10-Attachment B - KMH Walden Ponds Geotech Report.pdf

ATTACHMENT B

Kumar & Associates, Inc.®

TABLE OF CONTENTS

SUMMARY

PURPOSE AND SCOPE OF STUDY

PROPOSED CONSTRUCTION

SITE CONDITIONS

SUBSURFACE CONDITIONS

LABORATORY TESTING

GEOTECHNICAL ENGINEERING CONSIDERATIONS

FOUNDATION RECOMMENDATIONS

SOIL-SUPPORTED SLABS

SITE GRADING AND EARTHWORK

WATER-SOLUBLE SULFATES

PAVEMENT THICKNESS DESIGN

DESIGN AND CONSTRUCTION SUPPORT SERVICES

LIMITATIONS

FIGS. 1, 1A, and 1B LOCATION OF EXPLORATORY BORINGS

FIG. 2 LOGS OF EXPLORATORY BORINGS

FIG. 3 LEGEND AND NOTES

FIG. 4 SWELL-CONSOLIDATION TEST RESULTS

FIGS. 5 and 6 GRADATION TEST RESULTS

FIG. 7 MOISTURE-DENSITY RELATIONSHIPS

TABLE I SUMMARY OF LABORATORY TEST RESULTS

SUMMARY

1. A field exploration program consisting of drilling four (4) exploratory borings (Borings 1 through 4) was conducted to obtain information on subsurface conditions. The subsurface conditions encountered in the borings consisted of pre-existing fill underlain by naturally deposited (natural) soil at depths ranging from about 2 to 9 feet. The natural soil extended to claystone bedrock at depths ranging from about 7.5 to 16 feet. The borings were terminated in claystone bedrock at depths ranging from about 24 to 30 feet.

Groundwater was encountered in the borings during drilling at depths ranging from about 6 to 9 feet. The borings were left open for 6 days to allow for stabilized groundwater level measurements. Groundwater was measured in the borings at depths ranging from about

2.5 to 17 feet. The borings were backfilled after completion of these measurements.

2. Considering the subsurface conditions encountered in the exploratory borings and the nature of the proposed construction, the proposed structures may be founded on shallow foundations consisting of spread footings placed on the undisturbed natural soils or a minimum of 2 feet of structural fill extending to undisturbed natural soils.

As an alternative to shallow foundations, drilled footings and/or helical piers may be considered. Recommendations for spread footings, drilled footings, and helical piers are provided herein.

3. Pavement section alternatives based on the anticipated traffic volume, on-site material properties, and local industry standards of practice are presented below:

LOCATION

Full Depth Asphalt

Pavement (inches)

Asphalt Over Aggregate Base Course

(inches)

PCCP

(inches)

Standard Duty 5.5 4.0 over 6.0 6.0

Heavy Duty 6.5 5.0 over 6.0 7.0

PURPOSE AND SCOPE OF STUDY

This report presents the results of a geotechnical engineering study and pavement thickness design performed for the proposed renovations in the Walden Ponds Wildlife Habitat park, located at 3893 North 75th Street in Boulder, Colorado. The project site is shown on Figs 1, 1A, and 1B.

The study was conducted in general accordance with the scope of work in our revised Proposal

No. P-26-308 to JVA, Incorporated, dated April 21, 2026.

A field exploration program consisting of exploratory borings was conducted to obtain information on subsurface conditions. Samples of the overburden soils and bedrock materials 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 recommendations for use in design and construction of the proposed structures.

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 structures are included in the report.

PROPOSED CONSTRUCTION

Based on the information provided in the project request for proposal, we understand the existing boardwalk, fishing pier, and platform structures have experienced some movement and damage and will be replaced with new structures at two locations on the Walden Ponds Wildlife Habitat open space property. We also understand the park renovations may include paving some driveways and existing aggregate-surface parking lots.

