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GEOTECHNICAL INVESTIGATION HAMPTON INN & SUITES BY HILTON

4310 NORTH AIRPORT WAY DENVER, COLORADO

Prepared For:

TED R. LOCKE, ARCHITECT 1365 Garden of the Gods Road

Colorado Springs, Colorado 80907 Project No. DN44,200-125

Attention: Mr. Ted R. Locke

March 31, 2008

TABLE OF CONTENTS

SCOPE ......................................................................................................................................... 1 SUMMARY OF CONCLUSIONS.................................................................................................. 1 PREVIOUS INVESTIGATIONS .................................................................................................... 2 SITE CONDITIONS ...................................................................................................................... 3 PROPOSED CONSTRUCTION.................................................................................................... 3 INVESTIGATION .......................................................................................................................... 3 SUBSURFACE CONDITIONS ..................................................................................................... 4 Man-Made Fill .................................................................................................................. 4 Natural Sand and Clay .................................................................................................... 5 Bedrock............................................................................................................................ 5 Ground Water ..................................................................................................................5 Seismicity ........................................................................................................................ 6 SITE DEVELOPMENT.................................................................................................................. 6 Excavations ..................................................................................................................... 7 FOUNDATIONS............................................................................................................................ 8 Spread Footings or Mat ................................................................................................ 10 Intermediate Depth Drilled Piers Bottomed in Very Stiff Clay .................................. 11 Laterally Loaded Piers.................................................................................................. 12 Closely-Spaced Pier Reduction Factors ..................................................................... 13 FLOOR SYSTEMS ..................................................................................................................... 14 SWIMMING POOL AND POOL DECK ...................................................................................... 16 BELOW-GRADE CONSTRUCTION .......................................................................................... 17 PAVEMENTS.............................................................................................................................. 17 CONCRETE................................................................................................................................ 19 SURFACE DRAINAGE .............................................................................................................. 20 LIMITATIONS ............................................................................................................................. 21 FIG. 1 – LOCATIONS OF EXPLORATORY BORINGS FIGS. 2 AND 3 – SUMMARY LOGS OF EXPLORATORY BORINGS FIG. 4 – LEGEND FIGS. 5 THROUGH 7 – SWELL CONSOLIDATIN TEST RESULTS FIG. 8 – RECOMMENDED POOL DRAIN DETAIL TABLE I – SUMMARY OF LABORATORY TEST RESULTS APPENDIX A – FLEXIBLE AND RIGID PAVEMENT CONSTRUCTION RECOMMENDATIONS

TED R. LOCKE, ARCHITECT HAMPTON INN – GATEWAY PARK CTL | T PROJECT NO. DN44,200-125 S:\PROJECTS\44200\DN44200.000\125\2. Reports\R1\DN44200-125-R1.doc

SCOPE

This report presents the results of our Geotechnical Investigation for the Hampton Inn and Suites Hotel planned at 4310 North Airport Way, Denver, Colorado (Fig. 1). The report includes geotechnical criteria for design and construction of the building, access roads and parking lots. The scope was described in our Service Agreement (No. DN 09-0123) dated March 5, 2009.

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 found at this site included man-made fill with wood debris

to depths of 4 or 6 feet in three borings. Natural soils consist of clayey sand and sandy clay to depths of 28 to 30 feet, underlain by clean to clayey sand to a depth of 58 feet where weathered claystone bedrock was encountered to 60 feet. Ground water was about 30 feet below ground surface. Soils within depths likely to affect performance of foundations were non-expansive or low swelling.

2. Column loads as high as 500 kips are expected. Possible foundation

systems include footings or a mat, and drilled piers or piles bearing at intermediate depth or in the bedrock. Post-tensioned foundations are normally not used for buildings with six stories. Footings, because of their size and depth of influence, will have higher settlement if constructed on natural soils, up to 1.5 to 2 inches. Ground improvement such as intermediate depth rammed aggregate piers or a thick layer of stiff, densely compacted sand and gravel are options to potentially allow footings with higher design pressures


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and less potential settlement. Deep pier or pile foundations are likely to have the least potential movement. Design and construction criteria for foundations are presented in the report.

