state of california • the resources agency division of … · 17-01-1994 · we are placing on...

STATE OF CALIFORNIA • THE RESOURCES AGENCY

Da'ARTMENT OF CllllSERVATIOll DIVISION Of MINES ANO GEOLOGY 8A~ AREA REGIONA~ OFFICE 185 Berry Streetf Suite 3600 San Francisco, CA 94107 Phone (415> 904·7707

A TSS 539- 7707 ••• (415) 904·7715

Mr. Stephan Lashbrook Community Development Director city of Arcata 736 F Street Arcata, CA 95521

Dear Mr. Lashbrook:

• • • ~ElE WI~SON, Governor

February 17, 1994

We are placing on open file the following report, approved by the City of Arcata in compliance with Priolo Earthquake Fault Zoning Act (formerly the Special Studies Zones Act):

reviewed and the AlquistAlquist-Priolo

Fault and geotechnical investigations, planned Intermodal Transit Facility, Ninth and F Streets, Arcata, CA; by Trans Tech Consultants; Revised 1/17/94.

EWH:nld

Sincerely,

t'L t/ ~;~/ ~"1--1--tt :,,. -r Earl w. Hart, CEG 935 Senior Geologist &

Program Manager

736 F Street Arcata, California 9 5 521

February 10, 1994

Earl W. Hart Program Manager Div. of Mines & Geology Bay Area Region 185 Berry Street Suite 3600 San Francisco, Ca. 94107

Mr. Hart:

City Council 822-oYo.·i

A&MRTS 822-3770

Community n1..~vt.~lopm1..~n1 822-0900

IAX 822-8018

l'olke 822-2428

l'uhlic Wi:irk.o; 822-0957

l;inan1..:t.~ C:i1.y M<1n<iger 822-5953 822-S9S I

Mode1n 822-1208

Park.-; & RecreaLlon 822-7091

Enclosed is a copy of the Fault and Geotechnical Investigation prepared by TransTech Consultants for a site on 9th and F Streets in Arcata. Also enclosed is the review of that report prepared by SHN Engineers and Geologists.

Please note that the TransTech Report, dated January 17, 1994, contained the corrections requested by Mr, Stephens of SHN,

Based on this evaluation and the review conducted by SHN we will be proceeding with the planned development of this site.

If you have any questions about this information~ please feel free to contact me or Lia Sullivan of our staff.

Thanks,

~Z:~--£'_,,--7-------Stephan Lashbrook Community Development Director

cc: Lia Sullivan David Peterson, TransTech Tom Stephens, SHN

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' < I .:/· .;....: 1 •• ;.:t / .

Reference: 930176 RECEIVED

.JAN 171994

January 14, 1994

Mr. Stephan Lashbrook City of Arcata Department of Community Development 736 F Street Arcata, CA 95521

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SUBJECT: REVIEW OF FAULT EVALUATION REPORT FOR TI-IE PROPOSED INTERMODAL TRANSIT FACIUIY, NINTI-1 AND F STREETS, ARCATA, CALIFORNIA

Dear Mr. Lashbrook:

In res~onse ~o our agr~ement for geologic se~ces dated November 3, 1993, we are , ? "· .. ,µ11jl'f

providmg this final review of the fault evaluat10n report (FER) dated December 20,) l1f,,,.f~l l'I \ 1 ~ 1993, prepared by Trans Tech Consultants. /J

0

FER investigations were conducted by Trans Tech to detennine levels of surface fault rupture hazard that influence the development of the project site. Surface fault rupture hazards are generally considered to be low enough to pennit municipal development when geologic investigations demonstrate that soil or rock deposits that underlie the project site are greater than 11,000 years old (Pre-Holocene) and have not been ruptured by fault activity. If it can be shown that fault activity has resulted in rupture of geologic deposits that are less than 11,000 years old, or if the geomorphology of the fault trace is well defined, then surface fault rupture hazards arc considered too high to pennit development of structures intended for human occupancy within SO feet of the identified surface trace of the rupture feature.

Based on our agreement with the City of Arcata (City), the intent of this review is to assess the adequacy of the FER document; to assess the appropriateness of the depth of the FER study; and to render an opinion which either concurs or does not concur with the scope, methodology, interpretations, conclusions, and recommendations of the FER.

t

Mr. Stephan Lashbrook January 14, 1994 Page 2

Once SHN was retained by the City to provide review services, a meeting was held between Trans Tech, an SHN geologist registered in the State of California, and the City. The meeting was held in order to discuss project approach, methods of investigations, and location of an exploration trench that was to be excavated across the site. At the City's request, SHN conducted a site visit on September 30, 1993 for the purpose of examining trench wall exposures during the trenching effort. It should be noted that all of the trench wall exposures were not reviewed in the field. On, or about September 29, 1993, we were notified by Trans Tech that a portion of the exploration trench was ready to be reviewed. However, shortly after the notification, the trench collapsed, precluding direct observation by the reviewer. It was not considered practical to re-excavate the trench, solely for the purpose of review.

REVIEW CRITERIA

SHN's review was performed in accordance with guidelines set forth in California Division of Mines and Geology (CDMG) Special Publication 42, "Fault Rupture Hazard Zones in California'', Appendix C.

SUMMARY

It is our opinion that the fault investigation conducted by Trans Tech complies with the intent of the State guidelines for evaluating the hazard of surface fault rupture as outlined in Appendix C of CDMG Special Publication 42. SHN considers the report to be adequate and the investigation was conducted in a manner sufficient to assess the hazard of surface fault rupture at the project site. The conclusions drawn by Trans Tech are supported by the data cited in their report.

During SHN's review of the fault hazard evaluation report narrative, several minor errors were discovered. Rather than commenting on these minor issues in writing, the issues were discussed by telephone with Mr. David Peterson on January 13, 1994. Mr. Peterson concurred with our comments and agreed to make the necessary corrections to the report narrative.

•

Mr. Stephan Lashbrook January 14, 1994 Page 3

We trust that this letter provides the information that you require at this time. If you have any questions please contact us.

Sincerely,

SHN CONSULTING ENGINEERS & GEOLOGISfS

q{S~ !fv, THOMAS (0

!'.,-.._ s s ,, Ci c_o TEPl·l(N ·>

Tom A. Stephens, RG 5030 ----;,_ '"· .NO 5030-- ""~ I} /" • -&-"" .t_,"1

Geotechnical Department Director ~--

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L:\930176\LTR l.TAS

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I I I I I I I I I I I I I I I I I I I

"1f TRANS TECH CONSULTANTS ENVIRONMF.NTAt. AND GEOTECHNICAL SERVICES

FAULT AND GEOTECHNICAL INVESTIGATION PLANNED INTERMODAL TRANSIT FACILITY

NINTH AND F STREETS ARCATA, CALIFORNIA

Prepared For: Mr. Stephan Lashbrook

City of Arcata Department of Community Development

736 F Street Arcata, California 95521

Prepared By: Trans Tech Consultants 710 E Street, Suite 205

Eun:ka, California 95501 (707) 445-4228

Job No. 3040.01.01 Revised January 17, 1994

Gary F. Sitton Geotechnical Engineer

David H. Peterson Engineering Geologist

'.i100 DUTTON AVENUE. SUllF 110 S/\NT A HOSA. CA 05407 TCLErHONI- 707-,"'i?~-8622

,..:AC:""ilfv11LE: 707-~7S-338"1

710 E STREET, SUITE 205 EUREKA, CA 95501

TELEPHONE: 707-445-4228 FACSIMILE: 707-445-4270

I I

TABLE OF CONTENTS

INTRODUCTION ................................................ .

METHODS OF INVESTIGATION ...................................... .

I Data Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Field Exploration ....................................... . Laboratory Testing ...................................... .

~EGIONAL GEOLOGIC AND SEISMIC SETTING ........................... .

I Geology ............................................ . Faulting and Seismicity ................................... .

tOCAL GE?LOGIC/SEISMIC SETTING ................................. .

PRIOR FAULT INVESTIGATIONS ..................................... .

LITE CONDITIONS ............................................... .

mcoNCLUSIONS ................................................. . Geologic Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 Geotechnical Considerations . . . . . . . . . . . . . . . . . . . . . . . _ . . . . . . . . .

RECOMMENDATIONS ............................................ .

I I

Site Preparation and Grading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Foundations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Concrete Slabs-on-Grade . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Asphalt Pavements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Supplemental Services .................................... .

• LIMITATIONS .................................................. .

