Geotechnical Report 5-22-2015.pdf

Subsurface Exploration Program and Geotechnical Evaluation

Edgar Mine Improvements 365 8th Avenue

Idaho Springs, Colorado

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Prepared For:

Colorado School of Mines

1801 19th Street Golden, Colorado 80401

Attention: Ms. Tana Lane

Job Number: 15-3029 May 22, 2015

TABLE OF CONTENTS

Page

Purpose and Scope of Study

Proposed Construction

Site Conditions

Geologic Setting

Subsurface Exploration

Laboratory Testing

Subsurface Conditions

Seismic Classification

Geotechnical Considerations for Design

Foundation Systems

Floor Systems

Radon

Lateral Loads

Water Soluble Sulfates

Soil Corrosivity

Project Earthwork

Excavation Considerations

Utility Lateral Installation

Surface Drainage

Subsurface Drainage

Pavement Sections

Closure

Locations of Test Holes ..................................................................................... Figure 1

Logs of Test Holes ............................................................................... Figures 2 and 3

Legend and Notes ............................................................................................. Figure 4

Aggregate-Surfaced Roadway Nomograph ........................................................ Figure 5

Summary of Laboratory Test Results ........................................................ Tables 1 & 2

Edgar Mine Improvements

Job No. 15-3029 Ground Engineering Consultants, Inc. Page 1

PURPOSE AND SCOPE OF STUDY

This report presents the results of a geotechnical evaluation performed by GROUND

Engineering Consultants, Inc. (GROUND) in support of design and construction of improvements at the Colorado School of Mine’s Edgar Mine, in Idaho Springs, Colorado.

Our study was conducted in general accordance with GROUND’s Proposal No. 1502-

0531, dated March 27, 2015. Results of the field, office, and laboratory studies are presented below.

Field and office studies provided information at the test hole locations regarding surface and subsurface conditions. Material samples retrieved during the subsurface exploration were tested in our laboratory to assess selected engineering characteristics of the site earth materials, and assist in the development of our geotechnical conclusions.

This report has been prepared to summarize the data obtained and to present our findings and conclusions based on the proposed construction and the subsurface conditions encountered. Design parameters and a discussion of engineering considerations related to construction of the proposed improvements are included herein. Environmental consulting was beyond our present scope of services

PROPOSED CONSTRUCTION

We understand that the planned improvements consist largely of two 2-story buildings and widening of the approximately 1,200-foot reach of 8th Avenue that extends between them. An approximately 3,800-square foot Changing Building will be constructed in the northern portion of the facility. An approximately 6,500-square foot Training Building will be built in the southern portion. We understand that the buildings will be of conventional construction with no below-grade (basement) levels and will exert low to moderate structural loads. The widened road will not be paved. Only limited cuts and fills are anticipated to achieve lines and grades for the project, likely on the order of 2 feet or less.

If the proposed construction differs significantly from that described above, GROUND should be notified to re-evaluate the conclusions and parameters herein.

Job No. 15-3029 Ground Engineering Consultants, Inc. Page 2

SITE CONDITIONS

The proposed improvements will be constructed in portions of the existing teaching mine facility. The Changing Building (upper or northern building) is planned for an area of previously placed fill that consisted largely of mine tailings. The wedge of fill was placed against the hillside, deepest to the southeast and tapering to the west and northwest.

Near the Changing Building, the approximately 15-foot fill slope descends to the southeast and an angle of about 1½:1 (horizontal : vertical). The Training Building

(lower or southern building) was an area cut a few feet into the hillside on the northwest side and with several feet of fill to the south and east. The steep, existing roadway between the two areas also was constructed by cut/fill grading on the hill side.

The area of the Edgar Mine was a portion of the northern wall of the canyon of Clear

Creek, overlooking the City of Idaho Springs. The canyon wall at and around the facility descended relatively steeply to the south but has been dissected by ephemeral tributary channels to form a series of south-trending ridges separated by the drainages.

The building pads and road way exposed largely bare soil and rock. The surrounding native slopes supported numerous pine trees.

GEOLOGIC SETTING

Published geologic maps, e.g., Tweto (1979)1 depict the site as underlain by biotite gneiss, a hard, crystalline rock. The rock is overlain by variable, but limited depths of colluvial soil (slope wash).

SUBSURFACE EXPLORATION

Subsurface exploration for the project was conducted in April, 2015. Eight (8) test holes were drilled with a conventional, truck-mounted, drilling rig to evaluate the subsurface conditions as well as to retrieve samples for laboratory testing and analysis. Five of the test holes were advanced to approximate depths of 8 to 30 feet within the approximate building footprints. Test holes 1, 2 and 4 were offset and repeated when refusal was encountered at shallow depths. (Each of those three have ‘A’ and ‘B’ logs.) The other

1 Tweto, O., 1979, Geologic Map of Colorado, U.S. Geological Survey.

Job No. 15-3029 Ground Engineering Consultants, Inc. Page 3 three test holes were advanced to shallow depths along the roadway. A fourth roadway hole could not be drilled because of the steepness of much of the roadway.

