The North Texas Tollway Authority (NTTA) is building the 28 mile (45 km) long Chisholm Trail Parkway, a toll road which will connect Interstate 30 south of Fort Worth with the US Highway 67 near Cleburne, both in Texas, US. The NTTA faced two problems when planning the project. First, the planned route ran through rocky limestone terrain. Second, conventional drilling and blasting was not permitted because the scheme is inside the Fort Worth city limits. Contractor Mario Sinacola & Sons Excavating decided to tackle this dual challenge with surface miners to remove the hard limestone substrate selectively, rapidly and with millimetre precision. "The earth works cover a vast area, the amount of rock to be removed is relatively large and the work very intensive," explained Chris Logan, project manager for, Mario Sinacola & Sons. Indeed, there are 2.14 million m~3 of limestone to remove, mostly with a hardness from 6,000 to 10,000 PSI (40 to 70 MPa). However in some areas it reaches 16,000 PSI (110 MPa).
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