on a qentle south facing slope just north of San Marcos Creek. Previous cut and fill grading operations - have ,created two pad areas within the facility. Natural slopes , ascend onto off-site properties at variable gradients which generally approach 2:-l (horizontal to vertical) gradients at their steepest. .- - Locally steeper conditions occur beiow isolated outcrops of hard, resistant rocks. Drainage across the site is controlled by natural terrain and run-off is concentrated in several well developed drainage swales and ravines -which flow into San Marcos Creek. A tijor con- - tributary ravine to San Marcos Creek is located along the western - boundary of the existing facility. At the time of this investigation, only stream flow within San Marcos Creek was apparent. - GsoSoilr, Inc. ,~.. .~.~ - ,.. _. . -. - .- - - -. .- - .- 4 SITE LOCATION MAP GeoSofts, Inc. W.O. NO. 196-SD my BEE I Soil Mechanics l Geology l foundation Engineering - kX Engineering Associates .~ -. . Page 3 W.O. 196-SD March 24, 19bi - . - - Vegetation on hillside terrain within the site consists of a moderate to heavy growth of chapparal type brushes and native - grasses. - Existing tank facility sites in the northern portion were developed by previous cut and fill grading. on-site materials were apparently utilised in these fills. Remaining facilities were constructed largely either at or near natural grades. -’ - - - - GcoSoIIs, Inc. . \ - . - _-- - - - - - - 'CM Engineering Associates Page 4 W.O. 196-SD March 24, 1981 _ - PROPOSED IMPROVEMENTS We understand that an increase in the capacity of the existing treatment facility is planned. The construction of underground process tanks and small support buildings is proposed. The tanks. are concrete box'structures which will be placed up to 10 feet below the adjacent pad surface. Minor grading of the north areas will create the appropriate building sites. A 54-inch storm drain facility will transmit concentrated run-off to the San Marcos Canyon. Areas adjacent to the creek will be protected by either a continuous flood control wall or an earth and rock berm constructed along the southern property boundary. SITE INVESTIGATION The field conditions were determined by the excavation of 9 exploratory test pits at selected locations as shown on Plate 1. The pits were excavated utilising a track mounted crawler backhoe which enabled excavations within the upper hillside areas at the west and north where cut slopes are proposed. The test pits were logged by our field geologist and representative samples of the subsurface materials were retained for laboratory testing. Logs of the test pits and appropriate laboratory test data are enclosed. --. ~~~~-. . ..--.-... - -.-----.- - - ~ .iM Engineering Associates Page 5 - . W.O. 196-SD March 24, 1981 - Our investigation included a review of two geotechnical studies previously prepared by other consultants on the property. These - included (1) a soils investigation including boring information - completed by Benton Engineering, Incorporated (dated September 28, 1979) and (2) a rock excavation study utilising seismic refraction - data prepared by T. Punnekotter (dated August 6, 1979). Conclusions and recommendations given herein reflect applicable data presented in the previous studies. -’ - - GeoSoils, Inc. - *CM Engineering Associates .I . Page 6 W.O. 196-SD March 24, 1981 - - . - ~--* GEOTECHNICAL CONDITIONS - The subject property is situated at the eastern foot Off-the rugged, - mountainous terrain of San Marcos Canyon. The area is under- lain by hard, crystalline rocks of the Southern California Batholith. - Exposures occur oh the property in the hillside terrain to the - north of the existing facility. Surficial soils derived from bedrock erosion and artifically placed fill-are present in the lower reaches - of the site. - Earth Materials - The following earth materials are recognised on the property and , - will be encountered during site grading: - Bedrock - Hillside areas of the property are underlain by a - - variable series of granitic rocks. These consist chiefly of light colored, fine grained crystalline rock which is widely exposed in this area of San Marcos Canyon, and characterise rocks of the Southern.California Batholith. - - - Bedrock exposed in the ascending hillside in the western portion is moderately weathered and affected by joint and shear surfaces. Hard rock exposures are noted in surface outcrops. Bedrock beneath the gentle ascending slope north and-east of the existing tank structures is deeply weathered and in - contrast, will excavate much easier. GeoSoiIs, he. ,.