Bridges Specialties excavates 10 yds. (9.1 m) from Corpus Christi Bay in preparation to set a new lift station. The site required a full week of dewatering before excavating could be attempted.
It would be pretty tough to install any shoring system in an excavation 30 ft. (9.1 m) from a major body of water. However, that was the challenge facing Robstown, Texas, contractor Bridges Specialties when they were recently charged with installing a fiberglass lift station just 10 yds. (9.1 m) from the banks of Corpus Christi Bay.
The city of Corpus Christi-let project required the lift station to be set a modest 20 ft. (6 m) deep, however the water table started at about 7 ft. (2.1 m) deep.
“We had to set up dewatering pumps for a whole week prior to starting the excavation, just to get the water level low enough to set our lift station,” said Brian Bridges, owner and operator of his namesake company. “And the ground conditions changed during the dig. It was sand for 10 feet, then sandy clay after that,” Bridges explained.
“There was no way we could dig out a hole then set a [trench] box,” continued Bridges. “The only possible way to get down to grade was to install all the sheeting and then dig out within the system,” he said.
For help with this challenge, Bridges contacted the Houston branch office of trench shielding and shoring equipment supplier Trench Plate Rental. Steve Hanley, branch manager, had an immediate solution. “I proposed our Quicksheet Guideframe system,” said Hanley. “Bridges has used the guide frames before, and I knew Quicksheet would be perfect because it allows a contractor to push sheets down below the final grade of the excavation, and then dig out the pit,” Hanley said.
The Efficiency Production manufactured Quicksheet Guideframe has mitered corners with overlapping pockets that pin together like a door hinge, creating a four-sided “picture frame” system that can be set-up on the ground or in a shallow pilot hole. The 4 ft. (1.2 m) tall, 24 in. (61 cm) wide sheeting guide frame has a 7 in. (18 cm) slot where EP-10 sheeting can be stood up and overlapped, then pushed down with an excavator bucket. The guide frame for Bridges' project was 16 x 16 ft. sq. (4.8 x 4.8 m sq) with 25 ft. (7.6 m) lengths of overlap sheeting.
Bridges used a 60,000 lb. (27,215 kg) John Deere excavator for its work and a 120-ton (108.8 t) crane leased through T & T Crane.
In order to make the 5 ft. (1.5 m) diameter, 22 ft. (6.7 m) tall fiberglass FRP Vessel stand up straight and plumb, Bridges cast-in-place 36,000 lbs. (16,329 kg) of concrete around the bottom of the lift station to create a wider, square foundation. That addition also allowed eye bolts to be cemented into the foundation which the crane operator utilized to set the entire structure into the excavation.
Trench Plate Rental also supplied exclusive pin-on pushing caps for the top of the sheeting which have recessed lifting lugs and provide more surface area for pushing the sheets into the ground. Bridges also utilized ground quick-release shackles — exclusively manufactured by Efficiency Production — that enable the shackle to be released from the ground, eliminating the potential dangers of climbing a ladder to undo traditional threaded shackles.
“This was the third time using the Quicksheet Guideframes, and they worked great,” said Bridges. “We are using them again on another project, as well.”
Bridges Specialties offers a wide range of commercial, industrial, and residential services to South Texas government facilities, municipalities and local business.
With branch offices in California, Texas, Florida and Chicago, Trench Plate Rental is an official Efficiency Production Inc. trench shielding and shoring equipment distributor. Efficiency Production provides a wide selection of standard and custom trench shielding and shoring systems. Efficiency's versatile products are designed specifically for safe and cost effective installation of utility systems and infrastructure improvements. All products are P.E. certified to meet OSHA standards.
For more information, call 713/671-2551.