I I I I I I

ILLUSTRATIONS

REFERENCES

DISTRIBUTION

- I -

l

l 1 2 2

2 2 3

4

4

5

6 6 8

9 9

11 12 12 13

14


INTRODUCTION

This report presents the results of our fault and geotechnical investigation for the City of Arcata's (City) planned intermodal transit facility. The property is between 9th and 10th Streets and west of Highway 101, as shown on the Vicinity Geologic Map, Plate 1.

As shown on the Site Plan, Plate 2, the City plans to construct a transit facility, with associated asphalt paving, and two single-unit apartment buildings on the property. The three planned structures will be one story. We understand from Winzler and Kelley, project civil engineers, that foundation wall loads will be less than 2 kips per linear foot. Site grading requirements for the gently sloping site are not known at this time, but are anticipated to be relatively minor and limited primarily to preparing properly compacted fill pads for the structures, and upgrading (removal and replacement) of existing weak nearsurface fill soils.

The project lies within a Special Studies Zone (SSZ) established for the active Fickle Hill fault. An evaluation of the potential for ti.lture surface fault rupture is required by City and State law. The purpose of our fault study was to evaluate the surface fault rupture hazard, as well as other geologic hazards to the project. Our geotechnical investigation was directed at obtaining subsurface information to provide guidelines tor project design and construction. Our scope of services was presented in our proposals dated April 29 and July 7, 1993, and an September 14, 1993, addendum, and consisted of review of available stereo-paired aerial photographs and geologic reports, subsurface investigation, laboratory testing, engineering and geologic analysis, and pn:paration of this report

During the course ot' our investigation, we discussed our preliminary findings with Mr. Lashbrook of the City of Arcata, Mr. Lars Fredrickson of Winzler and Kelly, project civil engineers, and with Mr. Tom Stephens of SHN Consulting Engineers, reviewing geologist for the City.

METHODS OF INVESTIGATION

Data Review

We reviewed published and unpublished geologic reports from our files, and those of Humboldt State University for the site vicinity. These included site investigations performed in the vicinity by others, shown on Plate 3. The selected published information reviewed is presented on tl1e attached list or References. Stereo-paired aerial photographs were reviewed to evaluate the surface conditions, in particular, for geomorphic features indicative of active faults. The photographs reviewed are also listed in the References.

1


Field Exploration

Field exploration consisted of detailed geologic logging of one exploratory trench and two test pits, and drilling, logging, and sampling three test borings.

On August 23, 1993, we explored the subsurface conditions at the site by drilling three test borings, ranging from 30.0 to 41.0 feet deep, using a hollow-stem auger drill rig. Our geologist located the borings, observed the drilling, logged the conditions encountered, and obtained soil samples for visual examination, classification, and laboratory testing. Samples were obtained with a 2.43-inch inside diameter (l.D.) Sprague & Henwood sampler, driven with a 140-pound hammer dropped 30 inches. The test boring locations are indicated on Plate 2. Logs of the test borings are presented on Plates 4 through 6; soils on the logs were logged in accordance with the Unified Soil Classification System (USCS) shown on Plate 8.

Two test pits and 130 feet of exploratory trench were dug by backhoe and excavator equipment at the locations shown on the Site Plan, Plate 2, and logged by our geologists. The test pits were excavated to depths of 13 to 13.5 feet, and the trench was excavated to depths up to 19 feet below ground surface (BGS). The upper portion of the excavation was benched to reach the depth required to Jog geologic conditions in the trench; the limits of this excavation are also shown on Plate 2. The trench was excavated perpendicular to the projected traces of active faults in the project vicinity, and located so as to "shadow" the planned building area. The trench was also extended south, to just beyond the limit of the Special Studies Zone, shown on Plate 2. The test pit and exploratory trench logs are presented on Plates 7 and 9, respectively. Soils logged in the test pits and trench are also classified in accordance with the uses.

Laboratory Testing

Selected samples were tested in the laboratory to determine their moisture content, dry density, shear strength, particle size distribution and consolidation characteristics. The results of these tests are presented on the boring logs in the manner described on the Key to Test Data, Plate 8. The detailed results of the particle size, consolidation, and strength tests are summarized on Plates IO through 13.

REGIONAL GEOLOGIC AND SEISMIC SETTING

Geology

The site is located at the northwestern margin of the California Coast Ranges geomorphic province, a belt of northwest-trending mountain ranges and valleys extending from the Pacific Ocean, eastward to the Klamath Mountains. This northwest trend reflects the predominant orientation of topographic and geologic features, created in response to northwest-oriented faulting at the western margin of the north American continent during the

2


past 100 million years. Locally, the topographic and geologic features are considered to be influenced by the Cascadia Subduction Zone, where it extends from offshore, onto the northern California coast (see the Regional Structural Setting map, Plate 14).

The oldest geologic units in the region are deformed sedimentary and volcanic rocks of the Jurassic to Cretaceous age Franciscan Complex. The Franciscan rocks are not exposed at the surface within the site, but are exposed approximately 1h mile east and presumably underlie the site at depth. Locally, the bedrock is blanketed by non- to weakly-indurated estuarine and shallow marine deposits, ranging in age from Tertiary to Quaternary. Pleistocene to Holocene-age alluvial deposits cover large portions of the lowlands in the vicinity.

Faulting and Scismicity

The region has experienced several historic earthquakes from a series of active faults ass'ociatcd with the southern, offshore and on-land extension of the Cascadia Subduction Zone and northern extension of the San Andreas fault. Active faults (those experiencing seismic activity /surface rupture within the past 11,000 years) nearest the site arc summarized in the following table:

.. . . "" ::.:.

Distance From Site Direction From Site To . .. ..

I Fault System < (miles) Fault . .

Fickle Hill 0.1 North

Mad River 3.0 North

McKinlcyville 3.6 North

Blue Lake 4.8 Northeast

Trinidad 9.0 North

Little Salmon 12 South

Due to its close proximity to the site, the Fid.le Hill fault appears to pose the greatest seismic risk to the project. Historic earthquakes with associated surface ground rupture

.

.. ·. ....

have not been observed on the Fickle Hill fault. However, cumulative displacement of up to 2,700 feet (825 meters) appears to have occurred during the past 700,000 years, and a Holocene slip rate of over 1.2 millimeters per year has heen estimated for the Fickle Hill fault (Kelsey and Carver, 1988).

The region is seismically active, with several moderate to large earthquakes having occurred during historic times. These include magnitude 7.2 and 6.9 events west of Eureka, in 1923 and 1980, respectively. The magnitude 6.2 to 6. 9 earthquakes of April 1992 were centered

J


about 30 miles southwest of the site, and caused moderate to strong ground shaking in the site vicinity. The 1992 earthquake were the first documented subduction zone events (T. Stephens, personal communications, 1994).

LOCAL GEOLOGIC/SEISMIC SETTING

The local geologic units are shown on the Vicinity Geologic Map, Plate 1. In the project vicinity, the oldest exposed geologic unit is the early- to mid-Pleistocene age Falor formation, consisting of poorly consolidated interbedded clays, silts, sands, pebbly sands, and gravels deposited in conditions ranging from shallow open marine to beach, estuarine, and fluvial environments (Kelsey and Carver, 1988). Unconformably overlying the Falor formation are late-Pleistocene age marine terrace deposits consisting of nonindurated shallow marine sands and gravels.

Structurally, the Fickle Hill fault and the Fickle Hill anticline are part of the Mad River Fault Zone, a 6 mile wide system of northwest-trending, east-dipping imbricate thrust faults that extend from the coast approximately 25 miles inland. The Fickle Hill fault is mapped one mile north of Humboldt Bay and through the City of Arcata, trending southeast approximately 11 miles on the southern flank of Fickle Hill. The fault offsets the southem limb of the Fickle Hill anticline. On the south slope of Fickle Hill, at least 1, 148 feet of Falor formation section have been overthrusted by Franciscan melange on three main traces of the Fickle Hill fault (Aalto and Harper, 1989).

PRIOR FAULT INVESTIGATIONS

Locations of previous fault in the site vicinity are shown on the Previous Investigations map, Plate 3 and are summarized below.

In 1984, Northern Geotechnical Incorporated (NGI) excavated a 130-foot long trench, located on the northeast corner of 12th and G Streets in Arcata, perpendicular to the strike of the Fickle Hill fault. Observation of a road cut on F Street, and examination of aerial photographs were also used to interpret potential risk of faulting. No surficial or subsurface evidence of faulting were found. NGI concluded the risk of faulting was non-existent onsite.