~ ~~~ .-- -~~-~~ - 'CM Engineering Associates Page 7 * W.O. 196-SD March 24, 1981 - _- - - - - - 1 - - - - - - Bedrock on the property is mantled by a cover of natural topsoil and weathered bedrock. Depth of the surface soils vary from zero to a maximum indicated depth of 2.5 feet (test pit numbers 1, 2 and 9). The natural soils consists chiefly of silty sand in reflection of the underlying rock. types. Alluvium - Natural alluvial soils are present within San Marcos Creek and the larger drainage ravines on the property. Borehole data also indicates that alluvium is present beneath the fill on the south side of existing treatment facility. Alluvium present is predominately coarse grained, and consists of admixtures of ._- gravel to boulder sized materials with a clay silt-sand matrix. Fill - Fill is present within the existing treatment facility. The approximate limits have been identified by site reconnaissance mapping and are indicated on the Field Exploration Map, Plate i. The fill consists chiefly of silt, sand and gravel, and was derived . _ from the excavation of site materials. No information.was available regarding the manner of placement and compaction of these materials. Groundwater Surface water seeps were not encountered during our field study. Subsurface waters were not indicated in any of the borings or test pit excavations on the property. However, groundwatermay be expected during construction of the proposed flood control wall and may affect deeper excavations during tank facility construction. GeoSoiIs, Znc. - CM Engineering Associates ., . Page 8 W.O. 196-SD March 24, 1981 - *.- CONCLUSIONS - GENERAL Based on our investigation and knowledge of the site conditions, - the proposed construction and regrading is feasible from a geotechnical viewpoint. - - No evidence of existing or impending slope instability was discovered. On-site bedrock,materials are hard and will adequately support the proposed improvements. BEDROCK EXCAVATION - \ Cut slopes are planned along the western margin to create additional building pad areas. Bedrock materials in these areas are very hard - and will require blasting in order to achieve finished grade levels. . The degree of blasting will be dictated by bedrock conditions including _- : the abundance of natural joint and fracture surfaces. Heavy ripping utilising conventional equipment (D-9 or equivalent machinery) will - likely excavate uppermostweathered exposures to an estimated depth of 5 feet below the existing surface. Blasting for portions of the proposed storm drain structure may also be anticipated. - Excavation of bedrock in the north-central area will encounter weathered rock units which will likely excavate to the proposed grade with heavy ripping. The need for blasting in this area is‘not anticipated. - - GeoSoils, Inc. - CM Engineering Associates - Page 9 W.O. 196-SD March 24, 1981 - _ - GRODNDWATER Groundwater is believed to be locally present with fractures and - joint surfaces of the granitic rock. Dewatering of relatively deep tank excavations into natural materials may be necessary. In the event the-retaining wall (flood control devise) is constructed, groundwater will be encountered during removal operations of alluvium soils for the wall foundation. Dewatering of the affected area may include diversion of the present creek. - SLOPE DESIGN Graded cut slopes in natural bedrock materials should be programmed for gradients of 1 l/2 to 1, horizontal to vertical. , Fill slopes constructed of approved on-site materials should be - planned and constructed at 2 to 1 (horizontal to vertical) gradients. FLOOD CONTROL - Protection from flooding of San Marcos Creek may be provided by either an appropriately designed wall or an earth and rock berm: or - possibly a~ combination of both utilising a short wall atop a moderately sized berm. The necessary height of the flood control device is - reportedly about 6 feet. - .._ - - GeoSoiZs, Inc. - CM Engineering Associates ', Page 10 W.O. 196-SD March 24, 1981 - The flood control wall along the southern property boundary could - best be constructed within compacted fill utilising conventional - wall footings. Local groundwater