rfb_13199_for_info_only_3-geotechnical_evaluation.pdf

GEOTECHNICAL EVALUATION

COLE GRADE ROAD IMPROVEMENTS

VALLEY CENTER, CALIFORNIA

PREPARED FOR:

County of San Diego

Department of Public Works, Materials Lab 5555 Overland Avenue, Suite 5101

San Diego, California 92123

PREPARED BY:

Ninyo & Moore

Geotechnical and Environmental Sciences Consultants 5710 Ruffin Road

San Diego, California 92123

October 2, 2012 Project No. 106898005

Cole Grade Road Improvements October 2, 2012 Valley Center, California Project No. 106898005

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TABLE OF CONTENTS

Page

1. INTRODUCTION

2. SCOPE OF SERVICES

3. SITE AND PROJECT DESCRIPTION

4. FIELD EXPLORATIONS AND LABORATORY TESTING

4.1. Geologic Mapping

4.2. Soil Borings

4.3. Laboratory Testing

5. GEOLOGY AND SUBSURFACE CONDITIONS

5.1. Regional Geologic Setting

5.2. Site Geology

5.2.1. Fill

5.2.2. Alluvium

5.2.3. Granitic Rock

5.3. Groundwater

5.4. Faulting and Seismicity

5.4.1. Strong Ground Motion

5.4.2. Ground Surface Rupture

5.4.3. Liquefaction and Seismically Induced Settlement

5.4.4. Landsliding and Rock Slope Stability

6. CONCLUSIONS

7. RECOMMENDATIONS

7.1. Earthwork

7.1.1. Site Preparation

7.1.2. Excavation Characteristics

7.1.3. Temporary Excavations

7.1.4. Treatment of Existing Fill and Alluvial Soils

7.1.5. Materials for Fill

7.1.6. Compacted Fill

7.1.7. Utility Trench Backfill

7.1.8. Drainage

7.2. Fill Placement on Sloping Ground

7.3. Slopes

7.4. Rock Slope Stability

7.5. Cantilever Retaining Walls

7.5.1. Shallow Footings

7.5.2. Lateral Resistance

7.5.3. Lateral Earth Pressures

7.5.4. Static Settlement

7.6. Alternatives to Cantilever Retaining Walls

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7.7. Seismic Design Parameters

7.8. Preliminary Pavement Design

7.9. Corrosion

7.10. Concrete

7.11. Pre-Construction Conference

7.12. Plan Review and Construction Observation

8. LIMITATIONS

9. REFERENCES

Table Table 1 – Seismic Design Factors

Figures Figure 1 – Project Location Figure 2 – Exploration Locations Figure 3 – Geology Figure 4 – Fault Locations Figure 5 – Lateral Earth Pressures for Temporary Cantilevered Shoring Figure 6 – Lateral Earth Pressures for Braced Excavation (Granular Soil) Figure 7 – Lateral Earth Pressures for Yielding Retaining Walls

Appendices Appendix A – Boring Logs Appendix B – Selected Site Photographs Appendix B – Laboratory Testing

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1. INTRODUCTION

In accordance with your request, we have performed a geotechnical evaluation for the proposed im-provements along Cole Grade Road in Valley Center, California (Figure 1). This report presents the results of our field exploration and laboratory testing, our conclusions regarding the geotechnical condi-tions at the site, and our recommendations for the design and earthwork construction of this project. The focus of this report is on providing recommendations for the retaining wall and graded slopes. We under-stand the County will be designing the pavement improvements.

2. SCOPE OF SERVICES

The scope of services for this study included the following:

Reviewing of background information including available geologic and geotechnical reports, project plans, topographic maps, geologic maps, fault maps, and historical stereoscopic aerial photographs.

Siting and staking of the proposed exploratory boring location for clearance by Underground Service Alert (USA).

Preparing a traffic control plan for our field evaluation.

Obtaining a right-of-way permit from the County of San Diego, Department of Public Works.

Providing traffic control during our field evaluation.

Performing a geologic reconnaissance of the project to evaluate exposed existing conditions.

Drilling, logging, and sampling four hollow-stem auger borings along the project alignment.

Bulk and relatively undisturbed drive samples of soil were collected at selected intervals from the borings and transported to our in-house geotechnical laboratory for testing.

Performing laboratory testing including gradation analysis, in-situ density and moisture con-tent, R-Value, direct shear strength, and corrosivity.

Preparing this report presenting our findings, conclusions, and recommendations regarding the geotechnical design and construction of the project.

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3. SITE AND PROJECT DESCRIPTION

The project area is relatively hilly and generally descends to the south. Elevations range from approximately 1,420 feet MSL at the south end of Cole Grade Road to 1628 feet MSL at the in-tersection of Cole Grade Road and Cool Valley Road.

We understand that an approximately 2.6-mile section of Cole Grade Road will be widened to provide a turn lane and bike lanes along with a graded shoulder. The improvements include re-taining walls at four locations along the roadway (Stations 50+00, 55+50, 101+00, and 127+50).

Three of the retaining walls will be designed to support cut slopes, currently from near vertical to approximately 1:1 (horizontal to vertical), ascending from the roadway, and one retaining wall will be designed to support new fill over a slope descending from the roadway. We understand that as an alternative to the proposed retaining walls, graded slopes are being considered in con-junction with additional right-of-way acquisition.

4. FIELD EXPLORATIONS AND LABORATORY TESTING

Our field exploration of the site was conducted on August 30, 2012, and consisted of geologic recon-naissance, drilling, logging, and sampling of four soil borings. Figure 2 is a map showing the approximate locations of the borings. Boring logs are presented in Appendix A.

4.1. Geologic Mapping

Surface explorations consisted of observation of the geology of the site. Where observed, the orientation of fractures were noted using a geologic compass. Figure 3 is a geologic map of the site showing the regional geologic units. Selected photographs from our surface explora-tion are presented in Appendix B.

