23-141-SC_Geotechnical_Investigation_141_Archer.pdf

GEOTECHNICAL INVESTIGATION

DESIGN PHASE

FOR

PROPOSED RETAINING WALL MITIGATION

141 ARCHER DRIVE

SANTA CRUZ, CALIFORNIA

PREPARED FOR

SCOTT WINTON

PROJECT NO. 23-141-SC

PREPARED BY

BUTANO GEOTECHNICAL ENGINEERING, INC.

JUNE 2023

B U T A N O G E O T EC H N I C A L E N G I N E E R I N G , I N C .

404 WESTRIDGE DRIVE, WATSONVILLE, CALIFORNIA 95076

PHONE: 831.724.2612

WWW.BUTANOGEOTECH.COM

June 1, 2023 Project No. 23-141-SC

Scott Winton 141 Archer Drive Santa Cruz, Ca 95060

SUBJECT: GEOTECHNICAL INVESTIGATION - DESIGN PHASE

Proposed Retaining Wall Mitigation 141 Archer Drive Santa Cruz, California

In accordance with your authorization, we have completed a geotechnical investigation for the subject project. This report summarizes the findings, conclusions, and recommendations from our field exploration and engineering analysis. It is a pleasure being associated with you on this project. If you have any questions, or if we may be of further assistance, please do not hesitate to contact our office.

Sincerely, BUTANO GEOTECHNICAL ENGINEERING, INC.

Greg Bloom, PE, GE C. Scott Clark Principal Engineer Staff Engineer E.I.T. 162365

Appendices: 1. Appendix A Figures and Standard Details

2. Appendix B Field Exploration Program

3. Appendix C Laboratory Program

Distribution: (4) Addressee

Geotechnical Investigation - Design Phase June 1, 2023 141 Archer Drive Project No. 23-141-SC Soquel, Santa Cruz County, California Page 3

1.0 INTRODUCTION

This report presents the results of our geotechnical investigation for the proposed retaining wall mitigation at 141 Archer Drive in Santa Cruz, California.

The purpose of our investigation is to provide preliminary geotechnical design parameters and recommendations for the proposed residential construction. Conclusions and recommendations related to site grading, drainage, retaining walls and foundations are presented herein.

This work includes site reconnaissance, subsurface exploration, soil sampling, laboratory testing, engineering analysis, and preparation of this report. The scope of services for this investigation is outlined in our agreement dated January 31, 2023.

The recommendations contained in this report are subject to the limitations presented in Section 8.0 of this report. The Association of Engineering Firms Practicing the Geosciences has produced a pamphlet for your information titled Important Information About Your Geotechnical Report. This pamphlet has been included with the copies of your report.

2.0 PROJECT DESCRIPTION

A portion of the existing retaining walls failed during a heavy rainstorm in the winter of 2022/2034. Based on our discussions with the client, the project consists of replacing the failed section of walls with a new retaining wall(s).

3.0 FIELD EXPLORATION AND LABORATORY TESTING PROGRAMS

Our field exploration program included drilling, logging, and interval sampling of two borings on April 19, 2023. The borings were advanced to depths of 12 and 13 feet using a rope and cathead to advance continuous samples. Details of the field exploration program, including the Boring Logs and the Key to the Logs, are presented in Appendix B, Figures B-3 through B-5.

Representative samples obtained during the field investigation were taken to the laboratory for testing. Laboratory tests were used to determine physical and engineering properties of the in-situ soils. Details of the laboratory testing program are presented in Appendix C. Test results are presented on the Boring Logs and in Appendix C.

Soquel, Santa Cruz County, California Page 4

4.0 SITE DESCRIPTION

4.1 Location

The project site is located north of Highway 1 (Mission Street) at 141 Archer Drive in Santa Cruz, California. The site location is shown on the Site Location Plan, Appendix B, Figure B-1.

4.2 Surface Conditions

The parcel is approximately 0.26 acres in size and irregular in shape. The house is located on a coastal terrace at the crest of a steep slope. The site was graded for the residence. A wood post and lagging wall and terraced CMU wall retained about 12 feet of soil in total downslope of the residence. The hillside below the walls slopes at 65 percent towards Bay Avenue.

