2025-05-01 Geotech Report - Lafayette Waterlines.pdf

Kumar & Associates, Inc.®

TABLE OF CONTENTS

PURPOSE AND SCOPE OF WORK

PROPOSED CONSTRUCTION

SITE CONDITIONS

SUBSURFACE CONDITIONS

LABORATORY TESTING

PIPELINE RECOMMENDATIONS

SITE GRADING

LIMITATIONS

FIG. 1 – VICINITY MAP

FIGS. 1A AND 1B – LOCATION OF EXPLORATORY BORINGS

FIG. 2 – LOGS OF EXPLORATORY BORINGS

FIG. 3 – LEGEND AND NOTES

FIGS. 4 through 6 – SWELL-CONSOLIDATION TEST RESULTS

FIGS. 7 and 8 – GRADATION TEST RESULTS

FIGS. 9 and 10 – MOISTURE DENSITY RELATIONSHIPS

FIG. 11 – LABORATORY RESISTIVITY RESULTS

FIGS. 12 and 13 – HVEEM STABILOMETER TEST RESULTS

TABLE I – SUMMARY OF LABORATORY TEST RESULTS

APPENDIX A – PAVEMENT DESIGN CALCULATIONS

SUMMARY

1. A total of six (6) exploratory borings were drilled for this study at the approximate locations shown on Figs. 1A and 1B. Borings 1 and 2 (Keel Court Borings) encountered approximately 4 to 4.5 inches of asphalt overlying approximately 3.5 to 4.5 feet of man-placed fill material. The man-placed fill was underlain by naturally deposited (natural) clayey soils that extended to depths of about 11 to 12 feet below the ground surface.

Boring 1 encountered siltstone bedrock underlying the natural clayey soils that extended to the explored depth of about 15 feet below the ground surface. Boring 2 encountered weathered siltstone underlying the natural clayey soils that extended to the explored depth of about 15 feet.

Borings 3 through 6 (Cherrywood Drive Borings) encountered approximately 6 to 7.75 inches of asphalt overlying approximately 1.5 to 3 feet of man-placed fill. The man-placed fill was underlain by natural clayey soils which were in turn underlain by natural granular soils that extended to the explored depth of about 10 feet. Boring 4 encountered weathered claystone underlying the natural clayey soils that extended to the explored depth of about 10 feet.

The man-placed fill consisted of lean clay with sand to clayey sand to silty sand.

Occasional layers of chemically treated soils were noted in the man-placed fill. The natural clayey soils consisted of lean clay to sandy lean clay. The natural granular soil consisted of silty sand to poorly graded sand with silt and gravel with occasional layers of poorly graded gravel with silt and sand.

Groundwater was observed in Boring 2 at the time of drilling at a depth of about 7.5 feet below the ground surface and the borings were immediately backfilled with flowable fill for safety reasons.

2. We recommend that a modulus of soil reaction, E’, of 1,000 psi for portions of the pipe with a trench base that is primarily fine-grained soils and 1,800 psi be used for portions of the pipe that will be bedded with a trench base consisting of natural granular materials, provided the pipe-zone material is compacted to at least 75% relative density (ASTM D 4253 and ASTM D 4254). For evaluating the load on the pipe due to the backfill above the pipe, we recommend using a compacted unit weight of 125 pcf and a Rankine’s ratio of 0.31 for compacted trench-zone backfill consisting of existing on-site soils. We recommend using a coefficient of friction of 0.30 between backfill consisting of excavated on-site soils and the soils exposed on the trench walls.

3. Above a depth of 10 feet, thrust blocks used to resist thrust forces at horizontal bends in the pipe should be designed using an allowable bearing pressure for properly compacted fill and natural soils based on an equivalent fluid density of 175 pcf (this value is a working value). The allowable bearing pressure should be calculated by multiplying the equivalent fluid density value by the depth in feet below ground surface corresponding to the mid-point height of the face of the thrust block. For thrust blocks with a mid-point depth of 10 feet or more, a maximum allowable bearing pressure of 1,750 psf should be used.

4. The following table presents a summary of the recommended pavement thicknesses:

Pavement Thickness Alternatives

ASPHALT PAVED

AREA

Composite Section Asphalt/ABC

(inches)

Full Depth Asphalt (inches)

Local Roadway 4 / 6 5.5

The upper 2 feet of pavement subgrade should consist of the properly moisture conditioned and compacted on-site overburden soils.

