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HomeMy WebLinkAboutMASON PLACE - MAJOR AMENDMENT - MJA180003 - SUBMITTAL DOCUMENTS - ROUND 1 - GEOTECHNICAL (SOILS) REPORT400 North Link Lane | Fort Collins, Colorado 80524 Telephone: 970-206-9455 Fax: 970-206-9441 GEOTECHNICAL INVESTIGATION PROPOSED MIDTOWN ON THE MAX PSH Aka MASON PLACE 3750 SOUTH MASON STREET FORT COLLINS, COLORADO HOUSING CATALYST 1715 West Mountain Avenue Fort Collins, Colorado 80521 Attention: Kristin Fritz Project No. FC08258-120 April 23, 2018 HOUSING CATALYST MIDTOWN ON THE MAX PSH CTLT PROJECT NO. FC08258-120 TABLE OF CONTENTS SCOPE 1 SUMMARY OF CONCLUSIONS 1 SITE CONDITIONS 3 PROPOSED CONSTRUCTION 3 PREVIOUS INVESTIGATIONS 3 INVESTIGATION 3 SUBSURFACE CONDITIONS 4 Groundwater 4 GEOLOGIC HAZARDS 5 Expansive Soils 5 Seismicity 5 SITE DEVELOPMENT 6 Demolition 6 Excavations 6 Fill Placement 7 FOUNDATIONS 8 Drilled Piers Bottomed in Bedrock 8 Micropiles 9 BELOW GRADE AREAS 11 FLOOR SYSTEMS 11 WATER-SOLUBLE SULFATES 14 SURFACE DRAINAGE 15 CONSTRUCTION OBSERVATIONS 15 GEOTECHNICAL RISK 15 LIMITATIONS 16 HOUSING CATALYST MIDTOWN ON THE MAX PSH CTLT PROJECT NO. FC08258-120 FIGURE 1 – LOCATIONS OF EXPLORATORY BORINGS FIGURE 2 – SUMMARY LOGS OF EXPLORATORY BORINGS APPENDIX A – RESULTS OF LABORATORY TESTING APPENDIX B – SAMPLE SITE GRADING SPECIFICATIONS HOUSING CATALYST MIDTOWN ON THE MAX PSH CTLT PROJECT NO. FC08258-120 1 SCOPE This report presents the results of our Geotechnical Investigation for the proposed Midtown on the Max Permanent Supportive Housing (PSH) project also known as Mason Place in Fort Collins, Colorado. The purpose of the investiga- tion was to evaluate the subsurface conditions to provide geotechnical design cri- teria and construction recommendations for the proposed renovations. The scope was described in our Service Agreement (Proposal No. DN 18-0083Rev) dated February 21, 2018. The report was prepared from data developed during field exploration, la- boratory testing, engineering analysis and experience with similar conditions. The report includes a description of subsurface conditions found in our explora- tory borings and discussions of site development as influenced by geotechnical considerations. Our opinions and recommendations regarding design criteria and construction details for site development, foundations, floor systems, slabs- on-grade, lateral earth loads and drainage are provided. The report was pre- pared for the exclusive use of Housing Catalyst in design and construction of pro- posed Midtown on the Max PSH. If the proposed construction changes, we should be requested to review our recommendations. Our conclusions are sum- marized in the following paragraphs. SUMMARY OF CONCLUSIONS 1. Subsurface conditions encountered in our borings generally con- sisted of 0 to 12 feet of sandy clay overlying sandstone bedrock to the depths explored. Borings TH-3 and TH-5 had a 1 to 1½ foot layer of gravel and sand at depths of 6 and 4 feet respectively. The upper 3 to 6 feet of soil in three borings was determined to be fill. Approximately 5 inches of asphaltic concrete overlay borings TH-1, TH-4 and TH-5. The pertinent engineering characteristics of the subsoils and bedrock are described in more detail in the report. HOUSING CATALYST MIDTOWN ON THE MAX PSH CTLT PROJECT NO. FC08258-120 2 2. Groundwater was encountered at depths of 8 to 29 feet in all the borings during drilling. When measured several days later, ground- water was at depths of 4½ to 8½ feet in borings TH-2 and TH-3. The remaining borings were backfilled before secondary groundwa- ter measurements could be taken. Existing groundwater levels may affect site development including the elevator shaft and pier in- stallation. We recommend a minimum 3-foot separation between the lowest proposed floor elevation and groundwater. 3. Existing fill was encountered in three borings (TH-2, TH-3 and TH- 4), to depths of up to 5 feet. The fill was likely placed during previ- ous site grading activities. Existing fill should not support floor slabs. We recommend removal and recompaction of the existing fill beneath improvements. 4. The presence of expansive soils constitutes a geologic hazard. There is risk that slabs-on-grade and foundations will heave or set- tle and be damaged. We judge the risk is low. We believe the rec- ommendations presented in this report will help to control risk of damage; they will not eliminate that risk. Slabs-on-grade and, in some instances, foundations may be damaged. 5. The existing foundation is founded on a drilled pier system. It has been determined by the structural engineer that the existing foun- dation is insufficient to support new loads. Additional drilled piers and/or micropiles, bottomed into bedrock, are recommended to un- derpin the existing foundation and to allow for additional loads. De- sign and construction criteria for foundations are presented in the report. 6. Structural floors will be used for a pier system. We believe a slab- on-grade floor is also appropriate for this site. Some movement of slab-on-grade floors should be anticipated. We expect movements will be minor, on the order of 1 inch or less. If movement cannot be tolerated, structural floors should be considered. 