A 30 foot long (±) section of the wood wall and CMU wall failed this past winter.

4.3 Subsurface Conditions

The retaining wall location is geologically mapped as being underlain by Santa Margarita Sandstone. Our geotechnical exploration generally agrees with the geologic mapping of the area.

The borings were drilled in the area of the proposed improvements.

Boring B1 encountered 7 feet of non-engineered fill consisting of firm to stiff sandy lean clay over 4 feet of loose to medium dense silty sand. Very dense Santa Margarita Sandstone was encountered from 11 feet to the bottom of the boring at 13 feet.

Boring B2 encountered 9 feet of non-engineered fill consisting of loose silty sand over 1 ½ feet of loose silty sand. Very dense sandstone was encountered from 11 feet to the bottom of the boring at 12 feet.

We did not encounter groundwater in our borings. The depth of groundwater will vary seasonally.

Complete soil profiles are presented in the Boring Logs, Appendix B, Figures B-4 through B-5. The boring locations are shown on the Boring Site Plan, Figure B-2.

Soquel, Santa Cruz County, California Page 5

5.0 GEOTECHNICAL HAZARDS

5.1 General

In our opinion the geotechnical hazards that could potentially affect the proposed project are:

• Intense seismic shaking

• Collateral seismic hazards

5.1.1 Intense Seismic Shaking

The hazard of intense seismic shaking is present throughout central California. Intense seismic shaking may occur at the site during the design lifetime of the proposed structure from an earthquake along one of the regions many faults. Generally, the intensity of shaking will increase the closer the site is to the epicenter of an earthquake, however, seismic shaking is a complex phenomenon and may be modified by local topography and soil conditions. The transmission of earthquake vibrations from the ground into the structure may cause structural damage.

The City of Santa Cruz has adopted the seismic provisions set forth in the 2022 California Building Code to address seismic shaking. The seismic provisions in the 2019 CBC are minimum load requirements for the seismic design for the proposed structure. The provisions set forth in the 2022 CBC will not prevent structural and nonstructural damage from direct fault ground surface rupture, coseismic ground cracking, liquefaction and lateral spreading, seismically induced differential compaction, seismically induced landsliding, or seismically induced inundation.

Table 1 has been constructed based on the 2019 CBC requirements for the seismic design of the proposed structure. The Site Class has been determined based on our field investigation and laboratory testing.

Soquel, Santa Cruz County, California Page 6

Table 1. Seismic Design Parameters

SS

S1

Site

Class

Fa

Fv

SDS

SD1

FPGA

PGAM

Risk

Category

Seismic Design

Category

1.618

0.616

C

1.2

1.4

1.294

0.575

1.2

0.817

II

D

Design Coordinates - (Lat: 37.972068, Lng: -122.047467)

5.1.2 Collateral Seismic Hazards

In addition to intense seismic shaking, other seismic hazards that may have an adverse affect to the site and/or the structure are: fault ground surface rupture, coseismic ground cracking, seismically induced liquefaction and lateral spreading, seismically induced differential compaction, seismically induced landsliding, and seismically induced inundation (tsunami and seiche). It is our opinion that the potential for collateral seismic hazards to affect the site and to damage the proposed structure is low.

Soquel, Santa Cruz County, California Page 7

6.0 DISCUSSIONS AND CONCLUSIONS

A portion of the retaining wall system failed this past winter. Our firm has not reviewed an as-built drawing of the existing system. Based on our experience and site specific observations it is our opinion that the mode of failure was increased loading during intense rainstorms causing a hydrostatic load in combination with vertical members that were not embedded deep enough to prevent overturning of the wall.

Soquel, Santa Cruz County, California Page 8

7.0 RECOMMENDATIONS

7.1 General

Based on the results of our field investigation and engineering analysis it is our opinion that from the geotechnical standpoint, the subject site will be suitable for the construction of the new retaining wall(s).

7.2 Site Grading

7.2.1 Site Clearing

The site should be cleared of existing foundations, non-engineered fill, remaining root masses, loose soil, and organics.