4.2. Soil Borings

Four soils borings (B-1 through B-4) were drilled on August 30, 2012 using a truck-mounted, hollow-stem auger drill rig. The borings were drilled to depths of up to approxi-mately 15.5 feet below existing grades.

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4.3. Laboratory Testing

Geotechnical laboratory testing of representative soil materials obtained during our subsur-face exploration included in-situ moisture content and dry density, gradation, direct shear strength, soil corrosivity (i.e., electrical resistivity, pH, chloride content, and sulfate content), and R-Value. The laboratory tests were performed in our in-house laboratory by Ninyo &

Moore’s laboratory technicians. Results of the in-situ moisture content and dry density tests are shown at the corresponding sample depths on the boring logs in Appendix A. The results of the other laboratory tests performed are presented in Appendix C.

5. GEOLOGY AND SUBSURFACE CONDITIONS

Our findings regarding regional and site geology, including geologic structure, groundwater con-ditions, excavatability, faulting and seismicity, seismic hazards, and landslides and rockslides at the subject site are provided in the following sections.

5.1. Regional Geologic Setting

The project is situated in the central San Diego County section of the Peninsular Ranges Geo-morphic Province. This geomorphic province encompasses an area that extends approximately

900 miles from the Transverse Ranges and the Los Angeles Basin south to the southern tip of

Baja California (Harden, 1998; Norris and Webb, 1990). The province varies in width from approximately 30 to 100 miles. In general, the province consists of rugged mountains under-lain by Jurassic metavolcanic and metasedimentary rocks, and Cretaceous igneous rocks of the southern California batholith. The portion of the province in San Diego County that includes the project area consists generally of Cretaceous-age Cole Grade tonalite (Figure 3).

The Peninsular Ranges Province is traversed by a group of sub-parallel faults and fault zones trending roughly northwest. Several of these faults are considered active faults. The Elsinore, San Jacinto, and San Andreas faults are active fault systems located east of the project area and the Coronado Bank, San Diego Trough, San Clemente, and Rose Canyon faults are active faults located west of the project area. The Julian segment of the Elsinore Fault, the nearest active fault system, has been mapped approximately 7 miles northeast of the project site (Figure 4). Major

106898005 R Cole Grade Road.doc 4 tectonic activity associated with these and other faults within this regional tectonic framework consists primarily of right-lateral, strike-slip movement.

5.2. Site Geology

Per the regional geologic mapping, the site is dominantly underlain by the Cretaceous granitic rock. However, geologic units at the site include fills, alluvium, and granitic rock. Generalized descriptions of the earth units encountered during our field mapping and subsurface explora-tion are provided below. Additional descriptions of the subsurface units are provided on the boring logs in Appendix A.

5.2.1. Fill

Fill was observed in our borings to depths of up to approximately 7 feet below ground surface (bgs). From our borings, the fill consisted of fine- to medium-grained, loose to very dense silty sand. Documentation regarding placement of the fill was not provided.

5.2.2. Alluvium

Alluvium was observed in Boring B-2 from a depth of approximately 7 feet to 10 feet bgs.

The alluvium consisted of dense, silty sand.

5.2.3. Granitic Rock

As noted, bedrock at the project site consists of a granitic rock. The granitic rock is ex-posed in slopes adjacent to the roadway and was observed in our borings. This material generally consists of generally massive, fine- to medium-grained, moderately soft to very hard, weathered rock. Corestones were observed at numerous locations. We also observed widely spaced dikes and veins of more resistant material within the granitic rock. As noted, the bedrock was generally massive, however fractures were observed and the orientation of fractures were generally N30°W/25°SW. Although not perva-sively fractured, intersecting joints and fractures were noted. Refusal of the drilling rig was encountered on the granitic rock in Boring B-2 at a depth of about 15.5 feet.

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5.3. Groundwater

Groundwater was not encountered in our exploratory borings. As the project is in an area of bedrock, groundwater can be expected to occur within joints or fractures and may not occur at a specific elevation. Fluctuations in the groundwater level and local perched conditions may occur due to variations in ground surface topography, subsurface geologic conditions and structure, rainfall, irrigation, and other factors.

5.4. Faulting and Seismicity

Like the majority of southern California, the project area is considered to be seismically ac-tive. Based on our review of the referenced geologic maps and stereoscopic aerial photographs, as well as on our geologic field mapping, the subject site is not underlain by known active or potentially active faults (i.e., faults that exhibit evidence of ground dis-placement in the last 11,000 years and 2,000,000 years, respectively). However, the site is located in a seismically active area and the potential for strong ground motion is considered significant during the design life of the proposed structures.

In general, hazards associated with seismic activity include strong ground motion, ground surface rupture, liquefaction, and seismically induced settlement. These hazards are dis-cussed in the following sections.

5.4.1. Strong Ground Motion

The 2010 California Building Code (CBC) recommends that the design of structures be based on the horizontal peak ground acceleration (PGA) having a 2 percent probability of exceedance in 50 years, which is defined as the Maximum Considered Earth-quake (MCE) in Section 1613 of the CBC. The statistical return period for PGAMCE is approximately 2,475 years. Based on our review of subsurface data, the project site cor-responds to a Site Class B. The site modified PGAMCE was estimated to be 0.60g using the web-based United States Geological Survey (USGS) ground motion calculator

(USGS, 2012). The site modified design PGA (i.e., the site modified design earthquake ground acceleration) was estimated to be 0.40g. These estimates of ground motion do not include near-source factors that may be applicable to the design of structures on site.

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5.4.2. Ground Surface Rupture

Based on our review of the referenced literature and our field evaluation, no active faults are known to cross the project vicinity. Therefore, the potential for ground rupture due to faulting at the site is not a design consideration. However, lurching or cracking of the ground surface as a result of nearby seismic events is possible.

5.4.3. Liquefaction and Seismically Induced Settlement

Liquefaction of cohesionless soils can be caused by strong vibratory motion due to earthquakes. Research and historical data indicate that loose granular soils and non-plastic silts that are saturated by a relatively shallow groundwater table are susceptible to liquefaction. Since the site is underlain by bedrock materials at relatively shallow depths, it is our opinion that the potential for liquefaction and seismically induced set-tlement is not a design consideration at the site.

