Abstract: The response time of a tensiometer  can be used to estimate the hydraulic properties of unsaturated soils, and it is also a critical parameter to assess the applicability  to the measurement of the transient matric suction. In order to determine the response time of tensiometer more reasonably and efficiently, Jingyang loess, Dingbian loess and Maowusu sand column tests were conducted to investigate the characteristics of time response curve of tensiometer. In addition, the numerical optimization methods based on the universal global optimization (UGO) algorithm were used to evaluate the response time of tensiometer. The results of soil colum tests show that the time response curve of tensiometer for soils can be divided  into three stages: Tensiometer installing stage, delayed response stage (pressure difference response stage), and equilibrium stage. Comparing  the results of the graphical method and the numerical optimization method, it is recommended that the delayed response stage and equilibrium stage  are fitted by a quartic function equation and a linear function equation, respectively. Moreover, the Levenberg-Marquardt optimization method with UGO algorithm (LM+UGO), BFGS quasi-Newton method with UGO algorithm (BFGS+UGO), and conjugate gradient method with UGO algorithm (CGM+UGO) are the appropriate numerical optimization methods to determine the response time of tensiometer in general conditions. 

Key words: response time, matric suction, tensiometer, unsaturated soil, numerical optimization