3. Non-expansive or low swelling soils are expected near anticipated

first floor level. A structurally-supported floor is safest with respect to soil-related movement and distress. We estimate potential heave of about an inch or less for floor slabs constructed on the subgrade. Risk of damaging floor movement is judged to be low and better than average for sites in the Denver area. Floor movement is typically independent of more highly loaded foundations. For example, an inch of settlement of footing foundations relative to the floor could cause floor distress that appears to be heave. Therefore, if a slab-on-grade floor is used, ground improvement or a deep foundation could help the building perform better. Unless some movement and distress is acceptable for a slab-on-grade system, structurally-supported floors should be used.

4. 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. Surface 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.

PREVIOUS INVESTIGATIONS We were provided a copy of a previous investigation of the site by Terracon (Project No. 23045049; report dated August 5, 2004) and a follow-up letter dated February 6, 2009. The report was prepared prior to construction of the neighboring parcel and considered a hotel project with fewer stories and recommended either footing or post-tensioned slab foundations. The penetration resistance values Terracon reported were much higher than we found in our borings, particularly in the upper 10 feet. Although they recommended footings as a foundation alternative, which would appear to be justified based on their field data, we believe settlement of footings on the soils we sampled could exceed 1 inch. We considered the data in the Terracon report as we prepared this study.


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SITE CONDITIONS

The Hampton Inn and Suites will be constructed north of the existing Homewood Suites Hotel, at 4310 North Airport Way, in the Gateway Park Development, Denver, Colorado (Fig. 1). Commercial development is south and west of the site. The southbound lanes of Pena Boulevard are east. The ground surface slopes gently down to the north and is sparsely vegetated with weeds. There are several storm drainage inlets and a waterline present on the parcel.

PROPOSED CONSTRUCTION

We understand a six-story, concrete-framed hotel will be constructed at this site. The hotel will contain 115 units. The first floor will be at elevation 5377.9 feet, about 3 to 4 feet above existing grades. Upper floors are likely to be post-tensioned concrete. No basement is planned. The hotel will contain elevators. We assume the elevator pits will extend about 4 feet below the floor level. Relatively heavy structural loads are anticipated, with column loads up to 500 kips. An indoor pool is also planned. We anticipate a reinforced shotcrete (gunite) swimming pool with concrete decks. The pool will likely be about 2 to 4 feet deep. Surface parking for 124 cars is planned on the sides of the building.

INVESTIGATION

Subsurface conditions were investigated by drilling eight borings at the approximate locations shown on Fig. 1. Five borings were drilled in the building footprint and three borings were drilled in pavement areas. We located the borings using the provided site plan and GPS. The borings were drilled using a truck-mounted drill rig and continuous-flight auger. Samples were obtained using the 2.5-inch outer diameter modified California 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 Figs. 2 and 3.


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The samples were returned to our laboratory for observation and testing. Laboratory tests included moisture content, dry density, swell-consolidation, unconfined compressive strength, water-soluble sulfates, Atterberg limits, percent fines and gradation. Results of laboratory tests are presented on Figs. 5-7 and are summarized in Table I. SUBSURFACE CONDITIONS

The strata encountered in our borings included up to 6 feet of man-made clayey sand fill with wood debris in three of the borings, TH-4, TH-5 and S-1. The other borings penetrated natural soils from the ground surface. The natural soils consisted of clayey sand and sandy clay to depths of about 28 to 30 feet, underlain by clean to clayey sand to a depth of 58 feet, with two feet of weathered claystone bedrock to the maximum depth explored, 60 feet. Man-Made Fill Available aerial photographs show Pena Boulevard was constructed in the early 1990’s and the neighboring Homestead Suites was built in 2007. It appears the Hampton Inn site was used for construction staging during 2007. We understand some fill was borrowed from the Hampton Inn site and the excavation was later backfilled. We suspect fill may exist in a substantial portion of the Hampton Inn footprint. The samples we observed contained wood and brick fragments, and had erratic moisture and density. We recommend the fill be removed and re-worked or replaced with clean fill in areas that will support structures such as floors, exterior flatwork, curb and gutter and pavement. Our borings indicate up to 6 feet of material may have to be sub-excavated. The existing material is suitable for re-use in new fill if debris is substantially removed. Compaction and placement recommendations for fill are in SITE DEVELOPMENT, below.


