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Proceedings of the XVI ECSMGE
Geotechnical Engineering for Infrastructure and Development
ISBN 978-0-7277-6067-8
© The authors and ICE Publishing: All rights reserved, 2015
doi:10.1680/ecsmge.60678
REFERENCES
Amercian Society for Testing Materials. 2006, Standard test
method for identification and classification of dispersive clay soils
by the pinhole test, ASTM D 4647.
Bonala, M. & Reddi, L. 1998. Physicochemical and biological
mechanisms of soil clogging: an overview, ASCE Geotech. Spec. Optimisation of dewatering systems
Publ.78, 43–68.
Bolouri-Bazaz , J. and Saghafy, H.R. 2003. Properties and behav-L'optimisation des systèmes de dénoyage
ior of dispersive clayey soil treated by PVA, International Confer-
ence on Geotechnical Engineering *1 2
Bourdeaux, G. & Imaizumi, H. 1977. Dispersive clay at Sobrad- M. Preene and E Loots
inho dam, ASTM, STP 623, 13–24. 1 Preene Groundwater Consulting Limited, Wakefield, UK
DeJong, J.T. et al. 2013. Biogeochemical processes and geotechni-2
cal applications: progress, opportunities and challenges Geotech- Loots Groundwater International, Amsterdam, Netherlands
nique 63 (4), 287–301 * Corresponding Author
De Muynck, W., Cox, K., Belie, N. and Verstraete, W. 2008. Bac-
terial carbonate precipitation as an alternative surface treatment for
concrete, construction and building materials 22, 875-885.
Indraratna, B. and Nutalaya, 1992. Stabilization of a dispersive soil
by blending with fly ash, International Journal of Rock Mechanics
and Mining Sciences & Geomechanics, 29 (2).
McDaniel, T.N. 1979. Dispersive soil problem at Los Esteros dam, ABSTRACT : Dewatering systems involve the use of wells to lower groundwater levels, or low permeability cut-off walls to exclude
Journal of the Geotechnical Engineering Division 105, 1017-1030. groundwater, so that excavation and can be done in dry and stable conditions. There are a wide range of options for the design and imple-
Ouhadi , V., Goodarzi, A. 2006. Assessment of the stability of a such systems, and strategies to optimise dewatering systems are of interest to designers. Potential optimisation approaches in-
dispersive soil treated by alum, Engineering Geology 85, 91-101. mentation of
Rahimi ,H. and Fakour, K. 1995. Comparison of portland cement clude: empirical (experience and rules of thumb); numerical/analytical (calculation and/or modelling); and observational (field mea-
and asphalt emulsion for stabilization of dispersive soil, Iranian surements). There is no perfect optimisation method to address all the possible priorities for a dewatering system, and different aspects of
J.Agric.sci. 26 (4), optimisation may conflict, with a need for trade offs between different factors of design. The required conditions for effective optimisation
Ramachandran, S., Ramakrishnan, V. and Bang, S. 2001. Reme-of dewatering systems include: clarity of the objectives of optimisation; adequate site investigation data; development of a valid hydro-
diation of concrete using microorganisms, ACI Mater.j. 98, 3-9. geological conceptual model; and, selection of the most appropriate dewatering method at an early stage of optimisation.
Ravenscroft, N., Walker, S., Dutton, G. & Smit, J. 1991. Identifi-
cation, isolation and structural studies of extracellular polysaccha-RÉSUMÉ. Les systèmes d’assèchement impliquent l'utilisation de puits pour réduire les niveaux d’eau souterraines, ou l’utilisation des
s parafouille à faible perméabilité pour exclure les eaux souterraines, ainsi que l'excavation peut se faire dans des conditions sèches et
rides produced by Caulobacter crescentus, J. Bacteriol. 173, 5677–mur
5684. stables. Il ya plusieurs options pour la conception et l’implémentation de ces systèmes, et les stratégies pour optimiser les systèmes
Figure 7. SEM micrographs: a) untreated sample, b) treated Saderkarimi, J. 1998. Lime and distilled water treatment of disper-d’assèchement interessera les concepteurs. Les méthodes d’optimisation potentiels incluent: empirique (l'expérience et les règles générale);
(cured for 4 days), c) treated cured for two weeks sive soils by electro-osmosis effect," Journal of the Institution of numérique / analytique (le calcul et / ou la modélisation); et d'observation (le mesures sur le terrain). Il n'existe pas de méthode d'optimisa-
aborde toutes les priorités possibles pour un système d’assèchement, et les différents aspects de l'optimisation peuvent
Engineers (India) 79, 78-80. tion parfaite pour
Sajadi, M., Nikooee, E., Habibagahi, G. 2014, Biological treatment être contradictoires,, donc il peut y avoir un besoin de compromis entre les différents facteurs de conception. Les conditions requises pour
d’assèchement sont les suivants: clarté des objectifs d'optimisation; données adéquates d'enquête du
of swelling soils using microbial calcite precipitation, Unsaturated l'optimisation efficace de systèmes de
4 CONCLUDING REMARKS soils: Research and application, 917-922. site; le développement d'un modèle conceptuel hydrogéologique valide; et la sélection de la méthode d’assèchement au stade précoce pos-
Sherard, J. & Decker, R. 1977. Summary-evaluation of symposium sible d’optimisation.
