Special Provisions Appendix A - Geotech Report.pdf

REPORT COVER PAGE

Geotechnical Engineering Report

Timnath Pedestrian Bridge and Trail New Location

Timnath, Colorado

July 1, 2021

Terracon Project No. 20215048

Prepared for:

AVI, PC

Fort Collins, Colorado

Prepared by:

Terracon Consultants, Inc.

Fort Collins, Colorado

APPENDIX A

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REPORT TOPICS

INTRODUCTION

SITE CONDITIONS

PROJECT DESCRIPTION

GEOTECHNICAL CHARACTERIZATION

GEOTECHNICAL OVERVIEW

EARTHWORK

DEEP FOUNDATIONS

SEISMIC CONSIDERATIONS

BELOW-GRADE STRUCTURES

FLATWORK

CORROSIVITY

GENERAL COMMENTS

Note: This report was originally delivered in a web-based format. Orange Bold text in the report indicates a referenced section heading. The PDF version also includes hyperlinks which direct the reader to that section and clicking on the GeoReport logo will bring you back to this page. For more interactive features, please view your project online at client.terracon.com.

ATTACHMENTS

EXPLORATION AND TESTING PROCEDURES

SITE LOCATION AND EXPLORATION PLANS

EXPLORATION RESULTS

SUPPORTING INFORMATION

Note: Refer to each individual Attachment for a listing of contents.

http://client.terracon.com/

Timnath Pedestrian Bridge and Trail New Location ■ Timnath, Colorado

July 1, 2021 ■ Terracon Project No. 20215048

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REPORT SUMMARY

Topic Overview Statement

Project Overview

A geotechnical exploration has been performed for the proposed Timnath Pedestrian Bridge and Trail to be constructed south of the intersection of Oak Grove Street and Covenant Court in Timnath, Colorado. Four (4) borings were performed to depths of approximately 10 to 25 feet below existing site grades.

Subsurface Conditions

Subsurface conditions encountered in our exploratory borings generally consisted of about 4 feet of fill consisting of silt, sands and clays possibly interlayered with sugar beet waste over about 1 to 8 feet of lean to fat sandy clay over about 10 to 17 feet of poorly graded sand with silt and gravel to clayey sand. Claystone bedrock was encountered below the overburden soils in most of the borings at depths of approximately 9.5 to 17 feet below existing site grades. The upper approximately 2 feet of bedrock was highly weathered and comparatively soft. Boring logs are presented in the Exploration Results section of this report.

Groundwater Conditions

Groundwater was encountered in all of our test borings at depths of about 3.8 to 9.5 feet below existing site grades at the time of drilling. Groundwater levels can fluctuate in response to site development and to varying seasonal and weather conditions, irrigation on or adjacent to the site and fluctuations in nearby water features.

Geotechnical Concerns

■ Existing, undocumented fill was encountered to a depth up to about 4 feet in the borings drilled at the proposed bridge crossing and along the pedestrian path alignment on the site. Existing fill could exist at other locations on the site and extend to greater depths. We do not possess any information regarding whether the fill was placed under the observation of a geotechnical engineer. Undocumented fill can present a greater than normal risk of post-construction movement of foundations and other site improvements supported on or above these materials. Where the existing fill is present below the proposed trail concrete flatwork, we recommend over-excavating the fill materials to a depth of 2 feet below the bottom of the concrete. The subgrade soil at the base of the over-excavation should be sacrificed, moisture conditioned and compacter prior to placement of over-excavation backfill.

If over-excavated soils contain significant amounts of potential sugar beet waste materials, we recommend imported clean soils or utilizing clean soils from other areas of the site as over-excavation backfill below concrete trail flatwork.

■ Shallow groundwater was measured at depths ranging from about 3 to 9 feet below existing site grades. Terracon recommends maintaining a separation of at least 3 feet between the bottom of proposed concrete trail and measured groundwater levels. It is also possible and likely that groundwater levels below this site may rise as water levels in the Greeley Number 2 Canal rise. Final site grading should be planned and designed to avoid cuts where shallow groundwater is known to exist, and also in areas where such grading would create shallow groundwater conditions.

If deeper cuts are unavoidable, temporary construction dewatering and/or installation of a subsurface drainage system may be needed.

■ Loose sand soils were encountered at depth near groundwater elevation and within the upper approximately 5 to 10 feet and of the borings completed at this site. These materials can be susceptible to disturbance and loss of strength under repeated construction traffic loads and unstable conditions could develop. Stabilization of loose to soft soils may be required at some locations to provide adequate support for construction equipment and proposed structures. Terracon should be contacted if these conditions are encountered to observe the conditions exposed and to provide guidance regarding stabilization (if needed).

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Topic Overview Statement

Earthwork

On-site soils not containing significant amounts of what appears to be sugar beet waste typically appear suitable for use as general engineered fill and backfill on the site provided they are placed and compacted as described in this report. Import materials (if needed) should be evaluated and approved by Terracon prior to delivery to the site.

Earthwork recommendations are presented in the Earthwork section of this report.