PURPOSE AND SCOPE OF WORK

This report presents the results of a geotechnical engineering study performed for the proposed

Waterline Improvements project at 2 locations in Lafayette, Colorado. The first location is along

Keel Court located west of Waneka Lake Trail. The second location is along Cherrywood Drive located north of Empire Road. The study was conducted for the purpose of developing geotechnical engineering design recommendations and construction related considerations for the proposed pipeline. The study was conducted in general accordance with the scope of work in our Proposal No. P3-24-280 dated October 23, 2024.

A field exploration program consisting of exploratory borings was conducted to obtain information on subsurface conditions along the proposed pipeline alignment. Samples of the soils and weathered bedrock obtained during field exploration were tested in the laboratory to provide information on their classification and engineering characteristics. This report has been prepared to summarize the data obtained from this work and to provide geotechnical engineering related considerations and recommendations.

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 construction of the proposed development are included in the report.

PROPOSED CONSTRUCTION

Based on the information provided, we understand emergency repairs have been required along the existing waterline segments due to corrosivity of the soils. We also understand the existing waterline along Keel Court is approximately 10 feet below the ground surface and the existing waterline along Cherrywood Drive is approximately 5 to 6 feet below the ground surface.

If the proposed development varies significantly from that generally described above or depicted throughout this report, we should be notified to reevaluate the recommendations provided herein.

SITE CONDITIONS

Keel Court consisted of a 2-lane asphalt paved roadway with a cul-de-sac and Cherrywood Drive consisted of a 2-lane asphalt paved roadway. The alignment areas along Keel Court and

Cherrywood Drive are generally flat with a minimal slope down towards the east. Keel Court is generally bounded to the north, east and south by single-family residential properties and to the west by Paschal Drive. Cherrywood Drive is generally surrounded by single-family residential properties. Cherrywood Park borders the Cherrywood Drive site to the south near the eastern portion of the site.

SUBSURFACE CONDITIONS

Information on the subsurface conditions was obtained by drilling a total of six (6) exploratory borings at the locations shown on Figs. 1A and 1B. Graphic logs of the borings are presented on

Fig. 2 and a legend and notes describing the soil encountered are presented on Fig. 3.

Borings 1 and 2 (Keel Court Borings) encountered approximately 4 to 4.5 inches of asphalt overlying approximately 3.5 to 4.5 feet of man-placed fill material. The man-placed fill was underlain by naturally deposited (natural) clayey soils that extended to depths of about 11 to 12 feet below the ground surface. Boring 1 encountered siltstone bedrock underlying the natural clayey soils that extended to the explored depth of about 15 feet below the ground surface. Boring

2 encountered weathered siltstone underlying the natural clayey soils that extended to the explored depth of about 15 feet.

Borings 3 through 6 (Cherrywood Drive Borings) encountered approximately 6 to 7.75 inches of asphalt overlying approximately 1.5 to 3 feet of man-placed fill. The man-placed fill was underlain by natural clayey soils which were in turn underlain by natural granular soils that extended to the explored depth of about 10 feet. Boring 4 encountered weathered claystone underlying the natural clayey soils that extended to the explored depth of about 10 feet.

The man-placed fill consisted of lean clay with sand to clayey sand to silty sand. Occasional layers of chemically treated soils were noted in the man-placed fill. The natural clayey soils consisted of lean clay to sandy lean clay. The natural granular soil consisted of silty sand to poorly graded sand with silt and gravel with occasional layers of poorly graded gravel with silt and sand.

The man-placed fill contained a fine to coarse grained sand fraction and was moist and brown to dark brown to gray. The natural clayey soils contained a fine to coarse grained sand fraction and were moist to wet below groundwater and brown to gray. The natural granular soils were fine to coarse grained, moist and brown. The weathered claystone was fine to medium grained, moist and brown to gray. The weathered siltstone was fine to medium grained, moist and tan to gray.

The siltstone bedrock was fine to medium grained, moist and brown to gray. Based on sampler penetration resistance, the natural clayey soils had consistencies ranging from medium stiff to very stiff, the natural granular soils were medium dense to dense, and the bedrock was very hard.

