When Berkel & Company Contractors took on the shoring work for the Capital One complex in Tysons Corner, Virginia, they needed a drilling rig capable of installing nearly 400 grouted tieback anchors through varied subsurface conditions. The equipment they chose, a KLEMM KR 807-7G, became the centerpiece of a demanding foundation project that required precision, reliability, and high production rates. For contractors who regularly perform Dust Free Drilling Capturing Drywall Dust At the source in their finishing work, understanding the scale of heavy civil drilling operations provides valuable perspective on how foundation systems support the structures above grade.
Understanding Tieback Anchor Systems and Their Role in Deep Excavation
Tieback anchors are a critical component of shoring systems used in deep excavations. When a contractor needs to dig 50 feet below ground level adjacent to existing structures, roads, and utilities, the vertical cut walls must be prevented from collapsing inward. Soldier piles, lagging, and tieback anchors form a system that transfers the lateral earth pressure into competent soil or rock strata behind the excavation face.
How Grouted Tieback Anchors Work
A grouted tieback anchor consists of two functional zones:
- Unbonded zone adjacent to the shoring wall, where the tendon is free to stretch under tension without bonding to the surrounding ground
- Bonded zone deeper in the earth, where high-strength grout bonds the tendon to the surrounding soil or rock to develop the anchor capacity
The installation sequence follows a methodical process. First, a drill rig advances a casing to the design depth. A strand tendon is inserted through the casing, and grout is pumped to fill the void as the casing is extracted. Once the grout achieves an initial set, high-strength grout is applied under pressure to the bonded zone. The anchor reaches full design capacity after the grout has fully cured, at which point the tendon is tensioned and locked off against a bearing plate on the shoring wall.
Key Components of a Soldier Pile and Lagging System
The shoring system at the Capital One complex relied on three main components working together:
| Component | Function | Installation Method |
|---|---|---|
| Soldier Piles | Vertical steel beams that carry lateral earth loads | Drilled or driven into the ground at regular intervals along the excavation perimeter |
| Lagging | Horizontal timber or concrete panels spanning between soldier piles | Placed progressively as excavation proceeds downward, retaining the soil face |
| Tieback Anchors | High-strength steel tendons tensioned into the ground behind the wall | Drilled, grouted, and tensioned at each row of soldier piles to resist overturning forces |
The KLEMM KR 807-7G Drilling Rig: Design for High Production Anchoring
Berkel obtained the KLEMM KR 807-7G from Equipment Corporation of America (ECA) in July 2018. The rig is specifically engineered for installing tieback anchors with casing, making it suited to projects with large anchor quantities. As the largest model in KLEMM universal rig line, the KR 807-7G combines power, mobility, and automated handling systems that set it apart from conventional drill rigs.
Mag 7.0 Revolver Rod Handling System
One of the defining features of the KR 807-7G is the patented Mag 7.0 Revolver system. This carousel-style magazine allows the operator to rotate the barrel and install casing sections without manual handling. The system reduces the physical demands on the crew and accelerates the drilling cycle, particularly on projects requiring hundreds of anchors at depths of 65 to 75 feet.
Berkel operator Tyler Davis, a 20-year veteran, noted that the carousel system was a new capability compared to earlier KLEMM models. ECA provided a full day of onsite training, and Davis supplemented this by studying operational videos. Within two weeks, he had mastered the revolver functionality and was operating at peak performance. This learning curve highlights an important consideration for contractors adopting advanced drill rigs: the productivity gains of automated rod handling are real, but they require intentional training investment.
Energy Efficient Power System
The KR 807-7G incorporates KLEMM Energy Efficient Power (EEP) System, which improves fuel efficiency during operation. For projects that run for six months or more, the cumulative fuel savings can be significant. The rig also includes a radio remote control unit, giving the operator flexibility in positioning during drilling. However, Davis chose to work on the control panel arm positioned at a 90-degree angle to the tilted mast, finding this arrangement faster for his established workflow.
Drilling Through Variable Ground Conditions at Tysons Corner
The 25-acre Capital One complex site presented both ideal drilling conditions and significant challenges. Superintendent Art Rhodes, a 21-year Berkel veteran, described much of the project as a shoring contractors dream job due to the subsurface conditions, but the project was not without its difficult zones.
Favorable Conditions in Sandy Clay and Partially Weathered Rock
The majority of the site consisted of sandy clay with Partially Weathered Rock (PWR) beginning at approximately 50 feet down. PWR is ideal for tieback anchors because it provides good load-bearing capacity and stands up well when cut for lagging without caving in. In these favorable zones, the KR 807-7G drilled 75-foot-deep holes in as little as 20 minutes. The crew averaged six anchor installations in an eight-hour day, and easily achieved 10 or more in a 10-hour day when conditions aligned.