7. Surface drainage should be designed, constructed and maintained to provide rapid removal of surface runoff away from the building. Conservative irrigation practices should be followed to avoid exces- sive wetting. HOUSING CATALYST MIDTOWN ON THE MAX PSH CTLT PROJECT NO. FC08258-120 3 SITE CONDITIONS The site is located at 3750 Mason Street at the southeast corner of South Mason Street and Creger Drive in Fort Collins, Colorado (Figure 1). The existing building, constructed in 1982, is a 1-story steel and masonry structure founded on drilled piers. Midtown Arts Center currently occupies the building. There is an asphalt parking lot on the north, west and south sides of the building. The south- ern parking lot is shared with IBMC College. Landscaped berms with manicured grass and trees are located adjacent to Mason Avenue and Creger Drive. PROPOSED CONSTRUCTION Based on our understanding, the project includes adaptive reuse of the ex- isting Midtown Arts Center into 60-units of permanent supportive housing with space for onsite supportive services. Up to three stories are planned for the exist- ing single-story building. An elevator and requisite water-proof shaft pit will be constructed. Minor adjustments to the existing paved areas are desired to ac- commodate an outdoor amenity area. We have not been provided with founda- tion loads or sizes, but we anticipate heavy structural loads. Additional piers and/or underpinning will be required to carry the extra floors. PREVIOUS INVESTIGATIONS CTL | Thompson was provided structural plans for the existing building prepared by KTM Associates (Project Number 975, dated March 26, 1982) and a soils report by Empire Laboratories, Inc. (Project Number 4660-82, dated Janu- ary 27, 1982). Information from the plans and the geotechnical report were con- sidered in preparation of this report. INVESTIGATION The field investigation included drilling five exploratory borings at the loca- tions presented on Figure 1. The borings were drilled to depths of approximately HOUSING CATALYST MIDTOWN ON THE MAX PSH CTLT PROJECT NO. FC08258-120 4 30 to 35 feet using 4-inch diameter, continuous-flight augers and a truck- mounted drill. Drilling was observed by our field representative who logged the soils and bedrock. Summary logs of the borings, including results of field pene- tration resistance tests, are presented on Figure 2. Soil and bedrock samples obtained during drilling were returned to our la- boratory and visually examined by our geotechnical engineer. Laboratory testing was assigned and included moisture content, dry density, swell-consolidation, particle-size analysis and water-soluble sulfate tests. Swell-consolidation test samples were wetted at a confining pressure which approximated the weight of overlying soils (overburden pressures). Results of the laboratory tests are pre- sented in Appendix A and summarized in Table A-I. SUBSURFACE CONDITIONS Subsurface conditions encountered in our borings generally consisted of 0 to 12 feet of sandy clay overlying sandstone bedrock to the depths explored. Bor- ings TH-3 and TH-5 had a 1 to 1½ foot layer of gravel and sand at depths of 6 and 4 feet respectively. The upper 3 to 6 feet of soil in three borings was deter- mined to be fill. Approximately 5 inches of asphaltic concrete overlay borings TH- 1, TH-4 and TH-5. Samples tested for swell-consolidation exhibited nil to 0.8 per- cent swell potential. A sample of the sandstone indicated a fines content (percent passing No. 200 sieve) of 15 percent. Further descriptions of the subsurface con- ditions are presented on our boring logs and in our laboratory test results. Groundwater Groundwater was encountered at depths of 8 to 29 feet in all the borings during drilling. When measured several days later, groundwater was at depths of 4.5 to 8.5 feet in borings TH-2 and TH-3. The remaining borings were backfilled HOUSING CATALYST MIDTOWN ON THE MAX PSH CTLT PROJECT NO. FC08258-120 5 before secondary groundwater measurements could be taken. Since this is a de- veloped area we do not expect the groundwater levels to vary substantially from the levels measured in our borings. We recommend a minimum 3-foot separation between the lowest proposed floor elevation and groundwater if possible. GEOLOGIC HAZARDS Our investigation addressed potential geologic hazards, including expan- sive soils and seismicity that should be considered during planning and construc- tion. None of these hazards considered will preclude proposed construction. The following sections discuss each of these geologic hazards and associated development concerns. Expansive Soils Expansive soils and bedrock are present at the site. The presence of ex- pansive soils and bedrock, collectively referred to as expansive or swelling soils, constitutes a geologic hazard. There is a very low risk that ground heave will damage slabs-on-grade and foundations. We expect that the existing slabs and any new slab construction will perform satisfactory and will perform as the exist- ing slabs have since original construction. We believe the recommendations in this report will help control risk of foundations and/or slab damage; they will not eliminate that risk. Seismicity This area, like most of central Colorado, is subject to a low degree of seis- mic risk. As in most areas of recognized low seismicity, the record of the past earthquake activity in Colorado is incomplete. According to the 2015 International Building Code and the subsurface conditions encountered in our borings, this site probably classifies as a Site Class C. HOUSING CATALYST MIDTOWN ON THE MAX PSH CTLT PROJECT NO. FC08258-120 6 SITE DEVELOPMENT Demolition Modification of the existing structure will require demolition of some of the interior spaces. Exposed soils due to removed flooring or pavement should be cleared of debris, moisture treated and properly compacted to specifications in Fill Placement section below if they are to become loadbearing. A Phase I Envi- ronmental Site Assessment was conducted by National Inspection Services on December 23, 2016. No recognized environmental conditions, historical recog- nized environmental conditions or controlled recognized environmental condi- tions were identified on the property. Excavations We anticipate excavations up to approximately 3 feet below existing grades may by required. Excavation for elevator or stairway cores may extend deeper. 