Appendix 6 Geotechnical and Groundwater Investigation Report

GRANDVIEW COMMUNITY HOMES 5

Appendix 6 Geotechnical and Groundwater Investigation

Report

Attach project’s geotechnical and groundwater investigation report. Refer to Appendix C.4 to determine the reporting requirements.

GEOLOGIC REPORT FOR TENTATIVE MAP

GRANDVIEW POINTE PROJECT 1902 GRANDVIEW STREET

OCEANSIDE, CALIFORNIA

Prepared for GRANDVIEW COMMUNITY HOMES, LLC

Cardiff by the Sea, California

Prepared by TERRACOSTA CONSULTING GROUP, INC.

3890 Murphy Canyon Road, Suite 200 San Diego, California 92123

(858) 573-6900

Project No. 2869-02 March 15, 2016

Geotechnical Engineering

Coastal Engineering

Maritime Engineering

3890 Murphy Canyon Road, Suite 200 San Diego, California 92123 (858) 573-6900 voice (858) 573-8900 fax www.terracosta.com

Project No. 2869-02 March 15, 2016 Messrs. Jon Corn & Matthew Miller GRANDVIEW COMMUNITY HOMES, LLC 160 Chesterfield Drive, #201 Cardiff by the Sea, California 92007 GEOLOGIC REPORT FOR TENTATIVE MAP GRANDVIEW POINTE PROJECT 1902 GRANDVIEW STREET OCEANSIDE, CALIFORNIA Dear Messrs. Corn & Miller: TerraCosta Consulting Group, Inc. (TerraCosta) is pleased to present this geologic report for the proposed Tentative Map prepared for the Grandview Pointe project, located at 1902 Grandview Street in the City of Oceanside, California.

The accompanying report is intended to accompany the re-submittal of the tentative map application. Included in this report is the additional information requested by James Knowlton, geotechnical consultant to the City, and addresses his comments pertaining to our feasibility-level geotechnical report dated April 20, 2015. New items included in this report are the results and data of our field investigations, our slope stability analyses, and our conclusions and recommendations concerning the stability of the site slopes.

We appreciate the opportunity to be of service and trust this information meets your needs. If you have any questions or require additional information, please give us a call.

Very truly yours, TERRACOSTA CONSULTING GROUP, INC. Walter F. Crampton, Principal Engineer Matthew W. Eckert, PhD, Dir. of Engineering R.C.E. 23792, R.G.E. 245 R.C.E. 45171, R.G.E. 2316 Braven R. Smillie, Principal Geologist C.E.G. 207, P.G. 402 WFC/MWE/BRS/sr Attachments

GRANDVIEW COMMUNITY HOMES, LLC March 15 2016 Project No. 2869-02

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TABLE OF CONTENTS 1 INTRODUCTION AND PROJECT DESCRIPTION .................................................................1 2 SCOPE OF WORK ......................................................................................................................2 3 FIELD AND LABORATORY INVESTIGATIONS...................................................................2 4 SITE CONDITIONS AND GEOLOGY ......................................................................................3

4.1 Subsurface Soil Conditions............................................................................................... 3 4.2 Groundwater ..................................................................................................................... 4

5 GEOLOGIC HAZARDS..............................................................................................................5 5.1 Faulting and Seismicity..................................................................................................... 5 5.2 Geologic Hazards Associated with Earthquakes............................................................... 5

5.2.1 Ground Rupture ................................................................................................... 6 5.2.2 Ground Shaking ................................................................................................... 6 5.2.3 Tsunamis and Seiches .......................................................................................... 6 5.2.4 Seismic-Induced Flooding ................................................................................... 6 5.2.5 Liquefaction ......................................................................................................... 6 5.2.6 Seismic-Induced Settlement................................................................................. 7 5.2.7 Seismic-Induced Instability.................................................................................. 7

5.3 Collapsible Soils ............................................................................................................... 7 5.4 Expansive Soils ................................................................................................................. 7 5.5 Landslides ......................................................................................................................... 7

6 SITE SLOPE STABILITY...........................................................................................................8 6.1 Existing Conditions........................................................................................................... 8 6.2 Slope Stability Evaluation................................................................................................. 9

6.2.1 Strength Selection .............................................................................................. 10 6.2.2 Preliminary Screening........................................................................................ 11 6.2.3 Stability analyses of Specific Cases................................................................... 11

6.3 Site Remediation ............................................................................................................. 12 7 LIMITATIONS ..........................................................................................................................13 REFERENCES TABLE 1 SUMMARY OF STRENGTH PARAMETERS – SLOPE STABILITY

ANALYSES TABLE 2 BEDDING FEATURES OBSERVED IN TERRACOSTA CONSULTING

GROUP BORINGS TABLE 3 BEDDING FEATURES OBSERVED IN VINJE & MIDDLETON

BORINGS TABLE 4 SUMMARY OF SLOPE STABILITY ANALYSES FIGURE 1 VICINITY MAP FIGURE 2a REGIONAL GEOLOGY MAP

GRANDVIEW COMMUNITY HOMES, LLC March 15 2016 Project No. 2869-02

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TABLE OF CONTENTS (Continued)

