Prospect Arena Ph. 1 Geotech Report.pdf

Kumar & Associates, Inc.®

TABLE OF CONTENTS

SUMMARY

PURPOSE AND SCOPE OF WORK

PROPOSED CONSTRUCTION

SITE CONDITIONS

SUBSURFACE CONDITIONS

LABORATORY TESTING

WATER-SOLUBLE SULFATES

GEOTECHNICAL ENGINEERING CONSIDERATIONS

SITE GRADING AND EARTHWORK

FOUNDATION RECOMMENDATIONS

SLABS-ON-GRADE

EXTERIOR FLATWORK

SITE SEISMIC CRITERIA

SURFACE DRAINAGE

PAVEMENT THICKNESS DESIGN

DESIGN AND CONSTRUCTION SUPPORT SERVICES

LIMITATIONS

FIG. 1 – LOCATION OF EXPLORATORY BORINGS

FIG. 2 – LOGS OF EXPLORATORY BORINGS

FIG. 3 – LEGEND AND NOTES

FIGS. 4 and 5 – SWELL-CONSOLIDATION TEST RESULTS

FIG. 6 – GRADATION TEST RESULT

TABLE I - SUMMARY OF LABORATORY TEST RESULTS

SUMMARY

1. The subsurface conditions were explored on February 28, 2025, by drilling four (4) exploratory borings at the approximate locations shown on Fig. 1. The subsurface conditions encountered in the borings generally consisted of a veneer of topsoil overlying either approximately 1.5- to 2-feet of pre-existing fill or natural clay soils (Boring 2). All the borings excluding Boring D1 were terminated within the natural clay soils at depths of either 15 or 20 feet below the existing ground surface. Boring D1 encountered poorly graded sand with silt and gravel beneath the lean clay at a depth of about 7 feet, and was terminated in the natural granular soils at a depth of about 15 feet..

Groundwater was not encountered in the exploratory borings during drilling. When stabilized groundwater measurements were taken 7 days subsequent to drilling, groundwater was not encountered, and the borings were backfilled following these measurements.

2. Based on the information obtained from the exploratory borings and the results of the laboratory testing, the proposed structures may be founded on shallow foundations consisting of spread footings or drilled footings when placed on a prepared subgrade.

Spread footings placed on a prepared subgrade may be designed for a net allowable soil bearing pressure of 2,500 psf. An allowable end bearing pressure of 1,500 psf should apply to drilled footing design. Additionally, a skin friction value of 100 psf may be accounted for in design based on the interaction between the soil and sides of the drilled footing for use as axial support.

3. A slab-on-grade is considered feasible for the proposed basketball court. We recommend that slabs-on-grade be placed on a minimum of 3 feet of structural meeting the material and placement criteria presented in the “Site Grading and Earthwork” section of this report.

Based on the subsurface conditions, we believe the basketball court may also be constructed using a PT-Slab foundation placed on structural fill. We are available to provide recommendations for a PT-Slab foundation, if needed.

Areas not considered movement-sensitive that can tolerate some potential movement should be supported on a minimum of 12-inches of scarified, well-mixed, moisture conditioned, and recompacted to the moisture and density specifications presented herein.

4. The following table presents the recommended pavement thicknesses:

Pavement Type

Composite HMA/ABC

Pavement Section

(in)

Full-depth HMA

Pavement Section

(in)

PCCP

Thickness (in)

Parking Areas 4.0/8.0 6.0 6.0

Drive Lanes 4.5/8.0 7.0 6.0

PURPOSE AND SCOPE OF WORK

This report presents the results of a geotechnical engineering study and pavement thickness design for the proposed Prospect Arena Park improvements at 13805 West 52nd Avenue in

Arvada, Colorado. The project site is shown on Fig. 1. The geotechnical study was performed in general accordance with the scope of work presented in our revised Proposal No. P-24-901 to

Design Concepts, dated October 14, 2024.

A field exploration program consisting of drilling exploratory borings was conducted to obtain information on subsurface conditions. Representative samples of the pre-existing fill material and naturally deposited soils obtained during the field exploration program were tested in the laboratory to determine their classification and engineering characteristics. The results of the field exploration and laboratory testing programs were analyzed to develop geotechnical engineering recommendations for the design and construction of the proposed improvements.

