BACKGROUND: SUBSURFACE CONDITIONS:

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Kelly Garrett
6 years ago
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2 2 BACKGROUND: The planned project consists of a prefabricated modular apartment building with underground parking, located on the site bounded by Dexter Avenue N. to the east, multi-story residential/commercial structures to the north and south, and an alley to the west. The site slopes to the east, with the alley at elevation feet and Dexter Avenue ranging from elevation 13 feet in the north to 99 feet in the south. The buildings to the north and the south, as well as the structure presently located on the northern portion of the site, are benched into the steep slope that is adjacent the alley. The parking lot within the south portion of the site is separated from the steep slope to the west by a 1-foot-high cast in-place concrete retaining wall. The excavation will cover essentially the entire site with setbacks of 2 feet from the north and south property lines to accommodate shoring. In addition, the basement excavation will be set back from the east property line such that the building footprint will be 146 feet long by just over 1 feet wide (east-west). The excavation will extend to elevation 88 to 96 feet, with maximum depths of excavation along the west (alley) side of 37 feet. This design addendum addresses the re-design of the central section of the west wall, replacing anchored soldier pile shoring with internally-braced soldier piles, as a result of a lack of a temporary construction easement for the associated property to the immediate west of the alley. SUBSURFACE CONDITIONS: The geotechnical information indicates that the subsurface materials consist of fill/colluvium and landslide deposits overlying very stiff to hard glacially over-ridden silt and clay. The groundwater table is located below the planned base of excavation but perched groundwater seepage can be anticipated during construction. SHORING SYSTEM: The replacement shoring will consist of soldier piles supported by rakers and associated walers. The rakers will in turn be supported by toe piles and the rakers will be pre-loaded to control displacements of the alley. A single row of rakers will be employed. After installing the soldier piles, the construction sequence will consist of sequential excavation of the face and placement of the wood lagging. A berm will be left in place, starting at just below the planned elevation of the raker supports. Following excavation to the planned base of the excavation and installation of the toe piles, the rakers will be installed and pre-loaded. The berm will then be removed from beneath and between the installed rakers. In addition to the above, small bar anchors will be installed and attached to each of the internally braced soldier piles. These anchors will not contribute to overall stability, which will be provided by the raker supports, but will simply reduce the flexural demand on the soldier piles until the rakers can be installed. DESIGN PARAMETERS: Design earth pressures corresponding to the soil self-weight are recommended in the geotechnical report. For the raker supported soldier piles, the soil self-weight was modeled using an equivalent fluid density of 45 psf/ft, per the recommendations of the geotechnical report. Live load lateral surcharge pressures were taken as 1 psf. Ground Support PLLC

3 3 The following design values were used to evaluate the depth of embedment of the soldier piles below the base of the excavation: Passive Equivalent Fluid Density Active Equivalent Fluid Density Allowable Pile Skin Friction 3 pcf over 2 pile diameters 15 pcf over 2 pile diameters for berm 3 pcf over 3 pile diameters for toe pile 45 pcf over 1 pile diameter.75 ksf Raker Loads: Individual raker loads are developed from the design earth pressure diagrams presented on the Plans, using a tributary area method to assign loads to the rakers and to the toe shear in the piles. The results are presented in Appendix A (Table A1). Loads indicated are per pile, with the raker loads being twice these loads as each raker supports two adjacent soldier piles. Design calculations for the raker and associated walers are shown in Table 1. Soldier Piles: Soldier pile loadings were determined from the design earth pressure diagrams and the locations and inclinations of the raker supports. The spreadsheet output presented in Appendix A (Table A2) summarizes the following design aspects for the final condition following completion of the excavation: Calculation of soldier pile loads and bending moments, consistent with the design apparent earth pressure diagrams provided on the Plans. For each soldier pile, the calculated shear force, axial load and bending moment are provided. Representative earth pressure diagrams, together with calculated shear force and bending moment diagrams, are also shown for a number of piles, in Appendix A. Calculation of pile toe embedment requirements (for lateral support and uplift resistance) using the criteria indicated on the Plans. Pile structural steel sizing in accordance with the AISC 36-5 Specification for Structural Steel Buildings. Combined flexure and axial load, shear, and compact section steel design checks are performed for the critically loaded section of each pile along the length of the wall. The spreadsheet output summarizes the minimum steel section required for each pile. Also shown in Appendix A are the corresponding design calculations for the toe piles that support the rakers (Table A3 and Figure A4). Table A4 and Figure A5 show design calculations for the intermediate condition where the soldier piles act in a cantilevered condition, prior to the installation of the rakers, and where small bar anchors provide nominal support. Lagging: Timber lagging will be used to support the soil between adjacent soldier piles. The average design earth pressures for the lagging are indicated in Appendix A, and these design earth pressures are derived directly from the design earth pressure diagrams. Hem-Fir No. 2 lagging (4-inch) or equivalent will provide adequate support for the soil between the soldier piles, per the recommendations of the FHWA Engineering Circular No. 4. Ground Support PLLC