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Natural Sand and Clay The site is located in the Sand Creek drainage. Subsoils are mixtures of fine to medium grained sand and low to moderate plasticity silt and clay deposited by wind and water. Field penetration tests show the sand is loose to medium dense and the clay is stiff to very stiff. Selected samples of clayey sand were non-expansive and slightly compressive when wetted under a load of 1,000 psf. Similar tests on two samples of sandy clay showed low swell (0.7 and 0.2 percent) at depths of 4 and 9 feet, respectively. A sandy clay sample from 14 feet in boring TH-4 was moderate swelling (3.4 percent), but was nearly 18 feet below planned floor grade. We measured unconfined compressive strength on eight samples of sandy clay, with results ranging from 5,500 to 24,400 psf. A sample of the relatively clean sand from a depth of 49 feet in TH-1 had 9 percent silty fines. A sample of the sandy clay from the upper 5 feet in one of the pavement borings had 32 percent silty fines and was non-plastic. Bedrock We planned to drill to a maximum depth of 35 feet. When we did not penetrate bedrock to that depth in the first boring, we kept drilling with the available auger on the drill rig, 60 feet. We found weathered claystone at a depth of 58 feet in TH-1. Our experience in this area is that the bedrock becomes less weathered and can support relatively high foundation loads within about 5 to 8 feet. If bedrock-supported foundations are considered, we recommend supplemental exploration to better define the weathering profile and allowable design pressures. Ground Water

Ground water was noted in the three deepest holes at about 32-33 feet during drilling. When we returned to the site 9 days later to check the holes, we measured water at depths of 30-31 feet (elevation 5345). Ground water could affect installation of deep drilled pier foundation systems.


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Seismicity

This area, like most of central Colorado, is subject to a low degree of seismic 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, and the City of Denver Amendments, the site is Site Class D. It is possible a site-specific shear wave velocity study could allow an upgrade to Site Class C. Based on the data we have reviewed, we believe there is more than 50 percent probability the additional geophysical testing will verify the parcel is 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

Finished floor is planned to be elevation 5377.9. Based on existing storm sewer and improvements surrounding the site, we assume fills of about 3 feet or less will be required to bring the building area to construction grade. Prior to fill placement, all existing fill, vegetation, topsoil, and any other deleterious material should be removed. Sub-excavation of about 6 feet or less may be required to remove debris and fill.

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 other deleterious materials are substantially removed. If import material is required, we recommend importing granular soil (sand), similar to the on-site shallow soils. 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


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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). The use of modified Proctor (ASTM D 1557) compaction criteria is recommended if a footing or mat foundation is being considered, as discussed in FOUNDATIONS. 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. 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 and clayey sand classify as Type C soil. The deeper sandy clay is likely Type B soil. Type C soil requires slopes no steeper than 1.5:1, in dry conditions. Type B soil can typically use temporary excavation slopes of 1:1 or shallower. 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.


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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

Column loads as high as 500 kips are expected. Possible foundation systems include footings or a mat, and drilled piers or piles bearing at intermediate depth or in the bedrock. Post-tensioned foundations are normally not used for buildings with six stories.

Footings, because of their size and depth of influence, will have higher

potential settlement (up to 1.5 to 2 inches) if constructed on the loose to medium dense or stiff natural soils within about 12 feet from ground surface. Due to the non-uniform nature of the shallow subsoils, we believe there is a risk of damaging differential settlement for footings constructed directly on the natural soils. If footings are being considered, we recommend sub-excavating the soils down to elevation 5366 and compacting them to at least 95 percent of maximum modified proctor density, within 2 percent of optimum moisture content. Ground improvement such as intermediate depth rammed aggregate piers or a thick layer of stiff, densely compacted sand and gravel are options to potentially allow footings with higher design pressures and less potential settlement. Rammed aggregate piers are provided by design-build contractors such as Geopier. Providing a 3-foot thick layer of highly compacted sand and gravel (CDOT Class 6 Aggregate Road Base) directly below footings could allow an increase of allowable bearing pressure to 6,000 psf with reduced potential settlement to about an inch or less. All fill placed to support foundations should extend at least 3 feet outside footing lines. A mat can also be considered, and might require limited sub-excavation of about 3 feet to provide a uniform subgrade.


