## 2 Background Studies and Plate Load Test Technique Principles  
Since the definition of rock deformability by ISRM [6], various authors have investigated different aspects of the plate load test as a means of measuring in-situ rock mass deformation modulus. [PERSON] [7] gave a review of test principles and discussed the problems associated with commonly used modulus determination approaches. A stiff plate loading system and a multi-borehole displacement-measuring system were introduced. Emphasis was given to the description of the test set-up, test theory, and the interpretation of the test results. To illustrate this, typical results obtained from a test carried out in an underground test drift, are presented in the form of a stress-strain relation. The drawbacks of the ISRM-suggested method was discussed and alternative solutions were proposed. A comprehensive application of the plate load test at the Yucca Mountain project was presented by [PERSON] et al. [8]. The obtained results from sets of plate loading tests conducted by Sandia National Laboratories at the Yucca Mountain test site (Nevada, USA) was presented. The findings of these in situ tests as well as approaches undertaken for the determination of rock mass modulus were described. The obtained field data were compared against existing empirical methods and numerical modeling results. In this study, the in-situ rock mass stiffness was evaluated for both ambient temperature and thermally perturbed rock masses. Rock mass deformation modulus was estimated employing empirical techniques, borehole jacking test, numerical modeling, and the plate load test. The study suggests that the PLT rock mass modulus values better represent the actual response of the rock mass. [PERSON] and [PERSON] [4] presented a comprehensive comparison between in situ tests and indirect estimates of rock mass deformation modulus. The Goodman jacking test, rock mass classification-based methods (RMR, Q, RMi), and plate load test method of deformation modulus assessment were compared. The existing equations for indirect estimates of the rock mass deformation modulus from classification systems have been analyzed and adjustments are suggested. It was concluded that provided that a good in-situ characterization of the rock mass is carried out, these methods may determine comparable or possibly better modulus values taking into consideration the uncertainties associated with in situ deformation measurements caused by blast damage, test procedure, and test method. Estimates based on the RMR and RMi systems show better deformation modulus values for jointed rock masses than the Q system. It was suggested that the RMR system overestimates the rock mass modulus in massive and competent rock masses. RMi system gives better estimates of modulus for massive rock than the Q and the RMR systems. It was concluded that the plate jacking test, in which the deformations are measured by extensometers in drill holes, produces more realistic results compared with other direct measurement techniques. [PERSON] et al. [9] presented a comparison of empirical methods used in rock mass deformation modulus assessment. The plate load test data from a dam construction site was used in conjunction with a fuzzy interface system for the comparison of the results. A set of statistical analyses was conducted and it was concluded that a combination of empirical and fuzzy methods produces satisfactory results provided enough input that is available for the fuzzy interface system. The study concluded that the elasticity modulus of the intact rock, RQD, and weathering degree are the most important parameters affecting the rock mass deformation modulus. [PERSON] et al. [10] presented a comprehensive interpretation of plate load test data conducted at the Bakhtiary Dam site project in Iran. The results of 26 plate load tests carried out at the Bakhtiary dam site were investigated to delve into the mechanisms involved in the plate load test.