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HomeMy WebLinkAbout; La Costa Meadows Unit 4 Lot 673; Soils Report; 1987-02-03- &ND DEVELOPMENT ? yinn - Pcrc Tests . Lot Splits 6. ~,ng Plans k Compaction Tests - February 3, 1987 City of Carlsbad 2075 Las Palmas Drive Engineering Department Carlsbad, CA. 92008 .- c/o Mike Fiorito 3211 Piragua Street Carlsbad, CA. 92008 Re: APN 215-440-06 (Obelisco Place) Lot 673 of La Costa Meadows Unit #4 Map 7367 - Subject: Limited Preliminary Soils Investigation '~. -TO'WHOM IT MAY'CONCERN: : .~ .~ TV' - Per the request of Mr. Mike Fiorito, our firm has conducted a Pre- liminary Soils Investigation of the Soils found at the above refer- enced site. This report represents the findings and recommendations for the proposed development based upon the results of this ~investi- gation. - This investigation consists of a site geologic reconnaissance, and the collecting of representative soil samples from the site. - Laboratory testing was performed on representative soils samples obtained from this site in order to evaluate pertinent physical .- properites. The conclusions and recommendations that follow are based upon review of the proposed development,' inspection of the site, an analysis of the 'data obtained and our experience with - similiar soil conditions. - - - - - ENGINEERING DEPT. LIBRARY City of Carlsbad 2075 Las Palmas Drive Carlsbad, CA 92009-4859 - - PROJECT SCOPE - - - - Explore the subsurface conditions to the depths influenced by the proposed construction. Evaluate, by laboratory tests, the pertinent engineering pro- perties of the various strata which will influence the develop- ment, including their bearing capacities, expansive character- istics ‘and settlement potential. Define the general geology at the site including possible geolo gic hazards which could have an effect on the site develop- ment. Develop soil engineering criteria for the site grading and provide design information regarding the stability of cut/fill slopes. Determine potential construction difficulties and provide re- commendations concerning these problems. Recommend an appropriate foundation system for the type of structures anticipated and develop soil engineering design criteria for the recommended design. - \ - THE SITE The site consists of a trapezoidal shaped lot located at the terminus of the cul-de-sac on Obelisco Place in the subdivision known as La Costa Meadows Unit 4 in the City of Carlsbad. - .- - - - - J - This parcel is located at the top of a prominent ridge traversing this development. The lot is nearly level adjacent to the cul- de-sac access and then slopes in all directions at variable rates toward surrounding lots. The lots in all directions have been previ- ously developed with single family residences and associated im- provements and landscaping. The site is covered with low grasses and bushes native to the coastal region. Several rock out croppings were noted on the site. A plot plan of the ‘proposed development has been provided this office. A large single family residence is proposed with minimal grading for the garage area, while the remainder of the structure will be constucted on stem walls with foundations in native soils. - - . - - .- FIELD INVESTIGATION i * .- Our investigation consisted of a field review of the site and surr- ounding parcels. From our observations and familiarity with the project area, we can make applicable conclusions without the necess- ity of making exploratory excavations on the actual building site. We were able to observe the underlying formations in existing many made cut slopes on adjacent properties. - The site is typical of the area. The surface topsoils had been disturbed and partially removed by previous grading, presumably .- during grading of the subdivision improvements. However, a thin mantle of reddish clayey-silts to clayey sands covers the site - with several small rock out croppings protruding through the surface layers. This is underlain by fractured rock masses of the Santiago Peaks Volcanic formations. - - - - - - - -. LABORATORY TESTS Laboratory tests were performed \ ’ in accordance with generally accepted test methods of the American Society for Testing Andy Materials (ASTM) and other suggested procedures. Selected relatively undisturbed drive samples were tested for their inplace dry density, moisture content and expansive potential. The maximum dry density and optimum moisture content of the near surface soils were determined in accordance with ASTM Test D155770, Method A. In addit ion, a directshear test and an expansion test were performed on samples remolded to 9.08 of maximum dry density at optimum moisture content. - - - Field moisture content and dry density were determined for representative undisturbed samples. This information was an aid to classification and permitted recognition of variations in material consistency with depth. The dry unit weight is determined in pounds per cubic foot, and the field moisture content is determined as a percentage of the soils dry weight. - Field classifications were verified in the laboratory by visual examination. The final soils classifications are in accordance with the Unified Soil CLassification System. - Direct shear tests were performed to evaluate bearing potential along with maximum density testing and expansive analysis were conducted. Maximum dry weight was determined to be 125.0 #/c.f. @ 12% optimum moisture content. Testing was done for