- Introduction You Have Been Tasked To Produce A Geotechnical Engineering Report For The Design Of The Foundation Of A Br 1 (367.11 KiB) Viewed 39 times
ABUTMENT
INTRODUCTION: You have been tasked to produce a geotechnical engineering report for the design of the foundation of a bridge. The bridge is 110 feet long and 34 feet wide with a clearance height of 15 feet. Figure 1 shows the soil profile based on four boreholes located in the vicinity of the bridge location. The soil conditions consist mainly of four stratums (Fill, Alluvium, Terrace, and Potomac). These layers are non-cohesive soil. The average, max and min standard penetration number (N60) is reported for each layer based on the samples obtained from the four boring logs. Underneath the location of the eastside abutment a layer of highly compressible Marsh is present. The 9 feet thick layer is in between the Terrace and Potomac layers. The main objective for you is to design the east and west side abutment walls and the midspan support. For the westside abutment wall, a shallow foundation is proposed to be used. Because of the potential of excessive settlement within the highly compressible Marsh layer a eastside abutment wall is proposed to be supported on deep foundation. Finally for the mid-span support, a combined footing is proposed to support the three bridge piers. Table 1 lists the loading conditions of top of the bridge abutments and piers. -110'- -50'- -60'- Fill SM-ML y=120 pcf Nedag 13 Neomin=0 Neomax=45 Alluvium SW-SM y-118 pcf Neo.avg=20 Neomin=0 Neomax=89 Terrace SW-SP y-125 pcf Noo av 38 Noomin 11 Noo.max=100 Potomac SP-GP y=130 pcf Neo.avg=55 Neomin 11 Neoma 100 Figure 1: Bridge Design Soil Conditions 15' 12' 15' 17' 15' 8' Marsh y=100 pcf Net.avg=6 Neo.min=1 Neomax=13 e₂=1.9 C₂=0.7 C-0.14 C₂=0.025 C,-0.04 ft³/day
-34' -15' Section A-A Figure 2: Cross section of the mid-span bridge support -15' The following information was provided by the structural engineer: • Scour is not an issue at the site. • Frost penetration depth is 3.5 feet. • Tolerable settlement for the project is 1.5 inches. Tolerable lateral deflection for the project is 1.5 inches Design ground water depth is 8 feet. Bridge support DL East/West Abutments 18 kip/ft External Piers 153 kip Middle Pier 306 kip Table 1: Bridge Service Loads Axial LL 7 kip/ft 60 kip 119 kip DL 1 kip/ft 8.5 kip 17 kip Shear LL 0.5 kip/ft 4.25 kip 8.5 kip