Samples of the subsurface materials were retrieved with a 2-inch I.D. California liner sampler and a 1⅜-inch I.D. Standard Penetration Test sampler. The samplers were driven into the substrata with blows from a 140-pound hammer falling 30 inches, in general accordance with (in the case of the Standard Penetration Test sampler) ASTM

Method D1586. Penetration resistance values, when properly evaluated, indicate the relative density or consistency of soils. Depths at which the samples were obtained and associated penetration resistance values are shown on the test hole logs.

The approximate test locations are shown on Figure 1. Logs of the test holes are presented on Figures 2 and 3. Explanatory notes and a legend are provided on Figure

4.

LABORATORY TESTING

Samples retrieved from our test holes were examined and visually classified in the laboratory by the project engineer. Laboratory testing of soil samples included standard property tests, such as natural moisture contents, grain size analyses, and Atterberg limits. Water-soluble sulfates and a suite of corrosivity tests were completed on selected samples, as well. Laboratory tests were performed in general accordance with applicable ASTM protocols. Results of the laboratory testing program are summarized in Tables 1 and 2.

SUBSURFACE CONDITIONS

Generally, the test holes penetrated a highly variable depths of existing fill soils that we understand were placed progressively over many years as rock was excavated from the mine. The fill soils were underlain by native sands and gravels (interpreted to be colluvial soils) and/or crystalline rock (biotite gneiss). Samples of intact crystalline rock were not obtained for this study.

It should be noted that coarse gravel, cobbles and boulders are not well represented in small diameter liner samples collected from 4-inch diameter test holes. Therefore, such

Job No. 15-3029 Ground Engineering Consultants, Inc. Page 4 materials may be present even where not called out in the material descriptions herein, or present in greater proportions than the descriptions suggest.

Fill soils were recognized in the test holes and likely are present elsewhere on the site, as well. Delineation of the complete lateral and vertical extents of any fills at the site, or their compositions, was beyond our present scope of services.

Fill consisted of fine to coarse, silty to clayey sand, with gravel, cobbles and boulders.

They were dry to moist, non-plastic to low plastic, loose to very dense and gray to gray-brown to yellow-brown in color. (Although not recognized in the test holes, the fills may include debris, organic material, trash, and/or other deleterious material.)

Sand and Gravel were fine to coarse and clean to silty, with cobbles and boulders.

They were slightly moist to wet, non-plastic to low plastic, medium dense to dense, and brown to gray brown to gray in color.

Groundwater was not encountered in either of the upper test holes (Test Holes 1 and 2) to the depths explored at the time of drilling. Groundwater was encountered, however, in Test Holes 3 and 5 at depths of about 20 and 25 feet, respectively. Groundwater levels can be expected to fluctuate, however, in response to annual and longer-term cycles of precipitation, irrigation, surface drainage, land use, and the development of transient, perched water conditions.

Specifically, it has been our experience that surface and groundwater levels fluctuate greatly in mountainous areas, primarily due to seasonal conditions such as spring runoff.

These conditions are often highly variable and difficult to predict. Although these conditions generally exist for 1 to 3 months annually, their impact on design can be significant. This is particularly important for foundation and deep utility excavations, cut slopes, and culvert sizing, or during construction where effective surface drainage has not been established.

SEISMIC CLASSIFICATION

Based on extrapolation of available data to depth and our experience in the project area, we consider the site likely to meet the criteria for a Seismic Site Classification of D according to the 2012 IBC classification (Table 1613.5.2); however, a quantitative

Job No. 15-3029 Ground Engineering Consultants, Inc. Page 5 assessment of the site seismic properties should be performed to confirm this classification. Exploration and/or shear wave velocity testing to a depth of 100 feet or more was not part of our present scope of services.

According to the 2012 IBC, to evaluate the Seismic Site Classification quantitatively, seismic shear wave velocity testing and/or exploration to depths of at least 100 feet should be performed. We consider the likelihood of achieving a Site Classification of C at the subject location to be relatively high.

IBC SEISMIC PARAMETERS

Seismic Site Classification SDS SDl

D 0.267 0.099

GEOTECHNICAL CONSIDERATIONS FOR DESIGN

The variably dense and un-documented fill soils underlying the upper building site to a considerable depth and underlying the lower building to depths up to about 5 or 6 feet

(but possibly not present at all beneath some portions of the lower building) represent the primary geotechnical constraint on construction there. Significant total and differential settlements must be anticipated for structures supported directly on those soils. We estimate that likely settlements will range from 0 to about 3 inches. Two approaches appear viable for founding the proposed buildings on these fill soils: use of micro-piles that bear in the underlying crystalline rock, or using a stiff, shallow foundation such as a structural mat.

Micro-piles will limit foundation settlements likely to less than an inch. Similar values can be anticipated for the floors if they were constructed as structural floors also supported on micro-piles. Differential movements would be primarily between the foundation and adjacent flatwork and, if used, a slab-on-grade floor.