This report has been prepared to summarize the data obtained during this study and to present our conclusions and recommendations based on the proposed construction and the subsurface conditions encountered. Design parameters and a discussion of geotechnical engineering considerations related to the construction of the proposed arena and park improvement are included in the report.

PROPOSED CONSTRUCTION

Based on the information provided, we understand improvements will consist of a new basketball court (half-court), new playground areas, a new arena with 10-foot-wide equestrian paths, arena seating with an alternative option for a shade shelter, and a 60-foot-round pen and hitching posts/transition pen. Improvements will also include parking for vehicles and various sizes of trailers, a detention pond, portable restrooms throughout the site, and concrete flatwork connecting the entire site. Foundation loads are expected to be relatively light, typical for this type of construction.

If the proposed construction varies significantly from that described above or depicted in this report, we should be notified to reevaluate the recommendations provided in this report.

SITE CONDITIONS

Prospect Arena Park is a 5-acre site located in a residential neighborhood in Arvada, Colorado.

The northern section of the site features a small park, while the middle section contains two arenas. At the southern end, there is a dirt drive and parking area. The site is bordered to the north by Deframe Street and residential houses, with additional residential homes on the east and west sides, and West 52nd Avenue to the south. The terrain generally slopes from north to south over a distance of approximately 1,300 feet, with an elevation difference of about 38 feet. Large deciduous and coniferous trees are located throughout the site along with smaller shrubs.

SUBSURFACE CONDITIONS

Field Exploration: The subsurface conditions were explored on February 28, 2025, by drilling four

(4) widely-spaced exploratory borings at the approximate locations shown on Fig. 1. The borings were advanced through the pre-existing fill materials and into naturally deposited (natural) clay soils using 4-inch-diameter continuous-flight augers. Samples of the pre-existing fill materials and natural soils were obtained with a 2-inch-I.D. California-liner sampler driven into the various strata with blows from a 140-pound hammer falling 30 inches. Sampling with the California-liner sampler is generally similar to the standard penetration test described by the ASTM International (ASTM)

Method D1586. Sampler penetration resistance values (blow counts) when properly evaluated, indicate the relative density or consistency of the materials.

Depths at which samples were taken and the associated blow counts are shown on the Logs of

Exploratory Borings on Fig. 2. A Legend and Notes associated with the graphic logs and describing the soils encountered are presented on Fig. 3.

Subsurface Conditions: The subsurface conditions encountered in the borings generally consisted of a veneer of topsoil overlying either approximately 1.5- to 2-feet of pre-existing fill or natural clay soils (Boring 2). All the borings excluding Boring D1 were terminated within the natural clay soils at depths of either 15 or 20 feet below the existing ground surface. Boring D1 encountered poorly graded sand with silt and gravel beneath the lean clay at a depth of about 7 feet, and was terminated in the natural granular soils at a depth of about 15 feet.

The pre-existing fill materials consisted of sandy lean clay, and was moist and dark brown to brown. The exact lateral and vertical extents of the fill across the site were not determined as part of this study.

The natural clay soils encountered consisted of lean clay with variable sand content, and was moist and brown to light brown. Calcareous deposits were noted on the boring logs throughout the natural clay soils. The natural granular soils encountered in Boring D-1 consisted of poorly-graded sand with silt and gravel, and was fine- to coarse-grained with gravel, moist to very moist, and dark brown to brown to tan. Based on blow counts, the natural clay soils were stiff to hard in consistency and the natural granular soils were very dense.

Groundwater Conditions: Groundwater was not encountered in the exploratory borings during drilling. When stabilized groundwater measurements were taken 7 days subsequent to drilling, groundwater was not encountered, and the borings were backfilled following these measurements.

LABORATORY TESTING

Samples obtained from the exploratory borings were visually classified in the laboratory by the project engineer. Laboratory testing was performed on representative samples to evaluate in-situ moisture content and dry unit weight, liquid and plastic limits, swell-consolidation behavior, and concentration of water-soluble sulfates. These tests were completed in accordance with the corresponding ASTM standard test procedures. The percentage of water-soluble sulfates was determined in general accordance with the Colorado Department of Transportation (CDOT) test procedure. The results of the laboratory tests are shown to the right of the logs on Fig. 2, plotted graphically on Figs. 4 through 6, and summarized in Table I.

