Use Of Geosynthetic Material, To Enhance And Sustain Subgrade Characteristics

Use Of Geosynthetic Material, To Enhance And Sustain Subgrade Characteristics

Research Scholar, Government College of Engineering, Aurangabad (M .S.) -431 005, India

Department of Civil Engineering, Government College of Engineering, Aurangabad (M .S.) -431 005, India

ABSTRACT : Sustainable development can not be done without adaptation of new technology to ma ke th e structure cost effective and enduring. More than 40 years ago, a new composite construction material known as Re inforced Ea rth was invented. Reinforced Earth is a soil mass strengthened by using various materia ls – natural or synthetic to improve its performance. Fro m very beginning, the earth reinforce ment of choice was discrete linear strips made up of galvanized steel. Fro m t ime to time, fro m s mall walls, for co mme rcia l developments to enormous structures at industrial terminals, re inforced earth has b een selected for its significant cost benefits with savings in the range of 20-50 % when co mpared with a lternate solution. With the imp le mentation of the design built for majo r construction works, reinforced earth, more than ever before is in the forefron t of consideration by Civil Engineers and contractors. Now a days to increase the strength of soil, geosynthetic is wide ly used. Satisfactory performance of road depends on the sub grade soil conditions, the soil characteristics change under varied conditions, the maintenance operation involves assessing of road conditions diagnosis of the problems and adopting the most appropriate measures. The safety and convenience of traffic using the roads are governed to a large extent by the quality of maintenance which is carried out, but the maintenance is reduced to a large extent by using geosynthetic materia l. In this paper, it is best attempted to correlate between reduction in ma intenance expenditure and optimu m use of geosynthetic materia l. A case study has been narrated for a road length of 3.5 km of Aurangabad city (M.S.).

Keywords : Black cotton soil, Geosynthetic, Woven fabric

1. INTRODUCTION

   Satisfactory performance of road in rura l areas depends on the sub grade soil condition. If the sub grade soil consist of black cotton soil or the soil, wh ich swells after increase in water content and looses its strength, there by stability of road pavement reduces. Soil reinforce ment is an effective and reliable technique for improving strength and stability of soils. Also irrespective of the season, rural roads in India have invariably been observed to have puddles of water standing on the surface, regardless of whether or not they have been provided with a side trench. They are usually in a deplorab le state, caused not only by rainfa ll, poor drainage but also by sewage accumulating on the surface. Rein forcing blac k cotton soil by a geosynthetic is of great importance in the field of road construction. The well-built and maintained roads play major ro le in the development of nation, if the wea k subgrade of black cotton soil is stabilized or re inforced, the crust thickness will be less. The rutting is a lso restricted resulting in less repairs and overall economy. Use of

   geosynthetic in the subgrade assumes a great promise and comparatively easier for construction.

2. LITERATUR E REVIEW

   In the 1920s the state of South Carolina used a cotton textile to reinfo rce the underlying materials on a road with poor quality soils. Evaluation several years later found the textile in good workable condition. They continued their work in the area of reinforcement and subsequently concluded that combining cotton and asphalt materials during construction reduced cracking, raveling and fa ilu re and the base course.

   When synthetic fibers became more availab le in the 1960s text iles were considered more seriously for roadway construction and maintenance.

   The work of reinfo rced earth was done by Vida l H in 1969. Vida l mentions the use of reinforced earth mat to imp rove the bearing capacity of soft subsoil foundation in France.

   In 1972in Japan geogrids made of synthetic materia l where used as reinforce ment of soft ground under guidance of Prof. Ya manovchi. At the same time

   Japanese national railway used reinforce ment fo r railway e mban kment.

   Dr. Na rayana Swa mi K.R. and Shetty P.P. (1989) have reinforced soil for the pavement construction by making use of cement, coir, geosynthetic and fibre separately and together.

3. METHODOLOGY

   The effort in this work is made to assess the improve ment in strength and stability characteristics by using geosynthetics. A geosynthetics any permeable materia l used with foundation, soil, rock, ea rth etc. that is an integral part of a constructed project, structure or system. It may be made of synthetic or natural fibers.

   Te xtiles were first applied to roadways in the days of pharaohs. Even they struggled with unstable soils, which rutted or washed away. They found that natural fibers, fabrics or vegetation improved road quality when mixed with soils, particularly unstable soils only recently, however have textiles been used and evaluated for modern road construction. Geosynthetic related materia ls are fabrics formed into mats, webs, nets grids or formed plastic sheets. Modern geosynthetic are usually made fro m synthetic polymers, polypropylenes, polyesters, polyethylenes and polyamides that do not decay under biological and chemical processes. This makes them useful in road construction and maintenance. Geosynthetic can also be made of materia ls which are most commonly used. The properties of the same are tabulated in table 1

   Table 1 : Properties of Ge osynthetic

   Sr.No.	Particul ars	Values
   1	Fabric type	Woven Variety (polypropylene)
   2	Maximu m width (c m)	100
   3	Unit weight (g m/ m²)	250
   4	Specific gravity	0.91
   5	Thickness (mm)	0.80
   6	Pore size ( m)	150
   7	Tensile strength (N/ mm²)	200

   The fabrics used in the work are added in layers by percentage weight of soil at the rate of 1%, 1.5%, 2 % 2.5% & 3%respectively.

