A06_Project_Specs_GEO_Engineering_Report_Attachmnet_4.pdf

Report Cover Page

Mammoth Cave - Heritage Trail and Sand Cave Trail Geotechnical Engineering Report

Prepared for:

VHB Inc.

351 McLaw Circle Ste. 3

Williamsburg, VA 23185

611 Lunken Park Drive

Cincinnati, Ohio 45226

P (513) 321-5816

Terracon.com

Facilities | Environmental | Geotechnical | Materials

Report Cover Letter to Sign

August 1, 2023

VHB Inc.

351 McLaw Circle Ste. 3 Williamsburg, VA 23185

Attn: Vikrant Desai P: 757.279.2832 E: vdesai@vhb.com

Re: Geotechnical Engineering Report Mammoth Cave - Heritage Trail and Sand Cave Trail Mammoth Cave National Park Cave City, Edmonson County, Kentucky Terracon Project No. N1225082

Dear Mr. Desai:

We have completed the scope of Geotechnical Engineering services for the above-referenced project in general accordance with Task Order 140P5221F0045 executed on April 1, 2022. This report presents the findings of the subsurface exploration and provides geotechnical recommendations concerning earthwork and the design and construction of foundations and retaining walls for the proposed project.

We appreciate the opportunity to be of service to you on this project. If you have any questions concerning this report or if we may be of further service, please contact us.

Sincerely, Terracon

S. Taylor Taluskie, P.E. Jeffery D. Dunlap, P.E.

Group Manager Senior Associate – Group Manager

Geotechnical Engineering Report

Mammoth Cave - Heritage Trail and Sand Cave Trail | Cave City, Edmonson County, Kentucky

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Table of Contents Introduction Project Description Site Conditions Geotechnical Characterization

Groundwater conditions Geologic Hazards Seismic Site Class Geotechnical Overview Earthwork

Site Preparation Subgrade Preparation Fill Material Types Fill Placement and Compaction Requirements Earthwork Construction Considerations Construction Observation and Testing

Shallow Foundations Design Parameters – Compressive Loads Design Parameters – Overturning and Uplift Loads Foundation Construction Considerations

Lateral Earth Pressures Design Parameters Subsurface Drainage for Below-Grade Walls

Pavements Pavement Subgrade Support Characteristics General Pavement Comments Pavement Drainage Pavement Maintenance

General Comments

Figures GeoModel Kentucky Geological Survey - Karst Potential Map

Attachments

Exploration and Testing Procedures Site Location and Exploration Plans Exploration and Laboratory Results Supporting Information

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Note: This report was originally delivered in a web-based format. Blue 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 logo will bring you back to this page. For more interactive features, please view your project online at client.terracon.com.

Refer to each individual Attachment for a listing of contents.

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Introduction

This report presents the results of our subsurface exploration and Geotechnical Engineering services performed for the proposed improvements to the Mammoth Cave Hotel, Heritage Trail, and Sand Cave Trail located at Mammoth Cave National Park in Cave City, Edmonson County, Kentucky. The purpose of these services was to provide information and geotechnical engineering recommendations relative to:

Subsurface soil and rock conditions

Groundwater conditions

Seismic site classification per IBC

Site preparation and earthwork

Foundation design and construction

Lateral earth pressure

The geotechnical engineering Scope of Services for this project included the advancement of a test boring, the advancement of hand auger and Dynamic Cone Penetrometer (DCP) soundings, geophysical surveys, laboratory testing, engineering analysis, and preparation of this report.

Drawings showing the site and boring locations are shown on the Site Location and Exploration Plan, respectively. The results of the laboratory testing performed on soil samples obtained from the site during our field exploration are included on the boring logs and/or as separate graphs in the Exploration Results section.

Project Description

Our initial understanding of the project was provided in our proposal and was discussed during project planning. A period of collaboration has transpired since the project was initiated, and our final understanding of the project conditions is as follows:

Terracon’s original scope included the design of segmental retaining walls. The design team decided that concrete cantilever walls were the preferred approach, and the segmental wall design portion was removed from our scope in an updated Task Order executed on April 4, 2023.

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Item Description

Information Provided

Our understanding of the project as described in the NPS IDIQ Task Order (April 4, 2023), 100% Draft Concept Documents (VHB, May 2023), and various email and phone correspondence with VHB.

Project Description

The proposed project includes the following:

Improvements to the Mammoth Cave Hotel concrete patio. A new concrete patio south of the pedestrian bridge connecting the hotel to the Visitor Center. The patio will be partially supported by a new cantilever retaining wall and a partially elevated structural slab. A new pedestrian bridge connecting a new outdoor classroom area and the Heritage Trail. The outdoor classroom will also include a cantilever retaining wall.