The experimental investigation of the stabilization on dispersive clays, ASTM STP 623, 467-479.
using Bacillus sphaericus revealed that: Talebbeydokhti, N.,Nikooee, E., Kazemi, M.M., Habibagahi, 1 INTRODUCTION within the excavation. With the widespread availabil-
Dispersive soil can be stabilised and improved G.,Ghasemi, Y. 2013. Biological Stabilization of the Fine-Grained ity of computing power in everyday geotechnical en-
by means of adding Bacillus sphaericus and the Soils Using Microalgae: Evaluation of the Effective Parameters, Dewatering is often required to allow excavations to gineering it has become fairly straightforward to ana-
Proceedings of the U.S.-Iran Symposium on Air Pollution in lyse multiple groundwater flow scenarios (either as
precipitating agent (CaCl2). Megacities, American Association for the Advancement of Sci-be made in dry and stable conditions below ground-
With higher bacterial concentration, more pro-ence (AAAS), Beckman Center, Irvine, California, September 3-5, water level. Dewatering systems typically involve spreadsheet-based analytical models or numerical
nounced improvement in the dispersivity of soil 2013, 52-65 pumping from an array of wells or sumps to lower groundwater models) and apply these scenarios to
Tsang, P., Li, G., Brun, Y. & Tang, J. 2006. Adhesion of single groundwater levels, and may also involve low per-dewatering design.
can be achieved. bacterial cells in the micronewton range, Proc Natl Acad Sci USA It is a logical step to go from analysing multiple
Increasing curing time leads to considerable de-103, 11435–11436. meability cut-off walls to exclude groundwater.
crease in soil dispersivity up to 3 days, after Vakili, A.H., Selamat, M.R., Moayedi, H. & Amani, H. 2012. Sta-On any given site there may be several possible scenarios to deriving an ‘optimal’ dewatering design,
which minimal improvement was observed. bilization of dispersive soils by pozzolan, Forensic Engineering, configurations of dewatering system in terms of typically based on optimising the number of wells or
726-735. number and location of wells, cut-off walls, pump the pumped flow rate. Numerical solutions to optimal
Vandevivere ,P. & Baveye, P., 1992. Relationship between trans- dewatering design were tried as early as the 1970s
port of bacteria and their clogging efficiency in sand columns, capacity and other system parameters that will
Appl. Environ. Microbiol. 58, 2523–2530. achieve the required lowering of groundwater levels (Aguado et al. 1974), and since then have developed
2841
Geotechnical Engineering for Infrastructure and Development
along with emerging numerical decision making use low permeability cut-off walls to exclude tions to be identified, as well as relevant experience
tools of their time, such as expert systems (Davey- groundwater from the excavation (Figure 2). Pump- 4 METHODS OF OPTIMISATION from comparable projects. Adequate site investiga-
Wilson 1994), multi-attribute decision analysis (Go- ing and exclusion methods may be used in combina- tion data are essential to characterise site conditions,
lestanifar & Ahangari 2012) and artificial neural tion. There are four main approaches to dewatering de- otherwise it cannot be known whether the previous
networks (Ye et al. 2012) amongst others. sign and optimisation: sites, from which experience is drawn, are compara-
Previous studies have often taken a fundamentally ¥ Empirical: A design based largely on experi- ble. In practice, when problems occur with dewater-
mathematical approach to optimisation, in many cas- ence, local knowledge and ‘rules of thumb’. ing systems optimised by the empirical method, this
es in an attempt to provide better reliability or con- ¥ Analytical: Use of hydrogeological design is often due to applying empirical rules between sites
sistency in dewatering design, in part by reducing the equations, either manually or by spreadsheet. where underlying conditions are different.
role of ‘expert judgment’. The current paper will take ¥ Numerical: Use of 2 or 3 dimensional numeri-
a different approach to look at the challenges and pit- cal groundwater flow models.
falls of optimisation of dewatering systems and will ¥ Observational: Use of construction observations
discuss non-numerical optimisation strategies. to design and refine the dewatering system.