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

The overall site is the Walden Ponds Wildlife Habitat Park. The project site consists of two locations in the southern portion of the park, which include aggregate-surfaced parking lots, a fishing pier, platform structures, and shade structures. The overall site is bounded on the north by a wastewater treatment facility, on the east by Walden Ponds and residential properties and farms further east, and on the south and west by Sawhill Ponds and Walden Ponds Transportation facility. Based on available topographic information, the project sites slope down from south to north, with about 7 to 9 feet of elevation change between the parking lots and the north pond.

SUBSURFACE CONDITIONS

Field Exploration: The subsurface conditions were explored by drilling four (4) exploratory borings at the approximate locations shown on Figs. 1, 1A, and 1B. The borings were advanced through the overburden soils and into the underlying bedrock using 4-inch-diameter, solid-stem augers and were logged by a representative of Kumar and Associates, Inc. (K+A). Samples of the pre-existing fill, natural soils, and bedrock were obtained with either a 2-inch-I.D. California-liner sampler or a 1-3/8-inch-I.D. split-spoon sampler, driven into the various strata with blows from a

140-pound hammer falling 30 inches. The split-spoon sampler is the standard penetration test

(SPT) procedure described by ASTM International (ASTM) test procedure D1586. Sampling with the California-liner sampler is similar to the SPT procedure. Sampler penetration resistance values (blow counts) provide an indication of the relative density or consistency of the soils and bedrock.

Depths at which samples were taken and the associated blow counts are shown on the Logs of the Exploratory Borings, Fig. 2. Legend and Explanatory Notes describing the overburden soils and bedrock materials encountered are presented on Fig. 3.

Subsurface Soil Conditions: The subsurface conditions encountered in the borings consisted of pre-existing fill underlain by naturally deposited (natural) soil at depths ranging from about 2 to 9 feet. The natural soil extended to claystone bedrock at depths ranging from about 7.5 to 16 feet.

The borings were terminated in claystone bedrock at depths ranging from about 24 to 30 feet.

The pre-existing fill generally consisted of fine- to coarse-grained, poorly-graded sand with silt and gravel and isolated clayey sand and silty clayey sand zones. The pre-existing fill was generally slightly moist and tan to brown to dark brown.

The natural soils generally consisted of fine- to coarse-grained, poorly-graded gravel with silt and sand to poorly-graded sand with clay and isolated silty sand zones. The natural granular soils were generally slightly moist to wet (below groundwater) and tan to brown to dark brown. Based on blow counts, the natural soils were dense to very dense.

The claystone bedrock was moist and gray to dark gray. Based on blow counts, the claystone bedrock was very hard.

Groundwater Conditions: Groundwater was encountered in the borings during drilling at depths ranging from about 6 to 9 feet. The borings were left open for 6 days to allow for stabilized groundwater level measurements. Groundwater was measured in the borings at depths ranging from about 2.5 to 17 feet. The borings were backfilled after completion of 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, grain size distribution, liquid and plastic limits, concentration of water-soluble sulfates, swell-consolidation, and moisture-density relationships (standard

Proctor). The above testing was performed in accordance with the applicable ASTM standard test procedures. The percentage of water-soluble sulfates was evaluated in general accordance with the Colorado Department of Transportation (CDOT) CP-L 2103 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

7, and summarized in Table I.

Swell-Consolidation: Swell-consolidation tests were conducted on two representative samples of the claystone bedrock to determine the potential for swell and/or compressibility 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 1,000 psf and allowed to consolidate before being submerged in water. The samples were then inundated with water, and the change in sample height when deformation ceased was measured. The samples were then loaded incrementally to maximum surcharge pressures of 3,000 psf or 5,000 psf, and the sample heights were monitored until deformation practically ceased under each load increment.

Results of the swell-consolidation tests conducted on the samples are presented on Fig. 4 as plots of the curve of the final strain at each increment of pressure against the log of the pressure.

Based on the results of the swell-consolidation test, the claystone bedrock samples exhibited low

(0.1% and 1.4%) swell potential under the applied surcharge pressure when wetted.

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 passing the U.S. No. 200 sieve are presented in Table I and adjacent to the corresponding sample on the boring logs. The results of gradation testing performed on two samples of the pre-existing fill and one sample of the natural soils are presented on Figs. 5 and 6.