A structural mat foundation presumably could accommodate the total and differential settlements that may be realized across a building without transmitting much strain to the building frame. Such a foundation system also can be re-leveled relatively easily, if necessary. Differential movements between the foundation and adjacent flatwork or a slab-on-grade floor likely will be less than if a micro-pile foundation were used.

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Initial Slope Stability Analyses Initial slope stability analyses suggest that the fill slopes descending from the area of the Changing Building (upper or northern building) has a factor of safety of about 1.2 or less. Placing the Changing Building close to the top-of-slope will reduce that factor of safety if shallow foundations are used. The actual performance of the existing fill slopes and improvements above them, however, may indicate that the parameters used in our initial analyses were conservative. (A detailed slope stability analysis was not within our present scope of services, but a cost estimate for that service can be provided upon request.)

Based on our preliminary analyses, the foundation of the Changing Building should be placed no closer than 7 feet to the top-of-slope if a shallow mat foundation is used.

FOUNDATION SYSTEMS

Shallow Mat Foundation

Geotechnical Parameters for Shallow, Mat Foundation Design

1) Shallow, mat foundations should bear on firm, existing fill or firm, native soils.

2) Shallow, mat foundations bearing firm existing fill soils or firm, native soils may be designed for an allowable soil bearing pressure of 3,500 psf.

The above values may be increased by ⅓ for transient loads such as wind or seismic loading. For larger footings, lower allowable bearing pressures may be appropriate.

To reduce differential settlements between footings or along continuous footings, footing loads should be as uniform as possible. Differentially loaded footings will settle differentially.

Likely post-construction settlement from direct compression of the foundation soils for the allowable bearing pressure above is estimated to be about 1 inch, based on an assumption of drained foundation conditions. If foundation soils are subjected to an increase or fluctuation in moisture content, the effective bearing capacity will be reduced and greater post-construction movements than those

Job No. 15-3029 Ground Engineering Consultants, Inc. Page 7 estimated above may result. Settlements from consolidation of existing fill soils will be in addition to that value and likely will be strongly differential.

3) Shallow, mat foundations should bear at an elevation 3½ or more feet below the lowest adjacent exterior finish grades to have adequate soil cover for frost protection. Given that a partially below grade garden level is planned for construction, no additionally deepening of foundation elements is necessary for frost protection.

4) Continuous foundation elements should be reinforced as designed to span an unsupported length of at least 10 feet.

5) Geotechnical parameters for lateral resistance to foundation loads are provided in the Lateral Loads section of this report.

6) Connections of all types must be flexible and/or adjustable to accommodate the anticipated, post-construction movements of the buildings.

Shallow Foundation Construction

7) The contractor should take adequate care when making excavations not to compromise the bearing or lateral support for nearby improvements.

8) Care should be taken when excavating the foundations to avoid disturbing the supporting materials particularly in excavating the last few inches.

9) Footing excavation bottoms may expose loose, organic or otherwise deleterious materials, including debris. Firm materials may become disturbed by the excavation process. All such unsuitable materials should be excavated and replaced with properly compacted fill or the foundation deepened.

10) Foundation-supporting soils may be disturbed or deform excessively under the wheel loads of heavy construction vehicles as the excavations approach footing bearing levels. Construction equipment should be as light as possible to limit development of this condition. The movement of vehicles over proposed foundation areas should be restricted.

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11) All foundation subgrade should be compacted with a vibratory plate compactor prior to placement of concrete.

12) Fill placed against the sides of the footings should be properly compacted in accordance with the Project Earthwork section of this report.

Micro-pile Foundation

‘Micro-piles’ are proprietary foundation systems that are designed by the specialty contractor/supplier who will install them. We anticipate that the geotechnical information in this report will be adequate for them to develop their design in coordination with the structural engineer. We suggest contacting the following contractors for information or design, although others may be available, as well:

Hayward Baker (Broomfield, Colorado) 303 / 469 – 1136

Park Range Construction (Englewood, Colorado) 303 / 395 – 3234

Micro-pile foundation systems should bear in the gneissic, crystalline rock underlying the site. The specialty foundation contractor and the structural engineer should coordinate to determine the type, number, layout, length, and necessary vertical and lateral capacities of such a foundation system.

Micro-piles are relatively slender and should be, battered, grouped, or laterally braced for stability, as necessary.

The geotechnical parameters for lateral loading analysis provided in the Lateral Loads section of this report also may be used for analysis of proprietary foundation elements with appropriate adjustment for element width.

All foundation components should be evaluated for corrosion resistance.

We suggest that one or more test piles be advanced at the site prior to completion of design to evaluate installation conditions and to optimize the design, including anticipated installation lengths.

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FLOOR SYSTEMS

Slab-on-Grade Floor

Geotechnical Parameters for Design of Slab-on-Grade Floors

1) Concrete, slab-on-grade floors should bear on should bear on firm, existing fill or firm, native soils.

2) Floor slabs should be adequately reinforced. Floor slab design, including slab thickness, concrete strength, jointing, and slab reinforcement should be developed by a structural engineer.