seeps and boulders should be anticipated during removal operations in the course of providing - a firm foundation.for the construction of a compacted fill. Rip- rap rock generated from blasting operations may be used along the - creek side of the wall to mitigate potential erosion. The construction of a berm for flood control would require keying into the existing fill to provide a strong, stable base for the berm. - Depending upon the material selected or available, the side slopes - could vary from as cteep as 1:l for coarse rock fragments, to as flat as 2:l (horizontal to vertical) for fine grained soils. The 8 - width at the top should not be less than about 5 feet to permit compaction using small equipment. Erosion resistant treatment or - protection should be provided on the basis of anticipated, stream flow - : velocities and suspended load. ._. . _PROCESS TANK CONSTRUCTION - New tank facilities are expected to be constructed largely into fill and weathered bedrock materials in the central areas. These will - excavate with possibly heavy ripping and present no unusual foundation problems. - - GeoSofls, Inc. - - - - - - - - - , - - - CM Engineering Associates Page 11 W.O. 196-SD March 24, 1981 . - Tank construction along the southern property line will encounter minor amounts of fill and alluvial soils. These areas should first be regraded as recommended in a following section to provide suitable foundatian conditions. NEW BUILDING CONS;rRUCTION New buildings constructed within~gradqd bedrock pads (north portion) will encounter no foundation problems and may be supported by conventional foundations as recommended below. Buildings constructed atop existing fill and alluvial soils should be provided adequate foundation support by regrading underlying soils as recommended in the following section., GeoSoils, Inc. - C?4 Engineering Associates :. - - - - - , - - - - - - - Page 12 W.C. 196-SD March 24, 1981 Hard Rock Grading -'On site, excavated materials may be used in compacted fills. Blasting and ripping operations should be conducted to generate well graded soil and rock debris with sizes less than 30 inches in diamter. Blasting operations in proximity to programmed cut slopes shoiibd be conducted with care. Over-blasting near cut slopes may create instability in the completed slope which will be costly to mitigate. Flood Control-Wall Construction - Adequate foundation suooort for a flood control wall can best be achieved by removing existing soils beneath the planned wall to expose firm underlying materials approved by the project soils engineer or his field representative. The removal should maintain a maximum width of 10 feet along the centerline of the wall footing. Water intrusion into the . . . removal excavation can be mitigated by utilizing rock derived from blasting operations to provide working surfaces upon which ,properly compacted fill can be constructed. Larger rock debris derived from blasting operations should be placed along the creek side of the wall embankment as rip-rap. - CM Engineering Associates Page 13 W.O. 196-SD March 24, 1981 . BERM ,' -. - The design of the berm, as described previously, will depend upon the selected alignment and the materials used. For these reasons, it is suggested that additional recommendations be provided when - the above noted factors are known. - - * - - BUILDING AND TANK CONSTRUCTION - Building and additional tank improvements located on exposed bedrock materials (north areas), may be constructed utilising conventional footings. These should maintain a minimum depth of 12 inches into natural materials for ordinary one-story loads and should be at least 12 inches wide. New construction located within existing fill and natural soil areas should be provided foundation support by removing existing soils beneath these areas to a depth of 5 feet and rebuilding to grade with properly compacted fill as approved by the soils engineer : or his representative. Conventional foundations which maintain a . - minimum footing depth of 12 inches below the lowest adjacent grade and 12 inches wide may be used in compacted fill for ordinary one- tory loads. Allowable bearing capacities on undisturbed bedrock of 3000 psf and 15OO~,psf. for compacted fills should be used in footing design. GsoSoJls, Inc. -,- 'CM Engineering Associates I - Page 14 W.O. 196-SD March 24, 1981 - GRADIS& - Proposed-fili