7.2.2 Preparation of On-Site Soils

Areas to receive fill (subgrade) should be scarified, cleared of organics, moisture conditioned, and compacted in a good workmanship manner to provide a firm base for placing engineered fill.

All fill should be compacted to a minimum of 90 percent relative compaction based on the optimum moisture and density in accordance with ASTM D1557. See Paved Areas for additional requirements.

Engineered fill should be well mixed and homogenous, moisture conditioned to within 2 percent of optimum moisture, placed in relatively thin lifts, and compacted using heavy vibratory equipment.

Site Grading-General

The on-site soil may be re-used as engineered fill after any deleterious material is removed and it is moisture conditioned.

Imported fill material should be approved by a representative of Butano Geotechnical Engineering, Inc. prior to importing.

Imported fill should be primarily granular with no material greater than 2½ inches in diameter and no more than 20 percent of the material passing the #200 sieve. The fines fraction of fill should not consist of expansive material. The Geotechnical Engineer should be notified not less than 5

Soquel, Santa Cruz County, California Page 9 working days in advance of placing any fill or base course material proposed for import. Each proposed source of import material should be sampled, tested, and approved by the Geotechnical Engineer prior to delivery of any soils imported for use on the site.

Any surface or subsurface obstruction, or questionable material encountered during grading, should be brought immediately to the attention of the Geotechnical Engineer for proper processing as required.

Paved Areas

The paved areas should be prepared as above and the upper 6 inches of subgrade and all aggregate baserock in paved areas should be compacted to a minimum of 95 percent relative compaction. The subgrade compaction should extend a minimum of 2 feet laterally of all paved areas.

7.2.3 Cut and Fill Slopes

The fill encountered beneath the proposed improvements is very loose.

Temporary cuts made into the fill should be shored as required by the local regulatory agency, the State of California Division of Industrial Safety Construction Safety Orders, and Federal OSHA requirements. No permanent cuts or fill slopes are anticipated for this project.

7.2.4 Excavating Conditions

The on-site soil may be excavated with standard earthwork equipment. The sandstone is very dense and may require rock teeth to excavate and drill.

7.2.5 Surface Drainage

Positive drainage should be maintained away from the structures at a minimum gradient of 2 percent for 10 feet. If this is not feasible swales may be constructed to control drainage. Collected drainage should be released at approved locations as indicated by the project civil engineer or designer.

Surface runoff should be collected and dispersed at the base of the slope into an energy dissipater.

Soquel, Santa Cruz County, California Page 10

7.2.6 Utility Trenches

Utility trenches should be backfilled based on the City of Santa Cruz standard details. At a minimum this should consist of 4 inches of bedding sand below the utility and 8 inches of bedding sand above the utility.

Backfill of all exterior and interior trenches should be placed in thin lifts not to exceed 8 inches and mechanically compacted to achieve a relative compaction of not less than 95 percent in paved areas and 90 percent in other areas per ASTM D1557. Care should be taken not to damage utility lines.

The on-site native soils may be utilized for trench backfill above the bedding sand. If sand or granular material is used for trench backfill, a 3 feet concrete plug should be placed in each trench where it passes under the exterior footings.

Utility trenches that are parallel to the sides of a building should be placed so that they do not extend below a line sloping down and away at an inclination of 2:1 (V:H) from the bottom outside edge of all footings.

Trenches should be capped with 1 ½ feet of relatively impermeable material. Import material must be approved by the Geotechnical Engineer prior to its use.

Trenches must be shored as required by the local regulatory agency, the State of California Division of Industrial Safety Construction Safety Orders, and Federal OSHA requirements.

7.3 Foundations

7.3.1 Drilled Pier Foundations

Drilled piers may be used to support the new retaining wall.

The drilled, cast-in-place concrete shafts should have a minimum embedment depth of 5 feet into the dense sandstone and should have at least 10 feet of horizontal cover from the base of the pier to the adjacent slope face. The minimum recommended shaft diameter is 18 inches. Shafts should be spaced no closer than 2 ½ diameters, with a minimum of 3 diameters, center to center.

