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A Probabilistic Model to Determine Main Caving Span by Evaluating Cavability of Immediate Roof Strata in Longwall Mining


Caving process is a complex dynamic phenomenon influences safety and productivity of coal longwall mining. It improves safety due to reduction of load on support, face convergence and abutment stresses. Proper caving with respect to the quality and time of occurrence ensures continuity of operation and subsequently, the productivity of coal extraction. Therefore, a reliable prediction of strata behaviour and its caving potential are imperative in design of longwall projects. This paper presents a hybrid probabilistically qualitative–quantitative model to evaluate cavability of immediate roof and to estimate main caving span in longwall mining by combining empirical model and numerical solution. For this purpose, numerical simulation was incorporated to Roof Strata Cavability index (RSCi) as summation of ratings for nine significant parameters. Distinct element code was used to simulate numerically main caving span corresponding to various RSCi classes probabilistically. The newly proposed model was verified against actual field data collected from different longwall panels around the world. The results of proposed model agreed well with those of collected data.

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Fig. 9


C :


E :

Young’s modulus

E(X) :

Mean value of data distribution

F(x) :

Cumulative distribution function (CDF)

f(x) :

Probability density function (PDF)

L :

Rock Quality Index (RQI)

K :

Number of subsets

K 1 :

In situ strength coefficient

K 2 :

Creep coefficient

K 3 :

In situ water content coefficient

σ ci :

Intact compressive strength

K n :

Normal stiffness

K s :

Shear stiffness

n :

A constant value depending upon RQD

S m :

Main caving span

t :

Thickness of roof layer

t b :

Bed thickness

t m :

Thickness of main roof

γ :

Average unit weight of the bed

γ e :

Effective unit weight of rock

ν :

Poisson’s ratio

ρ :


σ :

Standard deviation

σ c :

Intact compressive strength

σ h :

Average in situ horizontal stress

σ t :

Tensile strength

φ :

Angle of internal friction

ψ :

Angle of dilatancy

RSCi :

Roof Strata Cavability index


Support vector machine


Cuckoo optimisation algorithm

I :

Number of roof layer

P :

Peak status

R :

Residual status


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Correspondence to Sadjad Mohammadi.

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Mohammadi, S., Ataei, M., Kakaie, R. et al. A Probabilistic Model to Determine Main Caving Span by Evaluating Cavability of Immediate Roof Strata in Longwall Mining. Geotech Geol Eng 39, 2221–2237 (2021).

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  • Longwall mining
  • Immediate roof
  • Cavability
  • Main caving span
  • Empirical model
  • Numerical simulation