June 2025 Vol. 80 No. 6
Features
Combining hand tunneling, HDD for El Paso sewer job
CORINNA HUNT, Contributing Editor
To accommodate new residential development in El Paso, Texas, crews have been working for more than a year on a project to install a 54-inch sewer force main for El Paso Water. The plan was to complete the installation by hand tunneling – until complications necessitated the addition of horizontal directional drilling (HDD).
The project originated in January 2024 with HDW Construction & Drilling, which was acquired by HardRock Infrastructure Services in October. HDW began launch end tunneling operations in February 2024, following with receiving end tunneling operations in July, said Cory Baker, chief operating officer for HardRock.
“The total length of the tunnel is 1,740 linear feet, with an 84-inch diameter,” he said. “They were going to hand tunnel through.”
Originally, it was proposed to be done using a rib and lagging method, consisting of digging out 4-foot increments of ground material at a time and inserting lengths of 84-inch steel liner plate lagging material. Engineers requested about 1,200 feet of 8-gauge liner plate for the hard rock section, and 500 feet of 5-gauge liner plate for a section of ground that was supposed to consist of gravel and clay.
With four crews of six laborers working around the clock – two crews during the day and two at night – the entire project was expected to be completed in 170-200 working days. However, conflicts including the inability to access the receiving end due to other ongoing work, pushed implementation of that 24-hour schedule to August 2024.
Around the clock
With crews working night and day, the assumed rate of penetration was 8-to-10 feet of a 500-foot section in the clay gravel material, per each of the four working shifts, for about 25 days; 5-to-6 feet per shift of an 800-foot section in the softer rock material for 40-to-50 working days; 3-to-4 feet per shift of a 200-foot section in the mild rock material for 15-to-25 days; and 1-to-2 feet per shift of a 240- to 250-foot section in the harder rock material for 60-to-70 working days.
The crew at the receiving end was to make up a larger amount of ground, with the understanding that it would have roughly 1,400 feet of soft rock and material to tunnel through before hitting the 5,000-to-8,000 psi material.
As it turned out, the average rate of penetration was 1.5-to-2 feet per 24-hour shift in the hard rock material – which ended up encompassing roughly 1,400 feet of the tunnel.
“When receiving end crews abruptly began hitting 1 to 2 feet a day in production numbers, roughly 200 feet within the tunnel, we understood there was an issue with the geo reports for the project,” Baker said. “So, we decided to go in there with an HDD rig and drill a pilot through the center.”
Incorporating HDD allowed for a drastic increase in the rate of penetration.
“If we knew from the beginning that ground conditions were going to be that difficult the entire length, then we would have priced the tunnel very differently, and it would have made it viable to complete as a hand tunnel,” he said.
Hand tunneling is advantageous because, regardless of ground conditions or machine failures, crews are able to maintain some production.
“Even when encountering the hardest ground conditions, crews were able to maintain some footage,” Baker said. “In the event that a microtunneling machine or tunnel boring machine were to fail, the need to remove your equipment, repair it and start over again results in tremendous financial loss.”
Exploring options
A Brokk 160 robotic excavator was used for most of the beginning sections of the El Paso project and would break about one foot of ground in a four-hour time frame. But the machine ended up having issues operating in a confined space and with the harder ground material rendering it inoperable and requiring crews to spend time removing it from the tunnel and servicing it. They turned to Rivet Busters pneumatic hammers.
“This method was allowing the production we did see,” Baker said. “An S83 Jackleg drill and Tehma hydraulic rock splitter were used at certain points, as well, to test viability. This is a system where you drill out multiple 3.25-inch holes throughout the rock facing and use the rock splitter to create fractures throughout. This method would work and was less wear and labor intensive on the crews but would also result in less footage than the Rivet Busters.”
A Vermeer 1000/900 rig was selected for the HDD part of the project, which began Jan. 24 of this year (2025), Baker said. The completed 400-foot tunnel on the exit side necessitated handling tools and pumps differently than that traditional way, so crew members constructed a trough along the tunnel floor to slide tools through the 60-inch opening. Additionally, the pilot bore had to follow an upward path including an elevation change of 27 feet.
The initial HDD process worked smoothly ahead of reaming operations, during which three passes were completed: 36-inch, 48-inch and 60-inch, and after which the HDD crew was able to demobilize, Baker explained. Each reaming pass took about 11 days to complete.
By early May 2025, when Baker spoke with Underground Infrastructure, crews were beginning to push in the 54-inch casing and clean out the cuttings and the hole from the HDD, anticipating full project completion at the end of the month. [Did that happen?]
“We went through all the scenarios, and HDD was just the best method to help keep it going,” he said. “The hand tunneling was the best method because it was a cheaper option, and the rock just ended up being harder than what was expected.”
FOR MORE INFORMATION:
HardRock Infrastructure/HDW Construction & Drilling, (210) 403-2086, hardrockis.com
Vermeer Corp., (888) 837-6337, vermeer.com
Comments