SUBSURFACE INVESTIGATION and FOUNDATION RECOMMENDATIONS

Transcription

1 A M E R I C A N GEOTECHNICAL Littleton, Colorado SUBSURFACE INVESTIGATION and FOUNDATION RECOMMENDATIONS at 3440 West Moncrieff Place Denver, CO for TK Morrison Homes May 17, 2013 DAVID E. BEASLEY, P.E. A.G. Project Number

2 Sub.surface Investigation Projecf No Pg 2 of 14 GENERAL American Geotechnical has completed a subsurface investigation of the site known as: 3440 West Moncrieff Place Denver, CO This report presents the results of that investigation. The investigation was performed at the request of TK Morrison Homes in order to comply with local requirements and to determine the allowable foundation construction at this site. This investigation was not intended to check for any chemical or hazardous materials. This report may contain references to structural components not specified by the client. These references are included in the unlikely event that a structure is built that is other than that which was specified to us. Please read this entire report. The most frequently missed areas of importance are the requirements for open hole inspections and the use of float in the construction of nonbearing partition walls. Please ensure that these sections are fully understood. If there are any questions regarding these or any other parts of this report, ask for clarification. FOLNDATIQxN RECOMMENDATIONS With respect to the soil investigation performed at this site, and the intended structure as described by the client named above, the following is one or more of the allowable foundation type(s): Footings A footing type of foundation system may be utilized at this site provided foundation components bear on undisturbed natural soil. Foundation components must also bear below all organic material. Some movement of the structure on this type of foundation system is expected, but this movement is anticipated to be less than 1 inch. The maximum soil bearing capacity at this site is 2000 psf Prior to placing concrete, all bearing surfaces must be cleared of loose material. Disturbed material may be re-compacted in place only after contacting, and with guidance from, this office. To verify the soil conditions and to verify the design bearing pressure for any footings, it is required that an open hole inspection be performed at this site. This inspection must be performed only after the entire excavation has been dug to final grade. Though unlikely, potentially expansive clay or other unsuitable conditions may necessitate revised construction and foundation recommendations. Failure to complete the open hole inspection voids this soil investigation and may be grounds for denial of the certificate of occupancy for the structure.

3 American Gcolcchnical Inc. Subsurface Investigalion Pg3 of 14 Ensure that the requirements contained herein are reflected in any construction plans developed for this site. The case equivalent fluid pressure at this site is 35 pcf Pressure can result from the presence of expansive soils - soils which can exert additional pressures when wetted. Often, more conservative foundation options are not shown - such as the use of drilled piers when footings are allowable. If a more conservative foundation option is desired, please contact this office. In order to minimize the chances of water damage to the structure(s), an exterior perimeter drain is required for any structures built on this site. This drain may daylight to an exterior outfall location or may flow into a sump pit fitted with a pump. Ensure that the excavation is adequately sized for the safe installation of an exterior drain. SITE DESCRIPTION The site contains an existing structure. The vegetation consists of conventional landscaping. The site is generally flat with terracing of the lot in the front (north), PROPOSED CONSTRUCTION It is our understanding that a single-family residential structure is planned for construction on this site. This structure will be constructed over a basement. This report is written based upon with the type of constaiction presented by the client. FIELD AND LABORATORY ANALYSIS A test hole was drilled in the vicinity of the proposed structure (see Site Map) using a Mobile 50,B power auger and/or manual equipment. Test holes are generally drilled to a depth of 20 feet. Holes may have been drilled to different depths if restrictions exist or if needed to make bedrock determinations. In-situ soil samples were retrieved from depths appropriate to adequately anticipate foundation requirements. These samples were retrieved utilizing a 2-inch California sampler. In-situ samples consist of relatively undisturbed soil. Additional loose samples may also have been brought to the laboratory in order to make a determination of the soil types encountered at depths other than those where in-situ samples were retrieved, or to indicate where changes in soil composition occur as a flmction of depth. These samples were returned to the laboratory' for analysis. Laboratory analysis consists of a determination of moisture content, density, swell and consolidation potential, and particle size distribution, where possible. In order to assure

