17.193 Georgetown Loop Visitor's Center Addition Report 12.08.17 (reduced file size).pdf

Corporate Office: 7108 South Alton Way, Building B • Centennial, CO 80112 Centennial Office • Frederick Office • Silverthorne Office • Crested Butte Office

Phone 303-220-0300 • www.cesareinc.com

GEOTECHNICAL STUDY

Georgetown Loop Visitor’s Center Addition

Georgetown, Colorado

Report Prepared for:

Steve Smith, P.E.

Applegate Group, Inc.

1490 West 121st Avenue, Suite 100 Denver, CO 80234

Project No. 17.193 December 8, 2017

17.193 Georgetown Loop Visitor's Center Addition Report 12.08.17 i

GEOTECHNICAL STUDY

Georgetown Loop Visitor’s Center Addition

Georgetown, Colorado

Report Prepared for:

Steve Smith, P.E.

Applegate Group, Inc.

1490 West 121st Avenue, Suite 100 Denver, CO 80234

Project No. 17.193 December 8, 2017

Report Prepared by:

Jonathan A. Crystal, P.E. Darin R. Duran, P.E.

Staff Engineer Principal, Geotechnical Engineering Manager

12/8/17

CESARE, INC.

17.193 Georgetown Loop Visitor's Center Addition Report 12.08.17 ii

TABLE OF CONTENTS

1. PURPOSE

2. PROPOSED CONSTRUCTION

3. INVESTIGATION

4. SITE CONDITIONS

5. LABORATORY TESTING

6. SUBSURFACE CONDITIONS

7. FOUNDATION RECOMMENDATIONS

7.1 DISCUSSION

7.2 STRUCTURES

7.2.1 PRIVACY WALLS

7.2.2 TANK BUILDING

8. LATERAL EARTH PRESSURES

9. STRUCTURAL FILL SOILS

10. SURFACE DRAINAGE

11. WATER SOLUBLE SULFATES

12. SUBSURFACE DRAINAGE

13. GEOTECHNICAL RISK

14. LIMITATIONS

TABLE FOLLOWING TEXT

SUMMARY OF LABORATORY TEST RESULTS ....................................................................... TABLE 1

TABLE WITHIN TEXT

TABLE 2. Lateral Earth Pressures

FIGURES

BORING LOCATION PLAN ................................................................................................. FIGURE 1 BORING AND PIT LOGS (INCLUDES KEY TO SYMBOLS) ................................................... FIGURE 2

APPENDIX

LABORATORY TEST RESULTS ....................................................................................... APPENDIX A

17.193 Georgetown Loop Visitor's Center Addition Report 12.08.17 1

1. PURPOSE

This report presents results of a geotechnical study of the proposed addition at the existing Georgetown Loop Visitor’s Center near Georgetown, Colorado. Cesare, Inc. (Cesare) performed the study to assist in evaluating design criteria for site development, foundation systems, drainage adjacent to structures, and to present other pertinent geotechnical issues. Factual data gathered during the field and laboratory work is summarized in Tables 1 and 2, Figures 1 and 2, and Appendix A. Cesare, Inc.’s (Cesare) opinions and recommendations presented in this report are based on the data generated during this field investigation, laboratory testing, and our experience with similar type projects.

2. PROPOSED CONSTRUCTION

The proposed construction includes adding privacy walls adjacent to the existing restroom facility’s entrance. Planning also includes a new building to house two new water tanks adjacent to the facility’s southwestern side. The tanks will bear on the floor. We understand the building will be single story with no basement and outside dimensions of 10 feet by 12 feet. The building’s construction will be masonry block, likely with a mat type foundation. We understand the foundation loads are likely controlled by the water tanks and roof snow loads, such that a structural floor loading would be on the order of 500 to 700 pounds per square foot (psf). Grading will likely be minimal, less than 2 feet in either cut or fill. Our boring location is shown in Figure 1.