internal shear based upon utilizing a 90% relative compaction. The apparent angle of shear for the soils encountered = 3f”. An expansion analysis of these soils was performed in accordance with the UBC 292 test procedures. The result of this test indicated an index value of 49, which is considered to be a low-expansion rate. - - -’ - - - - TECTONIC SETTING ‘\ ’ Carlsbad, along with most of the southwestern portion of Califp rnia, San Diego County, and parts of Mexico are located on a relatively stable tectonic plate. This plate is bounded on the east by the San Andreas Fault system and on the west by the San Clemente Fault System. These faults contain many other parallel faults which are essentially high angle strikeslip faults with a NW/SE trend. Although the bounding fault systems are active, the interior of the tectonic plate is not generally disturbed by the fault movement. Geological references indicate that not much damage will occur from earthquakes of magnitude of less than 6 for sites over eight miles from the fault. Since maximum probable earthquake for the general San Diego area is in the order of 6 and since the site is further than 8 miles from the major active faults we can infer that the shaking problem will not be to great. Current seismic design criteria as imposed by the U.B.C. should be satisfactory to compensate for seismic action. There are no existing landslides, faults or other natural disturbances noted on the site or in the immediate area as determined from air photos, and field inspections. This does not preclude the possibility of sliding by poor grading or other man made practic es. This site can be considered relatively free of geologic hazards. - RECOMMENDATIONS & CONCLUSIONS <\ The site may be utilized for the proposed development provided the recommendations of this report are carefully followed.- The undisturbed native soils, properly compacted native soils or combinations thereof, should adequately support the proposed structures without detrimental settlement. - - - - will be sloping 2:1, an active soil pressure of 45 pcf is reco- mmended. These values assume a drained backfill condition. Wall drainage details should be provided by the project archi- tect. All cut slopes shall be 2:l or flatter and all fill slopes shall not exceed 2:l slope ratio. When retaining walls are restrained at the top an active soil pressure of 65 pcf shall be used for design of the wall. A passive soil pressure value - of 400 psf shall be used. The site shall be cleared of all vegatation prior to any grading or placement of embankment. Any uncompacted native soils shall be compacted to a minimum of 90% relative compaction. The Soil Engineer shall determine when the native soils are ready for placement of embankment. Retaining walls, which are not fixed at the top and have a level backfill should be designed for an active soil pressure equivalent to a fluid pressure of 40 pcf. Where the backfill - A coefficient of friction of 0.45 may be assumed for resistance to sliding between concrete and soil. - The anticipated total and/or differential settlements for the proposed structures may be considered to be within tolerable limits provided the recommendations presented in this report are followed. - - - All embankment shall. be compacted to a minimum of 90% relative . compaction and all existing ground within 5.0 feet laterally and to a depth of 1.0 foot below the bottom of foundations shall be compacted to at least 90% relative compaction. - All existing topsoils and uncompacted soils shall be removed to a depth as determined by the Soils Engineer. Exact depth to be determined by the Soils Engineer at the time of grading. - This material shall then be recompacted into a dense embankment of at least 90% relative compaction, with a moisture content within 2.0% of optimum. - The recommendations presented in this report are contingent on review of final plans and specifications. It is recommended that H.L.~ Land Development, Engineering and Surveying, be re- tained to provide continuous soil engineering services during the earthwork operations. This is two observe compliance with the design concepts, specifications, and recommendat ions and to allow design changes in the event subsurface conditions differ from those anticipated prior to start of construction. - - Minimum foundation shall be 12 inches wide and founded 18 inches below grade and shall have two #4 bars of reinforcing steel. One bar shall be placed 4 inches below the top of foundation and the other bar shall .be placed 4 inches from the bottom of foundation. These recommendations are based.upon soil charac- teristics only and do not reflect any possible design considera- tions imposed by building design which might increase these recommendations. The proposed foundations may be designed util- izing an allowable bearing pressure of 1600 lb/sf. This value may be increased by l/3 for the designTloads that include wind and seismic analysis. Slab on grade shall be reinforced with 6x6xlOga wire mesh over 4 inches of clean sand or gravel. These recommendations are made based upon the assumption that the soils found on the site will be used for foundation embank ment. - _- ,- - - - - It should be noted that additional or final foundation recommen dations will be made and contained in the Final As Graded Report when a more complete evaluation of actual soil that the foundat ions will be founded in can be made. It is anticipated that on-site