PREAMBLE (NOT PART OF THE STANDARD)

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END OF PREAMBLE (NOT PART OF THE STANDARD)

IS 14458 (Part 1): 1998

Indian Standard
RETAINING WALL FOR HILL AREA—GUIDELINES PART 1 SELECTION OF TYPE OF WALL

ICS 93.020

©BIS 1998
BUREAU OF INDIAN STANDARDS
MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG
NEW DELHI 110002

May 1998

Price Group 4

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Hill Area Development Engineering Sectional Committee, CED 56

FOREWORD

This Indian Standard (Part 1) was adopted by the Bureau of Indian Standards, after the draft finalized by the Hill Area Development Engineering Sectional Committee had been approved by the Civil Engineering Division Council.

Retaining wall is a structure used to retain backfill and maintain difference in the elevation of the two ground surfaces. Retaining wall may be effectively utilized to tackle the problem of landslide in hill area by stabilizing the fill slopes and cut slopes.

From the initial construction cost considerations, one metre of extra width in filling, requiring retaining walls, costs much more than constructing the same width by cutting inside the hill. Similarly the cost of a breast wall is several times more than a non-walled cut slope. However, considering maintenance cast, progressive slope instability and environmental degradation from unprotected heavy excavations, the use of retaining walls on hill roads and terraces becomes essential. This standard (Part 1) is, therefore, being formulated to provide necessary guidance in selection of retaining walls for stability of hill slopes, the other parts of the standard being:

Part 2    Design of retaining/breast walls
Part 3    Construction of dry stone walls
Part 4    Construction of banded dry stone walls
Part 5    Construction of cement stone walls
Part 6    Construction of gabion walls
Part 7    Construction of RCC crib walls
Part 8    Construction of timber crib walls
Part 9    Design of RCC cantilever wall/buttressed walls/L-type walls
Part 10  Design and construction of reinforced earth retaining walls

In the formulation of this standard, considerable assistance has been provided by International Centre for Integrated Mountain Development, Kathmandu. Assistance has also been derived from Mountain Risk Engineering Handbook.

The composition of technical committee responsible for the formulation of this standard is given at Annex A.

For the purpose of deciding whether a particular requirement of this standard is complied with, the final value, observed or calculated, expressing the result of a test or analysis, shall be rounded off in accordance with IS 2: 1960 ‘Rules for rounding off numerical values (revised)’. The number of significant places retained in the rounded off value should be the same as that of the specified value in this standard.

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Indian Standard
RETAINING WALL FOR HILL AREA—GUIDELINES

part 1 selection of type of wall

1 SCOPE

This standard (Part 1) covers the guidelines for selection of various retaining walls to suit the site conditions, for the purpose of imparting stability to the slopes in hill areas.

NOTE—The retaining walls are normally not intended to stabilize slope failures. They are mainly meant to support the active or passive earth pressure from the assumed failure wedge above the base of the wall. The stabilization of existing or probable failure planes caused by landslides, flows and falls require separate treatment and specific design approaches. Only the fill slopes and cut slopes could be stabilized/retained by retaining walls.

2 CLASSIFICATION

2.1

The retaining walls shall be classified on the basis of type of construction and mechanics of behaviour (see Fig. 1) as follows:

  1. Gravity walls
  2. Tie back walls
  3. Driven cantilever walls
  4. Reinforced earth walls
  5. RCC walls

2.2

The classification of retaining walls with respect to their design and probable behaviour of construction medium may be as follows:

  1. Bin walls
    1. Rectangular
    2. Circular
    3. Cross tied
  2. Crib walls
    1. Concrete crib
    2. Timber crib
  3. Gabions walls and wire crated/sausage walls
  4. Cement masonry walls
  5. Dry stone masonry walls
  6. Drum walls
  7. Reinforced backfill walls

    FIG. 1 DIFFERENT TYPES OF RETAINING WALLS

    Fig. 1 Different Types of Retaining Walls

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    FIG. 1 DIFFERENT TYPES OF RETAINING WALLS

    Fig. 1 Different Types of Retaining Walls

    1. Reinforced earth
    2. Fabric
  8. Anchored walls
    1. Horizontal sheet pile
    2. Vertical sheet pile
    3. H-pile, timber logged
  9. RCC walls
    1. Cantilever
    2. L-type
    3. Buttressed wall
    4. Frame retaining walls

3 SELECTION OF TYPE OF WALLS

3.1

In general, the choice of wall depends on local resources, local skill, hill slope angle, foundation conditions, slope of backfill, compatibility of materials and seismicity of the region (see Tables 1 and 2). However, the guidelines given in 3.1.1 to 3.1.14 shall be considered for selection of the type of retaining wall to be constructed for the purpose of imparting stability to the slopes in hill area.

