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HomeMy WebLinkAboutCT 14-05; MAGNOLIA TOWNHOMES; PRELIMINARY GEOTECHNICAL ENGINEERING INVESTIGATION; DWG 490-4A, PUD 14-08, CDP 14-27; 2014-09-10~,J; .. S T RAT A - T E C H , I N C . c..;#lf? 13EOCONSULTANTS 7372 Walnut Avenue, Unit F,Buena Park, California 90620 September 10, 2014 (Revised January 15, 2016) DS Products, Inc. Tony Sfreddo 24 Amber Leaf Irvine, California, 92614 RECEIVED JAN 2 8 2016 LAND DEVELOPMENT ENGINEERING 714-521-5611 562-427-8099 FAX 714-521-2552 w.o. 273114 Subject: Preliminary Geotechnical Engineering Investigation, Proposed Multi Family Residential Development, 749-763 Magnolia Drive, Carlsbad, California. Gentlemen: Pursuant to your request and authorization, Strata-Tech, Inc., has prepared this geotechnical investigation at the subject site. The purposes of the investigation were to determine the general engineering characteristics of the soils on and underlying the site and to provide recommendations for the design of foundations, pavements and underground improvements. PROPOSED DEVELOPMENT It is our understanding that the proposed development will consist of approximately 12 attached town homes of wood-frame-stucco construction with parking and landscaping. PURPOSE AND SCOPE OF SERVICES The scope of the study was to obtain subsurface information within the project site area and to provide recommendations pertaining to the proposed development and included the following: 1. A cursory reconnaissance of the site and surrounding areas. 2. Excavation of exploratory geotechnical test borings to determine the subsurface soil and groundwater conditions. 3. Collection of representative bulk and/or undisturbed soil samples for laboratory analysis. -I STRATA-TECH,INC. GEOCONSULTANTS DS Products, Inc. Geotechnical Engineering Investigation 2 W. 0. 273114 January 15, 2016 4. Laboratory analyses of soil samples including determination of in-situ and maximum density, in-situ and optimum moisture content, shear strength and consolidation characteristics, expansion potential and liquefaction analysis. 5. Preparation of this report presenting results of our investigation and recommendations for the proposed development. SITE CONDITIONS The subject site is a rectangular lot on the south side of Magnolia Drive, app. 90-feet south-west of intersection with Jefferson Street, Carlsbad, California. The property is developed with single story residential structures, landscaping and appurtences. The site location is shown on the attached vicinity Map, Plate No. 1. Site configuration is further illustrated on the Site Plan, Plate 2. FIELD INVESTIGATION The field investigation was performed on September8, 2014, consisting of two hand auger borings. The locations are shown on the attached Site Plan, Plate 2. As the excavation progressed, personnel from this office visually classified the soils encountered, and secured representative samples for laboratory testing. Description of the soils encountered is presented on the attached Record of Subsurface Exploration Logs. The data presented on these logs is a simplification of actual subsurface conditions encountered and applies only at the specific boring location and the date excavated. It is not warranted to be representative of subsurface conditioris at other locations and times. EARTH MATERIALS Earth materials encountered within the exploratory test borings were visually logged by a representative from STRATA-TECH, Inc. The materials were classified as artificial fill and native soils. Native soils consisted of a silty residual sandy soil to a maximum depth explored of 12 feet in test pit 2. Groundwater was not encountered in any of our subsurface exploration. STRATA-TECH,INC. GECCCNSULTANTS DS Products, Inc. Geotechnical Engineering Investigation SEISMICITY 3 w. 0. 273114 January 15, 2016 Southern California is located in an active seismic region. Moderate to strong earthquakes can occur on numerous faults. The United States Geological Survey, California Division of Mines and Geology, private consultants, and universities have been studying earthquakes in Southern California for several decades. The purpose of the code seismic design parameters is to prevent collapse during strong ground shaking. Cosmetic damage should be expected. The principal seismic hazard to the subject property and proposed project is strong ground shaking from earthquakes produced by local faults. Secondary effects such as surface rupture, lurching, or flooding are not considered probable. 