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The intermediate depth, very stiff sandy clay has relatively high strength at its current moisture content, but could undergo some loss of strength and bearing capacity after post-construction wetting. We’ve included recommendations for an intermediate depth drilled pier foundation, intended to bottom the piers in the very stiff sandy clay above ground water. We believe this system will provide good performance with little potential settlement.

Deep pier or pile foundations are likely to have the least potential

movement because they would bear upon relatively incompressible materials. Ground water and potential caving-prone sand will likely necessitate the use of temporary casing to properly install conventional drilled piers. Total depths approaching 65 to 70 feet are likely. Drilled piers should have a minimum diameter of about 30 inches to meet normal slenderness ratios. Auger-cast piles are an option that substantially avoids the ground water and caving soil problem, but diameter may be limited to about 24 to 30 inches, and depth capability for available equipment should be checked. Available information about the depth and character of the bedrock is insufficient at this time. We do not provide design criteria for bedrock supported piers. These should be confirmed by additional exploration to evaluate the bedrock depth, allowable design pressures and required penetration. For preliminary planning purposes to evaluate foundation options, we suggest considering a design end pressure 40,000 psf and side shear of 4,000 psf for the portion of the pier in unweathered bedrock. We assume penetration of about 6 to 10 in bedrock and total pier lengths on the order of 70 feet.

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

will extend about 4 feet below floor level. The elevator pit should be supported with the same foundation as the rest of the building.

Design and construction criteria for footing or a mat and intermediate

depth pier foundations are presented below. These criteria were developed from analysis of field and laboratory data and our experience. If you would like to


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consider the other foundation alternatives, we can provide additional consultation.

Spread Footings or Mat

1. Footings should be constructed on new compacted fill. We recommend sub-excavation of the site soils down to elevation 5366 feet. All replacement soils should be compacted to at least 95 percent of maximum modified proctor density within 2 percent of optimum moisture content. Where on-site soil fill will immediately underlie the footings, we recommend a maximum allowable soil pressure of 3,000 psf. For this situation, total settlement should not exceed about 1.5 inches and differential settlement should not exceed 1 inch. If at least 3 feet of CDOT Class 6 Aggregate Road Base will underlie the footings, the maximum pressure can be increased to 6,000 psf, with similar potential settlement. Rammed aggregate piers may also work to support footings with the higher pressure. A mat foundation can be designed for a maximum pressure of 2,500 psf. 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. Continuous footings should have a minimum width of 30 inches.

Foundations for isolated columns should have minimum dimensions of 36 inches by 36 inches. Larger sizes may be required depending upon the loads and structural system used.

3. 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.

4. 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.

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

feet of frost cover is assumed in the area.

6. 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. We should also test compaction of fill.


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Intermediate Depth Drilled Piers Bottomed in Very Stiff Clay

1. Piers should be designed for a maximum allowable end pressure of 12,000 psf and a skin friction value of 15,000 psf for the portion of pier between elevations 5350 and 5360. We recommend the piers bottom no lower than 5350 feet to avoid the ground water level, and no higher than 5355 feet to assure good support conditions. We estimate the total pier lengths will be about 20 to 25 feet.

2. The piers should be designed for a minimum deadload pressure as

high as practical while still meeting the above design criteria.

3. A minimum pier diameter of 24-inches is recommended. Piers up to about 5 feet in diameter will likely be required to support the expected structural loads.

4. Piers should be reinforced their full length and the reinforcement

should extend into grade beams or foundation walls. A minimum steel to pier cross-sectional area ratio of ½ percent (Grade 60) is recommended. More reinforcement may be required due to structural considerations.

5. There should be at least a 4-inch continuous void beneath

foundation walls, between the piers, to concentrate the deadload on the piers.

6. Should wind or lateral load analysis result in tension loads or uplift

on the piers, the tension loads should be resisted by skin friction in the sandy clay. We recommend using the skin friction values discussed above to provide the uplift resistance.

7. Shear rings should be installed in the lower portion of all piers. We

recommend cut shear rings that extend about 3 inches beyond the pier shaft to increase the load transfer through skin friction. At least 3 shear rings should be spaced about 2 feet on center in the lower 6 feet of the pier.

8. Pier drilling should produce shafts with relatively undisturbed soil

exposed. Excessive remolding and caking of soil on pier walls should be removed.