Standard Proctor: A composite sample of the on-site pre-existing fill was obtained from the upper

5 feet in Borings 2 and 3 for moisture-density relationship testing (standard Proctor, ASTM D698) to determine the optimum moisture content and maximum dry density of the soil type. The standard Proctor test results are shown on Fig. 7. The rock-corrected maximum dry density of the on-site pre-existing soil was determined to be 124.3 pcf at an optimum moisture content of 9.2%.

The rock-uncorrected maximum dry density of the on-site pre-existing soil was determined to be

117.5 pcf at an optimum moisture content of 9.2%.

GEOTECHNICAL ENGINEERING CONSIDERATIONS

Pre-Existing Fill: As previously indicated, approximately 2 to 9 feet of pre-existing fill was encountered in the borings, which we assume was placed during pond embankment construction.

Ordinarily, we recommend all undocumented pre-existing fill beneath movement-sensitive structures be removed and replaced with non- to low-swelling structural fill, placed with moisture and density control, and thoroughly observed and tested to document proper placement in accordance with the specified material and placement criteria. The associated fill placement documentation was unavailable at the time of this report, leading to uncertainty about the condition of the fill at the site.

The borings drilled for this study were not intended to quantify the degree of compaction or confirm the condition of the fill across the site; however, based on the blow counts, in-situ moisture content, and dry density, we believe a partial fill removal and replacement option may be considered beneath foundations, soil-supported slabs and settlement-sensitive flatwork, provided the Owner accepts the risk that post-construction compression of pre-existing fill left in place may result in settlement in excess of normally accepted tolerances and associated distress. If the risk cannot be accepted by the Owner, all pre-existing fills should be removed and replaced with structural fill. We recommend a representative of the geotechnical engineer verify the competency of the foundation and floor slab subgrade prior to concrete placement.

Foundations: Shallow foundations consisting of spread footings are considered feasible for supporting the proposed structures. Shallow foundations should be placed on undisturbed natural granular soil or a minimum of 2 feet of structural fill

As an alternative to a spread footings, a foundation system consisting of drilled footings is considered feasible to support the proposed structures. Additionally, a foundation system consisting of helical piers is considered feasible to support the proposed structures. The advantages of helical piers include the ability to bypass the pre-existing fill and transfer the foundation loads to the natural soils or bedrock with limited foundation settlement through relatively high load-bearing capacity in relatively incompressible material. Helical piers would also result in minimal, if any, spoils generated during foundation installation. Recommendations regarding each of these foundation systems are presented in the following section of this report.

Soil-Supported Slabs: Soil-supported slabs are considered feasible for the proposed renovations.

For new concrete flatworks not considered movement-sensitive, we recommended the subgrade soils below the paths be scarified to at least 12 inches, moisture-conditioned, and recompacted section of this report.

Movement-sensitive flatworks should be done in accordance with the recommendations provided backfilling with structural fill.

FOUNDATION RECOMMENDATIONS

As discussed in the proposed structures may be founded on shallow foundations consisting of spread footings or on drilled footings, or helical piers.

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

1. Considering the subsurface conditions encountered in the exploratory borings and the nature of the proposed construction, we recommend the spread footings be placed on undisturbed natural granular soil or a minimum of 2 feet of structural fill. Footings should be designed for a net allowable bearing pressure of 2,000 psf. Structural fill should meet and Earthwork section of this report.

2. Areas of loose and/or soft material, or deleterious substances encountered within footing excavations should be removed and replaced with structural fill. New fill should extend down from the edges of the footings at a 1 horizontal to 1 vertical projection.

3. Based on experience, we estimate total settlement for spread footings designed and constructed as discussed in this section will be less than 1 inch. Differential settlements between individual foundations are estimated to be approximately ½ to ¾ of the total settlement. Due to the presence of granular soils, settlements should occur during or shortly after construction.

4. Spread footings should have a minimum footing width of 16 inches for continuous footings and of 24 inches for isolated pads.

