Tools of the Trade

June 14, 2021
Employing a gentler approach to digging with hydro-excavators

For most excavation jobs, brute force is perfectly acceptable. Standard long-arm excavators and backhoes can physically load dirt onto dump trucks to be hauled offsite. But what if a gentler approach is needed ("gentler" being a relative term for earthmoving operations)? Instead of using bucket excavators in areas where sensitive infrastructure exists, the equivalent of a bull in a china shop, a more nuanced approach should be tried. One that uses high-pressure water to blast loose soil without any collateral damage. This approach is called hydro-excavation.

Since at least the California gold rush days of the 1850s, hydro-excavation has been a tool in mining and excavation operations. Mechanical steam-powered pumps were first becoming available for firefighting in the big cities back east. Someone in the goldfields realized that this was a tool that could be used to essentially liquefy large masses of earth and allow for the easy extraction of gold flakes and nuggets, and is still used today especially in the goldfields of South Africa. Operators found that the techniques saved labor and overall operating costs. Safety also improves since workers rarely, if ever, have to enter the actual trench or pit being excavated.

The first commercially available machinery designed specifically for hydro-excavation came online in the late 1960s. At first, the sediment-laden slurry was discharged via gravity flow channels or pumped through pipelines to settling ponds. Vacuum trucks, which became available in the 1970s, provided a more efficient method of dealing with slurry, a method that did not require extensive ponds. Trucks provided the mobility for hauling the slurry offsite to secure disposal areas. Additional mobility was provided by the use of tractor treads instead of truck tires. By the 1990s vacuum trucks were augmented by pull behind, trailer-mounted units that can be configured for unique applications.

The Business of Hydro-Excavation

Hydro-excavation is what you do if you have assessed the job or job site and are faced with a tightly constrained work environment, one with either buried utilities that could be damaged with a standard bucket excavator and/or work sites with little or no elbow room in constricted or sensitive areas. These can include job site obstacles that can make traditional backhoe excavation difficult (structures, fencing, trees, or landscaping that has to be preserved). Under adverse conditions, hydro-excavators can more easily maneuver and operate. In either case, the excavation contractor is looking at the potential hazards of a job site every day with safety being top of mind. Safety always comes first (as explained by Chapman Hancock, Ditch Witch Product Marketing Manager—Vacuum Excavation), "The first step on any excavation job should always be to call 811 to get existing utilities located. If a job site has multiple existing utilities that are in the path of an excavation job, vacuum excavators are a particularly good investment. On jobs like these, vacuum excavators can be used to ensure existing utilities are properly exposed and avoided during a bore or excavation work. It’s also important to remember that vacuum excavators are not a replacement for traditional excavation or trenching methods, but instead a way to supplement and improve a contractor’s productivity.”

The above defines the types of jobs that hydro-excavation contractors are hired to do. One primary market is horizontal directional drilling (HDD). In addition to initially exposing buried utilities and later job site cleanup, hydro-excavators work in tandem with HDD operators to ensure that all utilities are daylighted, which helps avoid potential cross bores by being able to physically watch the bore head safely pass over or under the utility. Once the HDD contractor has completed the job and demobilized from the site, the hydro-excavator sticks around to perform site cleanup and spoils management. Hydro-excavator versatility makes it popular with other industries as well, such as landscaping, tree care, and irrigation installation.

The size of the job also has an impact on the use of hydro-excavators. When faced with larger jobs, hydro-excavation contractors should work closely with local equipment dealers to ensure that they have the right equipment for the job. In addition to their great versatility of uses, these machines can be configured in multiple ways. This includes fresh water and debris tanks, blowers, and the trucks and trailers themselves—they all get upsized as needed. Simply put, the larger the job, the larger the hydro-excavator, so a hydro-excavation contractor should be sure to take a holistic approach to the job site, matching both size and dexterity to the job requirements.

Vacuum excavators are growing in popularity and one of the major segments experiencing that growth is the rental market. For contractors or excavators looking to rent a vacuum excavator, we recommend visiting your local dealership or rental yard to see which configuration will work best for your job site and checking out a certified training option to get up-to-date on excavation best practices before operation. Many manufacturers—Ditch Witch included—offer online certified training modules for free.

Ditch Witch launched the HX30G in 2019 as an economical option for contractors looking to explore the benefits that vacuum excavation can bring to their operation. The HX30G is designed to provide quick ROI for contractors, with a 31-horsepower gas engine providing the optimal combination of power and suction for a wide array of excavation jobs. When paired with the VT9 trailer, the configuration is under 10,000 pounds GVWR, which allows transport without a CDL. The HX30G is the latest addition to Ditch Witch’s HX-series of vacuum excavators, which was launched in 2018.

