Transport Engineering - Assignment Example

CIV3703 – Transport Engineering Question 1 – (50 Marks) Calculate the design traffic in ESA for the follows cases: Case A Road type Urban arterial AADT (data year) 12 000 (5 years ago) HV % 10 Annual growth rate % 4 Design period 20 years Directional Factor 60:40 Lane distribution Factor 85% of HV using outer lane Solution Case A: Urban Arterial Annual average daily traffic (AADT) = 12000 Annual growth rate of heavy vehicles = 4% Percentage of heavy vehicles = 10% Design life 20 years i. The mean daily traffic for the year opening The data provided shows a traffic count carried out 5 years ago and revealed an AADT of 12000 With a growth rate of 4. Table 1: Traffic growth factor (g)* for calculation of average daily traffic Using Table 1 above, Therefore AADT= ii. Determine the average in design lane in the year opening Opening Directional factor 60:40 therefore DF will be 0.85% Table 2: Typical Values of ESA per HV From figure 2 above, the ESA for Heavy vehicles for urban roads is 1.8. i. Cumulative ESA over Design life of the lane The formula is used for determining Design Traffic in cumulative ESA CGF refers to the Cumulative Growth Factor as shown in figure below Table 3: Cumulative Growth Factor (CGF) For a growth rate of 4% and a design life of 20 years; CGF is 30 p.a. Case B: Urban Arterial Calculate the design traffic in ESA for the follows cases: Case B Road type Principal road between major regions AADT (data year) 5000 (last year) HV % 20 Annual growth rate % 8 Design period 15 years Directional Factor 50:50 Lane distribution Factor 95% of HV using outer lane Annual average daily traffic (AADT) = 5000 Annual growth rate of heavy vehicles = 8% Percentage of heavy vehicles = 20% Design life 15 years iii. The mean daily traffic for the year opening The data provided shows a traffic count carried out 1 years ago and revealed an AADT of 5000 With a growth rate of 8%. Using Table 1 above, Therefore AADT= iv. Determine the average in design lane in the year opening Opening Directional factor 50:50 therefore DF will be 0.95% From figure 2 above, the ESA for Principal road between major regions is 3.0 ii. Cumulative ESA over Design life of the lane The formula is used for determining Design Traffic in cumulative ESA CGF refers to the Cumulative Growth Factor as shown in figure below For a growth rate of 8% and a design life of 15 years; CGF is 27 p.a. Question 2 – (50 Marks) A granular pavement with bituminous seal is to be design for a collector road in urban area. The design lane traffic loading in Equivalent Standard Axles (DESA) is 20 million ESLs. Testing reveals a subgrade CBR of 3, and could be improved from CBR 3 to CBR 7 with lime stabilization. Available equipment and construction techniques dictate that the stabilised layer must be 150 mm compacted thicknesses and the cost for stabilisation will be $35.00 per m3. The minimum thickness of any layer is 100mm. The following materials are available for your use and are as placed. Material Cost Crushed rock, CBR 90 $55.00/ m3 Crushed river gravel, CBR 30 $35.00/ m3 River gravel, CBR 15 $15.00/ m3 Selected fill, CBR 7 $10.00/ m3 Consider possible pavement options and recommend a final pavement configuration for adoption. It is essential to provide justification as to why you have selected a particular design for construction. While cost is an important issue, include some discussion on the potential long-term performance of the selected pavement as compared with other pavements. Note: The pavement seal has already been designed, and you do not need to design either seal or other road elements such as slopes, drainage, etc. Solutions Table 4: Design chart for granular pavements with thin bituminous surfacing Use the design chart shown in table 4 above, on the horizontal axis we get the design traffic of 20million ESA i.e. ESA. Using and CBR 3, the required thickness of material is 550mm Assuming that all the assumptions through which Austroads Guide designs charts are valid, the below designs are given; Assuming a thickness of 100mm. then using the design traffic of ESA. For subgrade of modulus 50Mpa, the thickness of asphalt required is 150mm Considering the available pavement materials, given subgrade Crushed rock, CBR 90, Crushed River gravel, CBR 30, River gravel, CBR 15, selected fill, CBR 7, Using CBR 30, from the graph above, the needed cover for the CBR 30 material is 150mmthe required base thickness is 150mm, this means that to attain an overall pavement thickness of 550mm is 550-150=400mm thick base material. Question 3 – (30 Marks) a) List the functions of a primer in the application of a bituminous seal over a crushed rock or natural gravel base, and outline the materials which are typically used for primes. Answer Primer refers to the application of a primer binder on a prepared pavement, being covered with aggregate. The functions of the primer are: i. To serve as a temporary treatment prior to the final application of a permanent bituminous wearing course ii. Permit normal seal to be placed in more favourable weather conditions iii. Improves the bond thereby offering flexibility thus reducing the risk of early seal failure iv. Primer also prevents seepage of water through the permeable crushed rocks membrane. v. Primer materials provide bonding between the granular crushed stones materials forming the base layer. Primer materials Some of the common materials as primer used in various Austroroads and Australian standards include i. Bitumen Class 170 ii. Cutback bitumen iii. Bitumen emulsion iv. Cutter oil v. Polymer modified binders vi. Aggregate pre-coated with bituminous material b) Explain the basis of mechanistic pavement thickness design methods (i.e. what theories and assumptions are these methods based on). Answer