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IRC 89 : 2018
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Guidelines for Design and Construction of Soil-Nail Supported Structures

AASHTO LRFD Bridge Design Specifications (Section on Mechanically Stabilized Earth Walls and Soil Nails) · FHWA Geotechnical Engineering Circular No. 1: Soil Nailing · Eurocode 7: Geotechnical design – Part 1: General rules
CurrentFrequently UsedCode of PracticeTransportation · Roads and Pavement
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OverviewValues17InternationalTablesFAQ10Related

Overview

IRC 89:2018 is the Indian Standard (IRC) for guidelines for design and construction of soil-nail supported structures. This IRC code is essential for engineers involved in designing and constructing soil-nail supported structures for slope stability and excavation support in transportation infrastructure. It outlines the principles of soil nailing, including soil-structure interaction, nail design, facing design, and grouting. The document emphasizes thorough site investigation, appropriate soil characterization, and load assessment to ensure the stability and longevity of these structures. It details construction sequences, quality assurance protocols, and performance monitoring, providing a robust framework for safe and effective implementation in Indian road projects.

This IRC code provides comprehensive guidelines for the design and construction of soil-nail supported structures, commonly used for slope stabilization and excavation support in highway projects. It covers aspects from site investigation and material selection to detailed design methodologies, construction procedures, and quality control measures.

Status
Current
Usage level
Frequently Used
Domain
Transportation — Roads and Pavement
Type
Code of Practice
International equivalents
AASHTO LRFD Bridge Design Specifications (Section on Mechanically Stabilized Earth Walls and Soil Nails)FHWA Geotechnical Engineering Circular No. 1: Soil NailingEurocode 7: Geotechnical design – Part 1: General rules
Typically used with
IS 104
Also on InfraLens for IRC 89
17Key values6Tables10FAQs
Practical Notes
! Thorough site investigation is paramount; insufficient data leads to design errors.
! Soil nailing is most effective in fine-grained soils with a cohesive component.
! Groundwater conditions significantly influence design; proper dewatering might be required.
! Consider constructability challenges in confined urban areas.
! Adequate corrosion protection for steel elements is crucial for long-term performance.
! The facing system provides surface protection and distributes loads; its design should not be neglected.
! Regular monitoring is essential to detect any unforeseen behaviour or distress.
! The selection of drilling equipment should be based on soil conditions and site accessibility.
! The grouting process must ensure complete void filling and good bond with the soil and nail.
! Proof loading of a percentage of nails is a critical quality control measure.
! The sequence of excavation and nail installation significantly impacts stability.
! Careful consideration of nailing into adjacent structures or utilities is necessary.
! The coefficient of friction at the soil-nail interface is a key parameter and can be influenced by grout quality and soil type.
! Design should account for the long-term creep behaviour of certain soils if applicable.
! Face drainage should be incorporated to reduce pore water pressure behind the facing.
! Instrumentation such as inclinometers and settlement markers can provide valuable performance data.
Frequently referenced clauses
Cl. 1.0IntroductionCl. 2.0DefinitionsCl. 3.0Site Investigation and Soil CharacterisationCl. 4.0Design PrinciplesCl. 5.0Design of Soil NailsCl. 6.0Design of Facing SystemCl. 7.0Construction ProceduresCl. 8.0Quality Control and AssuranceCl. 9.0Performance Monitoring
Pulled from IRC 89:2018. Browse the full clause & table index below in Tables & Referenced Sections.
Soil NailingSlope StabilityExcavation SupportRetaining StructuresGeotechnical EngineeringHighway EngineeringConstruction GuidelinesIRC CodesIndian Roads CongressIRC

International Equivalents

Similar International Standards
AASHTO LRFD Bridge Design Specifications (Section on Mechanically Stabilized Earth Walls and Soil Nails)
MediumCurrent
FHWA Geotechnical Engineering Circular No. 1: Soil Nailing
MediumCurrent
Eurocode 7: Geotechnical design – Part 1: General rules
MediumCurrent
Key Differences
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Key Similarities
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Parameter Comparison
ParameterIS ValueInternationalSource
Design Philosophy
Minimum Nail Diameter
Minimum Nail Embedment Length
Corrosion Protection (Design Life)
Factor of Safety (Global Stability)
⚠ Verify details from original standards before use

Key Values17

Quick Reference Values
minimum nail diameter mm75
minimum nail spacing m1
maximum nail spacing m2.5
minimum nail embedment length m3
maximum nail inclination degrees15
minimum nail inclination degrees5
grout strength mpa20
corrosion protection requirement years75
maximum allowable settlement mm25
minimum cover to nail head mm50
coefficient of friction soil nail interface0.4
design factor of safety global stability1.5
design factor of safety local stability1.3
allowable tensile stress steel bar mpa230
allowable shear stress soil mpa0.15
typical nail length factor of excavation depth0.7
minimum facing thickness mm100
Key Formulas
FS_global = Sum(Resisting Moments) / Sum(Overturning Moments)
FS_local = (Sum of nail tensile capacities + Sum of soil shear capacities) / Sum of driving forces
T_nail = pi * D_hole * L_embed * c_soil + N_bar * A_bar * f_y / gamma_m
P_grout = 2 * c_soil * (1 + sin(phi_soil)) / (1 - sin(phi_soil))