5.4.4. Landsliding and Rock Slope Stability

Based on our review of published geologic literature and aerial photographs and our subsur-face exploration, no deep-seated landslides or related features underlie or are adjacent to the site. However, erosion of the existing cut slopes, shallow rockfall deposits, and individual boulders were observed along the existing slopes and adjacent to the site (Photographs 3 and 5). Due to the steep slopes along the alignment and the variable weathering of the mate-rials, the potential for rock falls to impact the site is considered high.

6. CONCLUSIONS

Based on our review of the referenced background data, subsurface exploration, and laboratory testing, it is our opinion that construction of the proposed roadway improvement project is feasi-ble from a geotechnical standpoint provided the recommendations presented in this report are incorporated into the design and construction of the project. In general, the following conclu-sions were made:

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The project site is underlain by fill soils, alluvium, and granitic bedrock materials. The fill and alluvium generally consist of loose to medium dense, silty sands. The bedrock was weathered but was observed to range up to very hard. Corestones are present in the bedrock.

Groundwater was not encountered during our field investigation.

Elements of the active Elsinore Fault are located approximately 7 miles east of the site. Accord-ingly, the potential for strong seismic ground motions should be considered in the project design.

Difficult ripping, rock breaking, or blasting should be anticipated for excavations in the bed-rock. Excavation will encounter corestones and hard to very hard rock, which will make such excavations difficult and require special provisions including heavy ripping, rock breaking, and/or blasting.

Areas of adverse jointing and fracturing may be encountered during trench excavation or cuts for the planned slopes. If encountered, the use of shoring or other methods of stabiliza-tion should be anticipated.

Much of the site excavations along the roadway alignment are anticipated to generate significant quantities of oversize rock. Disposal or crushing of this material should be anticipated.

The existing fill and near-surface alluvial soils are generally loose to medium dense, and are not considered to be adequate for the support of new structural fill in their present state.

The potential for rock falls to affect the site is considered high. Protection of the new road-way from rock falls is recommended.

7. RECOMMENDATIONS

Based on our understanding of the project, the following recommendations are provided for the design and construction of the proposed project. The proposed site improvements should be con-structed in accordance with the requirements of the applicable governing agencies.

7.1. Earthwork

In general, earthwork should be performed in accordance with the Caltrans Standard Speci-fications (Caltrans, 2006a) and the recommendations presented in this report. Ninyo &

Moore or the County’s designated representative should be contacted for questions regarding the recommendations or guidelines presented herein.

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7.1.1. Site Preparation

Site preparation should begin with the removal of existing improvements, vegetation, utility lines, asphalt, concrete, and other deleterious debris from areas to be graded. Tree stumps and roots should be removed to such a depth that organic material is generally not present. Clearing and grubbing should extend to the outside of the proposed excava-tion and fill areas. The debris and unsuitable material (e.g., oversize and organic materials) generated during clearing and grubbing should be removed from areas to be graded and disposed of per Section 16-104 Removal and Disposal of Materials of the

Caltrans Standard Specifications (Caltrans, 2006a).

7.1.2. Excavation Characteristics

As described in the boring logs in Appendix A, portions of the roadway are underlain by bedrock. Excavations will encounter corestones and hard rock, which will make such excavations difficult and require special construction considerations, including heavy ripping, rock breaking, and/or blasting. A specialty contractor with significant experi-ence in rock excavation may be utilized to achieve the desired construction. In addition, as noted, caving should be anticipated during performance of excavations in the fill and alluvium due to the loose condition and granular nature of the on-site soils.

7.1.3. Temporary Excavations

Temporary excavations into the bedrock materials may encounter intersecting joints which will result in blocks of rock that may be susceptible to falling. Ninyo & Moore should be contacted to evaluate the exposed joints, corestones, and rockfall potential dur-ing construction. The contractor should take precautionary measures to mitigate the potential for rockfall during construction. The precautionary measures may include, but are not limited to, reinforced shotcrete coverings, wire mesh and cable netting, setbacks, or debris barriers. For temporary excavations, we recommend that the following Occupa-tional Safety and Health Administration (OSHA) soil classifications be used:

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Fill and Alluvium Type C Granitic Bedrock Type A

Upon making the excavations, the soil classifications and excavation performance should be evaluated in the field in accordance with OSHA regulations. Temporary excavations should be constructed in accordance with OSHA recommendations. For trench or other ex-cavations, OSHA requirements regarding personnel safety should be met using appropriate shoring (including trench boxes) or by laying back the slopes to no steeper than 1.5:1 in fill and alluvium and 1:1 in bedrock. Temporary excavations that encounter seepage may be shored or stabilized by placing sandbags or gravel along the base of the seepage zone. Ex-cavations encountering seepage should be evaluated on a case-by-case basis. On-site safety of personnel is the responsibility of the contractor.

Shoring systems for excavations may be designed using the lateral earth pressure parame-ters presented on Figures 5 and 6. These lateral earth pressures should be evaluated by a structural engineer for the design of the shoring systems. These design earth pressures as-sume that spoils from the excavations, or other surcharge loads, will not be placed above the excavations within a 1:1 plane extending up and back from the base of the excavation.

For bracing subjected to surcharge loads, such as soil stockpiles or construction materi-als/equipment, an additional horizontal uniform pressure of 0.40q may be applied to the full height of the excavation, where “q” is the surcharge pressure.

7.1.4. Treatment of Existing Fill and Alluvial Soils

As noted, the existing fills and alluvial soils are loose to medium dense and not consid-ered adequate for structural support in their present condition. Where new fill slopes will be constructed we recommend that the existing fill and alluvial soils be removed to the underlying bedrock and replaced with compacted fill. The actual depths of fill re-movals will depend on the project layout and actual depths of the fill encountered during excavations. The extent and depths of removals should be evaluated by Ninyo &

Moore or the County’s designated representative in the field based on the materials ex-posed. The existing fill may be reused as engineered compacted fill if it meets the criteria described below.