Grading and Drainage

The amount of movement of foundations, flatwork, etc. will be related to the wetting of underlying supporting soils. Therefore, it is imperative the recommendations discussed in the Grading and Drainage section of the Earthwork section this report be followed to reduce potential movement. As discussed in the Grading and Drainage section of this report, surface drainage should be designed, constructed and maintained to provide rapid removal of surface water runoff away from the proposed pedestrian bridge and flatwork. Water should not be allowed to pond adjacent to foundations or on flatwork and conservative irrigation practices should be followed to avoid wetting foundation and flatwork subgrade. Excessive wetting of foundations and subgrade can cause movement and distress to foundations and concrete.

Foundations

The proposed bridge can be supported by a micropile or helical pile foundation system. Design recommendations for foundations for the proposed structure and related structural elements are presented in the Deep Foundations section of this report paragraphs.

Flatwork

Recommended Flatwork thicknesses for this project include 6 inches of concrete.

Additional flatwork discussion is presented in the report.

Seismic Considerations

As presented in the Seismic Considerations section of this report, the International Building Code, which refers to Section 20 of ASCE 7, indicates the seismic site classification for this site is D.

Construction Observation and Testing

Close monitoring of the construction operations and implementing drainage recommendations discussed herein will be critical in achieving the intended foundation and flatwork performance. We therefore recommend that Terracon be retained to monitor this portion of the work.

General Comments

This section contains important information about the limitations of this geotechnical engineering report.

1. If the reader is reviewing this report as a pdf, the topics (bold orange font) above can be used to access the appropriate section of the report by simply clicking on the topic itself.

2. This summary is for convenience only. It should be used in conjunction with the entire report for design making and design purposes. It should be recognized that specific details were not included or fully developed in this section, and the report must be read in its entirety for a comprehensive understanding of the items contained herein.

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INTRODUC TION

Geotechnical Engineering Report

Timnath Pedestrian Bridge and Trail New Location

South of Oak Grove Street and Covenant Court

Timnath, Colorado

July 1, 2021

INTRODUCTION

This report presents the results of our subsurface exploration and geotechnical engineering services performed for the proposed Timnath Pedestrian Bridge and Trail to be located south of the intersection of Oak Grove Street and Covenant Court in Timnath, Colorado. The purpose of these services is to provide information and geotechnical engineering recommendations relative to:

■ Subsurface soil and rock conditions ■ Foundation design and construction

■ Groundwater conditions ■ Seismic considerations

■ Site preparation and earthwork ■ Lateral earth pressures

■ Excavation considerations ■ Flatwork design and construction

The geotechnical engineering scope of services for this project included the advancement of four

(4) test borings to depths ranging from approximately 10 to 25 feet below existing site grades.

Previously, Terracon completed a Geotechnical Engineering Report (Project No. 20195016;

report dated July 3, 2019) for the proposed project about 1,000 feet to the west of the new bridge and trail location. Boring No. B-6 completed as part of the scope of work for this previous study is along the new pedestrian path alignment. The boring log and associated laboratory testing is included the Exploration Results section of this report.

Maps showing the site and boring locations are shown in the Site Location and Exploration

Plan sections, respectively. The results of the laboratory testing performed on soil and bedrock samples obtained from the site during the field exploration are included on the boring logs and as separate graphs in the Exploration Results section of this report.

SITE CONDITIONS

The following description of site conditions is derived from our site visit in association with the field exploration and our review of publicly available geologic and topographic maps.

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Item Description

Parcel Information

The project site is located south of the intersection of Oak Grove Street and

Covenant Court in Timnath, Colorado. The approximate Latitude/Longitude of the center of the site is 40.49530°N/104.94971°W. See Site Location.

Existing

Improvements

The site is currently vacant land and pasture land surrounding the existing

Greeley Number 2 Canal.

Current Ground

Cover The site is covered with native grasses and weeds.

Existing Topography The site is relatively flat with some rolling hills, total elevation change across the site is approximately 15 feet.

PROJECT DESCRIPTION

Our final understanding of the project conditions is as follows:

Item Description

Information Provided Terracon was provided a KMZ file displaying the new location of the proposed pedestrian bridge location from Tom Kent, P.E. with AVI, PC on June 1, 2021.

Project Description We understand the project includes the construction of a new pedestrian trail and a pedestrian bridge over the existing canal.

Proposed

Construction

We anticipate the pedestrian trail will consist of rigid (concrete) pavement and the bridge will likely be constructed on a helical pile or micropile foundation system.

Maximum Loads

(assumed)

■ Columns: 20 to 50 kips

■ Slabs: 150 pounds per square foot (psf)

Grading/Slopes We anticipate minor cuts and fills on the order of 5 feet or less will be required to achieve proposed grades.

If project information or assumptions vary from what is described above or if location of construction changes, we should be contacted as soon as possible to confirm and/or modify our recommendations accordingly.