9. Piers should have a center-to-center spacing of at least three pier

diameters when designing for vertical loading conditions, or they should be designed as a group. Piers aligned in the direction of lateral forces should have a center-to-center spacing of at least 6 pier diameters. Reduction factors for closely spaced piers are provided in following section.


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10. Piers should be cleaned prior to placement of concrete. Concrete should be on-site and placed in the pier holes immediately after the holes are drilled, cleaned and inspected using drill and pour construction procedure. Ground water should not be encountered during installation of intermediate depth drilled piers.

11. Installation of drilled piers should be observed by a representative

of our firm to identify the bearing strata and confirm subsurface conditions are as anticipated from our borings.

Laterally Loaded Piers

Several methods are available to analyze laterally loaded piers. With a pier length to diameter ratio of 7 or greater, we believe the method of analysis developed by Matlock and Reese is most appropriate. The method is an iterative procedure using applied loading and soil profile to develop deflection and moment versus depth curves. The computer programs LPILE and COM624 were developed to perform this procedure. Suggested criteria for LPILE analysis are presented in Table A.

TABLE A

SOIL INPUT DATA FOR LPILE or COM624

Sandy Clay Sand Bedrock

Soil Model Stiff Clay w/o Free Water

Sand w/o Free Water

Stiff Clay w/o Free Water

Density (pci) 0.07 0.07 0.07 Cohesive Strength,

c (psi) - - 56

Friction Angle, φ Degrees 28 38 -

Soil Strain ε50 (in/in) - - 0.004

p-y modulus ks (pci) 90 250 2,000

The ε50 represents the strain corresponding to 50 percent of the maximum

principle stress difference.


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Closely-Spaced Pier Reduction Factors

For axial loading, a minimum spacing of 3 diameters is recommended. At one diameter (piers touching) the skin friction load reduction factor for both piers would be 0.5. End bearing values would not be reduced provided the bases of the piers are at similar elevations. Interpolation can be used between 1 and 3 diameters.

Piers in-line with the direction of lateral loads should have a minimum spacing of 6 diameters (center-to-center) based upon the larger pier. If a closer spacing is required, the modulus of subgrade reaction for initial and trailing piers should be reduced. At a spacing of 3 diameters, the effective modulus of subgrade reaction of the first pier can be estimated by multiplying the given modulus by 0.6; for trailing piers in a line at 3-diameter spacing, the factor is 0.4. Linear interpolation can be used for spacing between 3 and 6 diameters.

Reductions to the modulus of subgrade reaction can be accomplished in LPILE by inputting the appropriate modification factors for p-y curves. Reducing the modulus of subgrade reaction in trailing piers will result in greater computed deflections on these piers. In practice, a grade beam can force deflections of all piers to be equal. Load-defection graphs can be generated for each pier in the using the appropriate p-multiplier values. The sum of the piers lateral load resistance at selected deflections can be used to develop a total lateral load versus deflection graph for the system of piers.

For lateral loads perpendicular to the line of piers a minimum spacing of 3

diameters can be used with no capacity reduction. At one diameter (piers touching) the piers can be analyzed as one unit. Interpolation can be used for intermediate conditions.

Other procedures require input of a horizontal modulus of subgrade reaction (Kh). For purpose of design, we believe the soil types can be assigned the following values:


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TABLE B MODULI OF SUBGRADE REACTION (for Intermediate-Depth Drilled Piers)

Sandy Clay (above water)

Modulus of Subgrade Reaction, Kh (tcf) Kh = (20 x z) d

Where z = depth (ft) and d = pier diameter (ft).

FLOOR SYSTEMS Non-expansive or low swelling soils are expected near anticipated first floor level. A structurally-supported floor is safest with respect to soil-related movement and distress. We estimate potential heave of about an inch or less for floor slabs constructed on the subgrade. Existing man-made fill should be replaced with clean compacted fill and should meet the criteria discussed in SITE DEVELOPMENT. Risk of damaging floor movement is judged to be low and better than average for sites in the Denver area. Floor movement is typically independent of more highly loaded foundations. For example, an inch of settlement of footing foundations relative to the floor could cause floor distress that appears to be heave. Therefore, if a slab-on-grade floor is used, ground improvement or a deep foundation to reduce potential settlement could help the building perform better. Unless some movement and distress is acceptable for a slab-on-grade system, structurally-supported floors should be used.