2 WHAT IS DEWATERING? 4.1 Empirical optimisation
The geotechnical process commonly known as de- Figure 2: Groundwater control by exclusion Optimisation by empirical methods has been success-
watering is more correctly described as groundwater fully used on many simple projects. A simple project
control. There are two principal groups of groundwa- 3 WHY OPTIMISE? can be defined as one where: the hydrogeological
ter control technologies as shown in Table 1. conditions are well defined and relatively straight-
Table 1. Groundwater control methods Groundwater control is one of first geotechnical pro- forward; where the excavation is relatively small and
Pumping methods Exclusion methods cesses required on a project, and is often the first that shallow; and, where environmental impacts are not a Figure 3: Range of application of pumped well groundwater con-
Sump pumping Steel sheet-piling must be proven to allow work to proceed. If ground- key concern. Examples might include shallow base- trol techniques (from Preene et al. 2000: reproduced by kind per-
Vertical wellpoints Vibrated beam walls water control does not work effectively, or causes de- ments, pipeline projects, sewers, etc. mission of CIRIA)
Horizontal wellpoint Cement-bentonite or soil- lays, these problems will occur at the start of the pro- Empirical optimisation uses experience of previ-
Deep wells with sub- bentonite slurry walls ject, and these can critically affect later stages of ous projects nearby or in comparable conditions. The 4.2 Numerical modelling or analytical
mersible pumps Concrete diaphragm walls construction. The cost of resultant delays can be dewatering method, flow rate and drawdown of a optimisation
Ejector wells Bored pile walls many times greater than the cost of the groundwater previous project can be used to optimise another pro-
Passive relief wells Grout curtains (permeation grout- control works themselves (Roberts & Deed 1994). ject where the conditions are comparable. Numerical modeling is used far more in dewatering
Electro-osmosis ing; rock grouting; jet grouting; In contrast to many other forms of geotechnical When geotechnical engineers become involved in design and optimisation than it was 10 years ago.
mix-in place methods) This popularity is because the necessary investments
Artificial ground freezing processes, dewatering design is not covered in detail dewatering design, the use of empirical design is in software, hardware and training have reduced
by geotechnical design codes. For example the de- sometimes viewed as being less rigorous compared to dramatically, and also because modern software can
watering section in Eurocode 7 (BS EN 1997-1 2004) numerical or analytical methods. However, there is a easily demonstrate results visually for non-technical
is only one page long, and there is no corresponding huge track record of empirical methods providing project clients. Numerical modelling offers the flexi-
execution standard for dewatering. Dewatering guid- successful dewatering designs. One of the reasons bility to take into account known or inferred varia-
ance documents do exist in the UK (Preene et al why this is the case is that, provided the correct tions in the aquifer within the range of influence.
2000), United States (Unified Facilities Criteria groundwater control method is selected, a given de- This might include assessing the effects of a nearby
2004) and the Middle East (ASHGHAL 2014; Abu watering technology can often successfully deal with river, another dewatering project, or a natural barrier
Dhabi City Municipality 2014), but tend not to be modest variations in ground conditions. This is illus- in the aquifer.
prescriptive and are typically in the form of ‘toolkits’ trated by Figure 3, which shows that individual The analytical approach uses hydrogeological
of design methods and construction techniques. methods are appropriate for a relatively wide range equations (as might be found in a textbook) to esti-
Therefore at the start of a project designer can be of drawdown and hydraulic conductivity conditions. mate pumped flow rates and drawdowns. It is typical-
faced with a bewildering arrangement of design and Conversely, this highlights the limits for each de- ly suited to relatively simple hydrogeological condi-
Figure 1: Groundwater control by pumping implementation options, and a rational optimisation watering method beyond which it is not effective. It
approach can look attractive. is essential to select the correct dewatering technolo- tions with few complex boundaries (rivers, faults,
The first group is pumping methods where Any attempts to optimise the design of dewatering gy for a project. other abstractions). Each set of analytical equations is
groundwater is pumped from an array of wells or systems must be appropriate to the design method The empirical method requires sufficient site in- only applicable to a relatively narrow range of hy-
sumps (Figure 1) to temporarily lower groundwater used. vestigation data to allow the hydrogeological condi- drogeological boundary conditions, and gross errors
levels. The second group is exclusion methods that can result if used in the wrong conditions.