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7.1.5. Materials for Fill

On-site soils with an organic content of less than approximately 3 percent by volume (or

1 percent by weight) are suitable for reuse as compacted fill material. In general, fill mate-rial should not contain rocks or lumps over approximately 6 inches in diameter, and not more than approximately 30 percent larger than ¾ inch. Oversize materials, if encountered, should be separated from material to be used for compacted fill and removed from the site.

Imported fill material should generally be granular soils with a low expansion potential

(i.e., an expansion index of 50 or less as evaluated by the ASTM International [ASTM]

Test Method D 4829). Import material should also be non-corrosive in accordance with the current version of the Caltrans corrosion guidelines (Caltrans, 2003). Materials for use as fill should be evaluated by Ninyo & Moore or the County’s designated represen-tative prior to filling or importing.

7.1.6. Compacted Fill

Prior to placement of compacted fill, the contractor should request an evaluation of the exposed ground surface by Ninyo & Moore or the County’s designated representative.

Unless otherwise recommended, the exposed ground surface should then be scarified to a depth of approximately 8 inches and watered or dried, as needed, to achieve moisture contents generally near the optimum moisture content. The scarified materials should then be compacted to 90 percent relative compaction as evaluated by California Test (CT) 216.

Compacted fill should be placed in horizontal lifts of approximately 8 inches in loose thickness. Prior to compaction, each lift should be watered or dried as needed to achieve a moisture content generally near the laboratory optimum, mixed, and then compacted by mechanical methods, to 90 percent relative compaction as evaluated by CT 216. Succes-sive lifts should be treated in a like manner until the desired finished grades are achieved.

Prior to placement of additional compacted fill material following a delay in the grading operations, the exposed surface of previously compacted fill should be prepared to receive fill. Preparation may include scarification, moisture conditioning, and recompaction.

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The evaluation of compaction by the geotechnical consultant should not be considered to preclude any requirements for observation or approval by governing agencies. It is the contractor's responsibility to notify the appropriate governing agency when project areas are ready for observation, and to provide reasonable time for that review.

7.1.7. Utility Trench Backfill

Based on our subsurface evaluation, the on-site earth materials should be generally suit-able for re-use as trench backfill provided they are free of organic material, clay lumps, debris, and rocks greater than approximately 3 inches in diameter. Fill should be mois-ture-conditioned to generally near the laboratory optimum. Trench backfill should be compacted to 90 percent relative compaction as evaluated by CT 216. Fill within the upper 12 inches of pavement subgrade should be compacted to 95 percent relative com-paction as evaluated by CT 216. Lift thickness for backfill will depend on the type of compaction equipment utilized, but fill should generally be placed in lifts not exceeding

8 inches in loose thickness. Special care should be exercised to avoid damaging the pipe during compaction of the backfill.

7.1.8. Drainage

Roadway and slope drainage should be directed such that runoff water is diverted away from slopes and structures to suitable discharge areas by nonerodible devices (e.g., gut-ters, downspouts, concrete swales, etc.). Positive drainage may be accomplished by providing drainage away from the structures at a gradient of 2 percent or steeper for a distance of 5 feet or more outside the structure, and further maintained by a graded swale leading to an appropriate outlet, in accordance with the recommendations of the project civil engineer and/or landscape architect.

Surface drainage on the site should be provided so that water is not permitted to pond. A gradient of 2 percent or steeper should be maintained and drainage patterns should be established to divert and remove water from the site to appropriate outlets. Best man-agement practice (BMP) design for site drainage should be evaluated by the Project

Civil Engineer.

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7.2. Fill Placement on Sloping Ground

Fills constructed on sloping ground having an inclination steeper than 6:1 should be keyed and benched into competent materials underlying loose soils. Keys should generally be 15 feet in width or greater and extent at least 3 feet into the competent material. The actual width of the toe keys and extent of removal of any existing loose surficial soil or other native materials should be evaluated by Ninyo & Moore or the County’s designated representative in the field during con-struction. In addition, toe key excavations should be observed by Ninyo & Moore or the County’s designated representative prior to placing fill.

7.3. Slopes

Unless otherwise recommended by Ninyo & Moore and approved by the County, fill slopes should not be constructed steeper than 2:1 and cut slopes should not be steeper than 1.5:1 in bedrock. Cut slopes in fill or alluvium should not be constructed steeper than 2:1. If excava-tions for cut slopes expose loose, cohesionless, significantly fractured, or otherwise unsuitable materials, overexcavation of the unsuitable material and replacement with a com-pacted stabilization fill should be evaluated.

Compaction of the face of fill slopes should be performed by backrolling at intervals of 4 feet or less in vertical slope height or as dictated by the capability of the available equipment, whichever is less.

Fill slopes should be backrolled utilizing a sheepsfoot-type roller. Care should be taken in maintain-ing the desired moisture conditions and/or reestablishing them, as needed, prior to backrolling. The placement, moisture conditioning, and compaction of fill slope materials should be done in accor-dance with the recommendations presented in the Compacted Fill section of this report.

Compacted fill slopes should be overbuilt and cut back to grade, exposing firm compacted fill. The actual amount of overbuilding may vary as filed conditions dictate. If the desired results are not achieved, the existing slopes should be overexcavated and reconstructed in accordance with the recommendations of Ninyo & Moore or the County’s designated repre-sentative. The degree of overbuilding may be increased until the desired compacted slope face condition is achieved. Care should be taken by the contractor to provide mechanical compaction as close to the outer edge of the overbuilt slope surface as practical.

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Site runoff should not be permitted to flow over the tops of slopes. Positive drainage should be established away from the slopes. This may be accomplished by incorporating brow ditches placed at the top of the slopes to divert surface runoff away from the slope face where drainage devices are not otherwise available. The project plans and specifications should contain design features and construction requirements to reduce the potential for ero-sion of the on-site soils both during and after construction.

