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HomeMy WebLinkAboutCOTTONWOOD RIDGE SUBDIVISION - FINAL - 31-94A - SUBMITTAL DOCUMENTS - ROUND 1 - GEOTECHNICAL (SOILS) REPORTL eqr-, 0 e G Tr6TzliJta l-gin q/Z8/�t4 • MaO I TAR I I/I O EU nRiL.l-�G 8/lo/`i4 bRI Ua gl%27/94 N ' S tit 70 BrI •I& ` coT•-�o1.IbJooP �InUE SUiid1�/ISIoN so,jTN s� I ELt�s. STR>✓�1" el i , f'ti :Mz c/r � e • 2�`I45��1 e o, IZ WILWPAY 9 2 SRN III MWIFIS `'-J C7� �CPOI Empire Laboratories, Inc. A Division of The Terracon Companies, Inc: Imp..�1-RlJ?pk�rP��Mor +li�.o+�i L���He • M�rJ 1JELL yRIL'Lr-'e &/l0/94 SAT ImAI o, 12 wlLWY JAY 2 0 � aZ 0 � I•Jo.13 • w _I �L �' -z rt M,. I F 9 p 14 910&F� ►I,,E 16 B rr ur Pro mL Ei-gAw •�' 7 vaLl.>:YixT idi EIGU ,: "j; s ITS 1�LA _ co-r-rotJ►•:Iooc jei t�caE..sUt3171�/ISIohJ 5oyTN .5H 1 aupep-.STF-e- �LI. Pi�?i✓C� fJ�Zo`I45o8`1 Flo. 20 0 Z � . to D` � �• 21 0 30o Coovl °fool Empire Laboratories, Inc. A Division of The Terracon Companies, Inc. ,;......11 Geotechnical Engineering Exploration Mr. Sandy Thayer ELI Project No. 20945089 Terracon that satisfactory bearing materials are present and is considered a necessary part of continuing geotechnical engineering services for the project. Construction testing, including field and laboratory evaluation of fill, backf ill, pavement materials, concrete and steel should be performed to determine whether applicable project requirements have been met. It would be logical for Empire Laboratories, Inc. to provide these additional services for continuing from design through construction and to determine the consistency of field conditions with those data used in our analyses. The analyses and recommendations in this report are based in part upon data obtained from the field exploration. The nature and extent of variations beyond the location of test borings may not become evident until construction. If variations then appear evident, it may be necessary to re-evaluate the recommendations of this report. our professional services were performed using that degree of care and skill ordinarily exercised, under similar circumstances, by reputable geotechnical engineers practicing in this or similar localities. No warranty, express or implied, is made. We prepared the report as an aid in design of the proposed project. This report is not a bidding document. Any contractor reviewing this report must draw his own conclusions regarding site conditions and specific construction techniques to be used on this project. This report is for the exclusive purpose of providing geotechnical engineering and/or testing information and recommendations. The scope' of services for this project does not include, either specifically or by implication, any environmental assessment of the site or identification of contaminated or hazardous materials or conditions. If the owner is concerned about the potential for such contamination, other studies should be undertaken. 25 Geotechnical Engineering Exploration Mr. Sandy Thayer ELI Project No. 20945089 Terracon In those locations where the bedrock is encountered within 3 feet of the bedrock and where movement of exterior slabs cannot be tolerated or must be held to an absolute minimum, consideration should be given to: • Constructing slabs with a stem or key -edge, a minimum of 6 inches in width and at least 12 inches below grade; • supporting keys or stems on drilled piers; or • providing structural exterior slabs supported on foundations similar to the building. • Underground Utility Systems: All piping should be adequately bedded for proper load distribution. It is suggested that clean, graded gravel compacted to 80 percent of Relative Density ASTM D4253 be used as bedding below the pipe. Where utilities are excavated below groundwater, temporary dewatering will be required during excavation, pipe placement and backfilling operations for proper construction. Utility trenches should be excavated on safe and stable slopes in accordance with OSHA regulations as discussed above. Backfill should consist of the on -site soils or existing bedrock. If bedrock is used, all plus 6-inch material should be removed from it prior to its use. The pipe backfill should be compacted to a minimum of 95 percent of Standard Proctor Density ASTM D698. • Corrosion Protection: Results of soluble sulfate testing indicate that ASTM Type 1-11 Portland cement is suitable for all concrete on and below grade. Foundation concrete should be designed in accordance with the provisions of the ACI Design Manual, Section 318, Chapter 4. GENERAL COMMENTS It is recommended that the Geotechnical Engineer be retained to provide a general review of final design plans and specifications in order to confirm that grading and foundation recommendations have been interpreted and implemented. In the event that any changes of the proposed project are planned, the conclusions and recommendations contained in this report should be reviewed and the report modified or supplemented as necessary. The Geotechnical Engineer should also be retained to provide services during excavation, grading, foundation and construction phases of the work. Observation of footing or pier excavations should be performed prior to placement of reinforcing and concrete to confirm 24 Geotechnical Engineering Exploration Mr. Sandy Thayer ELI Project No. 20945089 Terracon should be well compacted and free of all construction debris to reduce the possibility of moisture infiltration. 3. Downspouts, roof drains or scuppers should discharge into splash blocks or extensions when the ground surface beneath such features is not protected by exterior slabs or paving. 4. Sprinkler systems should not be installed within 5 feet of foundation walls. Landscaped irrigation adjacent to the foundation system should be minimized or eliminated.' • Subsurface Drainage: Free -draining, granular soils containing less than five percent fines (by weight) passing a No. 200 sieve should be placed adjacent to walls which retain earth. A drainage system consisting of either weep holes or perforated drain lines (placed near the base of the wall) should be used to intercept and discharge water which would tend to saturate the backfill. Where used, drain lines should be embedded in a uniformly graded filter material and provided with adequate clean -outs for periodic maintenance. An impervious soil should be used in the upper layer of backfill to reduce the potential for water infiltration. Additional Design and Construction Considerations: • Exterior Slab Design and Construction: Compacted subgrade or existing clay soils will expand with increasing moisture content; therefore, exterior concrete grade slabs may heave, resulting in cracking or vertical offsets. The potential for damage would be greatest where exterior slabs are constructed adjacent to the building or other structural elements. To reduce the potential for damage, we recommend: • exterior slabs be supported on fill with no, or very low expansion potential • strict moisture -density control during placement of subgrade fills • placement of effective control joints on relatively close centers and isolation joints between slabs and other structural elements • provision for adequate drainage in areas adjoining the slabs • use of designs which allow vertical movement between the exterior slabs and adjoining structural elements 23 Geotechnical Engineering Exploration Mr. Sandy Thayer ELI Project No. 20945089 Terracon • Excavation and Trench Construction: Excavations into the on -site soils will encounter a variety of conditions. Excavations into the clays and bedrock can be expected to stand on relatively steep temporary slopes during construction. However, the granular soils may cave, and groundwater will be encountered. The individual contractor(s) should be made responsible for designing and constructing stable, temporary excavations as required to maintain stability of both the excavation sides and bottom. All excavations should be sloped or shored in the interest of safety following local, and federal regulations, including current OSHA excavation and trench safety standards. The soils to be penetrated by the proposed excavations may vary significantly across the site. The preliminary soil classifications are based solely on the materials encountered in widely spaced exploratory test borings. The contractor should verify that similar conditions exist throughout the proposed area of excavation. If different subsurface conditions are encountered at the time of construction, the actual conditions should be evaluated to determine any excavation modifications necessary to maintain safe conditions. As a safety measure, it is recommended that all vehicles and soil piles be kept to a minimum lateral distance from the crest of the slope equal to no less than the slope height. The exposed slope face should be protected against the elements. Drainage: aJ • Surface Drainage: 1. Positive drainage should be provided during construction and maintained throughout the life of the proposed residences. Infiltration of water into J utility or foundation excavations must be prevented during construction. Planters and other surface features which could retain water in areas adjacent to the building or pavements should be sealed or eliminated. J2. In areas where sidewalks or paving do not immediately adjoin the structure, _ we recommend that protective slopes be provided with a minimum grade of J approximately 10 percent for at least 10 feet from perimeter walls. Backfill against footings, exterior walls, and in utility and sprinkler line trenches 22 J ] Geotechnical Engineering Exploration Terracon Mr. Sandy Thayer ELI Project No. 20945089 Estimated Shrink(-) Swell (+) Material Based on ASTM D698 On -site soils: J Clays........................15 to -20% Sands .................................... -10to-15% 1 On -site bedrock .................................. .10 to -15% • Slopes: 1. For permanent slopes in compacted fill areas, recommended maximum configurations for on -site materials are as follows: Material Maximum Slope Horizontal:Vertical Cohesive soils (clays) ...... : ........ : ... : ......... 2 Y2:1 Cohesionless soils (sands) 3:1 Bedrock ...................................... 1'/2:1 Detention pond slopes .............................. 4:1 If steeper slopes are required for site development, stability analyses should J be completed to design the grading plan. J Slopes subject to erosion by the Pleasant Valley and Lake Canal should be protected by rip rap or other suitable slope protection. Construction of drop structures along the canal bottom will lower flows and minimize the slope protection required. 2. The face of all slopes should be compacted to the minimum specification for fill embankments. Alternately, fill slopes can be over -built and trimmed to compacted material. • Compliance: Recommendations for slabs -on -grade, foundations and pavement elements supported on compacted fills or prepared subgrade depend upon compliance with "Earthwork" recommendations. To assess compliance, observation and testing should be performed under the direction of the geotechnical engineer. 21 Geotechnical Engineering Exploration Mr. Sandy Thayer ELI Project No. 20945089 Material Terracon Minimum Percent (ASTM D698) JSubgrade soils beneath fill areas ..................... 95 On -site soils: Beneath foundations ......................... 98 In ditch and pond slopes and bottom . ; ..:.... .: 95 Beneath slabs 95 Beneath pavements ......................... 95 1 In utility trenches ........................... 95 Imported fill: �j Beneath foundations ............. : ... : .:.:.. 98 J In ditch and ponds slopes and bottom . 95 95 Beneath slabs ............................. Beneath pavements ................:::::.... 95 In utility trenches 95 Miscellaneous backfill ............................. 90 5. If a well defined maximum density curve cannot be generated by impact compaction in the laboratory for any fill type, engineered fill should be compacted to a minimum of 80 percent relative density by determined by ASTM D4253 D4254. 6. On -site or imported soils should be compacted within a moisture content range of optimum moisture to 2 percent above optimum. On -site and imported clay soils below pavement and imported granular soils should be compacted within a moisture range of 2 percent below to 2 percent above optimum. • Shrinkage: For balancing grading plans, estimated shrink or swell of soils and bedrock when used as compacted fill following recommendations in this report are as follows: 20 Geotechnical Engineering Exploration Terracon Mr. Sandy Thayer ELI Project No. 20945089 3. Select granular materials should be used as backfill behind retaining walls. 4. Frozen soils should not be used as fill or backfill. 5. Imported soils (if required) should conform to the following: Percent fines by weight Gradation IASTM C136) 6.. ......................................... 100 3"....................................... 70-100 No. 4 Sieve .................................. 50-80 No. 200 Sieve .............................. 70 (max) • Liquid Limit ........................... 35 (max) • Plasticity Index ......................... 15 (max) 6. Aggregate base should conform to Colorado Department of Transportation Class 5 or 6 specifications. • Placement and Compaction: 1. Place and compact fill in horizontal lifts, using equipment and procedures that will produce recommended moisture contents and densities throughout the lift. 2. Uncompacted fill lifts should not exceed 10 inches loose thickness. 3. No fill should be placed over frozen ground. 4. Materials should be compacted to the following: 19 Geotechnical Engineering Exploration Mr. Sandy Thayer ELI Project No. 20945089 • Pavement Subarade Preparation: Terracon 1. The subgrade should be scarified, moistened as required, and recompacted for a minimum depth of 8 inches prior to placement of fill and pavement materials. 2. Soils excavated near the water table may be saturated and extensive drying of these materials may be required. 3. On -site clay soils may pump or become unstable or unworkable at high water contents. Workability may be improved by scarifying and drying. Overexcavation of wet zones and replacement with granular materials may be necessary. Lightweight excavation equipment may be required to reduce subgrade pumping. Use of lime, fly ash, kiln dust, cement or geotextiles could also be considered as a stabilization technique. Laboratory evaluation is recommended to determine the effect of chemical stabilization on subgrade soils prior to construction. 