Soquel, Santa Cruz County, California Page 11

An allowable bearing capacity of 10,000 psf may be assumed for shafts that are embedded at least 5 feet into dense sandstone with an additional 1,000 psf for each foot of embedment beyond 5 feet to a maximum of 20,000.

Bearing capacities may be increased by 1/3 for short term loading. An allowable passive resistance of 400 psf over 2 pier diameters may be used in the dense sandstone. Passive resistance should be ignored until there is at least 8 feet of horizontal cover from the face of the piers to the adjacent slope face. At a minimum the upper 12 inches of soil should be neglected in passive resistance.

A bench should be excavated at the base of the new wall. The bench should be embedded a minimum of 12 inches into sandstone. A representative of Butano Geotechnical Engineering should observe the bench prior to drilling piers.

The drilled excavations for the cast-in-place concrete shafts should be clean, dry and free of debris of loose soil. The drilled excavations should not deviate more than 1 percent from vertical. Due to the propensity for the loose soil in the upper 3 feet (±) to cave, care should be taken to keep holes clean of slough.

For drilled, cast-in-place concrete shafts, with depths in excess of 8 feet, concrete should be placed via a tremie. The end of the tube must remain embedded a minimum of 4 feet into the concrete at all times.

All shaft construction must be observed and approved by the Geotechnical Engineer. Any shafts constructed without the full knowledge and continuous observation of Butano Geotechnical Engineering, Inc. will render the recommendations of this report invalid.

7.3.2 Settlements

Total and differential settlements beneath the new foundation elements are expected to be within tolerable limits. Vertical movements are not expected to exceed 1 inch. Differential movements are expected to be within the normal range (½ inch) for the anticipated loads.

Soquel, Santa Cruz County, California Page 12

7.4 Retaining Structures

7.4.1 Lateral Earth Pressures

The lateral earth pressures presented in Table 2 are recommended for the design of retaining structures with a gravel blanket and backfill soil consisting of the on-site material.

Table 2. Lateral Earth Pressures

Soil Profile Soil Pressure (psf/ft)

Active At-rest

Level 45 65

2:1 70 115

Pressure due to any surcharge loads from adjacent footings, traffic, etc., should be analyzed separately. Pressures due to these loadings can be supplied upon receipt of the appropriate plans and loads. Refer to Appendix A, Figure A-1.

An earthquake load (ultimate) may be considered for retaining walls as follows:

For unrestrained walls over 6 feet, as measured from the base of the footing, a seismic load of 10H2 may be applied at a height of 0.6H from the base of the wall.

No evaluation of seismic earth pressure is needed for restrained walls under 12 feet in height, as measured from the base of the footing, provided a minimum static factor of safety of 1.5 is achieved. For rigidly restrained walls over 12 feet a seismic load of 15H2 should be added to the active earth pressure and applied at a height of 0.3H from the base of the wall. The greater of the seismic loading and at rest loading conditions should be used for design. The recommendations for restrained retaining walls are based on the SEAOC 2010 Conventions Proceedings: Seismic Earth Pressures on Deep Building Basements, Lew, Sitar.

Soquel, Santa Cruz County, California Page 13

A factor of safety of 1.1 is considered appropriate with respect to earthquake loading.

7.4.2 Backfill

Backfill should be placed under engineering control. Backfill should be compacted per Subsection 7.2.2; however, precautions should be taken to ensure that heavy compaction equipment is not used immediately adjacent to walls, so as to prevent undue pressures against, and movement of the walls. Refer to Appendix A, Figure A-2.

The granular backfill should be capped with at least 12 inches of relatively impermeable material.

7.4.3 Backfill Drainage

Retaining structures must be fully drained. Backdrains should consist of 4 inch diameter Schedule 40, PVC pipe or equivalent, embedded in 3/8 inch to 3/4 inch, clean crushed gravel, enveloped in Mirafi 180N or approved equivalent. The drain should be a minimum of 12 inches in thickness and should extend to within 12 inches from the surface. The pipe should be 4+ inches above the trench bottom; a gradient of 2+ percent being provided to the pipe and trench bottom; discharging into suitably protected outlets. As an option weep holes consisting ½ inch thick galvanized steel spacers should be placed between the lagging. Weep holes may also be used if a concrete cantilevered wall is constructed. See Appendix A, Figure A-2 for the standard detail for the backdrain.

