Unstable soil can cause a home’s foundation to settle, which can lead to cracked walls and sloping floors. In the past, the only solution entailed major excavation and enormous expense. But an anchoring system long used to support bridges, pipelines and telephone-pole guy wires is now available, offering an easier, more affordable way to stop settling and correct related problems.
The system sold and installed by the A.B. CHANCE Co., can be put to work with minimal disturbances to the surrounding property. It uses a load-bearing helical pier that consists of a steel, helix-shaped screw head attached to a galvanized steel rod. The piers are driven deep into the ground so that the weight of the house is supported by stable soil.
To install a pier, an engineer first selects precise locations around the foundation, based on the weight of the house and the existing soil conditions. The contractor digs each hole down to the footing. Then a 2ft-wide notch, which accommodates a support bracket, extends beneath the foundation wall.
Using a high-torque hydraulic or electric drive head, the contractor screws the helical pier into the ground until it reaches solid soil. An engineer can calculate the pier’s load-bearing capability based on the amount of torque it takes to drive the pier.
Next, a heavy-duty L-shaped support bracket is bolted to the base of the foundation wall. The contractor sandwiches a hydraulic piston between the pier top and the bracket, and the foundation is literally pumped up. With a central controlling device, multiple pistons can be precisely controlled from one location. Finally, heavy-duty lock-off plates are secured and the holes are backfilled.
If a concrete-slab floor has settled, the same piers can be used with different brackets to raise it. Here, The contractor cuts a 12-in.-dia. hole in the slab and drives a pier to the proper depth. Then a 16-in-long channel is fitted under the slab so it rests on the pier and spans the diameter of the hole. The channel has a threaded hole positioned directly above the pier. The contractor screws a bolt into the channel and tightens it against the top of the pier, thus drawing the channel upward to raise the slab. By using a torque wrench, he can avoid applying too much pressure to the slab. To finish, the hole is filled with concrete.
In new construction, helical piers can be used to support a foundation in unstable soil. In such a case, however, a foundation contractor will install helical piers before the footings are poured. The piers are capped with a steel bracket that’s tied to reinforcement bars prior to pouring the footings.
Contractors using this system offer different long-term guarantees based on local conditions. some last a lifetime and can be transferred to a new owner. Check with a contractor and the building department before proceeding.
Straightening Concrete Walls
Horizontal cracks along a foundation wall may indicate damage caused by soil movement. If allowed to continue, the cracks can undermine the home’s structure. However, with careful excavation and the use of helical anchors, buckled walls can be permanently straightened and secured.
To correct the problem, a contractor first digs a narrow trench along the outside of the foundation wall to relieve pressure and provide room for straightening the wall. the open trench also provides a way to see that the foundation drainage system is in order.
At the center of the buckled section and 6 ft. to the left and right, a 1 1/2-in.-dia. hole is drilled through the wall. From the inside, a 1/2-in. galvanized steel rod is inserted through the hole. Outside, a helical screw head is threaded onto the top of the rod, and together these pieces form the helical anchor.
From the inside, a hollow square shaft slips over the rob and through the hole; the shaft locks onto the screw head. Then using a drive motor, the contractor screws the helical anchor deep into the earth until it reaches the solid soil.
A ribbed steel plate is slipped over the protruding rob, followed by a nut. Tightening the nut draws the wall straight.
After the wall has been straightened, the excess threads are cut off the rod.