EXH1311053223

FROM: Michael Bailey, P.E.,Reda A. Mikhail, P.E., Hart Crowser, Inc. RE: Effect of Shear Modulus on Deformations and Reinforcing Stresses of MSE Walls chicago Third Runway Project 4798-40 cc: Mr. John Sankey, P.E.,RECo Denver This memo discusses sensitivity of the wall design to variations in the soil shear modulus. We present a "best estimate" and conservative "worst case" analysis of seismic performance, to serve asa basis for discussion with RECo, on comparison with their Fairbanks observed performance of MSE walls during real earthquakes. BAGKGROUND _er,e:c,_v The engineering study of the proposed Third Runway includes deformation analyses for the proposed MSE walls under dynamic loading using the finite difference analysis program FLAG The deformation analysis provides an independent check for the AASHTO-required Juneau limit equilibrium, pseudo-static method, because it accounts for critical ground motion and soil stiffness characteristics. One of the critical soil properties that is accounted for in the numerical analysis is the shear modulus. This memorandum summarizes the effect of shear modulus variation on the proposed MSE wall deformations and tensile stresses of the wall reinforcing elements. ,_o_seoc_ Shear modulus of soils is not a constant value, rather it depends on the shear strain level. At a very, low shear strain (typically less than O.OO1%),the maximum shear modulus is designated as Grnax. As the shear strain increases due to increasing shear stresses during an Portlantl earthquake, the shear modulus (designated as C), decreases as illustrated on Figure 1. Curves such as Figure 1 have been published for various soil…

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Call to order – Roll Call – Quorum Established – Land Acknowledgement We would like to acknowledge that our Agency operates in four present-day counties, which are the traditional lands of the Coast Salish people, past and present. This acknowledgement does not take the place of authentic relationships with indigenous communities in our jurisdiction and [...]