CHRISTIAN WHEELER E N G I N E E R I N G

Transcription

1 CHRISTIAN WHEELER E N G I N E E R I N G REPORT OF PRELIMINARY GEOTECHNICAL INVESTIGATION PROPOSED HIGH STREET APARTMENTS A.P.N. S & HIGH STREET, LA MESA, CALIFORNIA PREPARED FOR N.T.C. DEVELOPMENT, INC EL CAJON BOULEVARD EL CAJON, CALIFORNIA PREPARED BY CHRISTIAN WHEELER ENGINEERING 3980 HOME AVENUE SAN DIEGO, CALIFORNIA H o m e A v e n u e S a n D i e g o, C A F A X

2 CHRISTIAN WHEELER E N G I N E E R I N G October 7, 2015 N.T.C. Development, Inc. CWE El Cajon Boulevard El Cajon, California Attention: Michael Martineau Subject: Report of Preliminary Geotechnical Investigation Proposed High Street Apartments, A.P.N. s & High Street, La Mesa, California Ladies and Gentlemen: In accordance with our proposal dated July 29, 2015, we have completed a preliminary geotechnical investigation for the subject project. We are presenting herein our findings and recommendations. In general, we found the subject property suitable for the proposed development, provided the recommendations provided herein are followed. The main geotechnical condition to affect the proposed construction is the presence of potentially compressible fill of variable thickness, which underlies the entire site. This condition will require special site preparation considerations as described in the attached report. If you have any questions after reviewing this report, please do not hesitate to contact our office. This opportunity to be of professional service is sincerely appreciated. Respectfully submitted, CHRISTIAN WHEELER ENGINEERING Jesse D. Bearfield, R.C.E. #84335 David R. Russell, C.E.G. #2215 JDB:drr:dba ntc-michael@sbcglobal.net H o m e A v e n u e S a n D i e g o, C A F A X

3 TABLE OF CONTENTS PAGE introduction and Project Description... 1 Project Scope... 2 Findings... 3 Site Description... 3 General Geology and Subsurface Conditions... 3 Geologic Setting and Soil Description... 3 Artificial Fill... 3 Metavolcanic Rock... 4 Groundwater... 4 Tectonic Setting... 4 Geologic Hazards... 5 Seismic Hazard... 5 Landslide Potential and Slope Stability... 5 Liquefaction... 6 Flooding... 6 Tsunamis... 6 Seiches... 6 Conclusions... 6 Recommendations... 7 Grading and Earthwork... 7 General... 7 Observation of Grading... 8 Clearing and Grubbing... 8 Site Preparation... 8 Debris... 8 Oversized Rock Placement... 8 Processing of Fill Areas... 9 Compaction and Method of Filling... 9 Temporary Cut Slopes... 9 Surface Drainage... 9 Grading Plan Review Conventional Shallow Foundations General Dimensions Footing Reinforcing Lateral Load Resistance Settlement Characteristics Expansive Characteristics Foundation Plan Review Foundation Excavation Observation: On-Grade Slabs General Interior Slab Under-Slab Vapor Retarders Exterior Concrete Flatwork Earth Retaining Walls Foundations Passive Pressures CWE Proposed High Street Apartments A.P.N. s & High Street, La Mesa, California

4 Active Pressures Waterproofing and Wall Drainage Systems Backfill Preliminary Pavement Sections General Preliminary Asphalt Concrete Pavements Concrete Pavements Limitations Review, Observation and Testing Uniformity of Conditions Change in Scope Time Limitations Professional Standard Client's Responsibility Field Explorations Laboratory Testing TABLES Table I: CBC 2013 Edition Seismic Design Parameters... 5 Table II: Preliminary Asphalt Concrete Pavement Section Table III: Concrete Pavement Design Parameters Table IV: Minimum Concrete Pavement Thickness FIGURES Figure 1 Site Vicinity Map, Follows Page 1 PLATES Plate 1 Site Plan and Geotechnical Map Plate 2 Oversize Rock Placement Plate 3 Retaining Wall Subdrain Detail APPENDICES Appendix A Test Trench Logs Appendix B Laboratory Test Results Appendix C References Appendix D Recommended Grading Specifications General Provisions CWE Proposed High Street Apartments A.P.N. s & High Street, La Mesa, California

5 CHRISTIAN WHEELER E N G I N E E R I N G REPORT OF PRELIMINARY GEOTECHNICAL INVESTIGATION PROPOSED HIGH STREET APARTMENTS A.P.N. S & HIGH STREET, LA MESA, CALIFORNIA INTRODUCTION AND PROJECT DESCRIPTION This report presents the results of a preliminary geotechnical investigation performed for proposed apartment development to be constructed at a vacant lot located adjacent to and north of High Street in the city of La Mesa, California. The following Figure Number 1 presents a vicinity map showing the location of the project. We understand that it is proposed to construct two or three, two-story apartment structures with partially subterranean garages and associated improvements. The garage level finished floors are expected to be about 5 feet below proposed site grades with the 1 st level proposed to be about 5 feet above proposed grades. We anticipate that subterranean portions of the apartment structures level will be of masonry construction and will include a concrete floor slab. The above ground portions of the structures are anticipated to be of conventional, wood frame construction. We anticipate that the structures will be supported by conventional shallow foundations. Grading to accommodate the proposed improvements is expected to consist of cuts and fills of less than five feet from existing grades. To assist in the preparation of this report, we were provided with an topographic map of the site prepared by San-Lo Aerial Surveys, with a fly date of October 27, A copy of this plan was used as a base map for our geologic mapping, and is included herein as Plate Number 1. This report has been prepared for the exclusive use of N.T.C. Development, Inc. and its consultants for specific application to the project described herein. Should the project be modified, the conclusions and recommendations presented in this report should be reviewed by Christian Wheeler Engineering for conformance with our recommendations and to determine whether any additional subsurface investigation, laboratory testing and/or recommendations are necessary. Our professional services have been performed, our findings obtained, and our recommendations prepared in accordance with generally accepted engineering principles and practices. This warranty is in lieu of all other warranties, expressed or implied H o m e A v e n u e S a n D i e g o, C A F A X