The Techniques of Hydro-Excavation

Hydro-excavation combines a high-pressure stream of water to blast away loose soil, creating a slurry that is extracted with a high-speed vacuum via an air vacuum hose attached to a large tanker truck. The method is perfect for exposing buried utilities without the risk of damaging them, a method that is both safe and efficient. Most hydro-vacuum extraction trucks utilize fan blower air vacuums because of their efficiency and light weight. It also requires less manpower, reducing labor costs.

The water is ejected from hoses at a rate of 5 to 15 GPM at 3,000-4,000 psi. The lower pressure is generally used except in especially tough or frozen soils. More precise excavation will utilize higher pressure with less water volume. Broader excavation may require the opposite, utilizing larger volumes of water at lower pressure. Assuming a resultant slurry that is roughly 50% solids content by weight (and having a specific gravity of 2.5), approximately 2.5 volume units of water will be required to excavate one volume unit of soil. Such large amounts of water cannot be practically supplied from a mobile storage tank. It is much better to tap into a local source of water (hydrant, surface pond, etc.).

Hydrovac trucks can excavate up to 60 feet deep out to an operational radius of 600 feet. This greatly reduces traffic congestion at the excavation location and simplifies the requirements for choreographing the movement of the equipment. The hose utilized to extract the slurry is typically either 6 or 8 inches in diameter. The suction can be powerful enough to lift rocks that are larger than the hose diameter, and weighing up to 100 pounds, then place them to one side by maneuvering the hose with the rock stuck to its opening by negative pressure. The 6-inch tube can typically extract 3,000 cfm and the larger 8-inch tube can remove 5,500 cfm. However, the larger tube will need an engine with greater horsepower and have a higher fuel consumption rate. Though sandy soils are best for hydro-excavators, they can be utilized in almost any condition except hardpan clays and frozen soil or permafrost. Hydro-excavation can be used to cut long trenches and narrow slits to lay pipelines or deep vertical holes to allow the construction of pier footings. Hydro-vacuum excavation equipment can be adjusted to use a minimum required volume of water and the lowest necessary suction pressure. If a bucket excavator is an ax, a hydro-excavator is a scalpel.

Super Products, an Alamo Group Company located in southeast Wisconsin with seven rental facilities nationwide, has been a leading manufacturer of vacuum trucks since 1972 emphasizing innovative features, high quality, durability, and ease of operation.

Their Mud Dog Vacuum Excavators are designed for operator convenience and consistent performance in the harshest environments. The product line comes standard as a hydro-excavator with an optional air excavation package. The Mud Dog is available with 12-yard or 16-yard debris capacity, has a 1,500-gallon to 2,000-gallon water tank capacity, and ensures efficient workflow through variable blower and water pump speed and a quick filling water system. Each model comes standard with eject unloading, as well as safety features including backup cameras, visual and audio alarms, and emergency stop switches. Units are also equipped with a rear-mounted boom that reaches 27 feet, has 335-degree rotation, and can move in a 45-degree upward and 25-degree downward pivot allowing for versatility within dig areas.

The Camel Combination Sewer Cleaner is the most versatile combo unit in the industry. The product line comes in a variety of model configurations: 900 Dump, 1200 Dump, 1200 Eject, and 1200 Wastewater Recycle. All three 1200 models come standard with a high dump subframe eliminating the need to back up a ramp for debris removal. The 1200 Dump can dump into a 42-inch container while maintaining a low overhead height and a low center of gravity for increased stability. The 1200 Eject model allows operators to have a controlled way to dump safely into a 48-inch container without the need for additional containment products. The 1200 Wastewater Recycle model enables operators to clean sewers without the use of freshwater, and is capable of cleaning nearly 3,000 feet of sewer pipe per day and saving 60,000 gallons of water per week. Optional features offer increased performance capabilities, such as the hydro excavation package allows operators to jet, vacuum, and excavate continuously all day long and the pusher axle allows for increased legal payload.

The Supersucker Industrial Vacuum Loader cleans up industrial waste and debris, as well as recovering and reusing raw materials. The Supersucker uses high-power airflow to suck up solids, liquids, sludges and slurries and features single-mode filtration for loading of wet or dry material with no changeover required. Each model also comes standard with a full opening, six latch tailgate with multi-position safety properties.