4. Due to the plastic nature of the subsoils and shallow depth to groundwater in portions of the site, some roadway subgrade stabilization is anticipated. With properly designed stabilization, reductions in pavement sections may be possible. • Fill Materials: 1. Clean on -site soils or approved imported materials may be used as fill material for the following: •, general site grading • foundation areas • interior floor slab areas • exterior slab areas • pavement areas • foundation backfill 2. On -site bedrock materials are not recommended for use beneath structural ares of the site, or as backfill. Should bedrock materials be used for general site grading, placement in fills at non-structural locations on the site is recommended. 18 Geotechnical Engineering Exploration Terracon Mr. Sandy Thayer ELI Project No. 20945089 8. All exposed areas which will receive fill, once properly cleared and benched where necessary, should be scarified to a minimum depth of eight inches, conditioned to near optimum moisture content, and compacted. • Excavation: 1. It is anticipated that excavations for the proposed construction can be accomplished with conventional earthmoving equipment. 2. If excavations need to penetrate into the bedrock, use of a D-8 tractor and ripper tooth or large track-mounted'backhoe may be needed to advance the excavation. 3. Groundwater seepage should be anticipated for excavations approaching the level of bedrock. Pumping from sumps may be utilized to control water within the excavations. Well points may be required for significant groundwater flow, or where excavations penetrate groundwater to a significant depth. 4. Depending upon depth of excavation and seasonal conditions, groundwater will be encountered in excavations on the site. Temporary dewatering or pumping from sumps may be utilized to control water within excavations. Well points may be required for significant groundwater flow, or where excavations penetrate groundwater to a significant depth. • Slab Subarade Preparation: 1. Where existing soils will support floor slab, the soils should be scarified, moisture conditioned and compacted to a minimum depth of 8 inches. 2. A minimum 4-inch layer of clean -graded gravel should be placed beneath slabs. 3. A minimum 8-inch layer of free -draining gravel should be placed beneath basement floor slabs in conjunction with the underslab drainage system. 17 J Geotechnical Engineering Exploration Mr. Sandy Thayer ELI Project No. 20945089 Terracon implementing any maintenance, additional engineering observation is recommended to determine the type and extent of preventative maintenance. Earthwork: • Site Clearing: 1. Strip and remove existing vegetation, debris, and other deleterious materials from proposed building and pavement areas. All exposed surfaces should be free of mounds and depressions which could prevent uniform compaction. 2. If unexpected fills or underground facilities are encountered during site clearing, such features should be removed and the excavation thoroughly I cleaned prior to backfill placement and/or construction. All excavations should be observed by the geotechnical engineer prior to backf ill placement. 1 3. Stripped materials consisting of vegetation and organic materials should be wasted from the site, or used to revegetate exposed slopes after completion 1 of grading operations. If it is necessary to dispose of organic materials on - site, they should be placed in non-structural areas, and in fill sections not exceeding 5 feet in height. 4. Sloping areas steeper than 3:1 (horizontal:vertical) should be benched to reduce the potential for slippage between existing slopes and fills. Benches should be level and wide enough to accommodate compaction and earth moving equipment. 5. Demolition of existing buildings should include removal of any foundation system. 6. The site should be initially graded to create a relatively level surface to 1 receive fill, and to provide for a relatively uniform thickness of fill beneath proposed building structures. 7. All materials derived from the demolition of existing structures should be removed from the site, and not be allowed for use in any on -site fills. 16 Geotechnical Engineering Exploration Terracon Mr. Sandy Thayer 1 ELI Project No. 20945089 r J • maintaining stable moisture content of the subgrade soils; and, • providing for a planned program of preventative maintenance. Since the clay soils on the site have shrink/swell characteristics, pavements could crack in the future primarily because of expansion of the soils when subjected to an increase in J moisture content to the subgrade. The cracking, while not desirable, does not necessarily constitute structural failure of the pavement. The performance of all pavements can be enhanced by minimizing excess moisture which can reach the subgrade soils. The following recommendations should be considered at minimum: • Site grading at a minimum 2% grade away from the pavements; • Compaction of any utility trenches for landscaped areas to the same criteria as the pavement subgrade; • Sealing all landscaped areas in, or adjacent to pavements to minimize or 1prevent moisture migration to subgrade soils; • Placing compacted backf ill against the exterior side of curb and gutter; and, • Placing curb, gutter and/or sidewalk directly on subgrade soils without the use of base course materials. Preventative maintenance should be planned and provided for an on -going pavement management program in order to enhance future pavement performance. Preventative maintenance activities are intended to slow the rate of pavement deterioration, and to preserve the pavement investment. Preventative maintenance consists of both localized maintenance (e.g. crack sealing and patching) and global maintenance (e.g. surface sealing). Preventative maintenance is usually the first priority when implementing a planned pavement maintenance program and provides the highest return on investment for pavements. Recommended preventative maintenance policies for asphalt and jointed concrete pavements, based upon type and severity of distress, are provided in Appendix D. Prior to l 15 .d J Geotechnical Engineering Exploration Terracon Mr. Sandy Thayer ELI Project No. 20945089 conform to an approved mix design stating the Hveem properties, optimum asphalt content, job mix formula, and recommended mixing and placing temperatures. Aggregate used in plant -mixed bituminous base course should meet a particular gradation. Use of aggregates j meeting Colorado Department of Transforation Grading G or C specifications is recommended. The mix design should be submitted prior to construction to verify it adequacy. The asphalt material should be placed in maximum 3-inch lifts, and should be compacted to a minimum of 95% Hveem density (ASTM D1560). Where rigid pavements are used, the concrete should be obtained from an approved mix " design with the following minimum properties: • Modulus of Rupture @ 28 days ................. 650 psi minimum • Strength Requirements ........................... ASTM C94 • Minimum Cement Content ..................... 6.5 sacks/cu. yd. • Cement Type ................................ Type I Portland • Entrained Air Content .............................. 6 to 8% • Concrete Aggregate ............ ASTM C33 and CDOT Section 703 • Aggregate Size 1 inch maximum • Maximum Water Content ................... 0.49 lb/lb of cement • Maximum Allowable Slump .......................... 