Groundwater was observed in Boring 2 at the time of drilling at a depth of about 7.5 feet below the ground surface and the borings were immediately backfilled with flowable fill for safety reasons. Groundwater levels are expected to fluctuate with time and may fluctuate upward after wet weather.

LABORATORY TESTING

Laboratory testing was performed on samples from the borings. The laboratory testing was performed in our in-house laboratory on representative soil samples obtained from the borings to determine in situ soil moisture content and dry density, Atterberg limits, gradation, and swell-consolidation characteristics. The results of the laboratory tests are presented graphically on

Figs. 4 through 13 and summarized in Table I. The testing was conducted in general accordance with recognized test procedures, primarily those of ASTM and the Colorado Department of

Transportation.

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 moisture content, dry density, liquid limit and plasticity index, and the percent of soil passing the U.S. No. 4 and 200 sieves are presented in the Table I and adjacent to the corresponding sample on the boring logs.

Swell-Consolidation: Swell-consolidation tests were conducted on samples of the man-placed fill, natural clayey soils and weathered claystone to determine their compressibility and swell characteristics under loading and when submerged in water. Each sample was prepared and placed in a confining ring between porous discs, subjected to a surcharge pressure of 200 psf, and allowed to consolidate before being submerged in water. The samples were then inundated with water, and the change in sample height was measured with a dial gauge. The sample heights were monitored until deformation practically ceased under each load increment.

Results of the swell-consolidation tests are presented on Figs. 4 through 6 as plots of the curve of the final strain at each increment of pressure against the log of the pressure. Samples of the man-placed fill exhibited low swell potential (0.6% to 1.7%) upon wetting under a surcharge pressure of 200 psf. Samples of the natural clayey soils exhibited low to moderate swell potential

(0.6% to 3.1%) upon wetting under a surcharge pressure of 200 psf. A sample of the weathered claystone exhibited high swell potential (5.0%) upon wetting a surcharge pressure of 200 psf.

Moisture-Density Relationships Representative bulk samples were collected from Borings 1 and

2 between the depths of about 1 foot and 4 feet and from Borings 3 through 5 at depths between about 1 foot and 4 feet for the evaluation of the moisture-density relationship in accordance with the standard Proctor method (ASTM D698/AASHTO T99). The maximum dry density of the composite sample from Borings 1 and 2 was 113.8 pcf at an optimum moisture content of 13.2 percent and the maximum dry density of the composite sample from Borings 3 through 5 was

112.7 pcf at an optimum moisture content of 12.4%. Results of the tests are presented in Figs. 9 and 10.

Buried Metal Corrosion: The potential corrosive environment for metal was evaluated based on data collected during our field exploration and laboratory testing programs. The data included pH, laboratory resistivity, sulfides, Re-dox and concentrations of water-soluble sulfates and chlorides.

The laboratory test results are shown on the boring logs on Fig. 2, and are summarized in Table

I.

The test results indicated minimum laboratory electrical resistivity ranging from approximately 429 to 980 ohm-cm. Based on the Ductile Iron Pipe Research Association (DIPRA) handbook, the relatively low resistance material would classify as creating a potentially corrosive environment to buried metal.

The acidity of the soil was assessed by conducting a pH test, which resulted in pH levels of 7.10 and 8.06. Samples of soil resulted in 0 mg/L for sulfides. Redox testing resulted in values of 274 and 310 mv. The measured concentration of chlorides was 150 and 487 ppm.

The general chemical characteristics of the soils indicate the subsurface profile could result in a potentially corrosive environment, particularly under saturated conditions. We recommend a qualified corrosion engineer review the information presented above to design an appropriate level of corrosion protection for buried metal.

Water-Soluble Sulfates: The concentration of water-soluble sulfates measured in samples of the overburden soils obtained from the exploratory borings was 0.00% and 0.80%. This concentration of water-soluble sulfates represents a Class S2 severity exposure to sulfate attack on concrete exposed to these materials. The degree of attack is based on a range of Class S0, Class S1, Class S2, and Class S3 severity exposure as presented in ACI 201.