Improvements to the Heritage trail include a new boardwalk and two new overlooks.

Improvement to the Sand Cave Trail includes a new boardwalk and a new overlook on top of an exposed rock face.

Proposed Structures

The new hotel patio will be partially slab-on-grade and partially an elevated structural slab with a new cantilever retaining wall.

The pedestrian bridge includes two equal spans for a total length of about 47 feet. Piers are planned to support the bridge between spans.

The proposed boardwalks and overlooks will be supported by timber columns.

Maximum Loads

Maximum loading conditions have not been provided as of the date of this report. Based on experience with similar structures, we anticipated loadings on the following loading conditions in our analyses. We respectfully request that the loading conditions be confirmed before construction.

Patio Slab: 150 psf

Patio Columns: 15 kips

Pedestrian Bridge Abutment/Piers: 250 kips

Boardwalk Column:5 kips

Overlook Column: 10 kips

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Item Description

Grading/Slopes

Based on the provided grading plans, new fills will be required behind the proposed retaining walls. Other portions of the project will require limited earthwork. We understand that the trails and boardwalks are located in archeologically protected areas and cuts are limited

Free-Standing Retaining Walls

New retaining walls are required for the hotel patio and the new Outdoor Classroom. The walls will be concrete cantilevered retaining walls with decorative facing. Retaining wall design to be performed by others. Exposed retaining wall heights of less than 10 feet are anticipated.

Pavements

The hotel patio will be partially slab-on-grade. New pedestrian paths around the hotel will be slab-on-grade. Portions of the Heritage and Sand Cave trails will be paved with concrete.

Pavement design is to be performed by others.

Terracon should be notified if any of the above information is inconsistent with the planned construction as modifications to our recommendations may be necessary.

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.

Item Description

Parcel Information

Both sites are located within Mammoth Cave National Park near Cave City, Edmonson County, Kentucky. The Mammoth Cave Hotel and Heritage Trail are located at the address 171 Hotel Road. The Sand Cave Trailhead is off Old Mammoth Cave Road (KY 255) just east of the intersection with Park Ridge Road.

Hotel & Heritage Trail Latitude/Longitude: 37.1862° N, 86.1014° W

Sand Cave Trail Latitude/Longitude: 37.1527° N, 86.04769° W

See Site Location

Existing Improvements

The Mammoth Cave Hotel includes a restaurant and gift shop. A pedestrian bridge connects the hotel to the Visitor Center. The Heritage and Sand Cave Trails are unpaved.

Current Ground Cover

Various (concrete, grass, brush, wooden boardwalks, exposed earth, and wooded)

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Item Description

Existing Topography

There is a swale/ravine between the existing hotel and the existing Visitor Center, which the existing pedestrian bridge spans. A portion of the Heritage Trail follows the ridge of the swale and generally circles a pinnacle. Grades along the Heritage Trail range from about Elevation 722 feet to Elevation 735 feet, MSL.

The Sand Cave Trail generally goes down in topography toward the cave. Grades along the Sand Trail range from about Elevation 769 feet to Elevation 784 feet, MSL.

Existing topographical information is included in the provided 100% Draft Construction drawing.

Geology

According to USGS, both sites map within the Upper Mississippian-aged Rocks of Chesterian age, lower part, consisting of limestone and sandstone. According to the KGS, the majority of the area is the Big Clifty Sandstone Member, Golconda Formation. A small portion of the Sand Trail is the Haney Limestone Member, Golconda Formation. Areas adjacent to the sites are mapped as the Girkin Formation (very high karst potential).

Geotechnical Characterization

We have developed a general characterization of the subsurface conditions based on 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 the site. Conditions observed at each exploration point are indicated on the individual logs. The individual logs can be found in the Exploration Results and the GeoModel can be found in the Figures attachment of this report.

Model Layer

Layer Name General Description

1 Existing Fill Undocumented fill; lean to fat clay, brown.

Native

Overburden Lean clay, sandy lean, clay silty clay, clayey sand;

brown.

3 Bedrock Sandstone, slightly weathered.

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Groundwater conditions

No groundwater was observed at the exploration points while advancing or during the short amount of time the holes remained open upon completion. However, this does not necessarily mean that exploration terminated above stable groundwater levels. A relatively long period of time may be necessary for the groundwater level to develop and stabilize in a borehole in these materials. Long-term observations in piezometers or observation wells sealed from the influence of surface water are often required to define the field or in-situ groundwater level in materials of this type.

Groundwater level fluctuations occur due to seasonal variations in the 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 structure 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.

