ABSTRACT

INTRODUCTION

The city of Waxahachie, south of Dallas, Texas, will be the hub of the Superconducting Super Collider (SSC) now under construction. An 86-km oval tunnel around Waxahachie will house the superconducting magnets that will guide two opposing beams of protons at speeds approaching the speed of light. Within large underground hall% the two beams will cross, allowing the proton collisions to be studied. More than 52 shafts will be required to connect the tunnel to the surface. The SSC underground facilities will be constructed in three geologic strata:

§ Eagle Ford Shale (EFS) - a very weak, bedded shale.

§ Austin Chalk (AC) - a competent limestone.

§ Taylor Marl (TM) - a weak calcareoushale.

The EFS, and to a lesser degree the TM, exhibit characteristics between soft and rock. Laboratory tests were insufficient for the safe and adequate design of the underground facilities. Therefore, a series of in situ experiments were conducted to obtain parameters and performance data for verification of the design and analysis methods.

The most important experiments were carried out in an exploratory shaft. The shaft was drilled to a 5-m diameter to a depth of 60 m and then reduced to a 3-m diameter to 82 m. A 10.7-m long adit was excavated at the AC/EFS interface at a depth of 64 m.. Instrumentation included piezometers, multiple-point borehole extensometers (MPBXs), tape convergence points, inclinometers and heave gage casings, and an instrumented, rigid steel ring lining grouted in place.

Pressuremeter tests and hydraulic fracturing tests were also carried out. In addition, extensive laboratory testing and numerical modeling were performed to determine by back-calculation actual ground performance parameters.

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