Classification of the rock mass The rock mass quality (Q) is a very sensitive index and its value varies from 0.001 to 1000. Use of the Q-system is specifically recommended for tunnels and caverns with an arched roof.
How do you calculate the RMR of a rock?
The final RMR value of the rock is calculated as follows:(1) R M R = R 1 + R 2 + R 3 + R 4 + R 5 + R 6 where R1, R2, …, R6 are the ratings corresponding to six rock parameters as depicted in Table 2.
What is reduction factor?
The factor relating the allowable stress on a long column with that on a short column in order to prevent buckling.
What is RMR in geology?
The rock mass rating (RMR) is a geomechanical classification system for rocks, developed by Z. T. Recently RMR14 has been proposed to improve the RMR performance by incorporating new experiences from tunnel practices.
What is stress reduction factor?
The stress reduction factor (SRF) parameter (Table 8.6) is a measure of (1) loosening pressure during an excavation through shear zones and clay-bearing rock masses, (2) rock stress qc/σ1 in a competent rock mass where qc is the uniaxial compressive strength (UCS) of rock material and σ1 is the major principal stress …
What is Q-system in rock Mechanics?
The Q-system is developed to classify rock masses around an underground opening, as well as for field mapping. Based on estimation of six rock mass parameters, a Q-value for a rock mass can be calculated. This value gives a description of the rock mass quality.
What is RMR and SMR?
Rock Mass Rating (RMR) has been widely used as a method of classifying the strength of the rock mass. RMR values are then correlated into Slope Mass Rating (SMR) which is a system of classification of a rock slope.
What is stress reduction factor in masonry elements?
The stress reduction factor, v, used in this paper equals. the wall failure load divided by the axial compression fail- ure load, thus.
What is stress reduction factor in Masonry?
A stress reduction facto r method of design of masonry walls has recently been proposed(J) based on a simplified theoretical analysis of the response of the wall to combined axial compressive load and weak axis bending.
What is the value of non dimensional slenderness ratio in the equation of design compressive strength?
Explanation: The value of non dimensional slenderness ratio λ in the equation of design compressive strength is given by λ = √(fy /fcc) , where fy is yield stress of material and fcc = (π2E)/(KL/r)2, where E is modulus of elasticity of material and KL/r is effective slenderness ratio i.e. ratio of effective length.
What kinds of factor affect the rock quality?
The principal factors controlling the strength of solid rocks are: I) mineral composition, structure and texture; 2) bedding, jointing and anisotropy; 3) water content; 4) state of stress in the rock mass.
What is the stress reduction factor (SRF)?
• Stress condition given as the stress reduction factor (SRF); composed of − Loosening load in the case of shear zones and clay bearing rock, − Rock stress in competent rock, and − Squeezing and swelling loads in plastic, incompetent rock.
How to calculate the stress reduction factor of a tunnel?
The following guidelines are provided to obtain the stress reduction factor. 1. More than one weak zone occurs in the tunnel. In this case, use SRF = 10.0 2. Single weak zone of rock with clay or chemically disintegrated rock. (Excavation depth < 150 ft.) Use SRF = 5.0 3. Single weak zone of rock with clay or chemically disintegrated rock.
What are the factors that affect the strength of rocks?
• In addition to the mineral composition of the rock material, the strength is also considerably influenced by water content. This factor can be a great challenge in weak rocks in tropical area where some of the original minerals and fabric have undergone alteration.
How do you calculate the compressive strength of rock?
Rock mass compressive strength can be estimated from q cmass ≈ 7γ (Q) 1/3 (MPa); γ is the rock density in t/m 3, and q cmass = rock mass compressive strength. Source: Barton, 2002. 1. SRF should be reduced where micro-folding occurs and its axis is nearly parallel to the strike of walls of caverns or tunnels.