Geologic Hazards

The project site is in an area of significant karst potential. Karst Potential Maps by the Kentucky Geological Survey are included in the Figures section of this report. Karst is a distinctive landscape that commonly occurs where carbonate bedrock strata (i.e.

limestone and dolostone) are subjected to dissolution weathering by even slightly acidic surface and groundwater. Rainwater picks up carbon dioxide from the atmosphere and as it infiltrates down through the soil profile. The weathering is typified by a chemical solutioning process that progresses along joints, fractures and bedding planes in the bedrock.

This process often results in a highly irregular rock profile that contains deep weathered slots filled with soft soils. Voids are created as the bedrock dissolves and over time widened fractures, solution cavities, and caves form. This may progress to ground subsidence and/or sinkholes as soil overburden ravels into or is eroded by groundwater into the subsurface voids.

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Prediction of future subsidence or collapse is very difficult and even an extensive subsurface exploration cannot rule out the possibility of ground subsidence. As with any site underlain by a carbonate bedrock formation, karst activity is on-going and there is always the risk of future impact to ground-supported structures.

Auger refusal is defined as the depth below the ground surface at which a test boring can no longer be advanced with the soil drilling technique being used. In an area of uncontrolled fill, it is not uncommon to find boulders or large fragments of man-made debris in which the augers can refuse on. In an area of limestone bedrock, auger refusal can result on slabs of unweathered limestone suspended in the residual soil matrix ("floaters"), on rock "pinnacles" rising above the surrounding bedrock surface, in widened joints that may extend well below the surrounding bedrock surface, or on the upper surface of continuous bedrock. Several of these possible auger refusal conditions are illustrated in the adjacent figure.

Seismic Site Class

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 bedrock properties observed at the site and as described in the exploration logs and results, our professional opinion is that a Seismic Site Classification of B be considered for the project, provided that all foundations will be at least 10 feet from the top of bedrock.

This Seismic Site Classification is based on the shear wave velocity of the upper 100 feet. At Heritage Trail, the Multi-Channel Analysis of Surface Waves (MASW) data were considered in the evaluation to a depth of 100 feet at Lines 1, 2, and 3. The Sand Cave Trail site properties were estimated based on our experience and knowledge of the geologic conditions of the general area. Additional deeper borings or geophysical testing may be performed to confirm the conditions below the current boring depth.

Geotechnical Overview

The field exploration generally encountered native cohesive and cohesionless overburden soils over sandstone bedrock. Refusal or sandstone bedrock was encountered at depths ranging from about 1.4 to 5 feet below grades at the time of exploration. The majority of

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Facilities | Environmental | Geotechnical | Materials 7 the bedrock is mapped as the Big Clifty Sandstone Member, Golconda Formation, which is not mapped as having karst potential, but karst conditions could be encountered during construction or over the life of the structures, considering the caves at the Park.

The bedrock is mapped as the Haney Limestone Member, Golconda Formation, which is a limestone bedrock near Hand Auger/DCP Sounding S-2 at the Sandy Cave Trail site. The Hanely Limestone Member is mapped as having high karst potential.

Existing fill was encountered at Hand Auger/DCP soundings H-1 and H-2 to the refusal depths. We have not been provided records that this material was placed with engineering moisture and compaction controls and consider it to be undocumented.

Undocumented fill is not suitable for direct foundation support.

Due to archeological concerns at the site, we understand that grading for the trail projects will be limited. The deepest fills will be required around the hotel plaza and outdoor classroom areas, which will generally be supported by concrete cantilevered retaining walls.

The near-surface cohesive soils could become unstable with typical earthwork and construction traffic, especially after precipitation events. Effective drainage should be completed early in the construction sequence and maintained after construction to avoid potential issues. If possible, grading should be performed during the warmer and drier times of the year. If grading is performed during the winter and spring months, an increased risk for possible undercutting and replacement of unstable subgrade will persist until earthwork-related construction is complete. Additional site preparation recommendations, including subgrade improvement and fill placement, are provided in the Earthwork section.

Three Multi-Channel Analysis of Surface Waves (MASW) arrays were performed near the proposed pedestrian bridge and outdoor classroom. The results are included in the Exploration Results. The different seismic velocities, combined with the boring logs, were used to interpret the top of bedrock, changes in material/lithology, and potential karst features. In general, low-velocity zones (blue to green on the color scale) are indicative of overburden, clay seams, potential voids, and weathered/fractured rock.