4 Ainericciii Geoteclinical Inc. Pg 4 of 14 valid results, non-cohesive highly granular samples may not have been tested for swell or consolidation potential Subjective analysis of the soil conditions was also made in the field during the drilling operations. Investigations performed on nearby sites may also have been considered in these results. The following represents the results of the field observations, the laboratory analysis as well as our experience in the area and adjacent data. SUBSURFACE CONDITIONS In general, the subsurface conditions consist of 0-1' r - 11' 11'+ topsoil; moist; dark brown sih, V. clayey; moist; light brown to brown sihstone; slightly moist; dark brown No free water was encountered. See the Summary of Laboratory Analysis, the Boring Logs and the Swell-Consolidation Test Results for additional information. SLAB RECOMMENDATIONS The Slab Performance.Risk at this site is judged to be Tow' (defined as less than 3% swell with a 500 psf surcharge). These soils may be suitable for the construction of slabs. It must be understood however, that the risk of slab movement does exist. Changes in the water content of these soils may cause the soil to swell or shrink, which may cause movement or cracking of slabs. Potential water sources include but are not limited to: water line breaks; excessive precipitation; irrigation system malfunctions; over-watering; negative site grading (toward the structure); a rise in a water table; a leaking hot water tank, hot tub, or water feature; a nearby septic system; downspout malfunctions or incorrect gutter/downspout construction; failure to provide a pump in a sump pit. If some movement of a siab is not acceptable, finished room areas should be constructed using a structural floor system over a void space, rather than a slab.

5 Pg 5 of 14 GENERAL SLAB INFORMATION Should the owner elect to accept the risks of expansive / consolidating soils and the effects they may have on slabs, the following have been shown to be helpful when constructing slabs. The following must not be construed as an approval, release or exception, to construct slabs. It is merely an effort to limit the damage which can result from the construction of slabs. Slabs should bear on undisturbed natural soils, or on properly conditioned and recompacted materials, as opposed to gravel or other materials which may allow the migration of water below the slabs. If the on-site soils are potentially expansive or may consolidate, it is preferable to bear slabs on non-expansive imported materials. Materials which will also minimize the transfer and/or retention of any water below the slab. Materials with a Liquid Limit below 30 and a Plasticity Index less than 15 are preferred. Slabs shall be isolated from foundation components by slip joints constructed to allow the independent movement of the slab. Slabs shall also be separated from any utility components by isolation joints. Mechanical equipment resting on slabs must be fitted with expandable / collapsible sections in order to allow movement of the slab without damage to the equipment or to the structure. Non-bearing partition walls constructed over floating slabs must be constructed with a minimum of 2 inches of float to allow for movement of the slab without damaging any part of the structure above. Float shall be built into the framing AND dry wall AND trim. See the Float Diagram later in this report. All doors similarly built shall be constructed with at least a 1 inch gap at floor level. Door trim must also be isolated from slab movement. It is the owner's responsibility to monitor and maintain all floats and gaps as necessary. If additional information on float is needed, please contact this or any geotechnical office. Garage door trim must be isolated from floating garage slab movement. Slabs must be appropriately reinforced to resist the anticipated loads as well as the effects of the supporting soils. Floor slabs must also be scored in accordance with the.american Concrete Institute (AC I) recommendations in order to control cracking of the slab due to shrinkage or other factors. These scores should be a maximum of 12 feet apart. If some movement of a slab is not acceptable, finished room areas should be constructed using a structural floor system over a void space, rather than a slab.

6 American Geoteclmica] Inc. Pg 6 of 14 SITE PREPARATION We anticipate that additional grading may be necessary. Site preparation procedures should be performed such that the potential for accumulation and standing of water around the site is minimized. Clay soils should be kept from desiccating (drying and shrinking) by sprinkling the soils occasionally. Drainage swales or channels should be created where necessary in order to route water away from the excavation and construction area. BACKFILL The backfill placed around the foundation walls should be methodically compacted to help reduce settlement after completion of construction. The top one foot of the backfill material must be relatively impervious to aid in routing water away from the foundation. The on-site soils, exclusive of topsoil and organics, are suitable for use as backfill. First floor framing should be constructed prior to the backfill process, or the foundation walls should be supported by some other means. SURFACE DRAINAGE The area surrounding the structure should be graded so as to provide adequate drainage away from the structure. This is typically accomplished by utilizing a 10 percent (12 inches in 10 feet) slope down and away from the foundation. Low spots should be filled in order to prevent accumulation and standing of water near the structure Surface water running toward the structures from up slope areas should be diverted around and away from the structures by means of drainage swales or other similar measures. Decorative edging should be constructed to allow water to flow through, around or under the edging and not so as to cause damming of water behind the edging. Sprinkler systems should be constructed so as to keep the area within 5 feet of the structure as dry as possible. Sprinkler heads or other irrigation components should not be placed in, nor should they release water into, the area that is within 5 feet of the structure. Downspouts and sill cocks must terminate outside of the backfill area of the structure and a minimum of 6 feet from the structure. Downspouts and sill cocks should discharge into splash blocks that extend well beyond the limits of the backfill. The use of long downspout extensions in-place of splash blocks is advisable. See the attached graphical representation of some of the above.