FIGURE 2b REGIONAL GEOLOGY MAP LEGEND FIGURE 3a SITE PLAN AND GEOLOGIC MAP FIGURE 3b TENTATIVE MAP / PROPOSED GRADING PLAN FIGURE 4 CROSS SECTION A FIGURE 5 CROSS SECTION B FIGURE 6 CROSS SECTIONS C AND D FIGURE 7 1964 AERIAL PHOTO FIGURE 8 LOMA ALTA CREEK CHANNEL FIGURE 9 SLOPE BUTTRESS LIMITS FIGURE 10 BUTTRESS CROSS SECTION

APPENDIX A CITY OF OCEANSIDE MEMO, AUGUST 28, 2016

APPENDIX B LOGS OF EXPLORATORY EXCAVATIONS (TerraCosta Consulting Group, Inc. and Vinje & Middleton Engineering, Inc.)

APPENDIX C LABORATORY TEST RESULTS (TerraCosta Consulting Group, Inc. and Vinje & Middleton Engineering, Inc.)

APPENDIX D SLOPE STABILITY CALCULATIONS

GRANDVIEW COMMUNITY HOMES, LLC March 15, 2016 Project No. 2869-02 Page 1

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GEOLOGIC REPORT FOR TENTATIVE MAP

GRANDVIEW POINTE PROJECT 1902 GRANDVIEW STREET OCEANSIDE, CALIFORNIA

1 INTRODUCTION AND PROJECT DESCRIPTION

TerraCosta Consulting Group, Inc. (TerraCosta) has completed a geologic report for the development of a tentative map for the Grandview Pointe project located at 1902 Grandview Street in the City of Oceanside, California. This report was prepared in general accordance with the guidelines for geologic reports for tentative map as presented in the City of Oceanside’s Engineering Manual.

Figure 1, the Vicinity Map, shows the approximate site location in the context of major topographic features, freeways, and surface streets within the surrounding metropolitan area of Oceanside.

This report presents the results of our most recent document reviews, field investigations and laboratory testing, as well as our geologic and geotechnical findings concerning the stability of site slopes and their relationship to the proposed site development. Figures 2a and 2b, the Regional Geology Map and Accompanying Legend, locate the site in relation to the principal geologic features and formational soil units in the general Oceanside metropolitan area.

Figures 3a and 3b, respectively, present the Site Plan and Geologic Map (with the locations of all appropriate subsurface explorations as well as the alignments of four geologic cross sections) and the proposed Tentative Map/Grading Plan for the project. Figures 4, 5, and 6 present generalized geologic Cross Sections A, B, C, and D, extending down the natural slopes around the northerly half of the site.

We understand that the 27-lot single-family residential subdivision is planned with no significant cut or fill slopes between lots, and with 2:1 (horizontal to vertical) fill slopes at the top of the natural canyon slopes which are limited in lateral extent and which range in maximum height from 5 feet to 20 feet.



2 SCOPE OF WORK

The purpose of this investigation is to provide information to assist Grandview Community Homes, LLC, the project technical team, and the City of Oceanside in evaluating the site as it pertains to the submittal and approval of the proposed tentative map for the project. In addition, our study is prepared to address the specific slope stability issues posed by the comments of geotechnical consultant to the City, James Knowlton. A copy of the City’s memorandum stating Mr. Knowlton’s comments is presented in Appendix A of this report.

In general, our scope of work addressing the following geotechnical issues:

• The geologic/geotechnical setting of the site;

• General geologic hazards, such as faulting and seismicity;

• Landslide potential within the project site boundaries, on adjacent properties, and underlying the natural canyon and valley slopes surrounding the site;

• General engineering characteristics of the identified geologic units including analyses of on-site allowable soil-bearing and earth pressure values;

• The depth to groundwater where encountered by our explorations; and

• An assessment of the stability of site slopes and the associated remedial measures needed to maintain the stability of the site slopes in accordance with the City of Oceanside requirements.

3 FIELD AND LABORATORY INVESTIGATIONS

Our field investigations, performed between February 9, 2015, and December 1, 2015, included a geologic reconnaissance of the site and surrounding areas, and the drilling, sampling, and downhole logging of five 30-inch-diameter bucket-auger test borings ranging in depth from 55.0 feet to 83.5 feet. The approximate locations of our test borings are shown on Figure 3a, the Site Plan and Geologic Map, along with the locations of selected test



borings and test trenches from a previous site investigation performed by Vinje & Middleton Engineering, Inc. (V&M), reported October 13, 2004.

Samples obtained from the borings were sealed in the field to preserve in-situ moisture, and transported to the laboratory for additional inspection and testing. The drilling operations were observed, and the test borings were downhole logged, classified, and sampled by geologists from our firm (Greg Spaulding and Bob Smillie).

Field logs and materials encountered in the test borings were prepared based on downhole examination (bedding attitude measurements, pocket penetrometer testing, etc.), sampling, and on the action of the drilling equipment. The descriptions on the logs are based on our field observations, sampling inspection, and laboratory test results.