Swell-Consolidation: Swell-consolidation testing was conducted on representative samples of the pre-existing fill and natural clay soils to determine the swell and/or compressibility potential under loading and when submerged in water. The samples were prepared and placed in a confining ring between porous discs, subjected to a surcharge pressure of either 200 or 1,000 psf, and allowed to consolidate before being submerged in water. The samples were then inundated with water.

The change in sample height when deformation ceased was measured with a dial gauge. The samples were then loaded incrementally to maximum surcharge pressures of either 3,000, 5,000, or 10,000 psf. The sample heights were monitored until deformation practically ceased under each load increment.

Results of the swell-consolidation testing are plotted as a curve of the final strain at each increment of pressure against the log of the pressure. Based on the results of the swell-consolidation testing, the samples of pre-existing fill exhibited low to moderate swell potential

(0.3% to 6.6%) when wetted under a 1,000 psf and 200 psf surcharge pressure, respectively. The sample of natural clay soil exhibited moderate swell potential (2.4%) when wetted under a 1,000 psf surcharge pressure. Swell-consolidation test results are presented on Figs. 4 and 5.

Index Properties: Samples were classified into categories of similar engineering properties in general accordance with the Unified Soil Classification System. This system is based on index properties, including liquid limit, plasticity index, and grain size distribution. Values for in-situ moisture content and dry unit weight, liquid limit, plasticity index, and the percent of soil retained on the U.S. No. 4 sieve and percent soils passing the U.S. No. 200 sieve are presented in Table

I and adjacent to the corresponding sample on the boring log.

WATER-SOLUBLE SULFATES

The concentration of water-soluble sulfates measured in representative samples of the pre-existing fill material and natural clay soils were 0.05% and 0.00%, respectively. These concentrations represent a Class S0 exposure to sulfate attack on concrete exposed to these materials. The degree of attack is based on a range of Class S0 (not applicable), Class S1

(moderate), Class S2 (severe), and Class S3 (very severe) severity of exposure as presented in

ACI 201.2R-16.

Based on the laboratory data and our experience in the area, we believe special sulfate resistant cement will not be required for concrete exposed to the pre-existing fill material.

GEOTECHNICAL ENGINEERING CONSIDERATIONS

As indicated previously, up to 2 feet of pre-existing fill was encountered at the site. The boings were widely spaced and deeper fills may be present in other portions of the site, and should be anticipated. Without documentation of placement conditions or the extent of the past excavations, the existing fill materials are considered non-engineered and expected to exhibit variable and unpredictable settlement and/or heave behavior under structural loading. Accordingly, the fill is generally considered unsuitable in its current condition to support foundations and movement-sensitive exterior flatwork.

A shallow foundation system consisting of spread footings or drilled footings are considered feasible for the proposed structures, playground renovations, and the basketball court structures when placed on a prepared subgrade. The footings should be supported on a minimum of 3 feet of structural fill meeting the material and placement requirements presented in the “Site Grading and Earthwork” section of this report. The drilled footing should be placed directly on the undisturbed natural soils. Prior to placing structural fill and exterior flatwork, the exposed subgrade should be scarified to a depth of 12 inches, moisture-conditioned and well-mixed, and properly compacted.

We believe a slab-on-grade basketball court is considered feasible when placed on a prepared subgrade. Slabs-on-grade should be placed on a minimum of 3 feet of structural fill. Based on the subsurface conditions, we believe the basketball court may also be constructed using a PT-Slab foundation placed on structural fill. We are available to provide recommendations for a PT-Slab foundation, if needed.

SITE GRADING AND EARTHWORK

Existing Fill: Our borings encountered existing pre-existing fill up to 2 feet below the existing ground surface. As mentioned in the “Geotechnical Engineering Considerations” section, the fill should be considered non-engineered and is not suitable for support of foundation elements and soil-supported slabs due to potential for unpredictable movement unless the owner understands and accepts the risk of increased movements

The pre-existing fill materials are generally suitable for reuse as structural fill, provided they meet the material and placement criteria presented in this section. The geotechnical engineer of record should evaluate on-site and/or import fill material prior to placement.