Subsurface investigation by trenching was performed Busch Geotechnical Consultants (BGC) in 1987 for a project at 12th and H Streets. The trench encountered several west-dipping fault offsets of a few inches. The offsets were interpreted by BGC to be antithetic breaks, with a low potential for significant surface rupture. Of the investigations performed in the immediate site vicinity, this 1987 investigation by BGC is the only one that appears to have encountered fault offsets.

4


A 1987 fault study was also started by BOC at the southeast corner of 10th and 0 Streets in Arcata, but later abandoned when the property was found to be out of the Alquist-Priolo Special Studies Zone. From trenching performed onsite, no fractures or faults were observed. BOC concluded that fault rupture risk at this site was low.

A northeast-trending, 144-foot long trench was excavated by BGC in 1990, on the southwest corner of 12th and H Streets to investigate potential of faulting onsite. Stratigraphic evidence and aerial photographs indicated no fractures or faulting. BOC concluded the risk of fault rupture onsite was low.

During 1990, BGC also used data from the 1984 investigation performed by NOI on the adjoining property to the west for a project located on the northwest comer 12th and F Streets. Based on NGI's data, BOC concluded that a risk of faulting at 12th and F Streets was negligible.

SITE CONDITIONS

The property is situated adjacent and west of Highway 101. The site slopes gently southwest, with elevations ranging from 25 feet in the northwest, to 20 feet in the southwest. The site is bounded to the west by a brush-filled drainage ditch, and further west, by private residences. The site is now gravel- and asphalt-covered, and is being utilized as a parking area. Review of aerial photographs taken in 1931 and 1941 indicate the property was not developed and appeared to be a swalc approximate! y 10 feet he low current grade. Aerial photographs taken in 1974 indicate the low-lying swalc area had been backfilled to currem grade.

Our subsurface data indicate the site is blanketed by 7 to 15 feet of man-placed fill materials, consisting of sandy clayey gravel, gravelly clay, wood debris (Unit 1), and decomposed organic material (Unit 2). The fill materials are generally loose to medium dense or soft to medium stiff. The trench encountered logs one and two feet in diameter lying perpendicular to the excavation at Stations 0+75S and 0+90S.

Underlying the wood debris in Boring B-2 is sol't, compressible, silty peat. Because this peat unit corresponds to a former low-lying area on the site, we interpret the unit to he a marsh/estuarine deposit, probably of Holocene age. Underlying the fill and peat units at 25 feet BGS are sand, silty sand, gravelly sand, and sandy gravel. From their texture, composition, and stratigraphic position, we interpret these units to be part of the late Pleistocenee marine terrace deposits.

Within the exploratory trench, the upper most stratum of the terrace deposits (Unit 3), consists of massive, medium dense, dark gray brown. silty sand, with occasional carbonized wood fragments. Unit 3 is relatively flat-lying and about 2 feet thick. At Station 0+70S Unit 3 dips gradually to the southwest, and the unit thins to less than one toot. Unit 3

5


grades into the underlying Unit 4, a well stratified, medium dense, medium grained, silty sand. Unit 4 is relatively flat-lying from the north end of the trench to Station 0+ 75S, dipping gently to the southwest from station 0+75S to the southern end of the trench. Unit 4 thickens from 1.5 feet at Station 0+70S to approximately 4.5 feet at Station 0+95S. Unit 5 is in gradational contact with Unit 4, locally forming the basal unit of the terrace deposits. Unit 5 consists of loose to medium dense, well rounded gravel to 1/2-inch diameter.

Unit 6 consists of massive, stiff to very stiff clay strata interpreted to be part of the Falor formation. Unit 6 is iron oxide mottled in the upper l to 2 feet. The contact between overlying Units 4 and 5 of the terrace deposits and Unit 6 is very distinct and characterized by a somewhat irregular, erosional surface and ground-water seepage. The contact is sharp enough that fault offsets of one inch or less would be recognizable. No fault offsets were observed in the contact between Units 4/5 and Unit 6.

Free ground water was observed in at about 10.5 feet in Test Pit TP-1, on June 11, 1993, and saturated soils were noted at about 30 feet BGS in Boring B-2 on August 23, 1993. Seepage was encountered locally in the exploratory trench at depths of about 9 to 17 foet on September 30, 1993.

CONCLUSIONS

Geologic Hazards

Fault Rupture

We did not observe evidence of fault offsets in the sharp contact between geologic units of late Pleistocene and early to mid Pleistocene age. We therefore conclude that an active (Holocene age) fault does not traverse the planned building areas.

As shown on the Special Studies Zones map (1983), the active trace of the Fickle Hill fault is mapped about 400 feet northeast (see Plate 3). We understand the deformation associated with the thrust faults in the region typically is more intense on the upper plate of the fault (i.e. the northeast side) and less so on the lower (southwest) plate (Tom Stephens, 1993, personal communication). Based on the distance from and structural position of the site with respect to the active trace of the Fickle Hill fault (i.e., on the lower plate), we also considered the potential for future surface fault rupture to occur within the site to be very low.

Seismic Ground Shaking

The site is located in Seismic Zone 4 as assigned by the Uniform Building Code (UBC) and will be subject to moderate to strong earthquake-induced ground shaking. The intensity of ground shaking felt at the site from future earthquakes will depend on several factors,

6


including the distance of the site to the earthquake focus, the magnitude and duration of the earthquake, and the response of the underlying soil or bedrock. The past seismic history for earthquakes generated on the local faults, as well as the San Andreas fault, more distant from the site, suggests that strong ground shaking, in the range of Modified Mercalli Intensity VII to VIII, is likely during the life of the project. Ground shaking from a near~ field earthquake on the Fickle Hill fault would likely generate stronger ground shaking intensities, possibly as high as IX or X. We conclude that earthquake-related strong ground shaking is likely to occur during the life of the buildings therefore, they should be designed in accordance with local earthquake-resistance standards.

Liquefaction/Densification

Liquefaction and densification are phenomena that can occur in loose cohesionless soils below and above the water table, respectively, during strong earthquake ground-shaking. Liquefaction occurs during temporary increases in pore water pressure in the soil, causing los's of soil strength and leading to ground cracking, settlement, lurching, and lateral spreading. Densification occurs as the loose, unsaturated soil structure collapses, leading to settlement.

The soils encountered in Borings B-1 tlrrough B-3 were found to either have sufficient density or sufficient quantity of fines (i.e. silt or clay) that liquefaction of these soils is unlikely. In addition, there are no historic reports of liquefaction or densification ground failures caused by earthquakes at the site (Youd and Hoose, 1978). If zones of loose, clean sand arc present in the terrace deposits, beyond our test borings or trench; it is possible they may be susceptible to liquefaction. We consider the potential for extensive areas of liquefaction and/or densification to occur at the site to be low to low. If liquefaction and/or dcnsification should occur, we believe the effects would be localized and limited to ground cracking or ground displacements on the order of a few inches. However, if the building areas arc prepared following our recommendations, we consider the likelihood of damage to structures from liquefaction or densification effects to be low.

Flooding

From our discussions with representatives of the City, we understand the site does not lie within a flood prone area. The potential for localized or temporary flooding, following periods of heavy rainfall could be mitigated by surface drainage provisions.

Landsliding

We did not observe landslides on the site during our rield investigation or aerial photo review. In addition, landslides have not been mapped on the site (Kelley, 1984). We t11eretore do not consider landsliding to pose a risk to the site.

7


Concentrated surface water flows from roof downspouts and paved areas should not be allowed to discharge directly over the existing drainage channel bank, where they could erode the bank, eventually leading to localized sloughing. Should erosion or sloughing occur in the channel banks, it should be repaired promptly, before they can enlarge.

Geotechnical Considerations

We conclude that, from a geotechnical engineering standpoint, the proposed building can be constructed essentially as planned. Satisfactory foundation support can be obtained from spread footings bottomed in properly compacted fill. This will require removal and replacement of the existing weak, near-surface fill soils to upgrade their supporting capacity. The main soil engineering considerations affecting the design and construction of the project are the presence of the existing weak fill soils, anticipated settlement, and future strong earthquake shaking. These considerations (except for previously discussed future strong earthquake shaking) arc discussed in detail in the following sections.

'

Existing Weak Fill Soils

Foundation and concrete slabs supported on the weak, existing fill soils in their present condition would undergo erratic and excessive settlement (in the range of from 4 to 10 inches). Therefore, within building and slab areas, the supporting capacity of the nearsurface portions of these soils will require upgrading, (i.e. ,removal and replacement as properly compacted fill). We conclude the removal of these soils can be limited to:

1. 1.5 feet below the bottom of the lightly loaded building footings,

2. 3 feet below soil subgrade within concrete slab areas,

3. 1.5 feet below soil subgrade within asphalt paved areas.

