GEOLOGICAL AND GEOTECHNICAL INVESTIGATION · FOUNDATIONS Our field investigation indicates non-...

GEOTECHNICAL INVESTIGATION BRIGHTON HAMPTON INN HOTEL

BRIGHTON ROAD AND PLATTE RIVER BOULEVARD

BRIGHTON, COLORADO

Prepared For:

AAA HOTEL DEVELOPMENT 4308 St. Andrews Drive Pueblo, Colorado 81001

Project No. DN42,686-125

Attention: Mr. Ashwin A. Amin

March 26, 2007

AAA HOTEL DEVELOPMENT BRIGHTON HAMPTON INN HOTEL CTL | T PROJECT NO. DN42,686-125 S:\PROJECTS\DN42686.000\125\2. Reports\R1\DN42686-125-R1.doc

TABLE OF CONTENTS

SCOPE.................................................................................................................................... 1

SUMMARY OF CONCLUSIONS ............................................................................................ 1

SITE CONDITIONS................................................................................................................. 2

PROPOSED CONSTRUCTION.............................................................................................. 2

INVESTIGATION .................................................................................................................... 3

SUBSURFACE CONDITIONS................................................................................................ 3 Seismicity................................................................................................................... 3

SITE DEVELOPMENT............................................................................................................ 4 Excavations ............................................................................................................... 5

FOUNDATIONS...................................................................................................................... 5 Post-Tensioned Slab (PTS) Foundation.................................................................. 6 Spread Footings ........................................................................................................ 7

FLOOR SYSTEMS ................................................................................................................. 8

SWIMMING POOL AND POOL DECK................................................................................... 9

BELOW-GRADE CONSTRUCTION..................................................................................... 10

PAVEMENTS........................................................................................................................ 10

CONCRETE.......................................................................................................................... 12

SURFACE DRAINAGE......................................................................................................... 13

LIMITATIONS ....................................................................................................................... 14

FIG. 1 – LOCATIONS OF EXPLORATORY BORINGS

FIG. 2 – SUMMARY LOGS OF EXPLORATORY BORINGS

FIGS. 3 AND 4 – GRADATION TEST RESULTS

FIG. 5 – RECOMMENDED POOL DRAIN DETAIL

TABLE I – SUMMARY OF LABORATORY TEST RESULTS

APPENDIX A – FLEXIBLE AND RIGID PAVEMENT CONSTRUCTION RECOMMENDATIONS

AAA HOTEL DEVELOPMENT BRIGHTON HAMPTON INN HOTEL CTL | T PROJECT NO. DN42,686-125 S:\PROJECTS\DN42686.000\125\2. Reports\R1\DN42686-125-R1.doc

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SCOPE

This report presents the results of our Geotechnical Investigation for a

Hampton Inn Hotel planned at the northeast corner of Brighton Road and Platte River

Boulevard in Brighton, Colorado (Fig. 1). The report includes geotechnical criteria for

design and construction of the proposed building. The scope was described in our

Service Agreement (No. DN 07-0131) dated February 22, 2007.

The report was prepared from data developed during field and laboratory

investigations, engineering analysis of field and laboratory data, and our experience

with similar projects. This report includes descriptions of subsurface conditions

found in exploratory borings, our evaluation of engineering characteristics of the

subsoils, and our opinions and recommendations regarding design criteria for

foundations, floor systems, lateral earth loads, retaining walls, pavements, and other

design and construction details influenced by the subsoils. If the building location,

assumed finished floor level or proposed construction changes, we should be

notified. A summary of conclusions follows, with more detailed design and

construction criteria in the report.

SUMMARY OF CONCLUSIONS

1. Subsoils were sampled by drilling three deep borings and two shallow

pavement borings at the locations shown on Fig. 1. 2. Subsoils at this site consist primarily of clean to silty sand containing

some gravel. Samples of the sand are judged to be non-expansive.

3. We encountered ground water during drilling in borings TH-1 and TH-2 at a depth of 29 feet. No ground water was measured several days after drilling due to collapse of the holes at depths between 8.5 and 27.5 feet. Ground water is not expected to impact the proposed construction.