2013 I.B.C. SEISMIC DESIGN VALUES Site Coordinates 33.15414°N, 117.34029°W Site Soil Classification Site Class D -"Stiff Soil" Risk Category I/II/III Ss = 1.146 g St= 0.440 g SMs = 1.194 g SMt = 0.686 g CONCLUSIONS AND RECOMMENDATIONS Sos= 0.796 g Sot= 0.457 g Development of the site as proposed is considered feasible from a soils engineering standpoint, provided that the recommendations stated herein are incorporated in the design and are implemented in the field. Recommendations are subject to change based on review of final foundation and grading plans. It is recommended that the proposed structures be entirely supported by compacted fill. A minimum 2-foot thick compacted fill blanket below the bottom of the footings is recommended: The over excavation requirement is 2 foot below footings, or 4 feet deep for 2 foot footings. The upper 3-feet are loose unsuitable for structural support. For other minor structures such as property line walls or retaining walls less than 4 feet high, competent native soils or compacted fill may be used for structural support. PROPOSED GRADING Grading plans were not available at the time our work was performed. It is assumed that proposed grades will not differ significantly from existing grades. The following recommendations are subject to change based on review of final grading plans. STRATA-TECH,INC. GECCCNSULTANTS DS Products, Inc. Geotechnical Engineering Investigation GRADING RECOMMENDATIONS 4 w. 0. 273114 January 15, 2016 Removal and recompaction of existing fill and loose native soils will be required to provide adequate support for foundations and slabs on grade. The depth of removal shall be 2 foot below the bottom of the footings, which is estimated to be at least 4 feet below existing grade. The over excavation requirement is 2 foot below footings, or 4 feet deep for 2 foot footings. Earthwork for foundation support shall include the entire building pad and shall extend a minimum of 5 feet outside exterior footing lines where feasible or to property line. Care shall be exercised not to undermine hardscape, walls, or pavements that are located on adjacent properties. If removals extend to off site structures or concrete block perimeter walls that are located within 4-feet from the bottom excavation, then slot cutting or shoring will be required. The exposed excavation bottom shall be observed and approved by STRATA-TECH, Inc. and the City's grading inspector prior to processing. Dependent on field observations, removals may be adjusted up or down. Subsequent to approval of the excavation bottom, the area shall be scarified 6 inches, moisture conditioned as needed, and compacted to a minimum of 90 percent relative compaction. Fill soils shall be placed in 6 to 8 inch loose lifts, moisture conditioned as needed, and compacted to a minimum of 90 percent relative compaction. This process shall be utilized to finish grade. Grading for hardscape areas shall consist of removal and recompaction of soft surficial soils. Removal depths are estimated at 3 feet. Earthwork shall be performed in accordance with previously specified methods. Grading and/or foundation plans shall be reviewed by the soil engineer. All recommendations are subject to modification upon review of such plans. FOUNDATIONS ON COMPACTED FILL The proposed building may be supported by continuous spread and isolated footings placed a minimum depth of 24 inches below lowest adjacent grade utilizing an allowable bearing value of 2,000 pounds per square foot. This value is for dead plus live load and may be increased 1/3 for total including seismic and wind loads where allowed by code. STRATA-TECH,INC. GECCCNSULTANTS DS Products, Inc. Geotechnical Engineering Investigation Minimum Minimum Type Depth Width (inches) (inches) Continuous 24 12 Interior Pad 18 24 5 Bearing Value (psf) 2000 2000 Increase Width Depth (psf/ft) (psf/ft) 180 440 180 440 w. 0. 273114 January 15, 2016 Maximum (psf) 3500 3500 It is recommended that all footings be reinforced with a minimum of two no. 4 bars (1 top and 1 bottom). The structural engineer's reinforcing requirements should be followed if more stringent. Footing excavations shall be observed by a representative of STRATA-TECH, Inc. prior to placement of steel or concrete to verify competent soil conditions. If unacceptable soil conditions are exposed mitigation will be recommended. FOUNDATIONS ON COMPETENT NATIVE SOILS-for Minor Structures Minor structures may be supported by continuous spread footings placed a minimum depth of 24 inches below lowest adjacent grade. An allowable bearing value of 1,500 pounds per square foot may be used in design. This value is for dead plus live load and may be increased 1/3 for total including ~eismic and wind loads where allowed by code. All footing excavations shall be observed by a representative of STRATA-TECH, Inc. prior