Detailed fill removal and replacement recommendations are presented later in this report.

Settlement

Settlement due to the consolidation of the compressible zones in the existing fill can be minimized by providing at least 1. 5 feet of compacted fill below footing bottoms. This will dissipate much of the foundation loads, and bearing pressures, so that new loads on underlying old fill zones are minimal. Except for the compressible silty peat zone near Boring B-2, the natural soils underlying the existing old fill are "pre-consolidated" (previously consolidated under loads greater than the existing overburden pressures). Because the combined old fill and new loads on the underlying natural soils will be less than their pre-consolidation pressures, the resulting settlement caused by these natural soils will be negligible. Considering the old fill loads have been placed since at least 1974, we

8


estimate that most of the settlement due to these loads on the compressible peat zone has occurred. However, we estimate the old fill loads may cause an additional 114 inch of settlement where underlain by peat.

Assuming building pads arc properly prepared, and footings are designed and constructed in accordance with our recommendations, we estimate that the maximum post-construction settlement due to the planned light foundation loads will be less than 112 inch. We judge that post-construction differential settlement will be less than 1/4 inch between adjacent footings, along an individual wall footing, or between a footing and adjacent slab-on-grade tloor.

Since we understand from the project civil engineers that the above anticipated postconstruction settlements are tolerable, we conclude that more sophisticated foundation systems (such as piles or reinforced concrete mats) are not warranted for the planned buildings.

RECOMMENDATIONS

Site Preparation and Grading

For the purpose of definition, select fill areas referred to in tl1e remainder of this report are:

l.

2.

3.

The building areas, and the zom:s extending five t"eet beyond the outside edges of perimeter footings,

Exterior slab and asphalt paved areas, and the zones extending three feet beyond their edges,

Fill slope areas.

Areas to be graded should be cleared of existing vegetation, rubbish, and debris, and then stripped of surface soils containing organic matter. In general, the depth of required stripping will be about 2 inches; deeper stripping and grubbing may be required to remove isolated roots, and concentrations of organic matter. The cleared and stripped materials should be removed from the site; topsoil may be stockpiled for reuse in future landscape areas. Within select fill areas, except for asphalt paved areas, old fill soil should be removed to at least 3 feet below soil subgrade surfaces. Within asphalt-paved areas, old fill removal can be limited to 1.5 feet below soil subgrade surfaces. In addition, within footing areas and the zones extending downward from footing bottoms at an inclination of 1 horizontal to I vertical (1: I), old fill soil should be removed to at least 1.5 feet below footing bottoms. Within the area excavated for the exploratory fault trench (see Plate 2 for location), loose trench backfill should be removed to at least 5 feet below soil subgrade surface.

9


Following clearing, stripping, weak fill soil removal, and required excavations, the exposed soils should be scarified to a depth of 6 inches, moisture conditioned to near optimum moisture content (plus or minus 2 percent), and then recompacted to at least 90 percent relative compaction. 1 If isolated zones of soft or yielding soils are encountered within select fill areas during grading, they should be removed to expose firm soils. The depth and extent of excavation and over-excavation should be checked in the field by us.

Excavations may encounter temporary seepage if performed during the rainy season (late fall to spring). If dewatering is necessary, it can be accomplished by conventional pumping. However, installation of gravel drain blankets and sumps (at the contractor's option), will facilitate dewatering, and provide a dry working pad for subsequent fill placement and compaction.

Fill and backfill material should be free of organic material and rocks larger than 6 inches. In addition, select fill material should have a low expansion potential (liquid limit less than 40'percent and plasticity index less than 15 percent, as defined by ASTM D 4318-84 wet test method), and be free of organic material and rocks larger than about four inches. Fill material should be checked by TTC prior to use. In general, the on-site soils will be suitable for reuse as fill provided organics and debris are removed.

Fill and backfill should be placed in thin lifts (6 to 8 inches thick, depending on compaction equipment used), moisture conditioned to near optimum moisture content, and compacted to at least 90 percent relative compaction. Within traffic areas, the upper six inches of fill (subgrade) should be compacted to at least 95 percent relative compaction.

Cut or fill slopes, if constructed, should be excavated at 2: 1 or flatter. We recommend the tops (upper about 2.5 feet) of cut slopes be rounded back to about 3: 1. Cut slopes should be observed in the field by us to verify that exposed soil conditions are as anticipated.

Fill and cut slopes should be planted with erosion-resistant vegetation or protected from erosion by other measures upon completion of grading. The surface runoff should be intercepted and diverted away from slope surfaces.

Relative compaction (RC) refers to the in-place dry density of soil expressed as a percentage of the maximum dry density of the same soil, as determined by ASlM Dl557-78 test procedures. Optimum moisture content is the water content (percentage by dry weight) corresponding to the maximum dry density.

10


Foundations

The proposed buildings should be supported on spread footings bottomed on compacted select fill with at least 1.5 teet of below footing bottoms. Wall footings should be at least 12 and 18 inches wide, respectively, regardless ofload, and should be bottomed at least 12 inches below lowest adjacent compacted soil subgrade. Spread footings should be designed using the following allowable soil bearing pressures in pounds per square foot (pst):

Dead plus long-term live loads

Dead plus all live loads

Total design loads, including wind or s~ismic forces

2,000 psf

2,500 psf

3,000 psf

The soil profile approximates Type S3 of UBS. To calculate total lateral seismic forces acting on the structures in accordance with the UBC, a Seismic Zone Factor (Z) of 0.40, and a Site Coefficient (S FACTOR or S) of 1.5 are appropriate.

Resistance to lateral loads can be obtained from a combination of passive earth pressures against the face of foundations, friction across the bases, and sidewall resistance along faces of footings, using the following criteria:

Passive Pressure 800 psf (rectangular distribution)

Base Friction 0.35 times net vertical dead load

Sidewall Resistenace 400 psf

Neglect passive pressure and sidewall resistance in the top one foot where the soil surface is not confined by slabs (or pavement).

11


Concrete Slabs-on-Grade

During foundation installation and utility trench excavation and backfilling, previously compacted slab subgrade soils may be disturbed. These soils should be moisture conditioned to near optimum moisture content and rerolled to provide a smooth surface compacted to at least 90, and 95 percent relative compaction within non-traffic and traffic areas, respectively. Exterior concrete slabs can be placed directly on the prepared select fill subgrade soils.

Slab-on-grade floors should be underlain by at least 4 inches of clean, free draining slab base rock to act as a capillary moisture break. Slab base rock should be graded between 1/4 inch and 1-112 inches. Within traffic areas, crushed materials should be used to provide a tight interlock of the aggregates. Where movement of vapor through the slab would be objectionable, a vapor barrier should be installed between the slab and the rock.

, Asphalt Pavements

From our previous investigations in the general area, we have found that the silty sands have an average R-value of about 20. Using this R-value, traffic indexes (T.I.) provided by Winzler and Kelly, and the California Division of Highways Standard Design Manual 7-651.1 (December 1981), we recommend the preliminary asphalt pavement thicknesses presented in the following table:

Parking 5.0 A

" 5.0 B

Roadway 6.0 A

" 6.0 B

·· .• ~J.llllilf . . .. •· clails 2 ... WW cliiSs 4 · · Ciini:iiete / ~g;:~glittJ i . Aggi.~~w · ·

· · $iirf¥~lii~ / $\'lbljl1$e< << SJ.!bbiiii~ <3) .············tr (2)\

2.5 8.5

2.5 4.5 4

3 10.5

3 6 5

(l) These thicknesses are minimum recommended thickness only. Increasing Asphalt Concrete thickness in place of Class 2 Aggregate Base would increase life and durability of pavement section.

(2) R-Value = 78 minimum

(3) R-Value = 50 minimum

12


After the rough grading within paved areas has been completed, we should sample and test the soils at subgrade elevations to determine their actual resistance values. This may result in some modification of the preliminary pavement sections.

Class 2 Aggregate Base should conform to the requirements in Section 26, State of California Standard Specifications (Caltrans), current edition. Aggregate Subbase should have an R-value of at least 50 and conform to the requirements for select fill. Both aggregates should be placed in thin lifts and in a manner to prevent segregation, moisture conditioned to near optimum moisture content, and compacted to at least 95 percent relative compaction to provide smooth unyielding surfaces.