3. INVESTIGATION

Cesare drilled one boring to a depth of about 16 feet below existing grade. The boring was advanced using a CME-45 drill rig equipped with 4 inch diameter, continuous flight, solid stem auger. The boring was refused penetration at about 16 feet, likely on hard bedrock. We sampled the subsoils at frequent intervals using a modified California sampler driven into the soil by dropping a 140 pound hammer through a free fall of 30 inches. The modified California sampler is a 2.5 inch outside diameter by 2 inch inside diameter cylindrical device lined with brass tubes for relatively undisturbed sample recovery. The procedure to drive the sampler into the soils and record the number of blows required to do so is known as a penetration test. The number of blows required for the sampler to penetrate 12 inches gives an indication of the consistency or relative density of the soils encountered. We present the penetration test results and sampling locations on the Boring Logs in Figure 2 and Key to Symbols.

We also excavated a small pit by hand to a depth of about 2 feet in a landscaped area adjacent to the southern end of the building near the entrance, to evaluate the type of fill placed there. We present a log of this pit with the boring log and labeled as B-2 in Figure 2.

4. SITE CONDITIONS

The existing restroom facility is located at the southernmost end of the Visitor’s Center parking area.

Its longitudinal axis is generally aligned in a NNE/SSW direction such that the building faces ESE.

For the purpose of this report, we will refer to the building as facing east, and the entrance is it’s east side.

17.193 Georgetown Loop Visitor's Center Addition Report 12.08.17 2

The site is located within the Clear Creek drainage, south of Georgetown. The drainage is confined by steep mountain slopes on either side of the river. The building is on a terrace above Clear Creek, likely graded from its original topography. The general area is relatively flat with a gentle slope downward to the southeast. Much of the original topography and vegetation surrounding the building includes a sparse growth of native grasses and weeds, and a moderate growth of conifer trees.

The existing building is masonry block construction. The ground leading to the entrance is paved with brick pavers from the access road to the sidewalk adjacent to the facility. An unpaved road extends along the building’s west side to provide access to residences farther to the south.

5. LABORATORY TESTING

Cesare’s field engineer returned the samples to the Cesare laboratory where a professional engineer visually classified them and assigned appropriate testing to specific samples to evaluate pertinent engineering properties. The laboratory tests included five gradation and Atterberg limits tests to evaluate grain size distribution and plasticity of selected samples. A water soluble sulfate test was performed to evaluate the effect of the soils on concrete. A summary of the laboratory test results is presented in Table 1 and detailed test results are presented in Appendix A. Water soluble sulfates test results are discussed in Section 11. WATER SOLUBLE SULFATES.

6. SUBSURFACE CONDITIONS

Cesare’s boring and hand pit indicate the upper soils generally consist of fill to a depth up to about 3 feet over native soils, extending to the remaining depth explored of 16 feet. We described the fill as gravel, with silt and sand, well graded, grades to with cobbles up to 8 inches; and clayey sand, loose, moist, dark brown, medium dense, moist, and dark brown in color. We described the native soils underlying the fill in the boring as silty sand, with gravel, medium dense to very dense, slightly moist to moist, and dark brown to brown in color. Likely, very hard granite bedrock or a large, very hard, granite boulder refused further auger penetration at the boring’s terminated depth of 16 feet.

We did not recover a sample of the bedrock; however, the adjacent mountain slopes in the area, displayed the bedrock condition. According to the Tweto (1979)1 the bedrock is Precambrian Granite, 1,400 million years of age.

Groundwater was not encountered in the boring during drilling. The boring and hand pit were backfilled after completion for safety, so we performed no further groundwater measurements. A more complete description of the subsoil and groundwater is shown in Figure 2, including the Key to Symbols.

These observations represent conditions at the time of field exploration and may not be indicative of other times or other locations. Groundwater can be expected to fluctuate with various seasonal, irrigation, and weather conditions.

1 Tweto, Ogden; Geologic Map of Colorado, United States Geologic Survey, 1979.

17.193 Georgetown Loop Visitor's Center Addition Report 12.08.17 3

7. FOUNDATION RECOMMENDATIONS

7.1 DISCUSSION

Cesare considers the fill soils encountered as unsuitable to provide reliable support for foundations in their present condition, as we do not know how they were placed. Unless their placement records are made available, we recommend removing them and replacing them as compacted structural fill.

The underlying native soils are medium dense to very dense in their present condition. Cesare opines they will provide appropriate support for the privacy walls and tank building structures.