6 SITE VICINITY OpenStreetMap contributors PROJECT SITE DATE: OCTOBER 2015 BY: SRD PROPOSED HIGH STREET APARTMENTS A.P.N.'S & HIGH STREET, LA MESA, CALIFORNIA JOB NO.: FIGURE NO.: 1 CHRISTIAN WHEELER E N G I N E E R I N G

7 CWE October 7, 2015 Page 2 PROJECT SCOPE Our preliminary geotechnical investigation consisted of surface reconnaissance, subsurface exploration, obtaining representative soil samples, laboratory testing, analysis of the field and laboratory data and review of relevant geologic literature. Our scope of service did not include assessment of hazardous substance contamination, recommendations to prevent floor slab moisture intrusion or the formation of mold within the structure, an evaluation of the gross and surficial stability of the existing rock cliffs, nor does it include analysis of the global stability of the site and/or surrounding areas, or any other services not specifically described in the scope of services presented below. More specifically, our intent was to provide the services listed below. Explore the subsurface conditions of the site to the depths influenced by the proposed construction. Evaluate, by laboratory tests and our past experience with similar soil types, the engineering properties of the various strata that may influence the proposed construction, including bearing capacities, expansive characteristics, settlement potential, and corrosive characteristics. Describe the general geology at the site including possible geologic hazards that could have an effect on the proposed construction, and provide the seismic design parameters as required by the 2013 edition of the California Building Code. Address potential construction difficulties that may be encountered due to soil conditions, groundwater or geologic hazards, and provide recommendations concerning these problems. Develop soil engineering criteria for site preparation and grading. Provide temporary cut slope recommendations, as necessary. Recommend an appropriate foundation system for the type of structures anticipated and develop soil engineering design criteria for the recommended foundation design. Provide geotechnical design parameters for the construction or restrained and unrestrained retaining walls. Prepare this report, which includes, in addition to our conclusions and recommendations, a plot plan showing the aerial extent of the geological units and the locations of our exploratory borings, exploration logs, and a summary of the laboratory test results. Although a test for the presence of soluble sulfates within the soils that may be in contact with reinforced concrete was performed as part of the scope of our services, it should be understood Christian Wheeler Engineering does not practice corrosion engineering. If such an analysis is considered necessary, we recommend that the client retain an engineering firm that specializes in this field to consult with them on this

8 CWE October 7, 2015 Page 3 matter. The results of the test should only be used as a guideline to determine whether additional testing and analysis is necessary. FINDINGS SITE DESCRIPTION The subject site is an abandoned rock quarry, identified as Assessor s Parcel Numbers and The property is located adjacent to and north of High Street in La Mesa, California. The site is currently vacant and was previously used as a rock quarry sometime before the 1940 s. The property is bound by High Street to the south, vacant lots to the east and west, and developed residential lots to the north. Topographically, the site is characterized by a gently southeastern sloping pad that is surrounded by steep cliffs on the north, west and east sides. Based on the topographic map elevations, cliff heights range from about 30 feet to 135 feet. Numerous boulders are present along the base of the cliff and comprise a sloughed pile at the north side of the pad. The pad area slopes from an elevation of about 580 feet to about 550 feet from the north to south toward High Street. On-site vegetation consists of grasses and shrubs. GENERAL GEOLOGY AND SUBSURFACE CONDITIONS GEOLOGIC SETTING AND SOIL DESCRIPTION: The subject site is located in the Foothills Physiographic Province of San Diego County. Based upon the results of our subsurface exploration, analysis of readily available, pertinent geologic literature, and review of the referenced documents, it was determined that the project site is underlain by Mesozoic-age metavolcanic rock and artificial fill of varying thickness. These materials are described below. ARTIFICIAL FILL (Qaf): Man-placed fill soils were encountered within each of our six exploratory trenches. The thickness of the fill encountered in our trenches ranged from approximately 14 feet in trenches T-1 and T-2, to about 16 feet in trench T-5. The fill extended beyond the bottom of trenches for T-3, T-4, and T-6. The depth of the old existing fill was found to extend beyond the maximum excavation depth of 18 feet in T-4. The encountered fill materials generally consisted of orangish-brown clayey sand/silty gravel (SC/GM), dark brown clayey sand (SC), orangish-brown silty gravel (GM), and brown to orangish-brown, silty sand (SM). The artificial fills were found to be generally loose to medium dense, and was dry to damp. This material was found to include cobbles and boulders up to about 2 feet in length and minor debris consisting of pipes, paper, cloth, wood, and concrete and asphalt concrete.

