| Summary: | 碩士 === 國立中央大學 === 應用地質研究所 === 92 === Single-well tests are less expensive than multiple well tests in hydrogeologic investigation.
Single-well tests also withdraw limited amount of water and hence are suitable for
contamination sites. The dipole flow test (DFT) is a single-well circulation flow test (CFT),
which generates a circulation flow field in the aquifer by pumping water in the upper well
screen section using a constant flow rate +Q and discharging the pumped water through the
lower well screen section in -Q. In theory, DFT is able to estimate the horizontal hydraulic
conductivity (Kr), the vertical hydraulic conductivity (Kz), and the storage coefficient
(S).However, field experiments of DFT under different hydorgeological conditions showed
that DFTs reached steady state rapidly, unfavorable for the estimation of Kz and S. This
study improves the design of DFT, and develops the constant head circulation flow test
(CHCFT), which generates a circulation flow field in the aquifer by pumping water in the
upper well screen section using a positive constant head and discharging water through the
lower well screen section using a constant negative head (drawdown). This constant-head
condition renders CHCFT to reach steady state after a long period time, during which Kr,
Kz, and S can be determined without difficulty. However, current constant drawdown
pumping techniques can not discharge water continuously with a constant water level
between 8 to 45 meters below ground surface, and makes the application of CHCFT
limited. Hence we replace the constant drawdown pumping in CHCFT with a constant rate
pumping which has less limitation on the drawdown level and develop another CFT model:
constant rate – constant head circulation flow test (QHCFT). Due to two different pumping
techniques are applied in two different screen sections, QHSCT reaches steady state after a
long period as CHCFT, and Kr, Kz, and S can be determined without difficulty. When
developing CHCFT and QHSCT, both confined and unconfined condition with skin effect
are considered, and the type curve analysis is tested with hypothetical data for the
determination of skin factor (Sk), Kr, Kz, and S. It is found if skin exists but its effect is
neglected will result in a false determination of Kz and S.
|
|---|
