Significance and Use
5.1 The dilatometer test is usually performed in vertical boreholes. It can be used in inclined or horizontal holes, but the probe would drag along the borehole wall.
5.2 Deformation modulus of rock, creep characteristics, rebound, and permanent set data is obtained and is useful for engineering designs.
5.3 The rock mass discontinuities, in situ stresses, geologic history, crystallography, texture, fabric, and other factors will determine the rock mass properties that laboratory size tests alone may not be able to measure and that the dilatometer test may be better able to measure.
5.4 Determination of rock mass deformability yields a critical parameter in the design of foundations of dams, support of underground excavations, piers, caissons, and stability of rock slopes.
Note 2: Although a rock mass behaves in an anisotropic and inhomogeneous manner, the calculations for a rock mass deformation modulus are based on assumptions of elasticity and homogeneity. However, they still render results that are practical, simple, usable, and not significantly different from those obtained using inhomogeneity and inelasticity.
Note 3: The existing in situ stresses can only be estimated by in situ tests on the rock mass, such as this or other tests.
5.5 In situ tests such as this one provides general information regarding rock mass behavior. Dilatometer tests are advised when designing and constructing specific structures.
5.6 Dilatometer tests can be performed at a reasonable cost and effort. Dilatometer tests are also less expensive and time-consuming compared to other deformability tests like radial jack or flexible plate tests that require underground excavation and access too.
5.7 Dilatometer modulus can be correlated with the moduli obtained by other methods (for example, the plate loading or radial jacking methods). The correlated dilatometer modulus can then be used instead of other more expensive in situ modulus tests.
5.8 Dilatometer tests can provide a qualitative evaluation of a rock mass deformability before performing a large scale deformability test such as a radial jack test.
5.9 Dilatometers are valuable for rapid index logging of boreholes in jointed rocks that yield poor core recovery and inadequate specimens for laboratory testing.
5.10 Pressurization and depressurization of the dilatable membrane in this standard are unique. This is done immediately upstream of the dilatable membrane by a dual-action piston actuated from a manual pump at the surface. This configuration allows the use of the dilatometer at substantial depths and eliminates the parasitic expansion of the tubing and pumping system and forces the membrane to collapse completely regardless of if the drill hole column has fluid or not.
5.11 The results of dilatometer tests may be used to check against the serviceability limit state of spread foundations on rocks through a deformation analysis.
5.12 When performing a deformation analysis the Young's modulus, E, may be taken equal to Ed on the assumption that the rock is linearly elastic and isotropic.
Note 4: The quality of the result produced by this standard is dependent on the competence of the personnel performing it and the suitability of the equipment and facilities used. Agencies that meet the criteria of Practice are generally considered capable of competent and objective testing/sampling/inspection/etc. Users of this standard are cautioned that compliance with Practice does not in itself assure reliable results. Reliable results depend on many factors; Practice provides a means of evaluating some of those factors.
1.1 This test method establishes the guidelines, requirements, procedure, and analyses for determining the in situ deformation modulus of a rock mass and other ancillary data using a flexible volumetric dilatometer in an N-size, 75.7 mm (2.98 in.) drill hole ( and ). Cyclic, creep, and unloading cycles are not covered in detail in this standard but may be added in the future or with a separate test standard, practice, or guide.
FIG. 1 General Depiction of a Flexible Dilatometer, Deflated (a) and Inflated (b) in a Borehole
FIG. 2 Cross-Sections of the Borehole and Dilatable Membrane Portion of the Dilatometer in the Uninflated, r = 0, Starting Position
Note 1: Other rock mass deformability tests are radial jack tests, flat jack tests, flexible plate tests, and borehole jack tests.
1.2 This test method applies mainly to a commercially available flexible, volumetric dilatometer for an N-size, (75.7-mm (2.98-in.) I.D.) borehole that is inflated and deflated hydraulically in the borehole. However, the test method could apply to other dilatometers, including pneumatically inflated, or for different borehole sizes as well as covered under the British Standards Institute EN ISO 22476-5 (https://geotechnicaldesign.info). Use of a different diameter or type of volumetric dilatometer is up to the owner or project manager and shall not be regarded as nonconformance with this standard.
1.3 Purpose, Application, Range of Uses, and Limitations:
1.3.1 This designation is described in the context of obtaining data for the design, construction, or maintenance of structures on or in rock. This method can be conducted in any orientation but is usually conducted in a vertical or horizontal borehole as dictated by the design consideration.
1.3.2 The test has no depth limits other than those imposed by the limitations of the test equipment, drill hole quality, testing personnel, and equipment to drill the holes and position the testing assembly.
1.3.3 Since this is a volumetric test, only the average deformation is obtained around the borehole. If the rock properties, for any reason, including the in situ stress field or fracture density, are significantly anisotropic, then this device cannot detect that difference.
1.3.4 A large expansion of the probe in a test zone can occur due to either an oversized drill hole, weathering, lithology, or discontinuities. As a result, the maximum pressure and expansion of the dilatometer would be limited. For example, for one particular dilatometer to avoid damaging the membrane in a preferred N-size, 75.7 mm (2.98 in.) I.D., borehole, the maximum working pressure of 30,000 kPa (4,350 lbf/in.2) might be possible. In contrast, at 82.5 mm (3.25 in.), the maximum working pressure would drop to only 20,680 kPa (3000 lbf/in.2). Furthermore, regardless of if it an oversized drill hole or a low modulus test interval, the maximum diameter (inflated) of only 85.5 mm (3.37 in.) is allowed.
1.3.5 The radial displacements of the borehole walls during pressurization are calculated from the total volume change of the dilatometer. As such, the test results from a volumetric dilatometer indicates only the averaged value of the modulus of deformation.
1.3.6 The volumetric dilatometer test does not provide the anisotropic properties of the rock mass because it measures the average deformation and not the deformation in specific directions. However, by conducting dilatometer tests in boreholes oriented in different directions or taking impression packer data in any test intervals that had developed a hydraulic type fracture, some aspects of the in situ anisotropic conditions could be obtained.
1.4 Units—The values stated in SI units are to be regarded as standard. The values given in parentheses are provided for information only and are not considered standard. Reporting of test results in units other than SI shall not be regarded as nonconformance with this standard.
1.4.1 The gravitational system of inch-pound units is used when dealing with inch-pound units. In the system, the pound (lbf) represents a unit of force (weight), while the units for mass is slugs. The slug unit is not given, unless dynamic (F = ma) calculations are involved.
1.5 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice .
1.5.1 The procedures used to specify how data are collected/recorded or calculated in the standard are regarded as the industry standard. In addition, they are representative of the significant digits that generally should be retained. The procedures used do not consider material variation, a purpose for obtaining the data, special purpose studies, or any considerations for the user’s objectives; and it is common practice to increase or reduce significant digits of reported data to be commensurate with these considerations. It is beyond the scope of this standard to consider significant digits used in analysis methods for engineering design.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.