4 inches Concrete should be deposited by truck mixers or agitators and placed a maximum of 90 minutes from time the water is added to the mix. Other specifications outlined by the Colorado Department of Transportation should be followed. Longitudinal and transverse joints should be provided as needed in concrete pavements for expansion/contraction and isolation. The location and extent of joints should be based upon fi the final pavement geometry and should be placed (in feet), at roughly twice the slab thickness (in inches), on center in either direction. Sawed joints should be cut within 24- hours of concrete placement, and should be a minimum of 25% of slab thickness plus 1 /4 inch. All joints should be sealed to prevent entry of foreign material and dowelled where necessary for load transfer. Where dowels cannot be used at joints accessible to wheel I loads, pavement thickness should be increased by 25 percent at the joints and tapered to regular thickness in 5 feet. Future performance of pavements constructed on the clay soils at this site will be dependent upon several factors, including: 14 Geotechnical Engineering Exploration Mr. Sandy Thayer ELI Project No. 20945089 Terracon Recommended Pavement Section Thickness (inches) Asphalt Aggregate Plant -Mixed Portland Traffic Area Alternative Concrete Base Bituminous Cement Total Surface Course Base Concrete Ridge Drive A 3 8 11 B 2 4 6 North Ridge Drive & C 6 6 Cul-de-Sacs Dakota A 4 8 12 B 3 4 7 Drive Dakota C 6 6 Circle South A 5 9 14 Shields B 4 4 8 Street C g g Each alternative should be investigated with respect to current material availability and economic conditions. The existing South Shields Street can be brought up to current standards with an overlay of 1'h inches of asphalt concrete. The existing pavement should be crack sealed, and failed areas should be patched prior to placing the overlay. Aggregate base course (if used on the site) should consist of a blend of sand and gravel which meets strict specifications for quality and gradation. Use of materials meeting Colorado Department of Transportation Class 5 or 6 specifications is recommended. Aggregate base course should be placed in lifts and compacted to a minimum of 95% Standard Proctor Density (ASTM D698). Asphalt concrete should be obtained from an ap proved pproved mix design stating the Hveem properties, optimum asphalt content, job mix formula, and recommended mixing and placing temperatures. Aggregate used in asphalt concrete should meet a particular gradation. Use of materials meeting Colorado Department of Transportation Grading C or CX specification is recommended. The mix design should be submitted prior to construction to verify its adequacy. The asphalt materials should be placed in maximum 3-inch lifts, and should be 1 compacted to a minimum of 95% Hveem density (ASTM D1560). J Plant -mixed bituminous base course should be composed of a mixture of aggregate, filler and additives if required, and approved bituminous material. The bituminous base should 13 a JGeotechnical Engineering Exploration Terracon Mr. Sandy Thayer y ELI Project No. 20945089 moisture conditions. The AASHTO criteria suggests that these moisture conditions are prevalent for approximately 12-1/2% of the annual moisture variation cycle. Local drainage characteristics of proposed pavements areas are considered for vary from J fair to good depending upon location on the site. For purposes of this design analysis, fair drainage characteristics are considered to control the design. These characteristics, coupled with the approximate duration of saturated subgrade conditions, results in a design drainage coefficient of 1.00 when applying the AASHTO criteria for design. For flexible pavement design, terminal serviceability indices of 2.0 for all residential streets and 2.5 for South Shields Street were utilized along with inherent reliabilities of 70% for residential street and 90% for South Shields Street. Using the correlated design R-value of 5 for residential streets and 18.5 for South Shields Street, appropriate ESAL/days, environmental criteria and other factors, the structural numbers (SN) of the pavement sections were determined on the basis of the 1986 AASHTO design equation. In addition to the flexible pavement design analyses, a rigid pavement design analysis was completed, based upon AASHTO design procedures. Rigid pavement design is based on an evaluation of the Modulus of Subgrade Reaction of the soils (K-value), the Modulus of Rupture of the concrete, and other factors previously outlined. The design K-value of 100 for the subgrade soil was determined by correlation to the laboratory tests results. A modulus of rupture of 650 psi (working stress 488 psi) was used for pavement concrete. The rigid pavement thicknesses for each traffic category were determined on the basis of the AASHTO design equation. Recommended alternatives for flexible and rigid pavements, summarized for each traffic area, are as follows: 12 Geotechnical Engineering Exploration Terracon Mr. Sandy Thayer ELI Project No. 20945089 • Contraction joints should be provided in slabs to control the location and extent of cracking. Maximum joint spacing of 15 to 20 feet in each direction is recommended. • A minimum 2-inch void space should be constructed above, or below non - bearing partition walls placed on the floor slab founded on or within 3 feet of the bedrock stratum. Special framing details should be provided at door jambs and frames within partition walls to avoid potential distortion. Partition walls should be isolated from suspended ceilings. • Interior trench backfill placed beneath slabs should be compacted in accordance with recommended specifications outlined below. • In areas subjected to normal loading, a minimum 4-inch layer of clean -graded gravel should be placed beneath interior slabs. • A minimum 8-inch layer of free -draining gravel should be placed beneath basement floor slabs in conjunction with the underslab drainage system. • Floor slabs should not be constructed on frozen subgrade. • Other design and construction considerations, as outlined in the ACI Design Manual, Section 302.113 are recommended. Pavement Design and Construction: Design of pavements for the project have been based on the procedures outlined in the 1986 Guideline for Design of Pavement Structures by the American Association of State Highway and Transportation Officials (AASHTO). Areas within proposed pavements on the site will be divided into two categories based upon anticipated traffic and usage. JTraffic criteria provided by the City of Fort Collins for pavement thickness designs include single 18-kip equivalent axle loads (ESAL's) of 36,500 for Ridge Drive, North Ridge Drive and all cul-de-sacs, 109,500 for Dakota Drive and Circle and 1,679,000 for improvements to South Shields Street. Based upon AASHTO criteria, Colorado is located within Climatic Region VI of the United States. This region is characterized as being dry, with hard ground freeze and spring thaw. The spring thaw condition typically results in saturated or near -saturated subgrade soil 11 Geotechnical Engineering Exploration Mr. Sandy Thayer ELI Project No. 20945089 Terracon dewatering may be required during site grading where cuts are planned below existing groundwater. To reduce the potential for groundwater or perched groundwater to impact foundation bearing soils and enter the basement of the structure, installation of a perimeter drainage system is recommended for all structures placed in or within 3 feet of groundwater and/or bedrock. The drainage system should be constructed around the exterior perimeter of the basement foundation, and slope at a minimum 1 /8 inch per foot to a suitable outlet, such as a sump and pump system or area underdrain. The drainage system should consist