Temporary Excavations: All excavations should be constructed in accordance with OSHA requirements, as well as state, local, and other applicable requirements. Site excavations will generally encounter pre-existing fill and natural clay/cohesive soils classifying as OSHA Type B soil. If localized perched water or seepage is encountered, much flatter side slopes than those allowed by OSHA or temporary shoring may be required.

Where insufficient lateral space is available due to the proximity to property boundaries and existing structures and facilities, temporary shoring and underpinning may be required. It is our experience that temporary shoring systems are typically designed and built by specialty contractors and that the designers will typically develop their own design criteria based on soil data presented in the owner’s geotechnical study report. We are available upon request for further consultation on temporary shoring design criteria. Excavated slopes may soften or loosen due to construction traffic and erode from surface runoff.

Surface water runoff into the excavations can act to erode and potentially destabilize the excavation side slopes and/or result in soft or excessively loose ground conditions at the base of the excavation and should not be allowed. Diversion berms and other measures should be used to prevent surface water runoff into the excavations from occurring. If significant runoff into the excavations does occur, further excavation may be required to remove and replace the wet, soft or loose subgrade materials or to stabilize the excavation side slopes.

Fill Material Specifications: The following material specifications are presented for fills on the project site. We believe the on-site fill materials are suitable for reuse when used according to the specifications outlined below.

1. Structural Fill: Structural fill may consist of on-site soils, moisture-conditioned and compacted as recommended herein. Imported structural fill material, if necessary, should have a maximum of 70 percent passing the No. 200 sieve, a maximum liquid limit of 30, and a maximum plasticity index of 15. Imported fill materials not meeting the above liquid limit and plasticity index criteria may be acceptable provided the maximum percentage passing the No. 200 sieve specified above and the swell criteria for low-swell soils outlined below are satisfied.

2. General Site Grading Fill: Fill placed for general site grading or beneath exterior flatwork that is not sensitive to movement may consist of moisture-conditioned on-site overburden soils meeting the suitability requirements presented in Item 3 below.

3. Material Suitability: Unless otherwise defined herein, all fill material should be non- to low-swelling, free of claystone, vegetation, brush, sod, trash and debris, and other deleterious substances, and should not contain rocks or lumps having a diameter of more than 3 inches. A fill material should be considered low-swelling if the swell potential of the material, when remolded to 95% of the standard Proctor (ASTM D698) maximum dry density at optimum moisture content, does not exceed 0.5% when wetted under a 200 psf surcharge pressure.

Compaction Requirements: We recommend the following compaction criteria be used on the project:

1. Moisture Content: Fill materials should be compacted at moisture contents within 2 percentage points of the optimum moisture content for predominantly granular materials and to at least +2 percentage points of optimum for predominantly clay materials. The contractor should be aware that clay soils, including on-site and imported materials, may become somewhat unstable and deform under wheel loads if placed near the upper end of the moisture range.

2. Placement and Degree of Compaction: Structural fill beneath foundations, exterior flatwork, and adjacent to shallow foundations should be placed in maximum 8-inch loose lifts. A representative of the geotechnical engineer should observe fill placement operations. The following compaction criteria should be followed during construction:

Percentage of Maximum Standard Proctor Density

Fill Location: .......................................................................................... (ASTM D698) Beneath Spread Footing Foundations ............................................................ 98% Beneath Slab-on-Grade .................................................................................. 95% Beneath Exterior Flatwork and Pavements1 .................................................... 95% Landscape and Other Areas ........................................................................... 92%

1 Aggregate base course, if used beneath pavements, should be compacted to a minimum of 95 percent of the modified Proctor (ASTM D1557) maximum dry density at moisture contents within 2 percentage points of optimum.