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. Excavation slopes specified by OSHA are dependent upon types of soil and groundwater conditions encoun- tered. The contractor’s “competent person” should identify the soils and/or rock encountered in the excavation and refer to OSHA standards to determine appro- priate slopes. Soft soils may be encountered at the bottom of excavations. Soft soils should be stabilized. Stabilization can be accomplished by crowding 1.5-inch to 3-inch nominal size crushed rock or recycled concrete into the soft subsoils until the base of the excavation does not deform more than about 3 inches when com- pactive effort is applied. Acceptable rock materials include, but are not limited to, No. 2 and No. 57, or 1 to 3-inch recycled concrete. HOUSING CATALYST MIDTOWN ON THE MAX PSH CTLT PROJECT NO. FC08258-120 7 Fill Placement The existing onsite soils are suitable for re-use as fill material provided de- bris or deleterious organic materials are removed. Soil particles larger than 3 inches in diameter should not be used for fill. If import material is used, it should be tested and approved as acceptable fill by CTL|Thompson. In general, import fill should meet or exceed the engineering qualities of the onsite soils. Areas to receive fill should be scarified, moisture-conditioned and compacted to at least 95 percent of standard Proctor maximum dry density (ASTM D698, AASHTO T99). Fill placed on the upper clayey sand and sandy clay may be difficult to compact and may require a layer of granular material be crowded into soft soils and stabilized prior to fill placement. Sand soils used as fill should be moistened to within 2 percent of optimum moisture content. Clay soils should be moistened between optimum and 3 percent above optimum moisture content. The fill should be moisture-conditioned, placed in thin, loose lifts (8 inches or less) and compacted as described above. We should observe placement and compaction of fill during construction. Fill placement and compaction should not be con- ducted when the fill material is frozen. Existing fill was encountered in three borings to depths of up to 5 feet. Deeper fill areas may be encountered during site development. The fill is of un- known origin and age. We anticipate that the fill was placed during original site development and that risk of additional settlement is low. Site grading in areas of landscaping where no future improvements are planned can be placed at a dry density of at least 90 percent of standard Proctor maximum dry density (ASTM D 698, AASHTO T 99). Example site grading spec- ifications are presented in Appendix B. HOUSING CATALYST MIDTOWN ON THE MAX PSH CTLT PROJECT NO. FC08258-120 8 Water and sewer lines are often constructed beneath areas where im- provements are planned. Compaction of trench backfill can have a significant ef- fect on the life and serviceability overlying structures. We recommend trench backfill be moisture conditioned and compacted as described in the Fill Place- ment section of this report. Placement and compaction of fill and backfill should be observed and tested by a representative of our firm during construction. FOUNDATIONS The existing building is constructed on drilled piers which extended to shallow depths. Additional drilled piers and/or micropiles may be used for in- creased loads on existing foundation walls or for new load bearing walls. Design criteria for drilled pier and micropile foundations developed from analysis of field and laboratory data and our experience are presented below. Drilled Piers Bottomed in Bedrock 1. Piers should be designed for a maximum allowable end pressure of 50,000 psf and an allowable skin friction of 5,000 psf for the portion of pier in bedrock. Skin friction should be neglected for the upper 3 feet of pier below grade beams. Pier end pressure can be in- creased 30 percent for short duration live loads such as wind loads. 2. Piers should penetrate at least 5 feet into competent sandstone bedrock and have a minimum length of 25 feet. 3. There should be a 4-inch (or thicker) continuous void beneath all grade beams, between piers, to concentrate the dead load of the structure onto the piers. 4. Grade beams should be well reinforced. A qualified structural engi- neer should design the reinforcement. 5. Pier borings should be drilled to a plumb tolerance of 1.5 percent relative to the pier length. HOUSING CATALYST MIDTOWN ON THE MAX PSH CTLT PROJECT NO. FC08258-120 9 6. Piers should be carefully cleaned prior to placement of concrete. Ground water was encountered during this investigation. We rec- ommend a “drill-and-pour” procedure for pier installation. Concrete should be on site and placed in the pier holes immediately after the holes are drilled, cleaned and observed by our representative to avoid collecting water and possible contamination of open pier holes. We anticipate tremie equipment and/or pumping may be necessary for proper cleaning, dewatering, and concrete place- ment. Concrete should not be placed by free fall if there is more than about 3 inches of water at the bottom of the hole. 7. Concrete placed by the free fall method should have a slump be- tween 5 inches and 7 inches. Concrete placed by pump, tremie or when temporarily cased should have a slump between 6 inches and 8 inches. 8. Formation of “mushrooms” or enlargements at the top of piers should be avoided during pier drilling and subsequent construction operations. 9. We should observe installation of drilled piers to confirm the sub- surface conditions are those we anticipated from our borings. Micropiles Micropiles should be designed and detailed in accordance with Section 1810.3.10 of the 2015 International Building Code (IBC). Further, construction techniques and procedures contained in the FHWA “Micropile Design and Con- struction Guidelines Manual” (Report No. FHWA-SA-97-070 dated June 2000) should be implemented. We are available to review the design and specifications developed by our structural engineer and contractor. 