and Carbon Foot Print Analysis

Transcription

1 Geosynthetics in Flexible Pavements and Carbon Foot Print Analysis Prof. K. Rajagopal Department of Civil Engineering, IIT Madras, Chennai, India This work was part of M.Tech. projects of Avinash Unni, S. Chandramouli, K. Iniyan & Lt.Col. Tushar Vig Thanks are also due to Prof. A. Veeraragavan and Dr. Sivakumar Palaniappan

2 Outline Field and Laboratory tests performed to assess the influence of geocell layer Equivalent modulus of the geocell layer evaluated Influence on pavement thickness evaluated through stress analysis programs Carbon foot print analysis of construction activities

3 Back ground (GEOCELL) 3D Cellular confinement system (GEOCELL) Originally developed by US Army Corps of Engineers (1979) Expandable 3-d permeable, honeycomb or web structure, made of strips of polymer Invented by the US army corps of engineers in the 1970 s to construct temporary roads for heavy military vehicles over weak soils Extensively used by US Army during the Gulf war for effective moving of military vehicles/trucks over the desert sand.

4 Simultaneous Mechanisms in 3 Dimensions a) Unreinforced soil subjected to shear a. When pressure is applied on unreinforced weak soils, failure occurs immediately due to lateral flow of soil b) Pushing decrease by confinement b. When surface soil is confined by geocells, failure mechanism is suppressed from formation. c. Surface pressures are transferred to deeper strata due to interaction. c) Lateral stress on cell due to stress with in the cell Ofer and Rajagopal (2008)

5 Simultaneous Mechanisms in 3 Dimensions c) Hoop stress development d) Passive resistance of neighbouring cells e) Interface friction force developed along the cell walls. The three dimensional structure confines the infill soil, limiting lateral deformation. Lateral expansion of the infill is restricted by high hoop stress. Because of all the above phenomena, the pressure transmitted to the foundation soil reduces.

6 Trial Construction on an Expansive Clay soil Trial road section with geocell reinforcement built over a length of 200 m Subgrade Soil at Site CBR 4% Swell index 150% Liquid Limit 60% Plastic Limit 25% Shrinkage limit 8% Geocell Reinforced Flexible Pavements

7 GEOCELL Reinforced Road construction at Govind Dairy Factory Preparation of ground Stretching of the geocell layer Stapling to join different geocells Filling of stone aggregate in geocell Compaction by vibro-roller

8 Observations on the performance Unreinforced section Reinforced section Reinforced section could maintain good level surface Unreinforced section showed excessive surface depressions Road surface was quite uneven Frequent repairs by dumping large stones

9 Set Up for Laboratory Model Tests

10 Soft clay bed prepared in the laboratory

11 Pressure Settlement Pressure KPa Settlement cm Geocell Sand 150 Geocell GSB 100 Geocell GSB 50 Geocell GSB 100 WMM 50 Geocell Sand 50 Geocell Sand 2 The Avinash Unni Project Review

12 Measured Pressures below geocell layer The Avinash Unni Project Review

13 The Avinash Unni Project Review

14 Laboratory Model Tests 650 mm thick GSB base GSB + Geocell layer filled with sand or GSB

15 LABORATORY Model TESTS 100 mm geocell with sand fill layer 100 mm geocell+sand 100 mm geocell+gsb 150 mm geocell+gsb

16 Typical results from Plate Load Tests 0 pressure (kpa) ettlement t (mm) s mm Geocell+GSB 100 mm geocell + sand GSB alone

17 Analysis of pressure-settlement data 1) KENPAVE (Elastic layer analysis): Back calculation of modulus of geocell layer based on field plate load test t results Calculation of modulus values of 50 mm,100 mm,150 mm geocells layers with different in fills based on lab test results Optimization done by calculating damage ratio and design life 2) PLAXIS 2D Analyses B k l l ti f d l f ll l d t Back calculation of modulus of geocell layered pavement section Calculation of modulus values of 50 mm,100 mm,150 mm geocells layers with different in fills

