Attachment_4_-_Manila_District_Office_Geotechnical_Report_2018_(002).pdf

February 2, 2018

Geotechnical Engineering Investigation Report

Manila District Office Exapansion Project

Ashley National Forest

To Whom It May Concern:

This report presents the geotechnical findings for the proposed district office expansion in Manila, Utah.

The objectives of this study were to define subsurface soil and groundwater conditions, then prepare recommendations regarding site grading and foundations. A summary of our findings include:

The allowable bearing pressure for conventional spread footings placed on native undisturbed granular soil is 1,500 psf.

The soils observed included sandy clays, silty clays, and clays with gravel. If large roots, old foundations, buried concrete, or debris are discovered beneath footings, remove and replaced with granular fill to re-establish footing grade.

Footings are to be established on native soil or granular fill extending to native granular soil.

No groundwater was encountered during investigation.

All soils supporting foundations or pavements are to be inspected by a Forest Service representative before the placement of footings/slabs. If soil conditions are different from what was observed in this report, our office is to be notified for site specific recommendations.

If you have questions regarding this report or desire additional information please contact us.

Sincerely, Todd Touchard, P.E.

Regional Geotechnical Engineer

USFS Intermountain Region

(801) 625-5224 ttouchard@fs.fed.us

INTRODUCTION 1

Figure 1. Vicinity Map 1

2.0 PROPOSED CONSTRUCTION 1

3.0 FIELD AND LABORATORY INVESTIGATION 1

3.1 Field Investigation 1

Figure 2. Plan View of Proposed Facilities showing Testpit Locations. 2

3.2 Laboratory Investigation 3

4.0 SITE CONDITIONS 3

Picture 1. Testpit 1. 3

4.1 Surficial & Subsurface Soils 3

Picture 2. Testpit 1. 4 Picture 3. Testpit 2. 4

4.2 Groundwater 5

5.0 DESIGN RECOMMENDATIONS 5

5.1 Foundations 5

5.2 Estimated Settlement 6

5.3 Soil Class 6

5.4 Lateral Soil Pressures & Resistance 6

5.5 Liquefaction & Faults 6

5.6 Concrete Slabs & Cement Types 7

5.7 Drainage Recommendations 7

6.0 GENERAL CONSTRUCTION PROCEDURES AND RECOMMENDATIONS 7

6.1 Foundation Excavations 7

6.2 Subgrade Stabilization 7

6.3 Fill Installation & Compaction 8

6.4 Soil Special Inspection & Testing 8

Table 2. Minimum Frequency of Soil Inspection & Testing. 8

6.5 Aggregate Base Course 9

6.6 Granular Fill 9

7.0 LIMITATIONS 9

Geotechnical Investigation Manila District Office Expansion Site

INTRODUCTION

This report presents the geotechnical findings for the proposed buildings and pavements at the proposed district office expansion. The location of the site and proposed building location is shown on Figures 1 and 2, respectively. The objectives of this study were to define subsurface soil and groundwater conditions, then prepare recommendations regarding site grading and foundations.

To accomplish the objectives, a field investigation program and laboratory analysis of soil encountered at the site were conducted. The locations of the testpits are presented in Figure 2. The testpit logs are shown in Figures 3. A legend to log symbols and additional soil information is provided in Figure 4.

If the proposed type of structures, location of structures, or use of pavements change, our office shall be notified to review and potentially change recommendations contained in this report. This report should not be used for any other lots, buildings, or structures without prior approval.

Figure 1. Vicinity Map

2.0 PROPOSED CONSTRUCTION

The proposed construction is expected to have wall loads from 0.5 to 1 kips/lf and no columns loads.

3.0 FIELD AND LABORATORY INVESTIGATION

3.1 Field Investigation

To define the subsurface soil and groundwater conditions, we conducted two testpits using rubber tired backhoe (John Deere 410J). Soils were classified in the field and later verified with laboratory testing as

SITE

Manila, UT needed. Testpits were completed to a required maximum depth of 10-feet below grade. Groundwater was not encountered in any of the testpits.

Figure 2. Plan View of Testpit Locations.

Legend: Testpit (TP-X)

TP-2

TP-1

3.2 Laboratory Investigation

For soil classification and engineering properties, the samples obtained from exploratory borings were laboratory tested. Typical laboratory tests include:

Moisture Content

Soil Density

Sieve Analysis

Fine Particle Size Analysis

Atterberg Limits

Consolidation Tests

4.0 SITE CONDITIONS

The project site relatively flat with existing mobile homes, utilities, roads, and parking areas.