2842
Preene and Loots
along with emerging numerical decision making use low permeability cut-off walls to exclude tions to be identified, as well as relevant experience
tools of their time, such as expert systems (Davey-groundwater from the excavation (Figure 2). Pump-4 METHODS OF OPTIMISATION from comparable projects. Adequate site investiga-
Wilson 1994), multi-attribute decision analysis (Go-ing and exclusion methods may be used in combina-tion data are essential to characterise site conditions,
lestanifar & Ahangari 2012) and artificial neural tion. There are four main approaches to dewatering de-otherwise it cannot be known whether the previous
networks (Ye et al. 2012) amongst others. sign and optimisation: sites, from which experience is drawn, are compara-
Previous studies have often taken a fundamentally ¥ Empirical: A design based largely on experi-ble. In practice, when problems occur with dewater-
mathematical approach to optimisation, in many cas-ence, local knowledge and ‘rules of thumb’. ing systems optimised by the empirical method, this
es in an attempt to provide better reliability or con-¥ Analytical: Use of hydrogeological design is often due to applying empirical rules between sites
sistency in dewatering design, in part by reducing the equations, either manually or by spreadsheet. where underlying conditions are different.
role of ‘expert judgment’. The current paper will take ¥ Numerical: Use of 2 or 3 dimensional numeri-
a different approach to look at the challenges and pit-cal groundwater flow models.
falls of optimisation of dewatering systems and will ¥ Observational: Use of construction observations
discuss non-numerical optimisation strategies. to design and refine the dewatering system.
2 WHAT IS DEWATERING? 4.1 Empirical optimisation
The geotechnical process commonly known as de-Figure 2: Groundwater control by exclusion Optimisation by empirical methods has been success-
watering is more correctly described as groundwater fully used on many simple projects. A simple project
control. There are two principal groups of groundwa-3 WHY OPTIMISE? can be defined as one where: the hydrogeological
ter control technologies as shown in Table 1. conditions are well defined and relatively straight-
Table 1. Groundwater control methods Groundwater control is one of first geotechnical pro-forward; where the excavation is relatively small and
Pumping methods Exclusion methods cesses required on a project, and is often the first that shallow; and, where environmental impacts are not a Figure 3: Range of application of pumped well groundwater con-
Sump pumping Steel sheet-piling must be proven to allow work to proceed. If ground-key concern. Examples might include shallow base-trol techniques (from Preene et al. 2000: reproduced by kind per-
Vertical wellpoints Vibrated beam walls water control does not work effectively, or causes de-ments, pipeline projects, sewers, etc. mission of CIRIA)
Horizontal wellpoint Cement-bentonite or soil-lays, these problems will occur at the start of the pro-Empirical optimisation uses experience of previ-
Deep wells with sub-bentonite slurry walls ject, and these can critically affect later stages of ous projects nearby or in comparable conditions. The 4.2 Numerical modelling or analytical
mersible pumps Concrete diaphragm walls construction. The cost of resultant delays can be dewatering method, flow rate and drawdown of a optimisation
Ejector wells Bored pile walls many times greater than the cost of the groundwater previous project can be used to optimise another pro-
Passive relief wells Grout curtains (permeation grout-control works themselves (Roberts & Deed 1994). ject where the conditions are comparable. Numerical modeling is used far more in dewatering
Electro-osmosis ing; rock grouting; jet grouting; In contrast to many other forms of geotechnical design and optimisation than it was 10 years ago.
mix-in place methods) When geotechnical engineers become involved in This popularity is because the necessary investments
Artificial ground freezing processes, dewatering design is not covered in detail dewatering design, the use of empirical design is in software, hardware and training have reduced
by geotechnical design codes. For example the de-sometimes viewed as being less rigorous compared to dramatically, and also because modern software can
watering section in Eurocode 7 (BS EN 1997-1 2004) numerical or analytical methods. However, there is a easily demonstrate results visually for non-technical
is only one page long, and there is no corresponding huge track record of empirical methods providing project clients. Numerical modelling offers the flexi-
execution standard for dewatering. Dewatering guid-successful dewatering designs. One of the reasons bility to take into account known or inferred varia-
ance documents do exist in the UK (Preene et al why this is the case is that, provided the correct tions in the aquifer within the range of influence.