GEOTECHNICAL CHARACTERIZATION

Subsurface Profile

We have developed a general characterization of the subsurface conditions based upon our review of the subsurface exploration, laboratory data, geologic setting and our understanding of the project. This characterization, termed GeoModel, forms the basis of our geotechnical calculations and evaluation of site preparation and foundation options. Conditions encountered at

Responsive ■ Resourceful ■ Reliable 3 each exploration point are indicated on the individual logs. The individual logs and the GeoModel can be found in the Exploration Results section this report.

As part of our analyses, we identified the following model layers within the subsurface profile. For a more detailed view of the model layer depths at each boring location, refer to the GeoModel.

Model Layer Layer Name General Description Approximate Depth to

Bottom of Stratum

1 Fill

Fill possibly consisting of sugar beet waste interlayered with silt and clayey sand, tan to light brown, very loose to loose density to stiff consistency.

About 4 feet below existing site grades.

2 Sand

Poorly graded sand with silt and gravel to silty sand with gravel, dark brown to light brown to orange brown, very loose to medium dense.

About 14 to 17 feet below existing site grades.

3 Clayey Sand Clayey sand with varying amounts of gravel, orange to brown, very loose to loose, trace FeOx.

About 10 feet below existing site grades.

4 Clay Lean to fat sandy lean clay, light brown to brown, medium stiff to stiff, trace gravel.

About 5 to 8 feet below existing site grades.

5 Bedrock

Claystone to sandstone to siltstone bedrock, dark gray to light brown to orange brown to tan and orange, weathered to very hard.

To the maximum depth of exploration of about 25 feet.

As noted in General Comments, this characterization is based upon widely spaced exploration points across the site and variations are likely.

Groundwater Conditions

The boreholes were observed while drilling and shortly after completion for the presence and level of groundwater. The water levels observed in the boreholes are noted on the attached boring logs, and are summarized below:

Boring Number Depth to Groundwater

While Drilling, ft.

Depth to Groundwater

After Drilling, ft.

Elevation of

Groundwater After

Drilling, ft.

B-1 5 4.3 4,808.7

B-2 11 9.5 4,802.5

B-3 7 4.1 4,807.9

B-4 4 3.8 4,806.2

6 8 7.2 4,806.8

These observations represent short-term groundwater conditions at the time of and shortly after

Responsive ■ Resourceful ■ Reliable 4 the field exploration and may not be indicative of other times or at other locations. Groundwater levels can be expected to fluctuate with varying seasonal and weather conditions, and other factors.

Groundwater level fluctuations occur due to seasonal variations in the water levels present in nearby water features, amount of rainfall, runoff and other factors not evident at the time the borings were performed. Therefore, groundwater levels during construction or at other times in the life of the structures may be higher or lower than the levels indicated on the boring logs. The possibility of groundwater level fluctuations should be considered when developing the design and construction plans for the project.

Fluctuations in groundwater levels can best be determined by implementation of a groundwater monitoring plan. Such a plan would include installation of groundwater piezometers, and periodic measurement of groundwater levels over a sufficient period of time.

Laboratory Testing

Representative soil samples were selected for swell-consolidation testing and exhibited 0.1 percent compression to 0.1 percent swell when wetted. Three samples of clay soils and bedrock exhibited unconfined compressive strengths ranging from approximately 1,200 to 3,500 pounds per square foot (psf). Samples of site soils and bedrock selected for plasticity testing exhibited non-plastic to high plasticity with liquid limits ranging from non-plastic to 59 and plasticity indices ranging from non-plastic to 40. Laboratory test results are presented in the Exploration Results section of this report.

GEOTECHNICAL OVERVIEW

Based on subsurface conditions encountered in the borings, the site appears suitable for the proposed construction from a geotechnical point of view provided certain precautions and design and construction recommendations described in this report are followed. We have identified several geotechnical conditions that could impact design, construction and performance of the proposed structures and other site improvements. These included existing, undocumented fill, shallow groundwater, and potentially loose, low strength sand soils. These conditions will require particular attention in project planning, design and during construction and are discussed in greater detail in the following sections.

Existing, Undocumented Fill

As previously noted, existing, undocumented fill was encountered to a depth up to about 4 feet in the borings drilled at the proposed bridge crossing and along the pedestrian path alignment on the site. We believe the existing fill could possibly contain significant amounts of sugar beet waste.

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Existing fill could exist at other locations on the site and extend to greater depths. We do not possess any information regarding whether the fill was placed under the observation of a geotechnical engineer. Undocumented fill can present a greater than normal risk of post-construction movement of foundations and other site improvements supported on or above these materials. Where the existing fill is present below the proposed trail concrete flatwork, we recommend over-excavating the fill materials to a depth of 2 feet below the bottom of the concrete.

The subgrade soil at the base of the over-excavation should be sacrificed, moisture conditioned and compacter prior to placement of over-excavation backfill. If over-excavated soils contain significant amounts of potential sugar beet waste materials, we recommend imported clean soils or utilizing clean soils from other areas of the site as over-excavation backfill below concrete trail flatwork.

