Loading...
14039 Night Song Ct Report Of Geotechnical Update-ENGINEERING, INC: July 13, 2015 Randy Tan c/o Mike Carpenter 14039 Night Song Ct. Chino Hills, CA 91709 Subject: Report of Geotechnical Update Proposed 2 -Story Addition 14039 Night Song Ct. Lot 15, Tract 13814-2 Chino Hills, CA 91709 Job No. 15-050 Gentlemen, Thank you for the opportunity for Duco Engineering, Inc., to provide geotechnical services for the proposed development. As always, it is our pleasure to serve as the geotechnical consultants for the design and construction of your residential project. The following presents an update to the prior geotechnical reporting performed on, and pertinent to, your lot in the Payne Ranch development of Chino Hills. The recommendations contained herein, and referenced in prior reports, should provide the necessary design values and criteria premised upon the site plan provided by Carpenter Designs. Please notify our office if any significant changes are made to the proposed development or site plan, as such changes may warrant further geotechnical comment or revision of the provided recommendations. Our office welcomes any further questions or comments you may have. It is our desire to serve our clients with the utmost efficiency and professionalism. Respectfully, D�niel D. Dufrenr�e President, Duco Engineering, Inc. 74175 Telephone Ave., Ste. K Chino, California 91710 1 909.594.7414 1 800.650.4910 1 office@ducoengineering.com Duco Engineering, Inc. Job No. 15-050 Paae 2 TABLE OF CONTENTS 1.0 INTRODUCTION 3 1.1 Proposed Construction 3 2.0 SITE CONDITIONS 3 2.1 Site Description 3 2.1 Subsurface Conditions 3 3.0 CONCLUSIONS AND RECOMMENDATIONS 3 3.2 Grading Recommendations 3 3.3 Expansive Soils 4 3.4 Foundation and Slab Recommendations 3.5 Retaining Walls 3.6 Corrosivity 3.6 Recommended Seismic Design Factors 3.7 Liquefaction Potential 3.9 Drainage 3.10 Landscape/Hardscape Recommendations 3.11 Temporary Excavations 5 5 5 6 6 6 6 7 4.0 CLOSURE 7 REFERENCES g Duco Engineering, Inc. Job No. 15-050 Page 3 1.0 INTRODUCTION This geotechnical update has been initiated to provide review and analysis pertinent to the latest proposed development project. Work undertaken for this review included office review of the subject references and relevant published geotechnical materials, in addition to a site reconnaissance. 1.1 Proposed Construction The proposed construction consists of a two-story addition consisting of living space overlying a 1600 square foot garage, with frame -and -stucco construction and floor slabs on grade. The currently proposed construction maintains relative consistency with the existing structures and developments. No basement is proposed. 2.0 SITE CONDITIONS 2.1 Site Description The subject lot resides on the southeast corner of Giant Forest Loop and Night Song Court, in the Payne Ranch development of the City of Chino Hills. As of the time of our site inspection, the lot is developed and fully landscaped, with an existing two-story residence on the site. No signs of instability or significant surficial erosion were apparent at the time of site inspection. The southerly adjacent lot varies in elevation by approximately +1.5 feet, while the easterly adjacent slope descends some 10-15 feet to the bounding property line. 2.1 Subsurface Conditions According to the referenced rough grading report by Pacific Soils Engineering, Inc., the building pad is composed of a compacted fill overlying siltstone and sandstone bedrock. Fill depths for the subject lot were reported to extend to a maximum of 35.3 feet. The easterly adjacent slope reportedly consists of a compacted fill slope partially toeing into a natural slope, while the side yard slopes are entirely composed of compacted fill. 3.0 CONCLUSIONS AND RECOMMENDATIONS Development of the site as currently proposed is considered to be feasible from a geotechnical engineering standpoint. The original findings of this firm and Pacific Soils Engineering, Inc. are still considered valid, except as otherwise noted herein. Additionally, this firm offers the following amendments and reiterations: 3.2 Grading Recommendations Due to disturbance resulting from the required demolition and removal of existing site improvements in the area of the proposed building footprint, all soils extending to 5 feet outside any and all proposed foundations (where possible) shall be overexcavated and recompacted to a depth of 2 feet below existing or proposed pad grade, whichever is deeper. The placement of this fill, as well as any additional structural fill to be placed onsite, shall be in accordance with the recommendations contained herein. Duco Engineering, Inc. Job No. 15-050 Page 4 Prior to any construction or site grading, any and all existing surface vegetation, debris and any unusable materials shall be stripped and hauled offsite. Elevation surveying shall be provided and completed prior to commencing grading operations. Before placing of any additional required structural fill, the exposed excavation/fill bottom shall be inspected and approved by this firm. The