4. CAS E S TUDY

The road from Seven Hill Flyover to Shahnoormiya Darga is a ma jor road of Aurangabad city with heavy traffic intensity. This road starts from seven hill and runs through the major part o f the city, Ga janan Maharaj temple , Jawahar Nagar Po lice Station, Sutgirn i Centre, Shahnoormiya Darga. The total length of the road is

3.55 km. fo r the improve ment we selected this part of the road because

1. Fro m flyover onwa rds, towards Baba Petro l Pu mp , no heavy traffic is allowed in the city, due to which this traffic uses the said road for getting to the Beed by pass.

2. Due to rapid growth of the city, land along the road is occupied by residential and public buildings and hence, infiltrat ion of rainfall is not taking place. Also due to construction, natural drains are blocked and no proper care of constructing roadside drainage is taken during construction of the e xisting road. The te xture of the soil is black cotton soil. Soils samples are collected and tested in the laboratory for engineering properties of soil and CBR values. Soils samp lestaken at the depth of

0.6 meter. The properties obtained by conducting laboratory tests are given in table 2.

Table 2 : Engineering properties of Black Cotton Soil

1. Tr affic De tails

   The details of the traffic belonging to the site for certain duration is achieved by calculating the diffe rent type of vehicles on the common road. The spots for calculating the vehicles are at Seven Hills, Gajanan Maharaj Te mple , Ja waharnagar Po lice Station, Sutgirni Centre, Shahnoormiya Darga. The vehicles are diffe rentiated into light, mediu m, heavy categories.

   Traffic volu mes study is made by manual counting and then statistical analysis of peak hourly traffic is given in table 3.

   Table 3 : Traffic Volume in peak hours

   Sr No	Locations	Light	Me dium	He avy
   1.	Seven Hill	4100	1294	198
   2.	Gajanan Maharaj Temp le	1920	588	58
   3.	Jawahar Nagar Police	640	180	14

   	Station
   4.	Sutgirni Centre	3660	720	104
   5.	Shahnoor Miya Darga	3080	560	258
   	Total	13400	3342	632

2. Existing C/S. of Road and i ts Details

   1. It consists of carriage way – 8 m.

   2. Slope of ca mber 2.5 %

   3. The courses are

      1. Bituminous concrete 20 mm thic k.

      2. Bituminous macada m 50 mm thick

      3. Base Course 200 mm thic k.

      4. Granular sub base 200 mm thic k.

   4. The main d rawback is side drain is not provided.

1. Traffic separator The main function of traffic separator is to prevent head on collis ion between vehicles moving in opposite direction on adjacent lanes. Traffic separator i.e. d ivider is of 1.4 m. in width.

IRC : 37 -2001 reco mmends simple design chart and catalogue of pavement design for

1. Sub grade CBR values ranging fro m 2 to 10 % .

2. Design traffic varying fro m 1 msa to 150 msa.

Wearing Course is damaged due to improper pavement design, improper drainage and improper geometric design.

Computation of Design traffic

As per IRC : 37 -2001, the design traffic is considered in terms of cu mu lative nu mber of standard a xles to be carried during the design life of the road. This can be computed by using the relations

N = 365 { ( 1+r)n 1) x A x D x F

r

1. RES ULT AND DISCUSS ION

   The attempt is made to know the causes for the change in different characteristics of black cotton soil due to addition of varying % of woven fabric in the soil.

   1. Compac tion Charac teristics

      The optimu m mo isture content and ma ximu m dry density of soil without geosynthetic and with addition of geosynthetics are tabulated in table 4.

      Table 4 : Compac tion Char acteristics of Reinforce d Black Cotton Soil

      Sr No	Partic- ulars	Pe rcent Fabric
      		0%	1%	1.5 %	2%	2.5 %	3%
      1	Optimum moisture content (%)	17	20	21.3	23	26.7	16.3
      2	Maximum dry density (gm/cm3)	1.66	1.6	1.53	1.44	1.15	1.14

      Increase in OM C and decrease in M DD are due to the fact that woven fabric is very light materia l compared to soil and even a small quantity of it has a large bulk. Addit ion of this lighter material replaces a large a mount of heavier materia l like soil.

      The purpose of compaction is to imp rove the

      quality of soil used either as subgrade materia l for roads or in the da ms. The important properties are high shear strength, low permeability and little tendency to settle under repeated loading. The ma ximu m co mpaction is possible at the OMC and MDD of the soil. Therefore , these values of OMC and MDD serve as guide and basis to get the ma ximu m co mpaction in the fie ld

   2. Shear Strength Char acteristics

      The shear strength characteristics found by conducting direct shear tests on geosynthetic woven fabric reinforced soil samp le are g iven in table 5.