4. We recommend constructing the hotel on a shallow foundation system

consisting of either a post-tensioned, slab-on-grade or spread footings. Design and construction criteria for foundations are presented in the report.

AAA HOTEL DEVELOPMENT BRIGHTON HOTEL CTL | T PROJECT NO. DN42,686-125 S:\PROJECTS\DN42686.000\125\2. Reports\R1\DN42686-125-R1.doc

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5. Our field investigation indicates non-expansive sand soil will be

present near anticipated first floor level. We understand the first floor will be finished and assume a slab-on-grade is desired. We estimate nil potential floor movement for isolated slabs constructed directly on the subgrade. For post-tensioned, slabs-on-grade, the foundations are structurally integrated with the floor slab and should behave better than conventional slab-on-grade floors.

6. Automobile parking areas can be paved using 5 inches of asphalt. An

asphalt section of 6.5 inches is recommended for fire lanes, access drives, and truck traffic areas. Pavement design and construction criteria are provided in the report.

7. Subsurface drainage should be designed for rapid removal of water

away from the building and off the pavements. Water should not be allowed to pond adjacent to the building or on pavements.

SITE CONDITIONS

The Hampton Inn Hotel will be constructed on a site located northeast of Platte

River Boulevard and northwest of Brighton Road. An existing hotel occupies the lot

directly north of the site. Commercial development is south of the site and

commercial and retail buildings are to the east, across Brighton Road. The area to the

west is undeveloped at this time. The ground surface is relatively flat and sparsely

vegetated with weeds.

PROPOSED CONSTRUCTION

We understand a four-story, metal or wood-framed hotel will be constructed at

this site. The hotel will contain 77 units. No basement is planned. The hotel will

contain elevators. We understand the elevator pit will extend about 4 feet below the

floor level. Moderate structural loads are anticipated. An indoor pool is also planned

in the hotel. We anticipate a reinforced shotcrete (gunite) swimming pool with

concrete decks. The pool will likely be about 2 to 4 feet deep. Surface parking is

planned on the southeast and southwest sides of the building.


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INVESTIGATION

Subsurface conditions were investigated by drilling five borings at the

approximate locations shown on Fig. 1. Three borings were drilled in the

approximate building footprint and two borings were drilled in pavement areas. The

borings were drilled using a truck-mounted drill rig and continuous-flight auger.

Samples were obtained using 2.5-inch outer diameter sampler driven with a 140-

pound hammer falling 30 inches. A representative from our firm observed drilling

and obtained samples. Summary logs of the soils and bedrock found in our borings,

field penetration resistance tests, and a portion of laboratory data are presented on

Fig. 2.

The samples were returned to our laboratory for observation and testing.

Laboratory testing included moisture content, dry density and gradation. Results of

laboratory testing are presented on Figs. 3 and 4 and are summarized in Table I.

SUBSURFACE CONDITIONS

The strata encountered in our borings generally consisted of clean to slightly

silty sand. The sand contained some gravel. Bedrock was not encountered to the

maximum depth drilled of 35 feet. The sand was very loose to very dense based on

the results of field penetration resistance tests. Select sand samples contained

between 3 and 16 percent silt and clay-sized particles (passing the No. 200 sieve).

The sand is judged to be non-expansive.

Ground water was encountered during drilling at a depth of 29 feet in borings

TH-1 and TH-2. The holes had collapsed at depths between 8.5 and 27.5 feet, so

ground water could not be measured several days later. Ground water is not

expected to affect the planned construction.

Seismicity

This area, like most of central Colorado, is subject to a low degree of seismic


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risk. Based upon the 1997 Uniform Building Code, the site soils classify as Soil

Profile SD. According to the 2003 International Building Code for seismic design, the

site classifies as Site Class D. Only minor damage to relatively new, properly

designed and constructed buildings would be expected. Wind loads, not seismic

considerations, typically govern dynamic structural design in this area.

SITE DEVELOPMENT

No grading plans or finished floor elevations were provided. Based on existing

improvements surrounding the site, we assume the property is near construction

grade. We anticipate cuts and/or fills of 3 feet or less will be required to achieve

finished floor elevations. Prior to fill placement, all existing vegetation, topsoil, and

any other deleterious material should be removed. Areas to receive fill should be

scarified to a depth of at least 8 inches, moisture conditioned to within 2 percent of

optimum moisture content and compacted to at least 95 percent of standard Proctor

maximum dry density (ASTM D 698).