Navigating Hard Quartzite Formations
On the south side of the site, Berkel encountered a patch of stubborn Quartzite that was anticipated based on original test borings. The contrast in drilling performance was dramatic:
- Sandy clay and PWR zones: 75-foot hole in 20 minutes of drilling time
- Quartzite zones: Up to 20 minutes to penetrate a single foot of rock
This disparity underscores the importance of thorough geotechnical investigation before anchor installation. The test borings had correctly identified the Quartzite zone, allowing Berkel to plan for reduced production rates in that area rather than being surprised mid-project. For project owners and general contractors, understanding the impact of variable geology on anchor production rates is essential for realistic scheduling.
Production Metrics and Anchor Specifications
The anchor installation at the Capital One complex followed these parameters:
| Parameter | Value |
|---|---|
| Total anchors installed | Nearly 400 grouted tieback anchors |
| Anchor diameter | 6 inches |
| Anchor depth | 65 to 75 feet |
| Standard anchor length | 70 feet (longer where deeper competent material was needed) |
| Average production (8-hour day) | 6 anchors |
| Peak production (10-hour day) | 10+ anchors |
| Excavation depth | 50 feet from ground level |
| Additional work | Tower crane foundation piles, pedestrian bridge caisson |
Why Berkel Standardized on KLEMM Drilling Rigs
Berkel had accumulated a fleet of 11 KLEMM drilling rigs before acquiring the KR 807-7G for the Capital One project. The contractors loyalty to the brand did not happen by accident. It was earned through decades of operating virtually every major drilling rig brand on the market and comparing their performance under real project conditions.
Reliability, Durability, and Smooth Operation
Rhodes identified three qualities that set KLEMM rigs apart from competitors:
- Reliability The rigs keep working day after day with minimal unscheduled downtime. On a project where a rig breakdown could delay the entire excavation sequence, this reliability directly protects the schedule.
- Durability Berkel had experience with other brands showing issues such as hydraulic leakage and heads blowing out bearings. KLEMM rigs, by contrast, required only typical wear-item maintenance throughout the project.
- Smoothness of operation The control systems on KLEMM rigs provide the operator with precise control over drilling parameters, reducing operator fatigue and improving consistency across the work shift.
Operator Davis compared the KR 807-7G to the Cadillac of drilling rigs, noting that other brands simply did not hold up the same way. With other rigs, Davis recalled dreading the possibility of breakdowns that would make for a longer day. The KLEMM changed that expectation.
Historical Context: The World Trade Center Bathtub
Rhodes traced Berkel KLEMM preference back to the contractors work at the World Trade Center Bathtub after September 11, 2001. Berkel had ordered its first two KLEMM rigs, and Rhodes recalled watching them arrive by ship in New York Harbor. On that project, the crew ran 9-5/8-inch casing for tiebacks, with each casing section weighing 400 pounds. The anchors extended 130 feet to rock at a 45-degree angle. The KLEMM handled the weight and casing length in a way that Rhodes said was unlike anything he had seen before. That experience established a standard that other brands could not match in subsequent projects.
Schedule Commitment and Contingency Planning
Berkel started work on the Capital One complex in February 2019 and planned to complete the shoring by August 2019. Rhodes emphasized that staying on schedule was not optional given the demanding general contractor and owner. When asked what would happen if the rig broke down, his answer reflected a contractor who has learned to plan for the worst: Berkel would give the project 100 percent to get it done, whether that meant extended hours, weekend work, or bringing in a stand-in rig. The reliability of the KR 807-7G meant that question stayed rhetorical.
The Capital One complex project demonstrates that successful tieback anchor installation depends on matching the right equipment to the ground conditions. The KLEMM KR 807-7G delivered the production rates needed for nearly 400 anchors while navigating variable geology from sandy clay to hard Quartzite. For contractors evaluating drilling rig investments, the Berkel experience highlights the value of reliability and durability over lower initial cost, particularly on projects where schedule penalties make unplanned downtime expensive.
Contractors working on foundation and shoring projects may also find value in understanding how similar anchoring principles apply across different scales of construction. For those involved in residential or light commercial work, resources such as Shipping Containers Housing Complex projects and Detailed Analysis of All the Basics On Concrete anchors offer practical grounding in the fundamentals. Even the principles of Complete Guide to Well Water Systems Drilling Pumps share common ground with geotechnical drilling in terms of understanding subsurface conditions and selecting the right equipment for the formation.