TerraCosta’s logs of test borings as well as V&M logs of test borings and test pits are presented in Appendix B of this report.

Laboratory tests were performed to characterize soil properties, as needed, to develop engineering indices for slope stability analyses and to aid in the design of foundations, pavements, etc. The results of laboratory tests are provided in Appendix C, and on the test boring logs of both TerraCosta and V&M.

4 SITE CONDITIONS AND GEOLOGY

4.1 Subsurface Soil Conditions

Three generalized soil units mapped on the subject site are described below in order of increasing age.

Artificial Fill Soils (Qaf) – Uncompacted to moderately compacted, light brown to tan, silty sand fill soils and typically disturbed loose and porous silty to clayey topsoils were encountered at various locations across the site to depths on the order of 1 to 4 feet, the deeper fills existing around the edges of the area to be graded, at the top of the natural canyon slopes. These fill soils, which appear to be the result of minor surficial grading on the site, are mapped where trench logs indicate fill depths greater than 3 feet. The



maximum depth of fill and loose porous topsoils combined is noted in the log of V&M Test Pit T-2, a total of 7.5 feet.

Terrace Deposits (Qop) – Middle to late Quaternary-age terrace deposits generally consisting of medium dense to dense, damp, reddish-brown to tan, silty medium to fine sand (SM) were encountered over large areas of the site, generally above elevation 130 feet (MSLD). These deposits typically are capped by expansive clay soils ranging from 0 to 1½ feet in thickness.

Santiago Formation (Tsa) – Well-consolidated, moderately indurated, marine, very light gray clayey siltstones and sandstones containing interbedded layers and lenses of dark gray, fine sandy to clayey siltstone and silty claystone, characteristic of the Santiago Formation of middle Eocene-age (49 to 45 million years) underlie the terrace deposits and form the natural canyon slopes to the north and west beyond the limits of the property boundaries, and extend well below the nearby canyon bottoms and valley floors. It should be noted that gentle folding of the Santiago Formation strata across the region has resulted in westerly to northwesterly dips which are locally “adverse” or dipping out-of-the existing natural slopes to the west-northwest and north-northwest. Addressing this structural condition and its potential for creating slope instability and the potential for the type of landslides in the general project site area is the principal objective of the current geotechnical investigation, slope stability analyses, and recommendations provided in this report.

4.2 Groundwater

No groundwater was encountered in any of the backhoe test pits or large-diameter test borings logged by V&M and reported October 13, 2004.

Groundwater seepage was encountered in three of the five large-diameter test borings logged by TerraCosta at the following depths and elevations:

• B-2: Depth 65 feet/Elevation +72 feet





The groundwater in boring B-5 is likely reflective of the regional groundwater conditions.

Given that the site is anticipated to be developed with residential units and that the regional area has been in drought conditions, we anticipate that long term irrigation will likely result in an accumulation of water on perching horizons underlying the site. As such, the thickness of seep zones and number of seeps may likely increase over time.

5 GEOLOGIC HAZARDS

5.1 Faulting and Seismicity

The site is located in a moderately-active seismic region of Southern California that is subject to significant hazards from moderate to large earthquakes. Ground shaking from four relatively close major active fault zones in the region could affect the site in the event of a large earthquake. These are the Newport-Inglewood (offshore), Rose Canyon, Coronado Bank, and Elsinore (Temecula) fault zones, the nearest of these being the north-south to north-northwest trending Newport-Inglewood fault zone, that has been mapped approximately 4.9 miles west of the site. Using the computer program EQFAULT, these four faults are estimated to produce earthquakes having moment magnitudes of 6.8 to 7.6 which are anticipated to result in maximum peak ground accelerations from 0.13 to 0.42.

Using the computer program EQSEARCH, we searched the currently available database for historical earthquakes that may have impacted the site. The largest site acceleration that the site has experienced within the limits of the database is estimated to be approximately 0.2g. The earthquake event corresponding to that event occurred on November 11, 1800, and had an estimated moment magnitude of 6.5 and is estimated to have occurred approximately 13 to 14 miles from the site.

5.2 Geologic Hazards Associated with Earthquakes

Geologic hazards generally associated with earthquakes include ground rupture, ground shaking, tsunamis, seiches, seismic-induced flooding, liquefaction, seismic-induced ground settlement, and seismic-induced slope instability. With respect to these hazards, we have the following comments.



5.2.1 Ground Rupture

We have reviewed available geologic data, i.e., fault maps from the California Department of Mines and Geology and other geologic maps of the area. The site is not located within a State of California Alquist-Priolo Special Studies Zone for earthquake faults. In addition, no potentially-active faults have been mapped that traverse the site. Thus, it is our opinion that the risk associated with ground rupture is negligible to low.

5.2.2 Ground Shaking

The project site will be subjected to ground shaking. One common method for characterizing ground shaking for a project site is use of the response spectra. Two key spectral ordinates for the CBC response spectra are short period spectral acceleration and the spectral acceleration corresponding to a period of 1 second. Using procedures outline in the 2113 CBC, and for a soil profile classification of SITE CLASS D we estimate that for the Maximum Considered Earthquake (MCE) the short period and 1 second spectral accelerations are 1.188g and 0.683g, respectively. The corresponding design level spectral accelerations for the short period and 1 second period are 0.792g and 0.455g, respectively.