Based on the laboratory testing, we recommend all concrete exposed to the on-site materials meet the cement requirements for Class S2 exposure as presented in ACI 201. Alternatively, the concrete could meet the Colorado Department of Transportation’s (CDOT) cement requirements for Class S2 exposure as presented in Section 601.04 of the CDOT Standard Specifications for

Road and Bridge Construction.

PIPELINE RECOMMENDATIONS

Pipe Backfill: Bedding material supporting the pipe bottom should consist of an uncompacted layer of imported granular material meeting the manufacturer’s recommendations or local jurisdictions criteria for pipe bedding. Bedding and embedment zone material may consist of a granular soil with a maximum size of ¾ inch, less than 25% passing the No. 50 sieve, and less than 5% passing the No. 200 sieve. Based on the results of the laboratory analyses performed on selected samples obtained from the borings, the on-site soils do not meet the requirements for bedding and embedment zone material. The bedding layer should be of adequate thickness to fully support the pipes when seated on top of the bedding, and should have a minimum thickness based on the proposed pipe diameter and criteria established by American Water Works

Association (AWWA, M41). We recommend considering a minimum uncompacted thickness of

4 inches. Prior to placing the bedding, the subgrade should be excavated and loose material removed to provide firm subgrade support. Granular subgrade materials at the bottom of the trench (if encountered) should be densified with a vibratory plate compactor prior to placing the bedding material.

Depending upon the depth of burial, very soft clay soils with moisture contents well above optimum may be encountered at the bearing elevation for the pipe. Increasing the thickness of the bedding material to a minimum of 12 inches may be required for proper support of the pipe.

The pipe-zone material placed above the bedding and surrounding the pipe should consist of granular material similar to that described above for pipe bedding, and should be compacted to at least 75% relative density (ASTM D 4253 and ASTM D 4254). The pipe-zone material should also be placed and compacted in accordance with the requirements of the pipe manufacturer.

Special care should be taken to provide adequate compaction below the haunches of the pipe using a concrete vibrator, vibratory plates or other light compaction equipment as needed. In confined areas of the pipeline where compaction is difficult, placement of a controlled low strength material (CLSM), commonly referred to as flow fill, around the pipe should be considered.

Backfill placed above the pipe-zone materials to the surface should consist of suitable on-site soil obtained from the pipeline excavation. Suitable soils should have a maximum particle size of 3 inches and should be generally free of organics, wood, or other deleterious material that could decay over time. Most of the soils encountered in the exploratory borings satisfy the material requirements based on laboratory testing of selected samples. Bedrock, if encountered and reused in the trench, should be broken down into a soil like material. The backfill should be compacted to at least 95% of the standard Proctor (ASTM D 698) maximum dry density at a moisture content within 2 percentage points of optimum for granular soils and within 0 to +3 percentage points of optimum for clay soils.

Variable moisture contents were indicated for the soils encountered in the exploratory borings.

The contractor should anticipate that processing to add water, or allowing time for material to dry out, will likely be required.

The pipe should be buried an adequate depth below the surface to limit pipe deflections caused by current or planned future traffic loading. The minimum burial depth required for the pipe will depend on the material and physical properties of the pipe, the soil/structure interaction between the pipe and the backfill material, and traffic loading conditions. We recommend that the pipe burial depth be at least 4 feet and satisfy manufacturer requirements for maximum allowable deflection and minimum burial depth.

Pipeline Design Parameters: We recommend that a modulus of soil reaction, E’, of 1,000 psi for portions of the pipe with a trench base that is primarily fine grained soils and 1,800 psi be used for portions of the pipe that will be bedded with a trench base consisting of natural granular materials, provided the pipe-zone material is compacted to at least 75% relative density (ASTM

D 4253 and ASTM D 4254). For evaluating the load on the pipe due to the backfill above the pipe, we recommend using a compacted moist unit weight of 125 pcf and a Rankine’s ratio of

0.31 for compacted trench-zone backfill consisting of existing on-site soils. We recommend using a coefficient of friction of 0.30 between backfill consisting of excavated on-site soils and the soils exposed on the trench walls.

The above E’ values do not have a factor of safety applied. The Transportation Research Board

(TRB) Report 225 recommends that for shallow covers, the listed E’ value should be reduced by

50%. ASCE’s Gravity Sanitary Sewer Design and Construction Manual recommends that 75% of the listed E’ values should be used and the U.S. Soil Conservation Service applies a factor of 0.5 to the E’.