18 Analysis of the Plate Load Test Data E- Value for subgrade (CBR 4%) = 10*4 =40 MPa E-Value for stabilized subgrade (CBR 6%) = 17.6*6^0.64 = MPa E-value for GSB (225 mm thick) = 55400*0.2*225^0.45= MPa E-value for GSB (75mm thick) = 55400*0.2*75^0.45 = 77.3 MPa E-value for GSB (150 mm thick) = 55400*0.2*150^ = MPa E- value for GSB (400mm thick) = 55400*0.2*400^0.45 = MPa Geocell Reinforced Flexible Pavements

19 Modulus Improvement Factors Type of study Field tests Laboratory tests MIF 2.75 (150 mm geocell) 2.92 (150 mm geocell) 2.84 (50 & 100 mm geocell) Pavement sections were designed using this revised modulus values and different subgrade CBR values Geocell Reinforced Flexible Pavements

20 Pavement Thicknesses for 150 msa & 2% CBR Combinations IRCunreinforced Geocell at Subgrade Geocell in base and subgrade BC 50 mm 50mm 50 mm DBM 215 mm 185 mm 170 mm Geocell with GSB-200 WMM 250 mm 0 mm GSB 460 mm 500 mm 100 mm 200mm Geocell sub-grade 500 mm with soil infill on 300mm subgrade layer 200mm Geocell with soil infill on 300mm subgrade layer cost (Rs.) / m 2 2,635 2,490 2,450 Total thickness 975 mm 735 mm 520 mm Design Life 16 years 20 years 20 years Geocell Reinforced Flexible Pavements

21 Geocell reinforced dirt track being constructed t in a desert area Geocell Reinforced Flexible Pavements 21

22 Desert sand being filled in the geocell pockets

23 Mini-bucket wheel excavator for filling sand in geocell pockets

24 Heavy army trucks moving easily on the geocell track

25 Soil details (Ref: CBR 3% Plasticity index 45% Swell index 140 Shrinkage limit 8%

26 Section adopted at construction site Max damage ratio 0.865

27 Field Plate Load Test The following apparatus were required for conducting the test: Circular steel plate of 300 mm diameter and 30 mm thickness Hydraulic jack of capacity 300 kn Supporting steel beam of length 5 m Dial gauges having accuracy of 0.01 mm Plumb bob Spirit level Short steel supporting members Loaded truck

28 Compacted Subgrade

29 1. Test set up Over Subgrade

30 Test Result (Subgrade)

31 Pressure settlement curve for subgrade data Pressure (Kpa) Settlement (m mm) Test 1 Test

32 2. Plate load test over Granular Subbase

33 3. Geogrid Reinforcement Subbase

34 Installing flexible and rigid geogrid over subgrade

35 Compaction using roller

36 Set up Over Sub Base (Reinforced with flexible and rigid iidgeogrid)

37 Pressure Settlement Curve Se ettlement (m mm) Pressure (Kpa) PLAIN GSB Test 1 PLAIN GSB Test 2 GSB (with flexible GR) Test 1 GSB (with flexible GR) Test 2 GSB (with rigid GR) Test 1 GSB (with rigid GR) Test 2

38 Field Density Tests

39 Field Density Tests Field density tests were conducted over the subgrade and over the GSB (with and without reinforcement) Sand replacement method was performed as per IS2720 PART-28 For the same compaction efforts, the sub base p, layer compacted over geogrid layer achieved higher dry density

40 Data Analysis KENPAVE (Elastic layered analysis software): Back calculation of modulus of Geogrid reinforced pavement based on field plate load test results Optimization done by calculating damage ratio and design life

41 Data Inputs The following parameters required for analysis Thickness of layers Elastic Modulus Poisson's ratio Stress and contact area

42 STEP 1 As per IRC-37 the following formulas used for As per IRC 37 the following formulas used for calculation of modulus of pavement layers

43 Calculation of Modulus Theappliedloadinthefieldtest= load in test 150 kn corresponding settlement=10.47mm The contact radius of the test plate = 150 mm Modulus of the Sub base layer was obtained by trial and error procedure by matching the measured settlement of mm

