Loading...
HomeMy WebLinkAbout5360 5364 5368 5372 5376 Quail St (Quail Run)August 12, 2020 0� W heat CD 0 0,tng P& Wonderland Homes 8246 Northfield Boulevard Building J, Suite #2600 Denver. Colorado 80238 Subject: Soils and Foundation Summary Letter Quail Run Block 1, Lot 8 Wheat Ridge, Colorado Project No. DN49,619-120-R1 I N C O R P•O R A T E D I HOME BUYER ADVISORY Expansive and compressible soils and expansive bedrock are present at this subdivision; which results in a geologic hazard. This letter describes the soil conditions on this lot more specifically. Prospective home buyers are strongly advised to read this letter and the referenced documents. If you do not understand the risk(s) associated with the hazard and the important role you must accept to manage and mitigate the risk(s), we recommend you contact a competent geotechnical (soils) engineer for advice. CTL I Thompson, Inc. performed a Soils and Foundation Investigation for 56 lots within Quail Run and presented results in a report dated July 30, 2020. This letter presents a summary of our findings and recommendations for the sub- ject lot. The report referenced above should be reviewed for foundation design. Colorado is a challenging location to practice geotechnical engineering. The climate is relatively dry and the near -surface soils are typically dry and com- paratively stiff. These soils and related sedimentary bedrock formations tend to react to changes in moisture conditions. Some of the soils and bedrock swell as they increase in moisture and are referred to as expansive soils. Other soils can compress significantly upon wetting and are identified as compressible soils. Most of the land available for development east of the Front Range is underlain by expansive clay or claystone bedrock near the surface. The soils that exhibit compressible behavior are more likely west of the Continental Divide; however, both types of soils occur throughout the state. Expansive and compressible soils and expansive bedrock as well as shal- low groundwater that may affect basement construction are present at this subdi- vision, which constitutes a geologic hazard. There is risk that foundations and slab -on -grade floors will experience heave or settlement, and damage. Covering the ground with houses, streets, driveways, patios, etc., coupled with lawn irriga- tion and changing drainage patterns, leads to an increase in subsurface moisture conditions. Thus, some soil movement due to heave or settlement is inevitable. Fill can also soften and compress upon wetting. It is critical that all recommenda- tions in this report are followed to increase the chances that the foundations and slabs -on -grade will perform satisfactorily. After construction, homeowners must assume responsibility for maintaining the structures and use appropriate prac- tices regarding drainage and landscaping. 1971 West 121h Avenue I Denver, Colorado 80204 1 Telephone: 303-825-0777 Fax: 303-8254252 ,d° W heStR� U m 0 Gi/ping D�s� c In summary, the strata encountered in the boring on this lot consisted of 5 feet of fill and 10.5 feet of sandy clay underlain by claystone bedrock to the maximum depth explored of 25 feet. Groundwater was encountered at a depth of 10.2 feet. The clayey soils and bedrock are expansive. Use of footings with minimum deadload is recommended. A structurally supported basement floor is recommended. Further details are described in following paragraphs. Based on our investigation, predominantly low to moderate swelling mate- rials are present at depths likely to influence shallow foundation and slab perfor- mance, and we believe there is low to moderate risk of ground movement suffi- cient to damage slabs -on -grade and foundations. The risk of foundation and slab movements can be mitigated, but not eliminated, by careful design, construction, and maintenance procedures. We believe the recommendations in this report will help control risk of foundation and slab damage; they will not eliminate that risk. The builder and homebuyers should understand that slabs -on -grade and, in some instances, foundations may be affected by the subsoils. Homeowner maintenance will be required to control risk. We recommend the builder provide a booklet to homebuyers that describes swelling soils and includes recommenda- tionsfor care and maintenance of homes constructed on expansive soils. Colo- rado Geological Survey Special Publication 431 was designed to provide this in- formation. Laboratory tests were performed on samples from this lot and nearby lots. Samples from this lot compressed 0.1 percent ,did not swell, and swelled 0.6 to 1.3 percent when wetted. Based upon results of laboratory tests and other fac- tors, we judge basement slab performance risk for this lot to be low. Exhibit A provides a discussion of slab performance risk evaluation, as well as slab instal- lation and maintenance recommendations. We performed calculations of total po- tentialground heave and basement heave as part of our study. The calculations indicate the ground surface on low risk lots included in this investigation could heave less than 0.5 -inch to 3.2 inches and the basement floor slabs could heave less than 0.5 -inch to 2.0 inches. The