YEAR 2006

PERFORMANCE BASED LOW COST SPECIFICATIONS USING LOCALLY AVAILABLE MATERIAL FOR RURAL ROADS
By Ashwani Kumar1, R. K. Swami2, Sudhir Mathur3 & S.K. Soni4

1. INTORDUCTION
Roads are one of the main communication facility in rural areas. Roads help in the economic upliftment of rural population by providing access to market centre and other civic amenities like educational institutions, hospitals, etc. But rural areas in India are lacking adequate road network due to scarcity of funds. Conventional specifications cannot be adopted for rural roads in view of escalating cost for the conventional materials, shortage of manpower, machinery and funds. So efforts were made at Central Road Research Institute (CRRI) to explore the use of locally available materials as alternate materials for rural road construction. The locally available materials are cheaper, easily available and when suitably processed develop adequate strength. Inspite of their advantages, local materials have not been utilised to their fullest extent.

Central Road Research Institute has been conducting studies to explore the possibilities of using local materials for rural road construction and its impact on construction cost. Large number of test tracks were constructed in different parts of the country depending upon the materials available in that area to study the behaviour of these materials under different conditions. Efforts were made to include different variables i.e. topography, climate, nature of subgrade soil, traffic, ground water table, rainfall etc. while selecting the construction sites. Post construction performance of the test tracks was monitored for a period of 4 to 5 years.
In this paper only those specifications are discussed which gave good performance during the observation period and where locally available materials were used to the maximum extent. A simple approach to determine pavement thickness for rural roads has also been discussed.


2. MATERIALS
Locally available materials, like, soil, soil-gravel, soft aggregates, moorum and mine waste were effectively used as an alternate to conventional materials with significant economy after studying their physical and engineering properties.

2.1 Soil
(i) Alluvial Soils: These are light brown in colour and have low to medium plasticity and low strength when measured in term of California Bearing Ratio (CBR).

(ii) Black Cotton Soils: These soils are light to deep black in colour and are medium to highly plastic. These soils show swelling and shrinking properties during wetting and drying. In general these soil have low strength.

(iii) Desert Sand: It is non-plastic in nature and has uniform grain size.

2.2. Soft Aggregate

(i) Dhandla: It is a calcareous material and is found under the overburden of desert sand at depths of 1 to 1.5 m. It gets crushed under roller. After excavation, on exposure to atmosphere its strength improves slightly.

(ii) Moorum: This material vary widely in characteristics and is a product of decomposition and weathering of parent rocks. Properties of moorum depend upon parent rock and process of weathering. Visually this material looks like gravel except that percentage of fines is relatively much higher and fines are plastic.

(iii) Soil-gravel: These are coarse material with average particle size over 2.36 mm. These may have cohesion nd: It is non-plastic in nature and has uniform grain size.

2.3. Mine Waste

These wastes are low grade materials, which must be removed and disposed off in order to get valuable ore and other materials. Different types of waste materials are available at different mine sites and therefore have different physical and strength characteristics.

The samples of these materials were collected from different locations and were investigated in the laboratory for their physical and engineering characteristics. These properties are given in Tables 1 and 2. These materials cover all soil group of Unified Soil Classification System. Based on the laboratory data specifications were developed for construction of test tracks in different states. These materials were used as such or after improving their properties by adopting mechanical or lime stabilization techniques. Based on these specifications test sections were laid for field trials.

3. DETERMINATION OF PAVMENT THICKNESS


The conventional specifications for construction of rural roads in the country are comprised of stone/brick soling or WBM (over size) layer in sub base followed by WBM layer as base and generally topped with bituminous surfacing. Rural roads are low volume roads but specifications for the pavement have to be durable and economical as far as possible. In view of this CRRI undertook a detailed country


wide study of different factors relevant to the development of rural roads. The presence of slow moving ironed tyred carts in the rural roads leads to excessive damages of rural roads. So the computation of daily traffic in a rural road on the basis of number of commercial vehicles plying is misleading. Based on the study1 a formula was computed for Traffic Index (T.I.) based on the different categories of vehicles plying and their damaging factor. Based on the rut depth and transverse slope variance, the rural roads have been categorized into Category-I and Category-II and placed them in the lower spectrum below Category -A roads of IRC Categorisation.