1. Commonly available micropile systems have a maximum working capacity in the range of 20 to 100 kips. The micropiles should pene- trate a minimum 5 feet into competent bedrock. Piles should bottom in hard bedrock. Longer piles may be required for structural loads. 2. A 4-inch or thicker void should be established underneath the exist- ing foundation between piles. The ability of the foundation to span between micropiles should be determined by our structural engi- neer. HOUSING CATALYST MIDTOWN ON THE MAX PSH CTLT PROJECT NO. FC08258-120 10 3. Four distinct classifications of micropiles have been standardized based on various drilling and grouting techniques. A description of the various micropile types (A, B, C, and D) is provided in the refer- enced FHWA manual. The selection of micropile type should be left to the discretion of the designer and/or contractor. Based on the soil types encountered in our exploration (clay overburden under- lain by bedrock), we anticipate a “Type A” and/or “Type B” micro- piles will be utilized. Drilling methods should be determined by the contractor. 4. Reinforce micropiles their full length. The area of reinforcing steel should be sufficient to withstand axial compressive loads on the mi- cropile and tension due to uplift. At a minimum, reinforcing steel should be sized to resist 8 kips of uplift. Table 1810.3.2.6 of the 2015 IBC provides allowable stresses for material used in deep foundation elements which includes micropiles. We interpret utiliz- ing 0.3 f’c for micropile grout in compression, 0.4 Fy for micropile structural steel in compression, and 0.6 Fy for micropile structural steel in tension. We suggest utilizing minimum 28-day compressive strength of 4,000 psi for the grout and utilizing either Grade 75 or Grade 150 high-strength bar. 5. Drilling methods should be determined by the contractor. Dry rotary or air flush methods are preferable to water flush due to moisture- sensitive subsoils. 6. Micropiles should have a minimum diameter of 4 inches. Larger di- ameters may be used, but the minimum dead load and area of rein- forcing steel required for uplift tension should be increased propor- tionately with the circumference of the micropile (i.e. 30 kips for 6- inch diameter). 7. Values for the grout-to-ground nominal bond strength are com- monly based on experience of local contractors and their design engineers. Table 5-2 on page 5-16 of the manual presents ranges of typical values for various installation methods and ground condi- tions. For initial design calculations, micropiles should be designed using grout/ground interface bond strength of 10,800 psf in bedrock and a service load factor of 2.5 (i.e. = 4,320 psf allowable). The ac- tual value can be affected by grouting procedures. The contractor could verify whether the design value can be achieved by load tests. We suggest ignoring any bond stress contribution of overbur- den soils. HOUSING CATALYST MIDTOWN ON THE MAX PSH CTLT PROJECT NO. FC08258-120 11 8. At a minimum, micropiles should be spaced 3 feet apart or greater to avoid group efficiency effects. 9. The top of micropiles should be capped with an anchor plate em- bedded in concrete and sized to resist applied compression and ex- pansive soil tensile loads. The concrete should be designed as a haunch and rigidly doweled to the existing foundation. Effects of moment and load eccentricity should be accounted for by our struc- tural engineer. 10. A representative of our firm should observe the installation of micro- piles to confirm the depth and penetration. BELOW GRADE AREAS An elevator shaft pit is planned for the building. The pit is expected to be water proof; a perimeter drain is not necessary. Lateral earth pressure on the pit walls can be calculated using an equivalent fluid density of 50 pcf. This value is for horizontal backfill conditions and does not include pressure due to surcharge or hydrostatic pressure. Where interior areas are below exterior grades by more than 12 inches, we recommend installing a perimeter drain. The drain should consist of a 4-inch diameter open joint or slotted pipe encased in free draining gravel. The drain should lead to a positive gravity outlet, such as a storm drain or to a sump where water can be removed by pumping. FLOOR SYSTEMS In our opinion, it is reasonable to use slab-on-grade floors for the pro- posed construction. Any fill placed for the floor subgrade should be built with densely compacted, engineered fill as discussed in the Fill Placement section of this report. The existing fill is not an acceptable subgrade for a slab-on-grade floor and should be completely removed and re-compacted. HOUSING CATALYST MIDTOWN ON THE MAX PSH CTLT PROJECT NO. FC08258-120 12 It is impossible to construct slab-on-grade floors with no risk of movement. We believe movements due to swell will be less than 1 inch at this site. If move- ment cannot be tolerated, structural floors should be used. Structural floors can be considered for specific areas that are particularly sensitive to movement or where equipment on the floor is sensitive to movement. Where structurally supported floors are selected, we recommend a mini- mum void between the ground surface and the underside of the floor system of 4 inches. The minimum void should be constructed below beams and utilities that penetrate the floor. The floor may be cast over void form. Void form should be chosen to break down quickly after the slab is placed. We recommend against the use of wax or plastic-coated void boxes. Slabs may be subject to heavy point loads. The structural engineer should design floor slab reinforcement. For design of slabs-on-grade, we recom- mend a modulus of subgrade reaction of 100 pci for on-site soils. If the owner elects to use slab-on-grade construction and accepts the risk of movement and associated damage, we recommend the following precautions for slab-on-grade construction at this site. These precautions can help reduce, but not eliminate, damage or distress due to slab movement. 