5. Footings 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 supported, as recommended herein, will be a combination of the sliding resistance of the footing on the foundation 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 0.33. Passive pressure against the sides of the footings can be calculated using an equivalent fluid unit weight of

230 pcf. The above values are working values. Structural fill placed against the sides of footings to resist lateral loads should meet the material and placement requirements and Earthwork

7. Groundwater was encountered in the borings during drilling at depths near the anticipated depths of the excavation for foundations. Dewatering of the footing excavation may be required due to the expected saturated soil adjacent to the ponds. Dewatering should be conducted by using sumps, drains, and/or other dewatering methods to maintain water levels at least 2 feet below the footing subgrade elevation to mitigate against loss of soil support.

8. Natural granular soils at the bottom of foundations, if encountered, should be re-densified with a smooth vibratory compactor just prior to placement of concrete.

9. A representative of the geotechnical engineer should observe all footing excavations prior to concrete placement.

Drilled Footings: The following should be used for design and construction of the proposed structures using drilled footings terminating in natural soils or bedrock. Drilled footings should not terminate in the pre-existing fill.

1. Drilled footings with a minimum length of 4 feet and terminating in natural soils should be designed for an allowable soil bearing pressure of 4,000 psf. Drilled footings terminating in bedrock should be designed for an allowable soil bearing pressure of 7,500 psf.

2. We understand the depth of excavation for the drilled footings is of concern to the Owner.

If the Owner understands and accepts an elevated risk of post-construction consolidation of existing fills left in place below drilled footings, the minimum drilled footing depths can be reduced to 4 feet. The owner should understand that terminating the drilled footing at a depth of 4 feet may result in the footings bearing in undocumented fill. Accordingly, movements in excess of 2 inches may occur and should be anticipated. Drilled footings bearing in the existing fill soils with a minimum embedment of 4 feet, may be designed for an allowable soil bearing pressure of 1,500 psf.

3. Additionally, skin friction values of 140 psf and 400 psf may be accounted for the existing fill soils (greater than 3 feet deep) and the native granular soils, respectively, in design based on the interaction between the soil and sides of the drilled footing for use as axial support. We recommend the upper 3 feet of skin friction be ignored.

4. Based on experience, we estimate the total settlement for footings designed and constructed and bearing in the native granular soils or bedrock materials as discussed in this section will be 1 inch or less.

5. Drilled footings placed should have a minimum footing width of 18 inches and a minimum embedment of 4 feet.

6. The lateral resistance of a footing will be a combination of the sliding resistance of the footing on the foundation materials and passive earth pressure against the side of the footing. Resistance to sliding at the bottoms of the footings may be calculated based on a coefficient of friction of 0.33. Passive pressure against the sides of the drilled footings can be calculated using an equivalent fluid unit weight of 230 psf/ft. These lateral resistance values are working values.

7. The base of the excavation should be free of loose soil prior to placement of reinforcement steel or concrete.

8. The presence of water in the exploratory boring indicates dewatering equipment may be required. In no case should concrete be placed in more than 3 inches of water unless the tremie method is used. If water cannot be removed or prevented with the use of temporary casing and/or dewatering equipment prior to placement of concrete, the tremie method should be used after the hole has been cleaned.

9. Concrete used in the pier should be a fluid mix with sufficient slump so it will fill the annulus between reinforcing steel and the pier hole. We recommend a concrete slump in the range of 5 to 8 inches be used.

10. A representative of the geotechnical engineer should observe the open bore hole prior to placement of formwork or placement of concrete.

Helical Piers: The axial design load of helical piers should be determined in general accordance with the current International Building Code (IBC), which states the allowable axial design load, Pa, should be determined as follows:

Pa= 0.5 Pu, where Pu (the ultimate load) is the least value of:

1. Sum of the areas of the helical bearing plates times the ultimate bearing capacity of the soil or rock comprising the bearing stratum.

