Thermal expansion of Neapolitan Yellow Tuff

Summary In saturated rocks and soils it is possible to define different coefficients of thermal expansion depending on the drainage conditions. This topic is first examined from the theoretical point of view with regard to an ideal isotropic thermo-elastic porous medium. Some special features of the behaviour of natural soils and rocks during thermal expansion tests are subsequently discussed. An experimental evaluation of some of these coefficients is presented in the second part of the paper. The material investigated is a pyroclastic rock, the so-called Neapolitan Yellow Tuff. Thermal expansion coefficient in drairend conditions has been evaluated, when this material is saturated with water. The e pressure increase induced by heating has been measured in undrained tes temperatures investigated range between room temperature up to 225°C.Different types of apparatus have been used and, when possible, a comparison between the results has been proposed. The results obtained in undrained thermal expansion tests are in agreement with theoretical predictions. This research is part of an on-going study of the complex phenomena known as Bradyseism, which is occurring in a volcanic area a few kilometers from Naples (Italy). Some considerations on this phenomenon are drawn in the last paragraph of the paper.List of Symbols _l linear thermal expansion coefficient - _s volumetric thermal expansion coefficient of the solid phase - _ss volumetric drained thermal expansion coefficient of the solid skeleton - _st volumetric drained thermal expansion coefficient that takes into account variations of porosity induced by heating - _t volumetric drained thermal expansion coefficient of the whole system - _u volumetric undrained thermal expansion coefficient of the whole system - _v volumetric thermal expansion coefficient - _w volumetric thermal expansion coefficient of the water - _l^* volumetric thermal expansion coefficient of the distilled water - Biot's coefficient - _d dry specific gravity - _s specific gravity of the solid phase - _r^' uniaxial compressive strength - _r^' yield stress in isotropic compression - B_T parameter relating undrained thermally generated pore pressure with temperature change - d₀ maximum uplift during Bradyseismic crises - d_f residual uplift during Bradyseismic crises - K_s compressibility modulus of the solid phase - K_ss compressibility modulus of the solid skeleton - K_w compressibility modulus of the water - n porosity - T temperature - T₀ initial temperature in thermal expansion, tests performed in thermal expansion cell - T_m temperature at which the volume of waterV_Eexpelled from thermal expansion cell. is measured - V volume of the solid skeleton - V_E volume expelled from thermal expansion cell - V₀ volume of the expansion cell at temperatureT₀ - V_s volume of the solid phase