Supplemental Services

We recommend that we be retained to review the project plans and specifications to determine if they arc consistent with our recommendations. We also should be retained to observe geotechnical-related site preparation and grading, placement and compaction of fill and backfill and foundation and slab installations. We should also perform the required geotechnical-related field and laboratory testing during these construction operations. Our construction services should include sampling and testing the actual soil exposed at subgrades within asphalt-paved areas.

If, during construction, subsurface conditions different from those encountered during our exploration are observed, or appear to be present beneath excavations, we should be advised so that these conditions may be reviewed and our recommendations reconsidered. The recommendations made in this report are contingent upon our notification and review of the changed conditions.

If more than 18 months have elapsed between the submittal of this report and the start of work at the site, or if conditions have changed because of natural causes or construction operations at or adjacent to the site, the recommendations made in this report may no longer be valid or appropriate. In such cases we recommend that this report be reviewed to determine the applicability of the conclusions and recommendations, considering the time lapsed or changed conditions. The recommendations made in the report are contingent upon such a review.

These supplemental services are performed on an as-requested basis and are in addition to this geotechnical investigation. We cannot accept responsibility for conditions, situations or stages of construction that we are not retained to observe. If other engineers perform such construction observation, we cannot be responsible for their interpretation of our conclusions and recommendations.

13


LIMITATIONS

This report has been prepared by Trans Tech Consultants for the exclusive use of The City of Arcata for development of the proposed project described in this report.

Our services consist of professional opinions and conclusions developed in accordance with generally accepted geologic and geotechnical engineering principles and practices. This warranty is in lieu of all other warranties, either expressed or implied. Our conclusions and recommendations are based on the information provided to us regarding the proposed construction, the results of our field exploration and laboratory testing and our professional judgment. Verification of our conclusions and recommendations is subject to our review of the project plans and specifications, and our observation of construction.

The test borings represent subsurface conditions at the locations and on the date indicated. It is not warranted that they are representative of such conditions elsewhere or at other times. Site conditions and cul rural fearures described in the text of this report are those existing at the time of our field exploration, and may not necessarily be the same or comparable at other times.

The scope of our services did not include an environmental assessment or an investigation of the presence (or absence) of hazardous, toxic or corrosive materials in the soil, surface water, ground water or air on, below, or around this site, nor did it include an evaluation or investigation for the presence (or absence) of wetlands.

14

I I ILLUSTRATIONS

I Vicinity Geologic Map, Plate 1

I Site Plan, Plate 2 Previous Investigations, Plate 3 Log of Soil Borings, Plates 4 through 6

I Log of Test Pits I and 2, Plate 7 Unified Soil Classification System, Plate 8 Log of Exploratory Trench, Plate 9

I Laboratory Test Data, Plates 10 through 13 Regional Structural Setting, Plate 14

I I I I I I I I I I I I 15

I


EXPLANATION

Q Alluvium --------/ Qmts Marine Terrace Deposits ,.. ....... ,.. Qfa Falor Formation

10

KJfs Franciscan Complex .>-

.... TRANS TECH CONSULTANTS ¥ ENVIRONMENTAL AND GEOTECHNICAL SERVICES

JOB NUMPER

3040.01.01 DRAWN

PM

Ref~nce; Kelley, 1984 and CDMG, 1983_

Contact between geologic units

Traces of Fickle Hill Fault: teeth on upper plate

Attitude of bedding N

I 0 2000

SCALE IN FEET

Vicinity Geologic Map lntermodal Transit Facility 9th and F Streets Arcata, California, California APPROVED

~l~f

PLATi;.

1 DATE

10/93

I I I I I I I I I I I I I I I I I

I

I ... ·

\ ..... .

I i)

... ···t

i l i .i . ' i j I

'I •i \. ..

i "'<.

.' I

l I/

!L / . I' .... J

.rv

Iii w a:: lii ~ z

I

!!

I i

I I. '

i ..

:lw.rr ···· .. : I -~ i. .-.- .· _,,.,,.· .· ,,,.. .. ·:-:

. )_:~:./~:_:_-::.;.

Columns

./· .. ·

'I .. . ·t... ii

R33'-"1 ,• • j

i~/ L_

I

I ____ ,.,.,._.- I

--1--- I

_J ,_ •. _.-1 .... .-r . _.;c

EXPLANATION

$ Test Boring

-$- TestPit

REFERENCE: lntermodal facility site plan, by Holmes Biord Architects,

Revised November 29, 1993

..... TRANS TECH CONSULTANTS . # ENVIRONMENTAL AND GEOTECHNICAL SERVICES

JOB NUMBER DRAWN

3040.01.01 PM

Site Plan Planned lntermodal Facility

Arcata, California

APPROVED

\)\.ff

0

SCALE IN FEET

30

PLATE

2 DATE

12/93


t. i'

() M s

REFERENCE: California Division of Mines and Geology, 1983, Special

Studies Zones, Arcata North and Arcata South Quadrangles.

BGC-Busch Geotechnical Consultants; NGl-Northem Geotechnical

Incorporated. See report for discussion of previous investigations.

.... TRANS TECH CONSULTANTS # ENVIRONMENTAL ANO GEOTECHNICAL SERVICES

JOB NUMBER

3040.01.01 DRAWN

PM

N

I 0 2000

Previous Investigations lntermodal Transit Facility 9th and F Streets

SCALE IN FEET

Arcata, California, California APPROVED

v\--1-f

PLATE

3 DATE

10/93

I $' ~ Log of Boring B-1 ~ ., a. ~

Equipment Type: Mobile B-BO I!!- c: !S

I ::J c: GI -1i5 J!! c.;:-

., .c: Elevation: Date: ·- c: ~ Q. 23.3 8-23-93

Laboratory Test Data Oo ~8. GI ::!io c~ ID 0 Description

I GRAVEL FILL

•• MOTILED LIGHT YELLOW-BROWN AND GRAY ... SIL TY SAND (SM) dry, loose to medium dense, with ••• pockets of gravel

MA, see Plate 10 13.4 101 12 ••

I ... ...

5 •• ••

I •• __, •• __, • u:: • DARK BROWN SIL TY CLAY (OL) moist sell

6 : : I

I • LIGHT YELLOWISH BROWN SILTY SAND(SM)

10 • moist, loose, with pockets or gravel . . • •••

I DARK BROWN SIL TY GRAVEL (GM) molsL loose, with pockets of clay

I 12.1 12.8

6 22.6 109 15 ... LIGHT GRAY SILTY SAND (SM) moisL loose

BLACK SANDY CLAY (OL) moist soft

MOTILED LIGHT BROWN AND GRAY SANDY

I SILT (ML) moist to wet medium slilf

79% Passing #200 Sieve

I and Consol, see Plates 22.1 99 15 20 MOTILED ORANGE AND GRAY SANDY CLAY (CL)

10 and 12, respectively -.-

I 18 25 GRAY SANDY GRAVELLY CLAY (CL)

I weL stiff to very slllf

I MOTILED LIGHT BROWN AND GRAY SILTY SAND 16.0 115 17 30 (GM) satura1ed, medium dense

Bottom of hole at 30.0 ft

I I 35

I I 40

Log of Boring B-1 PLATE r TRANS TECH CONSULTANTS lntermodal Transit Facility 4 I ENVIRONMENTAL AND GEOTECHNICAL SERVICES 9th and F Street Arcata, California

JOB NUMBER DRAWN ED DATE

I 3040.01.01 PM 10/93

I ~ ~ Log of Boring B-2 ~ ., ;,, E' !!!- c - ~ .!! Equipment Type: Mobile B-80

I :J c ID - ID o""

., .c a. 20.9 .. - ;: 15. E Elevation: Date: 8-23-93 ·- c ~8. Laboratory Test Data

Co .2 ID m Description :; (.) a~ Ill a !/J

I GRAVEL FILL

-GRAY SILTY SANDY GRAVEL (GM) Tx uu 1273 (576), 13.9 116 21 moist, medium dense

see Plate 11 GRAY CLAYEY SAND (SC) moist, loose

I to medium dense, with some gravel

5

I Tx uu 537 (864), 15.0 118 6

see Plate 11; ...J

32% passing #200 sieve, ...J u:

I see Plate 10

10 Tx uu 813 (1152), 88.6 46 9. BLACK SIL TY CLAY (OL) mois~ soft to medium

see Plate 11 stiff, with chunks of organic material

I I 15 BLACK SIL TY PEAT (Pt) moist to we~ soft

Consol, 366.7 14 3 decomposed wood debris see Plate 13

I I

20 3

I 25 GRAY SILTY GRAVELLY SAND (SM)

I 34.4 88 22 ...

wet, medium dense, with some wood debris

I ... 13

30 ... MOTTLED GRAY AND LIGHT BROWN SILTY SAND (SM) saturated, medium dense, with

I some gravels

I ...