3) A vertical modulus of subgrade reaction (Kv) of 105 tcf (121 pci) may be used for design of concrete, slab-on-grade floors bearing a section of properly compacted fill.

These values are for a 1-foot x 1-foot plate; they should be adjusted for slab dimension.

4) Floor slabs should be separated from all bearing walls and columns with slip joints, which allow unrestrained vertical movement.

Slip joints should be observed periodically, particularly during the first several years after construction. Slab movement can cause previously free-slipping joints to bind. Measures should be taken to assure that slab isolation is maintained in order to reduce the likelihood of damage to walls and other interior improvements.

5) Concrete slabs-on-grade should be provided with properly designed control joints.

ACI, PCA and other industry groups provide guidelines for proper design and construction concrete slabs-on-grade and associated jointing. The design and construction of such joints should account for cracking as a result of shrinkage, curling, tension, loading, and curing, as well as proposed slab use. Joint layout based on the slab design may require more frequent, additional, or deeper joints, and should reflect the configuration and proposed use of the slab.

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Particular attention in slab joint layout should be paid to areas where slabs consist of interior corners or curves (e.g., at column blockouts or reentrant corners) or where slabs have high length to width ratios, significant slopes, thickness transitions, high traffic loads, or other unique features. The improper placement or construction of control joints will increase the potential for slab cracking.

6) Interior partitions resting on floor slabs should be provided with slip joints so that if the slabs move, the movement cannot be transmitted to the upper structure.

This detail is also important for wallboards and doorframes. Slip joints which will allow 2 or more inches of vertical movement should be considered.

Accommodation for differential movement also should be made where partitions meet bearing walls.

7) Post-construction soil movements may not displace slab-on-grade floors and utility lines in the soils beneath them to the same extent. Design of floor penetrations, connections and fixtures should accommodate 3 or more inches of differential movement.

8) Moisture can be introduced into a slab subgrade during construction and additional moisture will be released from the slab concrete as it cures.

Therefore, a properly compacted layer of free-draining gravel, 4 or more inches in thickness, should be placed beneath the slab. This layer will help distribute floor slab loadings, ease construction, reduce capillary moisture rise, and aid in drainage.

The free-draining gravel should contain less than 5 percent material passing the

No. 200 Sieve, more than 50 percent retained on the No. 4 Sieve, and a maximum particle size of 2 inches.

The capillary break and the drainage space provided by the gravel layer also may reduce the potential for excessive water vapor fluxes from the slab after construction as mix water is released from the concrete.

We understand, however, that professional experience and opinion differ with regard to inclusion of a free-draining gravel layer beneath slab-on-grade floors. If these issues are understood by the owner and appropriate measures are

Job No. 15-3029 Ground Engineering Consultants, Inc. Page 11 implemented to address potential concerns including slab curling and moisture fluxes, then the gravel layer may be deleted.

9) A vapor barrier beneath a building floor slab can be beneficial with regard to reducing exterior moisture moving into the building, through the slab, but can retard downward drainage of construction moisture. Uneven moisture release can result in slab curling. Elevated vapor fluxes can be detrimental to the adhesion and performance of many floor coverings and may exceed various flooring manufacturers’ usage criteria.

Per the 2006 ACI Location Guideline, a vapor barrier is required under concrete floors when that floor is to receive moisture-sensitive floor covering and/or adhesives, or the room above that floor has humidity control.

Therefore, in light of the several, potentially conflicting effects of the use vapor-barriers, the owner and the architect and/or contractor should weigh the performance of the slab and appropriate flooring products in light of the intended building use, etc., during the floor system design process and the selection of flooring materials. Use of a plastic vapor-barrier membrane may be appropriate for some building areas and not for others.

In the event a vapor barrier is utilized, it should consist of a minimum 15 mil thickness, extruded polyolefin plastic (no recycled content or woven materials), maintain a permeance less than 0.01 perms per ASTM E-96 or ASTM F-1249, and comply with ASTM E-1745 (Class “A”). Vapor barriers should be installed in accordance with ASTM E-1643.

Polyethylene (“poly”) sheeting (even if 15 mils in thickness which polyethylene sheeting commonly is not) does not meet the ASTM E-1745 criteria and, therefore, should not be used as vapor barrier material. It can be easily torn and/or punctured, does not possess necessary tensile strength, gets brittle, tends to decompose over time, and has a relatively high permeance.

Construction Considerations for Slab-on-Grade Floors

10) Loose, soft or otherwise unsuitable materials exposed on the prepared surface on which the floor slab will be cast should be excavated and replaced with properly compacted fill.

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11) Concrete floor slabs should be constructed and cured in accordance with applicable industry standards and slab design specifications.

12) All plumbing lines should be carefully tested before operation. Where plumbing lines enter through the floor, a positive bond break should be provided.

Structural Floor A structural floor should be supported on foundations like the building frame. Requirements for the number and position of foundation elements to support the floor should be developed by the structural engineer. Geotechnical parameters for foundation elements are provided in the Foundation Systems section of this report.

Separate, entryway floor slabs and similar areas also should be constructed as structural floors to reduce the potential for differential movements between such structures and the building.

