--- title: "Mass haul diagram and WBM construction" subject: "Transportation Engineering II" chapter: 3 key: "semester_7/transportation_engineering_ii:mass-haul-wbm-construction" source: https://www.bctengineer.com/q/semester_7/transportation_engineering_ii/mass-haul-wbm-construction site: BCT Engineering --- # Mass haul diagram and WBM construction Transportation Engineering II · Chapter 3: Road Construction Technology - Asked in: 2076 Chaitra, 2+6 marks - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/transportation_engineering_ii/mass-haul-wbm-construction - Whole chapter: https://www.bctengineer.com/md/semester_7/transportation_engineering_ii/chapter-3 ## Question Define mass haul diagram. Write down the construction procedure of WBM road. ## Short answer Mass haul diagram plots cumulative earthwork volume against chainage to plan haul, balance, and borrow/waste. WBM construction: prepare base, spread coarse aggregate (gradings 1-3), dry roll, apply screenings in stages with wet rolling to form slurry, then bind and allow to set. ## Answer #### Mass haul diagram A **mass haul diagram** is a curve of cumulative earthwork volume (cut positive, fill negative, after correcting for shrinkage or swell) plotted as ordinate against chainage as abscissa. It is used to plan the movement of earth along a road. ```text Cum. volume ^ peak | ,--*--. | A -----'-------'--- B balancing line | ,' '. | ____/ '. valley | '-._*______ +------------------------------------> chainage cut fill cut ``` It shows the earthwork balance, the direction and length of haul, and the quantities to be borrowed or wasted, so that the cheapest plan of earth movement can be made. #### Construction of WBM road **Water Bound Macadam (WBM)** is a base or surfacing course of clean crushed stone aggregate of graded sizes, bound by screenings, binding material and water, and compacted by rolling (IRC:19 and MoRTH Section 404; used in Nepal DoR specifications for base courses). **Materials** - **Coarse aggregate**: hard, tough crushed stone (Los Angeles abrasion value below 40 percent and aggregate impact value below 30 percent for base; up to 50 and 40 percent for sub-base), flakiness index below 15 percent, in three gradings: Grading 1 (90-45 mm), Grading 2 (63-45 mm) and Grading 3 (53-22.4 mm). - **Screenings**: crushed stone of 13.2 mm (Type A) or 11.2 mm (Type B) nominal size to fill the voids in the coarse aggregate; non-plastic moorum or gravel (liquid limit below 20, plasticity index below 6) may be used where economical. - **Binding material**: a small quantity of fine material such as crusher dust or moorum (PI below 6 percent), used only if needed to bind the screenings. - **Water**: clean and free from salts. **Equipment**: three-wheel power roller (8-10 t) or vibratory roller (8-10 t), motor grader or spreader, water tanker, brooms, screening spreaders. **Construction procedure** 1. Prepare the base: clean it, trim it to profile and fill depressions; provide lateral confinement by building the shoulders (or kerbs) along both edges to the thickness of the layer. 2. Spread the coarse aggregate to a uniform thickness and the correct camber by stone spreader or manually. The compacted thickness of one layer is 100 mm for Grading 1 and 75 mm for Gradings 2 and 3; the loose depth is about 1.25-1.30 times this. 3. Dry rolling: roll from the edges to the centre with an 8-10 t roller until the aggregate is firmly keyed (no creep ahead of the roller). 4. Apply the screenings gradually in 3 or 4 stages, with dry rolling and sweeping, so that the voids are filled. 5. Sprinkle water on the surface and roll; the slurry formed by the screenings and water fills the voids and binds the stone. Continue wet rolling until a wave of slurry forms ahead of the roller wheels. 6. Apply binding material (if required), sprinkle water, roll, and let the surface dry overnight. 7. Allow the layer to dry and set (1 to 2 days, with no traffic) before laying the next layer or the surface treatment/premix carpet. **Quality control**: aggregate tests (LAA, AIV, flakiness, water absorption, soundness), grading of aggregate and screenings, thickness and camber checks with a template, density by sand replacement, surface regularity by straight edge (max 12 mm undulation), and tests every 100-200 m. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is plotted in a mass haul diagram? A. Cumulative earthwork volume (cut positive, fill negative) against chainage B. Cross-sectional area against level C. Cost of earthwork against haul distance D. Ground level against chainage Answer: A. The ordinate is cumulative volume corrected for shrinkage or swell and the abscissa is chainage. (Key point: Mass haul diagram definition) 2. What is the purpose of screenings in WBM? A. To fill voids in the coarse aggregate B. To act as the bituminous binder C. To provide drainage D. To reduce the thickness of the layer Answer: A. Screenings of 13.2 mm stone dust are applied in stages with rolling to fill voids between coarse stones. (Key point: Role of screenings) 3. Why is dry rolling done before screenings are applied? A. To firmly key the coarse aggregate until it no longer creeps B. To wash fines out of the aggregate C. To form slurry D. To harden the bitumen Answer: A. Dry rolling from edges to centre interlocks the aggregate before voids are filled. (Key point: Dry rolling) 4. When is wet rolling of WBM continued until? A. Until the aggregate turns black B. Until a wave of slurry ahead of the roller stops C. Until the layer is 150 mm thick D. Until the surface is completely dry Answer: B. Rolling continues until slurry no longer forms a wave ahead of the roller, showing voids are filled and bound. 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