The existing on-site soils are suitable for reuse as fill material provided

vegetation, debris and deleterious organic materials are substantially removed. If

import material is required, we recommend importing granular soil (sand). Import fill

should contain 100 percent passing the 2-inch sieve with less than 40 percent silt and

clay-sized particles, and have a liquid limit less than 30 percent and a plasticity index

less than 15 percent. A sample of import material should be submitted to our office

for approval prior to stockpiling at the site.

The properties of the fill will affect the performance of the foundation, slabs-

on-grade and pavements. The fill should be moisture conditioned, placed in thin,

loose lifts (8 inches or less) and compacted to at least 95 percent of standard Proctor

maximum dry density (ASTM D 698). Granular (sand) fill should be moistened to

within 2 percent of optimum moisture content. Clay fill should be moistened to 0 to 3

percent above optimum moisture content. Placement and compaction of fill should

be observed and tested by a representative of our firm during construction.


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Excavations

We believe the materials found in our borings can be excavated using

conventional heavy-duty excavation equipment. Excavations should be sloped or

shored to meet local, state, and federal safety regulations. Based on our

investigation and Occupational Safety and Health Administration (OSHA) standards,

we believe the sand classifies as Type C soil. Type C soil requires slopes no steeper

than 1.5:1, in dry conditions. Excavation slopes specified by OSHA are dependent

upon soil types and ground water conditions encountered. The contractor’s

“competent person” should identify the soils encountered in the excavation and refer

to OSHA standards to determine appropriate slopes. Stockpiles of soils and

equipment should not be placed within a horizontal distance equal to one-half the

excavation depth, from the edge of excavation. A professional engineer should

design excavations deeper than 20 feet.

Water and sewer lines are often constructed beneath pavements. Compaction

of trench backfill can have a significant effect on the life and serviceability of

pavements. We recommend trench backfill be moisture conditioned and compacted

to the criteria above. Placement and compaction of trench backfill should be

observed and tested by a representative of our firm during construction.

FOUNDATIONS

Our field investigation indicates non-expansive sand soil is present at depths

likely to influence foundation performance. Based on the subsoil conditions,

proposed construction, and our experience, we recommend the structure be

constructed on a shallow foundation consisting of either a post-tensioned slab-on-

grade or spread footings. We estimate foundation movements of 1 inch or less for

foundations constructed directly on the existing natural soil or similar well-

compacted fill.


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We understand an elevator will be constructed in the hotel. The elevator pit

will extend about 4 feet below floor level. The elevator pit will be bottomed in the

natural sand.

Design and construction criteria for the foundation are presented below.

These criteria were developed from analysis of field and laboratory data and our

experience.

Post-Tensioned Slab (PTS) Foundation

PTS foundation design is based on a method developed by the Post-

Tensioning Institute (PTI, 3rd Edition, 2004 or 2nd Edition, 1996). Various climate and

relevant soil factors are required to evaluate the PTI design criteria. These include

the Thornthwaite Moisture Index (Im), suction compression index (γh), unsaturated

diffusion coefficient (α), depth of probable moisture variation, initial and final soil

suction profiles, percent clay fraction and predominant clay mineral. In the Denver

area, the Im is around negative 25.

Site soils are judged to be non-expansive and suitable for lightly-loaded

construction. For post-tensioned slabs constructed on stable soils, the Federal

Housing Administration’s BRAB Report No. 33 can be used. This report has defined

four different types of slabs. For this site, we assume a Type II lightly reinforced slab

will be used.

Our investigation indicates clean to silty sand or similar fill will be present at

depths likely to influence foundation performance. The following design criteria

should be used to construct the PTS foundation.

