anchors reviewed in his study, Berus mentioned that one anchor stands out as a potential mobile home anchor; this anchor is called the universal ground anchor by the military [86, 100] and is known commercially as the arrowhead or triangular shaped anchor and is discussed in detail in the next section.

4.2.2 Triangular or Arrowhead Ground Anchor

The arrowhead-shaped earth anchor is driven directly into the supporting soil. Anchors are typically one piece malleable iron castings, stamped steel, or aluminum in certain sizes, with attached wire, cable or metal rods as shown in figure 4.1. Some anchors have coatings protecting them from rusting. The anchors range in size from 2 inches to 17 inches (50 mm to .43 m) with a base width and height of the same dimension. For example, a 6 inch (150 mm) anchor is one having a top width of 6 inches and a height from top to arrowhead tip of 6 inches. The triangular-shaped ground anchors are driven by a steel driving rod which is positioned over the anchor spindle and driven at the desired angle with respect to the horizontal by means of repeated blows of some hammer. The method of driving depends on the soil type, anchor size, and desired depth of penetration. The anchor is driven to the desired depth (at least 6 times the anchor size) and the driving rod is removed. The anchor has an attached guy line or metal rod which follows the driving of the anchor. The guy line is attached off the center of gravity of the anchor such that when a pull-out force is applied, it causes the anchor to rotate in the ground through an angle of approximately 90°. In this way, the full triangular bearing surface becomes more or less perpendicular to the direction of pull and maximum pull-out resistance is developed. This means that preloading of the anchor after it is driven is an important aspect of the anchor installation.

The origins of the triangular anchor go back to the early 1950's. One of the earliest geotechnical investigations of the triangular shaped

ground anchor was performed by Haley and Aldrich for the Laconia Malleable Iron Company [44]. A U.S. Army Quartermaster report [86] documents initial tests on what is now the Army's universal ground anchor. Other anchors investigated by the military but excluded from further study in this report due to their low holding capacity include: the Air Force Standard Arrow Anchor, used to moor lightweight aircraft; the modified Standard Arrow Anchor; the Seaplane Auger, the Barbed Wire Entanglement Securing Pin; the Experimental Spade Pin; the Barbed Wire Picket Pin [20].

The federal supply system has a guy anchor that consists of a 2 foot (0.61-m) long, 3/4-inch (19-mm) diameter reinforcing rod welded to a 1/8-inch (3 mm) thick 12-inch (0.30-m) diameter steel plate. These anchors weigh 6 1/2 pounds (3.0 kg). These anchors were studied, together with a disc type anchor, a two leg anchor, and the universal arrowhead anchor, to see which anchor would be most suitable in holding down membrane surfaced assault airfields [104]. Not all of these anchors are capable of meeting the requirements for a mobile home soil anchor.

Tucker [97] studied the ability of flat plate anchors as well as 4-inch (0.10-m) arrowhead anchors used to hold in place a neoprene coated nylon membrane to be used as an Army helicopter landing pad. In all cases he found that the arrowhead anchor was superior to the flat plate anchor. However, the actual pull out capacity of these anchors was below that which is required for mobile homes due to the size of the anchors [4 inches (0.10 m)] and limited depth of embedment [30 inches (0.76 m) only]. The above results were confirmed in another study by Grau [43] in which the guy anchor, the disc anchor, the two-legged anchor and the arrowhead anchor were studied. For the prevailing soil conditions and depths of embedment, the arrowhead anchor proved to have the greatest holding capacity.

4.2.3 Other Government Studies on Anchor Types

Taylor et al., 1975 [92] lists approximately 2 dozen types of anchors of various sizes and manufacture that are primarily used in the marine

environment.

The types of anchors identified and documented include propellant-actuated direct-embedment anchors, vibrated direct-embedment anchors, screw-in anchors, driven anchors, drilled anchors, dead weight anchors, and free fall anchors. Most of the anchors discussed in this excellent handbook have capacities in excess of 10,000 lbf (44 kN) and would not be directly applicable to the anchoring of mobile homes. ever, some of the types mentioned, namely screw-in anchors and, driven anchors, when properly scaled down in size, could provide suitable tiedown for mobile homes. These anchors will be discussed in greater detail in the section dealing with commercial anchors.

How

Other military anchors include ballistic or explosive earth anchoring systems in which an explosive, or charge, or high pressure device would be used to drive an anchor into the ground. The suitability of such anchors in the mobile home industry is questioned for reasons of safety as well as licensing problems that no doubt would occur. These anchors

were not further studied nor referenced.

4.3 ANCHORS AND PROPRIETARY EQUIPMENT AVAILABLE FROM COMMERCIAL COMPANIES

4.3.1 General

Many types of commercial anchors are available for different soil and rock conditions and for conditions where the mobile home is to be tied directly to a concrete slab. Available anchors are identified generically and according to their intended use in certain soil and rock deposits. Although an all-inclusive description of available anchors was attempted, undoubtedly a few anchors escaped the attention of the authors.

The following discussions of anchor types are presented in random order and should not be construed to imply rating in terms of potential use.

There are many ways in which a mobile home anchor can be installed. For example, depending upon their type, soil anchors can be driven, turned in (twisted) under a normal (vertical or inclined) load, or placed in a

partially excavated hole and then either driven or turned in. In the case of rock anchors, a hole is usually excavated and the anchor is installed either by tightening of the anchor shaft itself or by filling the space around the rock anchor with cement grout (a mixture of water, sand, and cement in appropriate ratios to adequately bond the anchor to the rock). The various types of anchors are discussed in the following sections.

4.3.2 Helix and Multi-Helix Anchors

One of the more common (mobile home) anchors is the helix or multihelix anchor (see figure 4.2). Anchor sizes range from 3-in (0.08-m) diameter to 15-inch (0.38-m) diameter (for very high capacity anchors not used for mobile homes). Anchors are also available in twin 4-in or twin 6-in helix arrangement. Typical installation is performed by applying a vertical load to the anchor while it is "turned" into the ground to the desired depth. This turning or torquing can be done either by hand or by a power tool. Under these latter conditions it is appropriate to measure the installation torque in units of ft-lb or in-lb. In accordance with information obtained from anchor manufacturers, the pull-out capacity in lb is approximately 10 times the installation torque in ft-lb. This number should be field verified in each location. Minimum recommendations for anchor rod diameter and depth of embedment for both 6- and 8-inch diameter helix anchors suggested by Harris [46] are shown in figure 4.3. Klym's [60a] experiences at Ontario Hydro indicate that, to be fully effective, the helix anchor should have a minimum embedment of 5 helix diameters and that the top helix should be below the anticipated frost line. For multi-helix anchors, the pitch [and spacing] of the helix are designed to make the top helix follow the same helical path as the bottom helix to ensure minimum soil disturbance. soils, disturbance will cause a significant reduction in the holding capacity of the anchor. These considerations are discussed in the following sections of this report. Multi-helix anchors were found to be more suitable when installed in medium to stiff clays and medium

In some