Picture 1. Testpit 1.

4.1 Surficial & Subsurface Soils

Within the testpits, the surface soils consists of a reddish or brown silt clay with 8-inch major root zone, which overlays sandy clay or clayey sand with gravel to two feet below grade. Beneath the clay, a silty sand or sandy silt was observed to 4 to 6-feet below grade (depending on testpit). Beneath this layer a silty clay with sand layers were observed to full depth explored of 9-feet below grade.

A concrete foundation was observed along the edge of the testpit 2 approximately 3-feet below the surface.

Picture 2. Testpit 1.

Picture 3. Testpit 2.

4.2 Groundwater

Groundwater was not encountered in Testpits. Depending on site grading and time of construction, surface runoff water and soft soils may be encountered at pavement subgrades. Subgrade stabilization is discussed in Section 6.2.

5.0 DESIGN RECOMMENDATIONS

The following recommendations have been developed on the basis of the previously described project characteristics and subsurface conditions. A technical design review should be made by this office if actual loads are greater than anticipated or if there is any change in project criteria, including building location on the site.

Under no circumstances should the footings be installed upon potentially collapsible, non-engineered fills, loose or disturbed soils, sod, rubbish, construction debris, frozen soil, tree roots greater than 1-inch diameter, root wads, or other deleterious materials. If unsuitable soils are encountered, they must be removed and replaced with compacted granular fill. If granular soils become loose or disturbed, they must be recompacted prior to pouring the concrete.

Prior to the placement of footings, granular site grading fill, or floor slabs, the exposed natural subgrade must be proofrolled by passing moderate-weight rubber tire-mounted construction equipment over the surface at least twice. If any loose, soft, or disturbed zones are encountered, they must be completely removed in footing and floor slab areas and replaced with granular structural fill.

5.1 Foundations

Foundations should not be designed for more than the maximum allowable soil bearing pressures and other soil strength properties below. The allowable bearing pressure may be increased by 1/3 for temporary loads such as wind or seismic forces.

Recommended design parameters:

Minimum Depth of Exterior 30 inches

Footings and Unheated Areas

Minimum Depth of Interior Footings 14-16 inches

Recommended Minimum Width for 20 inches

Continuous Wall Footing

Recommended Minimum Width for 24 inches

Isolated Spread Footing

Recommended Allowable Bearing Pressure* 1,500 psf

*The provided bearing capacity is based on footings placed on native soil or compacted granular fill extending to native soil.

5.2 Estimated Settlement

The anticipated maximum total or differential settlement of foundations designed using the previously mentioned structural loads is not expected to exceed 1-inch.

5.3 Soil Class

For dynamic structural analysis, the Site Class D – Stiff Soil Profile as defined in Table

1613.5.2, Site Class Definitions, of the IBC 2015 can be utilized.

5.4 Lateral Soil Pressures & Resistance

Lateral soil pressures are dependent on the type of soil present. The pressures are based onsite clayey fill material is being used as backfill. The values below assume that the surface of the soils slope behind the wall is horizontal, and that the granular fill has been placed and lightly compacted, not as a structural fill.

The following equivalent fluid lateral soil pressures shall be used for design:

1. Use 100 pcf for the static at-rest case. That is when the wall is not allowed to yield.

2. Use 60 pcf for active static case. Full active pressures only develop when the wall is allowed to move a sufficient distance. For granular soil, the typical movement range is 0.001 to 0.004H, and a cohesive soil is 0.01 to 0.04H, where H is the height of the wall.

3. Use 300 pcf for the static passive case. That is when the wall exerts pressure on the soil.

For the determination of lateral resistance for continuous and spread footings placed on native soil, a friction value of 0.32 may be used for ultimate lateral resistance.

5.5 Liquefaction & Faults

Liquefaction is the result of saturated soils being shaken causing soil particles to easily move, resulting in loss of soil strength and stiffness. A liquefaction study was not completed on this site. However, due to the relative density of the site soils observed, type of soil, and the lack of shallow groundwater, the potential for high liquefaction potential at the site is considered low.

No active faults or potentially active faults were mapped near the site. The closest mapped fault is the

Faults on the north flank of Phil Pico Mountain quaternary fault system, which is mapped approximately

8.3 mile to the west of the site by the United States Geologic Survey (USGS). The USGS

(http://earthquakes.usgs.gov) provide information regarding this fault.

http://earthquakes.usgs.gov/

5.6 Concrete Slabs & Cement Types

All concrete slabs on grade should be placed over 4-inch minimum, of ½” to 1” diameter, poorly graded, clean, free-draining gravel. Below the 4-inch gravel layer shall be properly site grading fill extending to native soil. All fill supporting slabs should be placed in 8-inch loose lifts and compacted to 95% of modified proctor.