Higher velocity zones (green to red on the color scale) are indicative of competent bedrock. The MASW lines display multiple indications of a weathered/karstic zone within the top of the bedrock. The interpreted anomalies consist of low-velocity zones surrounded by apparent bedrock that may represent clay or air-filled voids within the bedrock. Some features are consistent with caprock underlain by weathered zones or clay seams. Areas of completely to highly weathered bedrock should be anticipated across the project site.

Considering the relatively shallow depths of bedrock at the exploration points, we recommend that all structures be supported by spread footings bearing directly on competent, slightly weathered sandstone or limestone bedrock encountered at depths of

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1.4 to 5.4 feet below the existing ground surface. Supporting structure foundations on a combination of bedrock and soil will result in unacceptable differential settlement between foundations supported on competent bedrock and overburden soils. Typically valleys in the bedrock surface with clay fill is softer and disturbed than residual soils and would not provide adequate foundation support. The Shallow Foundations section addresses support of the pedestrian bridge and overlooks directly bearing on bedrock.

Retaining walls are also recommended to bear directly on competent bedrock.

Where foundations will be adjacent to an exposed rock face (at the overlook for the Sand Cave Trail, e.g.), the outer edge of the footing should be at least 10 feet from the edge of the rock face.

Parameters for the design of the concrete cantilever walls are included in the Lateral Earth Pressures section.

The recommendations contained in this report are based upon the results of field and laboratory testing (presented in the Exploration Results), engineering analyses, and our current understanding of the proposed project. The General Comments section provides an understanding of the report limitations.

Earthwork

Earthwork is anticipated to include demolition, clearing and grubbing, excavations, and engineered fill placement. The following sections provide recommendations for use in the preparation of specifications for the work. Recommendations include critical quality criteria, as necessary, to render the site in the state considered in our geotechnical engineering evaluation for foundations and retaining walls.

Site Preparation

Prior to placing new fill, existing vegetation, topsoil, and root mats should be removed.

Complete stripping of the topsoil should be performed in the proposed building and parking/driveway areas.

Mature trees are located within or near the footprint of some of the proposed buildings, which will require removal at the onset of construction. Tree root systems can remove substantial moisture from surrounding soils. Where trees are removed, the full root ball and all associated dry and desiccated soils should be removed. The soil materials which contain less than 5 percent organics can be reused as engineered fill provided the material is moisture conditioned and properly compacted.

Where fill is placed on existing slopes steeper than 5H:1V, benches should be cut into the existing slopes prior to fill placement. The benches should have a minimum vertical

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Facilities | Environmental | Geotechnical | Materials 9 face height of 1 foot and a maximum vertical face height of 3 feet and should be cut wide enough to accommodate the compaction equipment. This benching will help provide a positive bond between the fill and natural soils and reduce the possibility of failure along the fill/natural soil interface.

Subgrade Preparation

The subgrade should be proof-rolled with an adequately loaded vehicle such as a fully-loaded tandem-axle dump truck or other heaviest piece of construction equipment being used for construction. The proof-rolling should be performed under the observation of the Geotechnical Engineer or representative. Areas excessively deflecting under the proof-roll should be delineated and subsequently addressed by the Geotechnical Engineer. Excessively wet or dry material should either be removed or moisture conditioned and recompacted.

All exposed areas which will receive fill, once properly cleared and benched where necessary, should be scarified to a minimum depth of 10 inches, moisture conditioned as necessary, and compacted per the compaction requirements in this report. Compacted structural fill soils should then be placed to the proposed design grade and the moisture content and compaction of subgrade soils should be maintained until foundation or pavement construction.

Based upon the subsurface conditions determined from the geotechnical exploration, subgrade soils exposed during construction are anticipated to be relatively workable;

however, the workability of the subgrade may be affected by precipitation, repetitive construction traffic or other factors. If unworkable conditions develop, workability may be improved by scarifying and drying. Based on the soil conditions observed in the boring and hand auger/DCP probes, earthwork operations should be planned for the historically drier and warmer summer and fall months, if possible, to limit potential deeper undercuts due to higher amounts of precipitation and lower temperatures and shorter daytime hours which limit drying of soils above optimum moisture content.

Subgrade soils may consist of soft to medium stiff soils. If weak subgrade soil conditions are encountered during construction, the subgrade could be improved by undercutting the subgrade soils, aerating them (discing and aeration) and recompacting the soils, which may be feasible during periods of sunny and dry weather. Alternatively, weak subgrade soils could be improved by partially undercutting 1 to 2 feet below subgrade elevation and placing a triaxial geogrid and compacting DGA crushed stone to subgrade elevation or performing chemical modification using quick lime or lime kiln dust containing free lime.

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Fill Material Types

Fill required to achieve design grade should be classified as structural fill and general fill.

