Guidelines for dewatering during construction
1981 Edition

Overview of IS 9759: Dewatering Flow Equations and Foreword

Foreword Summary

• Provides dewatering guidance for typical civil construction excluding river valley projects.
• Focuses on common soil types such as gravel, sand, and silt.
• Developed in collaboration with Central Building Research Institute, Roorkee.
• Values rounded according to IS 2-1960.

Principal Dewatering Discharge Equations (Clause 1.10, Tables 2 & 3)

• Discharge to a fully penetrating slot under artesian conditions: [Q = k D x L (H - h_e)]

• Discharge to a fully penetrating slot under gravity flow: [Q = 5.7 (H - h_e) k_x 2L]

• Discharge to a partially penetrating slot under gravity flow: [Q = (0.73 + 0.27 \frac{H - h_e}{H - h_o}) k_x H' L]

• Discharge to a slot from two partially penetrating line sources: [Q = 2 k D x (H - h_e) L + Y D] with (Y) dependent on the (W/D) ratio.

Parameter Definitions

Comparative Summary of Dewatering Techniques (Table 1)

Scope Summary for IS 9759

This standard offers directives for dewatering during construction activities, specifically excluding river valley projects and powerhouses located in boulder/gravel sections.

Core Discharge Formulas (Clause 6.2)

Well Discharge Correction (Clause 1.10)

• For fully penetrating wells: [H - h = \frac{n + \ln(N_f)}{k D} (N_f + 2 n^2) N_e]
• For partially penetrating wells: [H - h = \frac{n + 0.4}{k D}]

Where parameters include well spacing, depth, radius, and uplift factors.

Dewatering Systems Summary (Table 1)

IS 9759: Key Definitions and Discharge Formulas

Terminology (Clause 2.0)

• (H): Total hydraulic head or water table elevation.
• (h_e, h_{e2}, h_o): Various piezometric heads at designated locations.
• (k, k_x, k_D): Hydraulic conductivity coefficients.
• (L, D): Geometric dimensions (length and depth).
• (Q): Water discharge rate to slots or wells.

Discharge Equations (Clause 6.2, Tables 2 & 3)

Variable Substitution Notes

• Adjust (N_1 N_e') in place of (N_0 N_f).
• Replace (Q) in tables with corrected expressions involving hydraulic conductivity, depth, and head differences.
• Use linear interpolation for hydraulic head at distances beyond 1.3 times depth.

Flow to a Slot Illustration

flowchart LR
    A[Water Table Height H] --> B[Slot with Depth H']
    B --> C{Flow Condition}

IS 9759: Basic Principles of Dewatering

Extracts from Clauses 7.9 & 5.2:

• Operation Guidelines (7.9): Dewatering methods should be selected considering soil type, groundwater levels, and construction needs.

• Soil Particle Size Influence (5.2):

  • Particle size distribution is critical in choosing dewatering techniques.
  • Perform sieve analysis to develop grading curves.
  • Utilize soil classification charts (Fig. 1) to identify suitable methods.

Common Dewatering Techniques Based on Soil Types (Fig. 1 Concept)

Design Equations

• Drawdown (s): [s = H - h]

• Flow Rate for Wellpoint System (Q): [Q = \frac{2 \pi K D s}{\ln(R/r)}]

Where (K) is permeability, (D) aquifer thickness, (R) radius of influence, and (r) well radius.

Summary Steps

1. Conduct sieve analysis to determine soil gradation.
2. Use soil classification for selecting dewatering method.
3. Calculate drawdown and flow rates for system design.

IS 9759: Soil Exploration and Conditions

Highlights from Clauses 4.3.1 & 5.1

• Comprehensive subsurface exploration is crucial to identify soil characteristics for dewatering system design.
• Soil type classification guides appropriate dewatering selection (refer Table I, Clause 5.1).
• Accurate permeability determination should be based on field pumping tests.

Typical Permeability Values for Sands (Clause 4.3.1.5)

Estimating Permeability Without Pumping Tests

[k = C_1 \times D_{10}]

Where (k) is permeability, (C_1) is a constant (100-150), and (D_{10}) is effective grain size. Applicable for uniform sands with uniformity coefficient ≤ 2.

Notes

• In deep or large excavations, measure permeability through entire depth.
• Field pumping tests remain the most reliable method.

flowchart LR
    A[Subsurface Exploration] --> B[Soil Type Identification]
    B --> C[Permeability Assessment]
    C --> D{Pumping Test Conducted?}
    D -- Yes --> E[Use Measured Permeability]
    D -- No --> F[Estimate k via Formula]
    E & F --> G[Choose Dewatering System]

IS 9759: Selection Criteria for Dewatering Techniques

1. Soil Particle Size and Method Selection (Clauses 5.2 & Fig. 1)

• Dewatering method depends strongly on soil gradation.
• Perform sieve analyses and plot grading curves.
• Match soil type to recommended methods via classification charts.