The thickness of flexible pavement for a particular subgrade is a function of number and type of vehicles. The basis for evaluation of these curves are;

(a) Categorisation of rural road is based on the minimum acceptable serviceability level.
(b) Traffic index can be computed by the formula
Traffic Index (T.I.) = 2SWC + CV + 0.4 OV
SWC = Number of animal drawn solid wheeled carts per day; CV = Number of commercial vehicles per day; OV = Number of Other vehicles per day
(c) Subgrade strength/CBR

The evaluation of CBR of subgrade and other materials for design of pavement crust is time consuming and needs both well-trained manpower and well equipped laboratory set up. As these facilities are non existent in rural areas, therefore, a simple approach was needed to design rural roads. An earlier study found that the CBR can be computed from sieve analysis data. For computation of thickness for different categories of rural roads, simple nomographs2,3 were developed by incorporating simple sieve analysis and Traffic Index Data (Fig. 1 and 2). These nomographs directly give pavement thickness from soil gradation data and traffic index. (Stepwise procedure to determine pavement thickness is given at Appendix-I). These curves also take into account the slow moving traffic i.e. solid wheeled carts, which is predominant on rural roads and causes more damage to road than the pneumatic tyred vehicle.

4. PAVEMENT COMPOSITION ADOPTED USING LOCAL MATERIALS

Thickness of each specification was worked out either by pavement design curves developed by CRRI or by conventional pavement design curve ‘A’ as per existing traffic conditions and subgrade strength. Composition of each specification is given in Fig. 3.

4.1 DHANDLA
It is common observation in desert area that on account of non-cohesive nature of subgrade i.e. desert sand, it is difficult to compact the subgrade with roller and the subbase material has tendency to sink into subgrade during its compaction or on compaction of subsequent layers on it resulting in deformations in pavement. To avoid this, loose sand can be treated with additives but it will increase the cost of construction. It was found that if loose subgrade is watered and 10 to 12 passes of 35 h.p. tractor are given, an adequate compaction of subgrade can be achieved. It was further observed that if hand rammed layer of dhandla is provided as subbase over loose desert sand then upper layers of dhandla can easily be compacted by roller.

The specification given below was laid on the Lachadsar- Momasar Road in Rajasthan using dhandla in subbase and base course.

Specification No.-I (4)

Type of Subgrade Soil : Desert sand

Subbase : 10 cm thick layer of dhandla (Hand compacted by Durmut)

Base Course : 15 cm thick layer of dhandla (Roller compacted) with a layer of stone grafting @ 0.3 cu.m/10 sqm
Wearing course : 2 cm Premix carpet

This specification is very useful for low volume traffic in area of Rajasthan where dhandla is available. Performance of this section was rated good throughout the period of observation.

4.2. Black Cotton Soil

Black Cotton (BC) soil covers almost one-sixth part of the country. The roads constructed in such area need heavy maintenance. The roads in BC soil area develop waviness at the surface due to loss of strength of subgrade through softening during monsoon. Hence, road construction works need special attention in such areas. The research work carried out had shown that strength properties can be improved considerably by treating BC soil with lime. Table 1–2 shows that when BC soil was treated with 5per cent lime, strength in terms of CBR value increased from 2 to 49 in case of specification no. II ( Andhra Pradesh) and from 2 to 51 in specification III (Karnataka). This clearly indicate that when BC soil is treated with lime becomes more amenable and can effectively be used in lower layers of pavement to give firm foundation to subsequent layers. This fact has been proved in following two specifications, which were laid at two different sites at Kurnool - Ulchala Road (A.P.) and Bijapur – Ukkali Road (Karnataka)

Specification No.-II (5)
Type of Subgrade Soil : CH
Subbase : 11.25 cm thick layer of BC soil stabilized with 5per cent lime
Base Course : 11.25 cm thick layer of moorum stabilized with 3per cent lime
Wearing course : 7.5 cm thick layer of WBM
Specification No.-III5

Type of Subgrade Soil :CH
Subbase : 11.25 cm thick layer of BC soil stabilized with 5per cent lime
Base Course : 11.25 cm thick layer of mechanically stabilized moorum of low plasticity
Wearing course : 7.5 cm thick layer of WBM

The performance of these two specifications was identical at two different sites over a period of four years and was rated good for first three years and in fourth year it was rated good to fair for specification no. II and good for specification no. III.

4.3. Soil Gravel

4.3.1 From Ground Surface/below Surface: This material is available in huge quantity in many parts of the country in form of soil aggregate mixes. These are commonly known as soil mixes. Such mixes are found to exist either at ground surface or some times even 1 to 1.5 m below the surface. Soil-gravel as such or after minor processing can be compacted under controlled moisture conditions to higher state of densification resulting in higher bearing capacity. Further, when treated with traditional stabilizers like cement or lime, these materials can be effectively used in base as well.
The three specifications were laid on Kekeri – Baghara Road in Rajasthan.

The three specifications were laid on Kekeri – Baghara Road in Rajasthan.

