Frequently Asked Questions

Microtunneling is a trenchless method for installing pipe on a precise line and grade without digging a continuous trench. We build a launch shaft and a reception shaft at either end of the drive, then advance a remotely controlled microtunnel boring machine (MTBM) between them. Hydraulic jacks in the launch shaft push pipe segments in behind the machine, so the pipeline is installed as the tunnel is excavated. Because the excavation face and tunnel stay supported throughout the drive, the ground above remains stable.

Both methods avoid open trenches, but they suit different conditions. HDD drills a pilot bore along an arc, enlarges the bore, and pulls pipe back through, which works well for long crossings where some variation in line and grade is acceptable. Microtunneling jacks pipe directly behind a guided machine while supporting the excavation face, which gives much tighter control of alignment and grade. That control is the reason engineers specify microtunneling for gravity sewers and work near sensitive structures, while HDD often fits pressure lines and long river crossings.

Our fleet supports tunnel drives from 8 to 100+ inches in nominal diameter. Within that range we work with the pipe materials engineers commonly specify for jacking, including reinforced concrete, steel, fiberglass, polymer concrete, and vitrified clay. On some projects we install a larger casing and place a smaller carrier pipe inside it, which gives the owner added protection for the line over its service life.

The MTBM is guided by a laser or electronic navigation system that reports its position to the operator in real time, and the operator corrects course with steering jacks as the machine advances. This lets us hold line and grade to tight tolerances over the full length of a drive. With open cut, final accuracy depends heavily on bedding and backfill, and pipe can shift as the trench settles over time. That difference matters most on flat gravity sewers, where small grade errors affect flow.

Slurry microtunneling performs across a wide range of ground, including soft clays, silts, sands, gravels, and mixed conditions, and it is especially effective below the water table. With the right cutterhead, machines can also handle cobbles, boulders, and rock. The most challenging conditions are mixed faces, unexpected obstructions, and voids, which is why a thorough geotechnical investigation drives our equipment and cutterhead selection on every project.

Microtunneling becomes the stronger option as depth increases, as the corridor gets more crowded with existing utilities, and as the cost of closing a street rises. It is also well suited to gravity lines that demand precise grade, high groundwater, and crossings under highways, railroads, or waterways. Open cut still makes sense for shallow lines in open ground. We are glad to review an alignment with the engineer of record early in design to help weigh the options.

Depth is set mainly by shaft design and ground conditions, since the machine itself operates the same way at 15 feet as it does at 50 feet or more. This is a key reason owners choose microtunneling for deep lines, because open cut costs climb steeply with depth while tunneling costs rise much more gradually. Our deepest completed drive to date is 70 feet below grade at the jacking shaft.

Yes, and road and highway crossings are among the most common applications we see. Because the MTBM balances pressure at the excavation face, settlement at the surface is controlled, and traffic continues to move overhead while we work. We coordinate with the roadway owner, including TxDOT and other state agencies, on crossing requirements and settlement monitoring.

Slurry microtunneling is designed for work below the water table. The machine maintains pressure at the face that counteracts groundwater and earth pressure, and the slurry carries excavated material to a separation plant at the surface. Because of this, dewatering along the length of the drive is usually unnecessary. Shafts are designed to resist water inflow, and sealed entry and exit points keep water and soil from entering at launch and reception.

Requirements vary by jurisdiction and owner. Common permits include right of way or use permits from the city, county, or state, railroad license agreements for rail crossings, and traffic control plan approvals. Stormwater pollution prevention plans and discharge permits are often needed, and work near waterways may involve U.S. Army Corps of Engineers authorization. The owner or engineer of record typically secures project level permits, and we handle the construction related approvals within our scope.

On a per foot basis, microtunneling usually costs more than shallow open cut in open ground. That gap narrows and often reverses as depth increases, and in congested areas where restoration, traffic control, and utility relocation add up quickly. We find the most useful comparison is total installed cost, which counts surface restoration, schedule impacts, and disruption to the surrounding community alongside the cost of the pipe itself.

Ground conditions have the greatest influence, followed by pipe diameter, drive length, depth, and the number of shafts required. Groundwater, pipe material, site access, spoil disposal, and traffic control requirements also play a role. A strong geotechnical investigation tends to lower cost, since it reduces the uncertainty contractors must account for when pricing the work.

Schedules depend on the number of drives, ground conditions, and how long the shafts take to build. Shaft construction and setting up the separation plant often take as much time as the tunneling itself. Once the machine launches, production can be steady in favorable ground. A single road crossing may take a few weeks, while a multi drive sewer project can run several months.

Many of the largest costs on open cut projects come after the pipe is in the ground. Pavement replacement, extended traffic control, relocating conflicting utilities, and dewatering long trench sections add expense that rarely shows in a per foot comparison. Settlement damage to nearby structures, lost business access, and public complaints that slow a project down also carry real costs, and microtunneling keeps most of these to a minimum.

Work is concentrated at shaft sites, so most of the street, sidewalk, and storefronts along the alignment remain untouched. The tunnel can pass beneath existing utilities and foundations, which avoids costly relocations. Face pressure control protects nearby buildings from settlement, and the smaller work footprint reduces noise and dust for residents and businesses.

Open cut construction typically moves a lane closure down the street as the trench advances. With microtunneling, we place shafts off travel lanes where possible, in parking areas, medians, or available right of way, and the roadway between shafts stays open. Drivers, transit, and emergency vehicles keep moving while the pipeline is built beneath them.