It should be noted that structural floors tend to be flexible and move elastically under live loads. Building design also should account for floor movements of this type.

Because the site soils are not expansive, structural floors should be constructed either to span above a well-ventilated crawl space, or on grade. Floor system design should be coordinated with any radon-mitigations systems, etc.

Structural Floors Over Crawl Spaces New buildings generally lack ventilation due primarily to systematic efforts to construct air-tight, energy-efficient structures.

Therefore, areas such as crawl spaces beneath structural floors are typically areas of elevated humidity which never completely dry. This condition can be aggravated in some locations by shallow groundwater or a perched groundwater condition which can result in saturated soils within close proximity of finished building pad grades.

Persistently warm, humid conditions in the presence of cellulose, which is the base material found in many typical construction products, creates an ideal environment for the growth of fungi, molds, and mildew. Published data suggest links between molds and negative health effects. Therefore, GROUND recommends that crawl spaces beneath structural floors be provided with adequate, positive active ventilation systems or other active mechanisms such as specially designed HVAC systems (as well as properly constructed and maintained underdrains) to reduce the potential for mold, fungus and mildew growth. Crawl spaces should be inspected periodically so that remedial measures can be taken in a timely manner should mold, fungus or mildew be present and require removal.

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If utility lines are placed in the crawl space above the soil, the crawl space should be adequate to allow access to and maintenance of the utility piping. Utility lines can be displaced by soil movements which are not reflected in the building. Design and installation of associated fixtures should accommodate this potential differential movement, which could be on the order of 3 inches or more.

A vapor barrier meeting ASTM E-1745 (Class “A”) should be considered for installation below all structurally supported floors and if utilized, should be properly attached/sealed to the foundation. The sheet material should not be attached to horizontal surfaces such that condensate might drain to wood or corrodible metal surfaces.

Use of polyethylene (“poly”) sheeting as a vapor barrier is not recommended.

Polyethylene (“poly”) sheeting (even if 15 mils in thickness which polyethylene sheeting commonly is not) does not meet the ASTM E-1745 criteria and is not recommended for use as vapor barrier material. It can be easily torn and/or punctured, does not possess the necessary tensile strength, gets brittle, tends to decompose over time, and has a relatively high permeance.

Crawl spaces typically are vulnerable to moisture accumulation. Proper installation and maintenance of the underdrains, as outlined in the Subsurface Drainage section of this report, will assist drainage of free water and assist the ventilation system to reduce crawl space moisture.

RADON

Testing for the possible presence of radon gas prior to project construction does not yield useful results regarding the potential accumulation of radon in completed structures. Radon accumulations typically are found in basements or other enclosed portions of buildings built in areas underlain at relatively shallow depths by granitic crystalline rock. The gneissic rock at this site is sufficiently similar that it should be considered at a somewhat elevated risk for radon to accumulate in concentrations exceeding applicable health standards relative to sites underlain by relatively deep soils and sedimentary bedrock.

GROUND recommends that radon testing be performed in each building after construction is completed. Proper ventilation usually is sufficient to mitigate potential

Job No. 15-3029 Ground Engineering Consultants, Inc. Page 14 radon accumulations. Building designs should accommodate such ventilation for all building areas.

LATERAL LOADS

Shallow Foundations Resisting Lateral Loads A friction coefficient of 0.40 between the footing and the site soils may be used for design shallow foundations resisting lateral loads.

Passive soil pressure at this site may be estimated using an equivalent fluid pressure of

370 pcf for drained conditions, to a maximum of 3,700 psf. The upper 1 foot of embedment should be neglected for passive resistance, however. Where this passive soil pressure is used to resist lateral loads, it should be understood that significant lateral strains will be required to mobilize the full value indicated above, likely 1 inch or more. A reduced passive pressure can be used for reduced anticipated strains, however.

Note that the values above and the values for active and at-rest earth pressures below were based on a moist unit weight (γ') of 120 pcf and an angle of internal friction () of

31 degrees and are un-factored. Appropriate factors of safety should be included in design calculations.

At-Rest and Active Lateral Earth Pressures Site soils placed as backfill against a structure in an at-rest condition may be considered to exert an equivalent fluid unit weight of 59 pcf.

Site soils placed as backfill where the full, active earth pressure condition applies may be considered to exert an equivalent fluid unit weight of 39 pcf.

The active and at-rest earth pressures indicated above assume well drained conditions and a horizontal backfill surface. Design should incorporate any upward sloping backfills, live loads such as construction equipment, material stockpiles, etc., and other surcharge pressures. The build-up of hydrostatic pressures behind a structure also will increase lateral earth pressures on it.

Micro-Pile Foundations Lateral load analysis using the Terzaghi method may take the values tabulated below for the modulus of horizontal subgrade reaction (Kh) to be characteristic of the soils and bedrock underlying the buildings, based on a simplified soil

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/ bedrock profile. Resistance to lateral loads by deep foundations should be neglected in the upper 3 feet of soils (or the distance to a descending slope face, if greater than 3 feet, but less than 7 feet), whether fill or native.