35 ... GRAY SIL TY SAND (SM) saturated, loose to

I 11 medium dense

I 16.4 112 14 40 Bottom of hole at 41.0 fl

Log of Boring B-2 PLATE T TRANS TECH CONSULTANTS

I ENVIRONMENTAL AND GEOTECHNICAL SERVICES lntermodal Transit Facility 5 9th and F Street Arcata, California

JOB NUMBER DRAWN APPROVED DATE

I 3040.01.01 PM ~· -.-1\? 10/93


~ >.

"" a. 2!~ .. c:

::I c: GI -1ii .! 00 .. ·- c: ii

Laboratory Test Data oo <!' 8. ..Q :!:O o~ ID

8

4

.

• 8

23.8 101 4

21.0 106 18

19

T TRANS TECH CONSULTANTS ENVIRONMENTAL AND GEOTECHNICAL SERVICES

JOB NUMBER

3040.01.01 DRAWN

PM

E' ~ J! R Q.

E tD ~ 0

. ••• ... . . .. ••• . • ••

. ... • ••

5- ••• ... . • •• ••• . . .. ••• . • •• ... . •••

10- ••• ••• . . .. . .. .

' ' . • .

15 ----- ~ 20-

~ .

. ... . ...

. ••• • ••

25- ••• ... . • ••

••• . • •• -

~ -30-

-. . .

35-.

.

.

.

40-

Log of Boring B-3 Equipment Type: Mobile B-80

Elevation: 22.4 Date: 8-23-93

Description

GRAVEL FILL MOTJlED LIGHT YELLOW BROWN AND GRAY SIL TY SAND (SM) moist. loose. with wood debris

RED BROWN SIL TY CLAY f OL) moist. soft to medium still. with pockels o sUty gravel

GRAY SIL TY SANDY CLAY (CL) soft ID medium still

MOTTlED LIGHT BROWN AND GRAY SILTY SAND (SM) we1, medium dense

GRAY SANDY SILTY CLAY (CL) moist. medium still ID stiff

Bottom ot hole at 29.5 ft

Log of Boring B-3 lntermodal Transit Facility 9th and F street Arcata California

.... .... u:

-~

PLATE

6 DATE

10/93


Laboratory Test Data

5

:2: 10

15

Laboratory Test Data

5

10

15

••• ... ... ... ... ... ... ... ... ...

... ... ...

Log of Test Pit~TP~-1~----

Equipment Type: _s-='-ho_e'-------

Elevation:----- Date: 6-11-93

Description

BROWN SIL TY GRAVELLY SANO (SM) loose lo medium dense, moist lo wet (fiU)

BLUE-GRAY CLAYEY SANO (SC) loose lo medium dense, (filQ

DECOMPOSED WOOD I ORGANIC DEBRIS and clay I gravel I sand soil, moist to wet (filQ

water Level 6-11-93

saturated

LogofBoring_TP......_-~2,_ _____ ~

Equipment Type: Backhoe ---------Elevation:----- Date: 6-11-93

Description

BROWN SIL TY GRAVELLY SANO (SM) loose to medium dense, moist to wet (fill)

BLUE-GRAY CLAYEY SAND (SC) loose lo medium dense, moist to wet (fill)

DECOMPOSED ORGANIC DEBRIS ANO SOIL, moist lo wet (filQ

.... TRANS TECH CONSULTANTS ~ ENVIRONMENTAL AND GEOTECHNICAL SERVICES

Log of Test Pits 1 and 2 lntermodal Transit Facility 9th and F Street Arcata, California

JOB NUMBER

3040.01.01

DRAWN

PM

APPROVED

?LATE

7 DATE

10/93


~ffi -"' ~~w

MAJOR DMSIONS

GRAVELS

MORE THAN HALF COARSE FRACTION IS

CLEAN GRAVELS WITH LITil.E TO NO FINES

GW

lYPICAL NAMES

WELL GRADED GRAVELS WTlli OR WITHOUT SAND, LITTLE OR NO ANES

:;5'~ POORLY GRADED GRAVELS WITH OR WITHOUT GP 5• :di SAND, LITilE OR NO ANES

GM ~ SILTY GRAVELS, SR.TY GRAVELS WITH SAND I< ' co>

WO~ / Z !!l c GC '1)~JI CLAYEY GRAVELS, CLAYEY GRAVELS WITH SAND

LARGER THAN No. 4 SIEVE SIZE

GRAVELS WITH OVER 12%FINES

-u..o L- /c ~~Nl-----------1------------1-----"1:~~------------------------1 #ft :co ,.-.;.:. '""zZ SW •. • • WELL GRADED SANDS Willi OR WITHOUT Jicez : :•:•• GRAVEL,LITnEORNOFINES U> :>: <C SANDS CLEAN SANDS WITH ••·• • It: 1- i!: LITilE OR NO FINES •':•-.,•:•: - !:! SP •.•.•:•• POORLY GRADED SANDS WITH OR WITHOUT 0 .... O :.:.:.: GRAVEl, LITILE OR NO FINES U:::;; MORE THAN

HALF COARSE SM

·.· .. ..... .... .... SILTY SANDS WITH OR WITHOUT GRAVEL FRACTION IS SMALLER THAN No. 4 SIEVE SIZE

SANDS WITH OVER 12%FINES

SC fil CLAYEY SANDS WITH OR WllHOUT GRAVEL

~ (I) :i: ..Jl-

6ffi

ML

CL~ SILTS AND CLAYS

LIQUID LIMIT 50% OR LESS

U>~w 11••••

INORGANIC SILTS AND VERY FINE SANDS, ROCK FLOUR, SILTS WITH SANDS AND GRAVELS

INORGANIC CLAYS OF LOW TO MEDIUM PlASTICfTY. CLAYS WITH SANDS AND GRAVELS, LEAN CLAYS

~> 111111 fil "'!!! OL : : : : : : ORGANIC SILTS OR CLAYS WITH LOW PLASTICITY -w 1::1~:

z~c1-~~~~~~~~~~~~~~1--~+1'-1+1ri+~~~~~~~~~~~~~~~--1 <~?3 it:: :i: . C)ZO

I <(Z w :i: z>-_w IL~

Perm Consol

LL

Pl

G,

MA

• 181

--------

SILTS AND CLAYS

LIQUID LIMIT GREATER THAN5o%

HIGHLY ORGANIC SOILS

MH

CH

OH

pt

INORGANIC SILTS, MICACEOUS OR DIATOMACEOUS, ANE SANDY OR SILTY SOILS, ELASTIC SILTS

INORGANIC CLAYS OF HIGH PLASTICITY, FAT CLAYS

ORGANIC SILTS OR CLAYS OF MEDIUM TO HIGH PLASTICITY

i:::::::::i PEAT AND OTHER HIGHLY ORGANIC SOILS

UNIFIED SOIL CLASSIFICATION ·ASTM D2487-85

Permeability Shear Strength (psi) 1 r Confining Pn!aura

Consolidation TxUU 3200 (2800) - Unconsolldale<I Undrained Triaxlal Shear

Liquid llmtt (%) (FM) or (S) <- molallre or satwated)

TxCU 3200 (2800) - Cansoldalod Und-Trlaldal Shear Plastic Index (%) (P) (wilh or wlthaut pore prassure measurement)

TxCD 3200 (2600) - CorlllOlldafad Drained Tl1axlal Shear Specific Gravity sscu 3200 (2800) - Simple Shmr Ccnsalldaled Undmlned

Particle Size Analysis (P) (with or wlllout pore prassura mMsuremenl} SSCD 3200 (2600) - Simple Shear Ccnsaiidated Drained

"Undisturbed" Sample OSCO 2700 (2000) - Consoldatlld Dtalned Direct Shear

Bulk or Classification Sample UC 470 - Unconftned cornp11!181on LVS 700 - l.alloratary vane Shear