5.2.3 Tsunamis and Seiches

In our opinion, the risk associated with tsunamis and seiches is negligible.

5.2.4 Seismic-Induced Flooding

In our opinion, the potential for seismic-induced flooding of the site from retained bodies of waters is negligible. However, as with any urban location, the site could be subjected to flooding associated with seismic-induced rupture of water mains or pipes.

5.2.5 Liquefaction

Based on site and subsurface conditions, it is our opinion that the potential for liquefaction of the subsurface soils is negligible.



5.2.6 Seismic-Induced Settlement

In our opinion, the subsurface soils are not susceptible to significant amounts of seismic-induced settlement.

5.2.7 Seismic-Induced Instability

See Section 6 of this report for a discussion concerning seismic-induced slope instability.

5.3 Collapsible Soils

The surface fills on site were observed to be porous and potentially collapsible in their current condition. As such during the grading of the site, these soils will either have to be removed from the site or re-compacted within the proposed project limits.

5.4 Expansive Soils

Soils having an expansion potential of medium to high are present on the site. The risk associated with expansive soils is considered medium to high depending on the specific location of buildings. These soils consist of a relatively thin layer of soils within the terrace deposits and the siltstone and claystone layers of the Santiago Formation. These expansive soils will either need to be removed and replaced within the foundation areas of the proposed buildings or the building foundations will need to be designed to accommodate the potential expansion of these soils.

5.5 Landslides

We did not observe any features indicative of ancient natural landslides on, or adjacent to, the proposed project site limits. However, during our logging of our exploratory borings, bedding plane shears were observed in Boring B-2. As such, remediation of the site to address the stabilization of slopes may be needed. See Section 6 for our evaluation and discussion concerning the slope stability of site slopes.



6 SITE SLOPE STABILITY

6.1 Existing Conditions

The proposed development is located on an existing hill with descending natural slopes located to the northwest and northeast.

From our review of available geologic studies and maps, no landslides have been mapped at the site. However, in our interactions with the City of Oceanside, the City indicated concern regarding the stability of both onsite and offsite slopes in the study area. The City informed TerraCosta that the single-family residence located on a terraced property immediately to the west of the project site has been identified as having a possible ancient landslide. We further understand that no site investigation has been conducted for the property and that the limits of the suspected ancient landslide are unknown. In addition, the City informed TerraCosta that the entire west facing slope of the property to the east has been buttressed as part of the development grading.

In addition, from our review of V&M’s October 13, 2004, report titled “Preliminary Geotechnical Investigation, Proposed 7-Lot Subdivision, Grandview Street, Oceanside,” we note the following comments concerning the slope stability of the site (we have not included the various plates referenced in the V&M report in this report):

• On page 2 of V&M’s report they state “Structural orientations were chiefly noted along sandstone/siltstone contacts or along darker mineral beds within the exposed sandstone section. Noted bedding data are given on the enclosed logs and graphically presented on the enclosed Plate 2. The data confirm nearly flat-lying to low angle dips to the north for bedding conditions beneath the property.”

• Continuing on Page 2 of V&M’s report they state “Critical structure is also shown on geologic Cross-Sections enclosed within this report as Plate 13. These conditions suggest marginal stability within the north-facing slope at the property which is likely a near dip-slope condition.”

• On Page 10 in their conclusion section, they state “The main geotechnical factor at the site will be instability within the impacted project hillsides. Geologic structure conditions along the north perimeter of the project site are unfavorable, and marginal



conditions of stability are therefore indicated (see Plate 2 and Cross-Sections A-A’ and B-B’, Plate 13). Consequently surrounding terrain (designated Lot 6 on the enclosed map) should be excluded from residential development and may be designated as open space or for the support of non-habitual improvements. Stabilization of Lot 6 terrain could be achieved by the construction of buttress or shear key fills. However, such an effort would require a costly, off-site grading project.”

• “Significant landslide areas are known in nearby areas of the City of Oceanside. Similar north-facing terrain of the Skylark Terrace Subdivision, east of the project site developed an active landslide condition in 1977-78.”

Given the City’s concern and V&M’s comments, we reviewed the aerial photographs of the site slopes in 1964 when the down slope properties were developed (see Figure 7). These developments cut into the existing hillsides as part of their site grading efforts. We understand that during these grading operations relatively shallow slope failures occurred. From our review of the data, these slides appeared to be located within the colluvial soils that have subsequently been removed during grading. Photographs today show these cut portions of the slopes which appear to be in formation (see Figure 8).

In addition to reviewing historical photographs we conducted a site investigation consisting of the downhole logging of five large diameter bucket auger borings, ranging in depth from 55 to 83 feet, so as to observe the subsurface structure and conditions of the site slopes. The logs of our test borings as well as V&M’s logs of test borings are presented in Appendix B.