In most cases it is. Microtunneling removes far less material, requires fewer truck trips, and avoids tearing out and replacing pavement, which lowers fuel use and emissions. It also allows us to pass beneath wetlands, trees, and waterways without disturbing them. Slurry is recycled through a separation plant during the drive, and excavated material is managed for proper disposal.

We can set the alignment below or between existing lines rather than cutting through them at trench depth, which reduces conflicts and relocations. Precise guidance keeps the machine on its designed path, and pressure control at the face limits ground movement around nearby pipes and cables. Conflicts are identified and verified during design, and we monitor sensitive utilities during the drive when the project calls for it.

Gravity sanitary sewers and storm sewers are the most common applications. Microtunneling is also used for water mains, force mains, and culverts, and for casings that carry gas, petroleum, electrical, or fiber optic lines beneath roads, railroads, and other obstacles.

Yes, and gravity sewers are where microtunneling delivers its greatest value. These lines depend on consistent slope to flow properly, and many are deep and run through crowded corridors. Precise grade control allows us to install them accurately at depth without the traffic and restoration impacts of a deep open trench.

It can be a strong option, particularly for shorter crossings, saturated soils, or alignments where precise grade matters. Shafts are built on each side of the waterway, and the pressure balanced machine keeps the drive stable beneath the channel. HDD is often a better fit for very long crossings, and we help evaluate both methods against the project’s ground conditions and requirements.

Curved microtunneling is an established technique that allows horizontal and vertical curves within a single drive. Because a laser needs a clear line of sight, curved drives use gyroscopic or automated survey navigation, along with pipe joints designed to accommodate deflection. Curves can reduce the number of shafts needed and help an alignment follow a roadway or avoid obstacles, which often lowers cost and surface impact.

We are based in Houston and work primarily across Texas, Florida, Georgia, and Tennessee. We also consider projects outside these states and across the US on a case by case basis.

Our roots go back to 1986, when we completed Houston’s first microtunneling installation, one of the earliest in North America. Since then we have installed more than 200 miles of utility lines for public agencies, utilities, and private owners. That history has given our crews and project managers deep familiarity with how different ground behaves and how to plan around it.

The best time to reach us is early in design, when alignment and method decisions are still flexible. Share whatever you have, such as plans, the proposed alignment, or geotechnical data, and we can offer constructability input and help evaluate trenchless options. You can reach us through pategarver.com/contact or by calling 832-917-1611.

We provide constructability review with owners and consultants on design build and alternative delivery projects, bringing trenchless constructability input into design from the start. We also work as a prime contractor or trenchless subcontractor on traditional design-bid-build projects.

Safety is planned into every project, beginning with the first site visit, and continuing through completion. Our dedicated Safety Director and safety coordinators work directly with project leadership and field crews to support task planning, employee training, site inspections, and corrective action follow-up.

We track safety performance and use lessons learned to strengthen our practices and protect our employees. We currently maintain zero lost time incidents with a workers compensation Experience Modification Rate (EMR) of .088.

Pate Garver actively participates in the Underground Contractors Association of Texas (UCATX), supporting industry safety initiatives, sharing knowledge, and participating in hands-on training to advance safety throughout the underground construction industry.

An MTBM is a steerable tunneling machine operated remotely from a control unit at the surface, so no crew members work inside the tunnel. It includes a rotating cutterhead matched to the ground conditions, a pressurized chamber that supports the excavation face, steering jacks for directional control, and a guidance target that reports position to the operator. Pipe is jacked in directly behind the machine as it advances.

A laser set to the designed line and grade is mounted in the launch shaft and aimed at a target inside the MTBM. A camera reads where the beam strikes the target and sends that position to the operator’s control screen in real time. The operator steers the machine back toward the design path as it advances. Because the laser requires line of sight, curved drives and very long drives often rely on gyroscopic or automated survey systems instead.

Borings should be placed along the alignment and at shaft locations, extending below the planned tunnel depth, with spacing tightened where ground is variable. Lab testing should cover gradation, plasticity, strength, and abrasivity in rock, along with groundwater levels and permeability. The investigation should also look for boulders, obstructions, and contaminated soils. Many owners summarize findings in a Geotechnical Baseline Report, which gives all parties a shared basis for evaluating risk. ASCE 36 provides widely used guidance on these requirements.

Houston sits on clays that swell and shrink with moisture, interbedded with sand and silt layers that often carry water under pressure. Shallow groundwater is common, and the region’s flat terrain means sewer lines run at very shallow slopes, so grade accuracy matters a great deal. Add some of the densest utility corridors in Texas, and many projects benefit from a method that controls both ground movement and grade at depth.

Florida limestone varies widely in hardness and often contains solution cavities and voids, with sandy soils and a high water table above it. We address this with cutterheads capable of excavating rock and with careful control of face and slurry pressure, since voids can cause slurry loss or ground instability. A thorough geotechnical program is essential, and some projects call for grouting known voids before tunneling begins.

Tennessee’s residual clays are generally favorable for trenchless work, and auger boring, pilot tube guided boring, HDD, and microtunneling can all perform well in them. The greater challenge is the limestone beneath, which can rise sharply and unpredictably, along with chert and karst features. Pilot tube boring suits smaller gravity lines in consistent clay, while microtunneling handles larger diameters and drives where the tunnel may encounter rock.

Hurricane season runs from June 1 through November 30, and projects in Gulf and Atlantic coastal areas plan for it from the start. Shafts need protection from flooding, electrical equipment and separation plants should sit above expected water levels, and pumping capacity should account for heavy rain. We build storm preparation and recovery steps into the schedule, and we time critical activities such as machine launch and reception around the season where possible.