KEY TO TEST DATA

~ TRANS TECH CONSULTANTS Unified Soil Classification Chart and Key to Test Data

PLATE

# ENVIRONMENTAL AND GEOTECHNICAL SERVICES

JOB NUMBER

3040.01.01 DRAWN

PM

lntennodal Transit Facility 9th and F Streets Arcata. California

8 DATE

10193

I I I I I I I I I I I I I I I I I

1-w UJ u. ~

25

20

10

5 25

20

15

z 10 0 ;:: ~ UJ .... w

5

0

o+yos D+?os o+~os D+f!S o+7os o+fos o+1os o+oo

L.~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~-'-~~~~~~~~~~~~~~~~~~~I 25

@

carbonized woad fragments In root zone

'. 1 1 over1 \:!J .,,...---.L grada!onal 13'

~· -- -------------------------------------- , ---------©--_-_-_~-:::.. _______ -1-~ --------© _______ -f-.""®__ distinct--/;/' •

1+305 I

sand well stratifted

1+205 I

1+10S I Ground Surface

1+005 I

N10E

0+905 I

Slumps~

,,--i~ )-~)~, I I t • I I I \ # 1

caved section

(not logged)

distinct Interface lo unoxidized

o+805 I

Slumps I roots ~ , .. - •• •

-----------@ ----------c----------1" ___ - - - - - - - - ----:.._-:_ - - - - - gradational """' 1" ©

____ SI-<'::____ @ (caving) -------~ © © Seep ...... - - ...... Seep - - - - - - - - - distinct contact

0 5

HORIZONTAL AND VERTICAL SCALE IN FEET

@ distinct contact

coarse grained atbese

@ --'-

slightly oxidized to mamed gray .........__ arid yellow brown

.... TRANS TECH CONSULTANTS # ENVIRONMENTAL AND GEOTECHNICAL SERVICES

JOB NUMBER

3040.01.01 DRAWN

PM

25

20

m .m :i;; ::!

15 0 z

10

z .,, m ~

EXPLANATION

20

rn .rn :i;; ::!

15 0 z

10

5

z .,, rn rn ....

(D FILL - Materials cf varying campasltian and density; consists mainly cf sandy silly gravel (GM) and silly sand (SM); wtth accaslonal decomposed woad debris (generally less than 5%)

@ FILL - Decomposed woad debris, with accasional stumps

©

©

@

©

DARK GRAY BROWN SILTY SAND (SM) medium dense, moist lo wet, with occasional carbonized organic fragments (Native sell dewlaped on Terrace Depasils)

GRAY SILTY SAND (SP/SM) lease ta medium dense, wet, medium grained (Tamica Depasils)

GRAY SANDY GRAVEL (GP) lease ta medium dense, wet lo saturated, wtth rounded gnM!I ta 1/2" diameter ~ca Deposits)

GRAY CLAY (CH) stiff ta very still, we~ massive, axidlzed In upper portion (Faler Fannetlon)

5 ...... .- Contact between gealagic units, sarld where dlsllncl, dashed where gradational /

·//&///,.· zone of iron oxide mattting

Log of Exploratory Trench lntermodal Transit Facility 9th and F streets Arcata, California

PLATE

9 DATE

l!..J, 1/'\i 10/93


1300.--~~~~~~~-,-~~~~~~~....,.......,.......,.......,...~~~~.....,.~~....,...__,....,.......,.......,..........,

. . I . . I 1200 ............................... ..

1100 ........................... , ... .

1000 ...

900 ...................... .

800 ..................... .

700 ...... . ............ .

600 .....

qOO ············· ...................... .

400 ................... ..

300 ........

...... ; ....

. ... ... ~

2

Sample Source

··········l·····························.;. ............................. 1 ............................................................ 1-•••••••••••••••••••••••••••• : ............................ .

~ . : J 1 :

; : : : : : •• ••' •• •••••·' ••• .. •(•• •••··• •••' ••' ••'. ••·• •••' ••• ~ •••• ' •· ••· •. ,. '••·· ,, •• ,, ·•.·I• .. ' .. •••••••',,•••••••••••••.;. ., • ., •••••••••••••••••••••••• I•••••.,••••••'••••••""••• ••• .;. •• ',., •• ., •• ,.,,,.,,,•••••••' : . . : . j

. ~ ; l ~ ···········•·· .................... , ...................................................... ! ........................... 1 ............................ 1···· .. ·· .......... .

...................... ······················ --i············ ····l·····························t···-·· .. ·····················f·····························+·····························

. ........................ ;... •.. ~~~ .... , ........................ ; ............................. ; ............................ "' ..................... ..

··········:··········"""'"''"·"···+ ............................. ~ .......................... '':''"'"'"'"''"'''''

- ' ::":::-r r::-: 1 . ~

.... ; ............................. , .............................. ; ............................. ; ....................... ..

: : : : .......... ; ............................. ~ .......................... + ............................ t ............................. ~ ............................. f.

. ... , .............. :······--"·' ............... i .............................. ;• ......................... j

: : ............................................. ; .......................... ; ............................. + .......................... T .......................... + ......................... .

4 6

Classification

8

STRAIN(%) 10

Type of Confinemen Pr~~re Test*

12 14 16

Ultimate Strain °l'~ly Moisture

Stro~ri Co1~nt ,..., :') [email protected]' Gray Clayey Sand (SC) TX/UU 576 1273 5 116 13.9

:;:i [email protected]' Gray Clayey Sand (SC)

<!> B-2 @ 10.5' Black Silly Clay (OL)

* UC ""' Unconfined Compression

TX/UU= Unconsolidated Undrained Triaxial

TRANS TECH CONSULTANTS Job No: 3040.01.01 Job Id: INTER

Appr: \iWI. Drwn: LTS

Date: OCT 1993

TX/UU

TX/UU

864 537 11

1152 813 7

STRENGTH TEST DATA

lntermodal Transit Facility 9th and F Streets Arcata, California

118 15.0

46 88.6

PLATE

11


VOID RATIO- PRESSURE CURVE

o.,~ _..;. ,-;...

--~···············-····················-···························· .. ··-...... , ... ,. . ........ ; ... - .; .. + .; ... l··+·•··r·

I ················· .... , ............. , ....................... , ......... " .. '"I ~."'"""' .......... :SI__ ......... :" ....... : ..... ; ... ; ... c ... H :- :'. : t _: riti : ,, ..

0.68

• 0.67 • ; :

0.66

,,

' '' .......•..... " .. ' .. ; ..... ' .. ;., . " .. : .. '"""'''"" "'·' ·l" ............................................ ' , .. " ........ ·: ... .:.. .. : ... : .. :S.

0.65

\, ' .

.... , ..... , ........ , ... , ... , ....................... , ............. ; ......... , ...... .; ...... , ... ,, .... ~,··•· .. I················· .... j·····-···-···.:.········7· ···r····1·· .. 0.64 .............

•

' '

0.63 .... ····················l············~··· ···+··· -~····--;--··i .. ) ... ; ..

• ·············!···········-·+· ·····1 ······j······!···+···!··+-· • •

0 0.62 ·············· H I-<C a: . ' ··\ +· ...................................... ; ..... , .. ; ... ,.<-·! ............... , .............. ., ...................... , .. ! 0 0.61 ... H ( :)..... 0

....... !.... . ..... -~··· ····i··· '-•·! ····•··

I· .......... ~""" .. ; ....... ; ....... ; ...... ; .... ;. •··•+·····"·············••······ .......... , ... " .... , .. , ... , .. ., .. , ...................

. . -.......,.._ . ................. , .................. ~"''''+·························"''''· ' "'

.• .......... • ....... ; ........ ~ ...... is .•... ' ... ,"-."'-·····'"' .. ••. ' • • .... , .... , ... , ... , • ' . . ' ......... ; ..... • .. ; ... Hf .............. •'-,··················• • '

"'R I ~········

• • .._ .:--...• ", ···~h."'"'········""""" • . ' •

"" ......... , .. , • ' , ............ ,

..... •

'

•

..... ,

• • •

•

:> --............_ 0.60

. . . : : ; : ............... ·t·············.;. ......... : ...... ~ ..... j •••• ; .... j .( ••.

............ ·····•····• ·······:·······!······,·· 0.59

0.58 1············· ......... • •..

0.571·· .

0.56 1··················

o.ss•········ .. ········

.... . ·-:-········"" ····:····T·

.... ·~· .. • .• ·i· ••. t ... ·~··' l" ........... T ...... ..

........ -~· ......... .

