“To have maximum return on investment, the equipment should have maximum productivity and less rework,” says SM Roy, Chief Executive Officer, Lanco Infratech. In an exclusive chat with Equipment India, Roy elaborates on the evolution of compacting and grading technologies. Excerpts from the interview.
How, over a period, have the methods of compaction and grading evolved and to what extent does the contracting fraternity use the advanced equipment and methodology?The first road roller was horse-drawn; this was followed by steam and diesel rollers. For a long period, static compactors of various sizes were used. The introduction of vibratory compactor in 1946 opened a new era in construction industry.
A few decades ago, grading was done manually or with tractor dozers where operator skill was important for accuracy. Advanced technology has made the grading work simple by giving option of automatic slope and elevation offsets. GPS navigation and machine guidance systems have reduced the amount of external surveying required.
Almost every construction project or site preparation requires some kind of grading and compaction. The Indian contracting community extensively uses the graders and compactors for various purposes based on size and extent of projects.
Why vibratory compactors over static ones? What is the vibration effect in compaction over static loading?Static compactor functions with its own weight and hence compaction is confined to the top soil layer. Vibratory compactors use a mechanism to create a downward force in addition to the machine's static weight thereby affecting the top layers as well as deeper layers. Vibration moves through the material, setting particles in motion and moving them closer together for the highest possible density.
To what extent does the soil condition determine the selection of compactors?The desired level of compaction is best achieved by matching the soil type with its proper compaction method. Clay is cohesive; its particles stick together requiring high impact force to compact. Hence, the sheep-foot roller is the best choice. Best compaction of granular soils is possible with shaking or vibratory action. For mixed type of soils, it is a good idea to choose the compactor appropriate for a larger percentage of the mixture.
What is the return on investment on a compactor and on a grader?To have maximum return on investment, equipment should have maximum productivity and less rework. Production cost depends on depreciation, maintenance, fuel, working hours and labour. Smaller machines cost less in terms of ownership but more in labour and vice versa. In general, for each situation, one should study equipment productivity and try to strike a balance to get better value for money.
Could you tell us about the density achievable from the range of compactors? What determines the maximum achievable density?The maximum achievable density depends on fill type, compactive efforts and moisture content and it varies from 2.1 tonne/cu m for well graded gravels to 1.5 tonne/cu m for highly plastic clays. Most of the compactors can achieve maximum fill density with different compactive efforts and efficiencies.
What are the variants in compaction?The variants in compaction are soil type, moisture content, lift or fill thickness, compactive efforts or number of passes of compactors.
A selection criterion for graders and compactors is given below:• Size, weight and machine power.• Steering, direction control and maneuverability.• Functional automation.• Multi-tasking machine with various attachments.• Maximum possible thickness of the lift (for grader).• Accuracy of the grading (for grader).• Range of vibration frequency (for compactor).• Working and downtime.• Ownership and maintenance cost. • Availability of trained manpower to use the machine.