Thrust Forces: Thrust blocks should be located in relatively stiff soils (blow counts above 8 blows per foot). In relatively stiff soils less than a depth of 10 feet below finished grade, blocking used to resist thrust forces at horizontal bends in the pipe should be designed using an allowable bearing pressure for properly compacted fill and natural soils based on an equivalent fluid density of 175 pcf (this value is a working value). The allowable bearing pressure should be calculated by multiplying the equivalent fluid density value by the depth in feet below ground surface corresponding to the mid-point height of the face of the thrust block. For thrust blocks with a mid-point depth of 10 feet or more, a maximum allowable bearing pressure of 1,750 psf should be used. Site specific studies should be performed to evaluate if higher bearing pressure values are possible.

Excavation Considerations: The pipe trench should be excavated in accordance with all OSHA requirements, and other applicable local and state requirements. Based on the OSHA excavation guidelines, we believe that areas of natural clayey soils encountered in the borings generally classify as an OSHA Type B or C.

We believe that overburden soils, similar to those encountered within the explored depths of the exploratory borings, may be excavated with conventional heavy-duty excavation equipment.

Excavation of the bedrock materials, if encountered during excavation, may be more difficult when being performed in confined areas and will require heavy-duty excavation equipment with ripper teeth or possibly pneumatic chisels and/or light explosives.

Where insufficient lateral space is available to lay the slopes back during excavation due to the proximity to property boundaries and existing structures and facilities, 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 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.

Temporary shoring provided in close proximity to existing structures or traffic areas should be sufficiently stiff to prevent movement. We recommend that a pre-condition reconnaissance of adjacent existing structures be performed prior to beginning excavations, and temporary shoring, to document the condition of those structures (e.g., with photographs), and locate areas where instrumentation (e.g., crack monitors across existing cracks) should be considered for monitoring potential impacts to the structures caused by that work. Ideally, representatives of the owner of the adjacent structure, client, geotechnical engineer and contractor should perform the reconnaissance, and personnel responsible for monitoring the structures and any instrumentation should be identified.

Bottom of Trench Preparation: Fine grained materials such as clay and weathered claystone materials will be encountered at the bottom of the trench along most of the alignment. Bottom of trench excavation preparation in areas with firm, unyielding soils, as encountered in the majority of the pipeline alignment, should consist of removing all loose materials from the bottom of the excavation prior to placing bedding material. These soils should provide adequate support during densification of the bedding materials.

Potentially unstable bottom of trench soils may be encountered in isolated areas of the alignment.

Unstable soil remediation may be completed using a geotextile/gravel system. Alternate stabilization methods may be suitable, and may be discussed with the pipeline contractor. Bottom of trench stabilization may be achieved by removing the unstable soils and replacing them with a granular material such as aggregate base course meeting CDOT Class 6 criteria placed on top of a high-performance geotextile (HPG). The extent of the removal and replacement should be determined in the field, however a minimum replacement thickness of about 12 inches is recommended. Stabilization fill should extend the entire width of the trench excavation.

Additional thicknesses may be required to adequately bridge unstable soils and will need to be determined in the field using a test section.

The high-performance geotextile shall be placed directly below the stabilizing fill to provide separation and stabilization. The geotextile should be woven and meet or exceed the minimum properties presented below:

Geotextile Requirements

Mechanical Properties Minimum Average Roll Value (MARV) MD (#/ft) CD (#/ft)

Tensile Strength at 5% strain (ASTM D 4595) 1,400 1,400

Minimum permittivity (ASTM D 4491) 0.5 sec-1

Apparent Opening Size (AOS) 0.50 mm maximum

Mirafi RS280i meets the criteria presented above. Other products meeting the above criteria may be suitable as an approved equal.

Dewatering Considerations: Groundwater was encountered at depths ranging from about 7.5 feet below the ground surface in Boring 2 at the time of drilling. Groundwater levels are expected to fluctuate with time, and may fluctuate upward after wet weather especially near the drainages.

We believe that dewatering the excavations may be accomplished using trenches and sumps;

however, we recommend that a dewatering plan be designed by the contractor and reviewed prior to excavation in the event that trenches and sumps are not sufficient. Dewatering well points will likely not be an effective means of dewatering due to the clayey subsurface conditions.