Perforations in backdrains are recommended as follows: 3/8 inch diameter, in 2 rows at the ends of a 120 degree arc, at 3 inch centers in each row, staggered between rows, placed downward.

Backdrains should be approved by the Geotechnical Engineer after placement of bedding and pipe and prior to the placement of clean crushed gravel.

An unobstructed outlet should be provided at the lower end of each segment of backdrain. The outlet should consist of an unperforated pipe of the same diameter, connected to the perforated pipe and extended to a protected outlet at a lower elevation on a continuous gradient of at least 1 percent.

Soquel, Santa Cruz County, California Page 14

7.5 Plan Review

The recommendations presented in this report are based on preliminary design information for the proposed project and on the findings of our geotechnical investigation. When completed, the Grading Plans, Foundation Plans and design loads should be reviewed by Butano Geotechnical Engineering, Inc. prior to submitting the plans and contract bidding. Additional field exploration and laboratory testing may be required upon review of the final project design plans.

7.6 Observation and Testing

Field observation and testing should be provided by a representative of Butano Geotechnical Engineering, Inc. to enable them to form an opinion regarding the adequacy of the site preparation, the adequacy of fill materials, and the extent to which the earthwork is performed in accordance with the geotechnical conditions present, the requirements of the regulating agencies, the project specifications, and the recommendations presented in this report.

Butano Geotechnical Engineering, Inc. should be notified at least 5 working days prior to any site clearing or other earthwork operations on the subject project in order to observe the stripping and disposal of unsuitable materials and to ensure coordination with the grading contractor. During this period, a preconstruction meeting should be held on the site to discuss project specifications, observation and testing requirements and responsibilities, and scheduling.

Soquel, Santa Cruz County, California Page 15

8.0 LIMITATIONS

The recommendations contained in this report are based on our field explorations, laboratory testing, and our understanding of the proposed construction. The subsurface data used in the preparation of this report was obtained from the borings drilled during our field investigation. Variation in soil, geologic, and groundwater conditions can vary significantly between sample locations. As in most projects, conditions revealed during construction excavation may be at variance with preliminary findings. If this occurs, the changed conditions must be evaluated by the Project Geotechnical Engineer, and revised recommendations be provided as required. In addition, if the scope of the proposed construction changes from the described in this report, our firm should also be notified.

Our investigation was performed in accordance with the usual and current standards of the profession, as they relate to this and similar localities. No other warranty, expressed or implied, is provided as to the conclusions and professional advice presented in this report.

This report is issued with the understanding that it is the responsibility of the Owner, or of his Representative, to ensure that the information and recommendations contained herein are brought to the attention of the Engineer for the project and incorporated into the plans, and that it is ensured that the Contractor and Subcontractors implement such recommendations in the field. The use of information contained in this report for bidding purposes should be done at the Contractor’s option and risk.

This firm does not practice or consult in the field of safety engineering. We do not direct the Contractor's operations, and we are not responsible for other than our own personnel on the site; therefore, the safety of others is the responsibility of the Contractor. The Contractor should notify the Owner if he considers any of the recommended actions presented herein to be unsafe.

The findings of this report are considered valid as of the present date. However, changes in the conditions of a site can occur with the passage of time, whether they are due to natural events or to human activities on this or adjacent sites. In addition, changes in applicable or appropriate codes and standards may occur, whether they result from legislation or the broadening of knowledge. Accordingly, this report may become invalidated wholly or partially by changes outside our control. Therefore, this report is subject to review and revision as changed conditions are identified.

The scope of our services mutually agreed upon did not include any environmental assessment or study for the presence of hazardous to toxic materials in the soil, surface water, or air, on or below or around the site. Butano Geotechnical Engineering, Inc. is

Soquel, Santa Cruz County, California Page 16 not a mold prevention consultant; none of our services performed in connection with the proposed project are for the purpose of mold prevention. Proper implementation of the recommendations conveyed in our reports will not itself be sufficient to prevent mold from growing in or on the structures involved.