9 CWE October 7, 2015 Page 4 METAVOLCANIC ROCK (Mzu): Mesozoic-age metavolcanic rock, commonly referred to as the Santiago Peak Volcanics, was encountered below the fill in trenches T-1, T-2 and T-5 and is anticipated to underlie the fill soils throughout the site. Within our trenches, the metamorphosed volcanic rock primarily consisted of olive to dark brown crystalline rock, that when excavated or blasted, breaks down to angular sandy gravel, cobble, and boulders. GROUNDWATER: No groundwater or seepage was encountered in our subsurface explorations and we do not expect any groundwater related conditions during or after the proposed construction provided that proper drainage is maintained at the site. It should, however be recognized that minor groundwater seepage problems might occur after development of a site even where none were present before development. These are usually minor phenomena and are often the result of an alteration in drainage patterns and/or an increase in irrigation water. Given the anticipated geologic conditions of the site following development, resulting in artificial fill over metavolcanic rock, such problems can be most effectively corrected during site remedial grading and also on an individual basis if and when they occur. TECTONIC SETTING: No faults are known to traverse the subject site. However, it should be noted that much of Southern California, including the San Diego County area, is characterized by a series of Quaternary-age fault zones that consist of several individual, en echelon faults that generally strike in a northerly to northwesterly direction. Some of these fault zones (and the individual faults within the zone) are classified as active according to the criteria of the California Division of Mines and Geology. Active fault zones are those that have shown conclusive evidence of faulting during the Holocene Epoch (the most recent 11,000 years). The Division of Mines and Geology used the term potentially active on Earthquake Fault Zone maps until 1988 to refer to all Quaternary-age (last 1.6 million years) faults for the purpose of evaluation for possible zonation in accordance with the Alquist-Priolo Earthquake Fault Zoning Act and identified all Quaternary-age faults as potentially active except for certain faults that were presumed to be inactive based on direct geologic evidence of inactivity during all of Holocene time or longer. Some faults considered to be potentially active would be considered to be active but lack specific criteria used by the State Geologist, such as sufficiently active and well-defined. Faults older than Quaternary-age are not specifically defined in Special Publication 42, Fault Rupture Hazard Zones in California, published by the California Division of Mines and Geology. However, it is generally accepted that faults showing no movement during the Quaternary period may be considered to be inactive. The City of San Diego guidelines indicate that since the beginning of the Pleistocene Epoch marks the boundary between potentially active and inactive faults, unfaulted Pleistocene-age deposits are accepted as evidence that a fault may be considered to be inactive.

10 CWE October 7, 2015 Page 5 A review of available geologic maps indicates that the nearest active fault zone is the Rose Canyon Fault Zone (RCFZ), located approximately 9 miles west of the site. Other active fault zones in the region that could possibly affect the site include the Coronado Bank Fault Zone to the southwest; the Newport-Inglewood and Palos Verdes Fault Zones to the northwest; and the Elsinore, Earthquake Valley, San Jacinto, and San Andreas Fault Zones to the northeast. GEOLOGIC HAZARDS SEISMIC HAZARD: A likely geologic hazard to affect the site is ground shaking as a result of movement along one of the major active fault zones mentioned in the Tectonic Setting section of this report. Per Chapter 16 of the 2013 California Building Code (CBC), the Maximum Considered Earthquake (MCE) ground motion is that considered to have a two percent probability of being exceeded in 50 years. Figures (3) and (4) of the CBC present regional MCE spectral accelerations for short (0.2 sec.) and long (1.0 sec.) periods, respectively, based on a soil Site Class B (CBC Table ) and a structural damping of five percent. For the subject site, we expect that correlation with field penetration resistance values will indicate that the upper 100 feet of geologic subgrade can be characterized as Site Class D. In this case, the mapped MCE spectral accelerations are modified using the Site Coefficients presented in Tables (1) and (2). The modified MCE spectral accelerations are then multiplied by two-thirds in order to obtain the design spectral accelerations. These seismic design parameters for the subject site (32.752, ), based on Chapter 16 of the CBC, are presented in Table I below. TABLE I: CBC 2013 EDITION SEISMIC DESIGN PARAMETERS CBC Chapter 16 Section Seismic Design Parameter Recommended Value Table Soil Site Class D Figure (3) Mapped Spectral Acceleration for Short Periods (0.2 sec), S s g Figure (4) Mapped Spectral Acceleration for 1.0 Sec Periods (1.0 sec), S g Table (1) Site Coefficient, F a Table (2) Site Coefficient, F v Section S MS = MCE Spectral Response at 0.2 sec. = (S s)(f a) g Section S M1 = MCE Spectral Response at 1.0 sec. = (S 1)(F v) g Section S DS = Design Spectral Response at 0.2 sec. = 2/3(S MS) g Section S D1 = Design Spectral Response at 1.0 sec. = 2/3(S M1) g LANDSLIDE POTENTIAL AND SLOPE STABILITY: The Relative Landslide Susceptibility and Landslide Distribution Map of the La Mesa Quadrangle prepared by the California Division of Mines and Geology indicates that the site is situated within Relative Landslide Susceptibility Area 3-1. Area 3 is considered to be generally susceptible to slope failures; Subarea 3-1 includes areas that contain slopes at or near their