Surface water runoff into the excavations can act to erode and potentially destabilize the trench slopes and result in soft ground conditions along the trench bottom, and should not be allowed.

Diversion berms and other measures should be used to prevent surface water runoff into the trenches from occurring.

SITE GRADING

Permanent Cut Slopes: Permanent unretained cuts in the overburden soils less than 10 feet in height should be sloped to 3 horizontals to 1 vertical, although flatter slopes may be desired due to erosion and revegetation considerations. The risk of slope instability will be significantly increased if seepage is encountered in cuts. If seepage is encountered in permanent excavations, an investigation should be conducted to determine if the seepage will adversely affect the cut stability. Based on our understanding of the maximum depths anticipated for site grading, it does not appear that slope instability due to groundwater seepage will typically be a concern. However, it could be of concern regarding temporary stability in deep excavations for site utilities.

Permanent Fills and Embankments: Fill slopes up to 10 feet in height can be used if the fill slopes do not exceed 3 horizontals to 1 vertical and the fills are properly compacted and drained. The ground surface underlying all fills should be carefully prepared by removing all organic matter, scarification to a depth of 12 inches and compacting to 95% of the modified Proctor maximum dry density at a moisture content near optimum to provide a uniform base for fill placement. Fills should be benched into cuts exceeding 4 horizontals to 1 vertical.

Good surface drainage should be provided around all permanent cuts and fills to direct surface runoff away from the slope faces. Fill slopes, cut slopes and other stripped areas should be protected against erosion by revegetation or other methods.

Temporary Excavations: For temporary excavations that occur during site grading, the natural clays classify as OSHA Type C or Type B soils. All excavations should be constructed in accordance with the applicable OSHA regulations. If groundwater is encountered, the geotechnical engineer should be notified so that additional recommendations can be provided, if necessary.

Material Specifications: The following recommendations for material specifications are presented for new fills on the project site. A geotechnical engineer should evaluate the suitability of all proposed import fill material, if required, for the project prior to placement.

1. Imported Fill: Imported fill (if necessary) should contain 50 percent passing the No. 200 sieve, have a maximum liquid limit of 35 and a maximum plasticity index of 15. Also, the swell potential of non-expansive fill materials when remolded to 95% of the standard Proctor

(ASTM D-698/AASHTO T-99) maximum dry density at optimum moisture content should be less than 2% when wetted under a 200 psf surcharge pressure.

2. Pavement Subgrade: The upper 2 feet of pavement subgrade should consist of the properly moisture conditioned and compacted on-site overburden soils.

3. Aggregate Base Course: Material should satisfy material requirements for CDOT Class 5 or Class 6 aggregate base course.

4. Material Suitability: It is the intent of the recommendations provided herein to use the on-site soil for required fills on the site.

All fill material should be free of vegetation, brush, sod and other deleterious substances and should not contain rocks, debris or lumps having a diameter of more than 4 inches.

Rocks, debris or lumps should be dispersed throughout the fill and "nesting" of these materials should be avoided. The geotechnical engineer should evaluate the suitability of proposed import fill materials prior to placement.

Compaction Specifications: 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 materials with 35% or less passing the number 200 sieve. Materials with more than 35% passing the number 200 sieve should be compacted at moisture contents between 0 and +3 percentage points of optimum. The contractor should be aware that clay materials, 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. Unless otherwise noted, we recommend the soil types be compacted using the criteria below:

AASHTO Classification Applicable Proctor

A-1, A-2-4, A-2-5, and A-3 Modified Proctor (ASTM D1557 /

AASHTO T180

All other Classifications Standard Proctor (ASTM D698 /

AASHTO T99)

3. Degree of Compaction: The following compaction criteria should be followed during construction

Area

Percentage of Standard Proctor Maximum

Dry Density

(ASTM D 698/

AASHTO T-99)

Percentage Maximum Dry Density

(ASTM D 1557,

AASHTO T-180)

Embankment Fill less than 4 Feet below finished grade 95 92

Embankment Fill more and 4 Feet below finished grade 100 98

Adjacent to Foundations 95 92 Fills Beneath Pavements and Exterior

Flatwork 95 92

Utility Trenches 95 92 Base Course N/A 95

3. Subgrade Preparation: Areas receiving new fill should be prepared as recommended in specific sections of this report to provide a uniform base for fill placement. All other areas to receive new fill not specifically addressed herein should be scarified to a depth of at least 8 inches and recompacted to at least 95% of the standard Proctor (ASTM D698) maximum dry density at the moisture contents recommended above.