3.1.1

For hilly roads, being of low volume, walls may not be designed for earthquake forces. It is economical to repair failed walls after earthquake.

3.1.2

Earthquake considerations lead to excessive wall dimensions. High walls may, therefore, be avoided by alternative geometric designs of roads and terraces unless justified by risk analysis. Walls with dip at the base towards hillside will reduce the base width in seismic areas.

3.1.3

Front battered retaining walls are many times more expensive than back battered walls in steep hilly areas.

3.1.4

A retaining wall on a thin talus slope may not be able to prevent the failure of entire talus slope during monsoon because of the quick rise of water table above the relatively impervious bed rock.

3.1.5

The construction of series of retaining walls one above another on an unstable or marginally stable slope shall be avoided as it adds more pressure on the lower walls destabilizing the slope contrary to the aim of stabilizing the slope. In such cases, unstable slope shall be stabilized by afforestation, surface/subsurface drainage system, etc.

3.1.6

Improper backfill and poor drainage behind the wall involve complicated drainage conditions which are normally not considered in normal design. Proper drainage behind the walls shall, therefore, be provided.

3.1.7

The practice of undertaking wall construction after road/hill cutting poses the problem of disposal of excavated material and loss of top soil that could otherwise be used for vegetation. Hence during construction of retaining walls, the excavated material shall be disposed off at suitable identified sites.

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3.1.8

Breast walls are more economical for cut slopes. Batter (negative) of the backfill side reduce base width of the wall significantly.

3.1.9

Dry stone retaining walls, breast walls and timber crib are economical but least durable, non-ductile structures. These are most susceptible to earthquake damages.

3.1.10

Gabion/wire crated walls shall be used in case of poor foundation or seepage conditions. These can take considerable differential settlement and some slope movement.

3.1.11

Banded dry stone masonry (height ≤ 6 m) and cement masonry walls are most durable but being non-ductile structures, are susceptible to earthquake damages.

3.1.12

Reinforced earth is normally used as reinforced fill platform for road. Generally it is not used as preventive method of slope support.

3.1.13

Timber crib, dry stone masonry walls may be provided for hill slope angle less than 30° and, height less than 4 m in low volume roads. These are not suitable for terrace development because of short life.

3.1.14

Cement masonry, RCC walls, Gabion walls shall be considered for high volume roads, high cut slopes and terraces. These are also suitable for hill slope angles from 30° to 60°, where higher walls are needed.

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Table 1 Selection of Retaining Walls
(Clause 3.1)
  Type Retaining Walls
Timber Crib Dry Stone Banded Dry Stone/Masonary Cement Masonry Gabion Reinforced Earth
Low High
Diagrammatic Cross-section Image Image Image Image Image Image Image
CONSTRUCTION NOTES Top width 2m 0.6-1.0 m 0.6-1.0 m 0.5-1.0 m 1 m 1-2 m 4 m or 0.7-0.8 m
Base width 0.5-0.7 H 0.6-0.65 H 0.5-0.65 H 0.6-0.75 H 0.55-0.65H 4 m or 0.7-0.8 H
Front batter 4:1 vertical varies 10:1 6:1 6:1 3:1
Back batter 4:1 varies vertical varies varies varies 3:1
nward dip of foundation 1:4 1:3 1:3 horizontal or 1:6 1:6 1:6 horizontal
Foundation depth below drain 0.5-1 m 0.5 m 0.5-1 m 0.5-1 m 0.5 m 1 m 0.5 m
Range of height 3-9 m 1-6 m 6-8 m 1-10 m l-6m 6-10m 3-25 m
Hill slope angle <30° <35° 20° 35-60 35-60 35-60 <35
Toe protection in case of soft rock/soil Boulder pitching Boulder Pitching No
General Timbers 15 cm φ with stone rubble well packed behind timbers. 10% of all headers to extend into fill. Ecologically unacceptable. Set stones along foundation bed. Use long bond stones. Hand packed stones in back fill. Cement masonry bands of 50 cm thickness at 3 m c/c. Other specifications as for dry stone wall. weep holes 15 × 15 cm size at 1-2 m c/c. 50 cm rubble backing for drainage. Stones to be hand packed. Stone shape important, blocky preferable to tabular. Specify maximum/minimum stone size. No weathered stone to be used. Compact granular back fill in layers (< 15 cm). Use H type gabion wall. Granular back fill prefered. Use geogrid for H <4 m and tensur grid for H> 4 m. Provide drainage layer in case of seepage problems. Specify spacing of reinforcement grids. 4
   