7.2 STRUCTURES

The fill materials encountered in our exploration are not considered suitable to provide reliable support for the structure in their present condition. They should be removed in their entirety and replaced with properly placed and compacted structural fill. Cesare’s test results indicate the existing fill can be reused for structural fill.

7.2.1 Privacy Walls

Conventional spread footings or pad type footings bearing on the natural, undisturbed soils or on controlled, structural fill will provide adequate support for the proposed privacy walls. Design footings for 2,000 psf maximum allowable soil bearing pressure, based upon dead load plus full live load. Footings should have a minimum width of 12 inches. Observe the following design criteria as well:

a) Using the soil pressure recommended above, Cesare estimates the maximum settlement for the structure will be less than 1/2 inch, with differential settlement equal to the total.

Footings should be proportioned as much as practicable to reduce differential settlement.

b) Steel reinforcement for continuous concrete foundation walls should be designed to span localized settlements over a distance of 10 feet.

c) All soft or loose soils beneath footing areas should be densified in place, or removed and replaced with properly compacted structural fill or concrete prior to placement of footing concrete.

d) All footing excavations should be inspected prior to placement of concrete.

7.2.2 Tank Building

Due to the water tanks bearing on the concrete slab floor, design the floor as a mat type foundation.

Design the slab for 1,000 psf maximum allowable soil bearing pressure based upon dead load plus full live load. The mat should extend from wall to wall, at minimum, and extend outside the walls, as necessary. Observe the following design criteria as well:

a) Using the soil pressure recommended above, Cesare estimates the settlement for the structure will be less than 1/2 inch, with differential settlement equal to the total.

b) Densify all soft or loose soils beneath the slab area in place, or remove and replace them with properly compacted structural fill or concrete prior to placement of footing concrete.

c) Inspect all footing excavations prior to placement of concrete.

8. LATERAL EARTH PRESSURES

Lateral pressures on walls depend upon the type of wall, hydrostatic pressure behind the wall, type

17.193 Georgetown Loop Visitor's Center Addition Report 12.08.17 4 of backfill material, and allowable wall movements. Cesare recommends hydrostatic pressures be minimized by placing a properly designed drain system behind the wall. Where anticipated wall movements are less than approximately 0.5% of the wall height or wall movement is constrained, lateral earth pressures should be estimated for an "at rest" condition. Where anticipated wall movements are greater than 0.5% of the wall height, lateral earth pressures should be estimated for an "active" condition. Walls backfilled with onsite granular material should be designed for equivalent lateral fluid pressure as presented below in Table 2. These soil pressures are for horizontal backfill and no hydrostatic pressures. If these criteria cannot be met, Cesare should be contacted for additional criteria. We recommend a coefficient of sliding resistance between the concrete and bearing soils of 0.3 (includes factor of safety of 1.5) be assumed in your analysis.

TABLE 2. Lateral Earth Pressures At Rest

Pressure (pcf)

Active Pressure

(pcf)

Passive Pressure

(pcf) 60 40 350

9. STRUCTURAL FILL SOILS

Where fill soils are necessary, the suitable onsite inorganic soils may be used for structural fill beneath slabs and footings. The fill material beneath slabs and footings should be placed in 6 inch maximum, loose lifts within 2% of optimum moisture content, and should be compacted to at least 95% of standard Proctor density according to ASTM D698. All topsoil, existing manmade fill, frozen material, and soil containing organic material should be removed beneath structural areas prior to placement of fill or concrete. When placed, fill should be free of frozen and organic material.

10. SURFACE DRAINAGE

The following drainage precautions should be observed:

a) Backfill around the exterior foundation walls in non-structural areas should be moistened to within 2% of optimum moisture and compacted to at least 95% of standard Proctor density according to ASTM D698.

b) The ground surface around the foundation perimeter should be sloped to drain away from the structure in all directions. Cesare recommends a minimum slope of 12 inches in the first 10 feet, if possible. If properly compacted backfill is placed, then a slope of 5% is reasonable. Concrete and pavement adjacent to structures are recommended to slope at a rate of 2% away from the structure.

c) Watering directly adjacent to the structure should be minimized.

d) Roof downspouts and other water collection systems should discharge beyond the limits of the backfill. Splash blocks should be appropriately placed and maintained.

e) Sprinkler systems should be placed so that the spray from the heads, under full pressure, does not fall within 5 feet of the foundation perimeter.

