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IIT Tirupati Navavishkar I-Hub Foundation Website
Problem Statement
Problem Statement
Underground manholes and inspection chambers are vital for drainage, utility access, and maintenance. However, their depth, extent, and connectivity are often poorly documented, posing risks during construction, retrofitting, or urban expansion. Conventional intrusive methods are disruptive, whereas a non-destructive, high-resolution approach is essential for safe and precise infrastructure assessment.
Overview
At IIT Tirupati campus, a Ground Penetrating Radar (GPR) survey was conducted to investigate two different manholes and their surrounding subsurface conditions. The study aimed to map the depth, extent, internal structure, and connecting utilities, while also characterizing the geotechnical layers around the chambers.
Engineering Impact
The survey demonstrated the ability of GPR to:
Deliver accurate mapping of manholes and chamber volumes.
Detects deep-seated and hidden utilities beneath reinforced concrete layers.
Provide layer-specific geotechnical insights for soil and foundation conditions.
Support infrastructure planning, rehabilitation, and safe excavation.
Conclusion
This case study establishes GPR as a powerful tool for non-invasive investigation of underground manholes and chambers, offering detailed information on geometry, connectivity, and surrounding materials. The combination of 250 MHz ultra-wideband antenna and 3D grid survey design proved particularly effective for resolving complex subsurface conditions within a campus infrastructure setting.
Methodology
System Configuration: A 250 MHz ultra-wideband antenna was employed, providing deeper penetration and wide-frequency coverage.
Survey Design: Data acquisition was performed on 3D grids with 25 cm line spacing, enabling detailed volumetric imaging and depth slicing.
Processing Workflow: Advanced 2D/3D imaging, time-slicing, and amplitude analysis were applied to highlight manhole geometry, utilities, and surrounding strata.
Key Findings
Manhole Geometry: Both manholes were clearly mapped in terms of depth and lateral extent, with volumetric estimates generated.
Utilities and Connectivity: Subsurface pipelines connecting the manholes were identified, including utilities located beneath concrete reinforcement layers, which are typically difficult to detect.
Material Stratigraphy: Multiple subsurface layers were distinguished, including reinforced concrete, unsettled soil, and underlying bedrock at greater depths.
Airwave Reflections: Strong reflections from nearby building walls were recorded, producing distinct patterns due to indoor signal propagation.
Depth-Slice Imaging: The dense 3D grid and ultra-wideband configuration enabled clear visualization of manholes, chambers, and connecting utilities in successive depth slices.
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