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HomeMy WebLinkAbout1995-1; Calavera Hills Village L-1-Clurman Company; Calavera Hills Village L-1; 1997-05-15UPDATED AND SUPPLEMENTAL GEOTECHNICAL RECOMMENDATIONS PROPOSED CONDOMINIUM DEVELOPMENT VILLAGE L-l OF CALAVERA HILLS CARLSBAD, CALIFORNIA PREPARED FOR: THE CLURMAN COMPANY, INC. 455 LINDEN STREET LAGUNA BEACH, CALIFORNIA 92651 PREPARED BY: SOUTHERN CALIFORNIA SOIL AND TESTING, INC. 6280 RIVERDALE STREET SAN DIEGO, CALIFORNIA 92120 Providing Professional Engineering Services Since 1959 SOUTHERN CALIFORNIA SOIL & TESTING, INC. 6280 Riverdale Street, San Diego, CA 92120 RO. Box 600627, San Diego, CA 92160-0627 619-280-4321, FAX 619-280-4717 May 15, 1997 The Clurman Company, Inc. SCS&T 9711089 455 Linden Street Report No. 2 Laguna Beach, California 92651 ATTENTION: Don Clurman SUBJECT: Updated and Supplemental Geotechnical Recommendations, Proposed Condominium Development, Village L-l of Calavera Hills, Carlsbad, California. REFERENCES: See Attached Plate Number 2. Dear Mr. Clurman: In accordance with your request, this report has been prepared to update our previous geotechnical reports for the subject project. It is our understanding that the previously graded development will be regraded to receive a new product. Therefore, we are also providing supplemental grading recommendations to address the additional grading proposed. SITE BACKGROUND The subject site is an irregular shaped parcel of land covering approximately six acres in area. The property is bounded on the east by Harwich Drive, on the south by Edgewater Way and open space, on the west by Tamarack Avenue and open space, and on the north by a condominium project and open space. Roughly three-fourths of the site was previously graded into relatively level pads for a previously planned five-building apartment complex with associated streets, parking areas and recreation areas. The rest of the site is in a natural condition, except for a cut slope above Tamarack Avenue where it abuts the southwest corner of the lot and a fill slope leading down to a finger canyon north of the graded pads. The graded areas are practically void of vegetation while the natural areas are covered with a thick growth of indigenous vegetation. The previous grading took place in June, July and August of 1985 under a contract issued by Pacific Scenes, Inc. Southern California Soil and Testing, Inc. (SCS&T) provided the compaction testing and field observation services during the mass grading operation (see Reference Report No. 4). Basically, the previous grading consisted of cutting down the higher areas of the site by as SCS&T 9711089 May 15, 1997 Page 2 much as about 25 feet in the easterly portion, and filling in the head of a small north-draining finger canyon and along the top edge of a natural west-facing slope. The fill in the finger canyon has a maximum depth of about 30 feet and produced a 2.0:1.0 (horizontal to vertical), 50-foot-high fill slope. The fill along the west side of the property is about 10 to 15 feet thick with 2.0:1.0 slopes up to about 25 feet high. Plate Number 1, included in the pocket of this report, identifies the geologic units that underlie the site and the approximate locations of the contact lines between the various geologic units. The site originally was capped with about two feet of topsoil/colluvium that covered fractured granitic and metavolcanic rock. Rocky materials up to 24 inches in diameter were placed in structural fills near the face of the fill slopes. Rocky material up to six inches in diameter which was mixed with fines to prevent nesting of rocks was used to construct the rest of the fills up to three feet from finish grade in building areas and four and a half feet below grade in street areas. The cut areas were also undercut to this criterion. The site was then capped with imported silty sands. Prior to filling in the head of the north draining finger canyon, a subdrain was installed in the invert. Once the mass grading was completed, the only additional construction activity consisted of the installation of a storm drain leading from the Edgewater Way cul-de-sac northerly across the site to the bottom of the finger canyon fill slope. To our knowledge, no other underground utilities have been installed. The site has remained unused since the completion of mass grading and a recent site reconnaissance indicated that the site conditions are basically unchanged since the completion of the grading observed by SCS&T in 1985. PROPOSED CONSTRUCTION We understand that the proposed development of the site has been changed from the original five two-story buildings concept to a thirty-five unit complex comprised of detached, two-story, wood- frame structures. The buildings will have shallow foundations and on-grade concrete slabs. A recreation center with a swimming pool and private streets associated with the project are also proposed. In addition to showing the geologic units that underlie the site, the site plan included herewith