2. Ultimate capacity determined from well-documented correlations with installation torque.

3. Ultimate capacity determined from load tests.

4. Ultimate capacity of the pier shaft.

5. Ultimate capacity of pier couplings.

6. Sum of the ultimate axial capacity of helical bearing plates affixed to the pier.

Items 1 through 3 are related to the geotechnical capacity of the piers; Items 4 through 6 are related to the structural capacity and should be evaluated by the structural engineer. The owner and structural designer should be aware that certain proprietary helical pier systems have been subjected to acceptance testing administered by the International Code Council (ICC), while other systems provided by specialty contractors may be fabricated according to designs by registered professional engineers. The certified systems have documentation that addresses many of the structural capacity issues, while the non-certified systems require structural design by an engineer. Many of the lighter-duty helical pier systems available, with working capacities on the order of 50 kips or less, are certified, which can simplify the design and submittal process.

However, higher capacity systems, where single piers may have working capacities of 200 kips or more, sometimes referred to as screw piles, are often designed and fabricated and are not certified manufactured systems.

Based on consideration of bearing capacity theory and published correlations of boring penetration resistance values with ultimate bearing capacity, we recommend an ultimate bearing capacity for a helical pier embedded to a minimum depth of 10 feet (measured from the top of the ground surface) in the natural soils of 8,000 psf, for capacity based on bearing provided by the helices. The ultimate bearing capacity for helical piers embedded in claystone bedrock may be increased to an estimated 15,000 psf.

Helical piers are typically very slender foundation elements with limited capacity to resist lateral loads. Lateral restraint of a helical pier foundation system is normally provided through the use of passive pressure on pier caps or foundation walls or through the use of battered piers. It is normally assumed that a battered pier can be designed for the same axial load as a vertical pier, with the lateral restraint being provided by the horizontal component of the battered pier. Helical piers are often assumed to have tension capacities similar to the axial compressive capacity, although that should be evaluated through load testing or otherwise addressed by the specialty

Acceptance of helical pier installation should be based on attaining a specified torque in the recommended bearing stratum determined in accordance with correlations of installation torque to capacity based on calibrated torque measurements and axial load test data. In our opinion, the ultimate bearing capacity recommended above may be exceeded if supported by adequate site-specific load test data. If site-specific load tests are not performed, the specialty helical pier n torque-to-capacity data for their pier system in similar soil conditions. If that information cannot be provided, site-specific load tests should be performed in accordance with ASTM D1143.

We recommend a qualified helical pier specialty contractor be retained to provide the required design submittal and to provide and install the helical piers. The project design should include a performance specification indicating required capacities, structural requirements, and submittal requirements. At a minimum, the submittal should be required to contain information supporting the capacity determination, a description of equipment and installation procedures that will ensure penetration to the required depths, and acknowledgment that the helical bearing plates will be installed into the recommended bearing stratum, as well as all necessary information to satisfy the requirements of the project structural designer.

including monitoring depths and general conformance with the plans and specifications. Our observation and testing services are intended to document that all of the helix-bearing plates on the piers are installed into the design-bearing stratum.

SOIL-SUPPORTED SLABS

A discussion of the removal of existing fill to reduce settlement potential is presented in the

Ideally, all existing fill material should be removed from below soil-supported slabs and replaced with structural fill. However, it is our opinion a portion of the existing fill may remain in place if the potential for some distress resulting from post-construction compression of the fill is recognized and accepted by the Owner.

As a minimum, we recommend fill within 2 feet below non-movement-sensitive soil-supported slabs be removed and replaced with structural fill meeting the material and placement criteria presented in the following section of this report.

Complete fill removal and replacement with structural fill extending to undisturbed natural soil or bedrock should be considered beneath movement-sensitive slabs.

SITE GRADING AND EARTHWORK

Site Preparation: As previously stated, subgrade preparation should be performed by overexcavating below the shallow foundations and soil-supported slabs consistent with the recommendations presented of this report. Overexcavated areas should be backfilled with structural fill, meeting the material and compaction criteria in this section.

Excavations across the site are anticipated to encounter pre-existing fill and natural granular overburden soils. Excavation of the existing fills and natural soils can be accomplished by typical earth-moving equipment. The contractor should mobilize equipment of sufficient size and operating condition to penetrate through zones containing isolated to possibly frequent small to large gravels, cobbles, and possibly boulders to achieve the required excavation depths.