Using the data collected both from TerraCosta and V&M large diameter borings, we performed slope stability analyses to assess the general stability of the site and the possible need for remediation. The details of our analyses are presented in Section 6.2. On the basis of our analyses, portions of the slopes at the site need to be stabilized in order to comply with the City of Oceanside’s minimum stability requirements. A discussion and our recommendations for the slope stability remediation are presented in Section 6.3 of this report.

6.2 Slope Stability Evaluation

Our evaluation of the stability of the site slopes consisted of the following steps:



1. Selecting soil strengths for the various stratigraphic units and potential slide plane interfaces;

2. Preliminary stability screen of observed bedding dips and bedding plane shears;

3. Slope stability analyses of selected bedding plane controlled configurations;

4. Slope stability of slopes independent of bedding plane features; and

5. Slope stability of remediated slopes.

A brief discussion of these steps is presented below.

6.2.1 Strength Selection

As described in Section 4.1 there are three soil and geologic units at the site. Theses units are fill, Quaternary terrace deposits, and Santiago Formation. In addition, within the Santiago Formation there are structural features related to bedding dips and bedding plane shears which can potentially influence the stability of the site slopes. Strength parameters for each of these units and features were selected.

For the geologic units, we based our strength parameters on our experience with these materials. For the structural features we assumed that potential failures could occur along their orientation. As such, we assumed that the potential for failure along those features identified as bedding dips is controlled by the characteristics of a first time failure and we assigned a corresponding fully softened strength to this feature. For our evaluation of stability along features identified as bedding plane shears, we assigned strengths corresponding to their residual values.

Our assessment of fully softened and residual strengths was based on the empirically based correlations (Stark, 2013). Results of our laboratory testing of materials indicated that for the more plastic features these materials have liquid limits that ranged from 53 to 68, plastic indices that ranged from 18 to 36, fines content that ranged from 50 to 89 percent, and a clay contents that ranged from 12 to 15 percent.

A summary of the strengths used in our analyses is presented in Table 1.



6.2.2 Preliminary Screening

Bedding dips and bedding plane shears were observed in some of TerraCosta’s and V&M’s borings and V&M’s trenches. However, the frequency of observed bedding plane shears was significantly less than the observed bedding dips between the interbedded sandstones, siltstones, and claystones. The bedding attitudes of the observed features are summarized in Tables 2 and 3.

In order to sort out the relative significance of the various orientations of the bedding features, we computed the apparent dips of the various bedding features for various orientations of the slope faces at the site. In those cases where the feature had a computed factor of safety less than 1.5 we noted as being potentially significant and warranted further assessment. The computed factor of safety was based on a simple wedge block failure mechanism which compared the tangent of the angle of friction of the bedding feature to the tangent of the apparent dip. In other words we divided the tangent of the angle of friction of the fully softened and residual conditions by 1.5. Thus, bedding dips having an apparent dip less than or equal to 19 degrees were considered significant and bedding plane shears having an apparent dip less than 12 degrees was considered significant. The apparent dips satisfying these conditions are bolded and italicized in Tables 2 and 3.

From this screening there is one set of bedding plane shears located in TerraCosta Boring B-2 and a fracture zone in V&M test pit T-10 that have an orientation and estimated strength indicating that the factor of safety against block failure is less than 1.5. The orientation of this features are to the slopes that face generally to the north-west. For further examination we evaluated the stability of this slope face based on the orientation of geologic cross-section B shown on Figure 4. It is important to note that the fracture is not present in TerraCosta Boring B-2 or B-3 and as such is considered to not be an on going fracture for consideration.

6.2.3 Stability analyses of Specific Cases

We evaluated the stability of the site slopes by performing slope stability analyses on Section B shown on Figure 4 and Section C as shown on Figure 5. We used the identified bedding features shown on Borings B-2 and B-3 to describe the features within the slope section. We used the computer program GSTABL to evaluate both circular failures as well as block failures along bedding features. Lastly we assume that future conditions might lead to perched groundwater conditions. As such we assumed a 5 foot perched condition on each



bedding feature that we evaluated. For the general assessment of slope stability assuming no inherent structural defect, we have assumed that the groundwater level we encountered in our test boring B-1 at +4 feet msld reflects the regional groundwater table and as such, is below the zone of interest.

The results of our stability analyses are summarized in Table 4 with computer printouts presented in Appendix D.

The results of our stability analyses also indicated that the slope represented by Section C (see Figure 5) had a computed factor of safety greater than 1.5 for static conditions and 1.1 for pseudo-static conditions under a seismic coefficient of 0.15. for the condition of no perched water. When perching water conditions are assumed, the computed factor of safety is less than 1.5 for static and 1.1 for puesdo-static. Given that infiltration and the development of perching horizons pose potential impacts to the stability of the slope, remedial action, consisting of the installation of a hydroauger slope drainage system, is recommended for this slope.

However, the results for the slope represented by Section B (see Figure 4), had a computed factor of safety less than 1.5 for static conditions and less than 1.1 for pseudo-static conditions under a seismic coefficient of 0.15. As such this slope will require remediation consisting of a construction of a slope buttress.