1. The PTS foundation should be constructed on the natural sand soil.

Where soil is loosened during excavation or in the forming process, or if any soft or loose soils are exposed in excavations, the soils should be removed and compacted as outlined in SITE DEVELOPMENT, prior


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to placing concrete. 2. The foundation should be designed for a maximum allowable soil

pressure of 2,000 psf. 3. For these types of slabs, a slab-subgrade friction of 0.5 to 0.6 can be

used for slabs of uniform thickness cast on polyethylene sheeting. If the slab is cast directly on the sand; a friction value of 0.75 to 1.0 can be used.

4. We understand the PTI design method assumes the slab is somewhat

flexible. The above-grade construction, such as pre-fabricated framing, drywall, brick, and stucco may not be flexible. We are aware of situations where minor differential slab movement has caused distress in finish materials. One way to enhance performance would be to place reinforcing steel in the bottoms of stiffening beams. The structural engineer should evaluate the merits of this approach as well as other potential alternatives to reduce damage to finishes.

5. Stiffening beams may be poured “neat” into excavated trenches. Soil

may cave or slough during trench excavation for the stiffening beams. Disturbed soil should be removed from trench bottoms prior to placement of concrete. Formwork or other methods may be required for proper stiffening beam installation.

6. Exterior stiffening beams must be protected from frost action. Normally

3 feet of frost cover is assumed in the Denver metropolitan area.

7. A representative of our firm should observe the completed excavations. A representative of the structural engineer should observe the placement of the reinforcing tendons and reinforcement prior to placing the slabs and beams.

Spread Footings

1. The footing foundation should be constructed on the natural sand soil. If soft or loose soils are exposed in excavations, the soft soils should be removed and compacted as outlined in SITE DEVELOPMENT, prior to placing concrete.

2. Footings should be designed for a maximum soil pressure of 2,000 psf.

3. Continuous footings should have a minimum width of 16 inches.

Foundations for isolated columns should have minimum dimensions of 24 inches by 24 inches. Larger sizes may be required depending upon the loads and structural system used.


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4. Grade beams should be well reinforced, top and bottom. We recommend reinforcement sufficient to span an unsupported distance of at least 10 feet or the distance between pads, whichever is greater. Reinforcement should be designed by the structural engineer.

5. For lateral load resistance, passive earth pressure can be calculated

from an equivalent fluid density of 300 pcf. The coefficient of friction between sand soil and concrete foundation elements cast on soil can be taken as 0.4.

6. Exterior footings must be protected from frost action. Normally, 3 feet

of frost cover is assumed in the area.

7. The completed foundation excavation should be observed by a representative of our firm prior to placing the forms to verify subsurface conditions are as anticipated.

FLOOR SYSTEMS

Our investigation indicates the materials near the anticipated first floor level

will consist of non-expansive sand soil. We understand the first floor will be finished

and assume a slab-on-grade is desired. We estimate nil potential slab movement

due to expansive soils for conventional slabs constructed directly on the subgrade.

For post-tensioned, slabs-on-grade, the foundations are structurally integral

with the floor slab and should perform better than a conventional slab-on-grade floor.

Underslab utilities such as water and sewer should be pressure tested prior to

installing slabs. Utilities that penetrate slabs should be provided with sleeves and

flexible connections that allow for independent movement of the slab and reduce

likelihood of damaging buried pipes. We recommend these details be capable of

allowing at least 1.5 inches of differential movement between the slabs and pipes.

If movement cannot be tolerated, a structural floor should be used. Structural

floors can be considered for specific areas that are particularly sensitive to

movement, such as entry or restroom areas where brittle stone or tile floor coverings

could be damaged by small movements. The level of risk acceptable to the owner

should be considered when selecting the floor system.


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Where structurally supported floors are selected, we recommend a minimum

space between the ground surface and the underside of the floor system of at least 6

inches where non-decomposable materials are used. The minimum space should be

maintained below beams and utilities that penetrate the floor. If desired, the floor may

be cast over void form. Void form should be chosen that will break down quickly

after the slab is placed. We recommend against the use of wax or plastic-coated void

boxes. The void material should be placed directly on the exposed subgrade soil.

If a conventional slab floor is selected, we recommend a floor slab thickness

of at least 5 inches to help minimize damage caused by differential soil movement.

Bi-axial reinforcement should be installed in the floor slab to create a more rigid slab

and to help control crack propagation. Frequent control joints should be provided in

slabs to reduce problems associated with shrinkage and cracking, in accordance

with ACI recommendations.