Shallow Groundwater

As previously stated, shallow groundwater was measured at depths ranging from about 3 to 9 feet below existing site grades. Terracon recommends maintaining a separation of at least 3 feet between the bottom of proposed concrete trail and measured groundwater levels. It is also possible and likely that groundwater levels below this site may rise as water levels in the Greeley

Number 2 Canal rise. Final site grading should be planned and designed to avoid cuts where shallow groundwater is known to exist, and also in areas where such grading would create shallow groundwater conditions. If deeper cuts are unavoidable, temporary construction dewatering and/or installation of a subsurface drainage system may be needed.

Low Strength Soils

Loose sand soils were encountered at depth near groundwater elevation and within the upper approximately 5 to 10 feet and of the borings completed at this site. These materials can be susceptible to disturbance and loss of strength under repeated construction traffic loads and unstable conditions could develop. Stabilization of loose or soft soils may be required at some locations to provide adequate support for construction equipment and proposed structures.

Terracon should be contacted if these conditions are encountered to observe the conditions exposed and to provide guidance regarding stabilization (if needed).

Foundation and Floor System Recommendations

The proposed bridge can be supported by a micropile or helical pile foundation system. Design recommendations for foundations for the proposed structure and related structural elements are presented in the Deep Foundations section of this report paragraphs.

The General Comments section provides an understanding of the report limitations.

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EARTHWORK

The following presents recommendations for site preparation, excavation, subgrade preparation, fill materials, compaction requirements, utility trench backfill, grading and drainage and exterior slab design and construction. Earthwork on the project should be observed and evaluated by

Terracon. Evaluation of earthwork should include observation and/or testing of over-excavation, removal of existing fill, subgrade preparation, placement of engineered fills, subgrade stabilization and other geotechnical conditions exposed during the construction of the project.

Site Preparation

Prior to placing any fill, strip and remove existing vegetation, topsoil, and any other deleterious materials from the proposed construction areas. As previously stated, we also recommend over-excavation where the existing fill is present below the proposed trail concrete flatwork, we recommend over-excavating the fill materials to a depth of 2 feet below the bottom of the concrete.

The subgrade soil at the base of the over-excavation should be sacrificed, moisture conditioned and compacter prior to placement of over-excavation backfill. If over-excavated soils contain significant amounts of potential sugar beet waste materials, we recommend imported clean soils or utilizing clean soils from other areas of the site as over-excavation backfill below concrete trail flatwork.

Stripped organic materials should be wasted from the site or used to re-vegetate landscaped areas or exposed slopes after completion of grading operations. Prior to the placement of fills, the site should be graded to create a relatively level surface to receive fill, and to provide for a relatively uniform thickness of fill beneath proposed structures.

Excavation

It is anticipated that excavations for the proposed construction can be accomplished with conventional earthmoving equipment. Excavations into the on-site soils will encounter weak and/or saturated soil conditions with possible caving conditions.

The soils to be excavated can vary significantly across the site as their classifications are based solely on the materials encountered in widely-spaced exploratory test borings. The contractor should verify that similar conditions exist throughout the proposed area of excavation. If different subsurface conditions are encountered at the time of construction, the actual conditions should be evaluated to determine any excavation modifications necessary to maintain safe conditions.

Although evidence of underground facilities such as grease pits, septic tanks, vaults, basements, and utilities was not observed during the site reconnaissance, such features could be encountered during construction. If unexpected underground facilities are encountered, such features should be removed, and the excavation thoroughly cleaned prior to backfill placement and/or construction.

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Any over-excavation of the existing fill materials that extends below the bottom of the concrete trail flatwork should extend laterally beyond all edges of the concrete at least 8 inches per foot of over-excavation depth below the concrete trail. The over-excavation should be backfilled to the trail subgrade elevation in accordance with the recommendations presented in this report.

Depending upon depth of excavation and seasonal conditions, surface water infiltration and/or groundwater may be encountered in excavations on the site. It is anticipated that pumping from sumps may be utilized to control water within excavations.

The subgrade soil conditions should be evaluated during the excavation process and the stability of the soils determined at that time by the contractors’ Competent Person. Slope inclinations flatter than the OSHA maximum values may have to be used. The individual contractor(s) should be made responsible for designing and constructing stable, temporary excavations as required to maintain stability of both the excavation sides and bottom. All excavations should be sloped or shored in the interest of safety following local, and federal regulations, including current OSHA excavation and trench safety standards.

As a safety measure, it is recommended that all vehicles and soil piles be kept a minimum lateral distance from the crest of the slope equal to the slope height. The exposed slope face should be protected against the elements

Subgrade Preparation

After the undocumented existing fill and vegetative layer has been removed from the construction area, the top 12 inches of the exposed ground surface should be scarified, moisture conditioned, and recompacted to at least 95 percent of the maximum dry unit weight as determined by ASTM

D698 before any new fill, foundation or flatwork is placed.

After the bottom of the excavation has been compacted, engineered fill can be placed to bring the flatwork subgrade to the desired grade. Engineered fill should be placed in accordance with the recommendations presented in subsequent sections of this report.