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 footing.

Temporary Excavations: We assume site excavations will be constructed by generally over-excavating the side slopes to a stable configuration where enough space is available. Where insufficient lateral space is available due to the proximity to property boundaries, existing facilities, and traffic areas, temporary shoring may be required. It is our experience that temporary shoring systems are typically designed and built by specialty contractors and that the designers will geotechnical study report. Temporary shoring provided in close proximity to existing facilities or traffic areas should be sufficiently stiff to prevent movement.

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 soils and may encounter claystone bedrock. The on-site pre-existing fill and natural granular soils will classify as OSHA Type C soils. The bedrock, if encountered, will classify as

OSHA Type B. If localized perched water or seepage is encountered, much flatter side slopes than those allowed by OSHA, or temporary shoring may be required.

Excavated slopes may soften or loosen due to construction traffic and erode from surface runoff.

Measures to keep surface runoff from excavation slopes, including diversion berms, should be considered.

Dewatering Considerations: Groundwater may be encountered in excavations at the site. If local perched groundwater is encountered and dewatering is necessary, we believe construction dewatering can be accomplished with trenches sloping to sumps where the water can be pumped out of the excavation.

Selection of a dewatering system is the responsibility of the contractor. Dewatering systems should also be properly designed to prevent piping and the removal of soil particles, which could have damaging effects.

Cut and Fill Slopes: Permanent unretained cuts in the overburden soils and fill slopes up to 10 feet high should be constructed at a 2H:1V (horizontal-to-vertical) or flatter inclination for stability purposes and at a 3H:1V or flatter inclination for limiting the potential for erosion. Fills should be benched into cuts or natural slopes exceeding 4H:1V with bench heights between 2 and 4 feet. If water seepage is encountered during or prior to cut slope excavation, a stability evaluation should be conducted to determine if the seepage would adversely affect the cut.

Fill Material Specifications: The following material specifications are presented for the on-site overburden soil in the project site. We believe the on-site pre-existing fill and natural soils are suitable for reuse when used according to the specifications outlined below.

1. Structural Fill: Structural fill may consist of on-site overburden soil, including pre-existing fill, provided it meets the material suitability and placement criteria specified in this section.

Imported structural fill material, if necessary, should have a maximum of 45 percent passing the No. 200 sieve, a maximum liquid limit of 25, 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 outlined in Item 2 below are satisfied.

Claystone, if encountered, should not be used as structural fill.

2. Material Suitability: Unless otherwise defined herein, all fill material should be non- to low-swelling, free of vegetation, fat clay, claystone, brush, sod, trash and debris, and other deleterious substances, and should not contain rocks or lumps having a diameter of more than 4 inches. A fill material should be considered non-expansive if the swell potential under a 200 psf surcharge pressure does not exceed 1 percent when a sample remolded to 95 percent of the standard Proctor (ASTM D698) maximum dry density at optimum moisture content is wetted.

Fill Placement Criteria: Structural fill placed at the site should be adjusted to moisture content within 2 percentage points of the optimum moisture content (optimum) for granular materials and placed in maximum 8-inch-thick loose lifts.

Compaction Requirements: A representative of the geotechnical engineer should observe fill placement operations on a full-time basis. We recommend the following minimum compaction criteria be used on the project.

Fill Location Percentage of Maximum Standard Proctor Density

(ASTM D698)

Beneath and Adjacent to Spread Footing Foundations 98%1 Beneath Floor Slabs and Pavements2 95% General Site Grading and Landscape Areas 95%

1. Granular soils should be compacted to a minimum of 98% of the standard Proctor (ASTM D698) maximum dry density at moisture contents within 2% of optimum or should be compacted to a minimum of 95% of the modified Proctor (ASTM D1557) maximum dry density at moisture contents within 2% of optimum if used beneath floor slabs and pavements.

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

Subgrade Preparation: Prior to placing site grading fill or structural fill, the upper 12 inches of the subgrade soils at the base of the fill zone should be scarified, moisture-conditioned, 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 be proof rolled with moderately heavy to heavy compaction equipment to identify soft areas exhibiting excessive deflection. Those areas should be removed from suitable soils and replaced with structural fill.