to placement of steel or concrete to verify competent soil conditions. If unacceptable soil conditions are exposed, mitigation will be recommended. LATERAL DESIGN Lateral restraint at the base of footings and on slabs may be assumed to be the product of the dead load and a coefficient of friction of .30. Passive pressure on the face of footings may also be used to resist lateral forces. A passive pressure of zero at the surface of finished grade, increasing at the rate of 300 pounds per square foot of depth to a maximum value of 2,500 pounds per square foot, may be used for compacted fill or native soils at this site. When passive pressure and :friction are combined for evaluating the lateral resistance, the value of the passive pressure should be limited to 2/3 of the values given above. STRATA-TECH,INC. GECCCNSULTANTS DS Products, Inc. Geotechnical Engineering Investigation RETAINING WALLS 6 w. 0. 273114 January 15, 2016 ~ Unrestrained walls up { 5-feet n height retaining drained earth may be designed for the following: Surface Slope of Retained Material Equivalent Fluid Pressure Pounds Horizontal to Vertical Per Cubic Foot Level 30 5 to 1 32 4 to 1 35 3 to 1 38 2 to 1 43 These values include seismic loading. Backfill should consist of clean sand and gravel. While all backfills should be compacted to the required degree, extra care should be taken working close to walls to prevent excessive pressure. Retaining walls should include subdrains consisting of 4-inch, SCH 40 or SDR 35 perforated pipe surrounded by 1 cubic foot per lineal foot of crushed rock. All wall backfill should be compacted to a minimum of 90 percent relative compaction. All retaining structures should include appropriate allowances for anticipated surcharge loading, where applicable. In this regard, a uniformly distributed horizontal load equal to one-half the vertical surcharge shall be applied when the surcharge is within a horizontal distance equal to the wall heigh{. Retaining wall footing excavations shall be founded entirely in competent native soils or compacted fill. Footing bottoms shall be observed by a representative of STRATA-TECH, Inc., to verify competent conditions. EXPANSIVE SOILS Results of expansion tests indicate that the near surface soils have a low expansion potential. SETTLEMENT The maximum total post-construction settlement is anticipated to be on the order of 1/2 inch. Differential settlements are expected to be less than 1/2 inch, measured between adjacent structural elements. STRATA-TECH,INC. GEOC:ONSULTANTS DS Products, Inc. Geotechnical Engineering Investigation SUBSIDENCE & SHRINKAGE 7 w. 0. 273114 January 15, 2016 Subsidence over the site during grading is anticipated to be on the order of .5 feet. Shrinkage of reworked materials should be in the range of 10 to 15 percent. HARDSCAPE SLABS The surface soils are non-plastic with low expansion potential. Where concrete slabs on grade are utilized, the slab shall be supported on at least 1 foot of engineered fill compacted to a minimum of 90 percent relative compaction. Slabs should be at least 4 inches thick and reinforced with a minimum of no. 3 bars 24 inches on center both ways. The soil should be kept moist prior to casting the slab. However, if the soils at grade become disturbed during construction, they should be brought to approximately optimum moisture content and rolled to a firm, unyielding condition prior to placing concrete. In areas where a moisture sensitive floor covering will be used, a vapor barrier consisting of a plastic film (6 ml polyvinyl chloride or equivalent) should be used. The vapor barrier should be properly lapped and sealed. Since the vapor barrier will prevent moisture from draining from fresh concrete, a better concrete finish can usually be obtained if at least 2 inches of wet sand is spread over the vapor barrier prior to placement of concrete. UTILITY LINE BACKFILLS All utility line backfills, both interior and exterior, shall be compacted to a minimum of 90 percent relative compaction and shall require testing at a maximum of 2-foot vertical intervals. HARDSCAPE AND SLABS Hardscape and slab subgrade areas shall exhibit a minimum of 90 percent relative compaction to a depth of at least 1 foot. Deeper removal and recompaction may be required if unacceptable conditions are encountered. These areas require testing just prior to placing concrete. DRAINAGE Positive drainage should be planned for the site. Minimum drainage should be 2 percent for landscape areas and 1 percent for hardscape. Drainage should be directed away from structures via non-erodible conduits to suitable disposal areas. The structure should utilize roof gutters and down STRATA-TECH,INC. GECCONSULTANTS DS Products, Inc. Geotechnical Engineering Investigation 8 w. 0. 