Structural fill is material used below, or within 10 feet of structures or constructed slopes. General fill is material used to achieve grades outside of these areas.

Reuse of On-Site Soil: Excavated on-site soil may be selectively reused as fill below pavement and landscaping areas. Moisture conditioning may be required for reuse.

Portions of the on-site soil have an elevated fines content and will be sensitive to moisture conditions (particularly during seasonally wet periods) and may not be suitable for reuse when above optimum moisture content.

Material property requirements for on-site soil for use as general fill and structural fill are noted in the table below:

Property General Fill Structural Fill

Composition Free of deleterious material

Maximum particle size

6 inches

(or 2/3 of the lift thickness)

3 inches

Fines content Not limited Not limited

Plasticity Not limited Maximum plasticity index of 25

GeoModel Layer

Expected to be Suitable1 1,2 1,2

1. Based on subsurface exploration. Actual material suitability should be determined in the field at the time of construction.

Imported Fill Materials: Imported fill materials should meet the following material property requirements. Regardless of its source, compacted fill should consist of approved materials that are free of organic matter and debris. Frozen material should not be used, and fill should not be placed on a frozen subgrade.

Soil Type 1 USCS Classification

Acceptable Parameters (for Structural Fill)

Low Plasticity Cohesive

CL, CL-ML

Liquid Limit (LL) less than or equal to 40 Plasticity index less than or equal to 25

Less than 25% retained on No. 200 sieve

High Plasticity Cohesive

CL(LL>40), CH Not recommended for use as structural fill

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Soil Type 1 USCS Classification

Acceptable Parameters (for Structural Fill)

Granular

GW, GM, GC,

SW, SM, SC, GW-

GM, GW-GC, SW-

SM, SW-SC

Less than 50% passing No. 200 sieve

Granular (Drainage Only)

GP, SP, SP-SM,

GP-SM

Less than 10% fines

Less than 5% fines to be considered free-draining

Structural and general fill should consist of approved materials free of organic matter and debris. Frozen material should not be used, and fill should not be placed on a frozen subgrade. A sample of each material type should be submitted to the Geotechnical Engineer for evaluation prior to use on this site.

Additional geotechnical consultation should be provided prior to the use of uniformly graded gravel on the site.

Fill Placement and Compaction Requirements

Structural and general fill should meet the following compaction requirements.

Item Structural Fill General Fill

Maximum Lift Thickness

8 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

Same as structural fill

Minimum Compaction

Requirements 1,2,3 98% of max. dry density

95% of max. dry density

Water Content

Range 1

Low plasticity cohesive: -2% to +3% of optimum

Granular: -3% to +3% of optimum

As required to achieve min.

compaction requirements

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Item Structural Fill General Fill

1. Maximum density and optimum water content as determined by the standard Proctor test (ASTM D 698).

2. High plasticity cohesive fill is not recommended for use as structural fill.

3. If the granular material is coarse sand or gravel, or of a uniform size, or has a low fines content, compaction comparison to relative density may be more appropriate. In this case, granular materials should be compacted to at least 70% relative density (ASTM D 4253 and D 4254). Materials not amenable to density testing should be placed and compacted to a stable condition observed by the Geotechnical Engineer or representative.

Earthwork Construction Considerations

Shallow excavations for the proposed structures are anticipated to be accomplished with conventional construction equipment. Any excavations penetrating into the competent sandstone or limestone bedrock materials will require more effort using larger tracked excavators or hoe rams. Any utility excavations or wall footings may require the use of a rock trencher. Upon completion of filling and grading, care should be taken to maintain the subgrade water content prior to the construction of grade-supported improvements such as steps and slabs-on-grade. Construction traffic over the completed subgrades should be avoided. The site should also be graded to prevent ponding of surface water on the prepared subgrades or in excavations. Water collecting over or adjacent to construction areas should be removed. If the subgrade freezes, desiccates, saturates, or is disturbed, the affected material should be removed, or the materials should be scarified, moisture conditioned, and recompacted prior to floor slab construction.

The groundwater table could affect overexcavation efforts, depending on the time of year, especially for overexcavation and replacement of lower-strength soils. A temporary dewatering system consisting of sumps with pumps may be necessary to achieve the recommended depth of overexcavation depending on groundwater conditions at the time of construction.

As a minimum, excavations should be performed in accordance with OSHA 29 CFR, Part 1926, Subpart P, “Excavations” and its appendices, and in accordance with any applicable local and/or state regulations.

Construction site safety is the sole responsibility of the contractor who controls the means, methods, and sequencing of construction operations. Under no circumstances shall the information provided herein be interpreted to mean Terracon is assuming responsibility for construction site safety or the contractor's activities; such responsibility shall neither be implied nor inferred.

