Laboratory strength or Field strength?
Laboratory strength or Field strength?
(OP)
Hello There,
I want to model a room and pillar mine, so my task is to ensure that the pillars are safe and stable. I will use Abaqus software,
In ABAQUS, i need to input the material properties, i have the material properties for laboratory samples (2 in high, 1 in diameter). As you know, the strength of the laboratory rock samples is much higher than the in-situ strength.
the question is: what kind of input of parameters should i input in abaqus, is it the properties from the lab. or the laboratory from the field. i will reduce the laboratory strength to get the field strength.
Thanks
I want to model a room and pillar mine, so my task is to ensure that the pillars are safe and stable. I will use Abaqus software,
In ABAQUS, i need to input the material properties, i have the material properties for laboratory samples (2 in high, 1 in diameter). As you know, the strength of the laboratory rock samples is much higher than the in-situ strength.
the question is: what kind of input of parameters should i input in abaqus, is it the properties from the lab. or the laboratory from the field. i will reduce the laboratory strength to get the field strength.
Thanks





RE: Laboratory strength or Field strength?
RE: Laboratory strength or Field strength?
An example in one of my recent projects, a fractured sandstone with lab uniaxal compressive strenght of 35 Mpa turns out to have a rockmass, field strenght of just 1.5 Mpa. This pretty much agrees with oldestguys's observations, the smaller the lab sample is, the less likely it is that it encompasses joints or 'weak spots'.
Of course a specific site survey is necessary besides lab tests. Or extrapolation of rockmass quality by drill cores.
RE: Laboratory strength or Field strength?
Well, that means we should input the rockmass properties get more reliable results. not the laboratory test results for the intact cores.
RE: Laboratory strength or Field strength?
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RE: Laboratory strength or Field strength?
Mining will not be economic if we use a big safety factor. and as you know there is uncertainty about the properties of the rock mass since we depend only on small rock samples.
So i need to scale the laboratory values to get the field values.
Again, these [field values] not the [intact values] should be the input in the numerical modeling, right?
RE: Laboratory strength or Field strength?
It still might be of help to know the kind of mine for getting comments from this thread.
RE: Laboratory strength or Field strength?
Why are you still asking about lab strength? Your caves and pillars are not in the lab, are they?
TTFN

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RE: Laboratory strength or Field strength?
I agree with Oldestguy, that the back analysis might be one of the best approaches to get representative rockmass properties.
RE: Laboratory strength or Field strength?
There are other methods to determine if the pillars will be "safe and stable". You can calculate a pillar factor of safety, but you need the following information: load carrying capacity of the pillar (this is the strength of the pillar and is calculated using various methods, not necessarily Roclab), the tributary area that the pillar supports, an estimate of the geometry of the pressure arch and the peripheral load transfer distance (to calculate the load that the pillar will have to carry as mining sheds the load onto peripheral pillars). You may also want to look at abutment stresses or use a high factor of safety to account for an abutment from mining on other levels for example.
RE: Laboratory strength or Field strength?
Any i guess Abaqus would be my best bet. the development load can be calculated from the tributary area, and the abutment load can be estimated depending on the abutment angle, however in order to calculate the Safety factor you need to determine the strength, so the rockmass properties are necessary.
ebenzone are you familiar with Abaqus?
Thanks
RE: Laboratory strength or Field strength?
I think you're better off staying away from finite element analysis for your project. As you mentioned, there are other input parameters you need to come up with to run Abaqus and uncertainty in these parameters can lead to nebulous results. I think it's best to simplify the analysis and use input parameters that you can determine with greater confidence.
Best of luck.