|Publisher||American Rock Mechanics Association||Language||English|
|Content Type||Conference Paper|
|Title||Qualitative Factors For Evaluating Stability|
|Authors||Thomas L. Neff,|
|Source||The 14th U.S. Symposium on Rock Mechanics (USRMS), June 11 - 14, 1972 , University Park, PA|
|Copyright||1972. The American Society of Civil Engineers. Permission to Distribute - American Rock Mechanics Association|
The size and complexity of underground openings has been increasing in recent years. The amount of underground construction of all types is expected to double in the next decade over that of the previous ten years. Many more underground openings will be required to fill needs for transportation systems, parking facilities, power generation, storage of liquids, and water and sewage treatment. The design of such structures is continually being refined in order to place it on a more rational basis. There is still much progress to be made, however, before underground rock structures are designed on the same basis as above-surface structures built of concrete or steel. Because of this empirical aspect of much rock mechanics design, there are significant points to consider:
Thus, there is a need for planned observations and measurements to make the necessary field modifications and assure a good design.
Monitoring programs can involve quantitative and qualitative data. Quantitative data for underground projects usually requires measurements of load (or stress) and displacement (or strain). Because equipment to sense and record load and deformation is frequently expensive and sensitive to error, two common problems often result: the amount of data is either limited in scope, or the quality of the data is somewhat questionable (Neff, 1970). Quantitative data are expensive and sometimes difficult to interpret and thus qualitative observations should be made to evaluate quantitative measurements. Also, some factors do not lend themselves to only quantitative measurement.
In this paper, observations or measurements which are other than those of load (or stress) or deformation (or strain) will be considered to be qualitative. This does not mean that numbers are ignored, but the emphasis is perhaps more directed toward the phenomena occurring rather than toward the number which may or may not result.
This discussion deals with several "qualitative" observations that should be made during the construction of an underground opening, and how the results of each operation can be interpreted qualitatively to aid in an assessment of the stability of the openings. Methods are also suggested to better organize such qualitative observation programs.
DRILLING AND BLASTING PROCEDURES
The use of rapid excavation techniques in tunneling is becoming more common. Tunneling machines will most likely be used on an increasingly larger proportion of tunnel projects, and they will be modified to excavate larger openings in the future. For the present, however, and in the near future, drilling and blasting will probably continue to be the primary method of rock excavation. Excavation by blasting causes damage to the exposed surfaces of the openings. This damage is in the form of new fractures caused by the blasting or movement along existing joint systems as a result of the vibrations, both of which reduce the rock modulus immediately adjacent to the opening.
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