11 CWE October 7, 2015 Page 6 stability limits due to a combination of steep slope angles and weak underlying materials. Although slopes within Subarea 3-1 are not known to contain landslides, they may be expected to fail when adversely modified. Given the gently sloping topography of the areas within and adjacent to the site, the risk of slope failures at or adjacent to the subject site is considered to be low. We understand that the proposed construction includes the construction of two or three two-story apartment buildings at the subject site. It has been discussed that these structures may be located a distance of about 20 feet away from the base of the rock cliffs. We further understand it is proposed that the existing rock cliffs will not be altered or affected during the construction of site improvements. Our authorized scope of service did not include an evaluation of the gross and surficial stability of the existing rock cliffs, nor did it include analysis of the global stability of the site and/or surrounding areas. We understand that any required analysis of the gross and surficial stability of the rock cliffs including the potential for rock falls will be performed by others. If the project s reviewing agency does not require analysis of the existing rock slopes along the west, north, and east sides of the site, the client should contact our firm for further discussion. LIQUEFACTION: The near-surface soils encountered at the site are not considered susceptible to liquefaction due to such factors as depth to the groundwater table, soil density and grain-size distribution. FLOODING: The site is located outside the boundaries of both the 100-year and the 500-year floodplains according to the maps prepared by the Federal Emergency Management Agency. TSUNAMIS: Tsunamis are great sea waves produced by submarine earthquakes or volcanic eruptions. Due to the site s elevation and location, the site will not be affected by tsunamis. SEICHES: Seiches are periodic oscillations in large bodies of water such as lakes, harbors, bays or reservoirs. Due to the site s location, it will not be affected by seiches. CONCLUSIONS It is our professional opinion and judgment that no geotechnical conditions exist within the subject site that would preclude the construction of the proposed development, provided the recommendations presented herein are followed. The main geotechnical conditions affecting the proposed construction are the presence of relatively deep, potentially compressible fills soils of variable depth and the stability and rock fall potential of the steep slopes bounding the site. The presence of the existing old fills will require special site preparation considerations as described in the recommendations section of the report. Assessment of and

12 CWE October 7, 2015 Page 7 recommendations to mitigate any potentially hazardous conditions including slope stability and rock fall potential at or adjacent to the subject site should be evaluated by others. The site was found to be underlain by variable density, potentially compressible fill materials extending to variable depths. In general, the fill increases in depth from north to south and from west to east across the site. The depths of the fills were found to be 14 feet, 14 feet, and 16 feet, within test trenches T-1, T-2, and T-5, respectively. The fills extended deeper than the bottom of our test trenches excavations for T-3, T-4, and T-6 and depth of the fill was found to extend beyond the maximum excavation depth of 18 feet in T-4. The existing fill soils are considered unsuitable, in their present condition, for the support of settlement-sensitive improvements. This condition will require special site preparation, considerations and requirements as described herein. The site is located in an area that is relatively free of geologic hazards that will have a significant effect on the proposed construction. The most likely geologic hazard that could affect the site after development is ground shaking due to seismic activity along one of the regional active faults. However, construction in accordance with the requirements of the most recent edition of the California Building Code and the local governmental agencies should provide a level of life-safety suitable for the type of development proposed. The final project plans should be submitted to this office for review in order to ascertain that the geotechnical recommendations remain applicable to the final plan and that no additional recommendations are needed due to changes in the anticipated development. Additionally, while analysis of the surficial and global stability of the existing rock cliffs is not within our project scope, we do recommend that preventative measures be considered for rock fall potential including proper setbacks, rock fall barriers, fences or drapes. We understand that any required analysis of the gross and surficial stability of the rock cliffs including the potential for rock falls will be performed by others, and that the finding of such analyses will be made available for our review. RECOMMENDATIONS GRADING AND EARTHWORK GENERAL: All grading should conform to the guidelines presented in Appendix J of the California Building Code, the minimum requirements of the City of La Mesa, and the recommended Grading Specifications and Special Provisions attached hereto, except where specifically superseded in the text of this report. Prior to

13 CWE October 7, 2015 Page 8 grading, a representative of Christian Wheeler Engineering should be present at the pre-construction meeting to provide additional grading guidelines, if necessary, and to review the earthwork schedule. OBSERVATION OF GRADING: Continuous observation by the Geotechnical Consultant is essential during the grading operation to confirm conditions anticipated by our investigation, to allow adjustments in design criteria to reflect actual field conditions exposed, and to determine that the grading proceeds in general accordance with the recommendations contained herein. CLEARING AND GRUBBING: Site preparation should begin with the removal of vegetation, debris and other deleterious materials from the site. This should include all significant root material. The resulting materials should be disposed of off-site in a legal dumpsite. SITE PREPARATION: In order to support the proposed apartment structures on conventional shallow foundations, the existing fill materials will need to be removed in their entirety and recompacted. The removals should extend down to the contact with competent metavolcanic rock. Laterally, the removals should extend at least 5 feet outward of the proposed building footprints and associated improvements or equivalent to the depth of the excavation, whichever is greater. The bottom of all excavations should be approved by our project geologist, engineer, or technician supervisor prior to placing fills or constructing improvements. The fill material is expected to have a thickness of about 10 feet to in excess of 18 feet across the project site. DEBRIS: Various concrete, asphalt, metal, and organic debris was encountered within our trenches during our investigation. All debris encountered during grading should be removed from new fill materials and properly disposed of off-site. Concrete debris without protruding rebar may be included in new fill placemntas described in the Oversized Rock Placement section below. OVERSIZED ROCK PLACEMENT: For the purpose of placement in general compacted fill, oversized rock is defined as rock or concrete exceeding 12 inches in maximum dimension. However, for placement within four feet from finish pad grade it is defined as rock or concrete fragments exceeding 6 inches in maximum dimension. For retaining wall and trench backfill use, oversized material is defined as having a maximum dimension of 3 inches. Oversized material should be anticipated throughout the existing fills onsite. Oversized material may be broken into smaller pieces, utilized for landscaping purposes or placed in accordance with the recommendations contained in the Compaction and Method of Filling section of this report, Plate No. 2, or City of La Mesa specifications, whichever are more stringent.