  1. Foundations to be stepped up if rock encountered.
  2. All walls require durable rock filling of small to medium size.
  3. Drainage of wall bases not shown. Provide 15 cm thick gravel layer in case of clayey foundation.
 
Application Least durable Most durable Can take differential settlement and slope movement Huge potential used more as stable reinforced fill platform for road rather than preventive method of slope support.
Non ductile structure most susceptible to earthquake damage Very flexible structures
  1. Design as conventional retaining walls. Assume surcharge on road of 2T/m2.
  2. Used both as cut slope and fill slopes support. Breast wall is more economical for cut slope.
  3. Choice of wall depends on local resources, local skill, hill slope angle, foundation conditions and also shape of back fill wedges as illustrated in diagrams and compatibility of materials.
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Table 2 Selection of Breast Walls
(Clause 3.1)
Type Breast Walls/Revetment Walls Remarks
(1) Dry Stone
(2)
Banded Dry Stone Masonry
(3)
Cement Masonry
(4)
Gabion
(5)
Horizontal Drum Walls
(6)
(7)
Diagrammatic cross-section Image Image Image Image Image
  1. Wall construction requires special skills and practical labour. Curing of masonry walls generally not feasible in hills due to paucity of water.
  2. The typical dimensions shown rely both on well-drained backfill and good foundation conditions.
  3. Detailed design is necessary in case of soil slopes and walls higher than 6 m and poor foundation conditions.
  4. Gabion walls should be used in case of poor foundation/seepage conditions. They can take considerable differential settlement and some slope movement.
  5. Other measures should also be taken, for example, check drains, turfing, benching of cut slopes in soft rocks, sealing of cracks, etc. All preventive measures should be implemented in one season. Total system of measures is far more effective than individual measures.
Construction Notes Top width 0.5 0.5 0.5 2 1
Base width 0.29H 0.3H 0.33H   0.23H 2 1
Front batter              
Back batter 3:1 4:1 5:1 3:1 3:1 3 to 5:1 3:1
Inward dip of foundation 1:3 1:4 1:5 1:3 1:3 1:5 1:3
Foundation depth below drain 0.5 m 0.5 m 0.5 m 0.5 m 0.5 m 0.5-1 m 0.25 m
Range of height 6 m 4 m 3m 3.8 m 1.10m 1.8 m 2.2 m
Hill slope angle 35-60 35-60 35-70 35-60 35
Toe protection in case of soft rock/soil No pitching No No No No
General Pack stone along foundation bed. Use bond stones. Specify minimum stone size. Cement masonry (1:6) bands of 0.5 m thickness at 3 m c/c. Weep holes 15×15 cm at 1.5-2 m c/c and grade 1:10. Cement sand (1:6) Step in front face 20-50 cm wide. Otherwise as for retaining walls. Use vertical single drum for 0.7 m height. Anchor drum walls on sides. Fill debris material.
Revetment walls have uniform section of 0.5 m/0.75 m thickness for batter of 2:1 or more. Section shaped to suit variation and overbreak in rock cut slope.
Application Least durable/economical Little used Most durable/costly Quite durable/costlier or Very flexible Promising/most economical or Flexible
Non ductile structures most susceptible to earthquake damage.
Revetments are used to prevent only major erosion, rock fall, slope degradation particularly where vulnerable structures are of risk.
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ANNEX A
COMMITTEE COMPOSITION

(Foreword)