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Final cut and fill slopes should be constructed at 2.5H:1V or flatter. We recommend that slopes be over-built and then cut back to the final slope configuration to improve compaction at the face of the slope. Vegetation or erosion control should be established as soon as possible after construction to limit erosion occurring on the slopes. Slopes steeper than 2.5H:1V should be reinforced using geogrid/geotextile. A complete reinforced soil slope analysis should be performed for any reinforced slopes, including global stability analysis.

Excavations or other activities resulting in ground disturbance have the potential to affect adjoining properties and structures. Our scope of services does not include a review of available final grading information or consider potential temporary grading performed by the contractor for potential effects such as ground movement beyond the project limits. A preconstruction/ precondition survey should be conducted to document nearby property/infrastructure prior to any site development activity. Excavation or ground disturbance activities adjacent or near property lines should be monitored or instrumented for potential ground movements that could negatively affect adjoining property and/or structures.

Construction Observation and Testing

The earthwork efforts should be observed by the Geotechnical Engineer (or others under their direction). Observation should include documentation of adequate removal of surficial materials (vegetation, topsoil, and pavements), evaluation and remediation of existing fill materials, as well as proof-rolling and mitigation of unsuitable areas delineated by the proof-roll.

Each lift of compacted fill should be tested, evaluated, and reworked, as necessary, as recommended by the Geotechnical Engineer prior to the placement of additional lifts.

Each lift of fill should be tested for density and water content.

In areas of foundation excavations, the bearing subgrade should be evaluated by the Geotechnical Engineer or their representative. If unanticipated conditions are observed, the Geotechnical Engineer should prescribe mitigation options.

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

Shallow Foundations

If the site has been prepared in accordance with the requirements noted in Earthwork, the following design parameters are applicable for shallow foundations.

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Design Parameters – Compressive Loads

Item Description

Maximum Net Allowable Bearing

Pressure 1, 2

5,000 psf - foundations bearing on competent sandstone or limestone bedrock and 8,000 psf for foundations bearing a minimum of 1 foot below the top of competent sandstone or limestone.

Required Bearing Stratum 3 GeoModel Layer 3

Bearing material to be approved by Terracon

Minimum Foundation Dimensions Per IBC 1809.7

Ultimate Passive Resistance4 Uniform 500 psf for native clay or structural fill Uniform 3,000 psf for bedrock

Sliding Resistance 5

130 psf allowable cohesion (native/structural fill clay)

0.25 allowable coefficient of friction – granular/sandstone material

Minimum Embedment below

Finished Grade 6 24 inches

Estimated Total Settlement from

Structural Loads 2 Less than about 3/4 inch

1. The maximum net allowable bearing pressure is the pressure in excess of the minimum surrounding overburden pressure at the footing base elevation. Values assume that exterior grades are no steeper than 20% within 10 feet of a structure. Where foundations will be adjacent to an exposed rock face (at the overlook for the Sand Cave Trail, e.g.), the outer edge of the footing should be at least 10 feet from the edge of the rock face.

2. Values provided are for maximum loads noted in Project Description. Additional geotechnical consultation will be necessary if higher loads are anticipated.

3. Unsuitable or soft soils should be overexcavated and replaced per the recommendations presented in Earthwork.

4. The use of passive earth pressures require the sides of the excavation for the spread footing foundation to be nearly vertical and the concrete placed neat against these vertical faces or that the footing forms be removed and compacted structural fill be placed against the vertical footing face. Assumes no hydrostatic pressure. Ignore above frost depth.

5. Can be used to compute sliding resistance where foundations are placed on suitable soil/bedrock materials. For fine-grained materials, lateral resistance using cohesion should not exceed ½ the dead load. For the allowable coefficient of sliding, a factor of safety of 1.5 has been applied.

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Item Description

6. Embedment necessary to minimize the effects of frost and/or seasonal water content variations. For sloping ground, maintain depth below the lowest adjacent exterior grade within 5 horizontal feet of the structure. Recommended bearing capacity is based on completent bedrock bearing material and deeper bearing depths should be anticipated.

Design Parameters – Overturning and Uplift Loads

Shallow foundations subjected to overturning loads should be proportioned such that the resultant eccentricity is maintained in the center-third of the foundation (e.g., e < b/6, where b is the foundation width). This requirement is intended to keep the entire foundation area in compression during the extreme lateral/overturning load event.

Foundation oversizing may be required to satisfy this condition.

Uplift resistance of spread footings can be developed from the effective weight of the footing and the overlying soils with consideration to the IBC basic load combinations.