14 CWE October 7, 2015 Page 9 PROCESSING OF FILL AREAS: Prior to placing any new fill soils or constructing any new improvements in areas that have been cleaned out to receive fill and approved by the geotechnical consultant or his representative, any exposed soils should be scarified to a depth of 12 inches, moisture conditioned, and compacted to at least 90 percent relative compaction. COMPACTION AND METHOD OF FILLING: All structural fill and backfill material placed at the site should be compacted to a relative compaction of at least 90 percent of maximum dry density as determined by ASTM Laboratory Test D1557. Fills should be placed at or slightly above optimum moisture content, in lifts six to eight inches thick, with each lift compacted by mechanical means. Fills should consist of approved earth material, free of trash or debris, roots, vegetation, or other materials determined to be unsuitable by our soil technicians or project geologist. Fill material should be free of rocks or lumps of soil in excess of twelve inches in maximum dimension; however, this should be reduced to six inches within four feet of finish grade. All utility trench backfill 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 the materials 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 or operation. TEMPORARY CUT SLOPES: Based on the anticipated fill thickness, we anticipate that temporary excavations of up to about 20 feet or greater in depth will be required. Temporary cut slopes up to 25 feet in height can be excavated at an inclination of 1.0 to 1.0 (horizontal to vertical) or flatter. Our firm should be contacted to observe all temporary cut slopes during grading to ascertain that no unforeseen adverse conditions exist. No surcharge loads such as foundation loads, or soil or equipment stockpiles, vehicles, etc. should be allowed within a distance from the top of temporary slopes equal to half the slope height. The contractor is solely responsible for designing and constructing stable, temporary excavations and will need to shore, slope, or bench the sides of trench excavations as required to maintain the stability of the excavation sides. The contractor s competent person, as defined in the OSHA Construction Standards for Excavations, 29 CFR, Part 1926, should evaluate the soil exposed in the excavations as part of the contractor s safety process. Temporary cut slopes should be constructed in accordance with the recommendations presented in this section. In no other case should slope height, slope inclination, or excavation depth, including utility trench excavation depth, exceed those specified in local, state, and federal safety regulations. SURFACE DRAINAGE: The ground around the proposed structures should be graded so that surface water flows rapidly away from the structure without ponding. In general, we suggest that the ground adjacent to

15 CWE October 7, 2015 Page 10 structure slope away at a gradient of at least 2 percent. Densely vegetated areas where runoff can be impaired should have a minimum gradient of 5 percent within the first 5 feet from the structure. In our opinion, the project site is not suitable for storm water infiltration/percolation BMPs. We recommend that pervious pavements, bio retention areas, and bio swales be lined in such a manner as to prevent the storm water from infiltrating into the underlying soils and should be connected via pipes to the storm drain system. GRADING PLAN REVIEW: The final grading plans should be submitted to this office for review in order to ascertain that the geotechnical recommendations remain applicable to the final plan and that no additional recommendations are needed due to changes in the anticipated development. Our firm should be notified of changes to the proposed project that could necessitate revisions of or additions to the information contained herein. CONVENTIONAL SHALLOW FOUNDATIONS GENERAL: Provided the existing fill soils are removed and recompacted as recommended above, the proposed apartment structures and associated improvements may be supported by conventional shallow foundations founded in new compacted fill soil. The following recommendations are considered the minimum based on the anticipated soil conditions and are not intended to be in lieu of structural considerations. All foundations should be designed by a qualified structural engineer. DIMENSIONS: Conventional spread footings supporting the proposed apartment structures should be embedded at least 24 inches below the lowest adjacent finish grade. Continuous footings should have a minimum width of 12 inches for the buildings and 24 inches for retaining walls. Isolated footings should have a minimum width of 24 inches. Foundations with these dimensions can be designed for an allowable soil bearing pressure of 2,000 pounds per square foot. This bearing pressure can be increased by an additional 500 psf and 300 psf for each additional foot of embedment and width, respectively, up to a maximum of 4,000 psf. The allowable bearing capacity may be increased by one-third for combinations of temporary loads, such as those due to wind or seismic loads. Footings located adjacent to slopes should be extended to a depth such that a minimum horizontal distance of 10 feet exists between the bottom, outside edge of the footing and the face of the slope. New spread footings supporting minor at-grade structures such as trash enclosures should be embedded at least 18 inches below the finish pad grade. Continuous and isolated footings should have minimum widths of 12 and 24 inches, respectively. New spread footings supporting site retaining walls should be embedded at least 18 inches below the finish pad grade and should have a minimum width of 24 inches. For these