The stability of the subgrade may be affected by precipitation, repetitive construction traffic or other factors. If unstable conditions develop, workability may be improved by scarifying and drying. Alternatively, over-excavation of wet zones and replacement with granular materials may be used, or crushed gravel and/or rock can be tracked or “crowded” into the unstable surface soil until a stable working surface is attained. Use of fly ash, cement or geotextiles could also be considered as a stabilization technique. Laboratory evaluation is recommended to determine the effect of chemical stabilization on subgrade soils prior to construction, particularly because soils containing significant amounts of potential sugar beet waste are known to contain significant amounts of water-soluble sulfates which can have an adverse reaction with chemical treatment agents. Lightweight excavation equipment may also be used to reduce subgrade pumping.

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Fill Materials

The on-site soils free of significant amounts of potential sugar beet waste or approved granular and low plasticity cohesive imported materials may be used as fill material. Bedrock excavated during site development (if any) and construction can be reused as fill provided the material is broken down and thoroughly processed to a “soil-like” consistency, with no particles greater than 2 inches in size. The earthwork contractor should expect significant mechanical processing and moisture conditioning of the site soils and/or bedrock will be needed to achieve proper compaction

Imported soils (if required) should meet the following material property requirements:

Gradation Percent finer by weight (ASTM C136)

4” 100

3” 70-100

No. 4 Sieve 30-100

No. 200 Sieve 60 (max.)

Soil Properties Values

Liquid Limit 35 (max.)

Plasticity Index 15 (max.)

Other import fill materials types may be suitable for use on the site depending upon proposed application and location on the site, and could be tested and approved for use on a case-by-case basis.

Compaction Requirements

Engineered fill should be placed and compacted in horizontal lifts, using equipment and procedures that will produce recommended moisture contents and densities throughout the lift.

Fill lift thickness

9 inches or less in loose thickness when heavy, self-propelled compaction equipment is used

4 to 6 inches in loose thickness when hand-guided equipment (i.e. jumping jack or plate compactor) is used

Minimum compaction requirements 95 percent of the maximum dry unit weight as determined by

ASTM D698

Moisture content cohesive soil (clay) -1 to +3 % of the optimum moisture content

Moisture content cohesionless soil

(sand) -3 to +3 % of the optimum moisture content

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1. We recommend engineered fill be tested for moisture content and compaction during placement. Should the results of the in-place density tests indicate the specified moisture or compaction limits have not been met, the area represented by the test should be reworked and retested as required until the specified moisture and compaction requirements are achieved.

2. Specifically, moisture levels should be maintained low enough to allow for satisfactory compaction to be achieved without the fill material pumping when proof rolled.

3. Moisture conditioned clay materials should not be allowed to dry out. A loss of moisture within these materials could result in an increase in the material’s expansive potential. Subsequent wetting of these materials could result in undesirable movement.

Utility Trench Backfill

All trench excavations (if any) should be made with sufficient working space to permit construction including backfill placement and compaction.

All underground piping within or near the proposed structures (if any) should be designed with flexible couplings, so minor deviations in alignment do not result in breakage or distress. It is imperative that utility trenches be properly backfilled with relatively clean materials. If utility trenches are backfilled with relatively clean granular material, they should be capped with at least

18 inches of cohesive fill in non-pavement areas to reduce the infiltration and conveyance of surface water through the trench backfill.

It is strongly recommended that a representative of Terracon provide full-time observation and compaction testing of trench backfill within the bridge and flatwork areas.

Grading and Drainage

Grades must be adjusted to provide effective drainage away from the proposed pedestrian bridge and associated concrete flatwork during construction and maintained throughout the life of the proposed project. Infiltration of water into foundation excavations must be prevented during construction. Landscape irrigation adjacent to foundations (if any) should be minimized or eliminated. As a result, any estimations of potential movement described in this report cannot be relied upon if positive drainage is not obtained and maintained, and water is allowed to infiltrate the fill and/or subgrade.

Flatwork will be subject to post-construction movement. Maximum grades practical should be used for flatwork to prevent areas where water can pond. In addition, allowances in final grades should take into consideration post-construction movement of flatwork, particularly if such movement would be critical. Where flatwork abuts the bridge abutments, care should be taken that joints are properly sealed and maintained to prevent the infiltration of surface water.

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Exterior Slab Design and Construction

Exterior slabs on-grade, exterior architectural features, and utilities founded on, or in backfill or the site soils will likely experience some movement due to the volume change of the material.

Potential movement could be reduced by:

◼ Minimizing moisture increases in the backfill;

◼ Controlling moisture-density during placement of the backfill;

◼ Using designs which allow vertical movement between the exterior features and adjoining structural elements; and

◼ Placing control joints on relatively close centers.

Construction Observation and Testing

The earthwork efforts should be monitored under the direction of Terracon. Monitoring should include documentation of adequate removal of vegetation and topsoil, proof rolling, and mitigation of areas delineated by the proof roll to require mitigation. Each lift of compacted fill should be tested, evaluated, and reworked as necessary until approved by Terracon prior to placement of additional lifts.

In areas of foundation excavations, the bearing subgrade and exposed conditions at the base of the recommended fill removal should be evaluated under the direction of Terracon. In the event that unanticipated conditions are encountered, Terracon should prescribe mitigation options.

