and calculated anchor capacity is poor, particularly for granular soil. The mobile home industry uses the Standard Penetration Test (SPT), Soil Test Probe (STP) or visual soil descriptions to select anchors for given site conditions. The SPT provides a fairly reliable indication of soil properties for granular soils but only a very crude approximation when cohesive soils are investigated. It is questioned if those who use the SPT for anchor design are aware of these facts. The Soil Test Probe may provide an indirect measurement of soil shear strength which governs the pull-out capacity of anchors. However, based on the available data (or perhaps because of the absence of adequate data), the correlation between the STP readings and pull-out capacity is not obvious and further experimental (field) study is required. Since some soils change strength and therefore anchor holding capacity seasonally, some method of taking this strength change into account for design purposes is required. Available information and present design procedures do not account for this problem. Similarly, little information is available on adequate design of mobile home anchors in expansive soils and soils that undergo seasonal frost heave. There is an almost complete lack of information on the effects of cyclic (Dynamic) loading on anchor capacity. Since wind loads are cyclic and soil strength generally deteriorates with increasing numbers of loading cycles, dynamic loading effects should be further investigated. 4. TEST STANDARDIZATION One of the main reasons for our inability to correlate soil and rock properties with pull-out capacity is the overall lack of adequate data in the mobile home anchor literature. In order to determine this correlation, test data should convey the following information: A. Complete load versus uplift displacement data in order to establish the ultimate loads as well as displacement characteristics for a given anchor and depth of embedment in a specific soil 1 B. C. D. Complete description of the anchors used, their depth of An evaluation of the soil properties and the location of the ground water table at the site. The soil properties determined should include the shear strength parameters and the soil weight per unit volume (density). These properties should be determined by field and/or laboratory tests other than the SPT or STP. The results of Standard Penetration Tests, Soil Test Probe All four items should be provided together to develop correlations. Typically only 2 or at best 3 of the 4 items are available in existing data. In Item A above, the need for pull-out load-displacement data is mentioned. Presently, there is no standard method for performing pull-out tests in the mobile home anchoring industry. As a result, the precision, accuracy, and amount of information typically provided in a pull-out test report is deficient when compared with a typical ASTM standard test. Most available load test reports list the soil class as determined visually without any shear strength indicator. 5. RECOMMENDATIONS The following is recommended on the basis of this study: To adopt an industry-wide soil classification system including a standard nomenclature to define soils and rock; to prepare a standard method of performing anchor pull-out tests in the field, including minimum requirements for the characterization of soils; to conduct a test program in order to establish correlations between anchor pull-out capacity and several in-situ tests, and to determine effects of dynamic, cyclic, and sustained loading, loading which is not in the direction of the anchor shaft, and anticipated seasonal changes in the moisture content of the soil; to develop a standard performance test by which the adequacy of anchors can be determined. |