This paper documents changes to Technical Manual (TM) 5- 809-12 , "Concrete Floor Slabs on Grade Subjected to Heavy Loads." Changes to design criteria for thickness determination concerned impact factor, percent standard thickness versus coverage rel
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International Journal of Engineering Technology Science and Research IJETSR www.ijetsr.com ISSN 2394 – 3386 Volume 4, Issue 4 April 2017
Effect of Borrowed Subgrade Soil on Cost of a Rigid Pavement C Shanthakumar Naik* &Dr. S.N.Sachdeva** * Post Graduate Student (Department of Civil Engineering NIT KURUKSHETRA, Haryana) ** Prof (Department of Civil Engineering NIT KURUKSHETRA, Haryana)
ABSTRACT IRC: 58-2015 Recommends the use of selected soil of minimum (CBR 8%) in subgrade of a rigid pavement when traffic on the road is more than 450 CVPD. An attempt has been made in this paper to evaluate the effect of borrowed select subgrade soil on cost of the rigid pavement.It is observed that use of borrowed soil of CBR 8% to replace the existing soil to prepare subgrade of road is not an economical preposition for all types of existing soils. Cost estimation has been made in this paper for a rigid pavement with existing soil of CBR varyingfrom 2% to 6% with replaced borrowed soil subgrade of CBR 8%. The concept of effective CBR has been used while doing design of pavement thickness.
I.
INTRODUCTION The use of rigid pavements is increasingnowadays due to their maintenance free nature and Different methods are followed to design them. In India rigid pavements are designed as per IRC: 58-2015[1]. As per this method IRC has recommended the use of selected soil of minimum CBR 8% in subgrade for road trafficmore than 450 CVPD. In most of the cases the CBR of existing soil is less than 8% which calls for borrowing the soil from outside and replacing the existing soil in top 500mm portion with selected soil to form subgrade of the road.The borrowing of the soil from outside has an extra cost to the project which may get compensated to a great extent by reduction in thickness of pavement due to the use of stronger subgrade soil.It is to be seen, however, whether replacement of existing soil with selected soil is economical for all types of existing soil or not. In this paper design of a Rigid pavement has been made for 20 msa design traffic for a 7.5m wide carriageway road. The cost estimation is based on Analysis of Rates given in Standard Data Book of MoRTH [2].
II. DESIGN OF RIGID PAVEMENT The thickness design for 7.5m carriageway road for 20 msa design traffic has been made as per guideline of IRC: 58-2015, both with using the borrowed soil and without using borrowed soil. Details of axle load spectrum of rear single, tandem and tridem axles are taken from IRC: 58-2015[1]. The design thicknesses obtained in the study are given in table 1 and table 2. Table 1. Design thickness for 20 msa design traffic without Borrowed select soil in subgrade Existing Subgrade Thickness (mm) soil CBR% Granular SubDry Lean Pavement Quality
351
2
base(GSB) 150
Concrete(DLC) 150
Concrete(PQC) 270
3
150
150
270
4
150
150
260
5
150
150
260
6
150
150
260
C Shanthakumar Naik & Dr. S.N. Sachdeva
International Journal of Engineering Technology Science and Research IJETSR www.ijetsr.com ISSN 2394 – 3386 Volume 4, Issue 4 April 2017
Table 2. Design thickness for 20 msadesign traffic with borrowed select soil in subgrade Existing Selected Effective Thickness (mm) Subgrade Subgrade soil CBR% Granular Dry Lean Pavement soil CBR% SubConcrete(DLC) Quality CBR% base(GSB) Concrete(PQC) 2 5.41 150 150 260 3 5.83 150 150 260 8 4 6.45 150 150 260 5 6.87 150 150 260 6 7.29 150 150 260 As seen in above table 1 and table 2 the total thickness of rigid pavement doesn’t change much when the subgrade soil strength (CBR) increases due to replacement of existing soil by select soil of CBR 8%. III. COST ESTIMATION The cost estimation has been made based on Rate analyses given in Standard Data Book of MoRTH [1]. Various rates obtained from rate analysis are given in table 3. Table 3: Rates for various items S.N
Item description
Unit
Rate(Rs)
1
Excavation of existing subgrade soil
m3
63
2
(i)Replaced Subgradewith borrowed soil for lead 5 km
m3
243
(ii)Replaced Subgrade with borrowed soil for lead 10 km
m3
267
(iii)Replaced Subgrade with borrowed soil for lead 15 km
m3
290
(iv)Replaced Subgrade with borrowed soil for lead 20 km
m3
313
6
Compacting original ground supporting subgrade
