and soldier piles, as shown in figure 8-11.

INTERLOCKING SHEET PILES consist of steel pilings that can be reused many times and offer the additional advantage of being watertight. Each individual sheetpiling is lowered by crane into a template that holds it in position. Then the piling is driven into place with a pile driver. Install braces to help support the metal sheets.

SOLDIER PILES are H-shaped piles that are driven into the ground with a pile driver and are spaced between 3 and 10 feet apart. Refer to the plans and specifications for spacing requirements. Three-inch-thick wood planks, called

lagging, are placed between the flanges or directly against the front of the piles. You may use 2-inch blocks for spacing between each plank or butt the planks together depending on the specifications. Soil conditions and the depth of the excavation may require

tie-backs that consist of steel strand cables placed in holes drilled horizontally into the banks of the excavation. The holes are drilled into the banks of the excavation with a power auger and are often 50 feet or more in length. The tie-back cables are inserted through an opening in the pile and are secured in the earth by power grouting the hole.

After the grout has set up, a strand-gripping device, consisting of a gripper and gripper casing, is placed over the cables. A hydraulic tensioning jack is used to tighten the cables. When the jack releases the cables, the gripping device holds them and maintains the required tension against the pile. The number of tie-backs required should be determined by an engineer whose decision will be based on soil conditions and the depth of the excavation. Some soldier pile systems may also include a heavy horizontal steel waler held in place with tie-backs. This technique is similar to constructing a single waler system for concrete - same basic principle.

In many instances, it is necessary for the excavation for a new building to be carried right up to the foundation of an existing one. This presents a problem if the new excavation is to be deeper than the footings of the existing building. Part of the support for those footings will be removed, and it is the BU's responsibility to protect the building against movement caused by settlement during and after construction of the new building. Temporary support may be provided by SHORING or NEEDLING, while permanent support is provided by UNDERPINNING - extending the old foundation to the level of the new one.

A common method of support for adjacent structures is by the use of 12 by 12 timbers, called SHORES, inclined against the wall to be supported and extending across the excavation to a temporary FOOTING consisting of a framework or mat of timbers laid on the ground. Fit the upper ends of the shores into openings cut in the wall, or butt them against a timber bolted to the wall. Place steel SADDLES in openings cut in concrete or masonry walls to support lifting or to steady shores.

Figure 8-11. - Soldier pile systems.

As a good practice, set shores as vertical as possible to reduce lateral thrust against the wall. Whenever possible, locate the heads at floor level to minimize the danger of pushing the wall in.

Make the provision for inducing a lift or thrust in the shores by inserting jacks between the bases of the shores and the footing. Use a standard steel screw jack with the capabilities to lift as much as 100 tons for shores. When a single screw jack is used with a shore, a hole is bored in the base of the shore to admit the threaded portion of the jack, and the arrangement is called a PUMP. For a larger lifiing effect, a pair of jacks are attached to a short timber called a CROSSHEAD. An advantage of crosshead arrangements is that after the lift has been applied, the crosshead can be blocked and the jacks removed for use elsewhere.