Where concrete and metal structurally supported floors are installed, we

recommend a minimum void of 4 inches between the ground surface and the underside of the floor system. The minimum void should be constructed below beams and utilities that penetrate the floor. Concrete floor systems may be cast over void forming material. Void form should be chosen that will break down


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quickly after the slab is placed. We recommend against the use of plastic-coated void boxes. If the owner elects to use slab-on-grade construction and accepts the risk of movement and the associated damage, we recommend the following precautions for slab-on-grade construction. These precautions can help reduce, but will not eliminate damage or distress due to slab movement.

1. Slab-on-grade floor construction should be limited to areas where the risk of slab movement and associated cracking are acceptable.

2. Slabs should be placed directly on the natural soils or similar

moisture conditioned, compacted fill. The 2006 International Building Code (IBC) may require a vapor retarder be placed between the base course or subgrade soils and the concrete slab-on-grade floors. The merits of installation of a vapor retarder below floor slabs depend on the sensitivity of floor coverings and building use to moisture. A properly installed vapor retarder (10 mil minimum) is more beneficial below concrete slab-on-grade floors where floor coverings, painted floor surfaces or products stored on the floor will be sensitive to moisture. The vapor retarder is most effective when concrete is placed directly on top of it, rather than placing a sand or gravel leveling course between the vapor retarder and the floor slab. The placement of concrete on the vapor retarder may increase the risk of shrinkage cracking and curling. Use of concrete with reduced shrinkage characteristics including minimized water content, maximized coarse aggregate content, and reasonably low slump will reduce the risk of shrinkage cracking and curling. Considerations and recommendations for the installation of vapor retarders below concrete slabs are outlined in Section 3.2.3 of the 2006 report of American Concrete Institute (ACI) Committee 302, “Guide for Concrete Floor and Slab Construction (ACI 302.R-96)”.

3. We recommend the slabs be separated from exterior walls and

interior bearing members with a slip joint that allows free vertical movement of the slab.

4. As much as possible, slab-bearing partitions should be minimized.

Where partitions are necessary there should be a slip joint constructed at the top or bottom of partitions to allow vertical movement of the slab. We recommend a minimum slip joint of 2 inches; 3 inches would be preferable. If the slip joint is provided at the top of partitions, the connection between slab-supported partitions and foundation-supported walls should be detailed to allow differential movement.


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5. Non load-bearing masonry walls may be constructed on thickened slab sections; they should be provided with freedom of movement such as fireproof metal tracks to prevent heave from affecting the frame of the structure.

6. Underslab plumbing should be eliminated where feasible. Where

such plumbing is unavoidable, it should be pressure tested before the slabs are installed to reduce the risk of leakage.

7. Plumbing and utilities that pass through the slabs should be

isolated from the slabs. Heating and air conditioning systems supported by slabs (if any) should be provided with flexible connections. We recommend allowing for adequate slab movement depending on thickness of treated zone.

8. Exterior flatwork and sidewalks should be separated from the

structure. These slabs should be designed to function as independent units. Movement of these slabs should not be transmitted directly to the foundation of the structure.

SWIMMING POOL AND POOL DECK We were informed that an indoor pool is planned. 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 or low swelling soil. The pool should be designed and reinforced to function as an independent, rigid structure. We estimate about an inch of potential movement due to expansive soils for conventional deck slabs in the pool area. Settlement due to wetting also 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, or the decks should be designed as reinforced concrete. 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. 8. 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 clayey sand soil will be present at anticipated pavement subgrade levels. A sample of clayey sand subgrade from boring S-2 contained 32 percent silt and clay-sized particles (passing the No. 200 sieve) and was 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. Existing fill should be ideally sub-excavated and re-compacted in pavement or flatwork areas. At the least, it should be proof rolled to establish that it is strong enough to support pavements.

Sandy 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.


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The modified AASHTO design methods were used for design of pavements. 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 C below presents our recommendations.

TABLE C 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 0.01 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 in landscaped areas, 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 or into piped systems. 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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APPENDIX A FLEXIBLE AND RIGID PAVEMENT CONSTRUCTION RECOMMENDATIONS


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 Denver 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 Denver and the Colorado Department of Transportation Specifications should apply.


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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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