6.3 Site Remediation

Results of our stability analyses for the subject site slopes indicate that the northwesterly facing slope below TerraCosta boring B-2 needs to be remediated in order to comply with the City of Oceanside Grading Ordinance. Review of data collected during our investigation indicates that the portion of the slope that needs remediation is limited to the area shown on Figure 9. The results of our analyses indicate that a slope buttress can be used to bring the slope up to a minimum factor of safety of 1.5 for static conditions and 1.1 for pseudo-static conditions.

For the remediation of the slope for that portion delineated on Figure 9, we recommend that the buttress key be founded at elevation 86 feet and that the buttress key has a minimum width as measured at the bottom of the key of 30 feet. In addition we recommend that the buttress start at elevation 100 except for those portions outside the property line where the



buttress will start at the ground surface with a descending 1:1 (horizontal to vertical) inclination to the bottom of the key. The ascending slope of the key as shown on Figure 10 is to be inclined at a temporary construction slope inclination of 1:1. We recommend that a gravel chimney drain be constructed at the back of the buttress key and daylighted to drain to the north of the project site.

It should be noted that, during the process of grading the backcut for the buttress, the portion of the slope above the upper bedding plane shear may fail, in which case the construction-period geotechnical engineer-of-record should be consulted on the appropriate in-progress repair and (if necessary) the redesign of the buttress geometry.

In addition, and as indicated in the analyses presented above, the north- to northeast-facing slope that is characterized by Section C on Figure 5 will likely be impacted to some degree by the development of perching horizons. As such, we recommend that this slope be remediated by constructing a slope drainage system consisting of hydroauger slope drains. The suggested limits of the drainage system are indicated on Figure 9.

7 LIMITATIONS

This report, exploration logs, and other materials resulting from TerraCosta Consulting Group’s efforts were prepared exclusively for use in the preparation of the tentative map for the project. This report is not intended to be suitable for re-use on extensions or modifications of the project or for use on any other development, as it may not contain sufficient or appropriate information for such uses. If this report or portions of this report are provided to contractors or included in specifications, it should be understood that it is provided for information purposes only. Our recommendations and evaluations were performed using generally accepted engineering approaches and principles available at this time, and the degree of care and skill ordinarily exercised under similar circumstances by reputable geotechnical engineers practicing in this area. No other representation, either expressed or implied, is included in our report.

We have investigated only a small portion of the pertinent soil, rock, and groundwater conditions the subject site. The opinions and conclusions made herein are based on the assumption that those rock and soil conditions do not deviate appreciably from those encountered during our field investigation. We recommend that an engineer or geologist



from our office observe construction to assist in identifying soil conditions that may be significantly different from those anticipated in our design. Additional recommendations may be required at that time.


REFERENCES Bjerrum, L., 1967, “Progressive Failure in Slopes of Overconsolidated Plastic Clay and Clay

Shales,” in Journal of the Soil Mechanics and Foundations Division, Proceedings of the American Society of Civil Engineers, Vol. 93, No. SM5, pp. 3-49.

Eisenberg, L.I., and P.L. Abbott, 1985, “Eocene Lithofacies and Geologic History, Northern San Diego County,” in P.L. Abbott (ed.), On the Manner of Deposition of the Eocene Strata in Northern San Diego County, San Diego Association of Geologists, pp. 19-35.

Fischer, P.J., and G.I. Mills, 1991, “The Offshore Newport-Inglewood - Rose Canyon Fault Zone, California: Structure, Segmentation and Tectonics,” in P.L. Abbott and W.J. Elliott (eds.), Environmental Perils - San Diego Region, published by San Diego Association of Geologists, pp. 17-36.

Kennedy, M.P., and S.S. Tan, 2008, Geologic Map of the Oceanside 30’ x 60’ Quadrangle, Map Scale 1:100,000, California Department of Conservation, California Geological Survey, and the U.S. Geological Survey.

Mitchell, J.K., 1993, Fundamentals of Soil Behavior, Second Edition, John Wiley & Sons, Inc.

Skempton, A.W., and J.N. Hutchinson, 1969, “Stability of Natural Slopes,” in Proceedings of the 7th International Conference on Soil Mechanics and Foundation Engineering, Mexico, pp. 291-340.

Skempton, A.W., 1970, “First-Time Slides in Overconsolidated Clays,” in Géotechnique, Vol. XX, No. 3., pp. 320-324.

Skempton, A.W., 1985, “Residual Strength of Clays in Landslides, Folded Strata and the Laboroaty,” in Géotechnique, Vol. XXXV, No. 1, pp. 3-18.

Stark, T.D., 2013, Empirical Correlations: Drained Shear Strength for Slope Stability Analyses, Article in Journal of Geotechnical and Geoenvironmental Engineering, June 2013.

Tan, S.S., and D.G. Giffen, 1995, Landslide Hazards in the Northern Part of the San Diego Metropolitan Area, San Diego County, California, California Department of Conservation, Division of Mines and Geology, DMG Open-File Report 95-04.