Foundation Construction Considerations

As noted in Earthwork, the footing excavations should be evaluated under the observation of the Geotechnical Engineer. The base of all foundation excavations should be free of water and loose soil, prior to placing concrete. Concrete should be placed soon after excavating to reduce bearing soil disturbance. Care should be taken to prevent wetting or drying of the bearing materials during construction. Excessively wet or dry material or any loose/disturbed material in the bottom of the footing excavations should be removed/reconditioned before the foundation concrete is placed.

The recommended bearing material is competent sandstone or limestone bedrock, which was encountered at depths between 1.4 and 5.4 feet below the existing grade at the boring and the hand/auger /DCP soundings. As a result, foundation excavations will need to extend below the minimum bearing depth for frost considerations.

Item Description

Soil Moist Unit Weight 115 pcf

Soil Effective Unit Weight1 50 pcf

Soil weight included in uplift resistance

Soil included within the prism extending up from the top perimeter of the footing at an angle of 20 degrees from vertical to ground surface

1. Effective (or buoyant) unit weight should be used for soil above the foundation level and below a water level. The high groundwater level should be used in uplift design as applicable.

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If unsuitable bearing soils are observed at the base of the planned footing excavation or the footings need to extend deeper to bear on or into bedrock, the excavation should be extended deeper to suitable soils/bedrock, and the footings could bear directly on these soils/bedrock at the lower level or on lean concrete backfill (minimum 28-day f’c=2,000 psi) placed in the excavations between the bedrock and the design minimum bearing depth. Please note that MASW Line 2 indicated that weathered bedrock may be as deep as 10 feet below grade in one location and additional undercut should be anticipated.

The lean concrete replacement zone is illustrated in the sketch below.

Lateral Earth Pressures

Design Parameters

Structures with unbalanced backfill levels on opposite sides should be designed for earth pressures at least equal to values indicated in the following table. Earth pressures will be influenced by the 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 in the diagram below. Active earth pressure is commonly used for the design of free-standing cantilever retaining walls and assumes wall movement. The “at-rest” condition assumes no wall movement and is commonly used for basement walls, loading dock walls, or other walls restrained at the top. The recommended design lateral earth pressures do not include a factor of safety and do not provide for possible hydrostatic pressure on the walls (unless stated).

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Lateral Earth Pressure Design Parameters

Earth Pressure

Condition 1

Coefficient for

Backfill Type 2

Surcharge

Pressure 3 p1 (psf)

Equivalent Fluid Pressures

(psf) 2,4

Unsaturated 5 Submerged 5

Active (Ka) Granular - 0.31

Fine Grained - 0.41

(0.31)S

(0.41)S

(34)H

(50)H

(77)H

(85)H

At-Rest (Ko) Granular - 0.47

Fine Grained - 0.58

(0.47)S

(0.58)S

(52)H

(70)H

(85)H

(95)H

1. For active earth pressure, the wall must rotate about the base, with top lateral movements 0.002 H to 0.004 H, where H is wall height. For passive earth pressure, the wall must move horizontally to mobilize resistance. Fat clay or other expansive soils should not be used as backfill behind the wall.

2. Uniform, horizontal backfill, with a maximum unit weight of 120 pcf for cohesive soils and 110 pcf for granular soils.

3. Uniform surcharge, where S is surcharge pressure.

4. Loading from heavy compaction equipment is not included.

5. To achieve “Unsaturated” conditions, follow the guidelines in Subsurface

Drainage for Below-Grade Walls below. “Submerged” conditions are recommended when drainage behind walls is not incorporated into the design.

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 degrees from vertical for the active case.

Footings, labs-on-grade, or other loads bearing on backfill behind walls may have a significant influence on the lateral earth pressure. Placing footings within the wall backfill and in the zone of active soil influence on the wall should be avoided unless structural analyses indicate the wall can safely withstand the increased pressure.

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The lateral earth pressure recommendations given in this section apply to the design of rigid retaining walls subject to slight rotation, such as cantilever, or gravity-type concrete walls. These recommendations do not apply to the design of modular block-geogrid reinforced backfill walls (also termed MSE walls). Recommendations covering these types of wall systems are beyond the scope of services for this assignment.

However, we would be pleased to develop a proposal for the evaluation and design of such wall systems upon request.

Subsurface Drainage for Below-Grade Walls

A perforated rigid plastic drain line installed behind the base of walls and extending below the adjacent grade is recommended to prevent hydrostatic loading on the walls.