273114 January 15, 2016 spouts tied directly to yard drainage to allow stormwater to be dispersed away from the building foundations. Unlined flowerbeds, planters, and lawns should not be constructed against the perimeter of the structure. If such landscaping ( against the perimeter of a structure) is planned, it should be properly drained and lined or provided with an underground moisture barrier. Irrigation should be kept to a m1mmum. This report is issued with the understanding that it is the responsibility of the owner, or of his representative, to ensure that the information and recommendations contained herein are called to the attention of the engineers for the project and incorporated into the plans and that the necessary steps are taken to see that the Contractors and Subcontractors carry out such recommendations in the field. ENGINEERING CONSULTATION, TESTING & OBSERVATION We will be pleased to provide additional input with respect to foundation design once methods of construction and/or nature of imported soil has been determined. Grading and foundation plans should be reviewed by this office prior to commencement of grading so that appropriate recommendations, if needed, can be made. Areas to receive fill should be inspected when unsuitable materials have been removed and prior to placement of fill, and fill should be observed and tested for compaction as it is placed. AGENCY REVIEW All soil, geologic and structural aspects of the proposed development are subject to the review and approval of the governing agency(s). It should be recognized that the governing agency (s) can dictate the manner in which the project proceeds. They could approve or deny any aspect of the proposed improvements and/or could dictate which foundation and grading options are acceptable. Supplemental geotechnical consulting in response to agency requests for additional information could be required and will be charged on a time and materials basis. LIMITATIONS This report presents recommendations pertaining to the subject site based on the assumption that the subsurface conditions do not deviate appreciably from those disclosed by our exploratory excavations. Our recommendations are based on the technical information, our understanding of the proposed construction, and our experience in the geotechnical field. We do not guarantee the performance of the project, only that our engineering work and judgments meet the standard of care of our profession at this time. In view of the general conditions in the area, the possibility of different local soil conditions may exist. Any deviation or unexpected condition observed during construction should be brought to STRATA-TECH,INC. GEOCONSULTANTS DS Products, Inc. Geotechnical Engineering Investigation 9 w. 0. 273114 September 10, 2014 the attention of the Geotechnical Engineer. In this way, any supplemental recommendations can be made with a minimum of delay necessary to the project. If the proposed construction will differ from our present understanding of the project, the existing information and possibly new factors may have to be evaluated. Any design changes and the finished plans should be reviewed by the Geotechnical Consultant. Of particular importance would be extending development to new areas, changes in structural loading conditions, postponed development for more than a year, or changes in ownership. This report is issued with the understanding that it is the responsibility of the owner, or of his representative, to ensure that the information and recommendations contained herein are called to the attention of the Architects and Engineers for the project and incorporated into the plans and that the necessary steps are taken to see that the contractors and subcontractors carry out such recommendations in the field. This report is subject to review by the controlling authorities for this project. We appreciate this opportunity to be of service to you. Respectfully submitted, STRATA-TECH, INC. Enclosures: Larry Finley RCE46606 Appendix A: Laboratory Results and Engineering Calculations Appendix B: Specifications for Grading Plate 1: Vicinity Map Plate 2: Site Plan and Boring Location Map Test Boring Logs STRATA ... TECH,,INCE GECCDNSUL.TANTS APPENDIX A This appendix contains a description of the field investigation, laboratory testing procedures and results, site plan, and exploratory logs. FIELD INVESTIGATION The field investigation was performed on September 8, 2014, consisting of the excavation of two exploratory hand auger borings at locations shown on the attached Site Pl~ Plate 2. As excavation progressed, personnel from this office. visually classified the soils encountered, and secured representative samples for laboratory testing Sample Retrieval Undisturbed samples of earth materials were obtained at frequent intervals by driving a thin- walled steel sampler by slide hammer. The material was retained in brass rings of 2.41 inches inside diameter and 1.00 inch height. 