as Plate Number 1 shows the configuration of the buildings and the layout of the private streets. SCS&T 9711089 May 15, 1997 Page 3 The regrading of the site will consist of cutting down portions of the site by as much as about two feet from existing grade and filling other portions of the site by as much as about 6.5 feet. In addition, the existing storm drain extending from the end of Edgewater Way to the top of the slope on the north side of the site will be removed and relocated to fit the new street alignment. CONCLUSIONS AND RECOMMENDATIONS The subject site is, in our opinion, suitable for the proposed development. With the exception of the following supplemental recommendations, the findings and recommendations contained in our previous referenced geotechnical reports are still valid for the development of the site. 1) A review of the site plan showing the existing grades and proposed pad grades indicates that seven pads will be cut down from one to two feet below existing grade and 26 pads will receive from one to 6.5 feet of fill. Two pads will be at the approximate existing elevation. This indicates that soils will need to be imported to balance the site regrading work. All imported soils should be granular soils with an expansion index of less than 50, and should contain no rocks or lumps of soil larger than six inches in diameter. 2) Areas to receive fill and areas that will be cut down less than one foot from existing grade should be scarified to a depth of 12 inches, moisture conditioned and recompacted to at least 90 percent relative compaction. 3) The regrading of the site will alter the depth of the soils capping the site, and in some of the cut areas the regrading will remove some of the capping soils over the bedrock materials. In consideration of this, it is recommended that where foundation excavations will expose bedrock soils, the pads should be undercut to at least six inches below the bottom of the footings with the heavy grading equipment and be backfilled with compacted fill. This will allow excavation of footing trenches with normal trenching equipment. Overexcavation of utility alleys should also be considered. 4) The existing storm drain that will be abandoned should be entirely removed and the resulting excavation should be backfilled with compacted fill prior to site regrading. 5) During the previous grading operation, some blasting was necessary to make the planned grades. We anticipate that some nonrippable materials may be encountered in the new SCS&T9711089 May 15, 1997 Page 4 storm drain trench and that excavation of this material will produce oversize materials (rock over six inches in diameter). Since the site regrading will not result in any fills deep enough to dispose of such oversize material, export of oversize rock material may be necessary. This will most likely result in the need to import additional soil to replace the exported rock. 6) All earthwork and grading contemplated for site preparation should be accomplished in accordance with the attached Recommended Grading Specifications and Special Provisions. All special site preparation recommendations presented in the sections above will supersede those in the standard Recommended Grading Specifications. All embankments, structural fill and fill should be compacted to at least 90 percent relative compaction at or slightly over optimum moisture content. Utility trench backfill within five feet of the proposed structures and beneath asphalt pavements should be compacted to a minimum of 90 percent of its maximum dry density. The upper twelve inches of subgrade beneath paved areas should be compacted to 95 percent of its maximum dry density. This compaction should be obtained by the paving contractor just prior to placing the aggregate base material and should not be part of the mass grading requirements. The maximum dry density of each soil type should be determined in accordance with ASTM Test D-1557-91, Method A or C. 7) We recommend that the foundations for the proposed structures be founded at least 18 inches below lowest adjacent grade and have a minimum width of 12 inches. All continuous footings should be reinforced with at least four No. 4 bars, two top and two bottom. An allowable soil bearing pressure of 2500 psf may be used for footings with these minimum dimensions. 8) All footing excavations should be observed by a member of our engineering/geology staff to verify that the foundation excavations extend into a suitable bearing stratum. 