This standard establishes detailed procedures for measuring the deformability of rock masses on-site using a flexible dilatometer that records radial displacement within boreholes. It provides guidance to engineers and researchers on executing tests that evaluate rock behavior by applying controlled radial pressure and monitoring resulting expansions to determine deformability and anisotropy characteristics.
Overview
This standard establishes detailed procedures for measuring the deformability of rock masses on-site using a flexible dilatometer that records radial displacement within boreholes. It provides guidance to engineers and researchers on executing tests that evaluate rock behavior by applying controlled radial pressure and monitoring resulting expansions to determine deformability and anisotropy characteristics.
Audience
Contents
Structure
This section defines the scope of the practice, focusing on the detailed quantitative characterization and reporting of rock mass discontinuities essential for geotechnical investigations. It includes parameters such as orientation, spacing, persistence, roughness, wall strength, aperture, filling, seepage, number of sets, block size, core recovery, and overall rock quality. The section refers to related standards IS 11315 Parts 1 through 11 that address individual discontinuity features. It also outlines requirements for logging, calibration, and reporting methods.
Lists the Indian Standards referenced by this code to provide a framework for describing rock mass discontinuities quantitatively. These include IS 11315 Parts 1 to 11, each covering specific discontinuity attributes. The section emphasizes their role in interpreting dilatometer test data and ensuring compliance with BIS quality assurance.
Describes criteria and procedures for choosing test sites, including accurate recording of borehole and probe positions with a precision of ±15 cm. It specifies the documentation needed, such as drilling agency, methods, equipment, geotechnical logs, groundwater conditions, rock types, and discontinuity surveys within ±0.5 m around the test sections.
Details the preparation activities for the test site, including clearing debris, establishing stable platforms, marking test locations, and ensuring accessibility and safety during drilling and testing. It also specifies the documentation of drilling details, geotechnical logging, discontinuity characterization, and calibration procedures.
Describes the testing instruments including the flexible dilatometer probe with integrated displacement transducers, pressure measurement devices such as Bourdon gauges or electric transducers with ±2% accuracy, and suitable pressurizing fluids. It covers requirements for equipment calibration to ensure accurate conversion of raw data into deformability parameters.
Outlines the step-by-step methodology for conducting the dilatometer test, including pressure application and measurement, cyclic loading, and recording of pressure and radial expansion data. It specifies accuracy requirements, pressure ranges (≥ 20 MPa for hard rock), and the fluids used for pressurization. It also details the reporting format for raw and corrected data, deformability parameters, and anisotropy representation.
Focuses on the evaluation of test data, including tabulation of raw and corrected values, plotting pressure-dilation curves, calculation of deformability modulus and related parameters, and interpretation of anisotropy through directional analysis. It discusses probe rotation techniques to assess deformability variations and time-dependent rock mass responses.
Specifies comprehensive reporting requirements for each test and the overall site. Reports must include detailed logs of drilling and geotechnical conditions, discontinuity characteristics, calibration details, pressure and dilation data tables, graphical representations of deformability parameters, and anisotropy assessments. It references the IS 11315 series for discontinuity characterization.
Provides a tabulated summary of Indian Standards related to rock mass discontinuities referenced throughout the code. This annex includes IS 11315 Parts 1 to 11, detailing orientation, spacing, persistence, roughness, wall strength, aperture, filling, seepage, number of sets, block size, and core recovery with rock quality. It highlights their importance in supporting accurate geotechnical characterization.
Frequently Asked
The flexible dilatometer test requires an expandable probe inserted into the borehole to apply radial pressure, equipped with displacement transducers to directly measure radial expansion. A pressure control system regulates the applied pressure, and calibration tools are essential for verifying system accuracy before, during, and after testing. Additionally, a data acquisition system records pressure and displacement data, facilitating the calculation of rock deformability and anisotropy.
Calibration must be conducted before each test series, weekly during testing, and following significant repairs. The procedure involves verifying borehole clearance using a diameter gauge ensuring the hole diameter exceeds the probe's deflated size by 0.5 to 3.0 mm to prevent jamming. Membrane integrity and probe response are checked by inflating the membrane under controlled conditions and recording pressure-displacement behavior. Pressure sensors and displacement readings are then compared against known calibration standards to confirm accuracy.
Accurate radial displacement measurement is ensured by using multiple displacement transducers, typically at least three, positioned at 120-degree intervals around the probe circumference for comprehensive diameter monitoring with ±0.02 mm accuracy. Independent verification with a micrometer gauge between measuring pads confirms consistent sensitivity. The probe's position and orientation within the borehole must be controlled within ±15 cm and ±5 degrees respectively, and the probe diameter measured precisely with a micrometer.
The standard addresses anisotropy by employing multiple displacement transducers arranged circumferentially around the borehole, enabling measurement of radial expansions in different directions. By comparing pressure-dilation curves from each transducer, directional variations in deformability can be identified. While the basic theoretical equations assume isotropic behavior, the observed variation among transducer readings allows assessment of anisotropy in the plane perpendicular to the borehole.
Recommended borehole preparation includes selecting appropriate drillhole locations and depths based on rock quality and weathering conditions. Drilling must be performed with equipment suitable for achieving the required diameter and depth. Borehole integrity is inspected using a TV camera to detect fissures or voids that could damage the probe membrane. If unstable zones are encountered, borehole support through casing or cementing is advised to ensure stability during testing.
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