Schwing Line Pumps Instrumental in Economical New Construction Method 2003

Soil and rock nailing is a relatively new construction technique first utilized in Europe to stabilize and construct tunnels. In North America it is quickly becoming a popular method of soil and rock retention, slope stabilization, and shoring. Soil nailing provides project owners economic benefits and with the help of a reliable concrete pump, a rapid means of constructing earth and retention support systems and retaining walls. According to Ken Abud, Business Development Manager for The Judy Company, Kansas City, a reliable concrete pump is what makes the technique work. One of a relatively small number of contractors performing soil nailing, The Judy Company constructs retaining walls and barrier construction using Schwing 450 and 750 trailer-mounted concrete pumps.

Soil nailing projects generally follow the same basic procedure. Geotechnical engineers design the soil nailing taking into account soil compatibility, and direct the contractor in hole location, nail size, length, and location as well as strength requirements of the grout and shotcrete. The technique, appropriate in many cohesive soils or fragmented rock, is top-down construction.

A bench is excavated ranging between four and six feet in height. Holes are drilled into the excavated face typically measuring 6-8-inches in diameter in soil and 3-4 inches in rock. Typically holes are angled at 15 degrees below horizontal. The hole is pumped full of ready-mixed grout soon after drilling to ensure the hole remains open. Nails, generally continuously threaded steel bars, are long enough to penetrate the failure plane of the excavation, and are inserted immediately following grouting. The nails are equipped with centralizers to ensure central placement in the grouted hole. The concept is to stabilize the soil by creating a grouted mass that the surrounding soil will act upon in friction. The grout also provides corrosion protection for the nail. Once the grout sets, the protruding nails are fitted with a steel plate to transfer forces from the wall to the nail. Horizontal and vertical drain strips are then installed onto the facing to control seepage and eliminate hydrostatic pressure buildup.

Reinforcing steel is applied and the face is shotcreted. For temporary walls, as in shoring or behind a cast-in-place concrete finish, the surface can be left rough or lightly troweled. For permanent walls, the shotcrete can be hard troweled or even sculptured and stained to blend into the natural surroundings depending on the desired look.

Because of the potential that the soil will collapse after being excavated, a soil nailing contractor only cuts as long a bench as crews can complete in a 24-hour period. "You cut only what can be finished in a day, shotcrete and everything."

According to Abud, grouting is key to the process in a soil nailing project and stresses the importance of a reliable concrete pump for grouting the holes and applying shotcrete. "On any given job, whether it’s the 750 or the 450, the pump is almost continually working, so it must be reliable. It is the key to making the technique work, maintaining productivity, and staying on schedule and budget."

"It’s a precise technique, a terrific method for permanently retained walls, temporary excavation shoring or slope retention," says Abud.

Soil nailing has several applications, and Judy Company has been contracted for a range of projects across the nation. The Judy Company recently completed an 8500-square foot wall in Pike County, Kentucky as a subcontractor. The original plans required a cast-in-place wall in front of the shotcrete shoring. As an alternative, The Judy Company proposed a soli-nailed and shotcreted wall sculpted and stained to look like adjacent highway cuts. The proposal was accepted and Boulderscape, of Capistrano Beach, California, was contracted to place and sculpt the shotcrete. Working from a manlift the shotcrete was placed with a BP750 pump. Sculptors from another man lift carved the shotcrete from the top down using hand trowels and brushes, emulating natural rock formations in the area. After curing, the wall was stained making the finished product look like a natural cut.

The Judy Company at the same time was finishing a massive, 63,000 square foot soil nailing project on I-235 in Des Moines, as specified by the Iowa DOT. Crews finished over 1500 square feet a day.

Judy Company President Pat Carr says the Des Moines project was a true testimony to soil nailing as a successful soil retention technique. Using top-down construction and this technology, the highway could be constructed in the minimum right-of-way. Soil nailing allowed excavation very close to city streets and utilities and eliminated detours during construction."

Soil nailing is also applicable in building construction, particularly when job site space is limited and property lines leave no room for cut and slope methods. The Judy Company utilized soil nailing technology to construct a retaining wall in Gladstone, Missouri for construction of a new Home Depot. The site required a 26’ cut along two walls. The adjacent property owners would not allow easements for anchors and there was not enough room to lay back the soil. Conventional retaining systems such as a proposed concrete cantilevered wall would have been very expensive. The Judy Company proposed a soil nail wall system with a finished face and provided the owner significant savings. Even working under winter conditions, the 20,000 sq.ft. wall was finished in 40 work days. This couldn’t have happened without reliable equipment.

Judy Company utilizes their two Schwing pumps, a 450 and a 750, in soil nailing projects around the nation. Judy Company President Pat Carr commented on the value of Schwing products and service in the field. "Schwing, through their Kansas City distributor, Brundage Bone, provides us with everything we need. No matter where we are in the U.S., they coordinate with other Schwing distributors to make sure we have the parts and maintenance help we need to keep going. We need our pumps to be operational every second onsite, and the excellence of Schwing pumps and their backup organiza