9) Interior on-grade slabs should have a minimum thickness of four inches and should be reinforced with at least No. 3 bars at 18 inches on center each way. This reinforcing should be positioned in the center of the slab. Garage slabs should have the same reinforcing but may be free-floating in lieu of being connected to perimeter foundations. Interior slabs should be underlain by two inches of clean sand over a 6-mil vapor barrier over an additional two inches of clean coarse sand. SCS&T 9711089 May 15, 1997 Page 5 10) Site retaining walls should be designed using the following design criteria: Passive Pressure: The passive pressure for the prevailing soil conditions may be considered to be 350 pounds per square foot per foot of depth. This pressure may be increased one-third for seismic loading. The coefficient of friction for concrete to soil may be assumed to be 0,40 for the resistance to lateral movement. When combining frictional and passive resistance, the friction should be reduced by one-third. The upper 12 inches of soil should not be included in passive pressure calculations, unless pavement abuts the base of the wall. Active Pressure: The active soil pressure for the design of earth retaining structures with level backfills may be assumed to be equivalent to the pressure of a fluid weighing 30 pounds per cubic foot. An additional 13 pcf should be added to said value for 2:1 (horizontal to vertical) sloping backfill. These pressures do not consider any other surcharge. If any are anticipated, this office should be contacted for the necessary increase in soil pressure. These values assume a drained backfill condition. Waterproofing details should be provided by the project architect. Backfill: All backfill soils should be compacted to at least 90% relative compaction. Expansive or clayey soils should not be used for backfill material. The wall should not be backfilled until the masonry has reached an adequate strength. Factor of Safety: The above values, with the exception of the allowable soil bearing pressure, do not include a factor of safety. Appropriate factors of safety should be incorporated into the design to prevent the walls from overturning and sliding. If you should have any questions regarding this report, please do not hesitate to contact this office. This opportunity to be of professional service is sincerely appreciated. Respectfully submitted, SOUTHERN CALIFORNIA SOIL AND TESTING, INC. Charles H. Christian, R.G.E. #00215 CHC:mw cc: (4) Submitted (2) Hunsaker and Associates REFERENCES 1) Preliminary Geotechnical Investigation for Proposed Calavera Hills, Unit L, Carlsbad, California, Prepared by Woodward-Clyde Consultants, dated February 23, 1981. 2) Report of Updated Soil Investigation, Proposed Apartment Site, Village L-l, Calavera Hills, Carlsbad, California, Prepared by Southern California Soil and Testing, Inc., dated August 7, 1984 (File No. 25142, Report No. 1). 3) Earth Package Investigation, Calavera Hills, Village L-l, Carlsbad, California, Prepared by Southern California Soil and Testing, Inc., dated August 8, 1984 (File No. 25142, Report No. 2). 4) Report of Field Observation and Relative Compaction Tests, Village L-l, Calavera Hills, Carlsbad, California, Prepared by Southern California Soil and Testing, Inc., dated October 23, 1985, (File No. 8421142, Report No. 5). 5) Updated and Supplemental Geotechnical Recommendations, Proposed Apartment Complex, Village L-l of Calavera Hills, Carlsbad, California, Prepared by Southern California Soil and Testing, Inc., dated April 8, 1992 (File No. 9221025, Report No. 1). SCS&T 9711089 May 15, 1997 Plate No. 2 SCS&T 9711089 May 15, 1997 Appendix, Page 1 CONDOMINIUM DEVELOPMENT VILLAGE L-l OF CALAVERA HILLS, CARLSBAD, CALIFORNIA RECOMMENDED GRADING SPECIFICATIONS - GENERAL PROVISIONS GENERAL INTENT The intent of these specifications is to establish procedures for clearing, compacting natural ground, preparing areas to be filled, and placing and compacting fill soils to the lines and grades shown on the accepted plans. The recommendations contained in the preliminary geotechnical investigation report and/or the attached Special provisions are a part of the Recommended Grading Specifications and shall supersede the provisions contained hereinafter in the case of conflict. These specifications shall only be used in conjunction with the geotechnical report for which they are a part. No deviation from these specifications will be allowed, except where specified in the geotechnical report or in other written communication signed by the Geotechnical Engineer. OBSERVATION AND TESTING Southern California Soil & Testing, Inc., shall be retained as the Geotechnical Engineer to observe and test the earthwork in accordance with these specifications. It will be necessary that the Geotechnical Engineer or his representative provide adequate observation so that my may provided his opinion as to whether or not the work was accomplished as specified. It shall be the responsibility of the contractor to assist the Geotechnical Engineer and to keep him appraised of work schedules, changes and new information and data so that he may provided these opinions. In the event that any unusual conditions not covered by the special provisions or preliminary geotechnical report are encountered during the grading operations. The Geotechnical Engineer shall be contacted for further recommendations. If, in the opinion of the Geotechnical Engineer, substandard conditions are encountered, such as questionable or unsuitable