In addition to the documentation of the essential parameters necessary for construction, the continuation of Terracon into the construction phase of the project provides the continuity to maintain Terracon’s evaluation of subsurface conditions, including assessing variations and associated design changes.

DEEP FOUNDATIONS

Helical Pile Foundations

We believe helical piles bottomed in bedrock are appropriate for support of the proposed pedestrian bridge.

We do not recommend using vertically installed helical piles to resist lateral loads without approved lateral load test data, as these types of foundations are typically designed to resist axial loads. Only the horizontal component of the allowable axial load should be considered to resist the lateral loading and only in the direction of the batter. Terracon should be retained to observe

Responsive ■ Resourceful ■ Reliable 11 helical pile installation to verify that proper bearing materials have been encountered during installation.

In accordance with local building code requirements, a load test should be performed by the helical pile installer to validate achieving the allowable design load. Load tests should be performed using helical piles consistent in size and materials with those piles planned for use during construction. Similarly, the same installation techniques and equipment planned for use during installation of production piles should be used when installing piles for load testing.

If a helical pile foundation system is selected by the project team, we recommend the helical pile designer follow the recommendations presented in Chapter 18 of the applicable International

Building Code (IBC). We recommend the helical bearing plates for each helical pile bear in the claystone bedrock encountered below the site. We do not recommend helical bearing plates bottomed in native clay soils. The helical pile designer should select the size and number of helical bearing plates for each helical pile based on planned loads and bearing materials described in our exploratory boring logs. Torque measurements during installation of helical piles should be used to verify the axial capacity of the helical piles. Terracon should be provided with the torque to capacity relationships for each type of pile used on the project for our review and comment prior to mobilization to the site. We recommend the helical pile installation contractor provide confirmation that the installation equipment has been calibrated within one year of installation at this project. The helical foundations should be installed by a qualified specialty contractor per the manufacturer’s recommendations.

Micropile – Design Recommendations

As an alternative, we believe the proposed pedestrian bridge can be supported on a micropile foundation system. A micropile is a small diameter (typically less than 12 inches), drilled, and grouted pile that is usually heavily reinforced. A micropile is constructed by drilling a borehole, placing reinforcement, and grouting the hole using gravity, pressure, or post-grouting techniques.

Reinforcement is typically high-capacity steel bars, permanent casing, or a combination of both.

High axial load capacities are possible in both compression and tension because the steel elements are used to resist most or all of the applied load. Specialized grouting methods allow for high grout to soil bond values along the bond zone. A 4-inch void should be placed below all pile caps, between each of the micropiles.

Micropiles are often advantageous in difficult drilling and access-restrictive environments. Drilling equipment is similar to that used to install ground anchors and can penetrate most obstructions.

The above descriptions and following design recommendations are based on the Federal

Highway Administration’s (FHWA), Micropile Design and Construction: Reference Manual, dated

December 2005. The following are geotechnical recommendations for micropile design and

Responsive ■ Resourceful ■ Reliable 12 construction. The capacities of micropiles are highly dependent on each contractor’s specific means and methods. Therefore, the most effective design is one that is tailored to the contractor doing the installation. We recommend the final micropile design, including micropile capacities and related criteria, be reviewed by Terracon prior to implementation.

Axial Pile Capacity

The axial capacity of a micropile in both compression and tension is primarily dependent on the structural capacity of the pile elements, the grout to soil bond strength within the bond zone, and the length of the bond zone. The end bearing contribution of the pile is negligible and should be neglected. The actual bond length is dependent on the capacity desired from each pile and soil/bedrock types present within the bond zone.

The exploration program completed for this project encountered claystone bedrock at depths of about 9½ to 17 feet below existing site grades. Bedrock depths could be greater or less than those indicated in this report.

We have developed rock to grout bond values for use in micropile design for the bedrock encountered on the site. These values have been developed for Type A grouted micropiles, as defined by the referenced FHWA manual. Type A micropile grouting involves placing the grout in one continuous operation from the bottom of the boring with a tremie pipe until grout of similar quality to that being injected is freely flowing from the mouth of the borehole. No excess pressure is applied. The casing would be installed into bedrock to provide physical protection for the bar and grout during installation through the existing fill materials and to prevent the borehole form caving. The casing would also provide a larger bond/anchor area for transfer of loads from the micropile foundation elements. Design recommendations for the micropiles are presented below.

Description Value

Bond zone Claystone bedrock

Grout-to ground bond ultimate strength 1 50 psi

Anticipated hole diameter 9 5/8 inches

Casing (anticipated) 9 5/8 inches, N-80 casing; 0.472-inch wall minimum

Minimum embedment depth into bedrock 10 feet

Void thickness (beneath surficial foundation elements) 4 inches

1. The estimated grout to ground ultimate bond strength should not be applied for the soils above bedrock of each micropile.

