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IS 11208:1985 is the Indian Standard (BIS) for guide for subsurface investigation for power tunnels and pressure shafts. This guide outlines the procedures for subsurface geological and geotechnical investigations for power tunnels and pressure shafts. It covers the different stages of investigation, from reconnaissance to detailed exploration, specifying the methods and extent of work required. The objective is to gather sufficient data on rock/soil conditions, groundwater, and geological hazards for a safe and economical design.
Lays down guidelines for subsurface investigations specifically for power tunnels and pressure shafts, covering geological, hydrological, and geotechnical aspects.
Overview
Status
Current
Usage level
Specialized
Domain
Geotechnical — Tunneling and Underground Structures
BIM-relevant code. See the BIM Hub for ISO 19650, IFC, and LOD/LOIN frameworks used alongside it.
Practical Notes
! The primary focus during investigation should be on identifying major geological discontinuities like faults, shear zones, and areas of high groundwater ingress.
! The scope defined in this guide is a minimum; complex geological conditions or critical projects may require a significantly more intensive investigation program.
! Accurate logging and preservation of drill cores as per IS 4464 are crucial for correct geological and geotechnical interpretation.
BS 5930:2015+A1:2020BSI (British Standards Institution), UK
HighCurrent
Code of practice for ground investigations
Comprehensive guidance on all stages of ground investigation for civil engineering, including tunnels.
EN 1997-2:2007CEN (European Committee for Standardization), Europe
HighCurrent
Eurocode 7: Geotechnical design - Part 2: Ground investigation and testing
Focuses specifically on ground investigation and testing to obtain parameters for Eurocode 7 design.
EM 1110-2-2901USACE (U.S. Army Corps of Engineers), USA
HighCurrent
Engineering and Design - Tunnels and Shafts in Rock
Provides detailed guidance on planning, design, and construction, including extensive site investigation requirements for tunnels.
ASTM D420-18ASTM International, USA
MediumCurrent
Standard Guide to Site Characterization for Engineering, Design, and Construction Purposes
Provides a general framework for site characterization for all projects, not specific to tunnels.
Key Differences
≠IS 11208:1985 provides prescriptive recommendations (e.g., drill hole spacing of 300-500 m), whereas modern standards like EN 1997-2 are more performance-based, requiring the engineer to define an investigation scope sufficient to manage geotechnical risk.
≠Modern standards (e.g., BS 5930) explicitly integrate a formal risk management approach and the use of a Geotechnical Baseline Report (GBR) as a contractual tool, which is not formalized in IS 11208.
≠EN 1997-2 is tightly coupled with EN 1997-1 (Design), using partial factors and characteristic values derived from investigations. IS 11208 is a standalone investigation guide with a less formalized link to design codes.
≠Being from 1985, IS 11208 does not cover modern advancements in geophysical methods (e.g., seismic tomography, advanced GPR) or data management that are discussed in recent revisions of BS 5930.
Key Similarities
≈All standards advocate for a phased approach to investigation, typically starting with a desk study/reconnaissance, followed by preliminary and then detailed/design-stage investigations.
≈The fundamental portfolio of investigation techniques, including geological mapping, drilling and core logging, in-situ testing (e.g., permeability tests, plate load tests), and laboratory testing, is common across all standards.
≈The primary objective is identical: to develop a comprehensive ground model to understand rock mass characteristics, groundwater conditions, and geohazards for a safe and economical design.
≈All standards recognize the importance of rock mass classification systems (like RMR or Q-system) and the measurement of Rock Quality Designation (RQD) as key inputs for design.
Parameter Comparison
Parameter
IS Value
International
Source
Investigation Stages
Four stages: Reconnaissance, Preliminary, Pre-construction (Detailed), and Construction.
Four similar stages: Desk study, Preliminary investigation, Design investigation, and Construction.
BS 5930:2015
Drill Hole Spacing (Detailed Stage)
Prescribed as 300 m to 500 m along tunnel alignment.
Not prescribed; depends on geological complexity and risk. Can range from <150 m to >1500 m.
EM 1110-2-2901
Borehole Depth below Tunnel Invert
At least 1.5 times the tunnel diameter.
Typically 1 to 2 times the tunnel diameter or span, depending on geology and stress conditions.
General practice, e.g., referenced in USACE manuals
Required Core Recovery in Rock
Should normally be 90 to 100 percent.
High recovery (>90%) is the goal; the drilling method must be selected to maximize recovery for the ground conditions.
BS 5930:2015
In-situ Permeability Testing
Recommends water pressure (Lugeon) tests in drill holes.
Specifies water pressure tests (packer tests), including the Lugeon test, as a primary method.
EN 1997-2:2007
Deformability Testing
Recommends Plate Bearing Test and Flat Jack Test.
Recommends Plate Loading Test, Flat Dilatometer, Pressuremeter, and Flat Jack test for deformability.
EN 1997-2:2007
⚠ Verify details from original standards before use
Key Values5
Quick Reference Values
Preliminary drill hole spacing along tunnel300 to 500 m
Detailed drill hole spacing along tunnel100 to 300 m
Minimum drill hole depth below tunnel invertOne diameter of the tunnel
Minimum core recovery in rockGenerally not less than 85 percent
Minimum depth of exploration for shafts1.5 times the base width below foundation level