The invert of a drain line around a below-grade building area or exterior retaining wall should be placed near the foundation bearing level. The drain line should be sloped to provide positive gravity drainage to daylight or to a sump pit and pump. The drain line should be surrounded by clean, free-draining granular material having less than 5% passing the No. 200 sieve, such as No. 57 aggregate. The free-draining aggregate should be encapsulated in a filter fabric. The granular fill should extend to within 2 feet of the final grade, where it should be capped with a concrete slab or compacted cohesive fill to reduce infiltration of surface water into the drain system.

As an alternative to free-draining granular fill, a prefabricated drainage structure may be used. A prefabricated drainage structure is a plastic drainage core or mesh which is covered with filter fabric to prevent soil intrusion and is fastened to the wall prior to placing backfill.

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Pavements

Pavement Subgrade Support Characteristics

Sufficient information is not available for us to provide an opinion of minimum pavement thickness for the project. For pavement design by others, we recommend that a subgrade California Bearing Ratio, CBR, of 5 be used for the asphaltic concrete pavement designs. We recommend that a modulus of subgrade reaction of 125 pci be used for the Portland cement concrete pavement designs. These values were empirically derived based upon our experience with the sandy lean clay, lean clay and silty clay subgrade soils and our expectation of the quality of the subgrade as prescribed by the Site Preparation conditions as outlined in Earthwork.

General Pavement Comments

Pavement thickness designs provided by others are minimum thickness designs. The recommended modulus of subgrade reaction values recommended in this report can be used in determining the minimum trail thickness and slab-on-grade thickness designs, which assume the subgrade has been prepared as recommended in Earthwork.

Although not required for structural support of the trail, a minimum 4-inch thick base course layer is recommended to help reduce the potential for slab curl, shrinkage cracking, and subgrade pumping through joints (if equipment will use the trails for maintenance). For exterior slab-on-grade, a minimum 4 inches of granular base is recommended below between the prepared subgrade and the bottom of the slab to provide a capillary break, reduce shrinkage cracking, and reduce the potential for slab curling. Proper joint spacing will also be required to prevent excessive slab curling and shrinkage cracking. Joints should be sealed to prevent the entry of foreign material and doweled where necessary for load transfer. PCC pavement details for joint spacing, joint reinforcement, and joint sealing should be prepared in accordance with ACI 330 and ACI 325.

Where practical, we recommend early-entry cutting of crack-control joints in PCC trail pavements and exterior slab-on-grade. Cutting of the concrete in its “green” state typically reduces the potential for micro-cracking of the pavements prior to the crack control joints being formed, compared to cutting the joints after the concrete has fully set. Micro-cracking of pavements may lead to crack formation in locations other than the sawed joints, and/or reduction of fatigue life of the pavement.

Openings in pavements, such as decorative landscaped areas, are sources for water infiltration into surrounding pavement systems. Water can collect in the islands and migrate into the surrounding subgrade soils thereby degrading support of the pavement.

Islands with raised concrete curbs, irrigated foliage, and low permeability near-surface

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Facilities | Environmental | Geotechnical | Materials 20 soils are particular areas of concern. The civil design for the pavements with these conditions should include features to restrict or collect and discharge excess water from the islands. Examples of features are edge drains connected to the stormwater collection system, longitudinal subdrains, or other suitable outlets and impermeable barriers preventing lateral migration of water such as a cutoff wall installed to a depth below the pavement structure.

Pavement Drainage

Pavements should be sloped to provide rapid drainage of surface water. Water allowed to pond on or adjacent to the pavements could saturate the subgrade and contribute to premature pavement deterioration. In addition, the pavement subgrade should be graded to provide positive drainage within the granular base section. Appropriate sub-drainage or connection to a suitable daylight outlet should be provided to remove water from the subgrade if encountered during construction.

Pavement Maintenance

The pavement sections designed by others represent minimum recommended thicknesses and, as such, periodic upkeep should be anticipated. Preventive maintenance should be planned and provided for through an ongoing pavement management program. Maintenance activities are intended to slow the rate of pavement deterioration and to preserve pavement investment. Pavement care consists of both localized (e.g., crack and joint sealing and patching) and global maintenance (e.g., surface sealing). Additional engineering consultation is recommended to determine the type and extent of a cost-effective program. Even with periodic maintenance, some movements, and related cracking may still occur, and repairs may be required.

Pavement 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 pavements:

The final grade adjacent to paved areas should slope down from the edges at a minimum of 2%.

Subgrade and pavement surfaces should have a minimum 2% slope to promote proper surface drainage unless a 1% slope is required for ADA-accessible areas.

Install pavement drainage systems surrounding areas anticipated for frequent wetting.

Install joint sealant and seal cracks immediately.

Seal all landscaped areas in or adjacent to pavements to reduce moisture migration to subgrade soils.

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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.

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 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.