## 2 Background Studies and Plate Load Test Technique Principles
The test data were categorized based on the orientation of the rock mass discontinuity sets to the loading direction. The study showed that part of the scatter commonly observed in the moduli calculated from plate load tests is due to varying rock mass deformation mechanisms that occur during the test. Furthermore, it was concluded that the theoretical assumptions behind the plate load test are not in full harmony with the observed deformation mechanisms leading to scattering in plate load test data. [PERSON] et al. [11] conducted an investigation of the in-situ viscoelastic properties of a weak rock layer at the Dagangshan hydropower dam project in southwest China employing time-dependent plate load tests. To assess the deformation characteristics of a weak diabase alike layer, in situ large-scale compressive creep tests, using a rigid bearing plate, were carried out. The loading direction was perpendicular to the weak layer. A five-parameter Kelvin model was considered and mathematical equations were derived based on the Boussinesq problem through Laplace transform and inverse transform to describe the deformation-time history considered in the Kelvin model under three-dimensional stress-strain conditions. The finite-difference modeling was used for verification of the results. Based on the derived equations, the rock mass rheological parameters were estimated and it was concluded that the proposed five-parameter Kelvin model produces more realistic results compared to the three-parameter generalized Kelvin model or the standard Burgers model. [PERSON] et al. [12] developed a new constitutive model for the analysis of plate load test results in pyroclastic soft rocks. The developed model has a generalized yield surface including the known criteria and the elastic stiffness is related to stress by a hyper elastic formulation. The model is capable of simulating plastic strain by a set of appropriate isotropic hardening laws. The model was implemented into a finite element code and was used to simulate the plate load tests conducted in pyroclastic rocks. The test results showed specific features of rock response under applied loading conditions, including non-linear elastic behavior and structure degradation which was indicated by the reduction of shear strength parameters. The modeling results showed good agreement with the test data demonstrating the relevance of the developed model for soft rock material investigated. The damage to the rock mass, during loading and unloading cycles, was disclosed by irreversible straining which appeared in the form of plastic strain-induced damaged within the intact rock material. The macro-scale damage was demonstrated in the form of stiffness reduction and strength degradation by the reduction in rock mass cohesion and friction angle. [PERSON] et al. [13] presented a comprehensive comparison of plate load test (PLT) data versus large flat jack (LFJ) data which was carried out side-by-side at the Karun III hydroelectric project in Iran. The comparison included 16 plate load tests and 12 large flat jack tests. PLT moduli obtained from displacements measured in depth were much higher than the LFJ moduli and were sometimes even higher than the modulus of the intact rock material. The analyses showed that the uncertainties associated with plate load tests are caused by the confining effects of the adjoining rock, blast-induced damages induced to test gallery walls, distressing of gallery walls, and the insufficient volume of rock tested. In the plate load test, a cyclic load is applied to the rock mass in small test tunnels, audits, or at the ground surface and the rock mass deformation is measured at various depths beneath the loading plates. The loading system consists of four hydraulic jacks, steel spacers, and circular steel plates of 1 m in diameter which are fitted to flat rock surfaces prepared on the test gallery walls (for horizontal tests) or gallery roof/floor (for vertical tests).