exposed surface shall then be thoroughly scarified to an minimum depth of 6 inches, moisture conditioned to provide near optimum moisture content, and precompacted to the minimum requirement of 90% of the maximum dry density, as determined by ASTM D1557. Any fill soils required to bring the building pad or any retaining wall backfill to the desired grade elevation shall be spread in maximum 6 to 8 inch loose lifts and shall be moisture conditioned to provide near optimum moisture content. Each lift shall then be compacted throughout to a minimum of 90% of the maximum dry density, as determined in accordance with ASTM test method D1557, by rolling with rubber -tired or track -mounted grading equipment, a sheepsfoot roller or other approved compaction equipment. All compacted fill shall be inspected and tested by a representative of this firm to insure that the minimum specified compaction requirement has been met. The minimum recommended surface gradient for newly constructed both cut and compacted fill slopes is 2:1. Fill slopes shall be overfilled a minimum of 12 inches and cut back to expose the compacted inner core, or shall be surface rolled at frequent intervals to insure 90% compaction out to the slope surface. No additional slopes are anticipated. 3.3 Expansive Soils Expansion testing was performed on the upper onsite soils. These soils were found to have a medium expansion potential. During grading procedures it is possible that those soils used to finish the pad that will directly affect the surrounding foundations will vary. An expansion test and revision of these recommendations may be necessary. With an obtained Expansion Index of 78 for the surficial soils to support the proposed residence, it is recommended that the structural design include minimum engineering construction measures as follows. Floor slabs shall be a full 4 inches thick and reinforced with #4 rebar at 18 inches on center. Slabs shall be cast on 4 inches of washed concrete sand with a 10 -mil vapor barrier in the center of the sand layer. Subgrade soils shall be moistened to a minimum to 120% of optimum moisture to a depth of 12 inches—regardless of in-place moisture content—prior to pouring concrete slabs. All foundations shall be reinforced with two #4 rebar in each the top and bottom of the footings. Additional reinforcement may be necessary at the discretion of the structural engineer. A grade beam shall be placed across�arags-t-y-pe-deer-opertara continuous footings shall be placed beneath all bearing walls. Footing beam spacing should not exceed 20 feet. With the exception of the garage slab, floor slabs shall be dowelled into the adjacent continuous footings at 36 inches on center. The garage slab shall be poured independently of the stem walls utilizing a positive felt expansion joint or similar approved material. The garage slab shall be saw cut into maximum 10 -foot sections each way, in order to control cracking. Duco Engineering, Inc. Job No. 15-050 Page -5 3.4 Foundation and Slab Recommendations All footings adjacent to any descending slope shall provide a minimum of 1 /3 the slope height as daylight setback, as measured to the interface of bedrock/compacted fill along the slope or the slope face, whichever is closer. All footings shall bear entirely in to approved compacted fill, and be a minimum of 24 inches deep for external footings, and 18 inches deep for internal footings, as previously recommended. Square footings shall have a minimum 18 -inch width, while continuous footings shall be a minimum of 15 inches wide. All footings shall have an allowable bearing capacity of 2500 psf. Passive resistance may be designed for 300 psf/ft with a maximum of 2500 psf. The coefficient of friction for concrete poured in direct contact with compacted fill or undisturbed bedrock may be taken as 0.35. Due to the medium expansion potential of the onsite soils, all foundations shall be reinforced with a minimum of two #4 bars in the top and bottom of the footings. Concrete slabs shall be a full 4 inches thick, reinforced with #4 bars, 18 inches center -to -center each direction, and cast on 4 inches of washed concrete sand with a 10 -mil vapor barrier in the center. Prior to pouring concrete, the subgrade soils should be moistened to 120% of optimum. 3.5 Retaining Walls Though not proposed, cantilevered retaining walls shall be backfilled with compacted onsite soils or similar (at the discretion of this firm) and shall be designed for an equivalent fluid pressure of 45 pcf level backfill, and 58 pcf when retaining a 2:1 slope; these values do not include any additional surcharge. All backfill soils shall be compacted to a minimum of 90% of the maximum dry density, as per the previously specified grading recommendations. Aforementioned foundation recommendations as previously given may be used for any retaining walls. 3.6 Corrosivity The onsite soils were tested to determine the amount of soluble sulfate within the soils supporting the proposed pool and the potential corrosive affects on the concrete to be used in the proposed construction. The results such testing is as follows: Soluble Sulfates: Calif. 