1. Slabs should be separated from exterior walls and interior bearing members with a slip joint that allows free vertical movement of the slabs. This can reduce cracking if some movement of the slab oc- curs. 2. Slabs should be placed directly on exposed soils, sandstone bed- rock or properly moisture conditioned and compacted fill. The 2015 International Building Code (IBC) requires a vapor retarder be placed between the base course or subgrade soils and the con- crete slab-on-grade floor. The merits of installation of a vapor re- tarder below floor slabs depend on the sensitivity of floor coverings and building use to moisture. A properly installed vapor retarder (minimum 6-mil; 10-mil recommended) is more beneficial below HOUSING CATALYST MIDTOWN ON THE MAX PSH CTLT PROJECT NO. FC08258-120 13 concrete slab-on-grade floors where floor coverings, painted floor surfaces or products stored on the floor will be sensitive to mois- ture. 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 place- ment 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, max- imized coarse aggregate content, and reasonably low slump will re- duce 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 Con- crete Floor and Slab Construction (ACI 302.R1-04)”. 3. If slab-bearing partitions are used, they should be designed and constructed to allow for slab movement. At least a 3-inch void should be maintained below or above the partitions. If the “float” is provided at the top of partitions, the connection between interior, slab-supported partitions and exterior, foundation supported walls should be detailed to allow differential movement. 4. Underslab plumbing should be eliminated where feasible. Where such plumbing is unavoidable it should be thoroughly pressure tested for leaks prior to slab construction and be provided with flexi- ble couplings. Pressurized water supply lines should be brought above the floors as quickly as possible. 5. Plumbing and utilities that pass through the slabs should be iso- lated from the slabs and constructed with flexible couplings. Where water and gas lines are connected to furnaces or heaters, the lines should be constructed with sufficient flexibility to allow for move- ment. 6. HVAC equipment supported on the slab should be provided with a collapsible connection between the furnace and the ductwork, with allowance for at least 3 inches of vertical movement. 7. The American Concrete Institute (ACI) recommends frequent con- trol joints be provided in slabs to reduce problems associated with shrinkage cracking and curling. To reduce curling, the concrete mix should have a high aggregate content and a low slump. If desired, a shrinkage compensating admixture could be added to the con- crete to reduce the risk of shrinkage cracking. We can perform a mix design or assist the design team in selecting a pre-existing mix. HOUSING CATALYST MIDTOWN ON THE MAX PSH CTLT PROJECT NO. FC08258-120 14 WATER-SOLUBLE SULFATES Concrete that comes into contact with soils can be subject to sulfate at- tack. We measured water-soluble sulfate concentrations in two samples from this site. Concentrations were measured were less than 0.01 percent and 0.7 percent. Water-soluble sulfate concentrations between 0.2 and 2 percent indi- cate Class 2 sulfate exposure, according to the American Concrete Institute (ACI). For sites with Class 2 sulfate exposure, ACI recommends using a cement meeting the requirements for Type V (sulfate resistant) cement or the equivalent, with a maximum water-to-cementitious material ratio of 0.45 and air entrainment of 5 to 7 percent. As an alternative, ACI allows the use of cement that conforms to ASTM C 150 Type II requirements, if it meets the Type V performance require- ments (ASTM C 1012) of ACI 201, or ACI allows a blend of any type of Portland cement and fly ash that meets the performance requirements (ASTM C 1012) of ACI 201. In Colorado, Type II cement with 20 percent Class F fly ash usually meets these performance requirements. The fly ash content can be reduced to 15 percent for placement in cold weather months, provided a water-to-cementi- tious material ratio of 0.45 or less is maintained. ACI also indicates concrete with Class 2 sulfate exposure should have a minimum compressive strength of 4,500 psi. Sulfate attack problems are comparatively rare in this area when quality concrete is used. Considering the range of test results, we believe risk of sulfate attack is lower than indicated by the couple laboratory tests performed. The risk is also lowered to some extent by damp-proofing the surfaces of concrete walls in contact with the soil. ACI indicates sulfate resistance for Class 1 exposure can be achieved by using Type II cement, a maximum water-to-cementitious ma- terial ratio of 0.50, and a minimum compressive strength of 4,000 psi. We be- lieve this approach should be used as a minimum at this project. The more strin- gent measures outlined in the previous paragraph will better control risk of sulfate attack and are more in alignment with written industry standards. HOUSING CATALYST MIDTOWN ON THE MAX PSH CTLT PROJECT NO. FC08258-120 15 SURFACE DRAINAGE Performance of foundations and flatwork are influenced by changes in subgrade moisture conditions. Carefully planned and maintained surface grading can reduce the risk of wetting of the subgrade soils. Positive drainage should be provided away from foundations. Backfill around foundations should be moisture treated and compacted