Subgrade Preparation: Prior to placing structural fill, the upper 12 inches of the subgrade soils at the base of the fill zone should be scarified, moisture-conditioned as recommended above, and compacted to at least 95% of the standard Proctor (ASTM D698) maximum dry density at the moisture contents recommended above. Where feasible, the prepared subgrade should include proofrolling with a heavily loaded pneumatic-tired vehicle or a heavy, smooth-drum vibratory roller compactor to identify soft areas exhibiting excessive deflection. Areas that deform excessively during proofrolling should be removed and replaced to achieve a reasonably stable subgrade.

If grading is performed during times of cold weather, the fill should not contain frozen materials.

If the subgrade is allowed to freeze, all frozen material should be removed prior to additional fill placement or pavement construction.

Excessive wetting and drying of excavations and prepared subgrade areas should be avoided during construction. It is extremely important that moisture-conditioned fill placed during construction is not allowed to dry-out. Allowing the fill to dry after placement increases the materials’ potential to heave if the moisture content of the fill is increased in the future.

Construction Monitoring: A representative of the geotechnical engineer should observe prepared fill subgrades and fill placement on a full-time basis.

FOUNDATION RECOMMENDATIONS

Spread footing foundations are considered feasible for support of the proposed shade structures and playground renovations. As previously mentioned in the “Geotechnical Engineering

Considerations” section of this report, foundations should be supported on a minimum of 3 feet of structural fill.

The design and construction criteria presented below should be observed for a spread footing foundation system. The construction details should be considered when preparing project documents.

1. Spread footings should be supported on a minimum of 3 feet of properly compacted structural fill. The structural fill should satisfy the material and placement requirements presented in the “Site Grading and Earthwork” section of this report.

2. Spread footings supported as recommended should be designed for a net allowable soil bearing pressure of 2,500 psf.

3. Structural fill should extend down and out from the edges of the footings at a 1 (horizontal) to 1 (vertical) projection. Structural fill should be prepared and placed as recommended in the “Site Grading and Earthwork” section of this report.

4. Spread footings should have a minimum width of 16 inches for continuous footings and

24 inches for isolated pads.

5. Exterior footings and footings beneath unheated areas should be provided with adequate soil cover above their bearing elevation for frost protection. Placement of foundations at least 36 inches below the exterior grade is typically used in this area.

6. The lateral resistance of a spread footing will be a combination of the sliding resistance of the footing on the foundation-bearing materials and passive earth pressure against the side of the footing. Resistance to sliding at the bottoms of the footings can be calculated based on a coefficient of friction of 0.30. Passive pressure against the sides of the footings may be calculated assuming an equivalent fluid unit weight of 185 pcf. The above values are working values.

7. Areas of loose/soft material and pre-existing fill encountered within the foundation excavation should be removed and the footings extended to adequate natural bearing material. The areas removed should be replaced with structural fill as described in the

“Site Grading and Earthwork” section of this report.

8. Structural fill placed beneath footings, and against the sides of the footings to resist lateral loads should meet the material and placement criteria presented in the “Site Grading and

Earthwork” section of this report.

9. A representative of the geotechnical engineer should observe all footing excavations prior to placement of engineered fill or formwork.

Drilled Footings: We recommend the playground equipment and site structures be installed to the manufacturer’s recommendations. Drilled footings should bear on the undisturbed natural soils.

We recognize foundations for the vertical pole features planned for the site are commonly used for these applications and are commonly constructed as 1.5- to 2-foot diameter drilled footings.

Drilled footings are typically designed to resist downward and upward axial forces as well as significant lateral forces. An allowable end bearing pressure of 1,500 psf should apply to drilled footing design. Additionally, a skin friction value of 100 psf may be accounted for in design based on the interaction between the soil and sides of the drilled footing for use as axial support. We assume that some amount of movement is acceptable for the structures.

SLABS-ON-GRADE

We recommend that slabs-on-grade be placed on a minimum of 3 feet of structural meeting the material and placement criteria presented in the “Site Grading and Earthwork” section of this report. Before placing structural fill, the subgrade should be scarified, moisture conditioned, and compacted as described in the “Site Grading and Earthwork” section of this report.

Floor slab control joints should be used to reduce damage due to shrinkage cracking. Joint spacing is dependent on slab thickness, concrete aggregate size, and slump, and should be consistent with recognized guidelines such as those of the Portland Cement Association (PCA) and American Concrete Institute (ACI). The joint spacing and slab reinforcement should be established by the designer based on experience and the intended slab use. We suggest joints be provided on the order of about 12 to 15 feet apart in both directions. The requirements for slab reinforcement should be established by the designer based on experience and the intended slab use.