Specification No. IV6
Type of Subgrade Soil : SC
Subbase : 10 cm thick layer of soil-gravel
Base Course : 15 cm thick layer of soil-gravel stabilized with 3per cent lime with a layer of stone grafting @ 0.3 cum/10 sqm.
Wearing course : 2 cm Premix carpet

Specification No. V 6
Type of Subgrade Soil : SC
Subbase : 10 cm thick layer of soil-gravel
Base Course - I : 7.5 cm thick layer of local soil stabilized with 3per cent lime
Base Course - II : 7.5 cm thick layer of soil-gavel stabilized with 3per cent lime with a layer of stone grafting @ 0.3 cum/10 sqm.
Wearing course : 2 cm Premix carpet

Specification No. VI 6
Type of Subgrade Soil : SC
Subbase : 10 cm thick layer of soil-gravel
Base Course - I : 7.5 cm thick layer of local soil stabilized with 3per cent lime
Base Course - II : 7.5 cm thick layer of WBM.
Wearing course : 2 cm Premix carpet

The performance of specifications no. IV, V and VI was rated good throughout the period of five years.

4.3.2. From riverbed: In hilly regions soil gravel is available in large deposits in beds of stream and ‘nallahs’ and is generally termed as water borne pebbles. These gravel are hard and well graded but do not contain sufficient fines (passing 75 micron IS sieve) required for binding the cohesionless sand and gravel to give a firm base in pavement structure, and hence had limited use in road works. This material can be blended by adding missing gradation to conform to required gradation and plasticity requirements. In the following specification fines were mixed to conform the gradation as detailed below.

Specification No. VII 7
Type of Subgrade Soil : CL
Base Course - I : 7.5 cm thick layer of local soil-gravel passing 20 mm IS sieve blended with 15-25 per cent fine passing 75 micron IS sieve
Wearing course : 7.5 cm thick layer of local soil-gravel passing 20 mm IS sieve blended with 5-15 per cent fine passing 75 micron IS sieve.
This specification was constructed on Siligram-Krishangaon Road (J.K.) and performed good throughout the observation period.

4.4. Moorum

Moorum is other commonly available material in various parts of the country. It was observed that it can be a suitable alternate material for road construction. It can be used as such or after processing in sub base/base of road pavements. In specification no.VIII and IX moorum, sand and stone chips (10 mm) were mixed in such proportion to satisfy the IRC gradation and in specification no. X moorum was stabilized with 3per cent lime. Specification no. VIII and IX were laid on two different sites in Orissa i.e. Sambalpur-Naharpur Road and Nalanga-Betada Road, and specification no. X was laid on Bijapur –Ukkali Road (Karnataka).

Specification No. VIII 8
Type of Subgrade Soil : CL –ML
Base Course - I : 10 cm mechanically stabilized layer of
Moorum : sand : 2 : 1
Wearing course : 10 cm mechanically stabilized layer of
Moorum : stone chips : sand :: 3 : 1.5 : 0.5

Specification No. IX 7
Type of Subgrade Soil : CH
Base Course - I : 10 cm mechanically stabilized layer of
Moorum : sand : 1 : 1
Wearing course : 10 cm mechanically stabilized layer of
Moorum : stone chips : sand : 2 : 1 : 1

Specification No. X 5
Type of Subgrade Soil : CH
Sub Base : 11.25 cm compacted sand
Base Course : 11.25 cm Moorum + 3 per cent lime
Wearing course : 7.5 cm layer of WBM

The specification no. VIII and IX have same material but different mix proportions. They clearly show that depending upon the characteristics of material available, if mixed proportion are designed in such a way so as to satisfy the gradation and plasticity requirements, stable and durable pavement layers can be constructed. The specification no. VIII also stood to the worst condition of flooding due to cyclone. The performance was rated good for period of four to five years.

4.5. Mine Waste/Overburden

In mining system, three general types of material are produced i.e. mineral, overburden and waste material. Where overburden is a natural product, while waste material is generated during extraction of mineral ore. Waste materials are generally available in two varieties i.e. fine and coarse. Some of these are well graded and have sufficient strength for utilization in sub base/base courses of a road. There are other wastes, which can be used after processing. There are still other types for which processing is uneconomical and can be used in filling of low lying areas/road embankment. In the specification no. XI mine waste of fine and coarse variety was used in sub base and base for roads for Lambidhar Mines Residential Colony, Mussoorie.

Specification No. XI 9
Type of Subgrade Soil : SM-SC
Sub base : 15cm thick layer of mine waste (Fine variety)
Base Course - I : 7.5cm thick layer of WBM with mine waste (Coarse variety)
Wearing course : 2cm Premix carpet.
The performance data of the road was not available.

5. PERFORMANCE CRITERIA

The Performance of these specifications was divided into four groups i.e. Good, Fair, Poor and Bad based on the visual observation and by taking spot levels to study the rut depth and transverse slope variance as given below.

Performance of each specification is given in Table-3 and traffic in the final year of observation is given in Table-4.

