Theoretical Analysis On Response Lag Of Water-level Observation Well

The problem of response lag of water-level observation well of which engineers and technicians concerned deeply, has not been solved properly. It is very beneficial for the settlement of seepage problem in geotechnical survey, design and construction to further study this problem. Owing to the complexity of matter, the prehuman research fruit was founded generally on trials and numerical simulation, nevertheless, it is very lack of the research fruit in theory. Therefor, the questions including the settlement of observation-well lag time, the observation time requirement of the unsteady flow pumping tests in confined aquifer with completely penetrating wells and the water-level observation values approaching the true values etc. were studied theoretically and discussed in the text.The origin and balance mechanism of water-level differences inside and outside the observation well were analysed with a view to the basic structure of water-level observation wells. The contact area of the whole inlet part and soil surrounding well was treated as the water-collecting area of the observation well seepage quantity. The theoretical equation for solving the lag time of the observation well was derived.On account of the characteristic that the initial water-level difference was determined easily in slug tests, the method that ascertained the lag time of observation wells by water-level recovery tests was summarized, thereinto, the water-level recovery data were fitted optimally with multinomial curve by the optimized least-square method. The results of the text arithmetic and Hvorslev's means were analysed contrastingly, in virtue of the instance of the input fall-head slug test.Based on the drawdown Theis formula of the unsteady flow pumping tests in confined aquifer with completely penetrating wells, the drawdown formulas of water-level inside observation wells with response lag were derived, at the same time, considering the locality of initial water-level. The influence factors of the drawdown inside observation wells were analysed, and so as the observation time required for satisfying engineering requirement.Considering the non-visualisation of ground-water level, the analytic solutions of water-level equations outside the observation well were derived, based on the differential...