calculated potential heave for this lot is 0.6 inch at the ground surface and 0.7 inch at basement level. It is not certain this movement will occur. If home buyers cannot tolerate movement of a slab -on - grade basement floor, they should select a lot where a structurally supported floor will be constructed or request that a structurally supported floor be installed. �"A Guide to S ening Soils for Colorado Homebuyers and Homeowner ;Second Edition Revised and Updated by David C. Noe, Colorado Geologio I Survey, Department of Natural Resouro s, Denver Colorado, 200]. oUAIL RUN BLOCK 1, LOT 8 ,d° W hear R,a U 'flip d�,�'n9 D�s\oc Considering the subsurfaceconditions at this lot, we recommend construction of the proposed residence on a footing foundation with minimum deadload. Footings should be designed for a maximum allowable soil pressure of 3,000 psf with a minimum deadload pressure of 1,000 psf. Footings should be at least 16 inches in width. Column pads should be at least 18 inches square. There should be a 4 -inch continuous void between the footings to concentrate the deadload, if interrupted footings are necessary. Exterior footings should be protected from frost action with at least 3 feet of cover. It is sometimes necessary to alter the foundation design based on conditions exposed during construction. The buyer can discuss the changes, if any, with the builder. Basement and/or foundation walls and grade beams that extend below grade should be designed for lateral earth pressures where backfill is not present to about the same extent on both sides of the wall. Our experience suggests basement walls can deflector rotate slightly under normal design loads and that this deflection typically does not affect the structural integrity of the walls. We rec- ommend design of the basement walls on this lot using an equivalent fluid den- sity of at least 60 pounds per cubic foot. This value assumes slight deflection of the wall can occur, generally less than 0.5 to 1 percent of the wall height. Some minor cracking of the walls may occur. A subsurface drain is recommended around the entire perimeter of the lowest excavation area for this residence. The drain should lead to a positive gravity outlet or to a sump where water can be removed with a pump. The provi- sion of the drain will not eliminate slab movement or prevent moist conditions in crawl spaces. The pump must be maintained by the home owner. Proper design, construction and maintenance of surface drainage are criti- cal to the satisfactory performance of foundations, slabs -on -grade, and other im- provements. Landscaping and irrigation practices will also affect performance. Exhibit B contains our recommendations for surface drainage, irrigation, and maintenance. The concept of risk is an important aspect with any geotechnical evalua- tion, primarily because the methods used to develop geotechnical recommenda- tions do not comprise an exact science. We never have complete knowledge of subsurface conditions. Our analysis must be tempered with engineering judg- mentand experience. Therefore, the recommendations presented in any ge- otechnical evaluation should not be considered risk-free. We cannot provide a guarantee that the interaction between the soils and a proposed structure will be as desired or intended. Our recommendations represent our judgment of those measures that are necessary to increase the chances that the structure will per- form satisfactorily. It is critical that all recommendations in the referenced report are followed. Home owners must assume responsibility for maintaining the struc- ture and use appropriate practices regarding drainage and landscaping. ouni� RUN BLOCK 1, LOT 8 As this letter is meant only as a summary of our findings and recommen- dationsfor the subject lot, we recommend home buyers review the Soils and Foundation Investigation from which this summary is taken. CTL THOMPSON, INC. AIflT .�. LI504OV EiLla ti i�2� QUAIL RUN BLOCK I, LOTS �� W hear Ra U w. e`//�'n9 D�g`oC I of W heat RW EXHI BITA 0 ����dmg D'N`g SLAB PERFORMANCE RISK EVALUATION, --- INSTALLATION AND MAINTENANCE As part of our evaluation of the subsoils and bedrock, samples were tested in the labora- tory using a swell test. In the test procedure, a relatively undisturbed sample obtained during drilling is first loaded and then flooded with water and allowed to swell. The pressure applied prior to wetting can approximate the weight of soil above the sample depth or be some standard load. The measured percent swell is not the sole criteria in assessing potential movement of slabs -on -grade and the risk of poor slab performance. The results of a swell test on an individ- ual lot are tempered with data from surrounding lots, depth of tests, depth of excavation, soil profle, and other tests. This judgment has been described by the Colorado Association of Ge- otechnical Engineers (CAGE, 1996) as it relates to basement slab -on -grade floors. It can also be used to help judge performance risk for other slabs -on -grade such as garage floors, drive- ways, and sidewalks. CTL Thompson also performs potential heave calculations to aid in our judgment. The risk evaluation is considered when we