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M.I.T., Rotch Visual Collections
Construction preplanning for Sixty State was primarily logistical in nature. The slurry wall construction process, excavation sequencing, location of the excavation earth ramp, and placement of tower cranes had important consequences for the speed and ease of construction. Traffic control and ensuring the availability of ready-mix concrete were crucial to the pouring of the foundation mat. Particular activities were sequenced jointly by Aberthaw's project superintendent and field superintendents employed by subcontractors. Experience and customary practice are the basis of coordination between the trades.
Uncertainty best describes the foundation excavation process. Soil borings at best pinpoint needles of knowledge in a haystack of unknown silt, sand, blue clay and glacial till. Slurry waIl construction was begun in December, 1974 and excavation was completed eight months later. Excavation of the basements and drilling, grouting, and post-tensioning of the slurry wall tiebacks were completed by October, 1975. Bearing strata was located deeper than expected in some areas; additional excavation and back fill with lean concrete was required. Multiple layers of steel reinforcing bars were placed and the foundation mat was poured on November l, about three months behind schedule.
Placing the concrete mat recorded a major milestone. Sixty State's construction could proceed independent of terrestrial uncertainties and was prey only to the vagaries of Boston's climate.
The last portion of the site to be excavated was the northwest corner under the proposed landing for the Congress Street Bridge. The bridge provided a pedestrian link connecting Government Center with the rejuvenated Waterfront. The bridge had been planned for a decade, and its construction had always been a key element in the Sixty State project. But Mayor White began having second thoughts about the bridge, which was to be in direct view of his City Hall office. He was concerned that its mass might block the newly opened sightline between the Old State House and Faneuil Hall, and feared strong winds could make the bridge inhospitable. The architecture and planing community was not convinced. "[The bridge] is a very vital link in a brilliant urban design strategy. It allows City Hall to join with the life of the City, not stand alone," said Noel McKinnell, architect for the new City Hall. [43] The Mayor agreed to the formation of a committee of architects, businessmen and civic representatives to review the bridge.
The group began study on September 4, and concluded on December 22, 1975. On February 29, 1976, the Boston Globe reported "Almost all are in agreement over the new bridge design." [44] The preferred bridge was a steel tube Warren truss of fifteen feet in width, spanning Congress Street without need of a center support. The new design, straightened in direction, thinned in width, and reduced in depth, was "...thought to meet the Mayor's objections while, at the same time, costing less than the original proposal. "[45]
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