7.4. Rock Slope Stability

The global stability of the cut slopes into bedrock excavations is contingent on the strength of the rock mass. Based on the observations made in the field and the materials encountered in the borings, global failure of the proposed cut slopes is not a design concern. However, intersecting joint patterns and various degrees of weathering were observed in the existing rock materials. The stability of individual rock blocks within the cut slope will be governed by the discontinuities within the rock mass.

The potential for rockfall will be a design and construction consideration and should be mitigated with protective measures. The extent of the protection will be based on the conse-quence and cost of damage to the roadway, or life safety if workers or motorists will be present.

Possible mitigation alternatives may include but are not limited to, reinforced shotcrete coverings, wire mesh and cable netting, setbacks, or construction of debris barriers. A specialty contractor or manufacturer can provide specific mitigation measures appropriate for the project.

7.5. Cantilever Retaining Walls

Although details are not provided on the plans by the County (County of San Diego, 2012), we understand that cantilever retaining walls are being considered in three locations (Stations 50+00, 101+00, and 127+50). The proposed retaining walls may be supported on shallow, spread footings bearing on engineered fill compacted in accordance with the recommendations presented in this report or on bedrock. Foundations should be designed in accordance with structural considerations and the following recommendations. In addition, requirements of the appropriate governing juris-dictions and applicable building codes should be considered in the design of the structures.

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7.5.1. Shallow Footings

The proposed retaining walls may be supported on conventional shallow, spread foot-ings. Footings should extend 18 inches or more below the lowest adjacent finished grade and have a width of 24 inches or greater. Footings for the proposed retaining walls, as described and bearing on compacted fill or bedrock materials, may be de-signed using an allowable bearing capacity of 3,000 per square foot (psf). The footings should be setback from the toe or top of slopes in accordance with Figure 1808.7.1 of the CBC (CBC, 2010). The spread footings should be reinforced in accordance with the recommendations of the project structural engineer.

7.5.2. Lateral Resistance

For resistance of footings to lateral loads, we recommend an allowable passive pressure of 400 psf per foot of depth up to 4,000 psf. This value assumes that the ground is hori-zontal for a distance of 10 feet, or three times the height generating the passive pressure, whichever is greater. We recommend the upper 1 foot of soil not protected by pavement be neglected when calculating passive resistance. For frictional resistance to lateral loads, we recommend that a coefficient of friction of 0.35 be used between soil and con-crete. The allowable lateral resistance can be taken as the sum of the frictional and passive resistance provided the passive resistance does not exceed one-half of the total allowable resistance. The passive resistance values may be increased by one-third when considering loads of short duration such as wind or seismic forces.

7.5.3. Lateral Earth Pressures

Recommendations for lateral earth pressures to be used in design of the yielding retain-ing walls are provided on Figure 7. The values presented are based on non-expansive and free-draining (granular) backfill conditions. The quality and consistency of the backfill should be checked prior to its use behind the retaining walls.

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Measures should be taken to reduce the potential build-up of moisture behind the retaining walls. Drainage design should include free-draining backfill materials and perforated drains according to the Caltrans Standard Plans (Caltrans, 2006b). Solid outlet pipes should be connected to the perforated drains and then routed to a suitable area for discharge of accu-mulated water. The portions of retaining walls supporting backfill should be coated with waterproofing compound or covered with a similar material to reduce the potential for infil-tration of moisture through the walls. It is the responsibility of the project structural engineer and/or the retaining wall contractor to provide specifications for waterproofing materials and suitable methods of application.

7.5.4. Static Settlement

We estimate that the proposed retaining walls, designed and constructed as recommended herein, will undergo total settlement on the order of 1 inch. Differential settlement on the order of 0.5 inches over a horizontal span of 40 feet should be expected.

7.6. Alternatives to Cantilever Retaining Walls

As an alternative to cantilever retaining walls, we understand that the County may consider constructing other types of retaining walls, such as a rock anchored wall with a shotcrete facing, soldier pile and lagging wall, or a crib wall. If an alternate wall type is selected, addi-tional evaluation should be performed to provide geotechnical recommendations for the design and construction.

7.7. Seismic Design Parameters

The proposed improvements should be designed in accordance with the requirements of go-verning jurisdictions and applicable building codes. Table 1 presents the seismic design parameters for the site in accordance with CBC (2010) guidelines and mapped spectral ac-celeration parameters (USGS, 2011).

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Table 1 – Seismic Design Factors

Factors Values

Site Class B Site Coefficient, Fa 1.0 Site Coefficient, Fv 1.0 Mapped Short Period Spectral Acceleration, SS 1.500g Mapped One-Second Period Spectral Acceleration, S1 0.600g

Period Spectral Acceleration Adjusted For Site Class, SMS 1.500g One-Second Period Spectral Acceleration Adjusted For Site Class, SM1 0.600g Design Short Period Spectral Acceleration, SDS 1.000g Design One-Second Period Spectral Acceleration, SD1 0.400g

7.8. Preliminary Pavement Design

Laboratory testing on samples of the on-site soils resulted in R-Values of 55 and 63. We un-derstand that pavement recommendations will be provided by the County of San Diego for the proposed construction using the values provided herein.

7.9. Corrosion

Laboratory testing was performed on a representative sample of the on-site earth materials to evaluate pH and electrical resistivity, as well as chloride and sulfate contents. The pH and electrical resistivity tests were performed in accordance with CT 643 and the sulfate and chloride content tests were performed in accordance with CT 417 and CT 422, respectively.

These laboratory test results are presented in Appendix B.

The results of the corrosivity testing indicated an electrical resistivity of 4,000 and 5,200 ohm-cm, a soil pH of 6.9 and 7.1, a chloride content of 40 and 55 parts per million (ppm) and a sulfate con-tent of 0.005 and 0.007 percent (i.e., 50 and 70 ppm). Based on the Caltrans corrosion (2003) criteria, a site is classified as corrosive when the soils have more than 500 ppm chlorides, more than 0.2 percent sulfates, pH less than 5.5, or an electrical resistivity of 1,000 ohm-centimeters or less. Therefore, this site would be classified as non-corrosive.