44 KENPAVE RESULT S No E-Value of Unreinforced Vertical Displacement layer (MPa) (mm)

45 Snapshot from KENPAVE

46 IMPROVEMENT FACTOR Improvement Factor = E BC (reinforced) / E BC (unreinforced) Where E BC (reinforced) = the modulus of the reinforced base and E BC (unreinforced) = the modulus of the unreinforced base The average value of the plate settlement at an applied load of 150 kn for the flexible reinforcement was 8.06 mm Considered the contact radius = 150 mm Contact pressure = load/area =150/area of plate = 2140 kpa

47 Flexible Geogrid Reinforcement Improvement E-Value (Flexible Settlement (mm) Factor Geogrid) MPa on surface under 150 kn load

48 Rigid Geogrid Reinforcement Improvement E-Value (Flexible Geogrid) Settlement (mm) on Factor MPa surface under 15T load The average value of the plate settlement at an applied load of 150 kn for the flexible reinforcement was 7.55 mm.

49 Layer Optimization Geogrid reinforced layers were considered and the thickness of the various alternate sections were analysed Damage ratio should not exceed the designed unreinforced site Most economic and feasible section should be selected

50 Damage Ratio Where, D f n i N i D f is the damage factor, n i is the actual number of vehicle movements of the i th load group and N i is the maximum(allowable) number of vehicle movements the structure can support for the i th load group.

51 Data Inputs BC DBM WMM GSB Poisson s ratio Flexible GG reinforced section E value (MPa) Rigid GG reinforced section E value (MPa)

52 Cracking Model The failure criteria for cracking is given by N f = f 1 (Є r ) -f 2 (E 1 ) -f 3 Where, Nf = allowable number of load repetition to prevent fatigue cracking ε t =tensile strain at the bottom of asphalt layer E 1 =Elastic modulus of asphalt layer f 1, f 2, f 3 are constants Here f 1 = , f 2 = , f 3 = 0.854

53 Rutting Model N =f -f d 4 (Є c ) 5 Where, N d = allowable number of load repetition to limit permanent deformation ε c = compressive strain on top of sub grade f 4 and f 5 are aeconstants ts Here, f = x10,f 5 =

54 Optimised sections for different damage ratios (Flexible (l geogrid)

55 Optimised sections for different damage ratios (Rigid geogrid)

56 Reinforced Pavement Section

57 EMISSION CALCULATION

58 Sustainable Construction Key themes of sustainable construction practices Minimise the energy use in the all phases (production, construction, operation and end of life phases) Reduce environmental impacts during the life cycle Preserve andenhancebio bio diversity Conserve water and land resources Adopt innovative materials Reduce the generation of wastes at all level

59 Green house gas emissions Theprimary greenhouse gases are water vapour, carbon dioxide, methane, nitrous oxide, and ozone Greenhouse gases usually affect the temperature of the earth Anthropogenic activities lead to the increase in green house gases

60 Need for Assessment Majority of studies mainly focussed upon improving the energy efficiency of structures during the operational phase The environmental performance of onsite construction processes is not currently being measured (Palaniappan et al. 2009) Quantification of carbon emissions from road projects is not followed yet

61 Site layout Ref:

62 Material Collection details

63 Logistics Assessment The pavement layers are divided into subgrade, Granular Sub base (GSB), Wet Mix Macadam (WMM) and Hot Mix Asphalt (HMA) Study included 1. Raw material transportation to the yard, 2. Extraction 3. Processing of raw materials 4. Onsite operation

64 Data Collection Strategy Total length = 28 km No of Chainages = 14 1 chainage = 2 km Pilot Chainage 34 Dt Data collected tdfor Material Processing Transportation Onsite Operations

65 1. Material Transportation

66 Fuel Consumption details (Transportation)

67 Fu uel usage (D Diesel in Lit tres) 180, , , , ,000 80,000 60,000 40,000 20,000 0 Total fuel consumption for transportation Total fuel consumption (Litres) Total fuel consumption (L) Subgrade GSB WMM HMA