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

WATER-SOLUBLE SULFATES

The water-soluble sulfate concentration testing is in progress. The test results will be provided in the final report.

PAVEMENT THICKNESS DESIGN

A pavement section is a layered system designed to distribute concentrated traffic loads to the subgrade. 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.

Pavement design procedures are based on the strength and stiffness properties of the subgrade and pavement materials, assuming stable, uniform conditions.

Subgrade Materials: Based on the results of the field exploration and laboratory testing programs, the pavement subgrade materials at the site are anticipated to classify as A-1-a and A-2-4 soils with a group index of 0 in accordance with the American Association of State Highway and

Transportation Officials (AASHTO) soil classification system. Soils classifying as A-1-a would generally be considered to provide excellent subgrade support. Soils classifying as A-2-4 would generally be considered to provide good subgrade support. A design resilient modulus value of

4,195 psi was selected for flexible pavements, and a corrected design modulus of subgrade reaction of 30 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 paved parking surfaces (Standard-Duty), and an ESAL of 73,000 was assumed for drive and fire lane areas, trash collection points, and where turning points are concentrated (Heavy-

Duty). The values are selected based on our past experience with facilities of this nature. The

Heavy-Duty pavement section should be constructed in locations of concentrated heavier vehicular traffic movements.

If estimated daily traffic volumes for the facility are known to be different from those assumed, we should be provided with this information in order to reevaluate the pavement sections provided below.

Pavement Thickness Requirements: Recommendations for a full-depth asphalt section, composite section, and for a rigid Portland cement concrete pavement (PCCP) section are presented in the table below. The pavement sections were determined in accordance with 1993

AASHTO pavement design procedures. For design purposes, a design reliability of 80% was assumed for all pavement areas. The following table presents the minimum pavement thickness alternatives for the project:

LOCATION

Full Depth Asphalt

Pavement (inches)

Asphalt Over Aggregate Base Course

(inches)

PCCP

(inches)

Standard Duty 5.5 4.0 over 6.0 6.0

Heavy Duty 6.5 5.0 over 6.0 7.0

Dumpster pads and any areas of the pavement that will be subjected to concentrated truck turning movements should be paved using a minimum section consisting of 7.0 inches of PCCP. The

PCCP thicknesses presented above are for unreinforced sections.

Pavement Materials: The following are recommended materials 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 as a working surface below

PCCP should meet the material specifications for Class 5 or Class 6 ABC stated in the current CDOT Specifications. The ABC should be placed and compacted as outlined in

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. Sealing of the joints and installation of tie-bars, where necessary, should be in accordance with the latest CDOT M&S Standards.

Subgrade Preparation: Subgrade preparation below pavements should consist of thorough scarification and well-mixing to a minimum depth of 12 inches for flexible pavement and 24 inches for PCCP pavement, moisture-conditioning, and recompacting the material in accordance with the

Pavement design procedures assume a stable subgrade. Prior to placing the pavement section, the pavement subgrade should be proof-rolled with a heavily loaded pneumatic-tired vehicle with a tire pressure of at least 100 psi capable of applying a minimum load of 18-kips per axle. 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. Areas where excessive deflection occurs should be ripped, scarified, wetted, or dried if necessary and re-compacted to the required moisture and density specifications.

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.

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 K+A be retained to provide construction observation and testing services to document 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

This study has been conducted for exclusive use by the client for design purposes. The conclusions and recommendations submitted in this report are based upon the data obtained from the exploratory borings at the location indicated on Fig. 1, and the proposed type of construction.

This report may not reflect subsurface variations that occur, and the nature and extent of variations across the site may not become evident until site grading and excavations are performed. If during construction, soil or groundwater conditions appear to be different from those described herein, K+A should be advised at once so that a re-evaluation of the recommendations presented in this report can be made. K+A is not responsible for liability associated with interpretation of subsurface data by others.

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

KMH/ls Rev. by: DPC cc: File