106898005 R Cole Grade Road.doc 17

7.10. Concrete

Concrete in contact with soil or water that contains high concentrations of soluble sulfates can be subject to chemical deterioration. Laboratory testing indicated a sulfate content of the sample tested of 0.005 and 0.007 percent. According to the American Concrete Institute (ACI) 318 building code, the potential for sulfate attack is negligible for water-soluble sulfate contents in soils ranging from about 0.00 to 0.10 percent by weight. Therefore, the site soils may be consid-ered to have a negligible potential for sulfate attack. However, due to the potential variability of site soils, consideration should be given to using Type V or Type II/V cement and concrete with a water-cement ratio no higher than 0.45 by weight for normal weight aggregate concrete and a

28-day compressive strength of 4,500 pounds per square inch (psi) or more for the project.

7.11. Pre-Construction Conference

We recommend that a pre-construction meeting be held prior to commencement of construc-tion. The owner or his representative, the agency representatives, the civil engineer, Ninyo &

Moore, and the contractor should attend to discuss the plans, the project, and the proposed construction schedule.

7.12. Plan Review and Construction Observation

The conclusions and recommendations presented in this report are based on analysis of ob-served conditions in widely spaced exploratory borings. If conditions are found to vary from those described in this report, Ninyo & Moore or the County’s designated representative should be notified, and additional recommendations will be provided upon request. Ninyo &

Moore or the County’s designated representative should review the final project drawings and specifications prior to the commencement of construction. Ninyo & Moore or the

County’s designated representative should perform the needed observation and testing ser-vices during construction operations.

106898005 R Cole Grade Road.doc 18

The recommendations provided in this report are based on the assumption that Ninyo &

Moore will provide geotechnical observation and testing services during construction. In the event that it is decided not to utilize the services of Ninyo & Moore during construction, we request that the selected consultant provide the client with a letter (with a copy to Ninyo &

Moore) indicating that they fully understand Ninyo & Moore’s recommendations, and that they are in full agreement with the design parameters and recommendations contained in this report. Construction of proposed improvements should be performed by qualified subcon-tractors utilizing appropriate techniques and construction materials.

8. LIMITATIONS

The field evaluation, laboratory testing, and geotechnical analyses presented in this report have been conducted in general accordance with current practice and the standard of care exercised by geotech-nical consultants performing similar tasks in the project area. No warranty, expressed or implied, is made regarding the conclusions, recommendations, and opinions presented in this report. There is no evaluation detailed enough to reveal every subsurface condition. Variations may exist and conditions not observed or described in this report may be encountered during construction. Uncertainties rela-tive to subsurface conditions can be reduced through additional subsurface exploration. Additional subsurface evaluation will be performed upon request. Please also note that our evaluation was lim-ited to assessment of the geotechnical aspects of the project, and did not include evaluation of structural issues, environmental concerns, or the presence of hazardous materials.

This document is intended to be used only in its entirety. No portion of the document, by itself, is designed to completely represent any aspect of the project described herein. Ninyo & Moore should be contacted if the reader requires additional information or has questions regarding the content, interpretations presented, or completeness of this document.

This report is intended for design purposes only. It does not provide sufficient data to prepare an accurate bid by contractors. It is suggested that the bidders and their geotechnical consultant per-form an independent evaluation of the subsurface conditions in the project areas. The independent evaluations may include, but not be limited to, review of other geotechnical reports prepared for the adjacent areas, site reconnaissance, and additional exploration and laboratory testing.

106898005 R Cole Grade Road.doc 19

Our conclusions, recommendations, and opinions are based on an analysis of the observed site conditions. If geotechnical conditions different from those described in this report are encountered, our office should be notified, and additional recommendations, if warranted, will be provided upon request. It should be understood that the conditions of a site could change with time as a result of natural processes or the activities of man at the subject site or nearby sites. In addition, changes to the applicable laws, regulations, codes, and standards of practice may occur due to government ac-tion or the broadening of knowledge. The findings of this report may, therefore, be invalidated over time, in part or in whole, by changes over which Ninyo & Moore has no control.

This report is intended exclusively for use by the client. Any use or reuse of the findings, conclu-sions, and/or recommendations of this report by parties other than the client is undertaken at said parties’ sole risk.

106898005 R Cole Grade Road.doc 20

9. REFERENCES

American Concrete Institute, 1991b, Guidelines for Residential Cast-in-Place Concrete Con-struction, (ACI 332R).

American Concrete Institute (ACI), 2011, Building Code Requirements for Structural Concrete (ACI 318-08) and Commentary (ACI 318R-08).

American Public Works Association (APWA), 2011, “Greenbook,” Standards Specifications for Public Works Construction (SSPWC).

Blake, T.F., 2001, FRISKSP (Version 4.00) A Computer Program for the Probabilistic Estimation of Peak Acceleration and Uniform Hazard Spectra Using 3-D Faults as Earthquake Sources.

Boore, D.M., Joyner, W.B., and Fumal, T.E., 1997, Equations for Estimating Horizontal Re-sponse Spectra and Peak Acceleration from Western North American Earthquakes: A Summary of Recent Work, Seismological Research Letters, Vol. 68, No. 1, pp. 128-153.

California Building Standards Commission, 2010, California Building Code (CBC), Title 24, Part 2, Volumes 1 and 2.

California Department of Transportation (Caltrans), 2003, Corrosion Guidelines (Version 1.0), Divi-sion of Engineering and Testing Services, Corrosion Technology Branch: dated September.

California Department of Transportation (Caltrans), 2006a, Standard Specifications, State of California, Business, Transportation and Housing Agency, Department of Transportation: dated May.

California Department of Transportation (Caltrans), 2006b, Standard Plans, State of California, Busi-ness, Transportation and Housing Agency, Department of Transportation: dated May.

Cao, T., Bryant, W. A., Rowshandel, B., Branum, D., and Willis, C. J., 2003, The Revised 2002 California Probabilistic Seismic Hazards Maps: California Geological Survey: dated June.