of a properly sized perforated pipe, embedded in free - draining gravel, placed in a trench at least 12 inches wide. Gravel should extend a minimum of 3-inches beneath the bottom of the pipe, and at least 1 foot above the bottom of the foundation wall. The gravel should be covered with drainage fabric prior to placement of foundation backfill. Seismic Considerations: The project site is located in Seismic Risk Zone I of the Seismic Zone Map of the United States as indicated by the Uniform Building Code. Based upon the nature of the subsurface materials, a seismic site coefficient, "s" of 1.0 should be used for the design of structures for the proposed project (Uniform Building Code, Table No. 23-J). J Floor Slab Design and Construction: The variability of the existing soils at approximate slab subgrade elevation could result in differential movement of floor slab -on -grade should expansive soils become elevated in moisture content. Use of structural floor systems, structurally supported independent of the subgrade soils, is a positive means of eliminating the potentially detrimental effects of floor movement where slabs are founded on or within 3 feet of the bedrock stratum. A If slab -on -grade is utilized, the subgrade soils should be prepared as outlined in the earthwork section of this report. Additional floor slab design and construction recommendations are as follows: • Positive separations and/or isolation joints should be provided between slabs and all foundations, columns or utility lines to allow independent movement. 10 J Geotechnical Engineering Exploration Mr. Sandy Thayer Terracon ELI Project No. 20945089 To reduce potential uplift forces on piers, use of long grade beam spans to increase individual pier loading, and small diameter piers are recommended. For this project, use of a minimum pier diameter of 10 inches is recommended. A minimum 4-inch or greater void J space should be provided beneath grade beams between piers. The void material should be of suitable strength to. support the weight of fresh concrete used in grade beam construction, and to avoid collapse when foundation backfill is placed. Drilling to design depths should be possible with conventional single flight power augers. Groundwater conditions indicate that temporary steel casing will likely be required to properly drill and clean piers prior to concrete placement. Groundwater should be removed from each pier hole prior to concrete placement. Pier concrete should be placed immediately after completion of drilling and cleaning. If pier concrete cannot be placed in dry conditions, a tremie should be used for concrete placement. Due to potential sloughing and raveling, foundation concrete quantities may exceed calculated geometric volumes. If casing is used for pier construction, it should be withdrawn in a slow continuous manner maintaining a sufficient head of concrete to prevent infiltration of water or the creation of voids in pier concrete. Pier concrete should have a relatively high fluidity when placed in cased pier holes or through a tremie. Pier concrete with slump in the range of 6 to 8 inches is recommended. Free -fall concrete placement in piers will only be acceptable if provisions are taken to avoid striking the concrete on the sides of the hole or reinforcing steel. The use of a bottom - dump hopper, or an elephant's trunk discharging near the bottom of the hole where concrete segregation will be minimized, is recommended. To provide increased resistance to potential uplift forces, the sides of each pier should be 1 mechanically roughened in the bearing strata. This should be accomplished by a roughening tooth placed on the auger. Pier bearing surfaces must be cleaned prior to concrete placement. A representative of the geotechnical engineer should inspect the bearing surface and pier configuration. Basement Construction: In view of the relatively shallow depth to groundwater in the northeast and central portions of the site, it is recommended area dewatering systems be constructed in these parts of the project area. This may consist of construction of drains below the sewers in the streets. Area drains should be properly designed to lower flows below basement levels and should have a suitable outlet. Drains constructed within City rights -of -ways should be approved by the City of Fort Collins. In addition, temporary l 9 J Geotechnical Engineering Exploration Mr. Sandy Thayer ELI Project No. 20945089 Terracon J movements could occur if water from any source infiltrates the foundation soils; therefore, proper drainage should be provided in the final design and during construction. Foundations and masonry walls should be reinforced as necessary to reduce the potential for distress caused by differential foundation movement. The use of joints at openings or other discontinuities in masonry walls is recommended. u Foundation excavations should be observed by the geotechnical engineer. If the soil J conditions encountered differ significantly from those presented in this report, supplemental recommendations will be required. J Structures founded in or within 3 feet of the bedrock stratum should be supported by grade beam and drilled pier foundation systems..A depth to bedrock contour map is included as Figure 2 in Appendix A. Straight shaft piers, drilled a minimum of 5 feet into firm or harder bedrock, with a minimum shaft length of 12 feet are recommended. J For axial compression loads, piers may be design for a maximum end -bearing pressure of 15,000 pounds per square foot (psf), and skin friction of 1,500 psf for the portion of the pier in firm or harder bedrock. JRequired pier penetration should be balanced against potential uplift forces due to expansion of the subsoils and bedrock on the site. For design purposes, the uplift force on each pier can be determined on the basis of the following equation: U, = 20xD Where: UP = the uplift force in kips, and D = the pier diameter in feet Uplift forces on piers should be resisted by a combination of dead -load and pier penetration below a depth of 7 feet and in the bearing strata. All piers should be reinforced full depth for the applied axial, lateral and uplift stresses imposed. the amount of reinforcing steel for expansion should be determined by the tensile force created by the uplift force on each pier, with allowance for dead -load. Minimum lreinforcement of at least one percent of the cross -sectional area of each pier should be d specified. 