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Pile Load Testing

Prior to production drilling, we recommend at least two (2) micropiles (one at each abutment) be installed in representative locations at the site for the purpose of verification testing. The purpose of the verification tests is to confirm that the contractor’s equipment and installation methods are capable of producing the ultimate grout to soil bond values assumed during the design. The verification micropile should be tested to 2 times the design load and should be suitably reinforced to resist such loading.

The referenced FHWA manual recommends that about 5 percent of permanent production micropiles be proof tested to 1.6 times the design load. The purpose of the proof tests will be to confirm adequate and consistent installation by the contractor and that the production piles will carry the required design loads without excessive, long-term deflections. Micropile load testing methods and procedures, and load test set up and instrumentation, should be completed in accordance with Sections 7.3 and 7.4 of the referenced FHWA manual. Terracon is available to aid in the development of load testing specifications. The locations of the verification and proof tests should be chosen by the engineer in concert with the contractor to ensure that the contractor’s testing equipment can be installed at the desire locations. In order to document consistent installation between the tested and untested micropiles, we recommend Terracon monitor all micropile installation and testing.

SEISMIC CONSIDERATIONS

The seismic design requirements for buildings and other structures are based on Seismic Design

Category. Site Classification is required to determine the Seismic Design Category for a structure.

The Site Classification is based on the upper 100 feet of the site profile defined by a weighted average value of either shear wave velocity, standard penetration resistance, or undrained shear strength in accordance with Section 20.4 of ASCE 7 and the International Building Code (IBC).

Based on the soil/bedrock properties encountered at the site and as described on the exploration logs and results, it is our professional opinion that the Seismic Site Classification is D.

Subsurface explorations at this site were extended to a maximum depth of 25 feet. The site properties below the boring depth to 100 feet were estimated based on our experience and knowledge of geologic conditions of the general area. Additional deeper borings or geophysical testing may be performed to confirm the conditions below the current boring depth.

BELOW-GRADE STRUCTURES

Lateral Earth Pressures

Below-grade structures or reinforced concrete walls with unbalanced backfill levels on opposite sides should be designed for earth pressures at least equal to those indicated in the following

Responsive ■ Resourceful ■ Reliable 14 table. Earth pressures will be influenced by structural design of the walls, conditions of wall restraint, methods of construction and/or compaction and the strength of the materials being restrained. Two wall restraint conditions are shown. Active earth pressure is commonly used for design of free-standing cantilever retaining walls and assumes wall movement. The "at-rest" condition assumes no wall movement. The recommended design lateral earth pressures do not include a factor of safety and do not provide for possible hydrostatic pressure on the walls.

Earth Pressure Coefficients

Earth Pressure

Conditions

Coefficient for

Backfill Type

Equivalent Fluid

Density (pcf)

Surcharge

Pressure, p1 (psf)

Earth Pressure, p2 (psf)

Active (Ka) Granular - 0.28

Lean Clay - 0.49

(0.28)S

(0.49)S

(35)H

(60)H

At-Rest (Ko) Granular - 0.44

Lean Clay - 0.66

(0.44)S

(0.66)S

(55)H

(80)H

Passive (Kp) Granular – 3.5

Lean Clay – 2.0

Applicable conditions to the above include:

■ For active earth pressure, wall must rotate about base, with top lateral movements of about

0.002 H to 0.004 H, where H is wall height

■ For passive earth pressure to develop, wall must move horizontally to mobilize resistance

■ Uniform surcharge, where S is surcharge pressure

■ In-situ soil backfill weight a maximum of 120 for clay soils and 125 for granular soils pcf

■ Horizontal backfill, compacted between 95 and 98 percent of standard Proctor maximum dry density

■ Loading from heavy compaction equipment not included

■ No hydrostatic pressures acting on wall

■ No dynamic loading

■ No safety factor included

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■ Ignore passive pressure in frost zone

Backfill placed against structures should consist of granular soils or low plasticity cohesive soils.

For the granular values to be valid, the granular backfill must extend out and up from the base of the wall at an angle of at least 45 and 60 degrees from vertical for the active and passive cases, respectively.

FLATWORK

Flatwork – Subgrade Preparation

On most project sites, the site grading is accomplished relatively early in the construction phase.

Fills are typically placed and compacted in a uniform manner. However, as construction proceeds, the subgrade may be disturbed due to utility excavations, construction traffic, desiccation, or rainfall/snow melt. As a result, the flatwork subgrade may not be suitable for construction and corrective action will be required. The subgrade should be carefully evaluated at the time of flatwork construction for signs of disturbance or instability. We recommend the flatwork subgrade be thoroughly proof rolled with a loaded tandem-axle dump truck prior to final grading and placement. All flatwork areas should be moisture conditioned and properly compacted to the recommendations in this report immediately prior to paving. As previously stated, we also recommend over-excavation where the existing fill is present below the proposed trail concrete flatwork, we recommend over-excavating the fill materials to a depth of 2 feet below the bottom of the concrete.

Flatwork – Design Recommendations

Recommended minimum flatwork sections are provided in the table below.