areas should be provided adequate support by either excavating existing soils to expose bedrock or excavating - existing soils (including existing fill material) to a depth of five feet below the planned finished grade , whichever occurs first. The resulting excavations should be backfilled with properly compacted - fill. -_ - Compacted fill should be placed in thin horizontal lifts (maximum six inches thick), at near optimum moisture conditions and mechanically compacted to a minimum of 90 percent of the laboratory maximum density utilising ASTM Test Method D-1557-70. - Building pad areas created by cutting and filling and thus resulting in a cut-fill transition intersecting a planned facility.are susceptable \ to differential settlement. - To lessen the potential for differential movement, the cut portions beneath the affected pads should be under- - - - - - - cut by three feet and filled to provide a nearly uniform supporting , thickness of fill'material. INSPECTIONS - Removal and compacted fill operations should be inspected and approved by the project soils engineer or his field representative. Graded cut slopes should be inspected and approved by‘a qualified engineering geologist. .- - (*$M Engineering Associates - Page 15 W.O. 196-SD March 24, 1981 - . - INVESTIGATION LIMITATIONS The materials encountered on the project site and utilized in our - laboratory investigation are believed representative of the total area: however, soil and bedrock materials vary in characteristics - between excavations and natural outcrops. - since our investigation is ba~sed on the site materials observed, - selective laboratory testing and engineering analyses, the conclusions and recommendations are professional opinions. These opinions have - been derived in accordance with current standards of practice and no warranty is expressed or implied. - The opportunity to be of service is sincerely appreciated, and if you . should have any questions pertaining to this report please feel welcome to call. - Respectfully submitted, GeoSoils, Incorporated Dennis Middleton, CEG 980 Roy E. Moore, RCE 28119 Engineering Geologist Principal Engineer - RRM/DM/em GeoSolls, Inc. *GM Engineering Associates . . . - - TEST PIT LOGS - W.O. 196-SD March 1981 GeoSolls, Znc. 4 Engineering I - - - - - - - - - \ - - - - - 2. 6-f W-0. 196-SD March 1981 TGPSOIL: Silty sand: dark -brown; low plastic fines; iediur grained sand, mcderately graded; occasional fine to coarse gravel; damp. SIZDROCX: Granitic rock: fine grained; light greenish brown; intensely w-athered at upper surface to a very dense silty sand, at 4.0 feet moderately weathered; moderately fractured, fracture spacing 3-4 inches: very hard. _. 'TP-2 TOPSOIL: Silty sand; dark . . DFDRDCX: Granrtic rock; fine grained; light greenish brown: moderatsly weathered: mctieratley fractured, fracture spacing at 3-4 inches: very h.ard: SEDI!OCK: Granitic rock: fine -Fain ed. lioht ureenish brown: deeply Hnd intensely weathered to silty sand ir uppr 1.5 feet; mxlerately fr.actured below 2.5 / /AfCcI . 6 FE67 feet: very hard. - - CM Engineering : . . _ - W.O. 196-SD March 1981 - - I - - - - - - TEST PIT LOGS _ - TP-7 FILL: Silty sand; light gray brown; slightly to low plastic fines; medium grained sand: well no gravel: damp to moist. Drain tile near the base of unit. ..' ', . . . . . TOPSOIL: Clayey sand; yellow brown; medium plastic fines; medium grained sand; moderatley \ / ,/ graded; moist. BEDROCK: Granitic rock; fine grained; grennish brown; deeply weathered near upper surface to a very dense silty sand and silty gravel; friable with difficulty; moderatley fractured 7.D. 12.0' at 8.0 feet; varibale hardness, moderately hard to very hard. TOPSOIL: Silty~ sand; moderate 0.5’ yellow brown: lw plastic fines: medium grained sand, moderately in immediate area. ., . TP-9 BEDROCK: Granitic rock: medium g-; light greenish 'brown; moderately weathered; moderately fractured, fracture spacing 3-4 inches; very hard. TOPSOIL: Silty sand; dark yellow brown; low plastic fines; medium grained sand, moderately graded: little to no gravel: damp. Grades more clayey with depth. BEDROCK: Granitic rock: medium grained; greenish brown; deeply weathered near upper surface to a very dense silty sand and silty gravel; friable with difficulty; moderately fractured at 5.0 feet, fracture spacing 2-3 inches: very hard. - z D. q. 0 ’ sc*IL: I /#GC/ - J FEdrT