Subgrade preparation should include proofrolling with a heavily loaded pneumatic-tired vehicle or a heavy, smooth-drum roller compactor. Areas that deform excessively during proofrolling should be removed and replaced to achieve a reasonably stable subgrade prior to placement of compacted fill or flatwork.

SURFACE DRAINAGE

Proper surface drainage is very important for acceptable performance of the structures and flatwork 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 structure. The following recommendations should be used as guidelines and changes should be made only after consultation with the geotechnical engineer.

1. Excessive wetting or drying of the foundation and flatwork excavations should be avoided during construction.

2. The ground surface surrounding the exterior of the structures, flatwork, and paved areas should be sloped to drain away in all directions. We recommend a minimum slope of 6 inches in the first 10 feet in unpaved areas and a minimum slope of 3 inches in the first

10 feet in paved or landscape areas. Site drainage beyond the 10-foot zone should be designed to promote runoff and reduce infiltration. These slopes may be changed as required for handicap access points in accordance with the Americans with Disabilities

Act.

3. The upper 1 to 2 feet of backfill in unpaved areas adjacent to the project elements should be a relatively impervious material compacted as recommended above to promote runoff and limit infiltration of surface runoff.

4. Ponding of water should not be allowed in backfill materials or in a zone within 10 feet of project elements.

5. Good surface drainage should be provided around all permanent cuts and fills to direct surface runoff away from the slope faces. Fill slopes, cut slopes and other stripped areas should be protected against erosion by revegetation or other methods.

PAVEMENT 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. Pavement design procedures are based on strength properties of the subgrade and pavement materials assuming stable, uniform conditions. Soil is represented for pavement design purposes by means of a soil support value for flexible pavements. This value is empirically related to strength.

Subgrade Materials: Based on the results of the field and laboratory studies, most of the near surface subgrade materials at the site classify as A-6 soils with group indices between 1 and 10 in accordance with the American Association of State Highway and Transportation Officials

(AASHTO) classification system. These soils are generally considered to provide fair to good subgrade support. R-Value testing of the composite samples taken from the subgrade resulted in R-Values of 7 and 25. For design purposes, a soil support value of 5,875 psi was calculated for flexible pavements using CDOT design calculations.

Design Traffic: We understand Keel Court and Cherrywood are classified as Local Roadways.

The Boulder County Multimodal Transportation Standards document. Traffic information was not available at the time of this report and an EDLA of 10 was assumed for the roadways.

Pavement Design: The pavement thicknesses were determined in accordance with the 1993

AASHTO pavement design procedures. Printouts for the software outputs are provided in the appendix of this report. The following design parameters were assumed based on the type of roadway:

ITEM INPUT

Reliability 80% Overall Standard Deviation, S0 0.44 Standard Normal Deviate, ZR -1.282

Initial Serviceability, P0 4.5 Terminal Serviceability, Pt 2.5

Resilient Modulus, MR 5,875 psi Asphalt Structural Coefficient 0.44 Base Structural Coefficient 0.12

The following table presents a summary of the pavement thickness calculations presented in the appendix of this report:

Pavement Thickness Alternatives

ASPHALT PAVED

AREA

Composite Section Asphalt/ABC

(inches)

Full Depth Asphalt (inches)

Local Roadway 4 / 6 5.5

Pavement Materials: Hot mix asphalt (HMA) and Portland cement concrete (PCCP) pavement should meet the latest applicable requirements, including the CDOT Standard Specifications for

Road and Bridge Construction. We recommend that the asphalt placed for the project be designed in accordance with the Superpave Gyratory Mix Design method. The mix should generally meet

Grading S or SX requirements with a SuperPave gyratory design revolution (NDESIGN) of 75.