16 CWE October 7, 2015 Page 11 improvements, footings with the above recommended minimum dimensions may be designed for an allowable soil bearing pressure of 2,000 pounds per square foot. The allowable bearing capacities may be increased by one-third for combinations of temporary loads, such as those due to wind or seismic loads. FOOTING REINFORCING: Reinforcement requirements for conventional foundations should be provided by a structural engineer. However, based on the existing soil conditions, we recommend that the minimum reinforcing for new continuous footings consist of at least two No. 5 bars positioned near the bottom of the footing and at least two No. 5 bars positioned near the top of the footing. LATERAL LOAD RESISTANCE: Lateral loads against foundations may be resisted by friction between the bottom of the footing and the supporting soil, and by the passive pressure against the footing. The coefficient of friction between concrete and soil may be considered to be The passive resistance may be considered to be equal to an equivalent fluid weight of 350 pounds per cubic foot. This assumes the footings are poured tight against undisturbed soil. If a combination of the passive pressure and friction is used, the friction value should be reduced by one-third. SETTLEMENT CHARACTERISTICS: Provided the recommendations presented in this report are followed, the anticipated total and differential foundation settlement is expected to be less than about 1 inch and 1 inch over 40 feet, respectively. It should be recognized that minor cracks normally occur in concrete slabs and foundations due to shrinkage during curing or redistribution of stresses, therefore some cracks should be anticipated. Such cracks are not necessarily an indication of excessive vertical movements. EXPANSIVE CHARACTERISTICS: The foundation soils are expected to have a low expansive potential (EI between 21 and 50). The recommendations presented in this report reflect this condition. FOUNDATION PLAN REVIEW: The final foundation plan and accompanying details and notes should be submitted to this office for review. The intent of our review will be to verify that the plans used for construction reflect the minimum dimensioning and reinforcing criteria presented in this section and that no additional criteria are required due to changes in the foundation type or layout. It is not our intent to review structural plans, notes, details, or calculations to verify that the design engineer has correctly applied the geotechnical design values. It is the responsibility of the design engineer to properly design/specify the foundations and other structural elements based on the requirements of the structure and considering the information presented in this report.

17 CWE October 7, 2015 Page 12 FOUNDATION EXCAVATION OBSERVATION: All foundation excavations should be observed by the geotechnical consultant prior to placing reinforcing steel or formwork in order to determine if the foundation recommendations presented herein are followed. All footing excavations should be excavated neat, level, and square. All loose or unsuitable material should be removed prior to the placement of concrete. ON-GRADE SLABS GENERAL: It is our understanding that the floor system of the proposed apartment structures will consist of concrete slabs-on-grade. The following recommendations are considered the minimum slab requirements based on the soil conditions and are not intended to be in lieu of structural considerations. INTERIOR SLAB: We recommend that the interior slab-on-grade floor be at least 5 inches thick (actual) and be reinforced with at least No. 4 bars spaced at 18 inches on center each way. The reinforcing bars should extend at least 12 inches into the foundations and should be supported by chairs and be positioned in the center of the slab. UNDER-SLAB VAPOR RETARDERS: Steps should be taken to minimize the transmission of moisture vapor from the subsoil through the interior slabs where it can potentially damage the interior floor coverings. Local industry standards typically include the placement of a vapor retarder, such as plastic, in a layer of coarse sand placed directly beneath the concrete slab. Two inches of sand are typically used above and below the plastic, respectively. The vapor retarder should be at least 15-mil Stegowrap or similar material with sealed seams and should extend at least 12 inches down the sides of the interior and perimeter footings. The sand should have a sand equivalent of at least 30, and contain less than 10% passing the Number 100 sieve and less than 5% passing the Number 200 sieve. The membrane should be placed in accordance with the recommendation and consideration of ACI 302, Guide for Concrete Floor and Slab Construction and ASTM E1643, Standards Practice for Installation of Water Vapor Retarder Used in Contact with Earth or Granular Fill Under Concrete Slabs. It is the flooring contractor s responsibility to place floor coverings in accordance with the flooring manufacturer specifications. EXTERIOR CONCRETE FLATWORK: Exterior concrete on-grade slabs should have a minimum thickness of 4 inches and be reinforced with at least No. 3 bars placed at 18 inches on center each way. All slabs should be provided with weakened plane joints in accordance with the American Concrete Institute (ACI) guidelines. Alternative patterns consistent with ACI guidelines can also be used. A concrete mix with a 1-inch maximum aggregate size and a water/cement ratio of less than 0.6 is recommended for exterior slabs.

