The city of Bhopal is gearing up to commence construction activities of its own underground metro project, adopting cutting-edge technologies of the urban transportation sector. The success in building such an ambitious, eco-friendly, safe, and economically effective engineering structure relies largely on the characteristics of the ground that the structure is being built in. This is where the role of Geotechnical Studies/Investigation takes a crucial seat. Geotechnical Investigations encompass a wide range of techniques that are exercised to achieve acquaintance with the project area's sub-surface conditions and involve field work, collection of soil and rock samples, laboratory testing, analysis of data, and reporting.
Brief Geotechnical Study
The Bhopal underground metro comprises a 3.39 km length of tunnel and two underground stations named Bhopal and Nadra Bus Stand. The Bhopal Metro Rail Corporation Limited (MPMRCL) has carried out a brief Geotechnical study along the underground metro rail alignment. The study aimed to obtain preliminary sub-surface Geological and Geotechnical data to help the bidders understand the project area in terms of its sub-surface conditions and thus prepare the best bids. Availability of Geotechnical data helps engineers to conceptualize best-suited engineering designs, which are directly proportional to project cost estimates.
A total of 50 boreholes were executed, 38 of which were for the tunnel section and 6 each for both stations. These boreholes were planned to provide a brief understanding of the geology of the area and not as a basis for detailed designing. The tunnel section boreholes were planned and executed approximately 50 meters apart, while the station boreholes were executed to gather data from the entire station area. All the boreholes were explored to a depth of 30 meters from the existing ground level.
Field Work and Sample Collection
Sample collection is a key aspect of any Geotechnical Investigation assignment. To carry out the field work, MPMRCL has appointed a firm with expertise in the complete spectrum of Geotechnical services. Boreholes were executed using the rotary drilling method, wherein a setup powered by a rotary cutting head at the end of the shaft advances into the ground as it rotates with the help of mechanical/hydraulic engines. Different techniques were used to collect soil and rock samples, which were then logged for their Geological and Geotechnical properties at the site and dispatched to the laboratory with proper indexing.
A few in-situ geotechnical tests were also conducted at the site, such as the Standard Penetration Test and Pressure Meter Test.
Laboratory Test
Laboratory testing on soil and rock samples is carried out to determine their engineering properties, which are required for designing purposes. Necessary laboratory tests were carried out on soil and rock samples collected at the site, such as grain size analysis, triaxial test, tests for plasticity index and water absorption on soil samples, and unconfined compressive test, point load index test, and Brazilian tensile strength test on rock samples. The factual data from the tests were provided to the bidders.
Report
The Geotechnical report comprises the findings of the field work as well as the laboratory testing on the soil and rock samples. The data will be represented in the form of bore logs, test data, and interpretation of the results.
The present project area possesses soil strata from 0.00 to 9.20 meters of depth, and the thickness of the rock stratum varies from 10 to 25.0 meters. The stratum at tunnelling depth mostly consists of moderate to highly weathered sandstone.
Conclusion
The Geotechnical Investigation plays a crucial role in the successful construction of the underground metro rail in Bhopal. By obtaining detailed data on the sub-surface conditions, engineers can design the most appropriate structures, ultimately contributing to the overall success of the project. With the findings from the Geotechnical study in hand, the construction of the Bhopal underground metro rail can proceed with confidence, ensuring not only the safety and efficiency of the system but also its environmental sustainability and economic viability.
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