REFERENCES

ASTM International (2015). Annual Book of ASTM Standards, Section Four, Construction.

Volume 4.08, Soil and Rock (I): D 430 - D 5611.

ASTM International (2016). Annual Book of ASTM Standards, Section Four, Construction.

Volume 4.09, Soil and Rock (II): D 5714 - Latest.

California Building Code (2022).

Cochrane, G.R., Johnson, S.Y., Dartnell, P., Greene, H.G., Erdey, M.D., Dieter, B.E., …and Krigsman, L.M., 2016, California State Waters Map Series— offshore of Santa Cru, California, U.S. Geological Survey, Open-File Report OF-2016-1024, 1:24,000

APPENDIX A

FIGURES AND STANDARD DETAILS

Surcharge Pressure Diagram Figure A-1

Typical Retaining Wall Backdrain Detail Figure A-2

Passive Resistance Diagram Figure A-3

BUTANO

GEOTECHNICAL ENGINEERING, INC.

SURCHARGE PRESSURE DIAGRAM

FIGURE

A-1

NOTES:

1. DRAWING IS NOT TO SCALE.

2. 2±% GRADIENT TO PIPE AND TRENCH BOTTOM CONNECTED TO A CLOSED

CONDUIT THAT DISCHARGES TO AN APPROVED LOCATION.

12 ± INCH IMPERMEABLE CAP

FINISHED GRADE

INCH TO

INCH ANGULAR DRAINROCK

OR APPROVED EQUIVALENT

APPROVED FILTER FABRIC AS

RECOMMENDED IN THE GEOTECHNICAL

REPORT, COMPLETELY WRAPPING

DRAINROCK, OVERLAPPED AT TOP

4 INCH PERFORATED SCHEDULE 40 PVC

PIPE OR APPROVED EQUIVALENT

PERFORATIONS DOWN

4± INCHES

12± INCHES

BUTANO

GEOTECHNICAL ENGINEERING, INC.

TYPICAL RETAINING WALL BACKDRAIN DETAIL

A-2

MINIMUM OF 8 FEET OF

HORIZONTAL COVER

BELOW WHICH PASSIVE

PRESSURE MAY BE APPLIED

F0UNDATION WILL CONSIST

OF DRILLED PIERS

BUTANO

GEOTECHNICAL ENGINEERING, INC.

PASSIVE RESISTANCE DIAGRAM

A-3

APPENDIX B

FIELD EXPLORATION PROGRAM

Field Exploration Procedures Page B-1

Site Location Plan Figure B-1

Boring Site Plan Figure B-2

Key to the Logs Figure B-3

Logs of the Borings Figures B-4 and B-5

Cross Section X-X’ Figure B-6

Santa Cruz, California Page B-1

FIELD EXPLORATION PROCEDURES

Subsurface conditions were explored by advancing two borings below the existing grade.

The borings were advanced using through continuous sampling using a rope and pully.

The Key to The Logs and the Logs of the Borings are included in Appendix B, Figures B- 3 through B-5. The approximate locations of the borings are shown on the Boring Site Plan, Figure B-2. The borings were located in the field by tape measurements from known landmarks. Their locations as shown are therefore within the accuracy of such measurement.

The soils encountered in the borings were continuously logged in the field by a representative of Butano Geotechnical Engineering, Inc. Bulk and relatively undisturbed soil samples for identification and laboratory testing were obtained in the field. These soils were classified based on field observations and laboratory tests. The classifications are in accordance with the Unified Soil Classification System (USCS: Figure B-3).

A geologic cross-section (Figure B-6) was made based on topographic data collected by our firm with a field tape and clinometer and our boring logs.

