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Abstract

The aim of this research is to improve the design of working platforms for tracked plant in order to guarantee safety but also a more economical approach to the design. The reason for this concern derives in part from incidents of overturning plant which have taken place in the past, some of them resulting in injuries and/or death of operatives, but also from the consequent use of excessively conservative and therefore uneconomical design.

Common practice for the design of working platforms is the use of bearing capacity methods normally adopted for the construction of spread foundations. The objective of this approach is the definition of an appropriate platform thickness which is back calculated from a bearing capacity equation. According to this type of design, the thickness of the platform changes based on the characteristics of the platform material and of the subgrade. Among these factors, the one having more influence on the resulting thickness is the design angle of friction of the platform material, which therefore need to be accurately established.

A common laboratory method used to measure the angle of friction of soils is the direct shear test. Difficulties in the correct interpretation of the results of this test are mainly associated with the presence of scale effects. As extensively reported by literature, scale effects can derive from testing material with a large particle size which is not suitable for testing in a standard apparatus, that would cause the shear strength of the material to be overestimated. A solution to this issue often consists of testing a scaled sample of the material using the standard apparatus. Nonetheless, even this approach can induce scale effects leading to an underestimation of the angle of friction when an important reduction in particle size is produced.

Another method used to derive the angle of friction of the platform material is the plate bearing capacity test which is normally conducted on site. In order to guarantee reliable results for the bearing capacity of the material and the derived angle of friction, an appropriate ratio between plate diameter and particle size must be used. The problem of this method is associated with the high costs of the testing apparatus which are substantially increased by the large particle size of the material requiring large plate diameters to be used during the test and consequently high reaction forces to be applied.

In order to investigate the scale effects associated with testing the material at smaller scale using the standard shear box apparatus and with using different plate diameters in case of plate loading tests, a series of small scale direct shear tests and plate loading test using a centrifuge model were conducted on two small scale samples of crushed limestone. The results of these tests were used to derive the angle of friction of the material and were compared with the ones obtained from testing the same material at full scale using a large shear box apparatus which was designed and manufactured for the purpose of this research. Comparison of the results allowed to identify the magnitude of the scale effects on the value of the angle of friction of the material. Differences in results should be taken into account in order to define an appropriate value for the design.

Publication Type:	Thesis (Doctoral)
Subjects:	T Technology > TA Engineering (General). Civil engineering (General)
Departments:	Doctoral Theses School of Science & Technology School of Science & Technology > Computer Science

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