soil, unacceptable moisture content, inadequate compaction, adverse weather, etc.; construction should be stopped until the conditions are remedied or corrected or he shall recommended rejection of this work. Tests used to determine the degree of compaction should be performed in accordance with the following American Society for Testing and Materials test methods: SCS&T 9711089 May 15, 1997 Appendix, Page 2 Maximum Density & Optimum Moisture Content - ASTM D-1557-91 Density of Soil In-Place - ASTM D-1556-90 or ASTM D-2922 All densities shall be expressed in terms of Relative Compaction as determined by the foregoing ASTM testing procedures. PREPARATION OF AREAS TO RECEIVE FILL All vegetation, brush and debris derived from clearing operations shall be removed, and legally disposed of. All areas disturbed by site grading should be left in a neat and finished appearance, free from unsightly debris. After clearing or benching the natural ground, the areas to be filled shall be scarified to a depth of 6 inches, brought to the proper moisture content, compacted and tested for the specified minimum degree of compaction. All loose soils in excess of 6 inches thick should be removed to firm natural ground which is defined as natural soils which possesses an in-situ density of at least 90 percent of its maximum dry density. When the slope of the natural ground receiving fill exceeds 20 percent (5 horizontal units to 1 vertical unit), the original ground shall be stepped or benched. Benches shall be cut to a firm competent formational soils. The lower bench shall be at least 10 feet wide or 1-1/2 times the equipment width, whichever is greater, and shall be sloped back into the hillside at a gradient of not less than two (20 percent. All other benches should be at least 6 feet wide. The horizontal portion of each bench shall be compacted prior to receiving fill as specified herein for compacted natural ground. Ground slopes flatter than 20 percent shall be benched when considered necessary by the Geotechnical Engineer. Any abandoned buried structures encountered during grading operations must be totally removed. All underground utilities to be abandoned beneath any proposed structure should be removed from within 10 feet of the structure and properly capped off. The resulting depressions from the above described procedure should be backfilled with acceptable soil that is compacted to the requirements of the Geotechnical Engineer. This includes, but is not limited to, septic tanks, fuel tanks, sewer lines or leach lines, storm drains and water lines. Any buried structures or utilities no to be abandoned should be brought to the attention of the Geotechnical Engineer so that he may determine if any special recommendation will be necessary. SCS&T 9711089 May 15, 1997 Appendix, Page 3 All water wells which will be abandoned should be backfilled and capped in accordance to the requirements set forth by the Geotechnical Engineer. The top of the cap should be at least 4 feet below finish grade or 3 feet below the bottom of footing whichever is greater. The type of cap will depend on the diameter of the well and should be determined by the Geotechnical Engineer and/or a qualified Structural Engineer. FILL MATERIAL Materials to be placed in the fill shall be approved by the Geotechnical Engineer and shall be free of vegetable matter and other deleterious substances. Granular soil shall contain sufficient fine material to fill the voids. The definition and disposition of oversized rocks and expansive or detrimental soils are covered in the geotechnical report or Special Provisions. Expansive soils, soils of poor gradation, or soils with low strength characteristics may be thoroughly mixed with other soils to provide satisfactory fill material, but only with the explicit consent of the Geotechnical Engineer. Any import material shall be approved by the Geotechnical Engineer before being brought to the site. PLACING AND COMPACTION OF FILL Approved fill material shall be placed in areas prepared to receive fill in layers not to exceed 6 inches in compacted thickness. Each layer shall have a uniform moisture content in the range that will allow the compaction effort to be efficiently applied to achieve the specified degree of compaction. Each layer shall be uniformly compacted to the specified minimum degree of compaction with equipment of adequate size to economically compact the layer. Compaction equipment should either be specifically designed for soil compaction or of proven reliability. The minimum degree of compaction to be achieved is specified in either the Special Provisions or the recommendations contained in the preliminary geotechnical investigation report. When the structural fill material includes rocks, no rocks will be allowed to nest and all voids must be carefully filled with soil such that the minimum degree of compaction recommended in the Special Provisions is achieved. The maximum size and spacing of rock permitted in structural fills and in non- structural fills