Weber, F.H., Jr., 1982, Recent Slope Failures, Ancient Landslides, and Related Geology of the North-Central Coastal Area, San Diego County, California, California Department of Conservation, Division of Mines and Geology, Open-File Report 82-12.



TABLE 1

SUMMARY OF STRENGTH PARAMETERS SLOPE STABILITY ANALSYES

Material Unit Weight Pcf

Angle of Friction degree

Cohesion psf

Fill 125 30 200

Terrace 120 30 300

Santiago Formation 125 30 300

Bedding Dip (Fully Softened) 110 28 0

Bedding Plane Shear (Residual) 110 18 0



TABLE 2

BEDDING FEATURES OBSERVED IN TERRACOSTA CONSULTING GROUP BORINGS

Apparent Dips for Strike of Slope Face

Boring Elev. ft Strike Dip Feat.

N50W N28W N15E N58E N68E N90E

B-1 130 N30E 3N BD 0.5S 1.6S 2.9N 2.6N 2.4N 1.5N B-1 127 N25E 3N BD 0.8S 1.8S 3.0N 2.5N 2.2N 1.3N B-1 115 N40E 4N BD 0 1.5S 3.6N 3.8N 3.5N 2.6N B-1 106 N0E 3N BD 1.9S 2.6S 2.9N 1.6N 1.1N 0 B-1 98 N0E 0 BD 0 0 0 0 0 0 B-2 124 N55E 20N BPS 5.4N 2.5S 15.6N 20N 19.5N 16.6N B-2 122 N55E 14N BD 3.7N 1.7S 10.8N 14N 13.7N 11.5N B-2 121 N35E 8N BPS 0.7S 3.7S 7.5N 7.4N 6.7N 4.6N B-2 117 N40E 8N BD 0 3S 7.3N 7.6N 7.1N 5.2N B-2 109 N55E 5N BD 1.3N 0.6S 3.8N 5N 4.9N 4.1N B-2 105 N15E 17N BD 7.4S 12.6S 17N 12.6N 10.4N 4.5N B-2 102 N70E 6N BPS 3N 0.8N 3.4N 5.9N 6N 5.6N B-2 99 N35E 10N BD 0.9S 4.6S 9.4N 9.2N 8.4N 5.8N B-2 87 N45E 16N BD 1.4N 4.8S 13.9N 15.6N 14.8N 11.5 B-2 81 N5E 18N BD -10.4S 15.2S 17.7N 11.1N 8.4N 1.6N B-3 131 N42E 13N BD 0.4N 4.2S 10.7N 11.5N 10.8N 8.1N B-3 128 N45E 16N BD 1.4N 4.2S 13.9N 15.6N 14.8N 11.5N B-3 110 N12E 8N BD 3.8S 6.1S 8N 5.6N 4.5N 1.7N B-3 84 N18E 4N BD 1.5S 2.8S 4N 3.1N 2.6N 1.2N B-3 77 N85E 13N BD 9.3N 5.2N 4.5N 11.6N 12.5N 13N B-4 123 N10E 6N BD 3S 4.7S 6N 4N 3.2N 1N B-4 114 N0E 9N BD 5.8S 8S 8.7N 4.8N 3.4N 0 B-4 109 N8E 6N BD 3.2S 4.9S 6N 3.9N 3N 0.8N B-4 104 N6E 4N BD 2.2S 3.3S 4N 2.5N 1.9N 0.4N B-4 97 N15E 2N BD 0.8S 1.5S 2N 1.5N 1.2N 0.5N B-4 86 N0E 6N BD 3.9S 5.S 5.8N 3.2N 2.3N 0 B-5 56 N68E 4N BD 1.9N 0.4N 2.4N 3.9N 4N 3.7N B-5 53 N74E 5N BD 2.8N 1N 2.6N 4.8N 5N 4.8N B-5 32 N20E 4N BD 1.4S 2.7S 4N 3.2N 2.7N 1.4N B-5 21 N20E 4N BD 1.4S 2.7S 4N 3.2N 2.7N 1.4N



TABLE 3

BEDDING FEATURES OBSERVED IN VINJE & MIDDLETON BORINGS

Apparent Dips for Strike of Slope Face Boring Elev.

ft Strike Dip Feat. N50W N28W N15E N58E N68E N90E

B-1 125 N22E 20N BD 6.4S 13.2S 19.9N 16.4N 14.2N 7.8N B-1 120 N0E 12N BD 7.8S 10.6S 11.6N 6.4N 4.6N 0 B-1 118 N10E 18N BD 9.2S 14.4S 17.9N 12.3N 9.8N 3.2N B-1 114 N10W 10N BD 7.7S 9.5S 9.1N 3.8N 2.1N 1.8S

B-2 122 N15E 10N BD 4.3S 7.3S 10N 7.3N 6.1N 2.6 B-2 110 N25W 10N BD 9.1S 10S 7.7N 1.2N 0.5S 4.3S B-2 108 N10W 18N BD 14.0S 17.2S 16.4N 6.9N 3.9N 3.2S