2. Comparative Table of Methods (Table 1 Summary)

3. Flow to Slot from Line Source (Clause 6.2.2, Table 2)

IS 9759: Critical Equations and Tables for Design and Analysis

1. Discharge from Wells and Wellpoints (Clause 1.10)

• For fully penetrating wells: [H - h = \frac{n + \ln\left(\frac{a}{r_w}\right)}{f_a}] where (H) is initial groundwater level, (h) is drawdown, (a) is well spacing, (r_w) is effective radius, (f_a) uplift factor.
• Partially penetrating wells use modified formulas detailed in IS 9759.

2. Flow to Slot from Single Line Source (Clause 6.2.2)

3. Soil Suitability and Method Summary (Table 1)

IS 9759: Specifications and Formulas for Wellpoint and Deep Well Installations

1. Deep Well Pumps (Clause 6.3.13.6)

• Utilize turbine or submersible pumps for wells with diameter ≥ 150 mm.
• Select pumps based on capacity requirements rather than aquifer yield alone.
• Refer to Table 8 for estimated maximum pump capacities.
• Pumps should operate at rated speeds to maximize efficiency; higher speeds can be used with safety margins.

2. Wellpoint Pumping (Clauses 6.3.10 & 6.2.1)

• For closely spaced wellpoints, model the line of wells as a slot for flow calculation.
• Use the Dupuit-Thiem equation for steady-state flow to a line sink: [Q = \frac{2 \pi K (H^2 - h^2)}{\ln \frac{R}{r}}] where (Q) is discharge, (K) hydraulic conductivity, (H) initial water table, (h) drawdown, (R) radius of influence, (r) wellpoint radius.

3. Design Procedure (Clause 6.3)

• Measure soil permeability (K).
• Estimate drawdown (h) and radius of influence (R).
• Compute discharge per wellpoint or deep well.
• Choose pumps to meet calculated flow at rated speeds.
• Design spacing and number of wellpoints accordingly.

Typical Deep Well Pump Capacities (Example from Table 8)

Consult IS 9759 Table 8 for detailed data.

IS 9759: Guidelines for Installing and Operating Deep Well Systems

1. Pump Selection (Clause 6.3.13.6)

• Employ turbine or submersible pumps for wells of 150 mm diameter or larger.
• Choose pumps based on capacity rather than aquifer yield.
• Consult Table 8 for approximate maximum pump capacities.
• Operate pumps at rated speeds; operating at higher speeds increases capacity with a safety margin.

2. Installation Practices (Clause 8.1)

• Ensure proper alignment and secure anchoring of pump units.
• Prevent flooding or slushing at the pump base by managing water flow through sandy soils.
• Implement wellpoints and sand drains adjacent to the pump base to intercept flow and stabilize soil (Clause 7.9.4).

3. Pump Base Stability (Clause 7.9.4)

• Avoid tilting and soil erosion caused by water flow.
• Use sand drains and wellpoints to maintain stable soil conditions around the pump foundation.

Approximate Max Pumping Capacities (Table 8 Sample)

Refer to IS 9759 Table 8 for precise specifications.

flowchart LR
    A[Deep Well] --> B[Turbine/Submersible Pump]
    B --> C[Pump Base]
    C --> D{Is Water Flowing Through Soil?}
    D -- Yes --> E[Install Wellpoints & Sand Drains]
    D -- No --> F[Stable Pump Foundation]

IS 9759: Essential Formulas and Details for Sump Pumping

1. Pump Capacity Calculation (Clause 10.4.6)

Estimate pump capacity needed for surface runoff control:

[ID = QR - V \times T]

Where:

• (Q): Total pump discharge (volume/time)
• (QR): Average runoff rate (volume/time)
• (V): Sump volume
• (T): Duration of rainfall

This formula assists in sizing pumps to avoid overflow.

2. Suitable Pump Types (Clause 9.2.8, Table 9)

3. Surface Water Flow Calculation (Clause 6.2)

Apply standard discharge equations like Manning's formula for surface runoff estimation.

4. Wellpoint Pumps (Clause 6.3.10)

Used for groundwater lowering around excavations.

flowchart TD
    A[Rainfall] --> B[Surface Runoff (QR)]
    B --> C[Sump Volume (V)]
    C --> D[Pump Capacity (Q)]
    D --> E[Discharge]
    E --> F[Flood Prevention]

Summary: Calculate pump size using runoff and sump volume; select pump type based on application; apply hydraulic formulas for surface water management.