The SuperJet Truck Mounted Jetter blasts debris to clear blockages and maintain sewer lines when vacuuming extraction is not required. It utilizes the industry's strongest and smoothest single-piston water pump to create consistent high-water pressure. Units come standard with rotationally molded polyethylene water tanks in a modular design to accommodate water capacities ranging from 1,080 gallons up to 3,240 gallons. Additionally, they have convenient standard curbside and street side fill for municipal and residential sewer cleaning. The SuperJet also has an easy-to-use hose reel with 1,000 feet of 1-inch-diameter sewer hose, 200 degrees of rotation, and a digital monitor. This allows operators to work efficiently while positioning themselves out of traffic and other hazards. The monitor displays a hose footage count, offers 20 saved settings for hose reel payout, and is designed with LED panel lights to enable readability in a variety of environments. Lastly, their Durasucker Liquid Vacuum Truck is DOT certified to collect and transport hazardous and non-hazardous liquid and semi-liquid waste. This model is available in the Super Products' rental fleet in carbon steel and stainless-steel configurations with scrubber and transfer pump options.

Not only are they precise, but hydro-excavators are also extremely safe. They won’t tear up a sewer line, cut a buried power line, crack open a natural gas pipeline, or sever a communications cable. Three-quarters of all damage done to utility infrastructure comes from shovel strikes and bucket impacts. However, depending on site conditions, the excavation process may take longer, but this can be mitigated with the use of a high-pressure extraction tank. Once the water is deep enough (with enough depth to prevent cavitation of the vacuum pump) the vacuum truck's extraction hose is inserted and begins drawing out the sediment-laden water. At this point, provided that the water stream's flow rate can match the vacuum extraction rate, the vacuum truck can operate continuously. This results in a steady operation, however, the amount of water left in place can obscure observation of the excavation’s progress and still require lowering of the inlet elevation as the bottom of the excavation goes deeper. Working in tandem, the hydro excavator and high vacuum extraction tanker truck can achieve both safety and cost-effectiveness. The same technique can be used for no-excavation applications.

Hydro-excavation conforms to OSHA requirements for safe excavation operations, specifically 29 CFR Part 1926 Subpart P (Excavations), §1926.651 (Specific excavation requirements), govern methods for uncovering underground utility installations. Specifically, paragraph (b)(2): When utility companies or owners cannot respond to a request to locate underground utility installations within 24 hours or cannot establish the exact location of these installations, the employer may proceed, provided the employer does so with caution, and provided detection equipment or other acceptable means to locate utility installations are used. And paragraph (b)(3): When excavation operations approach the estimated location of underground installations, the exact location of the installations shall be determined by safe and acceptable means.” Hydro-excavation meets these requirements.

The use of tanker trucks is more environmentally friendly than traditional excavation spoil piles which can cause runoff of sediment into nearby streams as well as wind-blown debris and may require elaborate filter fencing and tarp covers. Further environmental protections are provided during site clean-ups. Vacuum pumps suck up the slurry of wet excavated material at a rate of at least 1,000 cfm. The slurry is then deposited in tanks on the back of the vacuum trucks that can hold between 300 to 5,000 gallons (40 to 668 cubic feet) of slurry. At the high-end 5,000-gallon tank capacity, the slurry described above with its density of almost 90 pcf would result in a truckload of 60,000 lbs or 30 tons. At 50% solids content by weight, this is equivalent to 15 tons of soil. Dumping at the point of deposit is via a wide-opening door at the end of the tank. Dumping is typically accomplished with just gravity, though some systems employ applied pressure to "pressure out" the slurry quicker with a direct discharge. Vacuum extraction tanker trucks can be used to remove already wet and loose materials such as toxic sludges and waste liquids from contaminated sites, open pits and septic systems.

But each type of excavation requires unique methods. For example, when working in sandy soils care must be taken to remove the sandy slurry from the extraction tank since sand tends to stick more than other soils. Frozen soil can be melted with hot boiler water (but with proportional increases in operating costs). The size and power of the vacuum extraction fan needs to match the distance and depth of the excavation from the tanker truck (the same considerations apply to local deep excavations like piling holes). Distance to the point where the contents of the tanker truck are to be dumped affect the overall operational efficiency given the potential long cycle times when the tanker truck is not onsite and operating. Some locations (especially oil and gas work) require off-road driving conditions so appropriate rigs should be chosen. And often overlooked are local bridge weight restriction and traffic laws which can indirectly impede hydro-excavation operations.