Mechanistic- empirical design method for designing flexible pavements refers to application of engineering mechanics principles to assess the response of pavement structures as a result of traffic loading as well as conducting distress prediction based on road performance dynamics over time. The critical aspect in using mechanistic- empirical method is the need to use laboratory setup to simulate adequately the key aspects of real behaviour of pavements under loading. Among the theories used in mechanistic – empirical design method include: Multi-layer linear elastic Theory This theory attempt to calculate dynamic displacements created by loading applied on an elastic half space for instance a road surface consisting of homogenous material both in depth and area. Some of the key parameters monitored include strain, stress and deflection of the medium used. The model is founded on a number of assumptions, this include: Each layer is homogenous, linearly elastic with characteristics parameters such Young’s modulus, poisons ratio The material is infinite horizontally and also weightless The subgrade is considered infinite while the thickness of each layer is finite Finite element method FEM permits the structural modelling of multilayer pavement section consisting of material properties that vary both horizontally and vertically throughout the profile. FEA has the ability to consider c) List the parameters used in the current Austroads methods for flexible pavement design, and outline how these parameters are determined. Answer; Some of this parameters include: Traffic: This involves analysing the vehicle load distributions such as axle type configuration and loading, structural numbers Material properties: this involves the analysis of the empirical interactions used in correlating the structural and modulus coefficient of layers. Environmental effects: this involves the representation of the seasonal variations in environmental conditions such as soils. Question 4 (20 Marks) An asphalt stiffness modulus of 4800 MPa was obtained in the laboratory. In the field, the following are observed: In-service Air Voids = 8% WMAPT = 27C Average traffic speed = 80 kph. a. Find the Austroads correction factors for the asphalt and obtain the design asphalt modulus. Austroads correction factors at 270C b. Using the calculated design asphalt modulus, design 3 alternative flexible pavements (granular, deep strength and full depth) using Austroads charts for a design traffic loading of 7.5x107 ESA. c. Explain the disadvantages and advantages of each pavement option considering issues such as subgrade strength, long term settlement, reflective cracking, durability, construction Question 5 – (50 Marks) You were involved in a dispute concerning the supply of asphalt for a full depth pavement construction. During the first summer after road opening, it was observed that the asphalt experienced extensive rutting. In addition, some bleeding occurred at a few locations. The available laboratory record indicated that the asphalt aggregate as supplied could be classified as well graded. The following data is obtained from a cored asphalt specimen taken from the site: Mass of asphalt specimen in air = 1200 g Mass of asphalt specimen in water = 680 g Bulk density of coarse aggregate = 2.68 t/m3 Bulk density of fine aggregate = 2.74 t/m3 Bulk density of filler = 3.10 t/m3 Density of binder = 1 .02 t/m3 % coarse aggregate of total mass = 60 % % filler of total mass = 10% Binder content by mass in asphalt mix = 6.4 % Maximum density of asphalt mix (AS 2891.7.1) = 2.51 t/m3 The asphalt laboratory suggested the effective binder content (% by volume) of typical asphalt mixes are as follows: Coated stone 7-9 Continuously graded asphalt mix 10-12 Gap graded asphalt mix 13-15 Gap graded wearing course 16-18 Mastic asphalt 24-28 a) Analyse the results of the laboratory test, do some calculations and draw a conclusion as to why the pavement experienced the above problems. Also suggest how to rectify the situation. Hints: Find the % Air Voids and % Effective Binder Content. b) Calculate (show calculation details and explain the meaning / significance of each item below): 1. Maximum theoretical density (t/m3) 2. Voids in mineral aggregate (%) 3. Voids filled with binder (%) c) Further tests revealed that the stiffness modulus of the recovered binder = 50 MPa. Estimate the laboratory stiffness modulus of the asphalt using the Shell nomograph. Solution % Air Voids and % Effective Binder Content Information to consider % coarse aggregate of total mass = 60 % % filler of total mass = 10% Binder content by mass in asphalt mix = 6.4 % Aggregate mix= course aggregate+ fine aggregate filler Calculating the %aggregate in total mass of asphalt=100 content -%binder % Course aggregate %aggregate in total mass of asphalt P=100%-6.4%=93.6% Calculating %mass course aggregate in aggregate mix Q = % Filler aggregate %aggregate in total mass of asphalt P=100%-10%=90% Calculating %mass course aggregate in aggregate mix Q = Calculating the %mass filler, S However, Q+R+S=100% Therefore, S=100-(64.1+11.1) =24.78% Calculating the bulk density of the aggregate mix, Y, Where; A is mass of sample in air B is Mass of SSD sample in air C is Mass of sample in water % effective binder by mass= Where =Total asphalt binder content =Mass binder in specimen =Mass of aggregate in a specimen % effective binder by mass= Calculating Percent air voids % air voids = (1 – B / E) * 100 Where: B = Bulk Specific Gravity E = Maximum Rice Specific Gravity = Volumetric proportion of effective binder = % effective binder by mass ÷ Density of binder = Y Volumetric proportion of effective binder Volumetric proportion of aggregate = % aggregate by mass ÷ bulk Density of aggregate mix = Z Volumetric proportion of aggregate Read More