is discussed in the geotechnical report, when applicable. Field observation and compaction tests to estimate the degree of compaction of the fill will be taken by the Geotechnical Engineer or his representative. The location and frequency of the tests shall be at the Geotechnical Engineer's discretion. When the compaction test indicates that a particular layer is at less SCS&T 9711089 May 15, 1997 Appendix, Page 4 than the required degree of compaction, the layer shall be reworked to the satisfaction of the Geotechnical Engineer and until the desired relative compaction has been obtained. Fill slopes shall be compacted by means of sheepsfoot rollers or other suitable equipment. Compaction by sheepsfoot roller shall be at vertical intervals of not greater than four feet. In addition, fill slopes at a ratio of two horizontal to one vertical or flatter, should be trackrolled. Steeper fill slopes shall be over- built and cut-back to finish contours after the slope has been constructed. Slope compaction operations shall result in all fill material six or more inches inward from the finished face of the slope having a relative compaction of at least 90 percent of maximum dry density or the degree of compaction specified in the Special Provisions section of this specification. The compaction operation on the slopes shall be continued until the Geotechnical Engineer is of the opinion that the slopes will be surficially stable. Density tests in the slopes will be made by the Geotechnical Engineer during construction of the slopes to determine if the required compaction is being achieved. Where failing tests occur or other field problems arise, the Contractor will be notified that day of such conditions by written communication from the Geotechnical Engineer or his representative in the form of a daily field report. If the method of achieving the required slope compaction selected by the Contractor fails to produce the necessary results, the Contractor shall rework or rebuild such slopes until the required degree of compaction is obtained, at no cost to the Owner or Geotechnical Engineer. CUT SLOPES The Engineering Geologist shall inspect cut slopes excavated in rock or lithified formational material during the grading operations at intervals determined at his discretion. If any conditions not anticipated in the preliminary report such as perched water, seepage, lenticular or confined strata of a potentially adverse nature, unfavorably inclined bedding, joints or fault planes are encountered during grading,, these conditions shall be analyzed by the Engineering Geologist and Soil Engineer to determine if mitigating measures are necessary. Unless otherwise specified in the geotechnical report, no cut slopes shall be excavated higher or steeper than the allowed by the ordinances of the controlling governmental agency. SCS&T 9711089 May 15, 1997 Appendix, Page 5 ENGINEERING OBSERVATION Field observation by the Geotechnical Engineer or his representative shall be made during the filling and compaction operations so that he can express his opinion regarding the conformance of the grading with acceptable standards of practice. Neither the presence of the Geotechnical Engineer or his representative or the observation and testing shall not release the Grading Contractor from his duty to compact all fill material to the specified degree of compaction. SEASON LIMITS Fill shall not be placed during unfavorable weather conditions. When work is interrupted by heavy rain, filling operations shall not be resumed until the proper moisture content and density of the fill materials can be achieved. Damaged site conditions resulting from weather or acts of God shall be repaired before acceptance of work. RECOMMENDED GRADING SPECIFICATIONS - SPECIAL PROVISIONS RELATIVE COMPACTION: The minimum degree 'of compaction to be obtained in compacted natural ground, compacted fill, and compacted backfill shall be at least 90 percent. For street and parking lot subgrade, the upper six inches should be compacted to at least 95 percent relative compaction. EXPANSIVE SOILS: Detrimentally expansive soil is defined as clayey soil which has an expansion index of 50 or greater when tested in accordance with the Uniform Building Code Standard 29-C. OVERSIZED MATERIAL: Oversized fill material is generally defined herein as rocks or lumps of soil over 6 inches in diameter. Oversized materials should not be placed in fill unless recommendations of placement of such material is provided by the geotechnical engineer. At least 40 percent of the fill soils shall pass through a No. 4 U.S. Standard Sieve. TRANSITION LOTS: Where transitions between cut and fill occur within the proposed building pad, the cut portion should be undercut a minimum of one foot below the base of the proposed footings and recompacted as structural backfill. In certain cases that would be addressed in the geotechnical report, special footing reinforcement or a combination of special fpoting reinforcement and undercutting may be required.