SWIMMING POOL AND POOL DECK

We were informed that an indoor pool is planned in this hotel. The pool will

likely be 2 to 4 feet deep. We anticipate a reinforced shotcrete (gunite) swimming pool

with concrete decks. Our investigation indicates the swimming pool and pool deck

will be constructed on non-expansive sand soil. The pool should be designed and

reinforced to function as an independent, rigid structure. We estimate nil potential

movement due to expansive soils for conventional slabs in the pool area. Settlement

due to wetting could cause slabs to distress. Cracking of the pool deck is likely and

will require maintenance. Cracks and joints in the deck should be sealed regularly.

Pool decking should be constructed directly on the exposed subsoils and be

isolated from the swimming pool. Movement of the deck should not be transmitted to

the swimming pool. The deck slab should be reinforced to function as an

independent unit. Frequent control joints should be provided to reduce problems

associated with shrinkage and swelling. Panels that are approximately square

generally perform better than rectangular areas.


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Cracking of the pool shell and deck will allow water to infiltrate the subgrade

soils. This water can affect performance of the subsoils and possibly create a

hydrostatic “uplift” force on the pool. A drain should be installed to help control the

water. The drain should be sloped to a sump where water can be removed by

pumping. In addition, an impermeable membrane consisting of PVC sheeting should

be placed between the gravel drain and the excavated subgrade. Field joints in the

membrane (if necessary) should be sealed. Details for construction of the drainage

layer are shown on Fig. 5.

BELOW-GRADE CONSTRUCTION

A basement is not planned. For this condition, a foundation drain is typically

not necessary. If plans change to include a basement or other habitable below-grade

area, our office should be contacted in order to provide lateral earth pressures and

foundation drain design criteria.

PAVEMENTS

Subgrade soils were investigated by drilling two borings in pavement areas.

Our field investigation indicates sand soil will be present at anticipated pavement

subgrade levels. Sand samples contained 3 to 16 percent silt and clay-sized particles

(passing the No. 200 sieve) and were non-plastic. This data indicates the subgrade

soils classify as A-2 using the American Association of State Highway and

Transportation Officials (AASHTO) classification system.

Sand soil is considered to have relatively good pavement support

characteristics. If imported fill is utilized below pavements, it should have equal or

better pavement support characteristics than the soil tested or the pavement sections

may require revision. Imported fill should be tested and approved by our firm before

use on the site.

The modified AASHTO design methods were used for design of pavements.


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We used an Equivalent Daily Load Application (EDLA) of 5 (ESAL = 36,500) for

automobile parking and an EDLA of 10 (ESAL = 73,000) for access drives and fire

lanes. Table A below presents our recommendations.

TABLE A

RECOMMENDED PAVEMENT SECTIONS

Traffic Classification Asphalt

(AC)

Asphalt (AC) + Aggregate

Base Course (ABC) Concrete

Automobile Parking 5" 3" (AC) + 8" (ABC) 5.5"

Access Drives and

Fire Lanes 6.5" 4.5" (AC) + 8" (ABC) 6"

Our experience indicates problems with asphalt pavements can occur where

heavy trucks drive into loading and unloading zones and turn at low speeds. In areas

of concentrated loading and turning movements by heavy trucks, such as at

entrances and trash collection areas, we recommend portland cement concrete

pavement placed directly on prepared subgrade. We recommend a 6-inch or thicker

portland cement concrete pad be constructed at dumpster locations, or other areas

where trucks will stop or turn. The concrete pads should be of sufficient size to

accommodate truck turning, trash pickup and delivery areas.

The design of a pavement system is as much a function of paving materials as

supporting characteristics of the subgrade. The quality of each construction material

is reflected by the strength coefficient used in the calculations. If the pavement

system is constructed of inferior materials, the life and serviceability of the pavement

will be substantially reduced. We recommend the materials and placement methods

conform to the requirements listed in the Colorado Department of Transportation

"Standard Specifications for Road and Bridge Construction." Materials planned for

construction should be submitted and tested to confirm their compliance with these

specifications.