grading will be very minimal as the primary structure will be founded on stem walls. The garage area will be of slab on grade and minor grading will be required. It is anticipated that need embankment material will be obtained from shallow cuts ~made on site from contour grading of the yard area. However, an alternate would be to import a non-expansive material to complete the embankment area ., In the even that this option is taken, the imported material shall be approved by the Soils Engineer prior to being delivered to the site. The recommendations and opinions expressed in this report re- flect OUT best estimate of the project requirements based on an evaluation of the subsurface soil conditions encountered at the subsurface exploration locations and the assumption that the soil conditions do not deviate appreciably from those encountered . It should be recognized that the performance of the foundations may be influenced by undisclosed or unforseen variations in the soil conditions that may.occur in the interme diate and unexplored areas. Any unusual conditions not covered in this report that may be encountered during site development should be brought to the attention of the Soils Engineer so that he may make modifications if necessary. - - - - - - -. .- - - - It is the responsibility of the Developer or’ltheir representa- tive to ensure that the information and recommendations con- tained herein are brought to the attention of the Engineer and Architect for the project and incorporated into the project plans and specifications. It is further their responsibility to take the necessary measures to insure that the contractor and his subcontractors carry out such recommendations during construction. All grading shall be monitored by a qualified Soils Engineer to insure compliance with these recommendations and applicable City of Carlsbad ordinances and good engineering practices. Recommended grading specifications are included in this report as the attached Exhibit “A”. Z/h Herald R. Lan is RCE 33220 - 1535 S. Ewmdido Blvd. Escondido. CA 9202s (619) 741.OS33 .&AND DEVELOPMENT Sdrvcying . Pert Tests . Lot Splits Grading Plans & Compaction Tests - RECOMMENDED GRADING SPECIFICATIONS ,. Prepared for: Mike Fiorito - for the development of: a SINGLE FAMILY RESIDENCE @ Lot 673 of La Costa Meadows Unit #4 Map 7367 Herald R. - Lantis hereinafter described as the Soil Engineer, should be consulted prior to.any site work connected with site development to ensure compliance with these specifications. These specifications shall only be used in conjunction with the soil report of which - they are attached and part thereto. 1.1 This item shall consist of all clearing and grubbing, prepar- - ation of land to be filled, filling of the land, spreading, compact- ing, and control of the fill and all subsidiary work necessary to complete the grading of the filled areas to conform with the _,- lines, grades and slopes as shown on the accepted plans. 1.2 The Soil Engineer shall test and observe all grading opera- tions. In the event that any unusual conditions not covered by the special provisions are encountered during the grading operations, the Soil Engineer shall be contacted for further information. - 2.0 Tests The standard test used to define maximum density of all compaction work shall be the ASTM Test Procedure D1557-70. All densities shall ,,- be expressed as a relative compaction in terms of the maximum density obtained in the laboratory by the foregoing procedure. 3.0 Clearing, Grubbing and Preparing Areas to be Filled. _- Any trees not utilized in landscaping, structures, weeds and other rubbish shall be removed, piled or otherwise disposed of so as to leave the areas that have been disturbed with a neat and finished appearance, free from unsightly debris. .- - 3.2 - 3.3 3.4 3.5 - - 3.6 - .- - Any septic tanks, if encountered, and debris must be removed from the site prior to any building, grading or fill operations. Septic tanks, \lncluding all con- netting drain fields and other lines, must be totally removed andthe resulting depressions properly reconstruct- ed and filled to the complete satisfaction of the super- vising soil engineer. All water wells on the site shall .be capped according to the requirements of the San Diego County Health Depart- ment. The strength of the cap shall be at least equal to the adjacent soil. The final elevation of the top of the adjacent grade prior to any grading of fill oper- ations. ,e All buried tanks, if encountered, must be totally removed and the resulting depressions properly reconstructed and filled to the complete satisfaction of the supervising soil engineer. All vegetable matter and soil designated as unsuitable by the soil engineer shall be removed under the direction of the direction of the soil engineer. The then exposed surface shall then be plowed or sacrified to a depth of at least eight inches and until the surface is free from ruts, hummocks, or other uneven features which would tend to prevent uniform compaction by the equipment to be used. The original ground upon which the fill is to be placed shall be plowed or sacrified deeply, and where the slope ratio of the original ground is steeper than 6.0 horizon- tal to 1.0 vertical, the band shall be stepped or benched. At the toes of the major fills and on the sideslope fills, the base key shall be, as described elsewhere in this report, at least 10 feet in width, cut at least three feet into the undisturbed or native soil, and sloped back into the hillside at a gradient of not less than - .