8 Geotechnical Engineering Exploration Mr. Sandy Thayer ELI Project No. 20945089 Terracon J Design criteria for alternative foundation systems is subsequently outlined. Use of the alternative foundation systems outlined in this report should be determined for individual residential structures prior to construction. Slab -on -grade construction is considered acceptable, provided that design and construction recommendations are followed. Where no movement can be tolerated and where slabs are Jfounded on or within 3 feet of the bedrock stratum, consideration should be given to use of structural floor systems. Due to the relatively shallow depth to groundwater over portions of the site, an area dewatering system and individual perimeter drainage systems will be required for basement construction in the northeast and central portions of the project area. Foundation Systems: Due to the presence of low -swelling soils on the site, spread footing J and grade beam foundations bearing upon undisturbed subsoils and/or engineered fill are recommended for support for the proposed structures founded a minimum of 3 feet above the bedrock stratum. The footings may be designed for a maximum bearing pressure of J 1,500 psf (dead load plus % maximum live load). In addition, the footings should be sized to maintain a minimum dead -load pressure of 500 psf. The design bearing pressure may be increased by one-third when considering total loads that include wind or seismic J conditions. J In order to maintain the minimum dead -load pressure, it may be necessary to design and construct a system of grade beams and isolated footing pads. To maintain the minimum dead -load pressure on footings, a minimum 4-inch void space should be provided beneath Jthe grade beams between footing pads (if utilized). Existing fill on the site should not be used for support of foundations without removal and recompaction. Exterior footings should be placed a minimum of 30 inches below finished grade for frost protection. Finished grade is the lowest adjacent grade for perimeter footings and floor level 1 for interior footings. d Footings should be proportioned to minimize differential foundation movement. Proportioning on the basis of equal total settlement is recommended; however, proportioning to relative constant dead -load pressure will also reduce differential settlement between adjacent footings. Total or differential settlement resulting from the assumed structural loads are estimated to be on the order of 3/4 inch. Additional foundation 7 JGeotechnical Engineering Exploration Mr. Sandy Thayer Terracon JELI Project No. 20945089 fluctuate with varying seasonal and weather conditions and irrigation demands. High water Jlevels at the site may be due to flood irrigation occurring just prior to drilling. 7 Based upon review of U.S. Geological Survey maps ('Hillier, at al, 1983), regional groundwater is expected to be encountered in unconsolidated alluvial deposits on the site, at depths ranging from 5 to 20 feet below the existing ground surface at the project site. J Zones of perched and/or trapped groundwater may also occur where water is not already encountered on top of the bedrock, at times in the subsurface soils overlying bedrock, on top of the bedrock surface or within permeable fractures in the bedrock materials. The location and amount of perched water is dependent upon several factors, including J hydrologic conditions, type of site development, irrigation demands on or adjacent to the site, fluctuations in water features, seasonal and weather conditions. Fluctuations in groundwater levels can best be determined by implementation of a groundwater monitoring plan. Such a plan would include installation of groundwater monitoring wells, and periodic measurement of groundwater levels over a sufficient period of time. Two groundwater monitor wells have been constructed on the site by Empire l Laboratories, Inc. on August 10, 1994. J The possibility of groundwater fluctuations should be considered when developing design and construction plans for the project. CONCLUSIONS AND RECOMMENDATIONS Geotechnical Considerations: The site appears suitable for the proposed construction. Potentially expansive soils and bedrock and shallow groundwater will require particular attention in the design and construction. The following foundation systems were evaluated for use on the site: J • spread footings and/or grade beams bearing on undisturbed soils; • spread footings and/or grade beams bearing on engineered fill; and • grade beams and straight shaft piers drilled in to bedrock. J 'Hillier, Donald E.; Schneider, Paul A., Jr.; and Hutchinson, E. Carter, 1983, Depth to Water Table (1979) in the Boulder -Fort Coffins -Greeley Area, Front Range Urban Corridor, Colorado, United States Geological Survey, Map I-855-1. 6 J Geotechnical Engineering Exploration Mr. Sandy Thayer ELI Project No. 20945089 Terracon lean clay with gravel and clayey sand. The fill is moist, medium stiff to very stiff and medium dense. • Lean Clay with Sand: This stratum underlies the topsoil and/or fill in Borings 1 through 5, 7 through 12, 14, 17 and 19 and extends to depths of 1'/2 to 11'% feet. The lean clay with sand varies to a lean clay, is moist to wet and medium to very stiff in consistency. • Sandy Lean Clay: A layer of red sandy lean clay underlies the upper clays and/or topsoil and fill in Borings 2, 6, 8 through 18, 20 and 21 at depths of '/: to 6 feet and extends to depths of 1'/2 to 12'/z feet below the surface. The sandy lean clay is moist to wet and medium to hard in consistency. • Clayey Sand with Gravel: This stratum was encountered below the upper clays in Borings 3, 5, 6, 8, 10, 16, 18 and 20 and extends to depths of 9 to greater than 15 feet. The clayey sand is slightly plastic, contains varying amounts of gravel, is loose to dense and dry to wet in situ. • Claystone-Siltstone Bedrock: The bedrock was encountered in all but Borings 5, 6, 13, 16, 18 and 20 at depths of 1'/Z to 14 feet and extends to greater depths. The upper 2 to 3'/2 feet of the bedrock is highly weathered; however, the underlying interbedded siltstone and claystone is hard. Field and Laboratory Test Results: Field and laboratory test results indicate the clay soils exhibit low to moderate expansive potential and moderate bearing characteristics. The bedrock exhibits moderate to high swell potential and high bearing characteristics. The clayey sand is nonexpansive and exhibits moderate bearing characteristics. Groundwater Conditions: Groundwater was encountered in Borings 2, 4, 5, 6, 8, 9, 10, 11 and 18 at approximate depths of 3 to 14'/2 feet below the surface at the time of field exploration. Borings 1, 3, 7, 12 through 17 and 19 through 21 were dry at the time of drilling. When checked 1 day after drilling, groundwater was measured in Borings 1, 2, 4, 6, 8, 9, 10, 11, 12, 14, and 17 at approximate depths of 1 to 11 '/2 feet below the surface. Boring 18 was caved at a depth of 6'/2 feet, Borings 19, 20 and 21 were filled in at the time of drilling, and the remaining borings were dry when checked 1 day after drilling. These observations represent only current groundwater conditions, and may not be indicative of other times, or at other locations. Groundwater levels can be expected to 5 Geotechnical Engineering Exploration Mr. Sandy Thayer Terracon ELI Project No. 20945089 SUBSURFACE CONDITIONS Geology: The proposed area is located within the Colorado Piedmont section of the Great Plains physiographic province. The Colorado Piedmont, formed during Late Tertiary and Early Quaternary time (approximately 2,000,000 years ago), is a broad, erosional trench which separates the Southern Rocky Mountains from the High Plains. Structurally, the site lies along the western flank of the Denver Basin. During the Late Mesozoic and Early Cenozoic Periods (approximately 70,000,000 years ago), intense tectonic activity occurred, causing the uplifting of the Front Range and associated downwarping of the Denver Basin to the east. Relatively flat uplands and broad valleys characterize the present-day topography of the Colorado Piedmont in this region. The site is underlain by the Cretaceous Pierre Formation. The Pierre shale in portions of the J project area consists of siltstone-claystone which was encountered over the majority of the site at depths of 1'/z to 14 feet. It is estimated the bedrock underlies the remainder of the site at depths of 20 to 25 feet below the surface. The bedrock is overlain by residual and alluvial soils of Pleistocene and/or Recent Age. l Mapping completed by the Colorado Geological Survey ('Hart, 1972), indicates the site in J an area of "Moderate Swell Potential". Potentially expansive materials mapped in this area include bedrock, weathered bedrock and colluvium (surficial units). 