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IS 9759:1981 is the Indian Standard (BIS) for guidelines for dewatering during construction. This standard provides guidelines for controlling groundwater during construction through various dewatering methods. It covers site investigation, selection criteria for techniques like sump pumping, wellpoints, and deep wells, and considerations for system design, operation, and potential side effects like ground settlement.
BIM-relevant code. See the BIM Hub for ISO 19650, IFC, and LOD/LOIN frameworks used alongside it.
Practical Notes
! A thorough geotechnical investigation, including permeability tests, is the most critical step; basing a dewatering design on assumed soil conditions is a common cause of failure.
! Always monitor adjacent structures and utilities for settlement, as lowering the water table can cause ground subsidence, especially in loose or organic soils.
! Plan for the legal and environmentally compliant disposal of pumped water. Unexpectedly high discharge volumes can cause flooding, erosion, or regulatory issues.
CIRIA C750 (2nd Edition, 2016)CIRIA (Construction Industry Research and Information Association), UK
HighCurrent
Groundwater control: design and practice
A comprehensive design and practice manual covering all aspects of dewatering, considered a de-facto global standard.
BS 6031:2009+A2:2018BSI (British Standards Institution), UK
HighCurrent
Code of practice for earthworks
Contains a dedicated and detailed section on dewatering and groundwater control methods within a broader earthworks context.
ASTM D7929-14ASTM International, USA
MediumCurrent
Standard Guide for Selection of Methods for Active Dewatering Systems
Focuses specifically on the selection criteria for dewatering systems based on soil type and drawdown, aligning with the IS code's guidance.
Geotechnical Engineering Office (GEO) Publication No. 1/2022Geotechnical Engineering Office, Hong Kong
HighCurrent
Guide to Dewatering for Excavations
Provides detailed guidance on the design, implementation, and monitoring of dewatering works, with a focus on urban environments.
Key Differences
≠The IS 9759:1981 is a high-level guideline, whereas modern equivalents like CIRIA C750 are exhaustive design manuals with detailed calculations, worked examples, and extensive case studies.
≠International standards place a strong emphasis on quantitative risk assessment for ground movement, settlement damage to adjacent properties, and environmental impacts, which is only qualitatively mentioned in the IS code.
≠Modern standards (e.g., BS 6031, CIRIA C750) incorporate advanced techniques such as ejector wells, numerical modeling for complex hydrogeology, and detailed guidance on environmental permitting and discharge quality, which are not covered in the 1981 IS code.
≠The IS code provides general applicability, while international guides like ASTM D7929 provide specific selection charts and criteria based on quantified soil permeability (k value) and required drawdown depth.
Key Similarities
≈All standards recognize the same fundamental dewatering methods: open sump pumping, wellpoint systems, deep well systems, and specialized methods like electro-osmosis.
≈There is a universal agreement on the critical importance of a thorough site investigation, including determination of soil stratification, permeability, and groundwater conditions, before selecting and designing a system.
≈All documents acknowledge the potential adverse effects of dewatering, such as ground settlement and its impact on nearby structures, and recommend monitoring as a key mitigation measure.
≈The basic principles for the applicability of each dewatering method to specific soil types are consistent across all standards (e.g., wellpoints for sands, sumps for gravels, electro-osmosis for silts).
Parameter Comparison
Parameter
IS Value
International
Source
Practical Suction Lift for Wellpoints
5 to 6 metres.
Typically 5 m to 6 m, limited by friction losses and pump efficiency below the theoretical maximum.
CIRIA C750
Applicable Soil Permeability for Wellpoints
Recommended for sandy gravel to fine sand.
Most effective in soils with permeability (k) in the range of 10⁻³ to 10⁻⁵ m/s.
CIRIA C750
Typical Wellpoint Spacing
Generally spaced 1 to 3 m apart.
Normally in the range of 1 m to 4 m, but depends on permeability and required drawdown.
BS 6031:2009+A2:2018
Applicability of Sump Pumping
Suitable for coarse-grained soils like gravels and coarse sands.
Best suited to high permeability ground (k > 10⁻⁴ m/s) where seepage faces are stable.
CIRIA C750
Applicability of Deep Wells
Used when drawdown is beyond the range of wellpoints (i.e., > 6 m).
Can be used for any drawdown depth, often exceeding 40-50m, limited only by aquifer depth and pump capacity.
CIRIA C750
Applicability of Electro-osmosis
For fine-grained soils like silts and silty clays.
For low permeability soils, typically where k < 10⁻⁷ m/s.
ASTM D7929-14
⚠ Verify details from original standards before use
Key Values5
Quick Reference Values
Practical suction lift for wellpoint systems5 to 6 m
Typical spacing of wellpoints0.75 to 3 m
Typical radius of influence for a single wellpoint5 to 15 m
Drawdown from deep wellsCan exceed 30 m
Typical drawdown for vacuum wellpoints in silty soils7 to 9 m
Tables & Referenced Sections
Key Tables
Table 1 - Applicability of Various Methods of Dewatering
Key Clauses
Clause 2 - Investigation
Clause 3 - Methods of Dewatering
Clause 4 - Selection of a Suitable Method
Clause 5 - Design of Dewatering Systems
Clause 7 - Effects of Dewatering and Remedial Measures
It is most effective for lowering the water table by 5-6 m in permeable soils like sands and gravels (Table 1).
What method is used for deep excavations or low permeability soils like silt?+
For deep excavations (>6m), deep well systems are used. For low permeability soils, vacuum wellpoints or ejector systems are needed to achieve the required drawdown (Clause 3.4 & 3.5).
What are the main risks associated with dewatering?+
Key risks include settlement of adjacent buildings, instability of excavation slopes or base, increased soil consolidation, and damage to timber piles by exposing them to air (Clause 7).
How is the appropriate dewatering method selected?+
Selection depends on factors like soil characteristics (especially permeability), required drawdown, size of excavation, and proximity to existing structures, as detailed in Table 1 and Clause 4.