11. WATER SOLUBLE SULFATES

Testing conducted on a sample collected from Boring B-2 indicated 0.0% water soluble sulfates. The American Concrete Institute (ACI) considers this to be in Exposure Class S0 for water soluble sulfate

17.193 Georgetown Loop Visitor's Center Addition Report 12.08.17 5 exposure according to 318-08 R4.3.1. No special precautions need to be taken for the cement in concrete for protection against water soluble sulfates.

12. SUBSURFACE DRAINAGE

Groundwater was not encountered during this study. Due to the relatively permeable nature of the onsite soils, it is considered unlikely that a perched system will develop over time. Complying with the recommendations for surface drainage presented above is considered sufficient precaution for subsurface drainage as well.

13. GEOTECHNICAL RISK

The concept of risk is an important aspect of any geotechnical evaluation. The primary reason for this is that the analytical methods used by geotechnical engineers are generally empirical and must be tempered by engineering judgment and experience. Therefore, the solutions or recommendations presented in any geotechnical evaluation should not be considered risk free, and more importantly, are not a guarantee that the interaction between the soils and the proposed structure will perform as predicted, desired, or intended. The engineering recommendations presented in the preceding sections constitute Cesare’s best estimate of those measures that are necessary to help the structure perform in a satisfactory manner based on the information generated during this and previous evaluations, and our experience in working with these conditions.

14. LIMITATIONS

The professional judgments expressed in this report meet the standard care of our profession. The borings drilled for this study were located to obtain a reasonably accurate picture of underground conditions for design purposes. Variations frequently occur from these conditions which are not indicated by the borings. These variations are sometimes sufficient to necessitate modifications in the design. If unexpected conditions are observed during construction or, if the size, type, elevation, or location of the structure should change, Cesare should be notified to review our recommendations. A member of our firm should observe structure foundation excavation as well as placement and compaction of fill.

Boring/ Test Pit

Depth (feet)

Gravel

Sand

Silt/ Clay

Liquid Limit

Plasticity Index

Water Soluble Sulfates

B-1 1 4.8 56 33 10.6 NV NP

GRAVEL, well graded, with silt and sand (GW-GM, A-1-a)

B-1 5 3.8 27 57 16.7 NV NP SAND, silty, with gravel (SM,A-1-b)

B-1 9 4.8 39 46 15.4 NV NP SAND, silty, with gravel (SM,A-1-b)

B-1 14 3.5 20 58 22.1 19 2 SAND, silty, with gravel (SM,A-1-b)

B-2 0 to 2 5.7 1 62 37.2 31 13 0.0 SAND, clayey (SC, A-6(1))

NV=no value NP=non plastic

Material Type

Atterberg Limits

TABLE 1

Summary of Laboratory Test Results

Sample Location Gradation

Georgetown Loop Visitor's Center Addition Project No. 17.193

Natural Dry

Density (pcf)

Natural Moisture Content

17.193 Georgetown Loop Visitor's Center Summary of Laboratory Test Results Table 1 Page 1 of 1

FIGURE 1

Boring Location Plan

PROJECT NO:

PROJECT NAME:

17.193

Georgetown Loop Visitor's Center Addition

DRAWN BY: CHECKED BY:JBE JAC2

DWG DATE: 11.06.17 REV. DATE:

0 40' 80'

APPROXIMATE SCALE: 1 INCH = 40 FEET

N

W C e n t e n n i a l

G e o r g e t o w n

L o o p

V i s i t o r s

C e n t e r

A d d i t i o n A C A D

B o r i n g

L o c a t i o n

M a p d w g

A M

BACKGROUND IMAGE FROM GOOGLE EARTH

LEGEND:

B-1

BORING NUMBER AND

APPROXIMATE LOCATION

B-1

B-2

B-1

15/12

22/12

29/12

50/8

B-2

D ep th i n F ee t

D ep th in

Feet

FIGURE 2

Boring Logs

PROJECT NO: 17.193

PROJECT NAME: Georgetown Loop Visitor's Center Addition

DWG DATE: 12/8/2017

1. 15/12 indicates 12 blows with a 140-pound hammer falling 30 inches were required to drive a split spoon barrel sampler 12 inches.

