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HomeMy WebLinkAbout_Geotechnical Engineering Addendum 2011 1207.pdfNAP December 7, 2011 PATRIOT ENGINEERING and Environmental, Inc. Engineering Value for Project Success Consulting Environmental, Geotechnical and Materials Engineers Janelle Wood Carmel Land Holding, LLC 222 West Colinas Boulevard, Suite 2100 Irving, Texas 75039 Re: Geotechnical Engineering Addendum Letter The Barrington of Carmel (Formerly Mayflower Communities) Guilford Road and 116th Street Carmel, Indiana Patriot Project No. 1-08-0647 Dear Janelle: Based on review comments recently submitted to Patriot Engineering and Environmental, Inc. (Patriot) for the above referenced project, we understand that additional recommendations are needed for the above referenced project (Report dated July 28, 2008). We now understand that a portion of the southwest wing of the building will be over an existing pond that is to be backfilled. Additionally, we understand a below grade parking structure is now to be located under the northwest portion of the building. Pond Backfill (Near Borings B-14, B-17, B-18, and B-21) Recommendations were provided in our original report to aid in the design and construction of the proposed facility, as well as the adjacent parking and roadway areas. However, prior to construction, there are some initial construction concerns due to an existing pond that is currently located within a portion of the west wing of the facility. This pond will need to be completely drained of water and all soft and/or loose soils or sediments must be properly removed prior to the backfilling of the pond. Upon completion of the dewatering and removal of unsuitable soils, the pond should be backfilled with well -compacted suitable structural fill material (See Section 5.3 "Structural Fill and Fill Placement Control" of our original report). It should be noted that some limited settlement of new fill could possibly occur, particularly in the areas of the deepest fill placement. Therefore to reduce any potential post construction settlement of the facility, the grade raise fill (structural backfill material) should be placed and given adequate time to settle prior to construction. In order to determine when settlement has reached an acceptable level, we recommend the implementation of a settlement monitoring program. 6330 East 751h Street, Suite 216, Indianapolis, Indiana 46250 (317) 576-8058 • (317) 576-1965 FAX • www.patrioteng.com Offices in Indianapolis, Evansville, Fort Wayne, Lafayette, and Terre Haute, IN, Louisville, KY, Dayton / Cincinnati, OH and Nashville, TN. The Barrington of Carmel Carmel Land Holding, LLC Carmel, Indiana Patriot Project No.: 1-08-0647 Below Grade Parkinq Structure Foundations The proposed parking structure is to be located beneath the northeast portion of the facility (Borings B-3, B-5, B-6, B-7, and B-10). We assume that this below grade structure will bear at a depth of approximately 10 to 12 feet below the existing ground surface. The below grade parking structure can be supported on spread footings bearing on the stiff to very stiff sandy clays, or on new well -compacted structural fill overlying the same. However, some undercutting of soft or unsuitable soils may be required at some locations. These footings should be proportioned using a net allowable soil bearing pressure not exceeding 3,000 pounds per square foot (psf) for column footings or 2,500 psf for strip (wall) footings. For proper performance at the recommended bearing pressure, foundations must be constructed in compliance with the recommendations for footing excavation inspection that are discussed in Section 5.0 "Construction Considerations" of our original report; which indicates careful field control during construction by Patriot to confirm that the exposed material is capable of supporting the design bearing pressure and minimize the post construction settlement potential. In using the above net allowable soil bearing pressures, the weight of the foundation and backfill over the foundation need not be considered. Hence, only loads applied at or above the minimum finished grade adjacent to the footing need to be used for dimensioning the foundations. We estimate that the total foundation settlement should not exceed approximately 1 inch and that differential settlement should not exceed about % inch. Careful field control during construction is necessary to minimize the actual settlement that will occur. Groundwater Considerations Groundwater was encountered at varying depths during our original field activities. Due to this, it is possible that significant dewatering will be necessary during the excavation and construction of the below grade parking structure. We recommend that the groundwater table be lowered to a minimum of 3 feet below the bottom of the excavation. Page 2 The Barrington of Carmel Carmel Land Holding, LLC Carmel, Indiana Patriot Project No.: 1-08-0647 We recommend that a perimeter drainage system be provided around the below grade walls (outside of the footings) and an underslab drainage system be installed beneath the entire below grade parking area. These drains may flow by gravity to a sump or to a storm sewer (if possible). The perimeter drain should consist of a 6 inch slotted, corrugated pipe surrounded by at least 6 inches of INDOT No. 5 stone. The stone should be completely wrapped in a drainage geotextile consisting of Mirafi 140N or an equivalent, in order to keep the stone clean or avoid clogging of the drainage layer with silt and sand. In addition, the zone adjacent to the below grade walls should be backfilled with a minimum 2 feet wide zone of free draining granular material (less than 3% by weight passing the No. 200 sieve) to prevent the buildup of hydrostatic pressure behind walls. Above this free draining material, a 2 feet thick clay fill should be compacted at the surface to prevent surface water infiltration. The clay fill should be compacted to a minimum 90% of the maximum Modified Proctor dry density (ASTM D-1557). The below grade slab should be underlain by a 9-inch layer of open -graded INDOT No. 5 stone that will serve as a drainage blanket beneath the entire basement area. We recommend that a system of perforated drain pipes, which could drain by gravity to an outlet or sump pit, be installed at a maximum spacing of 50 foot on centers into the granular fill. The basement drains consist of 4 inch slotted corrugated pipes surrounded by at least 6 inches of No. 5 stone. The stone should be completely wrapped in a drainage geotextile consisting of Mirafi 140N or equivalent. The drain tiles may be flat lying or sloped to allow for gravity flow into the sump pits. The underslab drainage layer should not extend under the basement walls in order to limit the water seepage to only that come through the basement slab area. The underslab drainage and the perimeter drainage should be independent of each other. It will be necessary to place a geotextile fabric separator between the subgrade and the gravel drainage layer to prevent clogging of the drainage layers. Lateral Earth Pressures The magnitude of the lateral earth pressure is dependent on the method of backfill placement, the type of backfill soil, drainage provisions and whether or not the wall is permitted to yield during and/or after placement of the backfill. When a wall is held rigidly against horizontal movement, the lateral pressure against the wall is greater than the "active" earth pressure that is typically used in the design of free-standing retaining walls. Therefore, rigid walls should be designed for higher "at -rest" pressures (using an at -rest lateral earth pressure coefficient, KO), while yielding walls can be designed for active pressures (using an active lateral earth pressure coefficient, Ka). Page 3 The Barrington of Carmel Carmel Land Holding, LLC Carmel, Indiana Patriot Project No.: 1-08-0647 The below grade parking structure walls proposed for the project site are expected to be rigid walls. Therefore, provided a clean well -graded granular material is used for backfill, a total soil unit weight (yt) of 125 pcf, an at -rest lateral earth pressure coefficient (Ko) of 0.45, an active lateral earth pressure coefficient (Ka) of 0.30, and a passive lateral earth pressure coefficient (Kp) of 3.4 can be used for calculating the lateral earth pressures. An equivalent fluid active pressure of 38 psf per foot of wall height is recommended for design purposes in conditions where the top of the wall is allowed to yield during backfilling. However, if the top of the wall will be fixed, an equivalent fluid at -rest pressure of 57 psf per foot of wall height is recommended for design purposes. This equivalent fluid pressure would increase linearly from zero (0) psf at the ground surface, to a maximum at the base of the wall. When calculating passive earth pressure, the upper 3 feet of soil should be neglected. Note also that the wall must move laterally about 0.04H (where H equals the wall height) in order for passive earth pressures to be fully developed. In most cases, passive earth pressures behind walls should not be considered. If hydrostatic pressure due to water build-up against the wall is anticipated, the equivalent fluid pressure method will be changed for the soil. Rather, the lateral earth pressure should be computed using a total soil unit weight of 125 pcf above the highest anticipated water level, and a buoyant soil unit weight of 63 pcf below the highest anticipated water level. The earth pressure coefficient indicated above should be used above and below the water level to compute the lateral earth pressure. The hydrostatic pressure should be computed using the highest anticipated water level. The lateral earth pressure and hydrostatic pressure should be added to obtain the total lateral pressure on the wall. It has been assumed that the static weight per axle of equipment utilized for the compaction of the backfill materials adjacent to the below -grade wall will not exceed 2 tons per axle for non -vibratory equipment and 1 ton per axle for vibratory equipment. All heavy equipment, including compaction equipment heavier than recommended above, should not be allowed closer to the wall (horizontal distance) than the vertical distance from the backfill surface to the bottom of the wall. The shear resistance against base sliding can be computed by multiplying the minimum normal force on the base of the footing times a coefficient of friction of 0.3. Lateral earth pressures can be computed as discussed above. A minimum factor of safety of 1.5 is recommended for sliding stability. Page 4 The Barrington of Carmel Carmel Land Holding, LLC Carmel, Indiana Patriot Project No.: 1-08-0647 Summary of Lateral Earth Design Pressures Soil Unit Weight g (Yt) (pcf) At -Rest Coefficient (Ko) Active Coefficient (Ka) Passive Coefficient (Kp) Coefficient of Friction Minimum Factor of Safety 125 0.45 0.30 3.4 0.3 1.5 We appreciate the opportunity to provide this Geotechnical Engineering Addendum Letter. If you have any questions regarding this letter, please do not hesitate to contact our office. Respectfully submitted, Patriot Engineering and Environmental, Inc. fit�lo Eric Wenz 7 Geotechnical Engineer William D. Dubois, P.E. President ',,j III iflII�11., \ 1� LJAf�fi -A 4 - 60018167 ; a - = o STATE OF I� - �O ��-•rNp pt�PS' � . Page 5