evaluate appropriate foundation systems for a given site. In general, more conservative foundation designs are used for higher risk sites to control the likelihood of excessive foundation movement. As a result of the Slab Performance Risk Evaluation, sites are categorized as low, mod- erate, high, or very high risk. This is a judgment of the swelling characteristics of the soils and bedrock likely to influence slab pertormance. REPRESENTATIVE MEASURED SWELL AND CORRESPONDING SLAB PERFORMANCE RISK CATEGORIES Slab Pertormance Risk Category Representative Percent Swell' (500 psf Surcharge) Representative Percent Swell' (1000 psf Surcharge) Low Oto <3 OtoQ Moderate 3 to <5 2 to <4 High Sto <8 4to <6 Very High > 8 > 6 *Note: The representative percent swell values presented are not necessarily measured values; rather, they are a judgment ofthe swelling characteristics of the soil and bedrock likely to inFluence slab performance. The rating of slab performance risk on a site as low or high is not absolute. Rather, this rating represents a judgment. Movement of slabs may occur with time in low, moderate, high, and very high risk areas as the expansive soils respond to increases in moisture content. Over- all, the severity and frequency of slab damage usually is greater in high and very high rated ar- eas. Heave of slabs -on -grade of 3 to 5 inches is not uncommon in areas rated as high or very high risk. On low and moderate risk sites, slab heave of 1 to 2 inches is considered normal and we believe in the majority of instances, movements of this magnitude constitute reasonable slab pertormance; more heave can occur. Slabs can be affected on all sites. On lots rated as high or very high risk, there is more likelihood of need to repair, maintain or replace main level and gar- agefloors and exterior flatwork. The home buyer should be advised slabs -on -grade may move and crack due to heave or settlement and that there may be maintenance costs associated during and after the builder oun�� RUN Exhibit A-1 BLOCK I, LOTS warranty period. Heave or settlement may require maintenance of finish details to control dam- age. Our experience suggests that soil moisture increases below residence sites due to cover- ing the ground with the house and exterior flatwork, coupled with the introduction of landscape irrigation. In most cases, slab movements (if any) resulting from this change occur within three to fve years. For portions of the houses where conventional slabs -on -grade are used, we recommend the following precautions. These measures will not keep slabs -on -grade from heaving; they tend to mitigate damages due to slab heave. 1. Slab -on -grade floor construction should be limited to areas where slab movement and cracking are acceptable to the builder and home buyer. 2. The International Residential Code (IRC R506) states that a flinch base course layer consisting of clean graded sand, gravel, crushed stone or crushed blast fur- p�vJ heatR nate slag shall be placed beneath below slab -on -grade floors (unless the under- ,�� o.. lying soils are free -draining), along with a vapor retarder. Installation of the base U a. course and vapor retarder is not common in this area. Historically, there has been some concern that installation of clean base course could allow wetting of expansive soils to spread from an isolated source. BGx��B �Mg��C _. IRC states that the vapor retarder can be omitted where approved by the building official. 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 is more benef tial below concrete slab -on -grade floors where floor coverings, painted floor surtaces, 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 va- por retarder and the floor slab. 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 5.2.3.2 of the 2015 American Concrete Institute (ACI) Committee 302, "Guide for Concrete Floor and Slab Construction (ACI 302.1 R-15)". 3. Conventional slabs should be separated from exterior walls and interior bearing members with a slip joint that allows free vertical movement of the slabs. These joints must be maintained by the home buyer to avoid transfer of movement. 4. Underslab plumbing (if any) should be thoroughly pressure tested during con- struction for leaks and be provided with flexible couplings. Gas and waterlines leading to slab -supported appliances should be constructed with flexibility. The homebuyer must maintain these connections. 5. Use of slab bearing partitions (if any) should be minimized. Where such partitions are necessary, a slip joint (or float) allowing at least 3 inches of free vertical slab movement should be used. Doorways should also be designed to allow vertical movement of slabs. To limit damage in the event of movement, sheetrock should oun�� RUN Exhibit A-2 BLOCK I, LOTS px VJ h eat /RW e���ding DN`S��C onnectiodns atnd re-establ sh the vo ds beforeldthey clltose to lelss thad and tither 6. Plumbing and utilities that pass through slabs (if any) should be isolated from the slabs. Heating and air conditioning systems constructed on slabs should be pro- vided with flexible connections capable of at least 3 inches of vertical movement so slab movement is not transmitted to the ductwork. These connections must