as described in Fill Placement. Roof drains should be di- rected away from buildings. Downspout extensions and splash blocks should be provided at discharge points. CONSTRUCTION OBSERVATIONS We recommend that CTL | Thompson, Inc. provide construction observa- tion services to allow us the opportunity to verify whether soil conditions are con- sistent with those found during this investigation. Other observations are recom- mended to review general conformance with design plans. If others perform these observations, they must accept responsibility to judge whether the recom- mendations in this report remain appropriate. GEOTECHNICAL RISK 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- ment and experience. Therefore, the recommendations presented in any ge- otechnical evaluation should not be considered risk-free. Our recommendations represent our judgment of those measures that are necessary to increase the chances that the structure will perform satisfactorily. It is critical that all recom- mendations in this report are followed during construction. Owners must assume responsibility for maintaining the structures and use appropriate practices regard- HOUSING CATALYST MIDTOWN ON THE MAX PSH CTLT PROJECT NO. FC08258-120 16 ing drainage and landscaping. Improvements performed by owners after con- struction, such as construction of additions, retaining walls, landscaping and ex- terior flatwork, should be completed in accordance with recommendations in this report. LIMITATIONS This report has been prepared for the exclusive use of Housing Catalyst for providing geotechnical design and construction criteria for the proposed pro- ject. The information, conclusions, and recommendations presented herein are based upon consideration of many factors including, but not limited to, the type of construction proposed, the geologic setting, and the subsurface conditions en- countered. The conclusions and recommendations contained in the report are not valid for use by others. Standards of practice evolve in the area of geotech- nical engineering. The recommendations provided are appropriate for about three years. If the proposed construction is not constructed within about three years, we should be contacted to determine if we should update this report. Five borings were drilled during this investigation to obtain a reasonably accurate picture of the subsurface conditions. Variations in the subsurface con- ditions not indicated by our borings are possible. A representative of our firm should observe the drilling of pier and micropile holes to confirm proper pier con- struction. We believe this investigation was conducted with that level of skill and care ordinarily used by geotechnical engineers practicing in this area at this time. No warranty, express or implied, is made. HOUSING CATALYST MIDTOWN ON THE MAX PSH CTLT PROJECT NO. FC08258-120 17 If we can be of further service in discussing the contents of this report or in the analysis of the influence of subsurface conditions on design of the struc- tures, please call. CTLTHOMPSON, INC. Trace Krausse, EIT Spencer Schram, PE Staff Geotechnical Engineer Project Manager Reviewed by: Marc E. Cleveland, PE Vice President TSK:SAS:MEC (2 Copies) Via e-mail: kfritz@housingcatalyst.com TH-5 TBM TH-4 TH-2 TH-1 TH-3 Creger Drive Mason Street College Avenue E. HARMONY RD. E. HORSETOOTH RD. DRAKE RD. TIMBERLINE RD. COLLEGE AVE. SHIELDS ST. LEMAY AVE. SITE MASON ST. LEGEND: INDICATES APPROXIMATE LOCATION OF EXPLORATORY BORING INDICATES APPROXIMATE LOCATION OF TEMPORARY BENCHMARK; FIRST FLOOR AT FRONT DOOR (ASSUMED ELEVATION 100') TH-1 TBM HOUSING CATALYST MIDTOWN ON THE MAX PSH CTL I T PROJECT NO. FC08258-120 FIGURE 1 Locations of Exploratory Borings VICINITY MAP (FORT COLLINS, COLORADO) NOT TO SCALE 150' APPROXIMATE SCALE: 1" = 150' 60 65 70 75 80 85 90 95 100 105 60 65 70 75 80 85 90 95 100 105 ELEVATION - FEET FIGURE 2 ELEVATION - FEET Summary Logs of Exploratory Borings HOUSING CATALYST MIDTOWN ON THE MAX PSH CTL | T PROJECT NO. FC08258-120 50/5 50/3 50/1 50/2 50/1 50/1 50/0 WC=9.1 DD=92 SW=0.0 SS=<0.01 WC=13.5 -200=15 TH-1 El. 100.0 14/12 50/3 50/1 50/1 50/1 50/2 WC=10.4 -200=29 WC=18.0 DD=101 SW=0.0 TH-2 El. 100.5 14/12 11/12 50/3 50/2 APPENDIX A RESULTS OF LABORATORY TESTING Sample of SANDSTONE, CLAYEY DRY UNIT WEIGHT= 92 PCF From TH - 1 AT 4 FEET MOISTURE CONTENT= 9.1 % Sample of SANDSTONE, CLAYEY DRY UNIT WEIGHT= 101 PCF From TH - 2 AT 14 FEET MOISTURE CONTENT= 18.0 % HOUSING CATALYST MIDTOWN ON THE MAX PSH CTL | T PROJECT NO. FC08258-120 APPLIED PRESSURE - KSF APPLIED PRESSURE - KSF COMPRESSION % EXPANSION Swell Consolidation Test Results FIGURE A-1 COMPRESSION % EXPANSION -4 -3 -2 -1 0 1 2 3 NO MOVEMENT DUE TO WETTING -4 -3 -2 -1 0 1 2 3 NO MOVEMENT DUE TO WETTING 0.1 1.0 10 100 0.1 1.0 10 100 Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT= 113 PCF From TH - 3 AT 4 FEET MOISTURE CONTENT= 18.0 % Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT= 104 PCF From TH - 3 AT 9 FEET MOISTURE CONTENT= 23.0 % HOUSING CATALYST MIDTOWN ON THE MAX PSH CTL | T PROJECT NO. FC08258-120 APPLIED PRESSURE - KSF APPLIED PRESSURE - KSF COMPRESSION % EXPANSION Swell Consolidation Test Results FIGURE A-2 COMPRESSION % EXPANSION -4 -3 -2 -1 0 1 2 3 EXPANSION UNDER CONSTANT PRESSURE DUE TO WETTING -4 -3 -2 -1 0 1 2 3 EXPANSION UNDER CONSTANT PRESSURE DUE TO WETTING 0.1 1.0 10 100 0.1 1.0 10 100 Sample of FILL, CLAY, SANDY, GRAVELLY DRY UNIT WEIGHT= 107 PCF From TH - 4 AT 2 FEET MOISTURE CONTENT= 17.7 % Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT= 104 PCF From TH - 5 AT 9 FEET MOISTURE CONTENT= 23.5 % HOUSING CATALYST MIDTOWN ON THE MAX PSH CTL | T PROJECT NO. FC08258-120 APPLIED PRESSURE - KSF APPLIED PRESSURE - KSF COMPRESSION % EXPANSION Swell Consolidation Test Results FIGURE A-3 COMPRESSION % EXPANSION -4 -3 -2 -1 0 1 2 3 