Recommended Flatwork Thicknesses (Inches)

Location Portland Cement Concrete

Along proposed trail alignment 6

Concrete should be produced from an approved mix design with the following minimum properties:

Properties Value

Compressive strength 4,000 psi

Cement type Type I or II portland cement

Entrained air content (%) 5 to 8

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Properties Value

Concrete aggregate ASTM C33 and CDOT section 703

Concrete should be deposited by truck mixers or agitators and placed a maximum of 90 minutes from the time the water is added to the mix. Longitudinal and transverse joints should be provided as needed in concrete flatwork for expansion/contraction and isolation per ACI 325. The location and extent of joints should be based upon the final pavement geometry. Joints should be sealed to prevent entry of foreign material and doweled where necessary for load transfer.

Flatwork performance is affected by its surroundings. In addition to providing preventive maintenance, the civil engineer should consider the following recommendations in the design and layout of flatwork:

■ Site grades should slope a minimum of 2 percent away from the flatwork;

■ The subgrade and the flatwork surface have a minimum 2 percent slope to promote proper surface drainage;

■ Consider appropriate edge drainage and flatwork under drain systems;

■ Install flatwork drainage surrounding areas anticipated for frequent wetting;

■ Install joint sealant and seal cracks immediately; and

■ Seal all landscaped areas in, or adjacent to flatwork to reduce moisture migration to subgrade soils.

CORROSIVITY

Results of water-soluble sulfate testing indicate Exposure Class S0 according to ACI 318. ASTM

Type I or II, portland cement should be specified for all project concrete on and below grade.

Foundation concrete should be designed for low sulfate exposure in accordance with the provisions of the ACI Design Manual, Section 318, Chapter 4.

Terracon was requested to perform laboratory testing on soil and bedrock samples collected from the site to determine the potential corrosive characteristics of the on-site soils and bedrock with respect to contact with the various underground materials that will be used for project construction. Laboratory test results for select samples tested exhibited the following properties:

Sample

Identification

Water-soluble

Sulfate

Redox

Potential Sulfide

Water-soluble

Chloride

Electrical

Resistivity pH

(%) (mV) (Presence)

(%) (ohm-cm)

B-1 at 14 feet 0.871 +345 Nil 0.0044 583 8.10

B-4 at 2 feet 0.0437 -- -- -- -- --

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Sample

Identification

Water-soluble

Sulfate

Redox

Potential Sulfide

Water-soluble

Chloride

Electrical

Resistivity pH

(%) (mV) (Presence)

(%) (ohm-cm)

1. Resistivity determined on saturated samples.

2. Nil representing not detectible.

Terracon recommends providing the laboratory test results regarding potential corrosive characteristics of the on-site soils and bedrock materials encountered below this site to a corrosion specialist to interpret the data and incorporate the test results into the design and selection of helical or micropile foundations.

GENERAL COMMENTS

Our analysis and opinions are based upon our understanding of the project, the geotechnical conditions in the area, and the data obtained from our site exploration. Natural variations will occur between exploration point locations or due to the modifying effects of construction or weather.

The nature and extent of such variations may not become evident until during or after construction.

Terracon should be retained as the Geotechnical Engineer, where noted in this report, to provide observation and testing services during pertinent construction phases. If variations appear, we can provide further evaluation and supplemental recommendations. If variations are noted in the absence of our observation and testing services on-site, we should be immediately notified so that we can provide evaluation and supplemental recommendations.

Our Scope of Services does not include either specifically or by implication any environmental or biological (e.g., mold, fungi, bacteria) assessment of the site or identification or prevention of pollutants, hazardous materials or conditions. If the owner is concerned about the potential for such contamination or pollution, other studies should be undertaken.

Our services and any correspondence or collaboration through this system are intended for the sole benefit and exclusive use of our client for specific application to the project discussed and are accomplished in accordance with generally accepted geotechnical engineering practices with no third-party beneficiaries intended. Any third-party access to services or correspondence is solely for information purposes to support the services provided by Terracon to our client.

Reliance upon the services and any work product is limited to our client, and is not intended for third parties. Any use or reliance of the provided information by third parties is done solely at their own risk. No warranties, either express or implied, are intended or made.

Site characteristics as provided are for design purposes and not to estimate excavation cost. Any use of our report in that regard is done at the sole risk of the excavating cost estimator as there may be variations on the site that are not apparent in the data that could significantly impact

Responsive ■ Resourceful ■ Reliable 18 excavation cost. Any parties charged with estimating excavation costs should seek their own site characterization for specific purposes to obtain the specific level of detail necessary for costing.

Site safety, and cost estimating including, excavation support, and dewatering requirements/design are the responsibility of others. If changes in the nature, design, or location of the project are planned, our conclusions and recommendations shall not be considered valid unless we review the changes and either verify or modify our conclusions in writing.

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ATTACHMENTS

Contents:

EXPLORATION AND TESTING PROCEDURES

SITE LOCATION AND EXPLORATION PLANS

Note: Refer to each individual Attachment for a listing of contents.

Responsive ■ Resourceful ■ Reliable EXPLORATION AND TESTING PROCEDURES 1 of 2

EXPLORATION AND TESTING PROCEDURES

Field Exploration

The…