4 4 TABLES Ground Support PLLC

5 Available Available Flexure Available Axial Bending Maximum Axial Flexural & Flexure Shear Load Shear Moment Span Steel Strength Axial Strength Axial & Strength Shear P V M L Steel Grade Pa Design Ma Design Axial Va Design Shear Case Analysis Case (k) (k) (ft-k) (ft) Section (ksi) (k) Ratio (ft-k) Ratio Status (k) Ratio Status 1 Waler W14x , OK OK 2 Waler Stubout HSS12x6x3/ OK OK 3 Raker Type Pipe18x5/ OK OK 4 Raker Type Pipe18x5/ OK OK TABLE 1 STRUCTURAL ELEMENT DESIGN

6 5 APPENDIX A DESIGN CALCULATIONS Ground Support PLLC

7 Anchor 1 Design Pile Top Pile Toe Pile Toe Pile Lagging L=NH 2 Unif. Press. Elevation Angle Anchor Load No. of Total Length Bond Length Beam Elevation Embed Elevation Length Pressure Pile ID Station (ft) Height (ft) Spacing (ft) No. Anchors N (psf/ft) P (psf) (feet) (degrees) (kips) Strands (feet) (feet) (feet) (feet) (feet) (feet) (psf) W W21x W8A W21x W W21x W9A W21x W W21x W1A W21x W W21x W W18x TABLE A1 RAKER DESIGN LOADS

8 Pile Vertical Load Analysis Toe Dist. 2 Soldier Beam Loads-Below Anchor 1 Axial Free Pile Pile Pile Pile Pile End Skin Axial Embed Design Load Moment Length Steel Flex/Ax Diameter End Area Skin Area End Bear Skin Frict Bearing Friction Load Length Pile ID Beam (kips) (ft-kips) (feet) Section Ratio (ft) (ft^2) (ft^2/ft) (ksf) (ksf) (kips) (klf) (kips) (ft) W8 W21x W21x W8A W21x W21x W9 W21x W21x W9A W21x W21x W1 W21x W21x W1A W21x W21x W11 W21x W21x W12 W18x W18x TABLE A2 SOLDIER PILE DESIGN

9 Soldier Beam Loads-Below Anchor 1 Axial Free Design Load Moment Length Steel Flex/Ax Pile ID Beam (kips) (ft-kips) (feet) Section Ratio TP W3x W3x TABLE A3 TOE PILE DESIGN

10 Soldier Beam Loads-Below Anchor 1 Axial Free Axial Load Shear Force Steel Shear Design Load Moment Length Steel Flex/Ax Pile ID (kips) (kips) Section Ratio Beam (kips) (ft-kips) (feet) Section Ratio C 9 31 W14x34.38 W18x W18x86.95 TABLE A4 SOLDIER PILE DESIGN LOADS STAGE 1 PRIOR TO RAKER INSTALLATION

11 Earth Pressure (psf) Shear Force (kips) Bend. Moment (ft-kips) Wall Height (ft) 36.4 Pile Spacing (ft) 6.25 FIGURE A1 SOLDIER BEAM - W9

12 Pressure (psf) Point Depth Pressure Width Force Depth(CG) Moment A 6.25 F AB B F BC. C F CD. D F AD E F EF F G F GH. H F HI I F IJ. J F JK. K F GK F LM F AD L F LM M N 6.25 F NO. O F EF P 6.25 F PQ. Q 6.25 R 6.25 F RS. S 6.25 T F TU. U F UV. V F VW. W F TW Anchor Amchor 2. Anchor 3. Anchor A 1 F NO F F RSTW PQ -4.L 1 A 23 4 F GK Load 1. S Forces S Moments -5. FIGURE A1 (cont'd) SOLDIER BEAM - W9

13 Earth Pressure (psf) Shear Force (kips) Bend. Moment (ft-kips) Wall Height (ft) 39. Pile Spacing (ft) 4.25 FIGURE A2 SOLDIER BEAM - W1