EXPANSION UNDER CONSTANT PRESSURE DUE TO WETTING -4 -3 -2 -1 0 1 2 3 EXPANSION UNDER CONSTANT PRESSURE DUE TO WETTING 0.1 1.0 10 100 0.1 1.0 10 100 Sample of FILL, SAND, CLAYEY, GRAVELLY GRAVEL 20 % SAND 51 % From TH - 2 AT 2 FEET SILT & CLAY 29 % LIQUID LIMIT % PLASTICITY INDEX % Sample of GRAVEL % SAND % From SILT & CLAY % LIQUID LIMIT % PLASTICITY INDEX % HOUSING CATALYST MIDTOWN ON THE MAX PSH CTL | T PROJECT NO. FC08258-120 FIGURE A-4 Gradation Test Results 0.002 15 MIN. .005 60 MIN. .009 19 MIN. .019 4 MIN. .037 1 MIN. .074 *200 .149 *100 .297 *50 0.42 *40 .590 *30 1.19 *16 2.0 *10 2.38 *8 4.76 *4 9.52 3/8" 19.1 3/4" 36.1 1½" 76.2 3" 127 5" 152 6" 200 8" .001 45 MIN. 0 10 20 PASSING WATER- MOISTURE DRY APPLIED NO. 200 SOLUBLE DEPTH CONTENT DENSITY SWELL* PRESSURE SIEVE SULFATES BORING (FEET) (%) (PCF) (%) (PSF) (%) (%) DESCRIPTION TH-1 4 9.1 92 0.0 500 <0.01 SANDSTONE, CLAYEY TH-1 9 13.5 15 SANDSTONE, CLAYEY TH-2 2 10.4 29 FILL, SAND, CLAYEY, GRAVELLY TH-2 14 18.0 101 0.0 1,800 SANDSTONE, CLAYEY TH-3 4 18.0 113 0.8 500 CLAY, SANDY (CL) TH-3 9 23.0 104 0.6 1,100 CLAY, SANDY (CL) TH-4 2 17.7 107 0.1 500 FILL, CLAY, SAND, GRAVELLY TH-5 9 23.5 104 0.1 1,100 0.73 CLAY, SANDY (CL) SWELL TEST RESULTS* TABLE A-I SUMMARY OF LABORATORY TESTING Page 1 of 1 HOUSING CATALYST MIDTOWN ON THE MAX PSH CTL|T PROJECT NO. FC08258-120 APPENDIX B SAMPLE SITE GRADING SPECIFICATIONS HOUSING CATALYST MIDTOWN ON THE MAX PSH CTLT PROJECT NO. FC08258-120 B-1 SAMPLE SITE GRADING SPECIFICATIONS 1. DESCRIPTION This item shall consist of the excavation, transportation, placement and compac- tion of materials from locations indicated on the plans, or staked by the Engineer, as necessary to achieve building site elevations. 2. GENERAL The Geotechnical Engineer shall be the Owner's representative. The Geotech- nical Engineer shall approve fill materials, method of placement, moisture con- tents and percent compaction, and shall give written approval of the completed fill. 3. CLEARING JOB SITE The Contractor shall remove all trees, brush and rubbish before excavation or fill placement is begun. The Contractor shall dispose of the cleared material to pro- vide the Owner with a clean, neat appearing job site. Cleared material shall not be placed in areas to receive fill or where the material will support structures of any kind. 4. SCARIFYING AREA TO BE FILLED All topsoil and vegetable matter shall be removed from the ground surface upon which fill is to be placed. The surface shall then be plowed or scarified to a depth of 8 inches until the surface is free from ruts, hummocks or other uneven fea- tures, which would prevent uniform compaction by the equipment to be used. 5. COMPACTING AREA TO BE FILLED After the foundation for the fill has been cleared and scarified, it shall be disked or bladed until it is free from large clods, brought to the proper moisture content and compacted to not less than 95 percent of maximum dry density as deter- mined in accordance with ASTM D 698 or AASHTO T 99. 6. FILL MATERIALS On-site materials classifying as CL, SC, SM, SW, SP, GP, GC and GM are ac- ceptable. Fill soils shall be free from organic matter, debris, or other deleterious substances, and shall not contain rocks or lumps having a diameter greater than three (3) inches. Fill materials shall be obtained from the existing fill and other approved sources. HOUSING CATALYST MIDTOWN ON THE MAX PSH CTLT PROJECT NO. FC08258-120 B-2 7. MOISTURE CONTENT Fill materials shall be moisture treated. Clay soils placed below the building en- velope should be moisture-treated to between optimum and 3 percent above op- timum moisture content as determined from Standard Proctor compaction tests. Clay soil placed exterior to the building should be moisture treated between opti- mum and 3 percent above optimum moisture content. Sand soils can be mois- tened to within 2 percent of optimum moisture content. Sufficient laboratory com- paction tests shall be performed to determine the optimum moisture content for the various soils encountered in borrow areas. The Contractor may be required to add moisture to the excavation materials in the borrow area if, in the opinion of the Geotechnical Engineer, it is not possible to obtain uniform moisture content by adding water on the fill surface. The Con- tractor may be required to rake or disk the fill soils to provide uniform moisture content through the soils. The application of water to embankment materials shall be made with any type of watering equipment approved by the Geotechnical Engineer, which will give the desired results. Water jets from the spreader shall not be directed at the em- bankment with such force that fill materials are washed out. Should too much water be added to any part of the fill, such that the material is too wet to permit the desired compaction from being obtained, rolling and all work on that section of the fill shall be delayed until the material has been allowed to dry to the required moisture content. The Contractor will be permitted to rework wet material in an approved manner to hasten its drying. 8. COMPACTION OF FILL AREAS Selected fill material shall be placed and mixed in evenly spread layers. After each fill layer has been placed, it shall be uniformly compacted to not less than the specified percentage of maximum dry density. Fill materials shall be placed such that the thickness of loose material does not exceed 8 inches and the com- pacted lift thickness does not exceed 6 inches. Compaction, as specified above, shall be obtained by the use of sheepsfoot roll- ers, multiple-wheel pneumatic-tired rollers, or other equipment approved by the Engineer. Compaction shall be accomplished while the fill material is at the specified moisture content. Compaction of each layer shall be continuous over the entire area. Compaction equipment shall make sufficient trips to insure that the required dry density is obtained. HOUSING CATALYST MIDTOWN ON THE MAX PSH CTLT PROJECT NO. FC08258-120 B-3 9. COMPACTION OF SLOPES Fill slopes shall be compacted by means of sheepsfoot rollers or other suitable equipment. Compaction operations shall be continued until slopes are stable, but not too dense for planting, and there is no appreciable amount of loose soil on the slopes. Compaction of slopes may be done progressively in increments of three to five feet (3' to 5') in height or after the fill is brought to its total height. Permanent fill slopes shall not exceed 3:1 (horizontal to vertical). 