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A primary cause of early pavement deterioration is water infiltration into the

pavement system. The addition of moisture usually results in softening of subgrade

and the eventual failure of the pavement. We recommend drainage be designed for

rapid removal of surface runoff. Curb and gutter should be backfilled and the backfill

compacted to reduce ponding adjacent to pavements. Final grading of the subgrade

should be carefully controlled so that design cross-slope is maintained and low spots

in the subgrade that could trap water are eliminated. Seals should be provided

between curb and pavement and at joints to reduce moisture infiltration. Irrigated

landscaped areas and detention ponds in pavements should be avoided.

We have included construction recommendations for flexible and rigid

pavement construction in Appendix A. Routine maintenance, such as sealing and

repair of cracks annually and overlays at 5 to 7-year intervals, are necessary to

achieve the long-term life of an asphalt pavement system. If the design and

construction recommendations cannot be followed or anticipated traffic loads

change considerably, we should be contacted to review our recommendations.

CONCRETE

Concrete in contact with soil can be subject to sulfate attack. We measured a

water-soluble sulfate concentration of 0.006 percent in one sample from this site.

Sulfate concentrations less than 0.1 percent indicate Class 0 exposure to sulfate

attack for concrete in contact with the subsoils, according to the American Concrete

Institute (ACI). For this level of sulfate concentration, ACI indicates any type of

cement can be used for concrete in contact with the subsoils. In our experience,

superficial damage may occur to the exposed surfaces of highly permeable concrete,

even though sulfate levels are relatively low. To control this risk and to resist freeze-

thaw deterioration, the water-to-cementitious material ratio should not exceed 0.50

for concrete in contact with soils that are likely to stay moist due to surface drainage

or high water tables. Concrete should be air entrained.


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SURFACE DRAINAGE

Performance of foundations, pavement and flatwork is influenced by the

moisture conditions existing within the subgrade soils. The risk of wetting subgrade

soils can be reduced by properly planned and maintained surface drainage. Surface

drainage should be designed to provide rapid runoff of water away from the building

and off pavement areas. We recommend the following precautions be observed

during construction and be maintained at all times after the construction is

completed.

1. Wetting or drying of the open foundation excavation should be

avoided. 2. Positive drainage should be provided away from all foundations. We

recommend providing a minimum slope of at least 5 percent in the first 10 feet away from the foundations, where possible. Sidewalks adjacent to the building should also slope to provide positive drainage away from the structure.

3. Backfill around the foundation walls should be moisture treated and

compacted as discussed in SITE DEVELOPMENT.

4. Roof downspouts and drains should discharge well beyond the limits of all backfill. Splash blocks and downspout extenders should be provided. We do not recommend directing roof drains below floor slabs.

5. Landscaping should be carefully designed to minimize irrigation. Plants used close to foundation walls should be limited to those with low moisture requirements; irrigated grass should not be located within 5 feet of the foundation. Sprinklers should not discharge within 5 feet of foundations. Irrigation should be limited to the minimum amount sufficient to maintain vegetation; application of more water will increase the likelihood of slab and foundation movements.

6. Impervious plastic membranes should not be used to cover the ground

surface immediately surrounding the additions. These membranes tend to trap moisture and prevent normal evaporation from occurring. Geotextile fabrics can be used to limit weed growth and allow for evaporation.


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LIMITATIONS

Our borings were spaced to obtain a reasonably accurate picture of

subsurface conditions. The borings are representative of conditions encountered

only at the exact boring location. Variations in the subsurface conditions not

indicated by our borings are possible. The placement and compaction of fill and

backfill should be observed and tested by a representative of our firm during

construction. The foundation excavation should be observed by a representative of

our firm to confirm that the subsurface conditions are as anticipated from our

borings.

We believe this investigation was conducted in a manner consistent with that

level of skill and care normally used by geotechnical engineers practicing in this area

at this time. No warranty, express or implied, is made. If we can be of further service

in discussing the contents of this report or in the analysis of the influence of the

subsoil conditions on design of the structure and pavements, please call.

