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
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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
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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.
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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)
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APPENDIX A
FLEXIBLE AND RIGID PAVEMENT CONSTRUCTION RECOMMENDATIONS
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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.
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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.