Tables & Referenced Sections

Key Tables
Minimum Borehole Requirements for Different Ground Conditions
Typical Soil Strength Parameters for Design
Allowable Stresses for Steel Reinforcement
Grout Mix Proportions and Properties
Minimum Thickness of Shotcrete Facing
Testing Requirements for Soil Nails
Key Clauses
Introduction
Definitions
Site Investigation and Soil Characterisation
Design Principles
Design of Soil Nails
Design of Facing System
Construction Procedures
Quality Control and Assurance
Performance Monitoring

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Frequently Asked Questions10

What is the primary purpose of soil nailing according to this IRC code?+
The primary purpose of soil nailing, as outlined in this IRC code, is to provide structural support for excavations and stabilize natural slopes. This is achieved by installing passive reinforcing elements (soil nails) into the soil mass, which are then grouted to create a composite structure. The nails resist tensile and shear forces, while the facing system provides surface protection and load distribution, collectively enhancing the overall stability of the soil mass and preventing collapses or excessive deformations.
What are the key soil characteristics that influence the design of soil-nail supported structures?+
Key soil characteristics include shear strength parameters (cohesion and angle of internal friction), groundwater conditions, soil compressibility, and potential for creep. The code emphasizes detailed geotechnical investigations to determine these properties accurately. Higher shear strength allows for longer nail spacing and shallower nails, while the presence of groundwater can significantly reduce effective stress and soil strength, necessitating measures like drainage or lower design parameters. Compressible soils may experience larger deformations, and creep in some soils can lead to long-term instability.
What is the role of the facing system in a soil-nail structure?+
The facing system, typically made of shotcrete or precast panels, serves multiple critical functions in a soil-nail supported structure. It provides immediate surface erosion control, preventing the soil from washing away and protecting the nail heads. More importantly, it distributes the loads from the soil mass onto the nail heads, ensuring that the forces are effectively transferred to the reinforcing elements. The facing also contributes to the overall integrity and stability of the retained soil mass by acting as a diaphragm.
What is the importance of quality control during soil nail construction?+
Quality control is crucial for the successful performance and long-term stability of soil-nail supported structures. This IRC code mandates rigorous testing at various stages, including soil testing, grout testing, and nail testing (e.g., proof loading and pull-out tests). Ensuring that the soil has adequate strength, the grout provides a strong bond, and the nails meet their design capacities is vital. Deviations from specified procedures or material properties can compromise the structural integrity, leading to premature failure or reduced service life.
How does groundwater affect the design and construction of soil nails?+
Groundwater significantly impacts the effective stress in the soil, thereby reducing its shear strength. High groundwater levels can also lead to issues during drilling and grouting, such as borehole instability and reduced grout effectiveness. The IRC code requires careful consideration of groundwater conditions and may mandate dewatering or the use of special grouting techniques to ensure proper bond development and overall stability. The presence of groundwater often necessitates a more conservative design with reduced allowable soil strengths and potentially closer nail spacing.
What are the typical failure modes that need to be checked in a soil-nail design?+
The IRC code requires checks for several potential failure modes to ensure the overall stability of the soil-nail system. These include global stability (rotational or translational sliding of the entire soil mass), local stability (failure of individual soil nails through pull-out, shear, or bending, or failure within the soil block supported by the nails), and facing failure. The design must ensure that the factor of safety against each of these failure modes meets the minimum requirements specified in the code.
What is proof loading, and why is it important for soil nails?+
Proof loading is a procedure where a certain percentage of installed soil nails are subjected to a predetermined tensile load to verify their load-carrying capacity and the quality of installation and grouting. This testing is critical for assuring the engineer that the installed nails are performing as designed and to detect any anomalies in material or construction that might compromise their effectiveness. It provides confidence in the soil-nail system's ability to withstand the design loads and contribute to the overall stability of the structure.
What are the considerations for corrosion protection of soil nails?+
Corrosion protection for steel soil nails is a critical aspect addressed by the IRC code, especially for structures intended for long service life. The code typically requires protective measures such as galvanization or the use of epoxy-coated bars, particularly in aggressive soil environments or where a long design life is specified (e.g., 75 years). The grout itself also provides some degree of protection. The extent of protection required is usually determined based on the anticipated aggressiveness of the soil and the desired service life of the structure.
Can soil nailing be used in all types of soil conditions?+
Soil nailing is most effective in soils that possess some cohesive strength and can stand with a near-vertical face for a short period during excavation. This includes stiff to very stiff clays, silts, and dense sands. It is generally less suitable or requires modifications in very soft soils, highly expansive clays, or soils with high organic content. The IRC code provides guidance on the suitability of soil nailing based on soil characteristics and emphasizes the need for thorough site investigations to determine its applicability.
What is the typical spacing and inclination of soil nails?+
The spacing and inclination of soil nails are crucial design parameters determined based on the soil properties, excavation geometry, and the required level of support. Generally, nails are inclined downwards into the slope or excavation face at an angle typically between 5 to 15 degrees from the horizontal. Spacing can vary significantly but often ranges from 1.0 to 2.5 meters both horizontally and vertically, depending on the soil's ability to span between nails and the overall stability requirements.

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