County of San Diego, Department of Public Works, 2012, Preliminary Plans for Construction of Cole Grade Road Improvements in the Vicinity of Valley Center: dated July 6.

County of San Diego, Department of Public Works, 2009, Design Standards, CIP Project Develop-ment Section: dated November.

Harden, D.R., 1998, California Geology: Prentice Hall, Inc.

Jennings, C.W. and Bryant W.A., 2010, Fault Activity Map of California: California Geological Survey, Geologic Data Map No. 6.: Scale 1:750,000.

Kennedy, M.P., and Tan, S.S., 2005, Geologic Map of the Oceanside 30x60 Quadrangle, California.

Munfakh, G., Wyllie, D., and Mah, C. W., 1998, Rock Slopes Reference Manual, Federal High-way Administration, FHWA HI-99-007.

Norris, R. M. and Webb, R. W., 1990, Geology of California, Second Edition: John Wiley & Sons, Inc.

106898005 R Cole Grade Road.doc 21

Prakash, S. and Sharma, H.D., 1990, Pile Foundations in Engineering Practice, Wiley-Interscience.

United States Department of the Interior, Bureau of Reclamation, 1989, Engineering Geology Field Manual.

United States Geological Survey, 2011, Ground Motion Parameter Calculator v. 5.0.8, World Wide Web, http://earthquake.usgs.gov/research/hazmaps/design/.

SOURCE: 2008 THOMAS GUIDE FOR SAN DIEGO COUNTY, STREET GUIDE AND DIRECTORY; MAP © RAND MCNALLY, R.L.07-S-129

NOTE: DIRECTIONS, DIMENSIONS AND LOCATIONS ARE APPROXIMATE

s l.m xd A

O B

PROJECT

805805

215215

MAP INDEX

San Diego County

0 2,400 4,8001,200

SCALE IN FEET

COLE GRADE ROAD IMPROVEMENTS

VALLEY CENTER, CALIFORNIA

PROJECT LOCATION FIGURE

1PROJECT NO. DATE

106898005 10/12

COOL VALLEY RD

COO L VALLEY RA N C H R

D

VIA VELTRI

MILLCO LN

MARGARITA LN

WHITE STAR LN

MILLER RD

CO

LE

G

RA

DE

R

D

HILLDALE RD

PAUMA HEIGHTS RD

AVA LN

OAK GLEN RD

FARAWAY PLCOLE GRADE LN

OAK MEADOW RD

MILLCO LN

CANE RD

HORSE CREEK TRL

BERNABEO CT

RESAVA LN

NOTE: DIRECTIONS, DIMENSIONS AND LOCATIONS ARE APPROXIMATE

LEGEND

PROJECT BOUNDARY

0 2,000 4,0001,000

SCALE IN FEET

BORING

TD=TOTAL DEPTH IN FEET

EXPLORATION LOCATIONS FIGURE

2PROJECT NO. DATE

B L

.m x d A

O B

B-4

TD=5.8'

B-1

TD=5.8'

B-2

TD=15.5'

B-3

TD=5.8'

B-4

TD=5.8'

SOURCE: AERIAL IMAGERY - PHOTO DATE: FEB 11, 2010, ESRI, I-CUBED, USDA FSA, USGS, AEX, GEOEYE, GETMAPPING, AEROGRID, IGP.