HORIZONTAL MODULUS SUBGRADE REACTION (Kh) – TERZAGHI METHOD

Material

Approximate Depth Range

Kh based on Foundation

Element Width / Diameter

8-inch 10-inch

Fill and Native Soils 3* – 25 feet 180 tcf (208 pci) 140 tcf (162 pci)

Gneiss Rock 25+ feet 675 tcf (781 pci) 540 tcf (625 pci)

* or up to 7 feet if the element is closer than 7 feet from a descending slope face.

Note that the Kh values tabulated above are dependent on micro-pile diameter. Values for other diameters can be provided upon request.

WATER-SOLUBLE SULFATES

The concentration of water-soluble sulfates measured in selected samples obtained from the test holes ranged up to about 0.10 percent by weight. (See Table 2.) Such concentrations of water-soluble sulfates represent a negligible degree of sulfate attack on concrete exposed to these materials. Degrees of attack are based on the scale of

'negligible,' 'moderate,' 'severe' and 'very severe' as described in the “Design and

Control of Concrete Mixtures,” published by the Portland Cement Association (PCA).

The Colorado Department of Transportation (CDOT) utilizes a corresponding scale with

4 classes of severity of sulfate exposure (Class 0 to Class 3) as described in the published table below.

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REQUIREMENTS TO PROTECT AGAINST DAMAGE TO

CONCRETE BY SULFATE ATTACK FROM EXTERNAL SOURCES OF SULFATE

Severity of Sulfate

Exposure

Water-Soluble Sulfate (SO4

In Dry Soil

Sulfate (SO4

In Water (ppm)

Water Cementitious

Ratio (maximum)

Cementitious Material

Requirements

Class 0 0.00 to 0.10 0 to 150 0.45 Class 0

Class 1 0.11 to 0.20 151 to 1500 0.45 Class 1

Class 2 0.21 to 2.00 1501 to 10,000 0.45 Class 2

Class 3 2.01 or greater 10,001 or greater 0.40 Class 3

Based on these data, no special, sulfate-resistant cement need be used in project concrete.

SOIL CORROSIVITY

Data were obtained to support an initial assessment of the potential for corrosion of ferrous metals in contact with earth materials at the site, based on the conditions at the time of GROUND’s evaluation. The test results are summarized in Table 2.

Soil Resistivity Samples of materials retrieved from the test holes were tested for resistivity in the laboratory, at approximately in-place moisture contents. Measurements of electrical resistivity indicated values of approximately 4,116 and 7,708 ohm-centimeters in a sample of site soils. Such moderately high resistivities typically indicate a less corrosive environment.

pH Where pH is less than 4.0, soil serves as an electrolyte; the pH range of about 6.5 to

7.5 indicates soil conditions that are optimum for sulfate reduction. In the pH range above 8.5, soils are generally high in dissolved salts, yielding a low soil resistivity.2

Testing indicated pH values of about 7.4 and 7.8.

Reduction-Oxidation testing indicated red-ox potentials of about -23 and -66 millivolts.

Such low potentials typically indicate a more corrosive environment.

Sulfide Reactivity testing indicated “positive” and “trace” results in the site soils. The presence of sulfides in the soils suggests a more corrosive environment.

2 American Water Works Association ANSI/AWWA C105/A21.5-05 Standard

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Corrosivity Assessment The American Water Works Association (AWWA) has developed a point system scale used to predict corrosivity. The scale is intended for protection of ductile iron pipe but is valuable for project steel selection. When the scale equals 10 points or higher, protective measures for ductile iron pipe are indicated. The

AWWA scale is presented below. The soil characteristics refer to the conditions at and above pipe installation depth.

Table A.1 Soil-test Evaluation

Soil Characteristic / Value Points

Soil Resistivity

<1,500 ohm-cm ..........................................................................................… 10 1,500 to 1,800 ohm-cm ................................................................……......…. 8 1,800 to 2,100 ohm-cm .............................................................................…. 5 2,100 to 2,500 ohm-cm ...............................................................................… 2 2,500 to 3,000 ohm-cm >3,000 ohm-cm ................................................................................… 0 pH 0 to 2.0

2.0 to 4.0

4.0 to 6.5

6.5 to 7.5 ......................................................................................................... 0 *

7.5 to 8.5 >8.5

Redox Potential

< 0 (negative values) 0 to +50 mV ................................................................................................…. 4 +50 to +100 mV ............................................................................................… 3½ > +100 mV

Sulfide Presence

Positive ........................................................................................................…. 3½ Trace .............................................................................................................… 2 Negative .......................................................................................................…. 0

Moisture Poor drainage, continuously wet ..................................................................…. 2 Fair drainage, generally moist ....................................................................… 1 Good drainage, generally dry

* If sulfides are present and low or negative redox-potential results (< 50 mV) are obtained, add three points for this range.

We anticipate that drainage at the site after construction will be effective. Nevertheless, based on the values obtained for the soil parameters, the overburden soils and bedrock appear to comprise a severely corrosive environment for ferrous metals (11½ points).