7 Pg 7 of 14 SUBSURFACE DRAINAGE Due to the presence of expansive clay soils, and in order to minimize the chances of water damage to the structure(s), an exterior perimeter drain is required for any structures built on this site. This drain may daylight to an exterior outfall location or may flow into a sump pit fitted with a pump. If an exterior outfall location is selected, ensure that the drain opening is protected by screen. See the drain detail diagram(s) later in this report for a typical perimeter drain cross section. Ensure that the excavation is adequately sized for the safe mstallation of an exterior drain. SHORING Depending on the municipality, shoring of the excavation may be required. Where space is limited, site excavation may result in slopes steeper than 1 to 1. Where site boundaries would otherwise result in cut banks steeper than a 1 to I slope, shoring may be required. On sites of limited size or where local regulations warrant, contact the local building agency for requirements. If shoring IS required, contact this office for an engineered shoring design. MOLD Mold has become an issue in building construction. The health risks resulting from the vast majority of mold spores are minimal or non-existent, however, the debate continues and litigation on this subject is increasing. The water content of the soils at this site are not high. The use of proper drainage techniques outside of the structure, and the use of subsurface perimeter drains, should keep water from accumulating in a way which would trigger mold formation. However, the most current building practices which reduce the likelihood of mold formation, should be gathered, studied and followed. LIMITATIONS / DISCLAIMER In any subsurface investigation, limited data is available from which to formulate soil descriptions and generate recommendations for foundations and related construction components. The samples taken are indicative of the subsurface materials at the time and at the location the samples were taken. Precipitation, seasonal changes, and excavating are just a few of the factors which may create changes in the composition of the site. If conditions are encountered which arc significantly different from those described in this report, contact this office before proceeding.

8 Pg 8 of 14 This report does not address nor was intended to address any environmental issues, hazardous materials or toxic waste issues, or other subsurface situations or conditions other than those described within this report. This report is intended for the sole use of the above named client and their approved agents. This office cannot be responsible for any conclusions or recommendations made by other parties based upon the data contained herein. This report is applicable only for the type of structure as described to us by the client. Failure to follow all of the recommendations contained herein voids this subsurface investigation and releases American Geotechnical from any and all responsibility as to the success and/or performance of the construction and structures at this site.

9 Pg 9 of 14 BORING LOGS 1 2 Itc:; soil SOli 7^^ silt. V ciaye 8 sand Vv'clay iclav'sand sandstone Iclaystcne

10 Pg 10 of 14 SUMMARY OF LABORATORY RESULTS Hole # Depth (ft.) Description % Passine #200 Sieve Moist. Drs' Density (%) (pcf) Penetration (blows/inch) 1 3 silt, clayey / silt, V. clayey / siltstone 71 7 _

11 Sub.surface Investigation Pg 11 ofl4 PfKm A WMMOM SIOPE Of 12' in W ms!!0 FT. OUT mu THE mctuhe smm aosd BEWNO THE GWVEI OR mm t k OCCOSAIWE i WOOO OR m>l SCE HOLES OR 1/2' SP«E '0 iucm hee mm aaw - J Grading Detail

12 American Gcolcchnical Inc. Pg 12 of 14 Framing Detail for Floating Walls or 'Float' _ 2"x4" stud wall 5 secured from above by metal straps or nailing 1./2" drywall nailed to studs, only Drill 3/8" dia. hole in top base plate and use 60 penny nails at about 3'-0" c.c. to stabilizs frame wall. Drive large nail into lower base platfi to base nallec inly ^ space to allow for independent movement cf the floor slab 1/2"K1'' nailing strip to hold base board in place 2";<4" base plata secured with 3"' concrete nails or ramset studs

13 American Geotechnical Inc. Pg 13 of 14, WEU. aopeo n' PER 50 fsef i 1 C0WW3B) awkpi i AND WE fltwl GRADE SHCUID 8E WEIL SLOPED TO.fSECLUDE rts3w3 OF SAiNFAU. IRKGA-ON WATER ANO SNOW Utu ADJACENT TO -uusdatlon WAUJ.- EAmON 00 NOT OIKE impeoe THE FIO* Of WATER AWAY ROM MiwvmoN WALLS w^ sac AJGING EECORATW SBAVEI AMS pf»wi>ttne^^3msi>.dis WK SiU CXks SHOULD OlSC-WCE IKTC E=-ASf' SUXKS OS DCreNSWNS Perimeter Drain Detail

14 Pg 14 of 14 Drilling location

15 Moisiure Conleni - Dry Uni! vveight - Sample of perccnl pcf From ' ( f r o I < H < 9 o CO o u ^ 2- C V atl ir di id 1.0 '0 A P P L I E D P R E S S U R E - ksf Moisture Content = Dry Unit Weight = Sample of: percent pct From: ^'f^ ^'C.Y-Y '0 APPLIED P R E S S U R E - ksf 100 Project No (2 -HQ Project SWELL-CONSOLIDATION TEST RESULTS Fig.