2000), United States (Unified Facilities Criteria groundwater control method is selected, a given de-This might include assessing the effects of a nearby
2004) and the Middle East (ASHGHAL 2014; Abu watering technology can often successfully deal with river, another dewatering project, or a natural barrier
Dhabi City Municipality 2014), but tend not to be modest variations in ground conditions. This is illus-in the aquifer.
prescriptive and are typically in the form of ‘toolkits’ trated by Figure 3, which shows that individual The analytical approach uses hydrogeological
of design methods and construction techniques. methods are appropriate for a relatively wide range equations (as might be found in a textbook) to esti-
Therefore at the start of a project designer can be of drawdown and hydraulic conductivity conditions. mate pumped flow rates and drawdowns. It is typical-
faced with a bewildering arrangement of design and Conversely, this highlights the limits for each de-ly suited to relatively simple hydrogeological condi-
Figure 1: Groundwater control by pumping implementation options, and a rational optimisation watering method beyond which it is not effective. It
approach can look attractive. is essential to select the correct dewatering technolo- tions with few complex boundaries (rivers, faults,
The first group is pumping methods where Any attempts to optimise the design of dewatering gy for a project. other abstractions). Each set of analytical equations is
groundwater is pumped from an array of wells or systems must be appropriate to the design method The empirical method requires sufficient site in-only applicable to a relatively narrow range of hy-
sumps (Figure 1) to temporarily lower groundwater used. vestigation data to allow the hydrogeological condi-drogeological boundary conditions, and gross errors
levels. The second group is exclusion methods that can result if used in the wrong conditions.
2843
Geotechnical Engineering for Infrastructure and Development
Both modeling and analytical approaches need to velop an effective dewatering system at the site, suit- dressed? There should be sufficient data to de- quire a total flow rate of 50 l/s. In fine sands the yield
be applied based on a ‘hydrogeological conceptual able for current conditions. velop some understanding of the likely varia- of an individual deep well pumped by a submersible
model’ which captures the important features of the tions in ground conditions. Here a geological pump will typically be limited by the hydraulic con-
groundwater system at the site and its environs. The 5 PROBLEMS WITH OPTIMISATION desk study can be of great value to help identify ductivity of the sand to between approximately 1 l/s
conceptual model will normally be developed direct- the likelihood of local geological variations. and 5 l/s. But it is possible for an analyst to model the
ly from the site investigation data, including a hydro- A wide range of problems can occur when dewater- The relevance of the data relates to whether the system as based on say five wells at 10 l/s. In theory
geological desk study. If the conceptual model is in- ing systems are optimised, as outlined below. necessary information is provided. For exam- this would achieve the overall flow rate, but in the
accurate or incomplete, the results of any subsequent ple, is information available from the right parts real world these well yields would never be achieved,
modeling or analysis are likely to be erroneous. 5.1 Lack of clarity in objectives of optimisation of the site and from the relevant strata? A and a five well system would be ineffective. Such
A fundamental problem with dewatering optimisation common issue is: are the site investigation problems can occur when designers are not familiar
4.3 Observational optimisation is lack of clarity in the objectives of optimisation, boreholes deep enough to identify the presence with the operational characteristics of dewatering
Perhaps the ultimate expression of optimisation is the and failure to recognise that optimising in one aspect of any confined aquifers beneath the base of the wells and systems. While manufacturers of dewater-
observational method. Construction observations (for may require compromises in other aspects. excavation that could cause an uplift hydraulic ing equipment do publish pumping capacities these
example pumped flow rates and groundwater draw- Traditionally, dewatering optimisation has focused failure of the base? rates are effectively ‘ideal’ values that do not take
down levels) are used to guide optimisation of the on optimising pumping rates (i.e. to avoid pumping A valid part of dewatering optimisation may ulti- well yields into account. It is important that any
system as part of a deliberate process of design, con- water unnecessarily) while still achieving the re- mately be to recommend additional ground investiga- modelled dewatering system is critically reviewed
struction control, monitoring and review (Nicholson quired lowering of groundwater levels. This has the tion to plug any identified data gaps, and/or to rec- against realistic pumping parameters.
