Atlas Engineering Group > Projects > Structural Engineering > CTA Red Purple Modernization Project – Lawrence to Bryn Mawr Modernization (LBMM)

Atlas, as a subconsultant, inspected and evaluated the condition of the existing century old retaining walls, and designed the rehabilitation and stabilization for the existing walls to support temporary CTA stations, platforms, and active train tracks. Columns supporting the temporary platforms adjacent to the existing walls complicated the analysis and design due to the loss of passive resistance in front of the toe of the footing to stabilize the wall; thus, a detailed construction phasing sequence was developed to provide adequate factor of safety. Drilled ground anchors were designed to stabilize and strengthen the existing retaining walls. The ground anchors consisted of bonded and unbonded zones within the embankment. The pre-stressing steel tendons within the bonded zones were encapsulated by grout filled tubes Performance, proof, and creep tests were required to pass specifications prior to the lock-off of the tendon to the trumpet.

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