18 CWE October 7, 2015 Page 13 Lower water content will decrease the potential for shrinkage cracks. Both coarse and fine aggregate should conform to the latest edition of the Standard Specifications for Public Works Construction ( Greenbook ). Special attention should be paid to the method of concrete curing to reduce the potential for excessive shrinkage and resultant random cracking. It should be recognized that minor cracks occur normally in concrete slabs due to shrinkage. Some shrinkage cracks should be expected and are not necessarily an indication of excessive movement or structural distress. EARTH RETAINING WALLS FOUNDATIONS: Foundations for retaining walls can be designed in accordance with the foundation recommendations previously presented. PASSIVE PRESSURES: The passive pressure for the anticipated foundation soils may be considered to be 300 pounds per square foot per foot of depth. The upper foot of embedment should be neglected when calculating passive pressures, unless the foundation abuts a hard surface such as a concrete slab. The passive pressure may be increased by one-third for seismic loading. The coefficient of friction for concrete to soil may be assumed to be 0.30 for the resistance to lateral movement. When combining frictional and passive resistance, the friction should be reduced by one-third. ACTIVE PRESSURES: The active soil pressure for the design of unrestrained earth retaining structures with level backfill surface may be assumed to be equivalent to the pressure of a fluid weighing 40 pounds per cubic foot. In the design of walls restrained from movement at the top (non-yielding walls), the at-rest soil pressure may be assumed to be equivalent to the pressure of a fluid weighing 60 pounds per cubic foot, provided there is a level backfill surface. An additional 15 pounds per cubic foot can be added to the above values for 2:1 (H:V) sloping backfill. Thirty percent of any area surcharge placed adjacent to the retaining wall may be assumed to act as a uniform horizontal pressure against the wall. Special cases such as a combination of shored and sloping temporary slopes, or other surcharge loads not described above, may require an increase in the design values recommended above. These conditions should be evaluated by the project geotechnical engineer on a case-bycase basis. If any other loads are anticipated, the Geotechnical Consultant should be contacted for the necessary increase in soil pressure. All values are based on a drained backfill condition. Seismic lateral earth pressures may be assumed to equal an inverted triangle starting at the bottom of the wall with the maximum pressure equal to 9H pounds per square foot (where H = wall height in feet) occurring at the top of the wall.

19 CWE October 7, 2015 Page 14 WATERPROOFING AND WALL DRAINAGE SYSTEMS: The need for waterproofing should be evaluated by others. If required, the project architect should provide (or coordinate) waterproofing details for the retaining walls. The design values presented above are based on a drained backfill condition and do not consider hydrostatic pressures. Unless hydrostatic pressures are incorporated into the design, the retaining wall designer should provide a detail for a wall drainage system. Typical retaining wall drain system details are presented as Plate No. 3 of this report for informational purposes. Additionally, outlets points for the retaining wall drain system should be coordinated with the project civil engineer. BACKFILL: All retaining wall backfill should be compacted to at least 90 percent relative compaction. Expansive or clayey soils should not be used for backfill material. Retaining walls should not be backfilled until the masonry/concrete has reached an adequate strength. PRELIMINARY PAVEMENT SECTIONS GENERAL: We expect that new pavement will be installed for new access driveways and parking areas leading to the proposed apartment structures. The following presents preliminary sections for asphalt concrete (AC) or Portland Cement Concrete (PCC) construction. The pavement sections provided in Table II and Table IV should be considered preliminary and should be used for planning purposes only. Final pavement designs should be determined after R-value tests have been performed in the actual subgrade material in place after grading. Presuming the grading recommendations presented previously are followed, we have assumed a subgrade R-Value of 25 for preliminary planning purposes. The Traffic Index and Traffic Categories shown below are also assumed. The client and/or project civil engineer should determine whether these assumed values are appropriate for the traffic conditions. PRELIMINARY ASPHALT CONCRETE PAVEMENTS: We expect that new streets and driveways will primarily support passenger vehicles with only occasional heavily loaded vehicles. The preliminary asphalt concrete pavement sections were calculated using the Caltrans design method using an assumed Traffic Index of 6.0 and 4.5 for driveways and parking areas, respectively. TABLE II: PRELIMINARY ASPHALT CONCRETE PAVEMENT SECTION Traffic Pavement Base Base Subgrade Pavement Type Index Thickness Thickness Material Compaction Asphalt Concrete Main Driveways in. 9.5 in. CAB or Class II 95% in upper 12 Parking Areas in. 5.0 in. CAB or Class II 95% in upper 12

20 CWE October 7, 2015 Page 15 Prior to placing the base material beneath asphalt concrete pavements, the subgrade soil should be scarified to a depth of 12 inches and compacted to at least 95 percent of its maximum dry density at a moisture content one to three percent above optimum. The base material could consist of Class II Aggregate Base. The Class II Aggregate Base should conform to requirements set forth in Section 26 of the Standard Specifications for California Department of Transportation. As an alternate, the base material for the pavements may consist of Crushed Miscellaneous Base (recycled base material) which conforms to the requirements set forth in Section of the Standard Specifications for Public Works Construction. It should be noted, however, that Crushed Miscellaneous Base material has lower durability characteristics than Crushed Aggregate Base or Class II Aggregate Base, which may result in a shorter pavement life. As such, the owner of the project should approve the use of this material for the pavement base. All aggregate base material should be compacted to at least 95 percent of its maximum dry density as determined by ASTM Test D1557. Asphalt concrete shall be compacted to attain at least 95 percent relative compaction. CONCRETE PAVEMENTS: Portland cement concrete (PCC) pavement thickness can be determined from Table IV below. The PCC pavement section was determined in general accordance with the procedure recommended within the American Concrete Institute report ACI-330R-08 Guide for Design and Construction of Concrete Parking Lots using the parameters listed in following Table III. TABLE III: CONCRETE PAVEMENT DESIGN PARAMETERS Design Parameter Design Value Modulus of Subgrade Reaction, k 125 pci Modulus of Rupture for Concrete, M R 500 psi Traffic Category (Main Driveways) A (ADTT = 25) ADTT = Average Daily Truck Traffic. Trucks defined as vehicles with at least six wheels. Based on the design parameters summarized in Table III, the PCC pavements should have the minimum thicknesses shown in Table IV. TABLE IV: MINIMUM CONCRETE PAVEMENT THICKNESS Pavement Use Main Driveway Parking Areas Thickness 6.0 in. 5.0 in.