be maintained by the home buyer. Roofs that overhang a patio or porch should be constructed on the same founda- tion as the residence. Isolated piers or pads may be installed beneath a roof overhang provided the slab is independent of the foundation elements. Patio or porch roof columns may be positioned on the slab, directly above the foundation system, provided the slab is structural and supported by the foundation system. Structural porch or patio slabs should be constructed to reduce the likelihood that settlement or heave will affect the slab by placing loose backfill under the struc- turally supported slab or constructing the slab over void -forming materials. Patio and porch slabs without roofs and other exterior flatwork should be isolated from the foundation. Movements of slabs should not be transmitted to the foun- dation. Decks are more flexible and more easily adjusted in the event of move- ment. Frequent control joints should be provided in conventional slabs -on -grade to re- duce problems associated with shrinkage cracking and curling. Panels that are approximately square generally perform better than rectangular areas. We sug- gest an additional joint about 3 feet away from and parallel to foundation walls. oun�� RUN Exhibit A-3 BLOCK I, LOTS of W heat RW EXHIBIT B ��id��9 p�,te��j �� SURFACE DRAINAGE, IRRIGATION AND MAINTENANCE Performance of foundations and concrete flatwork is influenced by the moisture condi- tions existing within the foundation soils. Surface drainage should be designed to provide rapid runoff of surtace water away from proposed residences. Proper surtace drainage and irrigation practices can help control the amount of surface water that penetrates to foundation levels and contributes to settlement or heave of soils and bedrock that support foundations and slabs -on - grade. Positive drainage away from the foundation and avoidance of irrigation near the founda- tion also help to avoid excessive wetting of backfill soils, which can lead to increased backfll settlement and possibly to higher lateral earth pressures, due to increased weight and reduced strength of the backfll. CTL � Thompson, Inc. recommends the following precautions. The home buyer should maintain surtace drainage and. if an irrigation system is installed. it should sub - stand ally conform to these recommendations Wetting or drying of the open foundation, utility and earthwork excavations should be avoided. The ground surface surrounding the exterior of each residence should be sloped to drain away from the building in all directions. For non -basement residences, we recommend a minimum constructed slope of at least 6 inches in the frst 10 feet (5 percent) in landscaped areas around each residence, where practical. For residences with basements, we recommend a minimum constructed slope of at least 12 inches in the frst 10 feet (10 percent) in landscaped areas around each residence, where practical. Between houses that are separated by a distance of less than 10 feet, the con- structed slope should generally be at least 5 percent to the swale used to convey water out of this area. Swales used to convey water across yards and between houses should be sloped so that water moves quickly and does not pond for extended periods of time. We suggest minimum slopes of about 2 to 2.5 percent in grassed areas and about 2 percent where landscaping rock or other materials are present. If slopes less than about 2 percent are necessary, concrete -lined channels or plastic pipe should be used. Backfill around the foundation walls should be moistened and compacted. Roof downspouts and drains should discharge well beyond the limits of all back- fill. Splash blocks and/or extensions should be provided at all downspouts so wa- ter discharges onto the ground beyond the backfll. We generally recommend against burial of downspout discharge. Where it is necessary to bury downspout discharge, solid, rigid pipe should be used and it should slope to an open gravity outlet. Downspout extensions, splash blocks and buried outlets must be main- tained by the home owner. oun��RUN Exhibit G1 BLOCK I, LOTS ments. Landscaping should be carefully designed and maintained to minimize irrigation. Plants placed 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. Plas- tic sheeting should not be placed beneath landscaped areas adjacent to founda- tion walls or grade beams. Geotextile fabric will inhibit weed growth yet still allow natural evaporation to occur. The design and construction criteria for foundations and floor system alternatives were compiled with the expectation that all other recommendations presented in this report related to surface and subsurtace drainage, landscaping irrigation, backf 11 compaction, etc. will be incorporated into the project. It is critical that all recommendations in this report are followed. o� W hearR: U ��' W\ ����CiOg pMg��C oun�� RUN Exhibit G2 BLOCK I, LOTS March 16, 2021 Wonderland Homes Re: Footing Inspection Letter Quail Run 5360, 5364, 5368, 5372, 5376 Quail St., 1-6-1-10 B2 Wheat Ridge, CO EVstudio was requested on March 10, 2021 to observe the footing form construction at the above listed address. An EVstuido representative verified