      Sr. No.	Percentage Woven Fabric	Cohesion (C) KN/ m²	Angle of internal friction ()
      1.	0	4.90	24.44
      2.	1	14.71	23.96
      3.	1.5	24.52	22.61
      4.	2	39.24	21.25
      5.	2.5	49.05	16.69
      6.	3	14.71	18.43

      Table 5 : Shear strength Charac teristics

      where

      N = cu mulat ive nu mber of standard axles to be cat ered for in the design in terms of msa.

      A = init ial tra ffic in the year of comp letion of

      construction in terms of number of comme rcia l vehicles per day.

      D = lane distribution factor F = vehicle da maged factor n = Design life in years

      r = annual growth of comme rcia l vehicles (for 7.5 % annual growth rate, r=0.075)

      Fro m the values given above, it is observed that there is reduction in angle of internal frict ion and increase in the value of cohesion due to the presence of

      woven fabric re inforce ment. Th is reduction may be due to low density of woven fabric and its smooth surface and the increase in the value of cohesion may be due to the bond developed between the soil and fabric.

      It appears that as the woven fabric content is increased, there is increase in cohesion and decrease in angle of internal friction up to 2.5 % woven fab ric . Beyond 2.5 %, addition of woven fabric, there is decrease in cohesion and increase in angle of internal friction. This is because of the fact that woven fabric of low density occupy relatively la rge volu mes in the reinforced soil.

      Thus with igher woven fabric content the quantity of soil mat rix availab le for holding the fabric is insufficient to develop an effective bond between fabric and soil. The plac ing of the fabric in soil is practically difficult afte r the fabric content is increased beyond 2.5

      % as balling up of fabrics takes place, and uniform distribution can not be made.

   3. Californi a Bearing Rati o values

      The CBR va lues for 2.5mm, 5mm, 7.5mm, 10mm, 12.5mm penetration are g iven in table 6

      Table 6 : California be aring ratio val ues

      S r. No.	Reinforcement status	CBR values % Plunger Penetration in mm.
      		2.5	5	7.5	10	12.5
      1.	Reinforcement status without geosynthetic	2.54	2.43	2.23	1.91	1.81
      2.	Black cotton soil + 1 % geosynthetic	3.18	2.65	2.32	1.98	1.87
      3.	Black cotton soil + 1.5 % geosynthetic	3.5	2.86	2.40	2.12	1.93
      4.	Black cotton soil + 2 % geosynthetic	3.81	2.97	2.48	2.12	1.93
      5.	Black cotton soil + 2.5 % geosynthetic	3.97	3.28	2.73	2.33	2.11
      6.	Black cotton soil + 3 % geosynthetic	3.18	2.48	1.98	1.71	1.57

      CBR % increase is 25.19 % for 1 % geosynthetic and

      56.29 % for 2.5 % geosynthetic. With addition of 3 %

      geosynthetic, there is decrease in CBR value.

2. CONCLUS IONS

Fro m the present study, follo wing conclusions are drawn:-

1. The value of optimu m mo isture content increas es

   with the increase in geosynthetic woven content up

   to 2.5 % and beyond 2.5 %, there is decrease in optimu m moisture content.

2. The ma ximu m dry density decreases with the increase in geosynthetic woven fabric content.

3. There is significant increase in the value of cohesion as the percentage of geosynthetic woven fabric increases up to 2.5 % and beyond 2.5 % , there is decrease in cohesion.

4. The angle of internal friction decreases with the increase in geosynthetic woven fabric content.

5. The soaked CBR value of the black cotton soil without any kind of reinforce ment is 2.54%.

6. Pavement of roads may be surfaced or

   subsurfaced can store large amount of water in diffe rent layers if there is no outlet for the water then it create a bath tub. The entrapped water in the base, subbase or subgrade of a pavement is one predominant single factor which causes premature deteriorat ion and destruction of pavement.

   Therefore it is necessary that the entrapped water should be removed fro m the layer of pave ment as early as possible to prevent the premature fa ilure

   REFERENCES

   1. Giroud P. and Noiray (1981). Geosynthetic reinforced unpaved road design ASCE Journal of Geotechnical engineering division, 107 GT 9, 1233-1254

   2. IRC 37-2001: Guidelines for the design of fle xib le pave ments .

   3. Mandal J.N (1988). Reinfo rced Soil and Geote xtile, proceeding of first Indian Geosynthetic conference, Mumbai.

   4. Mandal J.N (1994). Geosynthetics world , New age International Limited, New De lhi.

   5. Mandal J.N. and Dixit R.K. (1986). Under

      what situations are geosynthetic more effective than traditional methods for ground improve ment and drainage, Response paper to Indian Geotechnical conference, New De lhi. Vo l. 2,195-199

   6. Narayana Swa my K.R. and Shetty P.P.(1989) .

      Re inforced soil layersin pavement construction, International work shop on geotextile, Banglore.

   7. Vida l H.(1969). The Principle of re inforced earth, Highway Research Record No.282, 1-16.

   8. Vasan R.M.(1995). Fibre Re inforced Soil: A

new method of reinforc ing soil subgrade, Processing on national seminar on Emerging trends in highway engineering, Banglore.