5.7 Drainage Recommendations

Adequate surface drainage should be provided at the site to minimize any increase in moisture content of the foundation and pavement supporting soils and prevent water from migrating under the structure. All areas around the structure should be generously sloped to provide drainage away from these areas. We recommend a minimum slope of 6 inches in the first 10 feet away from the structure. This should minimize the potential problems that could occur if soils below the structure or pavements become wet. We also recommend that the pavement areas be generously sloped to insure that no ponding occur on the surfaces.

6.0 GENERAL CONSTRUCTION PROCEDURES AND RECOMMENDATIONS

The guidelines outlined below address the geotechnically related construction concerns for this project.

6.1 Foundation Excavations

Prior to placement of the foundations and floor sections, all areas that will support foundation loads or pavements should be inspected to insure that all loose, soft or otherwise undesirable material is removed and that the structures will bear on satisfactory material. All topsoil, fill and other deleterious materials underneath the proposed structures and pavements should be removed. All roots larger than 1” diameter , root wads, and other organics shall be removed beneath the foundations. Backfill with compacted granular fill.

All foundation excavations should be protected against any detrimental change in condition such as disturbance, rain and freezing. Surface runoff should be directed away from the excavation and not allowed to pond. If possible, all footing concrete should be poured the same day as the excavation is made. If this is not practical, the foundation excavation should be adequately protected and foundation placement should take place as soon as possible.

6.2 Subgrade Stabilization

If construction practices or weather conditions during the placement of the fill caused the native soils become soft in paved or footings areas one of the following should be done:

Remove areas where clays or silts are disturbed and place an additional 18-inches of granular fill

(crushed or pit-run gravel), gradation requirements are shown in Section 6.7.

Or place Geotextile grid between the undisturbed native soil and fill material to achieve proper compaction of the fill layers. Follow manufacture’s recommendations for lap length and installation. Manufacturer, type, and properties of geotextile grid used shall submitted to geotechnical engineer for approval prior to construction.

6.3 Fill Installation & Compaction

All fills supporting structural loads, pavements, or slabs should be compacted to at least 95 percent of the

Modified Proctor maximum density (ASTM D 1557). The compaction should be accomplished by placing the fill in 8-inch loose lifts and mechanically compacting each lift to the specified minimum density. Fill shall be moisture conditioned within two percent of optimum moisture. Field density tests should be performed on each lift as necessary to insure that compaction is being achieved.

All utility trench backfill below structurally loaded facilities (flatwork, floor slabs, roads, etc.) must be placed at the same density requirements established for structural fill. In these areas, backfill material shall consist of granular fill.

If the surface of the backfill becomes disturbed during the course of construction, the backfill should be proofrolled and/or properly compacted prior to the construction of any exterior flatwork over a backfilled trench. Proofrolling may be performed by passing moderately loaded rubber tire-mounted construction equipment uniformly over the surface at least twice. If excessively loose or soft areas are encountered during proofrolling, they should be removed to a maximum depth of two feet below design finish grade and replaced with structural fill.

6.4 Soil Special Inspection & Testing

As required by 2012 International Building Code, special inspections and testing shall be performed by an agency independent of the Contractor. During fill placement, the special inspector shall determine that proper materials and procedures are used in accordance with this report. Furnish all inspection and testing reports to Engineer.

Table 2. Minimum Frequency of Soil Inspection & Testing.

Inspection/Test Method Frequency

Verify materials below shallow foundation are adequate to achieve bearing capacity.

Periodic

Verify excavations are extended to proper depth and have reached proper material.

Periodic

Inspection/Test Method Frequency

Verify use of proper materials, densities and lift thickness during placement and compaction of fill. (ASTM D 1557, D

422, D 2922)

Perform proctor test (ASTM D 1557) at start of project for each type of soil being compacting or when material appears to change.

Submit particle size analysis (ASTM D 422) data for approval before any import fill material is delivered or when fill material appears to change.

Test compaction using nuclear density methods (ASTM D

2922) a minimum of: per 100 lf of backfill and each lift for trenches, every 800 sf and each lift for pavements base and subbase, and as directed by Engineer.

Prior to placement of compacted fill, observe subgrade and verify site has been properly compacted.

