A case history of field pumping tests in a deep gravel formation in the Taipei Basin, Taiwan

doi:10.1016/j.enggeo.2010.10.001

Engineering Geology

Volume 117, Issues 1–2, 10 January 2011, Pages 17-28

https://doi.org/10.1016/j.enggeo.2010.10.001 Get rights and content

Abstract

33 large-diameter wells embedded in 2-m thick, 63-m deep diaphragm walls were constructed to reduce both the uplift pressures and the groundwater inflow during the excavations. As the actual thickness of the pumped aquifer is unknown, the installed wells are regarded as partial penetration wells. Single-well and multi-well pumping tests were conducted in the deep gravel formation of Taipei Basin to derive the hydraulic parameters and to investigate the drawdown characteristics at both the construction and remote sites. However, the tidal effect on the drawdown of both the pumping well and nearby observation wells was found significant. Additionally, wellbore storage, skin, and leakage need to be taken into account for deriving the hydraulic parameters. Hence, a method to remove these five factors influencing the drawdown curve is developed, which takes advantage from the late-time characteristics of drawdown data and the early-time behavior of drawdown. Some currently available semi-log graphic techniques are therefore proven applicable for parameter determination. Validity of the proposed method is verified by the good agreement between the calculated and the measured drawdown of both the pumping well and observation well.

Graphical Abstract

Research Highlights

►Method accounting both the late-time characteristics and the early-time behavior is developed. ►Five factors involved in the hydraulic parameter estimates are taken into account in this method. ►This turns out to be of some relevance for a most reliable determination of hydraulic parameters.

Introduction

The construction site (CR) of 125 m in length and 14.9 to 25.9 m in width is located at the crossing of the Xinzhuang line and the Luzhou line of the Taipei Rapid Transit System (TRTS) (Fig. 1). As the northbound and southbound tunnels were constructed overlapping each other underneath the Tamshui River which directly runs into the Taiwan Strait, the excavation reached 39.5 to 41.5 m below the ground surface. 33 large-diameter wells embedded in 2 m thick and 63 m deep diaphragm walls along with a 5 m thick jet grouting were constructed to reduce the uplift pressures and retain substantial lateral pressures during such a massive underground excavation.

In the current study, five factors were involved in the derivation of hydraulic parameters, which include periodical fluctuation, partial penetration well effect, wellbore storage, skin, and leakage problem. As such the drawdown cannot be accommodated in theoretical well formulae, the pumping well cannot be properly and economically deployed at the construction site. For most of the coastal areas the groundwater level in the confined aquifer is affected by the tidal influence, which induces the periodical fluctuation of drawdown during the pumping test. Use of the drawdown data where there is a partial penetration well effect will result in a large error in the determination of storage coefficient. Neglecting both the wellbore storage and skin will cause serious overestimate of storage coefficient and underestimate of transmissivity. Before the derivation of parameters, it needs to know if the late-time drawdown is affected by either leakage from the overlying/underlying formation or recharge from the possible hydrogeologic boundary. Therefore, the purpose of this study is to propose a method to remove these five factors involved in the derivation of hydraulic parameters, which devotes much attention to the late-time characteristics of drawdown data and the early-time behavior of drawdown.

Section snippets

Geology and hydrogeology

Fig. 1 shows the location of the construction site CR and remote sites and two geological profiles derived from the geological database (GEOLOG) (Lee, 1990) of the Taipei Basin, which comprises the loggings from 248 boreholes drilled through a thick alluvial formation (the Sungshan formation) of alternating soft clay and silty sand layers, of which six has been distinguished, into a gravel formation (the Chingmei gravel formation). The thickness of the Sungshan formation varies from 40 to 55 m

Proposed method

The proposed method of removing those five influencing factors on the drawdown curve is described herein.

Method validation

For a confined, homogeneous, and isotropic aquifer, the dimensionless drawdown solution for a fully penetrating pumping well subject to both skin and wellbore storage is (Agarwal et al., 1970, Kabala, 2001): $\begin{array}{l} s_{wD} (τ) {= L}^{- 1} \\ 〈\frac{K_{0} (\sqrt{p}) + S_{k} \sqrt{p} K_{1} (\sqrt{p})}{p \{\frac{p}{2 α_{w}} [K_{0} (\sqrt{p}) + S_{k} \sqrt{p} K_{1} (\sqrt{p})] + \sqrt{p} K_{1} (\sqrt{p})\}}〉 \end{array}$ where τ = Tt/(r_w²S) is dimensionless time, and p is the Laplace transform parameter with respect to τ, and α_w = S(r_w/r_wc)² is wellbore storage coefficient of the pumping well. The symbol of L⁻¹ denotes the Laplace inversion, which can be calculated

Multi-well pumping test

The actual drawdown induced by a single-well pumping at some distance is the sum of s + Δs₂ where s is derived using Theis (1935) with the estimated hydraulic parameters, T = 3.50 m²/min and S = 0.00095, and Δs₂ is determined using Hantush, 1961a, Hantush, 1961b. The drawdown induced by multi-well pumping can be calculated by superimposing the drawdown induced by each single-well pumping. It can be seen from Fig. 19, the comparison between the calculated drawdowns and those measured from ELP8002,

Discussion and conclusion

As the excavation reached 40 m below the ground surface, 33 pumping wells embedded in 2 m thick and 63 m deep diaphragm walls along with a 5 m thick jet grouting were used to reduce both the uplift pressures and groundwater inflow during excavations. As the actual thickness of the pumped aquifer is unknown, the installed wells are regarded as partial penetration wells. Single-well test was conducted to derive the hydraulic parameter estimates. After the completion of single-well pumping test,

Acknowledgement

The authors wish to acknowledge Mr. G. Lee, the former graduate student, for the field investigation and the data collection that made this research possible and to express sincere thanks to one anonymous reviewer for the valuable comments and corrections to improve the article.

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A case history of field pumping tests in a deep gravel formation in the Taipei Basin, Taiwan

Abstract

Graphical Abstract

Research Highlights

Introduction

Section snippets

Geology and hydrogeology

Proposed method

Method validation

Multi-well pumping test

Discussion and conclusion

Acknowledgement

J. Hydrol.

Adv. Water Res.

J. Hydrol.

Adv. Water Res.

J. Hydrol.

An investigation of wellbore storage and skin effect in unsteady liquid flow: I. Analytical treatment

Trans. Soc. Pet. Eng. AIME

Observation well response time and its effect upon aquifer test results

J. Hydrol.

The Design, Performance, and Analysis of Slug Tests

Determining aquifer characteristics by the tidal method

Water Resour. Res.

Effects of monitoring and pumping well pipe capacities during pumping tests in confined aquifers

Can. Geotech. J.

Pumping test in a confined aquifer under tidal influence

Ground Water

Use of cumulative volume of constant-head injection test to estimate aquifer parameters with skin effects: field experiment and data analysis

Water Resour. Res.

A simple data analysis method for a pumping test with skin and wellbore storage effects

Terr. Atmos. Ocean Sci.

Analysis of interference test data influenced by wellbore storage and skin at the flowing well

J. Pet. Technol.

A generalized graphical method for evaluating function constants and summarizing well-field history

Trans. AGU

The effect of tidal fluctuation on a coastal aquifer in the UK

Ground Water

Cyclic fluctuations of water level as a basis for determining aquifer transmissibility

Int. Assoc. Sci. Hydrol. Publ.