68 2. Material Processing GSB Crushing of 50 m 3 GSB (litres) 250 Crushing of 1 m 3 GSB (litres) 5 Total quantity (m 3 ) Fuel consumption (litres) WMM Plant (pug mill type) (Runs using DIESEL GENERATOR) Processing of 25 m 3 WMM ( litres) Processing of 1 m 3 WMM 360 ( litres) 14.4 Total quantity (m 3 ) Fuel consumption (litres) HMA PLANT Processing of 10 m 3 HMA ( litres) Processing of 1 m 3 HMA ( litres) Total quantity (m 3 ) Fuel consumption (litres)

69 Total fuel consumption for material processing Fuel con nsumption Material Processing Fuel Consumption 8.6 % 50 % 41.3 % GSB WMM HMA Pavement Layer

70 3. ON-SITE OPERATION The processed materials a are aeta transported spotedtoto the required site location and will be dumped The materials will be spread properly using machineries or labours and compacted well to reach the desired density Compaction is one of the critical processes in the onsite operations (involvement of machineries)

71 Onsite operation GSB Layer GSB placement and compaction Fuel efficiency Duration for chainage 34 No of chainage Total working time Fuel use (diesel in Equipment (LPH) (hrs) s (hrs) litres) Back hoe Tractor dozer (D155A) 14 grader (GD623A1) Roller (l&t CASE 459) Total

72 Total fuel Consumption- Onsite operations Onsite operation 600, , Fuel consumption (Litres) 400, , , ,000 0 Subgrade GSB WMM HMA Excavation Pavement Layer

73 Total fuel consumption Total fuel consumption Transportation 12% Onsite activities 43% Raw material processing 45%

74 Emissions for unreinforced section CO2 Total consumption from transportation (L) Total consumption from processing(l) Total consumption from onsite activities(l) Emission factor (US EPA)(kg of CO2) One litre diesel = kg CO CO2 emission (Kg) CO2 emission (MT) Transportation Processing Onsite Total (for 28 km) Total (per km) 339.0

75 Emission for Reinforced Section Theoptimised section designed using the flexible and the rigid geogrid reinforcement has been taken The emissions were calculated for both flexible geogrid reinforced and rigid geogrid reinforced pavement section

76 Emissions for reinforced section CO2

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78 Emissions Comparison CO2 emission (MT) CO2 emission per lane Km (MT) Unreinforced section Flexible Geogrid Rigid Geogrid reinforcement reinforcement

79 Economic Analysis The layer wise cost has been calculated for the designed section without including the profit margin Thesame has been extended to reinforced section Reduction in construction duration in case of reinforced section is assessed

80 Cost of different sections Actual section Flexible Geogrid Layer Quantity per sq.m (m 3 ) Unit rate (Rs.) Cost (Rs. per sq.m) Layer Quantity per sq.m Unit rate (Rs.) Cost (Rs. per sq.m.) Subgrade GSB WMM HMA Sum Miscellaneous Total Subgrade 0.5 m GSB 0.15 m WMM 0.2 m HMA 0.14 m Geogrid 1 No Sum Miscellaneous Total Rigid Geogrid Layer Quantity per sq.m (m 3 ) Unit rate (Rs.) Cost (Rs. per sq.m.) Subgrade 0.5 m GSB 0.15 m WMM 0.2 m HMA 0.14 m Geogrid 1No Sum Miscellaneous Total

81 Schedule analysis The baseline schedule of this project is analysed and the time duration for completing each activity is taken for the study (reinforced and unreinforced) Duration of the roadwork activities has been reduced drastically from the original 883 days to 669 days in case of geogrid reinforced pavements

82 Summary of Results

83 NATIONAL HIGHWAY DEVELOPMENT PROJECT

84 Conclusions The geocell layer increases the structural stiffness Thickness of granular layers reduces by as much as 50%. Total cost of the pavement system per unit area is lower even with the use of expensive geocell layer. The long term performance and service life are increased Geocell layer near the surface leads to be best performance. In case of extremely soft subgrades, additional geocell layer could be placed at subgrade level. The reduction in thickness of the base layers leads to faster construction and lower carbon foot print. Geocell Reinforced Flexible Pavements

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