Still greater potentials for corrosion may be associate with acidic drainage from the mine or through mine tailings.

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If additional information is needed regarding soil corrosivity, GROUND suggests contacting the American Water Works Association or a Corrosion Engineer. It should be noted, however, that changes to the site conditions during construction, such as the import of other soils, or the intended or unintended introduction of off-site water, might alter corrosion potentials significantly.

PROJECT EARTHWORK

The earthwork criteria and standards below are based on our interpretation of the geotechnical conditions encountered in the test holes. Where these standards differ from applicable municipal or agency specifications, e.g., for compaction of utility trench backfill, the latter should be considered to take precedence.

Note that addressing any potential environmental considerations, if any, associated with the mine tailings at the site was beyond our present scope of services.

General Considerations Project grading should be performed as early as possible in the construction sequence to allow settlement of fills and surcharged ground to be realized to the greatest extent prior to subsequent construction.

Prior to earthwork construction, relic structures, foundations, construction debris, vegetation and other deleterious materials should be removed and disposed of off-site.

Relic underground utilities should be abandoned in accordance with applicable regulations, removed as necessary, and properly capped.

Drainage During Construction The contractor should take pro-active measures to control surface waters during construction, to direct them away from excavations and into appropriate drainage structures. Wetting of foundation soils during construction can have adverse effects on the performance of the proposed facility.

Filled areas should be graded to drain effectively at the end of each work day.

Use of Existing Fill Soils Fill soils were recognized in the test holes and fill soils likely are present elsewhere on-site. Because they were not all sampled and tested, however, some existing fill soils may not be suitable for re-use as fill for this project due to the presence of trash, organic material, construction debris, or other deleterious materials.

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Excavated fill materials should be evaluated and tested, as appropriate, with regard to re-use.

Cobbles and fragments of rock in existing fill soils, as well as inert construction debris, e.g., concrete or asphalt, up to 8 inches in maximum dimension may be included in project fills, in general. Such materials should be evaluated on a case-by-case basis where identified during earthwork.

Use of Native Soils The local native soils materials that are free of organic debris and other deleterious materials, are suitable, in general, for placement as compacted fill.

Cobbles and fragments of rock up to 8 inches in maximum dimension may be included in project fills, in general. Such materials should be assessed on a case-by-case basis as they are identified during earthwork.

Imported Common Fill Materials If it is necessary to import material to the project as common fill, the imported soils should be free of organic material, and other deleterious materials. Imported material should consist of soils that have 20 percent or less passing the No. 200 Sieve and should have a plasticity index of 15 or less, and be approved for the proposed use. Materials proposed for import should be tested and approved prior to transport to the site.

Fill Platform Preparation Prior to filling, the top 8 inches of in-place materials on which fill soils will be placed should be scarified, moisture conditioned and properly compacted in accordance with the criteria below to provide a uniform base for fill placement. (Scarification and re-compaction need not be performed in utility trench bottoms where bedding will be placed.)

If surfaces to receive fill expose loose, wet, soft or otherwise deleterious material, additional material should be excavated, or other measures taken to establish a firm platform for filling. A surface to receive fill must be firm and effectively stable prior to placement of fill, including pipe trench bottoms prior to placement of bedding.

Considerations for Fill Placement Fill soils should be thoroughly mixed to achieve a uniform moisture content, placed in uniform lifts not exceeding 8 inches in loose thickness, and properly compacted. It may be necessary to re-work the fill materials

Job No. 15-3029 Ground Engineering Consultants, Inc. Page 20 more than once by adjusting moisture and replacing the materials, in order to achieve the compaction and moisture criteria below.

No fill materials should be placed, worked, rolled while they are frozen, thawing, or during poor/inclement weather conditions.

Care should be taken with regard to achieving and maintaining proper moisture contents during placement and compaction. Materials that are not properly moisture conditioned may exhibit significant pumping, rutting, and deflection at moisture contents near optimum and above. The contractor should be prepared to handle soils of this type, including the use of chemical stabilization, if necessary.

Compaction areas should be kept separate, and no lift should be covered by another until relative compaction and moisture content within the indicated ranges are obtained.

Where soils supporting foundations or on which foundation will be placed are exposed to freezing temperatures or repeated freeze – thaw cycling during construction – commonly due to water ponding in foundation excavations – bearing capacity typically is reduced and/or settlements increased due to the loss of density in the supporting soils. After periods of freezing conditions, the contractor should re-work areas affected by the formation of ice to re-establish adequate bearing support.

Compaction Standards Fill materials should be compacted to 95 percent or more of the maximum dry density at moisture contents within 2 percent of optimum moisture content as determined by ASTM D1557, the ‘modified Proctor’.

Use of Squeegee Relatively uniformly graded fine gravel or coarse sand, i.e., “squeegee,” or similar materials commonly are proposed for backfilling foundation excavations, utility trenches (excluding approved pipe bedding), and other areas where employing compaction equipment is difficult. In general, however, squeegee should not be used on this project.