B-3 134 N0E 6N BD 3.9S 5.3S 5.8N 3.2N 2.3N 0 B-3 1132 N30W 7S BD 6.6N 7N 5S 0.2S 1N 3.5N

B-4 125 0 0 BD 0 0 0 0 0 0 B-4 120 0 0 BD 0 0 0 0 0 0

T-5 3 N60E 18N BD 6.3N 0.6S 12.9N 18N 17.8N 15.7N T-5 5 N30W 18N BPS -17S 18S 12.9N 0.6N 2.6S 9.2S

T-7 5 N10E 14N BD 7.3S 11.1S 13.9N 9.5N 7.5N 2.5N

T-9 5 N42E 14N BD 0.5N 4.9S 12.5N 13.5N 12.6N 9.5N T-9 7 N42E 14N BD 0.5N 4.9S 12.5N 13.5N 12.6N 9.5N

T-10 3 N70E 18N Frac 9.2N 2.6N 10.6N 17.6N 18N 17N T-10 5 N68E 8N BD 3.8N 0.8N 4.8N 7.9N 8N 7.4N T-10 7 N68E 8N BD 3.8B 0.8N 4.8N 7.9N 8N 7.4N

T-12 3.5 N10W 5N BD 3.8S 4.8S 4.5N 1.9N 1N 0.9S



TABLE 4

SUMMARY OF SLOPE STABILITY ANALYSES

Section Case Factor of Safety

B(2) No features - Static 1.98 B(2) No features - pseudo-static 1.40 B(2) Upper bedding plane shear – static 1.01 B(2) Upper bedding plane shear - pseudo-static 0.68 B(2) Lower bedding plane shear - static 1.34 B(2) Lower bedding plane shear – pseudo-static 0.88 B(2) Lower bedding plane shear – static with perched water 1.19 B(2) Lower bedding plane shear – pseudo-static with perched water 0.77 B(2) Buttress No Features - static 1.89 B(2) Buttress No Features – pseudo-static 1.34 B(2) Buttress Upper bedding plane shear static with perched water 1.74 B(2) Buttress Upper bedding plane shear- pseudo-static with perched water 1.16 B(2) Buttress Lower bedding plane shear – static with perched water 1.88 B(2) Buttress Lower bedding plan shear – pseudo-static with perched water 1.27 C(3) No features – pseudo-static 1.53 C(3) Bedding Dip a - static 1.73 C(3) Bedding Dip a – static with perched water 1.44 C(3) Bedding Dip a – pseudo-static 1.22 C(3) Bedding Dip a – pseudo-static with perched water 1.0 C(3) Bedding Dip b - static 1.98 C(3) Bedding Dip b – static with perched water 1.71 C(3) Bedding Dip b – pseudo-static 1.40 C(3) Bedding Dip b – pseudo-static with perched water 1.19 C(3) Bedding Dip c – static 2.32 C(3) Bedding Dip c – pseudo-static 1.58 C(3) Bedding Dip d – static 3.19 C(3) Bedding Dip d – pseudo-static 2.08

Project: 1902 Grandview Street Project No. 2869 Figure No. 1 Project: 1902 Grandview Street Project No. 2869 Figure No. 1

VICINITY MAP VICINITY MAP

5

NOTE:NOTE:

1) USGS Topographic base map reproduced from TOPO! National Geographic Holdings, 2000

0 200010000 2000

(Approx. Scale: Feet)(Approx. Scale: Feet)

1000

Consulting Group

TerraCosta TerraCosta TerraCosta

SITE LOCATION SITE LOCATION

Project: 1902 Grandview Street Project No. 2869 Figure No. 2a Project: 1902 Grandview Street Project No. 2869 Figure No. 2a

REGIONAL GEOLOGY MAPREGIONAL GEOLOGY MAP

5

0 200010000 2000

(Approx. Scale: Feet)(Approx. Scale: Feet)

1000

Consulting Group


SITE LOCATION SITE LOCATION

REFERENCE:REFERENCE:Geologic Map of the San Diego 30’ x 60’Quadrangle, California, Compiled by Michael P. Kennedy and Siang S. Tang, 2005. Qls

Qls

Qls

Tsa

Tsa

Tsa

Project: 1902 Grandview Street Project No. 2869 Figure No. 2b Project: 1902 Grandview Street Project No. 2869 Figure No. 2b

REGIONAL GEOLOGY MAP - LEGENDREGIONAL GEOLOGY MAP - LEGEND

Consulting Group


REFERENCE:REFERENCE:Geologic Map of the San Diego 30’ x 60’Quadrangle, California, Compiled by Michael P. Kennedy and Siang S. Tang, 2005.

ONSHORE MAP SYMBOLS

TerraCosta Consulting Group, Inc. 3890 Murphy Canyon Road, Suite 200

San Diego, California 92123 (858) 573-6900 Project Name

1902 Grandview Ave., Oceanside, CA Project No.

2869

Loma Alta Creek Channel

Figure No. 8

Looking southwest (down stream) along the concrete-lined Loma Alta Creek channel, constructed circa 1964 within the same general timeframe as the massive grading project illustrated on Figure 7.

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Appendix 6 Geotechnical and Groundwater Investigation Report

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