CTL | THOMPSON, INC. Amanda Welton Staff Engineer Reviewed by: David A. Glater, P.E., C.P.G. Principal Geological Engineer AW:DAG/hat (4 copies)


APPENDIX A

FLEXIBLE AND RIGID PAVEMENT CONSTRUCTION RECOMMENDATIONS


A-1

FLEXIBLE PAVEMENT CONSTRUCTION RECOMMENDATIONS

Experience has shown that construction methods can have a significant effect on the life and serviceability of a pavement system. We recommend the proposed pavement be constructed in the following manner:

1. Soils should be stripped of organic matter, scarified, moisture treated, and compacted. We recommend the top one-foot of the subgrade be moisture conditioned and compacted to at least 95 percent of standard Proctor maximum dry density (ASTM D 698, AASHTO T 99). Granular subgrade should be moisture conditioned to within 2 percent of optimum moisture content. The subgrade should be kept moist prior to paving.

2. Utility trenches and subsequently placed fill should be properly compacted

and tested prior to paving. Fill should be compacted as outlined above. 3. After final subgrade elevation has been reached and the subgrade compacted,

the area should be proof-rolled with a heavy pneumatic-tired vehicle (i.e. a loaded ten-wheel dump truck). Subgrade that is pumping or deforming excessively (about 1-inch) should be scarified, moisture conditioned and compacted. Asphalt should not be placed on soft, wet, frozen, or otherwise unsuitable subgrade. Where extensively soft, yielding subgrade is encountered, we recommend the area be observed by a representative of our office.

4. Asphaltic concrete should be hot plant-mixed material compacted to at least

95 percent of maximum Marshall density. The temperature at laydown time should be near 235 degrees F. The maximum compacted lift should be 3.0 inches and joints should be staggered.

5. The subgrade preparation and the placement and compaction of pavement

material should be observed and tested by a representative of our firm. Compaction criteria should be met prior to the placement of the next paving lift. Additional requirements of the City of Brighton and the Colorado Department of Transportation Specifications should apply.


A-2

RIGID PAVEMENT CONSTRUCTION RECOMMENDATIONS Rigid pavement sections are not as sensitive to subgrade support characteristics as flexible pavement. Due to the strength of the concrete, wheel loads from traffic are distributed over a large area and the resulting subgrade stresses are relatively low. The critical factors affecting the performance of a rigid pavement are the strength and quality of the concrete, and the uniformity of the subgrade. We recommend subgrade preparation and construction of the rigid pavement section be completed in accordance with the following recommendations:

1. Soils should be stripped of organic matter, scarified, moisture treated, and compacted. We recommend the top one foot of the subgrade be moisture conditioned and compacted to at least 95 percent of standard Proctor maximum dry density (ASTM D 698, AASHTO T 99). Granular subgrade should be moisture conditioned to within 2 percent of optimum moisture content. The subgrade should be kept moist prior to paving.

2. After final subgrade elevation has been reached and the subgrade compacted,

the area should be proof-rolled with a heavy pneumatic-tired vehicle (i.e. a loaded ten-wheel dump truck). Subgrade that is pumping or deforming excessively (about 1-inch) should be scarified, moisture conditioned and compacted. Concrete should not be placed on soft, wet, frozen, or otherwise unsuitable subgrade. Where extensively soft, yielding subgrade is encountered, we recommend the area be observed by a representative of our office.

3. Curing procedures should protect the concrete against moisture loss, rapid

temperature change, freezing, and mechanical injury for at least 3 days after placement. Traffic should not be allowed on the pavement for at least one week.

4. A white, liquid membrane curing compound, applied at the rate of 1 gallon per

150 square feet, should be used. 5. Construction joints, including longitudinal joints and transverse joints, should

be formed during construction or should be sawed shortly after the concrete has begun to set, but prior to uncontrolled cracking. Joints should be sealed.

6. Construction control and observation should be carried out during the

subgrade preparation and paving procedures. Concrete should be carefully monitored for quality control. Additional requirements of the City of Brighton and the Colorado Department of Transportation Specifications should apply.

The design section is based upon a 20-year period. We believe some maintenance and sealing of concrete joints will help pavement performance by helping to keep surface moisture from wetting and softening subgrade. To avoid problems associated with scaling and to continue strength gain, we recommend deicing salts not be used for the first year after placement.

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