that all void, forms and steel was placed per the construction documents prepared by EVstudio. It is EVstudio's professional opinion that the constructed footing was placed in substantial compliance to the plans and specifications prepared by this office for this address and will support the anticipated loading conditions. Please call our office with any questions or comments. Sincerely, Dominic Chapman Field Inspector �PDO tlOF1 TQC, f 46537, r Ross Maxwell, PE Assistant Director of Structural Engineering 5335 W. 48111 Ave. 303.670.7242 ph design@evstudio.com Denver, CO 80212 303.679.1862 fax www.evstudio.com March 16, 2021 Wonderland Homes Re: Footing Inspection Letter Quail Run 11152, 11160, 11168, 11176 W. 531 Dr. Lots 11 - 14 Wheat Ridge, CO EVstudio was requested on March 12, 2021 to observe the footing form construction at the above listed address. An EVstudio representative verified that all void, forms and steel was placed per the construction documents prepared by EVstudio. It is EVstudio's professional opinion that the constructed footing was placed in substantial compliance to the plans and specifications prepared by this office for this address and will support the anticipated loading conditions. Please call our office with any questions or comments. Sincerely, Tracy Stinson Field Inspector PDO LlOF�y`:lt� O�p�.�h1q��F :°C 46537�'� Ross Maxwell, PE Assistant Director of Structural Engineering 5335 W. 48111 Ave. 303.670.7242 ph design@evstudio.com Denver, CO 80212 303.679.1862 fax www.evstudio.com March 19, 2021 Wonderland Homes Re: Foundation Wall Steel Inspection Letter 11139 W. 53rd Dr. Station 53 L5 61 Wheat Ridge, CO EVstudio was requested on March 18, 2021 to observe the foundation wall steel and hold downs. An EVstuidio representative verified that all wall steel was placed per the construction documents prepared by EVstudio. The hold downs were observed for general compliance with the construction documents as well. It is EVstudio's professional opinion that the constructed foundation wall steel was placed in substantial compliance to the plans and specifications prepared by this office for this address and will support the anticipated loading conditions. Please call our office with any questions or comments. Sincerely, Dominic Chapman Field Inspector go/Q Je ?a 46537,x: Ross Maxwell, PE Assistant Director of Structural Engineering 5335 W. 4811, Ave. 303.670.7242 ph design@evstudio.com Denver, CO 80212 303.679.1862 fax www.evstudio.com January 27, 2021 TH Yarrow Gardens LLC 1875 Lawrence Street, Suite # 900 Denver, CO 80202 Re: Exterior Shear and Hold Down Letter Yarrow Gardens Townhomes 7803, 7807, 7811 W. 43rd Place L1 B3 F3 Wheat Ridge, CO 80033 On January 27, 2021 EVstudio was requested to observe the installation of exterior shear walls and hold downs at the above addresses. Our representative was able to verify the exterior shear and hold downs were installed in the proper locations per the structural drawings prepared by EVstudio. This letter does not include framing or interior shear, which was inspected at a later date or gypsum, and firewalls which are to be inspected by the city. Please feel free to contact our office with any questions or concerns. Sincerely, Sincerely, S a 46537 0 A Dominic Chapman Ross Maxwell, PE Field Inspector Assistant Director of Structural Engineering 5335 W 481h Ave. Suite 300 303.670.7242 ph design@evstudio.com Denver, CO 80212 303.679.1862 fax www.evstudio.com !York Engineering Structural Design ( 7 2 0 ) 990-5900 Date: March 22, 2021 Attn: Thrive Home Builders Subject: Shear Wall Observation, 7803, 7807, and 7811 West 43`d Place, Wheat Ridge CO The purpose of this letter is to report on the shear walls of the townhome, located at 7803, 7807, and 7811 West 43`d Place. A representative of EV Studio visited the site to inspect the shear walls and hold downs provided on their approved set of plans. See shear and hold down letter provided by EV Studio. It appears that the shear walls were installed according to the approved set of plans provided by York Engineering with the following retrofits: • Added blocking and straps to windows as needed where force transfer wall detail is called out. • Provided 11-7/8" LVL blocking at header height and HDUS hold downs on P1 at front garage for portal frame detail callout. This letter does not include framing or interior shear. Framing shall be inspected at a later date. Gypsum and firewalls are to be inspected by the city. Please feel free to call with any questions or concerns. Respectfully yours, Helena N. Dopita, P.E. York Engineering Structural Design (320) 990-5900 Date: March 22, 2021 Attn: Thrive Home Builders Subject: Framing Observation, 7803, 7807, and 7811 West 43rd Place, Wheat Ridge CO The purpose of this letter is to report on the framing of the townhome, located at 7803, 7807, and 7811 West 43rd Place. A representative of York Engineering visited the site to inspect the framing provided on the approved set of plans by York Engineering. It appears that the framing was installed according to the approved set of plans provided by York Engineering. Please feel free to call with any questions or concerns. Respectfully yours, Kelby M. York, P.E.