et al. 1999). The observational method is sometimes advantage that it will likely also minimise operational ommend that the dewatering system be implemented
combined with ‘inverse numerical modelling’ where costs and energy consumption. However, if pursued by the observational method to provide flexibility 5.4 Inappropriate dewatering method
series of numerical modelling scenarios are prepared single-mindedly this approach could result in a de- against variations in ground conditions. As discussed earlier, and shown in Figure 3, each
in advance for a range of possible hydrogeological watering system with little spare capacity to deal 5.3 Errors in conceptual model type of pumped dewatering method is applicable to a
conditions and then compared with the field data. with modest changes in ground conditions that may finite range of ground conditions. If an unsuitable
The observational method can be useful to deal require higher pumped flow rates. Also, such a sys- As has been described elsewhere in this paper, get- dewatering method is selected at the outset of design
with local variations in ground conditions. On larger tem might be designed without consideration of envi- ting the conceptual hydrogeological model correct is (e.g. if ejector wells are used in a high permeability
projects it may be the best solution to address these ronmental impacts on the groundwater regime; in- fundamental to the design and optimisation of de- soil) then even extensive and detailed optimisation
variations locally (using the flexibility of the obser- creasingly the minimisation of impacts is a necessary watering systems. Many significant dewatering prob- measures are likely to be futile.
vational method) instead of engineering the overall design consideration. lems can ultimately be traced back to an inappropri- It is essential that designers and analysts have an
system based on the worst-case conditions, as might ate conceptual model that either leads the designer understanding of the limits of performance of the
be necessary if the dewatering system was conserva- 5.2 Data quality and quantity down the wrong design avenue, or causes the design- chosen dewatering system, and consider this in de-
tively designed at the start with little flexibility. The data from site investigation and previous projects er to ignore a design condition that is, in fact, im- sign. For example, if the chosen dewatering method
are the foundation of the conceptual hydrogeological portant. Examples include: will be effective not just for the ‘design value’ of hy-
4.4 Optimisation in the field (troubleshooting) model and all subsequent calculations, modelling or ¥ Failure to identify layers of low vertical perme- draulic conductivity, but also for the ‘highest credi-
Occasionally, dewatering systems are not effective analysis and dewatering system design. If these data ability beneath the base of an excavation, which ble’ and ‘lowest credible’ values then the design is
when initially installed, and a ‘troubleshooting’ in- are inadequate in quality or quantity everything after may create a risk of unrelieved pore water pres- likely to be robust. However, if relatively small
vestigation is needed. This approach takes place dur- this step will be of limited value. No modelling effort sures at depth, which could cause base failure. changes in hydraulic conductivity may require a
ing construction, and so has access to field data (e.g. can correct false or poorly determined parameters. ¥ Failure to identify that the range of hydraulic change in pumping method this can cause major de-
dewatering well logs, pumped flow rates, drawdown ¥ Data quality: This can be a very subjective is- conductivity potentially includes soils of low lays and cost overruns to a project.
water levels) that were not available to the original sue and relates to how reliable the data are per- permeability that will limit the flow rates yield-
designer. These data need to be reviewed to identify ceived to be. There can be issues with the ed by pumped wells. 6 POSSIBLE PRIORITIES FOR OPTIMISATION
whether the lack of performance is related to: ‘unex- source of the data (e.g. by whom was the work ¥ Failure to identify groundwater contamination
pected ground conditions’ (i.e. ground conditions dif- carried out and how is it reported) or questions in the vicinity of a dewatering system that may Traditionally, the main priority for dewatering opti-
ferent to the assumed conceptual model); operational over internal consistency of the data (e.g. if be mobilised by pumping. misation is to reduce installation costs or occasional-
problems with the current system (e.g. existing borehole logs describe a sandy gravel, but the If these conditions are not identified then model- ly to meet regulatory requirements, such as when a
pumps and wells not delivering their design capaci- hydraulic conductivity tests report very low ling or analysis will not address the relevant ques- limit has been set on the maximum permitted dis-
ty); or the fundamental issue of the wrong dewatering values). tions, or will use unrealistic parameters. A common charge rate. Increasingly, there is also a focus on de-
technology or approach being used. The objective of ¥ Data quantity: There are two issues, is there modelling problem is where the well yields used in a veloping effective dewatering systems that have min-
troubleshooting is to develop a plan of action, to de- enough data and are the relevant issues ad- numerical model are unrealistically high. For exam- imal environmental impacts (such as ground
ple, a very large excavation in a fine sand might re- settlement). However, there are several different
2844
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