Asphalt mixes should have a PG 58-28 or PG 64-22 asphalt binder with preference given to the

PG 58-28 binder. The PG 58-28 binder performs better on lightly loaded pavements and reduces the tendency and magnitude for thermal cracks to appear in the pavement surface. We recommend that Grading S mixes be placed with compacted lift thicknesses between 2.25 and 3 inches. Grading SX mixes should be placed such that final compacted lift thicknesses range from

1.5 to 3 inches.

Concrete for cross pans should meet the current CDOT requirements for Class P concrete.

Subgrade Preparation: The pavement subgrade should be properly moisture conditioned and compacted as outlined in the “Site Grading” section of this report. Subgrade areas should be compacted to 95% of the standard Proctor maximum dry density (ASTM D 698/AASHTO T-99), the chemically treated subgrade should be compacted to 95% of maximum dry density (ASTM

D558) and the aggregate base course should be compacted to 95% of the modified Proctor maximum dry density (ASTM D 1557, AASHTO T-180).

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.

LIMITATIONS

This study has been conducted in accordance with generally accepted geotechnical engineering practice in this area for exclusive use of 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 locations indicated on Fig. 1, and the proposed type of construction. This report does not reflect subsurface variations that may occur between the exploratory borings, and the nature and extent of variations across the site may not become evident until site grading and excavations are performed. If during construction, fill, soil, bedrock or groundwater conditions appear to be different from those described herein, Kumar & Associates, Inc. should be advised at once so that a re-evaluation of the recommendations presented in this report can be made.

Kumar & Associates, Inc. is not responsible for liability associated with 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 building site 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 soil in this area. The owner should be aware that there is a risk in constructing a building 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.

JAH/ER

Rev. by: JLB cc: book, file

Kumar & Associates

Project No.: 25-3-111 Project Name: Lafayette Waterline Improvements Date Sampled:

Date Received:

Boring Depth (Feet) Gravel

(%) Sand (%) Liquid

Limit (%) Plasticity Index(%)

1 1 3/24/25 13.9 119.5 44 27 14 A-6 (2) Fill: Clayey Sand (SC) 1 9 3/24/25 16.8 113.0 88 44 27 0.80 Lean Clay (CL) 2 1 3/24/25 15.7 29 56 15 NV NP A-1-a (0) Fill: Silty Sand (SM) 2 9 4/2/25 21.3 104.8 56 38 22 429 150.0 7.10 310 0 A-6 (9) Sandy Lean Clay (CL) 2 14 3/24/25 17.7 112.7 97 33 16 Weathered Claystone 3 4 4/2/25 17.7 108.9 1 34 65 34 20 980 487.5 8.06 274 0 0.00 A-6 (10) Sandy Lean Clay (CL) 4 1 3/31/25 16.2 113.4 52 24 9 A-4 (2) Fill: Sandy Lean Clay (CL) 4 9 3/31/25 21.5 104.6 91 52 33 Weathered Claystone 5 4 3/31/25 16.8 112.0 59 33 18 A-6 (7) Sandy Lean Clay (CL) 6 1 3/31/25 16.9 113.9 74 34 19 A-6 (12) Fill: Lean Clay with Sand (CL) 6 9 3/31/25 5.7 53 36 1 NV NP Poorly Graded Gravel with Silt and Sand (GP-GM)

1-2 1-4 3/21/25 13.2* 113.8* 4 56 40 30 12 25 A-6 (1) Clayey Sand (SC) 3-5 1-4 3/28/25 12.4* 112.7* 6 32 62 32 18 7 A-6 (8) Sandy Lean Clay (CL)

Table I

Sample Location Gradation Atterberg Limits

Date Tested

Natural Moisture Content

Natural Dry

Density (pcf)

Percent Passing No. 200 Sieve

March 13 and 27, 2025 March 13 and 27, 2025

Minimum Electrical Resistivity (ohm-cm)

Chloride Content in Soils (ppm) pH

Redox (mV)

Sulfide (mg/L)

R-Value at 300

PSI

* - Optimum moisture content and maximum dry density as determined by standard Proctor (ASTM D 698/AASHTO T99)

Water Soluble Sulfates

AASHTO

Classification (Group Index) Soil or Bedrock Type

Summary of Laboratory Test Results

APPENDIX A

PAVEMENT DESIGN CALCULATIONS

25-3-111 Appendix A.pdf