Simplified Procedures for the Design of Tall, Stiff Tieback Walls

摘要

The equivalent beam on rigid support method of analysis using apparent earth-pressure envelopes is most often the design method of choice, primarily because of its expediency in the practical design of tieback wall systems. This method provides the most reliable solution for flexible wall systems, i.e., soldier beam-lagging systems and sheet-pile wall systems, since for these types of systems a significant redistribution of earth pressures occurs behind the wall. Soil arching, stressing of ground anchors, construction-sequencing effects, and lagging flexibility all cause the earth pressures behind flexible walls to redistribute to, and concentrate at, anchor support locations. This redistribution effect in flexible wall systems cannot be captured by equivalent beam on rigid support methods or by beam on inelastic foundation analysis methods where the active and passive limit states are defined in terms of Rankine or Coulomb coefficients. Full-scale wall tests on flexible wall systems indicated the active earth pressure used to define the minimum load associated with the soil springs behind the wall had to be reduced by 50 percent to match measured behavior. Since the apparent earth-pressure diagrams used in equivalent beam on rigid support analyses were developed from measured loads, and thus include the effects of soil aching, stressing of ground anchors, construction-sequencing effects, and lagging flexibility, they provide a better indication of the strength performance of flexible tieback wall systems.