1fhe central portion of the sample was in close-fitting, watertight containers for transportation to the laboratory. Descriptions of the soils encountered are presented on the attached boring Logs. The data presented on these logs is a simplification of actual! subsurface conditions encountered and applies only at the specific boring location and the date excavated. It is not warranted to be representative of subsurface conditions at other locations ahd times. Laboratory Testing Field samples were examined in the laboratory and a testing program was then established to develop data for preliminary evaluation of geotechnical conditions. Moisture Density Field moisture content and dry density were determined for each of the undisturbed soil samples. The dry density was determined in pounds per cubic foot. The moisture content was determined as a percentage of the dry soil weight. The results of the tests are shown in the test results section of this appendix, Compaction Character Compaction tests were performed on hulk sample of the existing soil in accordance with ASTM D1557-07. The results of the tests are shown in the test results section ofthls appendix. Shear Strength weathered ooc1roc,K tests were oerformed JC STRATA-TECH, INC .. GEDCCJNSULTANTS machine manufactured by GeoMati.c. The rate of deformation was 0.005 inches per minute. Samples were sheared under varying confining pressure, as shown on the "Shear Test Diagrams". The samples indicated as saturated were artificially saturated in the laboratory and were shear under submerged conditions. The results of tests are based on 80 percent peak strength or ultimate strength, whichever is lower, and are attached. In addition, a shear was performed on an upper layer sample remolded to 90*percent of the laboratory standard with low confining pressure. TEST RESULTS Maximum Density/Optimum Moisture {ASTM:D-1557-07) In-Situ Dry Density/ Moisture 1 2 112.0 7.1 2 5 114.l 9.0 2 10 113.7 10.8 Direct Shear VICINITY MAP Geotechnical Engineering Investigation 749-763 Magnolia Dr_ Carlsbad, California · Work Order 273114 . Plate No. 1 NEAR SOURCE FAULT MAP Geotechnical Engineering Investigation 7 49-763 Magnolia Dr. Carlsbad, California STRATA-TECHg INC,, Work Order 273114 d z a.. <( :::,,; I i I'' -+ RECORD OF SUBSURFACE EXPLORATION m '#. -:-:e? i Date 9/10/2014 Preliminary Geotechnical Investigation lei C: Q. ~'[ -jt .r:. 749-763 Magnolia Dr . E a. ~ 0-$, i:::' ...... (I) :!!:-C C Carlsbad, California u B Work Order 273114 Test Pit No. 1 Description of Earth Materials 0 -Brown, fn csand w/trace of clay 2 -Orange-brown , fn-med Sand,wltrace of clay, damp 7.1 112 4 Orange-tan, fn-med , silty sand, damp -mod-dence 6 - 8 -Bottom at 8' Feet. No Ground Water. No Caving. RECORD OF SUBSURFACE EXPLORATION '#. "'":'" :e? -Date 9/1012014 Preliminary Geotechnical Investigation t Cl) J C: it s c:' $ 'tr -E 1n "O C a. :g_ 749-763 Magnolia Dr. tU ·a .,I? 2--en ID ::i -a Q Carlsbad, California u B Work Order 273114 Test Pit No. 2 Description of Earth Materials 0 -Brown, Silty Sand w/ Roots 5 -Orange-Brown, fn-med, Sand wltrace of clay, damp 9 114.1 Decreasing clay 10 -10 113.7 Yellow-Tan Sand , Dense, damp 15 - Bottom at 12 Feet No Ground Water. No Caving. - STRATA-TECH, INC .. ALLOWABLE BEARING CAPACITY Reference: "Soil Mechanics · in Engineering Practice", Terzaghi and Peck, 1967 pages 222 and 223. Bearing Material: compacted fill Properties: Wet Density (g) = 130 pcf Cohesion (C) = 150 psf Angle of Friction (x") = 33 degrees Footing Depth (D) = 2 feet Footing Width (B) = 1.0 foot Factor of Safety = 3.0 Calculations -Ultimate Bearing Capacity from figure 33.4 on page 222 Ne= 38.64 Nq = 26.09 Ng =35_19 Ou = 1.2 C Ne + 'Yj., D Nq + 0.4 lJo B N (Square Footing) = 1.2 * 150*38.64+ 130"' 2* 26.09 + 0.4 * 130* 1 * 35.19 = &955 + 6783 + 1829=15567psf Allowable Bearing Capacity for Square Footing Qai,= au1F.S. = 5189 psf Use 2000 psf (Settlement Control) Q11 = 1.0 C Ne + 'Yj., D Nq + 0.5 '¥Jo B N (Continuous Footing) = 1.0 * 150 *38.64 + 130 *2 * 26.09 + 0.5 * 130* 1 *35.19 = 5796 + 6783 + 2287 = 14866 psf Allowable Bearing Capacity for Continuous Footing Clan= QulF.S. = 4955 psf Use 2000 psf (Settlement Control) Increases: 440 psf I ft in depth over 2 feet 200 psf I ft in. depth over 1 foot Geotechnic:at Engineering