SITE LOCATION PLAN

141 Archer Drive

FIGURE

B-1

N.T.S

Project Site

AutoCAD SHX Text N

BORING SITE PLAN

141 Archer Drive

FIGURE

B-2

BX Exploratory Boring Scale: 1" = 20'

AutoCAD SHX Text

AutoCAD SHX Text A'

AutoCAD SHX Text A

AutoCAD SHX Text B1

AutoCAD SHX Text B2

AutoCAD SHX Text 141 Archer Drive

AutoCAD SHX Text Approximate Location of Wood Wall (E)

AutoCAD SHX Text Approximate Location of CMU Wall (E)

AutoCAD SHX Text Bay Avenue

AutoCAD SHX Text Archer Drive

AutoCAD SHX Text Approximate Location of Failed Wood Wall (E)

N

* Number of blows of 140 pound hammer falling 30 inches to drive a 2 inch O.D. (1 3/8 inch I.D.) split spoon (ASTM D-1586).

2 - 4

4 - 8

8 - 16

16 - 32

C

L

A

Y

DRY

S

A

N

D

SATURATEDHARD

0 - 2

OVER 32

SOFT

FIRM

VERY SOFT

STIFF

VERY STIFF

MOIST

SATURATED

DRY

DAMP

WET

SAND

RELATIVE DENSITY

FINE

GRAINED

SOILS

More than half of the material is smaller than the

No. 200 sieve

SAND AND GRAVEL

OVER 50

VERY LOOSE

BLOWS/FT*

0 - 4

VERY DENSE

LOOSE 4 - 10

10 - 30

30 - 50

MEDIUM DENSE

DENSE

SECONDARY DIVISIONS

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

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

SILT AND CLAY

Inorganic silts, micaceous or diatomacaceous fine sandy or silty soils, elastic silts

Clayey sands, sand-clay mixtures, plastic finesSC

Peat and other highly organic soils

COARSE

GRAINED

SOILS

More than half of the material is larger than the

No. 200 sieve

GM

GC

Silty gravels, gravel-sand-silt mixtures, non-plastic fines

Inorganic clays of high plasticity, fat clays

Organic clays of medium to high plasticity, organic silts

Inorganic silts and very fine sands, silty or clayey fine sands or clayey silts with slight plasticity

Inorganic clays of low to medium plasticity, gravelly clays, sandy clays, silty clays, lean clays

GP

KEY TO LOGS

SW

SP

SM

CLEAN GRAVELS

(Less than 5% fines)

GRAVEL

WITH FINES

CLEAN SANDS

(Less than 5% fines)

SAND

WITH FINES

GW

Silty sands, sand-silt mixtures, non-plastic fines

UNIFIED SOIL CLASSIFICATION SYSTEM

GROUP

SYMBOLPRIMARY DIVISIONS

Clayey gravels, gravel-sand-clay mixtures, plastic fines

GRAVELS

More than half of the coarse fraction is larger than the

No. 4 sieve

SANDS

More than half of the coarse fraction is smaller than the

No. 4 sieve

Well graded sands, gravelly sands, little or no fines

Poorly graded sands, gravelly sands, little or no fines

Organic silts and organic silty clays of low plasticity

FIGURE

SILTS AND CLAYS

Liquid limit less than 50

SILTS AND CLAYS

Liquid limit greater than 50

ML

CL

HIGHLY ORGANIC SOILS

MH

CH

OH

Pt

SILT AND CLAY

OL

B-3

BUTANO GEOTECHNICAL ENGINEERING, INC.

GRAIN SIZE LIMITS

BOULDERSCOBBLES

GRAVEL

COARSE FINE COARSE

US STANDARD SIEVE SIZE

CONSISTENCY MOISTURE CONDITION

BLOWS/FT*

FINE MEDIUM

No. 200 No. 40 No. 10 No. 4 3/4 in. 3 in. 12 in.

Project No.: Boring: B1

Project: Location:

Elevation:

Date: Method of Drilling:

Logged By:

L .L

P .I

Af 7 5 28.3

(SC) 12 9 36.6

15 12 31.2

18 14 21.3

SM Dark brown Silty SAND, medium dense, wet, rootlets

15 5 14.7

55/6" N/A 15.3

Tsm 92 84

15 No groundwater encountered during drilling.

Boring terminated at a depth of 13 feet.