2. Exploratory boring B-1 was drilled on November 11, 2017, using a CME-45 drill rig equipped with 4-inch diameter continuous flight solid stem auger. Hand pit B-2 was hand excavated on November 11, 2017.

3. Groundwater was not encountered in Boring 1 during drilling. For safety purposes, the boring was backfilled upon completion.

4. Contacts between soil units are approximate and may be gradational.

5. These logs are subject to the limitations, conclusions, and recommendations in this report.

Project No. 17.193.

Notes:

Symbol Description

Strata symbols

FILL: GRAVEL, with silt and sand, well graded, grades to with cobbles up to 8 inches, medium dense, moist, dark brown (GW-GM, A-1-a); SAND, clayey, loose, moist, dark brown (SC, A-6).

SAND, silty, with gravel, medium dense to very dense, slightly moist to moist, dark brown to brown (SM, A-1-b).

Misc. Symbols

Practical sampler refusal

Soil Samplers

Modified California sample

Bulk/Grab sample

KEY TO SYMBOLS

APPENDIX A

Laboratory Test Results

Project Number: Date:

Project Name: Technician:

Lab ID Number: Reviewer:

Sample Location:

Visual Description:

AASHTO M 145 Classification: A-1-b Group Index: (0)

(SM)

Si ev e Si ze

P as si ng

2" 1.5" 1"

3/4" 100 1/2" 97 3/8" 95 #4 80 #8 #10 63 #16 56 #30 #40 42 #50 36 #100 28 #200 22.1

M, %: 3.5 D, pcf:

LL 19

PL 17

PI 2

D60

D30

D10

Cu Cc

SAND, silty, with gravel, brown

Moisture (M) & Density (D)

Silty sand with gravel Unified Soil Classification System

(ASTM D 2487):

GRADATION PLOT - SOIL & AGGREGATE

10-Nov-17 J. Weinerth

B-1 at 14' 1721678 J. Crystal

17.193, Applegate Group, Inc.

Georgetown Loop Visitor's Center Addition

.5

1.

5"

.4

1"

.1 3/

4"

.7

1/ 2"

3/ 8"

4.

No . 4

2.

No . 1

1.

No . 1

0.

No . 4

0.

No . 5

0.

No . 1

0.

No

. 2

2.

No . 8

0.

No . 3

.8

2"

0.

0.

1.

.0

0.

P

AS

SI

N G

(b y dr y m as s)

SIEVE SIZE, mm

Gradation 1721678 7108 South Alton Way, Building B • Centennial, Colorado 80112 • www.cesareinc.com

Phone 303-220-0300 • Fax 303-220-0442 Rev. 3/30/12

Lab ID Number: Reviewer:

Sample Location:

Visual Description:

AASHTO M 145 Classification: A-1-a Group Index: 0

(GW-GM)

Si ev e Si ze

P as si ng

2" 1.5" 100 1" 83

3/4" 73 1/2" 63 3/8" 56 #4 44 #8 #10 35 #16 31 #30 #40 23 #50 18 #100 13 #200 10.6

M, %: 4.8 D, pcf:

LL NV

PL NP

PI NP

D60 11.25 D30 1.01 D10 0.06 Cu 175.78 Cc 1.41

GRAVEL, with sand, with silt, brown

Moisture (M) & Density (D)

Well graded gravel with silt and sand Unified Soil Classification System

(ASTM D 2487):

GRADATION PLOT - SOIL & AGGREGATE

14-Nov-17 J. Holiman

B-1 at 1' 1721679 J. Crystal

17.193, Applegate Group, Inc.

Georgetown Loop Visitor's Center Addition

.5

1.

5"

.4

1"

.1 3/

4"

.7

1/ 2"

3/ 8"

4.

No . 4

2.

No . 1

1.

No . 1

0.

No . 4

0.

No . 5

0.

No . 1

0.

No

. 2

2.

No . 8

0.

No . 3

.8

2"

11.25 1.01 0.06

0.