14 Pressure (psf) Point Depth Pressure Width Force Depth(CG) Moment A 4.25 F AB B F BC. C F CD. D F AD E F EF F F LM F AD G F GH. H F HI I F IJ. J F JK. K F GK L F LM M F EF N 4.25 F NO. O 4.25 P 4.25 F PQ. Q 4.25 R 4.25 F RS. S T F TU. U F UV. V F VW. W F TW Anchor Amchor 2. Anchor 3. Anchor 4. A 1 F NO F -4. F RSTW PQ L 1 A 23 4 F GK Load 1. S Forces S Moments -6. FIGURE A2 (cont'd) SOLDIER BEAM - W1

15 Earth Pressure (psf) Shear Force (kips) Bend. Moment (ft-kips) Wall Height (ft) 36.7 Pile Spacing (ft) 4.5 FIGURE A3 SOLDIER BEAM - W11

16 P4 P3 W2a W3 A4 A3 A2 W1 P2 Pressure (psf) A1 A9 A5 A6 A7 A8 Resisting Driving Resisting Driving P1 A1 Wall Height (ft).5 Depth of Embed (ft) Depth to Top of Passive (ft) 2.5 moment moment Force p (psf) Kg (psf) h (ft) w (ft) phw (lbf) Kg h 2 w/2 (lbf) depth (ft) arm (ft) (ft-lbf) A A A A P P P P Moments about pile toe Sum of resisting moments (ft-lbf) Sum of driving moments (ft-lbf) FS 1.2 Depth to Zero Shear (ft) at "M" moment moment Force p (psf) Kg (psf) h (ft) w (ft) phw (lbf) Kg h 2 w/2 (lbf) depth (ft) arm (ft) (ft-lbf) a a a a p p p p Moments at Zero Shear Point Sum of shear forces (lbf) at "M" Sum of moments (ft-lbf) at "M" Earth Pressure M W2W FIGURE A4 SOLDIER BEAM - TP

17 P4 P3 W2a W3 P2 P1 Resisting Driving Resisting Driving W1 A1 A9 A6 A7 A8 Pressure (psf) A5 A1 A2 A3 A4 Wall Height (ft) 16.5 Depth of Embed (ft) 25.9 Depth to Top of Passive (ft) 18.5 moment moment moment moment Force p (psf) Kg (psf) h (ft) w (ft) phw (lbf) Kg h 2 w/2 (lbf) depth (ft) arm (ft) (ft-lbf) Force p (psf) Kg (psf) h (ft) w (ft) phw (lbf) Kg h 2 w/2 (lbf) depth (ft) arm (ft) (ft-lbf) A A A A A A A A P A P A P P Moments about pile toe Moments about pile toe Sum of resisting moments (ft-lbf) Sum of driving moments (ft-lbf) moment moment Force p (psf) Kg (psf) h (ft) w (ft) phw (lbf) Kg h 2 w/2 (lbf) depth (ft) arm (ft) (ft-lbf) FS 1.2 a Depth to Zero Shear (ft) at "M" a moment moment a Force p (psf) Kg (psf) h (ft) w (ft) phw (lbf) Kg h 2 w/2 (lbf) depth (ft) arm (ft) (ft-lbf) a a a a a a a p Moments at Zero Shear Point p p p moment moment Force p (psf) Kg (psf) h (ft) w (ft) phw (lbf) Kg h 2 w/2 (lbf) depth (ft) arm (ft) (ft-lbf) W Moments at Zero Shear Point Sum of shear forces (lbf) at "M" W Sum of moments (ft-lbf) at "M" W W W2a Earth Pressure Moments about pile toe moment moment Force p (psf) Kg (psf) h (ft) w (ft) phw (lbf) Kg h 2 w/2 (lbf) depth (ft) arm (ft) (ft-lbf) w w w w w2a M Moments at Zero Shear Point W2W FIGURE A5 SOLDIER BEAM - C

Client Project Job # Wall Loc. SBWall Report deg 120 pcf 950 psf deg 0.0 ft. 6.0 ft 6.0 ft 2.0 ft. W16x50.

Client Project Job # Wall Loc. SBWall Report deg 120 pcf 950 psf deg 0.0 ft. 6.0 ft 6.0 ft 2.0 ft. W16x50. SBWall Report Soils Data Soil Friction Angle, phi Soil Unit Weight, gamma Soil Surcharge (uniform), qs Passive Resistance, FSp Passive Wedge Width, PW*B Backfill Slope Angle, beta Ignore Passive Resistance,