COLE GRADE ROAD IMPROVEMENTS

VALLEY CENTER, CALIFORNIA106898005 10/12

STA 127+50

STA 101+00

STA 55+50

STA 50+00

NOTES: ALL DIRECTIONS, DIMENSIONS AND LOCATIONS ARE APPROXIMATE 0 2,000 4,000 FEET

APPROXIMATE SCALE

GEOLOGY FIGURE

3PROJECT NO. DATE

G .m xd A

O B

SOURCE: KENNEDY, M.P., AND TAN, S.S., 2005, GEOLOGIC MAP OF THE OCEANSIDE 30' X 60' QUADRANGLE, CALIFORNIA

PROJECT

Kcg

COLE GRADE ROAD IMPROVEMENTS

VALLEY CENTER, CALIFORNIA106898005 10/12

MZg

Kvc Kgd

Qyc

LEGEND

U D

FAULT - SOLID WHERE ACCURATELY

LOCATED, DASHED WHERE APPROXIMATE,

DOTTED WHERE CONCEALED. ARROW

AND NUMBER INDICATE DIRECTION AND

ANGLE OF DIP OF FAULT PLANE

TONALITE OF COLE GRADEKcg

YOUNG COLLUVIAL DEPOSITSQyc

OLD ALLUVIAL FLOOD PLAIN DEPOSITS, UNDIVIDEDQoa

GRANODIORITE, UNDIVIDEDKgd

MONZOGRANITE OF VALLEY CENTERKvc

METAGRANITIC ROCKSMZg

M E X I C O U S AP a c i f i c

O c e a n

SAN J AC I N T O

EL S IN OR E

IM PE R IA L

W H I T T I E R S A N A N D R E A S

NE W P O R T - I N G L EW O O D

CORONADO BANK

SAN DIEGO TROUGH

SAN CLEMENTE

SANTA CRUZ-SANTA CATALINA RIDGE

PALOS VERDES

OFFSHORE ZONE

OF DEFORMATION

GARLOCKWH IT E W

OLF

CL EARWATERSAN GAB RIEL

S IERRA MADR E

B A N N I N G

M I S S I O N C R E E K

BLACKWATERHARPER

LOCKHART

LENWOOD

CAMP ROCK

CALICO

LUD LOW

PISGAH

BULLION MOUNTAIN

JOHNSON VALLEY

EMERSON

PINTO MOUNTAIN

MANIX

MIRAGE VALLEY

NORTH

HELENDALE

FRONTAL

CHINO

SAN JOSECUCAMONGA

MA LIBU COAST SANTA MONICA

SAN

CAYETANO

SANTA

SUSANASIMI- SANTA

ROSA

NORTHRIDGE

CHARNOCK

SAWPIT

CANYON

SUPERSTITION HILLS

NEVADA

CALIFORN IA

ROS E CA NYO N

San Bernardino County

Kern County

Riverside County San Diego County Imperial County

Los Angeles County

Ventura County

Orange County

Riverside County

Sa n

Be rn ar di no C ou nt y

Los Angeles County

Ke rn

C ou nt y

Indio Irvine

Pomona

Mojave

Anaheim

Barstow

Temecula

Palmdale

El CentroSan Diego

Escondido

Oceanside

Santa Ana

Riverside

Tehachapi

Long Beach

Wrightwood

Chula Vista

Los Angeles

Victorville

San Clemente

Palm Springs

Big Bear City Thousand Oaks San

Bernardino

Lake Arrowhead

Twentynine Palms

Baker

Desert Center

CA LIF OR N IA

0 30 60

SCALE IN MILES

LEGEND

HOLOCENE ACTIVE

CALIFORNIA FAULT ACTIVITY

HISTORICALLY ACTIVE

LATE QUATERNARY

(POTENTIALLY ACTIVE)

STATE/COUNTY BOUNDARY

QUATERNARY

(POTENTIALLY ACTIVE)

SITE

SOURCE: Jennings, C.W., and Bryant, W.A., Fault Activity Map of California, 2010, California Geological Survey.

4_

5_

F.

m xd A

O B

NOTE: DIRECTIONS, DIMENSIONS AND LOCATIONS ARE APPROXIMATE.

FAULT LOCATIONS FIGURE

4PROJECT NO. DATE

COLE GRAD ROAD IMPROVEMENTS

VALLEY CENTER, CALIFORNIA106898005 10/12

pP

D

H

CONSTRUCTION MATERIALS ARE NOT INCLUDED

5. SURCHARGES FROM EXCAVATED SOIL OR

4. ASSUMES GROUNDWATER IS NOT PRESENT

3. PASSIVE LATERAL EARTH PRESSURE, P

P = 400 D psf

2.

P = 120 psf

CONSTRUCTION TRAFFIC INDUCED SURCHARGE PRESSURE, P

1.

P = 21 H psf

APPARENT LATERAL EARTH PRESSURE, P

NOTES:

Pa Ps a a s s p p

6. H AND D ARE IN FEET

FIGURE

6PROJECT NO. DATE

LATERAL EARTH PRESSURES FOR

BRACED EXCAVATION (GRANULAR SOIL)

SHORING

BRACES

d-be g.

dw g

106898005

VALLEY CENTER, CALIFORNIA10/12

H+

PE

aPpP

D

PASSIVE

PRESSURE

ACTIVE

PRESSURE

DYNAMIC

PRESSURE

LATERAL EARTH PRESSURES

FOR YIELDING RETAINING WALLS

RESULTANT

2/3H

RESULTANT

H/3

RESULTANT

D/3

NOTES:

ASSUMES NO HYDROSTATIC PRESSURE BUILD-UP

BEHIND THE RETAINING WALL

1.

2.

BEHIND THE RETAINING WALL

WALL DRAINAGE DETAIL SHOULD BE INSTALLED

DRAINS AS RECOMMENDED IN THE RETAINING3.

BASED ON A PEAK GROUND ACCELERATION OF 0.40g

DYNAMIC LATERAL EARTH PRESSURE IS4.

RECOMMENDED GEOTECHNICAL DESIGN PARAMETERS

Equivalent Fluid Pressure (lb/ft /ft) Lateral Earth

Pressure

Level Backfill with Granular Soils

2 (1)

(2) with Granular Soils 2H:1V Sloping Backfill

(2) aP pP 400 D

EP

32 H 45 H

Level Ground

12 H

H AND D ARE IN FEET6.

SETBACK SHOULD BE IN ACCORDANCE WITH7.

FIGURE 1808.7.1 OF THE CBC (2010)

FIGURE

7PROJECT NO. DATE

RETAINING

WALL

SURCHARGE PRESSURES CAUSED BY VEHICLES5.

OR NEARBY STRUCTURES ARE NOT INCLUDED

d-yr w .d w g

STRUCTURAL, GRANULAR BACKFILL MATERIALS

SHOULD BE USED FOR RETAINING WALL BACKFILL

106898005

VALLEY CENTER, CALIFORNIA10/12

106898005 R Cole Grade Road.doc

APPENDIX A

BORING LOGS

XX/XX

SM

CL

Bulk sample.

Modified split-barrel drive sampler.

No recovery with modified split-barrel drive sampler.

Sample retained by others.

Standard Penetration Test (SPT).

No recovery with a SPT.

Shelby tube sample. Distance pushed in inches/length of sample recovered in inches.

No recovery with Shelby tube sampler.

Continuous Push Sample.

Seepage.

Groundwater encountered during drilling.

Groundwater measured after drilling.

MAJOR MATERIAL TYPE (SOIL):

Solid line denotes unit change.

Dashed line denotes material change.

Attitudes: Strike/Dip b: Bedding c: Contact j: Joint f: Fracture F: Fault cs: Clay Seam s: Shear bss: Basal Slide Surface sf: Shear Fracture sz: Shear Zone sbs: Shear Bedding Surface

The total depth line is a solid line that is drawn at the bottom of the boring.

BORING LOG

Explanation of Boring Log Symbols

PROJECT NO. DATE FIGURE

D E

P T

H fe et

B ul k S

A M

P

LE

S D riv en

B

LO

W S

/F O

O T

M O

IS

T

U R

E

D R

Y D

E N

S

IT

Y

P C

F

S Y

M B

O L

C

LA

S S

IF

IC

A T

IO

N

U .S

.C .S

BORING LOG EXPLANATION SHEET

lcarson Text Box Rev. 11/11

TYPICAL NAMES

GW Well graded gravels or gravel-sand mixtures, little or no fines

GP Poorly graded gravels or gravel-sand mixtures, little or no fines

GM Silty gravels, gravel-sand-silt mixtures

GC Clayey…