7 Soil and Bedrock Conditions: As presented on the Logs of Boring, the subsurface soils are presented as follows: • Silty Topsoil: The majority of the area tested. is overlain by a 6-inch layer of silty topsoil. The topsoil has been penetrated by root growth and organic matter. • Pavement: Six to 12 inches of asphalt were encountered in Borings 19, 20 and 21. The asphalt is underlain by 7 to 8 inches of gravel base course in Borings 20 and 21. • Fill Material: A layer of fill underlies the pavement in Borings 19 through 21 and extends to depths of 3'/2 to 4'/2 feet. The fill consists of a varying mixture of sandy J 'Hart, Stephen S., 1972, Potentiapy Swang Soo and Rock In the Front Range Urban Condor, Colorado, Colorado Geological Survey, Environmental Geology No. 7. 4 Geotechnical Engineering Exploration Mr. Sandy Thayer ELI Project No. 20945089 Terracon Laboratory Testing: All samples retrieved during the field exploration were returned to the laboratory for observation by the project geotechnical engineer, and were classified in accordance with the Unified Soil Classification System described in Appendix C. Samples of bedrock were classified in accordance with the general notes for Bedrock Classification. At that time, the field descriptions were confirmed or modified as necessary, an applicable laboratory testing program was formulated to determine engineering properties of the subsurface materials. Boring logs were prepared and are presented in Appendix A. Selected soil and bedrock samples were tested for the following engineering properties: • Water content • Expansion • Dry density • . Plasticity Index • Consolidation • R-Value • Compressive strength • Water soluble sulfate content The significance and purpose of each laboratory test is described in Appendix C. Laboratory test results are presented in Appendix B, and were used for the geotechnical engineering analyses, and the development of foundation and earthwork recommendations. All laboratory tests were performed in general accordance with the applicable ASTM, local or other accepted standards. SITE CONDITIONS The site consists of a 34-acre tract of land vegetated with low, dense grass, weeds and trees. An existing residence and horse corrals are located in the southwest portion of the site and an existing house is located along South Shields Street. The Pleasant Valley and Lake Canal runs north -south across the west -central portion of the site and forms a deep ravine through the southern portion of the project area. A concrete diversion structure is located across the Pleasant Valley and Lake Canal in the southern portion of the site. The Trilby Lateral extends from the center of the west property line and connects with the Pleasant Valley and Lake Canal. The Applewood Lateral begins at the diversion structure and runs eastward and then turns southward to the south property line. The property slopes to the east and southeast and has positive drainage in these directions. Drainage in the southwest portion of the project area is directed into two large drainages, The Pleasant Valley and Lake Canal flows in the west drainage. The property is bordered by fields on the north and south, by Shields Street to the east, and by The Ridge Subdivision to the west. 3 Geotechnical Engineering Exploration Terracon Mr. Sandy Thayer ELI Project No. 20945089 3 maximum wall loads of 3 kips per linear foot and maximum column loads of approximately 30 kips. SITE EXPLORATION The scope of the services performed for this project included site reconnaissance by an engineering geologist, a subsurface exploration program, laboratory testing and engineering analysis. Field Exploration: A total of 21 test borings were drilled on September 27 and 30, 199.4 to depths of 10 to 15 feet at the locations shown on the Site Plan, Figure 1. Ten borings J were drilled within proposed building areas, and 11 borings were drilled in the area of J proposed and existing streets. All borings were advanced with a truck -mounted drilling rig, utilizing 4-inch diameter solid stem auger. A preliminary geotechnical engineering report was prepared for the site May 11, 1994. Four test borings were drilled on the site on April 28, 1994. In addition, two groundwater monitor wells were constructed on the site August 10, 1994. The borings were located in the field by pacing from property lines and/or existing site features and survey stakes provided by ET Designs. Elevations were taken at each boring location by interpolation from a topographic map provided by ET Designs. The accuracy of boring locations and elevations should only be assumed to the level implied by the methods used. Continuous lithologic logs of each boring were recorded by the engineering geologist during the drilling operations. At selected intervals, samples of the subsurface materials were taken by pushing thin -walled Shelby tubes, or by driving split -spoon samplers. Representative bulk samples of subsurface materials were obtained from selected pavement borings. Penetration resistance measurements were obtained by driving the split -spoon into the subsurface materials with a 140-pound hammer falling 30 inches. The penetration resistance value is a useful index to the consistency, relative density or hardness of the materials encountered. Groundwater measurements were made in each boring at the time of site exploration, and one day after drilling. The borings were filled in after the one day measurements. 2 GEOTECHNICAL ENGINEERING REPORT COTTONWOOD RIDGE FORT COLLINS, COLORADO ELI Project No. 20945089 November 2, 1994 INTRODUCTION Terracon JThis report contains the results of our geotechnical engineering exploration for the proposed residential development to be located on South Shields Street south of Harmony Road in south Fort Collins, Colorado. The site is located in the Northeast 1 /4 of Section 3, Township 6 North, Range 69 West of the 6th Principal Meridian. The purpose of these services is to provide information and geotechnical engineering recommendations relative to: • subsurface soil and bedrock conditions • groundwater conditions • foundation design and construction • basement construction • floor slab design and construction • pavement design and construction 0 earthwork • drainage The conclusions and recommendations contained in this report are based upon the results of field and laboratory testing, engineering analysis, and experience with similar soil conditions, structures and our understanding of the proposed project. PROPOSED CONSTRUCTION The project as we understand it will be to construct a 71-lot single-family residential development. The property will be served by residential streets, and improvements will be made to South Shields Street along the east edge of the site. Detention ponds will be constructed in the northeast and southeast corners of the project area. Improvements are planned for Pleasant Valley and Lake Canal through the southern portion of the project area. The improvements will include regrading of slopes, construction of drop structures and providing slope protection. The Applewood Lateral is to be placed in a pipe through the southwest portion of the project area. Minor amounts of cut and fill of less than 2 feet are anticipated for street construction. It is anticipated the proposed residences will have J Geotechnical Engineering Exploration Mr. Sandy Thayer Terracon 1 ELI Project No. 20945089 J 1 TABLE OF CONTENTS (Cont'd) J APPENDIX A J Site Plan................Figure No. 1 .......................... Depth to Bedrock Contour Map Figure No. 2 Logs of Borings .................................... Al thru A21 JAPPENDIX B Consolidation Tests 61 thru B3 Hveem Stabilometer Curve ............................. • B4 thru B7 Summary of Test Results B8 thru 1312 APPENDIX C: GENERAL NOTES Drilling & Exploration C1 Unified Soil Classification .................................... C2 Bedrock Classification, Sedimentary Bedrock ....................... C3 Laboratory Testing, Significance and Purpose ...................... C4 C5 Report Terminology ........................................ APPENDIX D Recommended Preventative Maintenance -Asphalt Concrete Pavements . D1 Recommended Preventative Maintenance -Jointed Concrete Pavements .... D2 Geotechnical Engineering Exploration Terracon Mr. Sandy Thayer ELI Project No. 20945089 TABLE OF CONTENTS Page No. Letter of Transmittal ............................................... ii INTRODUCTION................................................ 1 PROPOSED CONSTRUCTION ...................................... 2 SITE EXPLORATION ............................................. 2 Field Exploration .......................................... 3 Laboratory Testing ......................................... SITE CONDITIONS .............................................. 3 SUBSURFACE -CONDITIONS ....................................... 4 Geology.............................................. 4 Soil and Bedrock Conditions ................................ 4 Field and Laboratory Test Results ............... ..... ........ 5 Groundwater Conditions ..................................... 5 CONCLUSIONS AND RECOMMENDATIONS ............................ 6 Geotechnical Considerations ... 6 Foundation Systems ........................................ 7 Basement Construction ...................................... 9 Seismic Considerations ...................................... 10 Floor Slab Design and Construction 10 Pavement Design and Construction ............................. 11 Earthwork .................. 16 SiteClearing ........................................ 16 Excavation ......................................... 17 Slab Subgrade Preparation ............................... 17 Pavement Subgrade Preparation ........................... 18 Fill Materials ........................................ 18 Placement and Compaction .............................. 19 Shrinkage.......................................... 20 Slopes............................................ 21 Compliance......................................... 21 Excavation and Trench Construction ........................ 22 Drainage ................................................ 22 Surface Drainage ..................................... 22 Subsurface Drainage .................................. 23 Additional Design and Construction Considerations .................. 23 Exterior Slab Design and Construction 23 Underground Utility Systems ............................. 24 Corrosion Protection ................................... 24 GENERAL COMMENTS ........................................... 24 Geotechnical Engineering Exploration Mr. Sandy Thayer ELI Project No. 20945089 Terracon Other design and construction details, based upon geotechnical conditions, are presented in the report. We appreciated being of service during the geotechnical engineering phase of this project, and are prepared to assist during the construction phases as well. If you have any questions concerning this report or any of our testing, inspection, design and consulting services, please do not hesitate to contact us. Sincerely, EMPIRE LABORATORIES, INC. A Division of The Terracon Companies, Inc. ;7 � -tell Neil R. herr d Senior Engineering Geologist Reviewed by: 6,©`�4 Larry G. O'Dell, P.E. J Office Manager i NRS\LGO\cic Copies to: Addressee (1) ET Designs - Mr. Eric Thayer (2) Empire Laboratories, Inc. A Division of The Terracon Companies, Inc. P.O. Box 503.301 No. Howes Fort Collins, Colorado 80522 (303)484-0359 Fax (303) 484-0454 Chester C. Smith, P.E. Larry G. O'Dell, P.E. Neil R. Sherrod, C.P.G. November 2, 1994 Mr. Sandy Thayer 1827 Mitchell Lane Fort Collins, Colorado 80526 Re: Geotechnical Engineering Report, Cottonwood Ridge Fort Collins, Colorado ELI Project No. 20945089 Empire Laboratories, Inc. (ELI) has completed a geotechnical engineering exploration for the proposed residential development to be located on South Shields Street south of Harmony Road in south Fort Collins, Colorado. This study was performed in general accordance with our proposal number D2094323 dated September 2, 1994. The results of our engineering study, including the boring location diagram, laboratory test results, test boring records, and the geotechnical recommendations needed to aid in the design and construction of foundations and other earth connected phases of this project are attached. The subsurface soils consisted of lean clay, lean clay with sand, sandy lean clay with gravel, and clayey sand with gravel. The upper subsoils are underlain by claystone-siltstone bedrock. The information obtained by the results of field exploration and laboratory testing completed for this study indicates the clay soils at the site have low to moderate expansive potential and moderate bearing characteristics. The bedrock exhibits moderate to high expansive potential and high bearing characteristics. Structures founded a minimum of 3 feet above the bedrock may be supported by a spread footing and/or grade beam foundation system. Structures founded in or within 3 feet of the bedrock should be supported by grade beam and straight shaft pier foundation systems. The bedrock is encountered at relative shallow depths in the northeast and central portions of the site. Slab -on -grade may be utilized for the interior floor system provided that care is taken in the placement and compaction of the subgrade soil. If no movement can be tolerated, consideration should be given to structural floor systems. In view of the relatively shallow depth to groundwater in the northeast and central portions of the site, basement construction is not feasible in these portions of the project area without construction of an area dewatering system and individual dewatering systems around residences in this portion of the development. Offices of The Terracon Companies, Inc. Geotechnical, Environmental and Materials Engineers Arizona ■ Arkansas ■ Colorado ■ Idaho ■ Illinois ■ Iowa ■ Kansas ■ Minnesota Missouri ■ Montana 0 Nebraska ■ Nevada ■ Oklahoma 0 Texas 0 Utah ■ Wyoming GEOTECHNICAL ENGINEERING REPORT COTTONWOOD RIDGE FORT COLLINS, COLORADO ELI PROJECT NO. 20945089 November 2, 1994 Prepared for: MR. SANDY THAYER 1827 MITCHELL LANE FORT COLLINS, COLORADO 80526 Prepared by. Empire Laboratories, Inc. A Division of The Terracon Companies, Inc. 301 North Howes Fort Collins, Colorado 80521 Empire Laboratories, Inc. A Division of The Terracon Companies, Inc. f ! GEOTECHNICAL ENGINEERING REPORT COTTONWOOD RIDGE FORT COLLINS, COLORADO ELI PROJECT NO. 20945089 November 2, 1994 A Division of The Terracon Companies, Inc.