IS 9759: Guidelines for Ensuring Safety and Stability in Dewatering

Key Discharge Equations (Clause 6.2, Table 2)

Filter Design Standards (Clause 6.3.5)

Proper filter design prevents soil piping under high hydraulic gradients.

Dewatering Methods and Suitability (Table 1)

• Sump pumping for clean gravels/coarse sands; risk of instability.
• Wellpoint systems for sandy gravels to fine sands; economical but limited suction.
• Deep bored wells and others covered similarly.

IS 9759: Overview of Electro-Osmosis Method

1. Principle (Clause 2.4 and Appendix A)

• Electro-osmosis employs an electric field to induce movement of water in fine-grained soils (silts, clays) where gravity drainage is insufficient.
• Applicable for soils with permeability below approximately (0.5 \times 10^{-4}) cm/sec.

2. Discharge Calculation (Appendix A-1.8)

[Q = -k_g \times i \times z / a]

• (k_g) is assumed consistent across sands, silts, and clays.

3. Precautions (Clause 11.2)

• Discharge water should be released into absorption ditches at surface for shallow deposits.
• Recharging wells may be used to maintain lower layer head.

4. Usage Notes (Appendix B)

• Electro-osmosis is costly and reserved for very low permeability soils.
• Effective in soils where capillary forces inhibit gravitational drainage.

flowchart LR
    A[Electric Field Applied] --> B[Pore Water Movement]
    B --> C[Water Collected at Wells]
    C --> D[Discharge to Absorption or Recharge Wells]

Summary: Use electro-osmosis for very low permeability soils; calculate discharge with (Q = -k_g i z / a); ensure proper disposal to maintain groundwater balance.

IS 9759: Summary of Hydraulic Calculations and Flow Formulas

Main Discharge Formulas (Clauses 6.2 & 6.2.2)

• Flow to fully penetrating slots is double that from a single line source.
• For distances greater than 1.3 times stratum depth (D), head (h) changes linearly:

[h = h_e + (H - h_e) \frac{y + D}{L + y D}]

Well Penetration Corrections (Clause 1.10)

[H - h = (n + \ln \frac{a}{r_w}) \frac{Q}{2 \pi k D} \quad \text{(fully penetrating wells)}]

[H - h = \text{similar with correction factor for partial penetration}]

Where (a) is well spacing, (r_w) is effective radius, (f_a) uplift factor.

Notation Table

IS 9759: Formulas and Specifications for Selecting Pumps

1. Calculating Pump Horsepower (Clause 6.3.7)

Required pump power is computed as:

[Horsepower = \frac{\text{Total discharge (gpm)} \times \text{Total dynamic head (m)}}{3960 \times \text{Efficiency}}]

• Total dynamic head includes vacuum at pump intake minus friction losses.
• Efficiency is the combined pump and engine efficiency (decimal).

2. Deep Well Pump Selection (Clause 6.3.13.6)

• Use turbine or submersible pumps for wells with diameter ≥ 150 mm.
• Choose pumps based on capacity requirements from Table 8.
• Operate pumps at rated speeds; higher speeds increase capacity with safety margin.

3. Wellpoint Pumping (Clauses 6.3.10 & 6.3.10.1)

• Use self-priming centrifugal pumps coupled with vacuum pumps.
• Design for vacuum levels typically between 6 and 7.5 meters.
• Jet eductor pumps are suited for lowering water tables beyond 4.5 meters with low flow rates.

Summary Table

flowchart TD
    A[Pump Selection] --> B[Calculate Horsepower]
    B --> C{Discharge x Head}
    C --> D[Divide by 3960 x Efficiency]
    A --> E[Choose Pump Type]
    E --> F[Deep Well Pump (≥150 mm)]
    E --> G[Wellpoint Pump]

IS 9759: Maintenance Procedures and Troubleshooting Guidance

1. Discharge Calculations (Clause 6.2)

• Fully penetrating wells:

[H - h = \frac{n + \ln(\frac{a}{r_w})}{k D} \times Q]

• Partially penetrating wells:

[H - h = f_a \times \frac{n + \ln(\frac{a}{r_w})}{k D} \times Q]

Where parameters include groundwater levels, well spacing, depth, and uplift factors.

2. Filter Design to Prevent Soil Piping (Clause 6.3.5)

Proper filter design is essential to prevent piping under high hydraulic gradients.

3. Maintenance and Troubleshooting Tips

• Maintain standby pumps for emergencies.
• Regularly inspect filters and wells for clogging.
• Ensure continuous operation of wellpoint systems.
• Monitor pumps for unusual noise or vibration.
• Track water levels and drawdown to detect issues promptly.

Quick Reference Table: Dewatering Methods (Table 1)