21 CWE October 7, 2015 Page 16 Prior to placing concrete pavement, the subgrade soils should be scarified to a depth of 12 inches and compacted to at least 90 percent of their maximum dry density at a moisture content one to three percent above optimum. Concrete pavement construction should comply with the requirements set forth in Sections and of the Standard Specifications for Public Works Construction (concrete Class 560-C- 3250). Portland Cement Concrete slabs are recommended in front of each trash enclosures. These slabs should have a minimum thickness of 7.0 inches of concrete and should be underlain by at least 4 inches of base and minimum slab reinforcement should consist of at least No. 4 bars placed at 16 inches on center each way. A similar concrete section may be used inside the enclosures. Concrete slab construction should comply with the requirements set forth in Sections and of the Standard Specifications for Public Works Construction. The concrete materials should be a Class 560-C-3250 mix. All slabs should be provided with weakened plane joints in accordance with the American Concrete Institute (ACI) guidelines. Special attention should be paid to the method of concrete curing to reduce the potential for excessive shrinkage cracking. It should be recognized that minor cracks occur normally in concrete slabs due to shrinkage. Some shrinkage cracks should be expected and are not necessarily an indication of excessive movement or structural distress. LIMITATIONS REVIEW, OBSERVATION AND TESTING The recommendations presented in this report are contingent upon our review of final plans and specifications. Such plans and specifications should be made available to the geotechnical engineer and engineering geologist so that they may review and verify their compliance with this report and with the California Building Code. It is recommended that Christian Wheeler Engineering be retained to provide continuous soil engineering services during the earthwork operations. This is to verify compliance with the design concepts, specifications or recommendations and to allow design changes in the event that subsurface conditions differ from those anticipated prior to start of construction. UNIFORMITY OF CONDITIONS The recommendations and opinions expressed in this report reflect our best estimate of the project requirements based on an evaluation of the subsurface soil conditions encountered at the subsurface exploration locations and on the assumption that the soil conditions do not deviate appreciably from those encountered. It should be

22 CWE October 7, 2015 Page 17 recognized that the performance of the foundations and/or cut and fill slopes may be influenced by undisclosed or unforeseen variations in the soil conditions that may occur in the intermediate 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 geotechnical engineer so that he may make modifications if necessary. CHANGE IN SCOPE This office should be advised of any changes in the project scope or proposed site grading so that we may determine if the recommendations contained herein are appropriate. This should be verified in writing or modified by a written addendum. TIME LIMITATIONS The findings of this report are valid as of this date. Changes in the condition of a property can, however, occur with the passage of time, whether they be due to natural processes or the work of man on this or adjacent properties. In addition, changes in the Standards-of-Practice and/or Government Codes may occur. Due to such changes, the findings of this report may be invalidated wholly or in part by changes beyond our control. Therefore, this report should not be relied upon after a period of two years without a review by us verifying the suitability of the conclusions and recommendations. PROFESSIONAL STANDARD In the performance of our professional services, we comply with that level of care and skill ordinarily exercised by members of our profession currently practicing under similar conditions and in the same locality. The client recognizes that subsurface conditions may vary from those encountered at the locations where our test pits, surveys, and explorations are made, and that our data, interpretations, and recommendations be based solely on the information obtained by us. We will be responsible for those data, interpretations, and recommendations, but shall not be responsible for the interpretations by others of the information developed. Our services consist of professional consultation and observation only, and no warranty of any kind whatsoever, express or implied, is made or intended in connection with the work performed or to be performed by us, or by our proposal for consulting or other services, or by our furnishing of oral or written reports or findings.

23 CWE October 7, 2015 Page 18 CLIENT'S RESPONSIBILITY It is the client s responsibility, or its representatives, to ensure that the information and recommendations contained herein are brought to the attention of the structural engineer and architect for the project and incorporated into the project's 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. FIELD EXPLORATIONS Six subsurface explorations were made at the locations indicated on the Site Plan included herewith as Plate Number 1 on July 31, These explorations consisted of six trenches excavated by a Case 580L backhoe equipped with an 18-inch bucket. The fieldwork was conducted under the observation of our engineering geology personnel. The explorations were carefully logged when made. The trench logs are presented within Appendix A. The soils are described in accordance with the Unified Soils Classification System. In addition, a verbal textural description, the wet color, the apparent moisture and the density or consistency are provided. The density of granular soils is given as very loose, loose, medium dense, dense or very dense. The consistency of silts or clays is given as either very soft, soft, medium stiff, stiff, very stiff, or hard. LABORATORY TESTING Laboratory tests were performed in accordance with the generally accepted American Society for Testing and Materials (ASTM) test methods or suggested procedures. A brief description of the tests performed is presented in Appendix B.

24 T-1 Qaf Mzu T-3 T-2 Qaf Mzu T-6 T-5 T-4 Qaf Mzu 0 100' 200' SCALE: 1" = 100' CWE LEGEND T-6 APPROXIMATE TEST TRENCH LOCATION Qaf Mzu ARTIFICIAL FILL UNDERLAIN BY METAMORPHOSED VOLCANIC ROCK SITE PLAN AND GEOTECHNICAL MAP DATE: OCTOBER 2015 BY: SRD PROPOSED HIGH STREET APARTMENTS A.P.N.'S & HIGH STREET, LA MESA, CALIFORNIA JOB NO.: PLATE NO.: 1 CHRISTIAN WHEELER E N G I N E E R I N G