Engineering Geology. 5. Engineering Properties of Rocks. Engineering Geology is backbone of civil engineering. 1 st semester - 2011-2012 Eng. Iqbal Marie. Rock properties tend to vary widely, often over short distances. Engineering Properties of Rocks = Rock Mechanics ,
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
the in situ stress state and Hydro-geological regime
will be important for all engineering.
Index Properties of Rocks:
Measured by Franklin and Chandra’s (1972) :slake durability test.
Approximately 500 g of broken rock lumps (~ 50 g each) are placed inside a rotating drum which is rotated at 20 revolutions per minute in a water bath for 10 minutes. The drum is internally divided by a sieve mesh (2mm openings)
After the 10 minutes rotation, the percentage of rock (dry weight basis) retained in the drum yields the “slake durability index (SDI)”.
A six step ranking of the index is applied (very high- to very low) as shown in tables 1 and 2.
Used to evaluate shales and weak rocks that may degrade in service environment.
Uniaxial unconfined compressive strength ( UCS)
Triaxial compressive strength
Simple means' field tests that make use of hand pressure, geological hammer, etc. (Burnett, 1975), are used to determine intact rock strength classes in the British Standard (BS 5930, 1981)
fractures. However, on the small scale it is composed of grains with
the form of the microstructure being governed by the basic rock forming
processes. Subsequent geological events may affect its mechanical properties and its susceptibility to water penetration and weathering effects.
Four stages of deformation recognized:
All are dependent on the elasticity, viscosity and rigidity of the rock, as well as temperature, time, pore water, anisotropy and stress history.
Chalk: low stiffness, low strength, quite brittle
Stress- strain Diagrams
limestone rock with a variation in the grain geometry has a medium stiffness, medium strength and a more gentle descending part of the curve caused by the gradual deterioration of the microstructure as it is progressively and increasingly damaged
D= distance between the point loads.
All of the above are measured on Lab specimens, not rock masses/ outcrops, which will differ due to discontinuities at different scales.
Indirect tests such as Point Load Index (Is(50)) are used to predict the UCS. These tests are easier to carry out because they necessitate less or no sample preparation and the testing equipment is less sophisticated. Also, they can be used easily in the field.
Relation between UCS and Is(50) for Group A Rocks
The RQD values also can serve to identify potential problems related to bearing capacity, settlement, erosion, or sliding in rock foundations.
The RQD can provide an indication of rock quality in quarries for concrete aggregate, rockfill .
The RQD must be used in combination with other geological and geotechnical input
Also bedding, cleavage, schistosity.
Fractures allow inelastic deformation and reduce rock mass strength to 1/5 to 1/10 of the intact rock strength. This fraction known as rock mass factor.