If moisture-sensitive floor coverings are used, mitigation of moisture penetration into the slabs, such as by use of a vapor retarder, may be required. If an vapor retarder is used, special precautions may be required to prevent differential curing problems which could cause the slabs to warp. ACI 302.1R addresses this topic.

EXTERIOR FLATWORK

We understand concrete sidewalks and flatwork may be constructed. Subgrade preparation for exterior flatwork considered movement-sensitive, such as exterior flatwork within 10 feet of the movement-sensitive structures, should be done in accordance with the “Slabs-on-Grade” section of this report. To limit potential of flatwork movement due to settlement of the existing fill, subgrade preparation beneath exterior flatwork that can tolerate some potential movement should consist of a minimum of 12-inches of scarified, well-mixed, moisture conditioned, and recompacted soils as presented in the “Site Grading and Earthwork” section.

SITE SEISMIC CRITERIA

The soil profile after construction will generally consist of structural fill underlain by natural clay soils. Overburden soils will generally classify as Site Class D in accordance with the International

Building Code (IBC).

Based on our experience with similar profiles (including shear wave velocities measured for similar subsurface profiles), and the weighted average of estimated shear wave velocities calculated for the upper 100 feet of the site, we recommend a design soil profile of IBC Site Class

D. Based on site seismicity, the subsurface profile, and the depth to groundwater, liquefaction is not a design consideration.

SURFACE DRAINAGE

Proper surface drainage is very important for the acceptable performance of the site structures during construction and after construction has been completed. Drainage recommendations provided by local, state, and national entities should be followed based on the intended use of the site structures. Excessive wetting or drying of foundations should be avoided during construction.

We recommend the ground surface adjacent to new structures and flatwork be sloped to drain away in all directions. We recommend a minimum slope of 6 inches in the first 10 feet, with site drainage beyond the 10-foot zone designed to promote runoff and reduce infiltration. These slopes may be changed as required for handicapped access points in accordance with the

Americans with Disabilities Act. Landscaping which requires relatively heavy irrigation and lawn sprinkler heads should be located at least 10 feet from movement-sensitive structures.

PAVEMENT THICKNESS DESIGN

A pavement section is a layered system designed to distribute concentrated traffic loads to the subgrade. The performance of the pavement structure is directly related to the physical properties of the subgrade soils and traffic loadings. Soils are represented for pavement design purposes by means of a subgrade resilient modulus for flexible pavements and a modulus of subgrade reaction for rigid pavements.

Subgrade Materials: Based on the results of the field and laboratory studies, the near-surface subgrade materials at the site classify as A-4, A-6 and A-7-6 soils with group indices between 2 and 19 in accordance with the American Association of State Highway and Transportation

Officials (AASHTO) classification. Soils that classify as A-4, A-6 and A-7-6 soils are generally considered to provide fair to poor subgrade support. For design purposes, a resilient modulus value of 3,025 psi was selected for flexible pavements and a corrected modulus of subgrade reaction of 45 pci was selected for rigid pavements.

Design Traffic: Since anticipated traffic loading information was not available at the time of this report preparation, an 18-kip equivalent single axle loading (ESAL) value of 36,500 was assumed for the automobile parking spaces and an ESAL value of 73,000 for the trailer parking and drive lanes. The ESAL assumptions above are typical values we have used in the past for similar projects based on our experience. We should be contacted to reevaluate the recommendations provided herein if the any of the traffic distribution assumptions are found to be different than those described above.

Pavement Thickness Requirements: The pavement thicknesses were determined in accordance with the 1993 AASHTO pavement design procedure and the City of Arvada Engineering Code of

Standards and Specifications. Recommendations for a full depth asphalt section, a composite section of hot mix asphalt (HMA) over aggregate base course (ABC) and for a rigid Portland cement concrete pavements (PCCP) section are presented in the table below. For flexible pavement design, initial and terminal serviceability indices of 4.5 and 2.0, respectively, were selected with a reliability of 85 percent. The following table presents the minimum pavement thickness alternatives for the project:

Pavement Type

Composite HMA/ABC

Pavement Section

(in)

Full-depth HMA

Pavement Section

(in)

PCCP

Thickness (in)

Parking Areas 4.0/8.0 6.0 6.0

Drive Lanes 4.5/8.0 7.0 6.0

The concrete sections presented above are assumed to be un-reinforced. Providing dowels at construction joints would help reduce the risk of differential movements between panel sections.

