BTE provided design and permitting expertise to Strand Associates of the City of Dubuque for 6 101” steel storm drains beneath multiple sets of CPRR tracks. Earth cover was adjacent to the Mississippi River and only 12-14’, with about 9-10’ of loose wet fill with debris underlain by soft wet clay in the tunnel horizon. Another layer of loose wet sand was encountered below the clay. The parallel microtunnels had only 8’ horizontal separation.
An extensive settlement risk evaluation monitoring program were implemented, with stringent constraints for allowable settlements. The contractor was required by CPRR to maintain rail tamping crew on-call. The parallel crossings were completed while protecting the rail yard. No excessive settlement occurred. No CORs or DSC claims were made. Huxted Microtunneling was the microtunneling subcontractor; Tricon was the General Contractor.