m3
68
7
GSB(Granular Sub-base)
m3
1335
8
DLC(Dry Lean Concrete)
m3
2762
m3
6705
9
PQC(Pavement Quality Concrete) Table 4: Total cost of 1 km Road Pavement (2%CBR of existing subgrade soil) Road Pavement Dimension
Total Quantity(m 3)
Rate per (m3)
Total Cost of Material Rupees lacs per (km)
Width (m)
Depth (m)
Length (m)
Subgrade compaction GSB DLC
1 7.5 7.5 7.5
2 0.500 0.150 0.150
3 1000 1000 1000
4 = 1*2*3 3750 1125 1125
5 68 1335 2762
6 = 4*5 2.55 15.01 31.07
PQC
7.5
0.270
1000
2025
6705
130.74
Type of Material
Total Cost of 1 KM Road Pavement
352
C Shanthakumar Naik & Dr. S.N. Sachdeva
184.41
International Journal of Engineering Technology Science and Research IJETSR www.ijetsr.com ISSN 2394 – 3386 Volume 4, Issue 4 April 2017
Table 5: Total cost of 1 km Road Pavement (2%CBR existing subgrade soil replaced with 8% CBR selected soil lead of 20 km) Total Cost of Road Pavement Dimension Total Rate Material Quantity(m per Width Depth Length Rupees lacks Type of Material 3) (m3) (m) (m) (m) per (m3) 1 2 3 4 = 1*2*3 5 6 = 4*5 Excavation of Sub grade 7.5 0.500 1000 3750 63 2.36 Replaced Sub grade 7.5 0.500 1000 3750 313 11.73 GSB 7.5 0.150 1000 1125 1335 15.01 DLC 7.5 0.150 1000 1125 2762 31.07 PQC 7.5 0.260 1000 1950 6705 130.74 Total Cost of 1 KM Road Pavement 190.93 Fig.2 Rigid pavement Total Cost Comparison for Existing subgrade Soil(3%CBR) and Borrowed subgrade soil(8%CBR) for 20 msa design traffic
Existing Subgrade Soil 2% CBR
Existing Subgrade Soil 3% CBR
Borrowed Subgrade Soil 8% CBR
Borrowed Subgrade Soil 8% CBR
192 190 188 186 184 182 180 5
10
15
20
T.Cost Rupees Lack/km
T.Cost Rupees Lack/km
Fig.1 Rigid pavement Total Cost Comparison for Existing subgrade Soil(2%CBR) and Borrowed subgrade soil(8%CBR) for 20 msa design traffic
192 190 188 186 184 182 180 5
Lead (km) for borrowed subgrade soil
Existing Subgrade Soil 4% CBR
Existing Subgrade Soil 5% CBR
Borrowed Subgrade Soil 8% CBR
Borrowed Subgrade Soil 8% CBR
200 190 180 170 5
10
15
20
Lead (km) for borrowed subgrade soil
C Shanthakumar Naik & Dr. S.N. Sachdeva
20
Fig.4 Flexible pavement Total Cost Comparison for Existing subgrade Soil(5%CBR) and Borrowed subgrade soil(8%CBR) for 20 msa design traffic
T.Cost Rupees Lack/km
T.Cost Rupees Lack/km
15
Lead (km) for borrowed subgrade soil
Fig.3 Flexible pavement Total Cost Comparison for Existing subgrade Soil(5%CBR) and Borrowed subgrade soil(8%CBR) for 10 msa design traffic
353
10
200 190 180 170 5
10
15
20
Lead (km) for borrowed subgrade soil
International Journal of Engineering Technology Science and Research IJETSR www.ijetsr.com ISSN 2394 – 3386 Volume 4, Issue 4 April 2017
Fig.5 Rigid pavement Total Cost Comparison for Existing subgrade Soil(6%CBR) and Borrowed subgrade soil(8%CBR) for 20 msa design traffic
T.Cost Rupees Lack/km
Existing Subgrade Soil 6% CBR
Borrowed Subgrade Soil 8% CBR
195 190 185 180 175 170 5
10
15
20
Lead (km) for borrowed subgrade soil
Similarly the cost of pavement per km has been calculated for all other values of CBR of existing soil varying from 2% to 6% for both cases, that is, with and without replacement of existing soil with select soil of CBR 8% .The cost thus obtained for various values of lead are shown in Fig 1 to 5. IV. RESULTS AND DISCUSSION From Table 1 and Table 2 it is observed that after replacement of existing soil subgrade with borrowed soil of 8% CBR there is no much difference in thickness of the pavement. From all the figures 1 to 5 it is observed that replacement of soil subgrade with 8% CBR of borrowed soil will be uneconomical for all the leads of borrowed soil. It is observed that the Strength of Soil Subgrade doesn’t affects much in the case of rigid pavements. V.
CONCLUSION IRC has recommended using select soil of minimum CBR 8% in subgrade for roads having traffic more than 450 CVPD. However, it is seen that use of select soil does not lead to economical design for all values of CBR of existing soil subgrade. For any value of lead of borrowed soil of CBR 8%, the replacement of existing soil with borrowed soil in subgrade is found to be uneconomical for all values of CBR of existing soil from 2% to 6%. The decision for replacement of soil, therefore need to be taken carefully and judiciously. REFERENCE 1. 2.
IRC: 58-2015 “Guidelines for the Design of Rigid Pavements” Indian Roads Congress, New Delhi, 2015. MORTH (2003) “Standard data book for analysis of rates”, Ministry of Road Transport and Highways, Indian Roads Congress, New Delhi.