Instead, excavations not backfilled with properly compacted fill should be backfilled with

“Controlled Low Strength Material” (CLSM), i.e., a lean, sand-cement slurry (“flowable fill”) or a similar material.

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Where “squeegee” or similar materials are proposed for use by the Contractor, the design team should be notified by means of a Request for Information (RFI), so that the proposed use can be considered on a case-by-case basis. Where “squeegee” meets the project requirements for pipe bedding material, however, it is acceptable for that use.

Settlements Settlements will occur in filled ground, typically on the order of 1 to 2 percent of the fill depth. For a 3-foot fill, for example, that corresponds to a total settlement of about ½ inch. If fill placement is performed properly and is tightly controlled, in GROUND’s experience the majority (on the order of 60 to 80 percent) of that settlement typically will take place during earthwork construction, provided the contractor achieves the compaction levels indicated herein. The remaining potential settlements likely will take several months or longer to be realized, and may be exacerbated if these fills are subjected to changes in moisture content.

Cut and Filled Slopes Permanent, graded slopes supported by local soils up to 8 feet in height should be constructed no steeper than 2:1 (horizontal : vertical). (Steeper slopes may be feasible where supported by bedrock. Such proposed slopes should be evaluated on an individual basis.) Minor raveling or surficial sloughing should be anticipated on graded slopes until vegetation is well re-established. This can be reduced by the use of flatter slopes, if feasible. Surface drainage should be designed to direct water away from slope faces into designed drainage pathways or structures.

Slope Creep Native and fill slopes up to about 25 feet in height are near the proposed buildings and taller slopes are adjacent to reaches of the roadway. The shallow soils supporting the slopes will tend to ‘relax’ or ‘creep’ downslope with time. Improvements placed in proximity to the tops-of-slope can be displaced and/or rotated by these soil movements with associated (typically limited) distress. Curbs, pavements, flatwork, fences, and other improvements that are intolerant of this displacement and potential distress should be set back from the tops-of-slope or anchored below the zone of ‘active’ or ‘creeping’ soils: typically about 4 feet. GROUND can provide additional recommendations in this regard upon request.

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EXCAVATION CONSIDERATIONS

Excavation Difficulty Test holes for the subsurface exploration encountered refusal in the fill soils at various depths ranging from about 4 to 22 feet. Caving also was encountered commonly. These conditions likely reflect the highly variable gradation and density of the fill soils, as well as the underlying, very hard crystalline rock. Coarse, nested cobbles and boulders, as well as running sands, likely are present in the fill and should be anticipated by the contractor at any depth.

Similiarly, nested cobbles and boulders likely are present at various depths in the native, colluvial soils. Caving, high penetration resistance values, and drilling rig refusal at various depths were encountered in these materials, as well.

The in-place crystalline rock was not sampled, but based on our experience in the project area, it can range from massive to highly fractured and from hard to very hard.

The intact rock will be very difficult to excavate, particularly in narrow excavations.

Therefore we anticipate greater than typical excavation difficulties with conventional, heavy-duty, excavation equipment in good working condition. Specialized equipment or limited, light blasting may be cost-effective to facilitate excavations into some of the site earth materials.

Temporary Excavations and Personnel Safety Excavations in which personnel will be working must comply with all applicable MSA Standards and Regulations. The contractor’s “responsible person” should evaluate the soil exposed in the excavations as part of the contractor’s safety procedures. GROUND has provided the information in this report solely as a service to the Colorado School of Mines and is not assuming responsibility for construction site safety or the contractor’s activities.

The contractor should take care when making excavations not to compromise the bearing or lateral support for any adjacent, existing improvements.

In general, temporary, un-shored excavation slopes up to 12 feet in height may be cut no steeper than 2 : 1 (horizontal : vertical) in the on-site soils and bedrock in the absence of seepage. Some surface sloughing may occur on the slope faces at these angles.

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Should site constraints prohibit the use of the above slope angle, temporary shoring should be used. GROUND is available to perform shoring design upon request.

Lateral Loading The geotechnical parameters regarding lateral loads on structures at the site and for resisting lateral loads are provided in the Lateral Loads section of this report may be used for preliminary design of temporary retaining wall systems. Effective drainage should be included in retaining system design or design should incorporate hydrostatic loads. The contractor should have these parameters evaluated/verified for actual soils exposed during excavation.

Groundwater and Surface Water Groundwater was encountered in the test holes at depths below about 20 feet. Therefore, based on conditions at the time of this subsurface exploration, shallow excavations at the site appear unlikely to encounter groundwater except, limited volumes of perched groundwater.

Should seepage or flowing groundwater be encountered in project excavations, the slopes should be flattened as necessary to maintain stability or a geotechnical engineer should be retained to evaluate the conditions and provide additional discussion or parameters, as appropriate. The risk of slope instability will be significantly increased in areas of seepage along excavation slopes.

The contractor should take pro-active measures to control surface waters during construction and maintain good surface drainage conditions to direct waters away from excavations and into appropriate drainage structures. A properly designed drainage swale should be provided at the tops of the excavation slopes.