type anchor is shown in figure 4.5. To install this type of anchor, it is necessary for a hole to be drilled slightly larger than the expansion parts. The hole is usually made with an auger and bit capable of penetrating the existing rocky soil or rock-like material. For harder rock, air-percussion or core drilling may be necessary. The expanding rock anchor may be anywhere from 24 to 48 inches (0.6 1.2 m) in overall length. The installation principle is very simple. Once the hole has been cleaned out to the desired depth, the anchor is inserted to the appropriate depth. The anchor head is turned, forcing the two anchor components to slide upon each other and thereby increasing their diameter. The anchor is turned until the installation torque, as specified by the manufacturer, is reached which allows the expandable part of the anchor to bear against the sides of the hole surface. The anchor is then available for immediate loading. In softer or weathered rocks, there may be a tendency for the outside portion of the rock anchor to punch into the sides of the hole, allowing the center portion to slip out. If this is the case, then grouting is necessary to hold the anchor in place. Under these conditions, a second anchor is installed, tightened to a lower torque (less chance of wall punching), and the hole is filled with grout (91b). Another type of anchor may be used in soil or rock locations where drilling is necessary. This circular shaft anchor is inserted into a pre-drilled hole 30 to 48 inches (0.8-1.2 m) in length and about 2 inches. (50 mm) in diameter, then expanded by means of hydraulic pressure. The hydraulic pressure forces out a multiple internal split tube anchor, forming six individual curved prongs which enter into or bear against the soil or rock hole. Finally, the top portion of the anchor tube is expanded. This type of anchor performs very well in softer or weathered rocks, as intimate contact is made with the side walls. (A) Inserted Figure 4.5 Principle of Expanding Rock Anchor: 4.3.6 Miscellaneous Anchors Several other anchor types are either presently available for mobile home use or could be modified to serve this purpose. Some of these are discussed hereafter. Several manufacturers offer an "X" type anchor for use in rock or rocklike material. Manufacturers suggest that this type of anchor be used when it is impossible to install, for example, a helix anchor due to rocky conditions. Pointed rods approximately 3/4 inch (19 mm) in diameter and 3 to 4 feet (0.9 1.2 m) long are either driven directly into the ground or into a pre-drilled hole at an angle of 45° from the horizontal. A second member is driven at an angle of 90° to the first anchor rod. The anchors are driven so that they fit inside a welded brace made of tubing as shown in figure 4.6. Anchor straps are attached to hardware which is welded to the top of the X-brace. This type of anchor obtains its load capacity when both members bear against the surrounding foundation material. In the event that this material yields under this load, or if bending occurs in the steel rods, the resulting displacement may exceed the allowable displacement. The soil conditions under which this anchor is useful appear to be limited. In order for the anchor to be installed, the foundation material has to be soft enough for penetration, yet hard enough to resist lateral deformation. Test data on this device are limited. It has been found that grouted rods provide economical anchorage in relatively firm soils, such as dense sands and gravels, stiff clays, glacial tills, and weathered rock. Typically, a 6-inch (0.15-m) diameter hole (sometimes having a bell at the bottom) is made, and deformed or plain steel rods up to approximately 1-inch (25-mm) in diameter or heavy duty chains are inserted in the hole. The top of the rods or chains must contain some mechanism to tie down the mobile home. The hole is either partially or completely filled with grout and allowed to cure. [The grout generally used consists of equal amount of sand and Portland cement ANCHOR ROD RIGIDLY ATTACHED CROSS BRACE (ROUND OR SQUARE) ROD DRIVEN IN SOIL/ROCK Figure 4.6 "X Type Rock" Anchor with a water-cement ratio approximately 0.5 [87].] The larger diameter of the grouted hole provides considerable horizontal load resistance to the anchor. Economical tiedowns can also be provided by dead-man anchors. They can be improvised in many different ways, provided the system is durable enough. Examples of dead-man anchors are shown in figure 4.7. In both examples in the figure a hole is dug and either a J-shaped anchor rod is placed in concrete and properly backfilled or an anchor rod is attached to some element and placed at a minimum depth of at least 5 feet (1.5 m) [46]. 4.3.7 Tie-down Systems Other Than Soil Anchors Tie-down of mobile homes can also be provided by methods which do not require the use of soil anchors. These could include footings similar to those used for conventional single-family homes or any other suitably durable system capable of resisting the vertical and horizontal forces exerted by the mobile home when subjected to extreme wind or flood conditions. Safety factors against sliding and overturning should not be less than 1.5 and factors against bearing capacity failures not less than 2. Examples of such tie-down systems are shown in figure 4.8. These systems are 4 in. (0.10 m) thick wire mesh reinforced concrete slabs on grade, which may have other configurations in addition to the ones shown. Examples of tie-down connections to the slabs are shown in figure 4.9. The tie rods may be installed in finished slabs by drilling a hole and inserting a bolt, as shown in the figure. A single excavation would then be required to gain access for installation and tightening of the nut and washer. Alternately, commercially available expanding concrete inserts could be used. Another option is to use the J or L shaped anchors shown in figure 4.9b. Problems may arise with the use of cast-in-place anchor bolts if the |