Periodic

6.5 Aggregate Base Course

For the base material directly below pavement, we recommend a granular soil free of organic or other deleterious material. We recommend a graded sand and fractured gravel material having between 5 and

11 percent passing the #200 sieve and no particles greater than approximately 1-1/2 -inches in maximum dimension. The minimum CBR value (ASTM D 1883) of 80% is required.

6.6 Granular Fill

Granular soils free of organics, debris, or other deleterious materials are recommended for use as granular fill at this site. Granular fill is defined as a well graded sand and gravel material (pitrun or crushed gravel), with less than 15 percent passing the #200 sieve and no particles greater than 4 inches in maximum dimension. Granular fill should not exhibit plasticity characteristics. Approved soil types as defined using the Unified Soil Classification are considered to be GW, GP, or GM or combinations thereof. Submit proposed fill material samples and sieve analysis to Engineer prior to placement. See Figure 4 for soil type definitions.

7.0 LIMITATIONS

The recommendations provided herein were developed by evaluating the information obtained from the testpits. The testpit data reflects the subsurface conditions only at the specific location at the particular time designated on the testpit log. Soil and ground water conditions may differ from conditions encountered at the actual testpit locations. The nature and extent of any variation in the testpit may not become evident until during the course of construction. If variations do appear, it may become necessary to re-evaluate the recommendations of this report after we have observed the variation.

Our professional services have been performed, our findings obtained, and our recommendations prepared in accordance with generally accepted geotechnical engineering principles and practices. This warranty is in lieu of all other warranties, either expressed or implied.

Enclosures: Appendix :

Figure 3 : Logs of Testpits

Figure 4 : Soil Classification Chart

Project:

Method: Rubber Tired Backhoe 9'

Surface Elevation: Groundwater Depth: none

End of excavation 9'

Remarks: Figure:

3AField Engineer: Todd Touchard

12.0

Stopped excavating at 9', required depth.

11.0

9.0

10.0

8.0

7.0

6.0

4.0

4' to 9': Silty Clay (CL) with occasional sand layers, fine to medium sand, blocky, stiff, moist, brown

5.0

2' to 4': Sandy Silt (ML), fine to medium sand, dense, moist, reddish brown

3.0

2.0

8" to 2': Sandy Clay with some Silt (CL), very stiff, moist, brown

0 to 8": Topsoil Major Root Zone

Sandy Clay with Some Silt, loose, dark reddish brown

1.0

Unconfined Comp (UU)

Field Vane

0.0

1.0 2.0P la st ic L im it

M o is tu re

Shear Strength, TSF

Miniature Vane

Residual Mini Vane

Pocket Pentrometer

N/A

D

EP

TH

ft

G R

A P

H

IC

L O

G

W A

TE

R

L

EV

EL

SA

M

P

LE

Soil Description

B lo w C o u n ts ft

P as si n g #2

S ie ve

D ry

D en si ty p cf

Li q u id

L im it

Date: 16-Aug-17

TP-1

TESTPIT LOG

Manila District Office

Location: SE of Site

Total Depth:

Project:

Method: Rubber Tired Backhoe 9'

Surface Elevation: Groundwater Depth: none

End of excavation 9'

Remarks:

Sandy Clay with Some Silt, loose, dark reddish brown

6' to 9': Silty Clay (CL) with occasional sand seams and layers, fine to medium sand, blocky, medium stiff, moist, sand layers wet, layers 1" to 6"thick, grey

8" to 2': Clayey Sand with some gravel (SC), stiff, moist, reddish brown grades to Silty Sand (SM) with some clay, fine to coarse sand, medium dense, moist, reddish brown

Date: 16-Aug-17

TP-2

TESTPIT LOG

Manila District Office

Location: NW Site

N/A

Li q u id

L im it

Shear Strength, TSF

Miniature Vane

Residual Mini Vane

Pocket PentrometerSoil Description

Total Depth:

M o is tu re

P la st ic

L im it

5.0

G R

A P

H

IC

L O

G

W A

TE

R

L

EV

EL

SA

M

P

LE

B lo w C o u n ts ft

0.0 P

as si n g #2

S ie ve

D ry

D en si ty p cf

D

EP

TH

ft

2.0

1.0

0 to 8": Topsoil Major Root Zone

3.0

9.0

7.0

8.0

10.0

2' to 6': Silty Sand (SM), fine to coarse sand, medium dense, moist, reddish brown

4.0

6.0

11.0

3BField Engineer: Todd Touchard

12.0

Stopped excavating at 9', required depth. Figure:

Unconfined Comp (UU)

Field Vane

1.0 2.0