- .^ - - two percent. Subsequent keys should be cut into the hillside as the fill is brought up the slope. The con- struction of subsequent keying operations, shall be deter- mined by the soil engineer during grading operations. Ground slopes which are flatter than 6 to 1 shall be bench- ed when considered necessary by the soil engineer. 3.7 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 the proper moisture content by adding water or aerating: and recom- pacted to a relative compaction of not less than 90 percent. - - - - - - - - - - - - .~- 4. Materials Native soil, free .of organic material and undesirable de- leterious material, may be used as fill. Native soil which is expansive, shall not be placed on the, top two feet of building pads without the approval of the soil engineer. 4.2 The materials for fill shall be approved by the soil engin- eer before commencement of grading operations. Any import- ed material must be approved for use before being brought to the site. The materials used shall be free from veget- able matter and other deleterious material, and be nonex- pansive. Expansive soil is defined as soil which expands more than three percent when saturated at 90 percent relat- ive compaction and optimum moisture content under a sur- charge of 150 psf. 5. Placing, Spreading, and Compaction Fill Material 5.1 The selected fill material shall be placed in layers which, when compacted. shall allow adequate bonding and compaction. Each layer shall be spread evenly and shall be thoroughly blade mixed during the spreading to ensure uniformity of material in each layer. 5.2 When the moisture content of the fill material is below that specified by the soil engineer, water shall be added until the moisture content is as specified to assure thor- ough bonding during the compaction process. When the moist- ure content of the fill material is above that specified by the soil engineer, the fill material shall be aerated by blading or other satisfactory methods until the moist- ure content is as specified. 5.3 After each layer has been placed, mixed and spread even- ly. it shall be thoroughly compacted to a relative compac- tion of not less than 90 percent. 5.4 When fill material includes rock, no rock will be allowed to nest, and all voids must be carefully filled with small stones or earth and properly compacted. No rocks larger than six inches in diameter will be permitted in the fill. 5.5 Compaction shall be by sheepsfoot rollers, multiple wheel pneumatic-tired rollers, or other types of acceptable com- pacting rollers. Rollers shall be of such design that they will be able to compact the fill to the specified moisture content range. Rolling of each layer shall be continuous over it's entire area and until the required density has been obtained. - __ - ~. .- - - - - - ,- 5.6 Field density tests shall be made by the soil engineer where sheepsfoot rollers are used, the soil may be dis- turbed to a depth of several inches. Density tests shall be taken in compacted material below the disturbed sur- face. When these tests indicate 'tha't the density of any layer of fill or portion thereof is below the required 90 percent relative compaction, the particular layer of portion shall be reworked until the required density has been obtained. 5.7 The fill operation shall be continued in compacted layers as specified above, until the fill has been brought to the finished slopes and graded as shown on the accepted plans. 5.8 Fill slopes shall be compacted by means of sheepsfoot rollers or other suitable equipment. Compaction oper- ations shall be continued until the slopes are stable. 5.9 All earthmoving and working operations shall be controlled to prevent water from running into excavated areas. All water shall be promptly removed and the site kept dry. 6. Disposal of Oversize Rock 6.1 Oversize rock shall be either exported from the site, used for landscaping purposes, 01;~ placed in designated non-structural fill areas. 6.2 Prior to grading, the soil engineer shall be consulted to approve any proposed nonstructural fill area, In General, nonstructural fill areas will be acceptable if located outside of the"zone of influence" of proposed structures: e.g. rear yard fills at least 15 feet from structures and beneath street areas (deeper than pro- posed utility lines). 6.3 Oversize rock shall not exceed four feet in greatest dimension, shall be placed in lifts not exceeding four feet in thickness, and shall be placed in a manner that will not produce "nesting" of the rock. The voids between the rocks shall be completely filled with fine granular material. 6.4 No oversize rock shall be placed within four feet of finish lot grade nor within the anticipated depth of utility lines, whichever is deeper. - - - - - - I. Engineering Observation Field observations by the soil engineer shall be made during the fill and compaction operations so that he can express his opinion regarding the conformance of the grading with the accepted specifications. a. Seasonal Limits No fill material shall be placed, spread, or rolled while it is at an unsuitable high moisture content, nor during unfavorable weather conditions. When the work is inter- rupted by heavy rain, fill operations shall not be resumed until field tests by the soil engineer indicate that the moisture content and density of fill are as previous- ly specified. - - -