(Non-Engineered FILL)

Yellowish brown SANDSTONE, dense, damp

BUTANO GEOTECHNICAL ENGINEERING, INC. FIGURE

B-4

Dark brown Sandy Lean CLAY with Gravel, stiff, damp

N

D ry

D en si ty p cf

M o is tu re C o n te n t

E x p an si o n I n d ex

P ar ti cl e S iz e f in es

U n co n fi n ed q u p sf

Description

B lo w s

F o o t

Atterberg

Limits

LOG OF EXPLORATORY BORING

23-141-SC

141 Archer Drive

April 19, 2023 Continous Sampling Access

SC

D ep th ft

S o il T y p e

U n d is tu rb ed

B u lk

Gradation or Minor

Change in Classification

Change in Soil

Classification

2" Ring

Sample

2.5" Ring

Sample

Bulk

Sample Terzaghi Split

Spoon Sample

Static Water

Table Water Encountered

During Drilling

Perched Water

Table

Project No.: Boring: B2

Project: Location:

Elevation:

Date: Method of Drilling:

Logged By:

L .L

P .I

Af 5 2 42.6

(SM)

9 3 43.9

Dark Brown

5 10 4 37.1

12 4 30.2

SM Dark brown Silty SAND with Gravel, loose, wet

37 13

98 89 13.6

Boring terminated at a depth of 12 feet.

No groundwater encountered during drilling.

BUTANO GEOTECHNICAL ENGINEERING, INC. FIGURE

B-5 loose, moist

(Non-Engineered FILL)

Atterberg

Limits

Dark yellowish brown Silty SAND with Gravel, very

N

D ry

D en si ty p cf

M o is tu re C o n te n t

E x p an si o n I n d ex

P ar ti cl e S iz e f in es

U n co n fi n ed q u p sf

April 19, 2023 Continous Sampling Access

SC

D ep th ft

S o il T y p e

U n d is tu rb ed

B u lk

Description

B lo w s

F o o t

LOG OF EXPLORATORY BORING

23-141-SC

141 Archer Drive

Gradation or Minor

Change in Classification

Change in Soil

Classification

2" Ring

Sample

2.5" Ring

Sample

Bulk

Sample Terzaghi Split

Spoon Sample

Static Water

Table Water Encountered

During Drilling

Perched Water

Table

Yellowish brown SANDSTONE, dense, dampTsm

0 10 20 30 40 50 60 70 80 90 100

110 120 130

BUTANO

GEOTECHNICAL ENGINEERING, INC.

CROSS SECTION A-A'

141 Archer Drive

FIGURE

B-6

AutoCAD SHX Text Af

AutoCAD SHX Text

SM

AutoCAD SHX Text Tsm

AutoCAD SHX Text Approximate Location of Original Walls

AutoCAD SHX Text Existing Grade after Wall Failure

AutoCAD SHX Text A

AutoCAD SHX Text A'

AutoCAD SHX Text Residence (E)

AutoCAD SHX Text

AutoCAD SHX Text

AutoCAD SHX Text

AutoCAD SHX Text

AutoCAD SHX Text Legend Af - Artificial Fill - Artificial Fill SM - Silty SAND - Silty SAND Tsm - Santa Margarita Sandstone - Santa Margarita Sandstone ? - Queried Where Approximate - Queried Where Approximate BX - Exploratory Boring- Exploratory Boring

AutoCAD SHX Text Relative Elevation in Feet Horizontal = Vertical Scale 1" = 20'

Bay Avenue

APPENDIX C

LABORATORY TESTING PROGRAM

Laboratory Testing Procedures Page C-1

Geotechnical Investigation – Design Phase June 1, 2023

Santa Cruz, California Page C-1

LABORATORY TESTING PROCEDURES

Classification

Soils were classified according to the Unified Soil Classification System in accordance with ASTM D 2487 and D 2488. Moisture content and density determinations were made for representative samples in accordance with ASTM D 2216. Results of moisture density determinations, together with classifications, are shown on the Boring Logs, Figures B-4 through B-5.