417 71 ppm The soils are considered negligably corrosive to concrete based on the results of the soluble sulfate content. Concrete shall consist of Type I or 11 cement with a normal compressive strength. Duco Engineering, Inc. Job No. 15-050 Page 6 3.6 Recommended Seismic Design Factors The following parameters based on ASCE 7-10 may be used for the proposed structural design in accordance with Section 1613 of the CBC: Site Class D S, 2.192 g S1 0.790 g SDS 1.461 g Sol 0.790 g SMS 2.192 g SM, 1.185 g 3.7 Liquefaction Potential The depth to bedrock, clayey compacted nature of subgrade soils, and great depth to mapped water table levels make the possibility of liquefaction susceptibility very remote. 3.9 Drainage The completed onsite drainage shall be equivalent to that provided at the completion of the original site grading and in accordance with code requirements. A 3.0 -inch diameter pipe is deemed adequate to meet any onsite hydrology requirement. Any proposed subsurface drainpipe shall extend through the curb to the street for outlet into the gutter or other approved drainage device. Sand bags should be placed around any drain inlets or across exiting flow lines to provide temporary erosion control measures to minimize the amount of water -borne silt leaving the construction area until permanent landscaping and drainage systems can be installed to effectively provide onsite erosion control. 3.10 Landscape./Hardscape Recommendations The homeowner should be made aware that some additional amount of movement is common in expansive soil and is expected for the site, as well as most natural and man-made fill building pads. Rear yard improvements are not generally considered structural; however, we do recommend that walkways, patios, garden walls, and other landscape features be constructed with the ability to accommodate the effects of expansive soil. Separation of flatwork and distortion of other landscaping improvements may occur. Typical remediation includes construction joints, flexible pavers and structures, and additional reinforcement. The resident is responsible for proper maintenance, landscaping, and irrigation. Landscaping improvements must not cause surface water to collect adjacent to any foundation, causing saturated soils adjacent to the foundation. Planters adjacent to the building should be avoided or at least properly designed to reduce the amount of water penetration adjacent to footing subgrades, thereby reducing moisture related foundation damage. Any planned area drains should be recessed below grade to allow the free flow of water into the drain inlet. Flatwork and concrete walks should be at an elevation such that they will not obstruct the flow of surface water. Water should not be allowed to pond or flow at or over the top of any slope. Irrigation methods should promote uniformity of moisture. It should be noted that, upon our site inspection, overwatering was observed. Overwatering and underwatering must be avoided. Heavy irrigation and inadequate runoff gradients can create moisture problems. Maintaining Duco Engineering, Inc. Job No. 15-050 Page 7 adequate surface drainage and controlled irrigation will significantly reduce the potential for nuisance -type moisture issues. Additionally, it is recommended that all flatwork be constructed so that a minimum of 1/2 inch exists between the concrete flatwork and structures, such as residential buildings, retaining walls and sound privacy walls. 3.11 Temporary Excavations All excavations must comply with current OSHA standards, state, local and federal safety regulations. Excavations should not exceed three (3) feet then be sloped at an angle of 1:1. Surcharge loading, including stockpiled soil, should be placed 1:1 the total excavation height back from the top of the excavation. 4.0 CLOSURE The recommendations contained in this report are based on the results of our field observations and review of the referenced geotechnical reports combined with the principles of modern soil mechanics and sound engineering judgment. No other warranty is hereby expressed or implied. Should any unusual conditions be encountered during the site development, or should drastic design changes be contemplated, this firm shall be notified immediately in order that proper modifications to the recommendations contained herein may be made as deemed necessary. Should you have any questions with regard to this report or the recommendations contained herein, please contact this office. Respectfully submitted, F��..��ry,�< DUCO ENGINEERING, INC Approved by: �.0\ Q Fy g'C14�-M �1GP� Daniel D. bufre ne Frank C. Stillman rq OF C' GE No. 805 No / Collett Duco Engineering, Inc. Job No. 15-050 Page 8 REFERENCES Carpenter Designs. (2015, June 16). Project Plans, Tan Addition and Remodel, 14039 Night Song Court, Chino Hills, CA 91709. Plans. Pacific Soils Engineering, Inc. (1997, April 2).Project Grading Report, Lots 4 through 19 incl., Tract 13814-2, City of Chino Hills, California. Geotechnical Report.