• 0.54 .... - ······················· ····~·-·····"";""

; ········· • ·•···".··•··I 0.53 ...... ~~~~~~~~~~ ....... ~~~~~~~---....... ~ ....... .,....~~---~---~~~ ............. ~

0.1 10 100 I

• • •••

PRESSURE (psi x 1,000)

Reference: ASTM D 2435

Type of specimen Undisturbed Before Test After Test

Diameter (in.) 2.43 Height (in.) 0.80 Moisture Content WO 22.1 % wf 22.1 %

Overburden Press., Po 2,580 psi Void Ratio eo 0.694 el 0.606

Preconsol Press., Pc 4,000 psi Saturation So 86 % SI 100 %

Compression Index, Cc 0 .13 Dry Density d 99 pcf d 104 pcf

LL PL Pl Gs 2.68

Class: Mottled Orange and Gray Sandy Clay (CL) Source: Boring B-1 @ 20.0'

TRANS TECH CONSULTANTS Job No: 3040.01.01 Job Id: INTER

Appr: \)\-'\'?

Drwn: LTS

Date: OCT 1993

CONSOLIDATION TEST DATA


PLATE


VOID RATIO- PRESSURE CURVE

... , ::r , L~:. :r.:11.:~.1 ::: :: :::::: I : : ~ : : ; : ; ......... i ....... j· ·· ·· ··-················: ·············~· · ·· ····-~·- · · -~ .... j .• · ·r···i ··

6.4 ·····················

6.0 ......... .

..

. +····:--··; ... : .. :.: ....................... . . ........... .:. ...... ·-:-······T·····j···-~·-··!··-~···

5.6 ............ . . ...... i·······r····-=-····=···r·+· ....................... : ............. :- ........ : .... ···~· .... -~ .... :... . .

5.2 ··················

····'·······'····•-.:J.1.· J .••............. ;.. . "" 7

............••......•.. :···. . . ··~·- ... -~- ... !··. -~· .. !·.

..... .l ..... l. ... L.i .. ., ....... ., .. ····················

4.8 ············•···· ····-········-······ ·················· ..

. :-· ..•.. :- ..•. ·:. ···:·- ··!-· ....•...•..•.....•. ·•··•· ~-·· ..... ·····-:.·-· ..... 7.

·······-··~·········· .... ~· .... ·-~·-·· ··~ ... ·~

...... '

.. ·······················:·············:·-

.. -~ .... ;

3.6•·························"·································'·····'············"··•

Type of specimen Undisturbed

Diameter (in.) 2.43 Height (in.)

Overburden Press., Po 1,938

Preconsol Press., Pc 1,200 Compression Index, Cc 3.7

LL PL

Class: Black Silty Peat (Pt)

mANS TECH CONSULTANTS

100 PRESSURE (psfx 1,000)

Reference: ASTM D 2435

Before Test After Test

0.80 Moisture Content WO 366.7 % wf 263.6 %

psf Void Ratio eo 6.645 el 4.483

psf Saturation So 92 % Sf 100 %

Dry Density d 14 pct d 19 pct

Pl Gs 1.66

Job No: 3040.01.01 Job ld: INTER

Appr : \)\\I.

Drwn: LTS

Date: OCT 1993

Source: Boring B-2@ 15.5'

CONSOLIDATION TEST DATA


PLATE

3


+

EXPLANATION

--- Fault

= = Spreading Ridge

___ ....._ ...... Thru$t Fault

+

Direction of plate motion (plate motion n1iiauve to the North American plate>

Plate motion uncertain

0 20 40mi

0 25 SO km

Reference: Woodward-Clyde Consultants, 1980.

T TRANS TECH CONSULTANTS ENVIRONMENTAL AND GEOTECHNICAL SERVICES

JOB NUMBER

3040.01.01

DRAWN

DHP

+

OR.ECON 7-cwr0ii1A--·-·

\

PACIFIC PLATE

Regional Structural Setting lntermodal Transit Facility 9th and F Streets Arcata, California

APPROVED

~

PLATE

14 DATE

12193


REFERENCES

Aerial Photograph, 1931, Black and White, scale unknown, Photo No. 1680 D3, obtained from Humboldt State University.

Aerial Photogragh, 1941, Black and White, scale 1" = 20,000, Photo No. CVL-6B-83, obtained from Humboldt State University.

Aerial Photographs, 1974, Black and white, scale l" = 1000', Photo No. HC-74-llA-24 and 25, obtained from Humboldt State University.

Alto, K.R. and Harper, G.D., 1989, Geologic Evolution of the Northernmost Coast Ranges and Western Klamath Mountains, California, Field Trip Guidebook T308; 28th International Geological Congress, July 20-28, 1989, 82 pp.

Busch Geologic Consultants, 1986, Fault-Rupture Hazards and Risk Levels at the Downing Property (AP# 503-135-03), with Comments on the State's Mapping of the Northernmost Zoned Splay of the Fickle Hill Fault, Mad River Fault Zone, Arcata, CA. Unpublished open-file report, Community Development, Arcata, 19pp.

Busch Geologic Consultants, 1987, Narrative, with a qualitative assessment of risk levels associated with a potential fault rupture hazard, Bank of Loleta, Unpublished open-file report, Community Development Department, Arcata, 3pp.

Busch Geotechnical Consultants, 1990, Result of an Alquist-Priolo Special Studies Zones Fault Investigation, Orlando Property, Fickle Hill Fault, Arcata, CA. Unpublished open-file report, Community Development, Arcata, 31pp. plus plates.

Busch Geotechnical Consultants, 1990, Negligible Level Of Risk Of Fault Rupture At The Peterson Lot, Corner Of 12th and F Streets, Arcata, Humboldt County, CA: Geologic Background Documentation For An Alquist-Priolo Special Studies Zones Waiver Application, Community Development, Arcata, 21pp. plus plates.

California Division of Mines and Geology, 1983, Special Studies Zones, Arcata South Quadrangle, July 1, 1983 Edition, Scale 1 :24,000.

Carver, G.A. and Burke, R.M., 1989, Final Report Trenching Investigations of Northwestern California Faults Humboldt Bay Region, USGS Grant 14-0001-G1082,

Kelley, R. F., 1984, Geology and geomorphic features related to landsliding, Arcata South 7 .5-minute quadrangle, Humboldt County, California: California Division of Mines and Geology Open File Report, Scale 1:24,000.


Lawson, A.C., Editor, 1908, The California Earthquake of April 18, 1906, Report of the State Earthquake Investigation Commission: Carnegie Institute of Washington, Pub. No. 84, 2 Vols, with Atlas.

Kelsey, H. M. and Carver, G. A., 1988, Late Neogene and Quaternary Tectonics Associated With Northward Growth of the San Andreas Transform Fault, Northern California, Journal Of Geophysical Research: V. 93. No. B5, p. 4797-4819.

McPherson, R. C., 1989, Seismicity and Focal Mechanisms Near Cape Mendocino, Northern California: 1974-1984: Master of science thesis, Humboldt State University, Geology Dept.

Northern Geotechnical Incorporated, 1983, Surface Fault Rupture Hazard Evaluation for A.P. Nos. 503-091-09 and 503-091-08, City of Arcata, California, Unpublished open-file report, Community Development, Arcata, 4pp.

Northern Geotechnical Incorporated, 1984, Special Studies Zone Fault Evaluation for a proposed commercial building site located on the northwest corner of 12th and G Streets, Arcata, California, Unpublished open-file report, Community Development, Arcata, 7pp.

Stoddard, P. R., 1987, A kinematic Model for the Evolution of the Gorda Plate: Journal Of Geophysical Research, V. 92, No. Bll, Pages 11,524-11,532.

Wesnousky, S.G., 1986, Earthquakes, Quaternary Faults, and Seismic Hazard in California: Journal of Geophysical Research, v.91, no.B12, p.12,587-12,631

Woodward-Clyde Consultants, 1980, Evaluation of potential for resolving the geologic and seismic issues at the Humboldt Bay Power Plant Unit 3: unpublished consultant's report to Pacific Gas and Electric Company, October 1, 1980, 74p.

Youd, T.L. and Hoose S.N., 1978, Historic ground failures in northern California triggered by earthquakes: U.S. Geological Survey Professional Paper 993.

r


T ~~!!..~,!o'='!.o.~~~SULTANTS

5 copies:

3100 DUTTON AVENUE, SUITE 110 SANT A ROSA, CA 95407 TELEPHONE: 707-575-8622 FACSIMILE: 707-575-3394

DISTRIBUTION Fault and Geotechnical Investigation

3040.01.01

Mr .~Stephan Lashbrook City of Arcata Department of Community Development 736 F Street Arcata, California 95521

710 E STREET, SUITE 205 EUREKA, CA 95501

TELEPHONE: 707-445-4228 FACSIMILE: 707-445-4270

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