Hill Area Development Engineering Sectional Committee, CED 56

Chairman Representing
Dr Gopal Ranjan University of Roorkee, Roorkee
Members
Shri Sheikh Nazir Ahmed Public Works Department, Jammu & Kashmir
Prof A. K. Chakraborty Indian Institute of Remote Sensing, Dehra Dun
     Shri R. C. Lakhera (Alternate)
Chairman-cum-Managing Director National Buildings Construction Corporation, New Delhi
     Shri B. B. Kumar (Alternate)
Chief Engineer (Dam Design) Uttar Pradesh Irrigation Design Organization, Roorkee
     Suptdc Engineer (Tehri Dam Design Circle)(Alternate)
Chief Engineer (Roads) Ministry of Surface Transport, New Delhi
     Suptdg Engineer (Roads)(Alternate)
Deputy Director General (D & S DTE, DGBR) Indian Roads Congress, New Delhi
     Deputy Secretary (T), IRC (Alternate)
Director, HCD (N & W) Central Water Commission, New Delhi
     Director (Sardar Sarovar)(Alternate)
Dr R. K. Dubey Indian Meteorological Department, New Delhi
     Dr D. S. Upadhyay (Alternate)
Shri Paw an Kumar Gupta Society for Integrated Development of Himalayas, Mussorie
     Field Coordinator (Alternate)
Shri T.N. Gupta Building Materials & Technology Promotion Council, New Delhi
     Shri J. Sengupta (Alternate)
Shri M. M. Harbola Forest Survey of India, Dehra Dun
     Shri P. K. Pathak (Alternate)
Dr U. C. Kalita Regional Research Laboratory, Jorhat
     Shri B. C. Borthakor (Alternate)
Shri S. Kaul Ministry of Railways, New Delhi
Shri Kireet Kumar G.B. Pant Institute of Himalayan Environment and Development, Almora
Prof A. K. Maitra School of Planning and Architecture, New Delhi
     Prof Arvind Krishan (Alternate)
Drg. S. Mehrotra Central Building Research Institute, Roorkee
     Shrin. C. Bhagat (Alternate)
Shri P. L. Narula Geological Survey of India, Calcutta
     Shri S. Dasgupta (Alternate)
Shrimati M. Parthasarathy Engineer-in-Chief s Branch, Army Headquarters, New Delhi
     Shrin. K. Bali (Alternate)
Shri D. P. Pradhan Sikkim Hill Area Development Board, Gangtok
Shri P. Jagannatha Rao Central Road Research Institute, New Delhi
     Shri D. S. Tolia (Alternate)
Dr K.S.Rao IIT, New Delhi
Shri P. K. Sah Directorate General Border Roads (D&S), New Delhi
     Shri j. Gopalakrishna (Alternate)
Shri G. S. Saini Central Mining Research Institute, Dhanbad
Dr Bhawani Singh University of Roorkee, Roorkee
     Dr P. C. Jain (Alternate)
Shri Bhoop Singh Department of Science and Technology, New Delhi
Shri R. D. Singh National Institute of Hydrology, Roorkee
     Dr Sudhir Kumar (Alternate)
Prof C. P. Sinha North-Eastern Regional Institute of Water and Land Management, Assam
     Shri D. K. Singh (Alternate)
Shri Lakhbir Singh Sonkhla Public Works Department, Simla
Dr P. Srinivasulu Structural Engineering Research Centre, Chennai
     Shri N. Gopalakrishnan (Alternate) 7
Suptdg Surveyor of Works (NZ) Central Public Works Department, New Delhi.
     Surveyor of Works-1 (NZ) (Alternate)
Shri V. Suresh Housing & Urban Development Corporation (KODCO). New Delhi
     Shri D. P. Singh (Alternate)
Shri S. C. Tiwari U.P. Hill Area Development Board, Lucknow
Shri K. Venkatackalam Central Soil & Material Research Station, New Delhi
     Shri S. K. Babbar (Alternate)
Dr N. S. Virdhi Wadia Institute of Himalayan Geology, Dehra Dun
Shri Vinod Kumar, Director (Civ Engg) Director General, BIS (Ex-officio Member)

Member Secretaries
Shri T. B, Narayanan
Joint Director (Civ Engg), BIS

Shri Sanjay Pant
Deputy Director (Civ Engg), BIS

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