0.

1.

.0

0.

P

AS

SI

N G

(b y dr y m as s)

SIEVE SIZE, mm

Gradation 1721679

Lab ID Number: Reviewer:

Sample Location:

Visual Description:

AASHTO M 145 Classification: A-1-b Group Index: 0

(SM)

Si ev e Si ze

P as si ng

2" 1.5" 1"

3/4" 100 1/2" 96 3/8" 88 #4 74 #8 #10 57 #16 49 #30 #40 37 #50 32 #100 23 #200 16.7

M, %: 3.8 D, pcf:

LL NV

PL NP

PI NP

D60

D30

D10

Cu Cc

SAND, silty, with gravel, brown

Moisture (M) & Density (D)

Silty sand with gravel Unified Soil Classification System

(ASTM D 2487):

GRADATION PLOT - SOIL & AGGREGATE

10-Nov-17 J. Weinerth

B-1 at 5' 1721680 J. Crystal

17.193, Applegate Group, Inc.

Georgetown Loop Visitor's Center Addition

.5

1.

5"

.4

1"

.1 3/

4"

.7

1/ 2"

3/ 8"

4.

No . 4

2.

No . 1

1.

No . 1

0.

No . 4

0.

No . 5

0.

No . 1

0.

No

. 2

2.

No . 8

0.

No . 3

.8

2"

0.

0.

1.

.0

0.

P

AS

SI

N G

(b y dr y m as s)

SIEVE SIZE, mm

Gradation 1721680

Lab ID Number: Reviewer:

Sample Location:

Visual Description:

AASHTO M 145 Classification: A-1-b Group Index: 0

(SM)

Si ev e Si ze

P as si ng

2" 1.5" 1" 100

3/4" 88 1/2" 79 3/8" 72 #4 61 #8 #10 50 #16 44 #30 #40 32 #50 28 #100 21 #200 15.4

M, %: 4.8 D, pcf:

LL NV

PL NP

PI NP

D60

D30

D10

Cu Cc

SAND, silty, with gravel, brown

Moisture (M) & Density (D)

Silty sand with gravel Unified Soil Classification System

(ASTM D 2487):

GRADATION PLOT - SOIL & AGGREGATE

10-Nov-17 J. Weinerth

B-1 at 9' 1721681 J. Crystal

17.193, Applegate Group, Inc.

Georgetown Loop Visitor's Center Addition

.5

1.

5"

.4

1"

.1 3/

4"

.7

1/ 2"

3/ 8"

4.

No . 4

2.

No . 1

1.

No . 1

0.

No . 4

0.

No . 5

0.

No . 1

0.

No

. 2

2.

No . 8

0.

No . 3

.8

2"

0.

0.

1.

.0

0.

P

AS

SI

N G

(b y dr y m as s)

SIEVE SIZE, mm

Gradation 1721681

Lab ID Number: Reviewer:

Sample Location:

Visual Description:

AASHTO M 145 Classification: A-6 Group Index: 1

(SC)

Si ev e Si ze

P as si ng

2" 1.5" 1"

3/4" 100 1/2" 100 3/8" 100 #4 99 #8 #10 98 #16 95 #30 #40 73 #50 61 #100 45 #200 37.2

M, %: 5.7 D, pcf:

LL 31

PL 18

PI 13

D60

D30

D10

Cu Cc

CLAY, sandy, brown

Moisture (M) & Density (D)

Clayey sand Unified Soil Classification System

(ASTM D 2487):

GRADATION PLOT - SOIL & AGGREGATE

10-Nov-17 J. Holiman

B-2 at 0' to 2' 1721682 J. Crystal

17.193, Applegate Group, Inc.

Georgetown Loop Visitor's Center Addition

.5

1.

5"

.4

1"

.1 3/

4"

.7

1/ 2"

3/ 8"

4.

No . 4

2.

No . 1

1.

No . 1

0.

No . 4

0.

No . 5

0.

No . 1

0.

No

. 2

2.

No . 8

0.

No . 3

.8

2"

0.

0.

1.

.0

0.

P

AS

SI

N G

(b y dr y m as s)

SIEVE SIZE, mm

Gradation 1721682