Hydro-excavation can be used for the removal of debris as well as soil. The debris consists of organic landscaping material and vegetation as well as inorganic construction and demolition debris. Hydro-excavation provided a cost-effective alternative to burning, grinding, and chipping debris. Using its inherent precision and accuracy, hydro-excavation can be used to remove debris without increasing the hazardous nature of a construction and demolition site without damage to surrounding areas. While not suitable for the removal of large chunks of steel and concrete, hydro-excavation can remove soil and debris from in and around structures with pressurized blasts of water.

Hydro-excavation can also be used in an exploratory mode. It can be used effectively in potholing operations, digging test holes to locate and daylight buried utilities while leaving the adjacent soils undisturbed. Exact locations (horizontal alignment, depth, vertical orientation) can be directly measured and in the process exposing other utilities that may not be shown on the site’s construction plans.

It's in these utility-rich environments populated by industrial facilities (a.k.a. "urban areas") where hydro-excavation shines. “Cities, counties, and state entities are always discovering new ways to use vac systems,” said Jake Jeffords, director of sales, marketing and global accounts at Vermeer MV Solutions. "Beyond some of the traditional applications, workers employ vacuum excavators to remove roots and debris around water meters and valves and remove waste from storm drains, catch basins, and culverts. High-pressure water wands help them with digging and cleaning. Air vacuum excavators are also excellent for pressure testing sewer lines.

"Vacuums aren't new for cleaning at industrial plants. Facility managers used to have to employ service companies with big trucks to work during scheduled shutdowns. With smaller vacuum excavators, they can now make cleaning an ongoing effort, which has helped extend the intervals between scheduled shutdowns…These drains tend to get plugged up with mud, grease, and waste oil while cleaning dirty equipment, and doing the work with a shovel is a job no one wants. Vacuum excavators do a better job in a fraction of the time.”

But there are also non-utility and even non-construction applications for hydro-excavators in the fields of agriculture and landscaping. “Bedding and waste used to have to be manually removed from a stall or with a small loader and then hauled away before pressure washing the area—there can be a lot of trips involved,” he explained. “With hydro-vacs, workers suction up everything with the debris hose and have a high-pressure washer right there to spray everything down and then collect all of the loose material and water in one step.”

Vermeer produces a solid and versatile line of hydro-excavators. The Vermeer VXT500 VXP series is an 8-inch vac with an 8-yard spoil tank capacity. It is ideal for utility applications where a higher-capacity machine with a smaller footprint is desired. The VXT500 joins a family of Vacuum X-Traction Products, Inc. (VXP) vacs featuring vacuum blowers that deliver 4,800 to 6,400 cubic feet per minute and spoil tank capacities ranging up to 16 yards. To help better meet the marketplace’s growing needs, Vermeer has introduced the XR2 vacuum excavator. The truck-mounted unit is the first on the market to offer an onboard shaker deck to separate solids from liquids once the material has decelerated through an airlock. This enables operators to reclaim downhole fluid while the dry material is separated and discharged onsite.

The Specifications of Hydro-Excavation

According to Jake Jeffords, you can learn a lot about a vacuum excavator’s performance capabilities by its hose size. “Vacuum excavator hoses can tell a contractor a lot about the volume of air being moved by the vacuum pump—typically referred to as vacuum CFM (cubic feet per minute),” he said. “Hose diameter sizes can also help a contractor determine a unit’s mercury level and onboard horsepower.”

After hoses, the buyer of a hydro-excavator should look at their pumps and flow rates measured in CFM. But bigger isn’t always better. “It would be overkill for a contractor who only needs to suction drill slurry to invest in a high CFM model if they don’t intend to pothole. On the other hand, many contractors who are potholing utilities want the most compact machine available to maneuver in confined areas, which is why they would seek out a small-hosed, high CFM model.”

High CFM is produced by larger, more powerful engines that must be used. Higher horsepower engines will deliver more torque to the vacuum and water pumps to give you higher mercury levels (suction) and pounds per square inch. Contractors should also note a vacuum excavator's mercury level to ensure it's high enough to accommodate their needs. All of the specs should be viewed as performance-related specs. Hose size, vacuum CFM, mercury levels, water pump capacities, and engine horsepower are all connected and will ultimately tell you what a vacuum excavator is capable of. Now, you need to move on to capacities.

Tank capacity on the other hand has an indirect effect on overall operational efficiency since it determines how long a contractor can stay on a job and the costs to transport it. Most manufacturers will offer spoil tank capacities starting at around 300 gallons up to 2,000 gallons. Water tank capacity needs are also tied to how a vacuum excavator is being used. Crews need more water when potholing and very little, if any at all when supporting a drilling crew.