Providing a grid mat of deformed rebar within the concrete pavement section would assist in mitigating corner breaks and differential panel movements. If a rebar mat is installed, we recommend the bars be placed in the lower half of the pavement section. On projects electing to install rebar mats, we have commonly seen No. 4 rebar placed at 24-inch centers in each direction, however we recommend a structural engineer evaluate the placement and spacing of rebar if needed.

Pavement Materials: The following are recommended material and placement requirements for pavement construction for this project site. We recommend that properties and mix designs for all materials proposed to be used for pavements be submitted for review to the geotechnical engineer prior to placement.

1. Aggregate Base Course: Aggregate base course (ABC) used beneath hot mix asphalt

(HMA) pavements or as a working surface below PCCP, should meet the material specifications for Class 6 ABC stated in the current CDOT Specifications. The ABC should be placed and compacted as outlined in the “Site Grading and Earthwork” section of this report.

2. Hot Mix Asphalt: Hot mix asphalt (HMA) materials and mix designs should meet the applicable requirements indicated in the current CDOT Specifications. We recommend that the HMA used for this project is designed in accordance with the SuperPave gyratory mix design method. The mix should generally meet Grading S or SX specifications with a SuperPave gyratory design revolution (NDESIGN) of 75. The mix design for the HMA should use a performance grade PG 58-28 asphalt binder. A PG 64-22 binder will also be sufficient to carry the traffic loads, but will be more susceptible to low temperature cracking. Placement and compaction of HMA should follow current CDOT standards and specifications.

3. Portland Cement Concrete Pavement: PCCP should meet Class D or P specifications and requirements in the current CDOT Specifications. Rigid PCCP pavements are more sensitive to distress due to movement resulting from settlement or heave of the underlying base layer and/or subgrade than flexible asphalt pavements. The PCCP should contain sawed or formed joints to 1/3 of the depth of the slab at a maximum distance of 12 feet on center. The PCCP thickness design presented above is for an unreinforced pavement section.

Subgrade Preparation: Ordinarily, we recommend that all pre-existing undocumented fill beneath pavements be removed and replaced with properly placed and compacted, non- to low-swelling structural fill. This recommendation is made to avoid the potential for excessive total and differential settlement under structural loading due to post-construction consolidation of the unpredictable fill materials. Based on the proposed construction, we anticipate light pavement loads, and that the asphalt pavement will be able to tolerate some additional movement. As an alternative to complete fill removal, we believe a portion of the existing fill may be left in place beneath pavements, provided the risk of movement in excess of normally accepted tolerances is acceptable to the owner. While we believe the risk to be low, it should be carefully considered by the owner. Provided this alternative is accepted by the owner, we recommend the upper 12-inches of the subgrade be scarified and recompacted as indicated in the “Site Grading and Earthwork” section of this report.

The prepared pavement subgrade should be proofrolled with a heavily loaded pneumatic-tired vehicle with a tire pressure of 100 psi capable of applying an 18-kip axle load, or a heavy smooth drum roller compactor. Pavement design procedures assume a stable subgrade. Areas that deform excessively under heavy wheel loads are not stable and should be removed and replaced to achieve a stable subgrade prior to paving. The contractor should be aware clay soils may become somewhat unstable and deform under wheel loads if placed near the upper end of the moisture range. Paving should be completed within 24 hours of completion of the subgrade preparation.

The owner should be aware partial overexcavation and replacement will reduce but not eliminate potential movement of pavements should moisture levels increase within the remaining existing fill beneath the replacement fill. If this risk cannot be accepted, the pavement should be underlain by structural fill extending to natural undisturbed soils.