10. DENSITY TESTS Field density tests shall be made by the Geotechnical Engineer at locations and depths of his choosing. Where sheepsfoot rollers are used, the soil may be dis- turbed to a depth of several inches. Density tests shall be taken in compacted material below the disturbed surface. When density tests indicate that the dry density or moisture content of any layer of fill or portion thereof is below that re- quired, the particular layer or portion shall be reworked until the required dry den- sity or moisture content has been achieved. 11. COMPLETED PRELIMINARY GRADES All areas, both cut and fill, shall be finished to a level surface and shall meet the following limits of construction: A. Overlot cut or fill areas shall be within plus or minus 2/10 of one foot. B. Street grading shall be within plus or minus 1/10 of one foot. The civil engineer, or duly authorized representative, shall check all cut and fill areas to observe that the work is in accordance with the above limits. 12. SUPERVISION AND CONSTRUCTION STAKING Observation by the Geotechnical Engineer shall be continuous during the place- ment of fill and compaction operations so that he can declare that the fill was placed in general conformance with specifications. All site visits necessary to test the placement of fill and observe compaction operations will be at the ex- pense of the Owner. All construction staking will be provided by the Civil Engi- neer or his duly authorized representative. Initial and final grading staking shall be at the expense of the owner. The replacement of grade stakes through con- struction shall be at the expense of the contractor. HOUSING CATALYST MIDTOWN ON THE MAX PSH CTLT PROJECT NO. FC08258-120 B-4 13. SEASONAL LIMITS No fill material shall be placed, spread or rolled while it is frozen, thawing, or dur- ing unfavorable weather conditions. When work is interrupted by heavy precipi- tation, fill operations shall not be resumed until the Geotechnical Engineer indi- cates that the moisture content and dry density of previously placed materials are as specified. 14. NOTICE REGARDING START OF GRADING The contractor shall submit notification to the Geotechnical Engineer and Owner advising them of the start of grading operations at least three (3) days in advance of the starting date. Notification shall also be submitted at least 3 days in ad- vance of any resumption dates when grading operations have been stopped for any reason other than adverse weather conditions. 15. REPORTING OF FIELD DENSITY TESTS Density tests performed by the Geotechnical Engineer, as specified under "Den- sity Tests" above, shall be submitted progressively to the Owner. Dry density, moisture content and percent compaction shall be reported for each test taken. 16. DECLARATION REGARDING COMPLETED FILL The Geotechnical Engineer shall provide a written declaration stating that the site was filled with acceptable materials, or was placed in general accordance with the specifications. 30 40 50 60 70 80 90 100 CLAY (PLASTIC) TO SILT (NON-PLASTIC) SANDS FINE MEDIUM COARSE GRAVEL FINE COARSE COBBLES DIAMETER OF PARTICLE IN MILLIMETERS 25 HR. 7 HR. HYDROMETER ANALYSIS SIEVE ANALYSIS TIME READINGS U.S. STANDARD SERIES CLEAR SQUARE OPENINGS PERCENT PASSING 0 10 20 30 50 60 70 80 90 100 PERCENT RETAINED 40 0.002 15 MIN. .005 60 MIN. .009 19 MIN. .019 4 MIN. .037 1 MIN. .074 *200 .149 *100 .297 *50 0.42 *40 .590 *30 1.19 *16 2.0 *10 2.38 *8 4.76 *4 9.52 3/8" 19.1 3/4" 36.1 1½" 76.2 3" 127 5" 152 6" 200 8" .001 45 MIN. 0 10 20 30 40 50 60 70 80 90 100 CLAY (PLASTIC) TO SILT (NON-PLASTIC) SANDS FINE MEDIUM COARSE GRAVEL FINE COARSE COBBLES DIAMETER OF PARTICLE IN MILLIMETERS 25 HR. 7 HR. HYDROMETER ANALYSIS SIEVE ANALYSIS TIME READINGS U.S. STANDARD SERIES CLEAR SQUARE OPENINGS PERCENT PASSING PERCENT RETAINED 0 10 20 30 40 50 60 70 80 90 100 50/3 50/3 50/3 WC=18.0 DD=113 SW=0.8 WC=23.0 DD=104 SW=0.6 TH-3 El. 98.0 12/12 3/12 50/2 50/2 50/2 50/2 50/2 WC=17.7 DD=107 SW=0.1 TH-4 El. 98.0 36/12 9/12 50/3 50/2 50/1 50/2 WC=23.5 DD=104 SW=0.1 SS=0.730 TH-5 El. 98.0 5" AC 5" AC 5" AC FILL, SAND AND CLAY, GRAVELLY, MOIST, MEDIUM DENSE, STIFF, BROWN - - - - - WC DD SW -200 SS INDICATES MOISTURE CONTENT (%). INDICATES DRY DENSITY (PCF). INDICATES SWELL WHEN WETTED UNDER OVERBURDEN PRESSURE (%). INDICATES PASSING NO. 200 SIEVE (%). INDICATES SOLUBLE SULFATE CONTENT (%). BULK SAMPLE FROM AUGER CUTTINGS. DRIVE SAMPLE. THE SYMBOL 50/5 INDICATES 50 BLOWS OF A 140-POUND HAMMER FALLING 30 INCHES WERE REQUIRED TO DRIVE A 2.5-INCH O.D. SAMPLER 5 INCHES. 2. 3. ASPHALTIC CONCRETE (AC) THE BORINGS WERE DRILLED ON MARCH 7 AND 8, 2018, USING 4-INCH DIAMETER CONTINUOUS-FLIGHT AUGERS AND A TRUCK-MOUNTED DRILL RIG. 1. LEGEND: NOTES: CLAY, SANDY, MOIST, STIFF TO VERY STIFF, DARK GRAY, BLUE (CL) GRAVEL, SANDY, MOIST, MEDIUM DENSE, TAN (GP) SANDSTONE, SLIGHTLY SILTY, MOIST, VERY HARD, OLIVE, BROWN (BEDROCK) BORING ELEVATIONS WERE SURVEYED BY BY A REPRESENTATIVE OF OUR FIRM REFERENCING THE TEMPORARY BENCH MARK SHOWN ON FIGURE 1. THESE LOGS ARE SUBJECT TO THE EXPLANATIONS, LIMITATIONS AND CONCLUSIONS IN THIS REPORT. 4. WATER LEVEL MEASURED SEVERAL DAYS AFTER DRILLING. WATER LEVEL MEASURED AT TIME OF DRILLING.