6. CONCLUSIONS

1. The essential requirement for successful performance of gravel and moorum roads is that the material should be well graded and compacted to maximum dry density at optimum moisture content.

2. In order to provide suitable sub base for the road pavement, the local materials could be compacted to the desired state of densification without any detrimental effect.

3. The performance showed that mechanically stabilized moorum with stone chips and sand is comparable to conventional WBM in wearing course, hence a good substitute to WBM where moorum is locally available.

4. Stabilization of moorum with small percentage of lime makes it more viable material for use in sub base and base courses.

5. Lime stabilized black cotton soil can effectively be used on lower layers of road pavements.

6. Nomographs based on Pavement Design Curves developed by CRRI give stable and economical design, and also takes into account solid wheeled cart traffic.

7. Locally available materials could be effectively and meaningfully utilised for rural road construction work. Substantial economy to the tune of 20 to 30per cent can be achieved by using these materials.

ACKNOWLEDGEMENT


Authors are thankful to Director, Central Road Research Institute, New Delhi for his kind permission to publish this paper. Authors are also thankful to Sh. Ramesh Chandra for preparing the drawings used in this paper.

REFERENCES


1. Swaminathan, C.G., Lal N.B. (Dr.) “ Appropriate Technologies for Rural Road Development” Journal of Indian Roads Congress, New Delhi, Vol. 40-2, 1979.

2. Goswami N.K., Dhawan P. K., Lal N.B. (Dr.), Computation of Values of Proctor and CBR from Soil Gradation Data”, Indian Highway, June1981, IRC, New Delhi.

3. Goswami N.K., Ashwani Kumar, “Some Nomographs for Rural Road Pavement Design,” Proceeding of Seminar on ‘Roads and Road Transport in Rural Areas’ Volume-I, Nov 19-20, 1985, held at CRRI, New Delhi.

4. Bhasin N.K., P. Oli, Sharma N.K., Jagdish Chandra, Ashwani Kumar, “Use of Low Grade Material for Rural Road Construction in Desert Areas” Proceeding of Seminar on ‘Roads and Road Transport in Rural Areas’ Volume-I, Nov 19-20, 1985, held at CRRI, New Delhi.

5. Dhawan P. K., Goswami N.K., Swami R.K., “Five Years Performance Evaluation of Rural Road Test Track in Black Cotton Soil Areas, Proceeding of Seminar on ‘Roads and Road Transport in Rural Areas’ Volume-I, Nov 19-20, 1985, held at CRRI, New Delhi

6. Bhasin N.K., Sharma N.K., P. Oli, Ashwani Kumar, , Jagdish Chandra “Use of Low Grade Material for Rural Road Construction in Rural Areas”, Indian Highways, May,1987, Vol-15, No-5, IRC, New Delhi.

7. Wason O.P., Bhatnagar O.P., Mehta H.S., Lal N.B., “Development of Low Cost Specifications for Rural Roads in Kashmir Valley”, Proceeding of Seminar on ‘Roads and Road Transport in Rural Areas’ Volume-I, Nov 19-20, 1985, held at CRRI, New Delhi.

8. Ashwani Kumar, Dhawan P.K., Murty A.V.S.R., “Evaluation of Rural Road Test Track – Validation of Design Curves,” Highway Research Bulletin No. 55, 1966, IRC, New Delhi.

9. “The Pavement Design for Roads in Township Area at Khanij Nagar, Mussoorie, (UP)” Internal Report of CRRI 1988.

Appendix – I
Stepwise procedure to determine pavement thickness
Following procedure may be adopted to calculate the pavement thickness from the Fig. 2 and 3 .

1. A representative sample of material should be prepared by the process of quartering on dried sample, preferably oven dried, or dried by other suitable method.

2. Depending upon the maximum grain size the quantity of dry sample for sieve analysis should be as given below.

3. The weighted sample should be soaked overnight in water and subjected to wet sieve analysis through 75 micron BIS sieve.

4. Fraction retained on 75 micron BIS sieve should be dried and then sieve through 425 micron BIS sieve. Percentage of three different fractions is calculated from step 3 and step 4 results.

5. Join the per cent passing 75 micron sieve, as read on axis ‘1-1’ by a straight line passing through point “X” with line ‘A-A’ meeting at a point, say S.
(Point ‘X’ in the nomograph is derived from the statistical analysis of the data used for formulating the nomograph)

6. Similarly join the per cent passing 425 micron BIS sieve but retained on 75 micron BIS sieve, as read on axis ‘2-2’ by a straight line passing through point “X” with line “A-A’, meet at a point, say, T.

7. Starting with ‘O’ on axis ‘B-B’ mark OC = ST and add the per cent retained on 425 micron BIS sieve to OC, say getting up to ‘D’.

8. Perpendicular line from ‘D’ meets the relevant curve at required total pavement thickness in cm.