Investigation 7 49-763 Magnolia Dr. Carlsbad, California STRATA.,, TECH:; INC~ Work Order 273114 STRATA-TECH,.BNC. GECCONSULTANTS SITE CLEARING APPENDIXB SPECIF1CATIONS FOR GRADING All existing vegetation shall be stripped and hauled from the site. PREPARATION After the foundation for the fill has been cleared, plowed or scarified, it shall be disced or bladed until it is uniform and free from large clods, brought to a proper moisture content and compacted to not less than 90 percent of the maximum dry density in accordance with ASTM:D-1557-02 (5 layers -25 blows per layer; 10 lb. hammer dropped l 811; 4" diameter mold) . .MATERIALS On-site materials may be used for fill, or fill materials shall consist of materials approved by the Soils Engineer and may be obtained from the excavation of banks, borrow pits or any other approved source. The materials used should be free of vegetable matter and other deleterious substances and shall not contain. rocks or lumps greater than 8 inches in maximum dimension. PLACING, SPREADING,AND COMPACTING FILL MATERIALS Where natural slopes exceed five horizontal to one vertical, the exposed bedrock shall be benched prior to placing fill. The selected fill material shall be placed in layers which, when compactedt shall not exceed 6 inches in thickness. Each layer shall be spread evenly and shall be thoroughly mixed during the spreading to ensure uniformity of material and moisture of each layer. Where moisture of the fill material is below the limits specified by the Soils Engineer, water shall be added until the moisture content is as reqmred to ensure thorough bonding and thorough compaction. Where moist"Qre content of the :fill :material is above the limits specified· by the Soils Engineer, the fill materials shall be aerated by blading or other satisfactory methods until the moisture content is as specified. After each layer has been p~ mixed and spread evenly, it shall be thoroughly compacted to not less than 90 percent of the maximum dry density in accordance with ASTM:D-1557-02 (5 layers - 25 blows per layer; 10 lbs. hammer dropped 18 inches; 411 diameter mold) or other density tests which V\,1ll aittain equivalent results. \ -' STRATA•TECH,BNC .. GEOCDNSUL.TANTii Compaction shall be by sheepsfuot roller. multi-wheel pneumatic tire roller or other types of acceptable rollers. Rollers shall be of such design that they will be able to compact the fill to the specified density. Rolling shall be accomplished while the fill material is at the specified moisture content. Rolling of each layer shall be continuous over the entire area and the roller shall make sufficient trips to ensure that the desired density has been obtained. The final surface of the_ lot areas to receive slabs on grade should be rolled to a dense, smooth surface. The outside of all fill slopes shall be compacted by means of sheepsfoot rollers or other suitable equipment. Compaction operations shall be continued until the outer 9 inches of the slope is at least 90 percent compacted. Compacting of the slopes may be progressively in increments of 3 feet to 5 feet of fill height as the fill is brought to grade, or after the fill is brought to its total height. Field density tests shall be made by the Soils Engineer of the compaction of each layer of fill. Density tests shall be made at intervals not to exceed 2 feet of fill height provided all. layers are tested. Where the sheepsfoot rollers are used, the soil may be disturbed to a depth of several inches and density readings shall be taken in the compacted material below the disturbed surface. When these readings indicate that the density of any layer of fill or portion there is below the required 90 percent density, the particular layer or portion shall be reworked until the required density has been obtained. · The grading specifications should be a1part of the project specifications. The Soil Engineer shall review the grading plans prior to grading. INSPECTION The Soil Engineer shall provide continuous supervision of the site clearing and grading operation so that he can verify the grading was done in accordance with the accepted plans and specifications. SEASONAL LlMITATlONS No fill material shall be placed, spread or rolled during unfavorable weather conditions. When work is interrupted by heavy rains, fill operations shall not be resumed until the field tests by the Soils Engineer indicate the moisture content and density of the fill are as previously specified. EXPANSIVE SOIL CONDITIONS VVhenever expansive soil conditions are encountered,, the moisture content of the fill or recompacted soil shall be as recommended in the expansive soil recommendations included herewith.