GEOTECHNICAL INVESTIGATION I-15 MILE POST CL 120 INTERCHANGE MESQUITE, NEVADA PREPARED FOR:

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1 GEOTECHNICAL INVESTIGATION I-15 MILE POST CL 120 INTERCHANGE MESQUITE, NEVADA PREPARED FOR: HORROCKS ENGINEERS 2162 WEST GROVE PARKWAY, SUITE 400 PLEASANT GROVE, UTAH ATTENTION: BRIAN ATKINSON, P.E. PROJECT NO MAY 19, 2011 (Revised June 22, 2011)

2 TABLE OF CONTENTS EXECUTIVE SUMMARY...Page 1 SCOPE...Page 3 SITE CONDITIONS...Page 5 FIELD STUDY...Page 5 SUBSURFACE CONDITIONS AND LABORATORY TESTING...Page 5 SUBSURFACE WATER... Page 10 PROPOSED CONSTRUCTION... Page 11 RECOMMENDATIONS... Page 12 A. Site Grading... Page 12 B. Permanent Shallow Foundations... Page 24 C. Temporary Pile Foundations... Page 27 D. Concrete Slab-on-Grade/Curb... Page 31 E. Lateral Earth Pressures... Page 31 F. Seismicity... Page 33 G. Liquefaction... Page 34 H. Water Soluble Sulfates and Cement Type... Page 35 I. Corrosion... Page 35 J. Construction Testing and Observation... page 36 LIMITATIONS... Page 37 FIGURES Vicinity Map Figure 1 Site Plan Figure 2 Logs of Test Pits Figure 3 Logs of Exploratory Borings Figures 4-9 Legend and Notes of Test Pits and Exploratory Borings Figure 10 Consolidation Test Results Figures Direct Shear Test Results Figures Gradation and Moisture-Density Relationship Results Figures Sieve Analysis Test Report Figures Factored Bearing Resistance vs Effective Footing Width Figure 46 Driven H-Pile Capacities Figure 47 Pile Head Deflection Figure 48 Maximum Moment Figure 49 Pile Deflection Figures Summary of Laboratory Test Results Table 1 Summary of Chemical Laboratory Test Results Table 2 Subcontracted Laboratory Tests Appendix

3 Page 1 EXECUTIVE SUMMARY 1. The subsurface soil profile observed in the test pits excavated and the borings drilled at the site generally consists of varying thicknesses of site grading fill overlying natural poorly graded sand with silt to silty sand. The fill thickness observed varies from approximately 1 foot to approximately 31 feet. Fill was not encountered in Test Pit TP- 4 and Borings B-10 through B-13 on the eastern portion of the site. Poorly graded gravel with sand was encountered near the surface in Borings B-11 through B-13. Fat clay was encountered near the bottom of B-13 at a depth of approximately 27 feet and a layer of lean clay was encountered in Test Pit TP-2 at a depth of approximately 10 feet. 2. Subsurface water was not encountered in the borings and test pits by AGEC to the maximum depth investigation, approximately 70 feet with the exception of boring B- 12. Groundwater was encountered at approximately 37 feet in Boring B-12 at the time of the exploration. This corresponds to an elevation of approximately 1,558½ feet. Review of the Baseline Geotechnical Investigation indicates groundwater was encountered at depths ranging from approximately 67 to 75 feet below the existing grade. This corresponds to an elevation ranging from approximately 1,557½ feet to 1,561 feet. Fluctuations in groundwater level may occur over time. We anticipate the groundwater depth/elevation will likely remain relatively constant throughout the year. 3. The subject site is suitable to support the proposed construction provided recommendations included within this report are followed. 4. Observations, penetration values (blow counts) and laboratory testing indicates the fill observed is generally moderately to well compacted and consists of silty sand to poorly graded sand with varied amounts of gravel mixed with some clay. 5. The proposed bridge overpass may be permanently supported on conventional spread footings bearing on a properly compacted subgrade as provided in the Permanent Shallow Foundations section of the report. Factored bearing resistances are provided on Figure Observations and laboratory testing indicate the on-site fill soils and natural sand soils (including soils sampled by NDOT during preparation of the Baseline Geotechnical Investigation), are suitable for use as Borrow, Selected Borrow and Backfill in accordance with Sections 203 and 207 of the State of Nevada DOT, Standard Specifications for Road and Bridge Construction, 2001 and Pull Sheets from the contract documents. Chemical tests conducted by NDOT and by AGEC should be referred to if corrosion to buried structures is a concern. 7. Geotechnical information related to foundations, subgrade preparation, excavation, compaction and materials, retaining structures and seismic design criteria are included within this report. APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC

4 Page 2 8. Information presented in this summary should not be used independent of that contained within the body of the report. APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC

5 Page 3 SCOPE This report presents the results of a geotechnical investigation for the proposed I-15 Mile Post CL120 Interchange in Mesquite, Nevada at the approximate location shown on Figure 1. This report presents the subsurface conditions encountered, laboratory test results, and recommendations for the geotechnical aspects of the project. Geotechnical aspects include temporary and permanent bridge foundation support recommendations, material suitability/grading recommendations, retaining design parameters and seismic characteristics of the subsurface soils. Field exploration was conducted to obtain information on the subsurface conditions. Samples obtained from the field investigation were tested in the laboratory to determine physical and engineering characteristics of the on-site soil. Information obtained from the field and laboratory along with information contained in the Baseline Geotechnical Investigation was used to define conditions at the site for our engineering analysis and to develop recommendations for the proposed construction. This report has been prepared to summarize the data obtained during the study and to present our conclusions and recommendations based on the proposed construction and the subsurface conditions encountered. Design parameters and a discussion of geotechnical engineering considerations related to construction are included in the report. The geotechnical design criteria and recommendations are based upon the following supporting documents and information: 1. Geotechnical Policies and Procedures Manual, 2005, Nevada DOT. 2. Baseline Geotechnical Report, I-15 Milepost CL120 Interchange, Design Build, July, 2010, prepared by Nevada DOT, Material Division. APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC

6 Page 4 3. Subsurface investigation and laboratory testing completed by AGEC. 4. AASHTO LRFD Bridge Design Specifications, Fifth Edition, Guide Design Specification for Bridge Temporary Works, published by AASHTO, Standard Specifications for Road and Bridge Construction, State of Nevada DOT, West Mesquite Interchange Design-Build Project, Part 9 - Contract Documents Appendix A Pull Sheets, April 4, Drawings and plans, prepared by Horrocks Engineers. 9. Structures Manual, Nevada DOT, September, Manual for Design & Construction Monitoring of Soil Nail Walls, Publication No. FHWA-SA R, October Geotechnical Circular No. 7", Report No. FHWA0-IF , prepared for FHWA, March Foundation Analysis and Design, Fourth Edition, Joseph E. Bowles. APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC

7 Page 5 SITE CONDITIONS The subject site is located in Mesquite, Clark County, Nevada at the I-15 mile post CL120 interchange as shown on Figure 1. There is currently an existing 3 span bridge super structure. We understand the existing bridge is supported on conventional spread footings. The existing bridge facilitates the travel of the north and south bound I-15 traffic over Falcon Ridge Parkway. Falcon Ridge Parkway is aligned beneath the overpass extending east and intersects Mesquite Blvd. There is cultivated, undeveloped property and residences to the east and developed commercial portions of Mesquite to the east and west. FIELD STUDY On March 14, 15, 16 and 17, an engineer from AGEC visited the site and observed the excavation of 5 test pits and the drilling of 13 borings at the approximate locations shown on the site plan, Figure 2. The test pits were excavated using a rubber tired backhoe. Borings were drilled utilizing a truck mounted drill rig equipped with 8-inch diameter hollow-stem augers. The test pits and borings were logged and soil samples obtained by an engineer from AGEC. Logs of the subsurface conditions encountered in the test pits and borings are shown graphically on Figures 3-9 with the Legend and Notes of Test Pits and Borings shown on Figure 10. SUBSURFACE CONDITIONS AND LABORATORY TESTING The subsurface soil profile observed in the test pits excavated and the borings drilled at the site generally consists of varying thicknesses of site grading fill overlying natural poorly graded sand with silt to silty sand. The fill thickness observed varies from approximately 1 foot to approximately 31 feet. Fill was not encountered in Test Pit TP-4 and Borings B-10 through B-13 on the eastern portion of the site. Poorly graded gravel with sand was encountered near APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC

8 Page 6 the surface in Borings B-11 through B-13. Fat clay was encountered near the bottom of B-13 at a depth of approximately 27 feet and a layer of lean clay was encountered in Test Pit TP-2 at a depth of approximately 10 feet. Asphaltic concrete pavement overlying base course was encountered at the surface in Boring B-6. Descriptions of the subsurface soils and encountered in the test pits and borings follows: Asphalt - Moderate condition and black in color. Base Course - Appears well compacted, moist and brown in color. Cultivated soil - The cultivated soil consists of silty to clayey sand. It is loose to medium dense, moist, contains roots and is brown in color. Fill - (USC Soil Classification: SM to SC, AASHTO Soil Classification: A-2-4) - The fill consists of silty sand to poorly graded sand mixed with varied amounts of gravel and clay. It generally appears moderately to well compacted, moist, non to low plastic and light brown in color. Laboratory tests conducted on samples of the fill indicate in-place moisture contents ranging from 3 to 12 percent, in-place dry densities ranging from 103 to 113 pounds per cubic foot (pcf), gravel contents (percent retained on the No. 4 sieve) ranging from 0 to 28 percent and fines contents (percent passing the No. 200 sieve) ranging from 9 to 25 percent. Atterberg Limits tests conducted on samples of the fill indicate the material tests is non-plastic. Moisture-density Relationship (modified proctor) tests conducted on samples of the fill indicate maximum dry densities ranging from to pcf with optimum moisture contents ranging from 6.5 to 11.0 percent. R- value tests conducted on samples of the fill indicate R-values ranging from 64 to 75 at 300 psi exudation pressure. APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC

9 Page 7 Direct shear tests conducted on samples of the fill remolded at approximately 95 percent of the maximum dry density and near the optimum moisture content indicate peak friction angles ranging from 40 to 42 degrees and peak cohesion values ranging from 340 to 550 pounds per square foot (psf). A direct shear test conducted on a sample of the fill in its existing condition indicates a peak friction angle of 32 degrees and peak cohesion value 780 psf. Several water soluble sulfate tests conducted on samples of the fill indicate water soluble sulfate concentrations ranging from 300 to 1,200 parts per million (ppm). Laboratory resistivity tests conducted on the fill indicate resistivities ranging from 450 to 1,400 ohm-cm. Chloride concentrations ranging from 11 to 161 ppm and ph values ranging from 8.1 to 9.0 were also measured on samples of the fill. A one-dimensional consolidation test conducted on a sample of the fill indicates it is slightly moisture sensitive (collapsible) when wetted under a constant pressure of approximately 1,000 psf and slightly compressible under additional loading. We anticipate a portion of the measured collapse in the boring drive sample is related to disturbance during the sampling process. Sandy lean clay to fat clay - (USC Soil Classification: CL to CH, AASHTO Soil Classification: A-4 to A-7-5) - The clay is medium stiff to very stiff, moist, low to high plastic and brown in color. Laboratory tests conducted on samples of the clay indicate in-place moisture contents ranging from 12 to 21 percent, in-place dry densities ranging from 99 to 111 pcf and fines contents ranging from 51 to 69 percent. Atterberg Limits tests conducted on a samples of the clay indicate liquid limits ranging from 22 to 58 percent and a plasticity indices ranging from of 7 to 39 percent. APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC

10 Page 8 A one-dimensional consolidation test conducted on a sample of the clay (at a depth of 29 feet) indicates it is non moisture sensitive when wetted under a constant pressure of approximately 2,000 psf and slightly compressible under additional loading. Silty sand - (USC Soil Classification: SM, Soil Classification: AASHTO A-2-4) - The silty sand is dense to very dense, moist, fine-grained and light brown in color. Laboratory tests conducted on samples of the silty sand indicate in-place moisture contents ranging from 3 to 10 percent, in-place dry densities ranging from 97 to 117 pcf, a gravel content of 2 percent and fines contents ranging from 13 to 28 percent. A direct shear test conducted on a sample of the silty sand in its existing condition indicates a peak friction angle of 33 degrees and peak cohesion value 350 psf. Several one-dimensional consolidation tests conducted on samples of the silty sand indicate the material is non to slightly moisture sensitive (collapsible) when wetted under constant pressures of approximately 1,000 and 2,000 psf and slightly compressible under additional loading with the exception of the near surface soil in test pit TP-5. The consolidation tests indicate the near surface soils tested are moderately collapsible when wetted under a constant pressure of 500 psf. We anticipate a portion of the measured collapse in the boring drive samples is related to disturbance during the sampling process. Poorly graded sand with silt - (USC Soil Classification: SP-SM, AASHTO Soil Classification: A-2-4 to A-3 to A-1-b) - The poorly graded sand with silt contains interbedded silty sand layers and occasional gravel. It is loose to very dense, moist to slightly moist, fine-grained, and light brown in color. APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC

11 Page 9 Laboratory tests conducted on samples of the poorly graded sand with silt indicate inplace moisture contents ranging 1 to 8 from percent, in-place dry densities ranging from 101 to 126 pcf, a gravel content ranging from 0 to 19 percent and fines contents ranging from 5 to 12 percent. Several one-dimensional consolidation tests conducted on samples of the poorly graded sand with silt indicate it is non to slightly moisture sensitive (collapsible) when wetted under constant pressures of approximately 1,000, 2,000 and 4,000 psf and slightly compressible under additional loading with the exception of the near surface soil in test pit TP-5 and Boring B-4. The consolidation tests indicate these near surface soils (in the area of TP-5 and B-4) tested are moderately collapsible when wetted under a constant pressure of 500 psf. We anticipate a portion of the measured collapse in the boring drive samples is related to disturbance during the sampling process. Poorly graded gravel with sand - (USC Soil Classification: GP, AASHTO Soil Classification: A-1-a to A-1-b) - The poorly graded gravel with sand contains occasional cobbles. It is medium dense to very dense, moist, sub-rounded gravel and brown in color. Laboratory tests conducted on samples of the poorly graded gravel with sand indicate in-place moisture contents ranging from 2 to 3 percent, gravel contents ranging from 60 to 71 percent and fines contents ranging from 2 to 4 percent. Logs of the subsurface conditions encountered in the test pits and borings are shown graphically on Figures 3-9 with the Legend and Notes of Test Pits and Borings shown on Figure 10. Results of the laboratory tests are also shown on Figures 3-9 and are summarized on the Summary of Laboratory Test Results, Table 1 and the Summary of Chemical Test Results, Table 2. One-dimensional consolidation test results are shown graphically on Figures Direct shear test results are shown on Figures Moisture-Density Relationship (Proctor) and Gradation/Soil Classification Test Results are shown on Figures APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC

12 Page 10 Gradation Test Results are shown on Figures R-value and chemical test results subcontracted to outside laboratories are included in the Appendix of this report. Laboratory test results were conducted in accordance with the following Test methods: 1. Atterberg Limits: AASHTO T89 and T Gradation (Percent passing the No. 200 sieve): AASHTO T Gradation (All sieves): AASHTO T Soil Class: AASHTO M One Dimensional Consolidation: AASHTO T Moisture Density Relationship Test (Modified Proctor): AASHTO T Direct Shear: AASHTO T Chlorides: AASHTO T Resistivity: AASHTO T Water Soluble Sulfates: AASHTO T290 and SM4500E. 11. R-Value: AASHTO T ph: AASHTO T Moisture of Soils: AASHTO T265. SUBSURFACE WATER Subsurface water was not encountered in the borings and test pits by AGEC to the maximum depth investigation, approximately 70 feet with the exception of boring B-12. Groundwater was encountered at approximately 37 feet in Boring B-12 at the time of the exploration. This corresponds to an elevation of approximately 1,558½ feet. Review of the Baseline Geotechnical Investigation indicates groundwater was encountered at depths ranging from approximately 67 to 75 feet below the existing grade. This corresponds to an elevation ranging from approximately 1,557½ feet to 1,561 feet. Fluctuations in groundwater level may occur over time. We anticipate the groundwater depth/elevation will likely remain relatively constant throughout the year. APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC

13 Page 11 PROPOSED CONSTRUCTION We understand it is proposed to construct new, single span bridges at the I-15 mile post CL 120 interchange. The new, single span bridge (overpass) structures will be constructed adjacent to the existing bridges (on either side, extending over Falcon Ridge Parkway) and will be temporarily supported on driven pile foundations. The permanent bridge foundations are proposed to consist of conventional spread footings and will be constructed concurrently to support the new single span bridge structures in their permanent locations. The single span bridges will allow for widening of the underpass and Falcon Ridge Parkway. In order to construct the permanent foundations, the slope beneath the existing bridges will require cutting on the order of 17 to 19 feet high to provide a location for the new foundations. In order to safely support the proposed cut, we understand it is proposed to construct a staged, temporary soil nailed wall with a reinforced or shot-crete facing on both the north and south bridge abutments. The soil nailed wall will also extend to the east and west to support permanent cuts on either side of Falcon Ridge Parkway. It is our understanding that upon completion of the temporary soil nailing and the permanent bridge foundations, the bridge structures will be moved onto and permanently attached to the new foundations after removal of the existing bridge structures. The foundation walls will subsequently be backfilled. The new bridge placement is planned to utilize a Fast Track procedure to allow the process to be completed quickly and reduce road closure requirements. In addition, we understand it is proposed to slightly re-align the existing on and off-ramps as well as construct roundabouts on the east and west ends of Falcon Ridge Parkway. The roundabouts will tie into the on-ramps, off-ramps, Falcon Ridge Parkway and Mesquite Blvd. as shown on Figure 2. In addition, it is proposed to extend Falcon Ridge Parkway south to Leavitt Lane. This will require fill depths of up to approximately 14 feet to fill eastern portion of the eastern roundabout and the beginning of the roadway extension. The fill depths are planned to taper down to near the existing grade at Leavitt Lane. The side slopes of the APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC

14 Page 12 extensions will be graded at 4:1 (Horizontal:Vertical). The following loading conditions and construction criteria have been provided by Horrocks Engineers to facilitate our engineering analysis: 1. Temporary foundations will consist of HP 14X89 or HP 14X117 H-piles. 2. Unfactored axial load on the temporary pile foundations = 205 kips per pile. 3. Unfactored axial load on temporary support piles = 70 kips. 4. Unfactored lateral load on the temporary foundations = 12 kips per pile. 5. Strength 1 loading applied to the permanent foundations = 87.4 kips/foot. 6. Service 1 loading applied to the permanent foundations = 66.0 kips/foot. 7. Estimated preliminary foundation footing size = 12 feet wide by 70 feet long. If the proposed construction or building loads are significantly different from what are described above, we should be notified so that we can reevaluate the recommendations given. RECOMMENDATIONS Based on the subsurface conditions encountered, the referenced Baseline Geotechnical Investigation, laboratory test results and the proposed construction, the following recommendations are provided. A. Site Grading Based on a description of proposed grading and the preliminary cut/fill map provided by Horrocks, the following table provides a brief description of the proposed grading: APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC

15 Page 13 Location Permanent bridge foundation West roundabout and Underpass - Falcon Ridge Parkway Description of proposed grading Requires cuts on the order of 17 to 19 feet Constructed near the existing grade with significant cuts on either side. Falcon Ridge Parkway and roundabout East end of east roundabout North bound off ramp east of east Requires up to 14 feet of fill tapering to near the existing grade at Leavitt Lane Requires up to 14 feet of fill Will be cut below the existing grade South bound on and off ramps and north bound on ramp Bridge approaches Shallow fill or constructed near the existing grade Near the existing grade 1. Subgrade Preparation a. Grubbing: Portions of the proposed alignment contain near surface vegetation or cultivated soil, particularly along the portions of the on/off ramps and along the alignment of the east end of Falcon Ridge Parkway. Prior to placing site grading fill to support roadways, the existing organics and soil containing roots and organics should be removed. We anticipate the thickness may vary from approximately 2 to 6 inches in areas where vegetation is observed. Clearing and grubbing should follow the requirements of Section 201 of the NDOT Standard Specifications for Road and Bridge Construction. b. General: Prior to placing fill, the existing asphalt should be removed the full depth. Consideration may be given to roto-milling the pavement section to the full depth and re-using the material for the embankment fill beneath Falcon Ridge Parkway or as base course beneath roadways, if acceptable. Use of cold millings as a base layer (in the bottom half) should be in accordance with the Pull Sheet for Section 302 of the APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC

16 Page 14 NDOT Standard Specifications for Road and Bridge Construction. Cold millings used as embankment fill should meet the requirements of Section 203 of the NDOT Standard Specifications for Road and Bridge Construction. Subsequent to grubbing and asphalt/base removal, undiscovered loose soils or disturbed soils should also be removed. Prior to placing fill, base course or concrete, the exposed subgrade should be scarified at least 8 inches, moisture conditioned and compacted to at least 90 percent of the maximum dry density as determined by Test Method No. Nev. T101. c. Dry/Collapsible soil removal: AGEC s laboratory testing and observations indicate the near surface soil in the area just east of the cultivated field (area not currently cultivated) is loose and/or moderately collapsible when wetted (Test Pit TP-5). The zone appears to extend to approximately 4 feet below the existing grade. We estimate that on the order of c inch of post construction settlement (of the roadway) may occur for each foot of the underlying collapsible soil which is wetted after construction. To reduce the potential post construction settlement (resulting from collapse), we recommend the exposed subgrade be overexcavated (in this area) to remove the natural soils at least 2 feet below the existing grade. In addition, the near surface soils along the east edge of Mesquite Blvd (Boring B-10) were also observed to be loose. We recommend this area be overexcavated to remove the natural soils at least 1 foot below the existing grade. The approximate locations which require additional overexcavation are shown on Figure 2. The overexcavation should extend at least 2 feet beyond the limits of edge APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC

17 Page 15 of roadway or the embankment. Subsequent to overexcavation (one or 2 feet) and prior to placing fill or base course, the exposed subgrade should be scarified 8 inches, moisture conditioned and compacted to at 90 percent of the maximum dry density as determined by Test Method No. Nev. T101. The removed soil may be replaced in properly compacted lifts. 2. Excavation We anticipate excavation of the on-site soils can be accomplished with typical excavation equipment. Excavations of temporary cut slopes should be sloped in accordance with OSHA Soil Site Class C. This will require the slopes to be graded at a maximum slope of approximately 1½:1 (horizontal to vertical). As an alternative, the slopes may be reinforced, shored or retained. We understand the cut slopes along the north and south sides of Falcon Ridge Parkway (beneath the bridge) are proposed to be reinforced with a soil nails and a reinforced facing or shot-crete. The following section provides details which should be considered for the soil nailed wall design and construction. We understand the final soil nailed wall design will be provided by others. 3. Soil Nailed Walls During and after construction, a soil nailed wall and the soil behind it tend to deform outwards. The deformation has two components: (1) During excavation and (2) after the soil nails are constructed due to mobilization of the soil to achieve capacity (interaction between the soil and nail). APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC

18 Page 16 We understand this movement will not be critical in the permanent soil nailed wall locations where the wall is not supporting the existing bridge spread footing. Controlling the anticipated movement will be necessary where the temporary soil nailed wall is constructed adjacent and beneath the existing bridge footings. Due to the critical nature of the temporary soil nailed wall and facing system, it is recommended that the proposed design include construction techniques and analysis to control movement at the face and subsequent settlement of the adjacent bridge foundation to allow the bridge to remain in service. The following options may be considered to reduce potential movement of the foundation due to lateral movement/bending of the soil nailed wall: a. The soil nails may be drilled, partially grouted along their length and pretensioned to mobilize some of the nail strength while reducing the soil mass deformation near the wall face. b. The spacing of the soil nails may be decreased to reduce the stresses developed on each nail to reduce mobilization of the soil. c. The length of the soil nails may be increased to reduce the stresses developed on each nail which will likely reduce mobilization of the soil. d. The soil nailed wall facing may be designed and constructed to provide increased stiffness to assist in reducing movement at the face. e. The face may be battered. APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC

19 Page 17 Additional recommendations which should be considered for design and construction of the soil nailed walls are provided below: a. Preliminary analysis by AGEC indicates additional nail length may be necessary for the temporary soil nailed walls to increase factors of safety against failure due to potential deep seated failure resulting from the underlying looser sand. b. The construction of the soil nailed walls should incorporate staged construction methods. This method will be particularly critical adjacent to the existing bridge footings. We recommend the first cut be conducted only to allow for installation of the first row of soil nails beneath the existing spread footings. This may be accomplished by cutting notches for each nail to assist in minimizing movement/caving until the first row of nails are complete and have achieved strength. Prior to cutting for the second row, the reinforced wall facing should be constructed over the first row and allowed to achieve strength. This process may require alternating between the north and the south abutment. c. The soil nailed walls should be designed in accordance with the referenced FHWA guidelines. Loading combinations (Including dead load, live load and earth quake) and acceptable factors of safety should be implemented in the design as provided by FHWA. d. The soil nailed wall design should consider internal stability, external stability and global stability in the analysis during various stages of the construction. APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC

20 Page 18 e. Corrosion of the permanent soil nailed wall should also be assessed. A Summary of Chemical Laboratory Test Results is attached. f. We understand the NDOT has expressed concern regarding drainage behind the soil nailed wall face. We understand a geo-composite drain will be placed behind the facing and will be specified in the final soil nail design. g. Based on observations by AGEC during our field investigation, we anticipate that the staged cut heights should remain stable temporarily during construction. We recommend the length of the exposed cut face be minimized during the staged construction process and the slope face should be excavated/cut in front of the soil nailing equipment as soil nailing progresses. All exposed cuts should be nailed the same day as excavation occurs. Excavations should be made with care to reduce disturbance. If caving of the cut occurs during drilling or excavation, the nails may need to be drilled/installed though a stabilizing berm. h. Due to the granular nature of the soils, casing may be necessary during drilling operations. The soils behind the proposed soil nailed walls consist of sandy fill which contains some clay which may allow the nail borings to remain open. I. Inspections and load tests should be accomplished (prior to and during construction) in accordance with the previously referenced FHWA publications and the Pull Sheet for Section Soil Nail Retaining Walls. APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC

21 Page 19 j. The soil nail retaining walls should be constructed in accordance with the Pull Sheet for Section Soil Nail Retaining Walls. Particular attention should be paid to the excavation procedures as provided in section of the referenced Pull Sheet. 4. Fill Slopes/Embankments We understand an embankment will be constructed to support the east alignment of Falcon Ridge Parkway and the east end of the adjacent roundabout. The fill depths are proposed to be approximately 14 feet tapering down to near the existing grade at Leavitt Lane. Fill slopes constructed with the on-site soil should be constructed no steeper than 2:1 (horizontal:vertical). The on-site soils will be susceptible to erosion. We understand the side slopes on either side of the embankment will be constructed at a 4:1 slope to reduce the potential for erosion. Fill slopes should be constructed to assure a properly compacted slope face. This may be accomplished by wheel rolling the exposed face during grading. As an alternative, the compacted face may be constructed by overbuilding the slope and then cutting back the slope face to the desired grade to provide a properly compacted slope face. Fill placed on an existing slope should be benched into the existing slope to provide a level surface for placement and compaction of the fill. This will also serve to the key the fill into the slope and to potentially reduce differential movement. This will be critical when placing fill to construct the east roundabout and the east side of Mesquite Blvd. The west portion of the roundabout is near the existing grade while the east portion requires up to approximately 14 feet of fill. Fill should be placed in accordance with Section of the NDOT Standard Specifications for Road and Bridge Construction. APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC

22 Page 20 AGEC conducted analysis to estimate the potential settlement of the embankment resulting from the densification of the underlying support soils. The proposed embankment will support Falcon Ridge Parkway from the east roundabout to Leavitt Lane and varies from approximately 14 feet high and tapers down to near the existing grade at Leavitt Lane. The estimated settlement was calculated using the Hough method for normally consolidated, cohesionless soils and is based on a layered profile which was developed from corrected penetration values (N1 60 ). A representative profile was developed utilizing borings B-11, B-12 and B-13 which indicates alternating layers of dense and very dense of sand and gravel. The following table summarizes the estimated settlement of the embankment depending on the fill depth: Embankment Height (ft) Estimated Settlement (inches)* 14 1½ 10 1c 5 b *Settlement estimates assume the subgrade beneath the fill is properly prepared. We predict the estimated settlement will occur rapidly during the construction process due to the granular nature of the underlying support soils and should not affect the performance of the roadway or embankment provided the fill is properly compacted. APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC

23 Page Imported Materials In accordance with the NDOT Standard Specifications for Road and Bridge Construction, the table below provided material specifications for soils which will be imported site grading and structural fill. Fill Type/Use Borrow / Embankment and Site Grading Selected Borrow / Embankment and Site Grading - Surface beneath paved areas Material Requirements Non-expansive granular soil R value $ 45 Non-expansive granular soil R value $ 45 Percent Passing 3" Sieve: 100 Backfill / Behind retaining walls/below grade structures unless granular backfill is specified Granular Backfill / Behind retaining walls/below grade structures Percent Passing 3" Sieve: 100 Percent Passing 3" Sieve: 100 Percent Passing No. 4 sieve: Percent Passing No. 30 sieve: Percent Passing No. 200 sieve 0-12 LL = 35 max., PI = 10 max. ph = 5 to 9 - Concrete and steel, ph 4.0 min. - Aluminum Resistivity = 1000 ohm-cm min. - Concrete and steel Resistivity = 500 ohm-cm min. - Aluminum Shouldering Material Approved base aggregate - See NDOT Standard Specifications for Bridge and Road Construction Base Aggregate / Asphalt Support, Concrete Slab and curb Support Approved base aggregate - See NDOT Standard Specifications for Road and Bridge Construction Base Aggregate / Drain Rock Crushed Aggregate Percent Passing 2" Sieve: 100 Percent Passing the No. 200 Sieve: 0-2 All materials should be free of sod and organics LL=Liquid Limit, PI = Plasticity Index APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC

24 Page Material Suitability of On-site Soils AGEC conducted laboratory testing on soil samples obtained during our field investigation to determine suitability for use as fill. Areas included the cut behind the bridge abutments (Borings B-4, B-5 and B-7) and the infield cut areas between the north bound traffic lane and the north bound off ramp (Test Pits TP-1, TP-2 and TP-3). The following laboratory test results were conducted by AGEC and are provided: AASHTO Soil Classification = A-2-4. USCS Soil Classification = Mainly SM, and occasional SP-SM. R-value = 64 to 75. PI = non-plastic. Water Soluble Sulfates = 300 to 1,200 ppm. ph= 8.1 to 9.0. Resistivity = 450 to 1,400 ohm-cm. The following summary of the particle size distribution is provided: Sieve Size Percent Passing 3" 100 No to 99 No to 98 No to25 APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC

25 Page 23 Based the listed laboratory test results, the on-site soils encountered are suitable for use as Borrow, Selected Borrow and Backfill in accordance with Sections 203 and 207 of the NDOT Standard Specifications for Bridge and Road Construction and Pull Sheets from the contract documents. Testing indicates most of the soil tested does not meet the No. 200 sieve for Granular Backfill and a portion of the resistivity results are too low (3 of 5 are less than 1,000). A layer of lean clay was encountered at a depth of 10 feet in Test Pit TP-2. This layer of soil is not suitable for use as Borrow, Selected Borrow and Backfill. AGEC s test results correlate with results provided in the Baseline Geotechnical Investigation with the exception of resistivity. AGEC s resistivity results are generally lower in magnitude, thus indicating more corrosive soils. We anticipate this may be due to the different test methods utilized and/or shallower depths that AGEC s samples were obtained. NDOT followed Nevada test methods while AGEC followed AASHTO test methods. Further, NDOT samples ranged from 13 to 36 feet below the existing grade while AGEC s samples ranged from 1 to 14 feet below the existing grade. 7. Compaction Compaction of fill materials placed at the site should equal or exceed the following percentages: Area/Location Compaction Structure foundation subgrade $ 95% Wall backfill $ 95% Embankment $ 90% Pipe backfill $ 90% Base Course $ 95% Natural Subgrade $ 90% APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC

26 Page 24 Compaction of materials placed at the site should be compared to the maximum dry density as determined by Test Method No. Nev. T101. To facilitate the compaction process, fill should be compacted at a moisture content within 2 percent of the optimum moisture content as determined by Test Method No. Nev. T101. Fill placed for the project should be frequently tested to verify compaction. The moisture content of the on-site fill soils and natural soils are varied from below to above the optimum moisture content. Fill should be placed in loose lifts which do not exceed 8-inches in thickness. 8. Drainage The ground surface should be sloped to provide positive site drainage during and following construction. Maintaining positive site drainage during and following construction should be implemented. Ponding of water should be minimized. Methods should also be implemented to reduce infiltration of water into the subsurface soils behind retaining structures. The collection and diversion of drainage away from the pavement surface is extremely important to the satisfactory performance of the pavement section. Proper drainage should be provided B. Permanent Shallow Foundations The proposed bridge overpass may be permanently supported on conventional spread footings as provided below: 1. Bearing Resistance Footings/foundations may designed using the factored bearing resistances plotted on Figure 46. APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC

27 Page 25 The following table summarizes resistance factors used to calculate the factored bearing resistances provided on Figure 46: Limit State Resistance Factor (N b )* Service I 1.0 Strength I 0.45 Extreme Event I 1.0 *In accordance with Section 10 (specifically Sections , and ) of AASHTO LRFD Bridge Design Specifications, Bearing capacity analysis in the strength limit state is based a theoretical analysis method (Section of AASHTO LRFD Bridge Design Specifications, 2010) for cohesionless soils. This method uses corrected penetration values measured in the field during drilling/sampling to estimate the soil strength (friction angle) and associated bearing capacity factors. Direct shear data was compared the estimated soil friction angle. The service limit state bearing values correlate to an estimated total settlement of approximately 1 inch and a differential settlement of approximately ½ inch after the bridge structure is placed on the permanent foundation. Prior to placing concrete, we recommend the exposed subgrade be compacted to at least 95 percent of the maximum dry density as determined by Test Method No. Nev. T101. APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC

28 Page 26 A 12 foot wide footing was selected based on the factored bearing resistances provided on Figure 46. With this footing width, the following table summarizes the limit states and associated bearing resistances: Limit State* Location Bearing Soil Service Limit I Strength Limit I Extreme Event I q n q r q n q r q n q r (ksf) (ksf) (ksf) (ksf) (ksf) (ksf)) All abutments Compacted sand *Where q n = nominal bearing resistance and q r = factored bearing resistance. 2. Settlement AGEC conducted analysis to estimate the potential settlement of the foundations to establish the Service Limit State bearing resistance resulting densification of the underlying support soils. The estimated settlement was calculated using the Hough method for normally consolidated, cohesionless soils and is based on a layered profile which was developed from corrected penetration values (N1 60 ). A representative subsurface profile was developed based on the loosest soil conditions after reviewing SPT values measured/corrected for AGEC Borings B-4, B-5 and B-7 and NDOT Borings RMI-1 and RMI-4. Corrected penetration values indicated AGEC Boring B-5 contained the loosest soils. This boring profile was used to provide a conservative settlement estimate for the subsurface conditions encountered at various bearing pressures. APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC

29 Page 27 Based on the analysis described above and the proposed construction, we estimate total settlement for the permanent foundations designed as indicated above to be approximately 1 inch after the bridge superstructure is placed on the permanent foundation. Differential settlement is estimated to be approximately ½ inch. Foundation settlement will likely occur rapidly due to the presence of granular soils supporting the foundation. 3. Footing Embedment Spread footings should be embedded such that at least 2 feet of cover soil is provided over the footings. This should be measured from the ground surface to the top of the footing. 4. Foundation Base The base of foundation excavations should be cleared of loose or deleterious material prior to concrete placement. 5. Construction Observation A representative of the geotechnical engineer of record should observe footing excavations prior to concrete placement. C. Temporary Pile Foundations The proposed bridge super structure may be supported on temporary foundations consisting of driven H-piles (during construction of the bridge structure) as provided below: APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC

30 Page Pile Axial Capacity The axial capacity of the temporary piles was derived using a theoretical analysis method for cohesionless soils. This method uses corrected penetration values measured in the field during drilling/sampling to estimate the soil strength (friction angle), the critical depth, skin friction parameters and the associated bearing capacity factors. Ultimate axial capacity curves (ultimate capacity vs depth) and ultimate uplift capacity curves are provided on Figure 47. A depth of 0" feet on the capacity curves shown on Figure 47 refers to the ground surface elevation at each pile. 2. Pile Length We estimate the piles will need to be driven on the order of 25 feet to achieve the necessary capacity. 3. Estimated Settlement The pile settlement was estimated using 2 methods for piles bearing in the zone of loose to medium dense sand. The first method (by Hannigan) models a group of piles which act as a large spread footing at b the pile length (See AASHTO LRFD Bridge Design Specifications, 2010, Section ). This method assumes the total load at the surface is transferred to this depth and does not include skin friction capacity because of the grouped pile affect. It is our professional opinion that this method would overestimate settlement for piles with a relatively large spacing. A second method (By Mindlin) was utilized to model the relatively large pile spacing for the proposed temporary foundations. This method assumes the pile capacity includes skin friction which varies depending on the pile spacing. This method calculates a load or stress transferred to the tip of the pile which is reduced due to the capacity achieved with skin friction resulting in less estimated settlement. APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC

31 Page 29 With the anticipated axial loads and pile lengths, the following table summarizes the estimated settlement for piles bearing in the underlying loose to medium dense sand for each of the methods: Method Estimated Total Settlement (inches) Differential Settlement Temp Abutment Temp. Support (inch(es)) Hannigan ¾ to 1½ ½ ½ to 1 Mindlin ½ ¼ <½ It is our professional opinion that the Mindlin method more accurately models the proposed construction and we anticipate the settlement for piles bearing on loose to medium dense sand will be on the order of ½ inch. This would include the North bound abutment - south side. Tip elevations by Horrocks indicate the piles supporting the North bound abutment - north side and both of the South bound abutments will bear on or near the underlying dense to very dense sand. We estimate the total settlement for these abutment piles will be less than ½ inch. We further stress that these methods are empirical and only provide estimates. The anticipated settlement may be verified/measured in the field prior to construction by driving a pile to the design depth and conducting a load test to measure the associated deflection under the proposed loads. If the risk of settlement for piles bearing in the loose to medium dense sand (as described above) is not acceptable, the piles may be driven to bear in the underlying dense to very dense sand. The following Table summarizes the approximate elevation where the relatively dense sand was encountered. APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC

32 Page 30 Boring No. Approximate elevation of dense to very dense sand (feet) AGEC B-4 1,586 AGEC B-5 1,580 AGEC B-7 1,591 NDOT RMI-1 1,573 NDOT RMI-4 1, Lateral Capacity The L-pile analysis was conducted using loads provided by Horrocks Engineers and the listed soil parameters provided in the following table to model the subsurface profile. The parameters are based on laboratory test data and corrected penetration values measured during sampling. Depth (ft) Soil Type Unit wt (pcf) N ( " ) cohesion (psf) K h (pci) 0-25 SM SM SM ML/CL , Based on the L-pile analysis, we recommend a minimum pile length of 20 feet for lateral stability. Lateral capacity curves (Pile Head Deflection, Maximum bending moment and p-y curves) are shown on Figures APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC

33 Page 31 D. Concrete Slab-on-Grade/Curb Concrete slabs should be supported on a properly prepared and compacted subgrade as recommended in the Subgrade Preparation and Compaction sections of this report, pages and 23-24, respectively. A 4-inch layer of free-draining gravel or approved road base material should be placed below concrete slabs for ease of construction, to promote even curing of the slab concrete and to provide a firm and consistent subgrade. E. Lateral Earth Pressures 1. Lateral Resistance for Footings Lateral resistance for spread footings placed on compacted sand is controlled by sliding resistance developed between the footing and the subgrade soil. An ultimate friction value of 0.50 may be used in design for ultimate lateral resistance of footings bearing on properly compacted on-site sand. Prior to placing concrete, we recommend the exposed subgrade be compacted to at least 95 percent of the maximum dry density as determined by Test Method No. Nev. T101. Sliding resistance for footings should be reduced using a resistance factor N J = Subgrade Walls and Retaining Structures The following equivalent fluid weights are given for design of subgrade walls and retaining structures. The active condition is where the wall moves away from the soil. The passive condition is where the wall moves into the soil and the at-rest condition is where the wall does not move. The values listed below assume a horizontal surface adjacent the top and bottom of the wall. APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC

34 Page 32 Soil Type Active At-Rest Passive On-site sand 35 pcf 50 pcf 300 pcf Earth pressure coefficient It should be recognized that the above values account for the lateral earth pressures due to the soil and level backfill conditions and do not account for hydrostatic pressures. Lateral loading should be increased to account for surcharge loading if present above the wall and within a horizontal distance equal to the height of the wall or if the ground surface slopes up away from the wall. Lateral loading should be increased to account for surcharge loading if structures are placed above the wall and are within a horizontal distance equal to the height of the wall or if the ground surface slopes up away from the wall. Care should be taken to prevent percolation of surface water into the backfill material adjacent to the retaining walls. The risk of hydrostatic buildup can be reduced by placing subdrains behind the walls consisting of free-draining gravel wrapped in a filter fabric. As an alternative, weep holes may be provided every 10 feet at the base of the wall to assist in drainage of water. 3. Seismic Conditions Under seismic conditions, the equivalent fluid weight should be modified as follows according to the Mononobe-Okabe method assuming a level backfill condition: APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC

35 Page 33 Lateral Earth Pressure Condition Active Seismic Event *PGA = 0.23g - 1,000 yr event 18 pcf increase At-rest ** 0 pcf increase Passive 41 pcf decrease * The PGA is adjusted for site conditions (Site Class D), but not reduced as stated on page (AASHTO LRFD Bridge Design Specifications) due to the critical nature of the structure. ** The total equivalent fluid weights (static plus seismic increase) in an at-rest condition should not exceed the total active condition (static plus seismic increase). We recommend the resultant from the seismic forces be placed at the midheight of the retaining wall in accordance with LRFD Methods. 4. Resistance Factors The values recommended above for active and passive conditions assume mobilization of the soil to achieve the soil strength. Appropriate resistance factors for structural analysis for such items as overturning and sliding resistance should be used in design. F. Seismicity Seismic design parameters are provided below for the 1,000 year seismic event as requested: APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC

36 Page 34 Description Seismic Event 1,000 yr event (.7% PE in 75 yrs)* 2010 AASHTO Site Class D** Site Location Clark County, Nevada PGA - Site Class B 0.15g S s (0.2 second period) - Site Class B 0.40g S 1 (1 second period) - Site Class B 0.15g F PGA 1.50 F a 1.48 F v 2.2 S D1 0.33g (AASHTO Seismic Zone 3) *These values (tabulated in the 2008 NDOT Structures Manual for Clark County) are approximately equivalent to the Site Specific (by Coordinates) 2,500 year event. ** Based on weighted average (N 1 ) 60 values and REMI survey data. G. Liquefaction Liquefaction is a condition where a soil loses strength due to an increase in soil pore water pressures during a dynamic event such as an earthquake. Research indicates that the soil type most susceptible to liquefaction during a severe seismic event is loose, clean sand. For the sand to liquefy, it must be located beneath the groundwater level. The liquefaction potential for soil tends to decrease with an increase in fines content and density. Based on our field investigation and the baseline Geotechnical Report (Reference No. 2), the following subsurface conditions exist at the subject site: 1. The groundwater level is on the order of 70 feet below the existing grade (see Reference No. 2). APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC

37 Page The subsurface soils generally consist of medium dense to very dense sand. 3. The subsurface soils located beneath approximately 30 to 50 feet are very dense with an average (N 1 ) 60 greater than 50 blows per foot. Based on these conditions, it is our opinion the subsurface soils above the groundwater level are generally non-liquefiable during a severe seismic event and the soils located beneath the groundwater level present a very low potential for liquefaction during a severe seismic event. H. Water Soluble Sulfates and Cement Type Laboratory tests results indicate a water soluble sulfate concentration ranging from 300 to 1,200. According to Table of ACI , the on-site soils posses a moderate severity for corrosion of buried concrete structures. Therefore, we recommend that concrete that will be in contact with the on-site soil contain Type V sulfate resistant cement with 20% Type F pozzolan using a sulfate exposure category of moderate. Further, this is in accordance with the NDOT Standard Specifications for Road and Bridge Construction. I. Corrosion Corrosion tests were performed on samples of the on-site soils. Results of laboratory tests indicate a chloride range of 14 to 161 ppm and a ph range of 8.1 to 9.0. Resistivity tests conducted in the laboratory indicate resistivities ranging from 450 to 1,400 ohm-cm at relatively high water contents. The test results indicate the on-site soil is corrosive to buried metal, particularly under high moisture conditions which would result from poor drainage. Controlling drainage and infiltration into the subsurface soils will reduce corrosion. APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC

38 Page 36 J. Construction Testing and Observation We recommend testing fill and concrete materials at a frequency which meets or exceeds project specifications NDOT Standard Specifications for Road and Bridge Construction. We also recommend the following testing and observations be done as a minimum. 1. Verify the subgrade is prepared as recommended beneath fill areas. 2. Conduct compaction testing on fill placed in accordance with the State of Nevada DOT Standard Specifications for Road and Bridge Construction. 3. Verify the subgrade beneath the permanent spread footings is properly compacted. 4. Verify the capacity of the pile foundations using PDA testing or another approved method. 5. Conduct special inspections (concrete and steel) as required by LRFD and the State of Nevada DOT. A final summary report may be provided for the structures if the recommendations in this report are followed and verified by AGEC. APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC

39 Page 37 LIMITATIONS This report has been prepared in accordance with generally accepted soil and foundation engineering practices in the area for the use of the client for design purposes. The conclusions and recommendations included within the report are based on the information obtained from the borings drilled at the approximate locations indicated on the site plan, the data obtained from laboratory testing, the referenced Baseline Geotechnical Investigation and our experience in the area. Variations in the subsurface conditions may not become evident until additional exploration or excavation is conducted. If the proposed construction, subsurface conditions or groundwater level is found to be significantly different from what is described above, we should be notified to reevaluate our recommendations. APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC. Arnold DeCastro, P.E. Reviewed by: Jared Hanks, P.E. AD/sd P:\2010 Project Files\2010 Project Files\ \ West Interchange, Mesquite\ report.wpd cc Mike Dobry, P.E. - Horrocks Engineers, miked@horrocks.com Matt Horrocks, P.E. - Horrocks Engineers, MattH@Horrocks.com Derek Stonebraker, E.I.T. - Horrocks Engineers, dereks@horrocks.com APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC

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