Drainage: The collection and diversion of surface drainage away from paved areas is extremely important to the satisfactory performance of pavement. Drainage design should provide for the removal of water from paved areas and prevent the wetting of the subgrade soils. Joints should be routinely inspected, and joints and cracks that develop after construction should be sealed to reduce the potential for water to migrate through the pavement.

Maintenance: Periodic maintenance of paved areas is critical to achieve the design pavement life.

Crack sealing should be performed annually as new cracks appear. Joint seals in concrete should be replaced as they deteriorate. Chip seals, fog seals, or slurry seals applied at approximate intervals of 3 to 5 years are usually necessary for asphalt. As conditions warrant, it may be necessary to perform patching and structural overlays at approximate 10-year intervals.

DESIGN AND CONSTRUCTION SUPPORT SERVICES

K+A should be retained to review the project plans and specifications for conformance with the recommendations provided in our report. We are also available to assist the design team in preparing specifications for geotechnical aspects of the project, and performing additional studies, if necessary to accommodate possible changes in the proposed construction.

We recommend that K+A be retained to provide construction observation and testing services to document that the intent of this report and the requirements of the plans and specifications are being followed during construction. This will allow us to identify possible variations in subsurface conditions from those encountered during this study and to allow us to re-evaluate our recommendations, if needed. We will not be responsible for implementation of the recommendations presented in this report by others, if we are not retained to provide construction observation and testing services.

LIMITATIONS

The conclusions and recommendations submitted in this report are based upon the data obtained from the exploratory borings at the locations indicated on Fig. 1 and conditions observed or measured at the site at the time of this study. This report may not reflect subsurface conditions that occur beyond or between the exploratory borings. The nature and extent of variations across the site may not become evident until further site construction activities occur, including site grading and excavations. If during site construction, fill, soil, rock, or water conditions appear to be different from those described herein, K+A should be advised at once so a re-evaluation of the recommendations presented in this report can be made. K+A is not responsible for liability associated with the interpretation of subsurface data by others.

Swelling soils occur on this site. Such soils are stable at their natural moisture content but will undergo high volume changes with changes in moisture content. The extent and amount of perched water beneath the structure as a result of area irrigation and inadequate surface drainage is difficult, if not impossible, to foresee.

The recommendations presented in this report are based on current theories and experience of our engineers on the behavior of swelling soils in this area. Standards of practice in this area evolve over time. The owner should be aware there is a risk in constructing in an expansive soil area. Following the recommendations given by a geotechnical engineer, careful construction practice and prudent maintenance by the owner can, however, decrease the risk of foundation movement due to expansive soils.

The scope of services for this project does not include any environmental; assessment of the site or identification of contaminates or hazardous materials or conditions.

If you have any questions, or if we can be of further assistance, please contact us.

RAE/db Rev. by: RRK Enclosures cc: File

Kumar & Associates

Project No.: 25-1-158 Project Name: Prospect Arena Improvements Date Sampled:

Date Received:

Boring Depth (Feet)

Gravel (%) Sand (%)

Liquid Limit

Plasticity

1 1 3/7/25 10.3 106.6 48 40 8 0.05 A-4 (2) Fill: Clayey Sand (SC) 1 9 3/7/25 15.8 116.2 4 36 60 42 25 Sandy Lean Clay (CL) 2 4 3/7/25 16.0 108.4 80 45 24 A-7-6 (19) Lean Clay with Sand (CL) 2 14 3/7/25 19.5 106.4 2 42 56 34 17 Sandy Lean Clay (CL) 3 1 3/7/25 20.3 103.1 3 43 54 39 17 A-6 (6) Fill: Sandy Lean Clay (CL) 3 9 3/7/25 24.9 99.2 85 58 39 0.00 Lean Clay with Sand (CL)

D1 9 3/7/25 2.2 126.0 45 49 6 Poorly-graded Sand with Silt and Gravel (SP-SM)

Table I

Sample Location Gradation Atterberg Limits

Date Tested

Natural Moisture Content

Natural Dry

Density (pcf)

Percent Passing No. 200 Sieve

2/28/2025 3/3/2025

Water Soluble Sulfates

AASHTO

Classification (Group Index) Soil or Bedrock Type

Summary of Laboratory Test Results