<p>Accurately assessing the stability of an underground excavation poses a crucial problem to rock engineers due to various sources of uncertainties inherent in the rock mass mechanical parameters. Ignoring uncertainties in rock mass properties can lead to over-conservatism and based on the distributive character of the rock property, may sometimes produce misleading results. There is therefore the need for probabilistic approaches that systematically account for uncertainties in underground stability assessment. This study analyzed the effect of uncertainties in the peak and post-peak rock mass mechanical parameters on the displacement and the plastic zone depth for a section of the Pahang-Selangor Raw Water Tunnel (PSRWT), Malaysia. The uncertainties in the rock mass parameters were quantified using Monte Carlo Simulation, and the best-fit probability distribution function was verified by the Kolmogorov–Smirnov (K–S) test at a 95% confidence level. The point estimate method (PEM) incorporated in RS2 was used to model two case scenarios. In case 1, uncertainties in both peak and post-peak rock mass strength parameters were considered whereas in case 2, only uncertainties in the peak parameters were considered. A comparison of the two cases with the measured displacements revealed that the predicted displacement and probability of failure were significantly underestimated when the uncertainties in the post-peak rock mass parameters were ignored and rock mass is assumed as elastic-perfectly plastic. A parametric study of the various input rock parameters revealed that the most sensitive parameter to the total displacement and yield zone depth is the UCS, followed by the residual Hoek–Brown frictional constant (<InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40808_2025_2448_Article_IEq1.gif" Format="GIF" Height="18" Rendition="HTML" Resolution="72" Type="Linedraw" Width="24" /> </InlineMediaObject> <EquationSource Format="TEX">${m}_{b}^{r}$</EquationSource> <EquationSource Format="MATHML"><math> <msubsup> <mi>m</mi> <mrow> <mi>b</mi> </mrow> <mi>r</mi> </msubsup> </math></EquationSource> </InlineEquation>), and peak Hoek–Brown frictional constant (<InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40808_2025_2448_Article_IEq2.gif" Format="GIF" Height="20" Rendition="HTML" Resolution="72" Type="Linedraw" Width="24" /> </InlineMediaObject> <EquationSource Format="TEX">${m}_{b}^{p}$</EquationSource> <EquationSource Format="MATHML"><math> <msubsup> <mi>m</mi> <mrow> <mi>b</mi> </mrow> <mi>p</mi> </msubsup> </math></EquationSource> </InlineEquation>).</p>

Probabilistic analysis of underground rock excavation stability using point estimate method

期刊论文
发表日期：

2025年5月31日

查看全文

Sylvanus Sebbeh-Newton,
Jamel Seidu,
Rodney Ewusi-Wilson,
Hareyani Zabidi

摘要

Accurately assessing the stability of an underground excavation poses a crucial problem to rock engineers due to various sources of uncertainties inherent in the rock mass mechanical parameters. Ignoring uncertainties in rock mass properties can lead to over-conservatism and based on the distributive character of the rock property, may sometimes produce misleading results. There is therefore the need for probabilistic approaches that systematically account for uncertainties in underground stability assessment. This study analyzed the effect of uncertainties in the peak and post-peak rock mass mechanical parameters on the displacement and the plastic zone depth for a section of the Pahang-Selangor Raw Water Tunnel (PSRWT), Malaysia. The uncertainties in the rock mass parameters were quantified using Monte Carlo Simulation, and the best-fit probability distribution function was verified by the Kolmogorov–Smirnov (K–S) test at a 95% confidence level. The point estimate method (PEM) incorporated in RS2 was used to model two case scenarios. In case 1, uncertainties in both peak and post-peak rock mass strength parameters were considered whereas in case 2, only uncertainties in the peak parameters were considered. A comparison of the two cases with the measured displacements revealed that the predicted displacement and probability of failure were significantly underestimated when the uncertainties in the post-peak rock mass parameters were ignored and rock mass is assumed as elastic-perfectly plastic. A parametric study of the various input rock parameters revealed that the most sensitive parameter to the total displacement and yield zone depth is the UCS, followed by the residual Hoek–Brown frictional constant ( ${m}_{b}^{r}$ $m_{b}^{r}$ ), and peak Hoek–Brown frictional constant ( ${m}_{b}^{p}$ $m_{b}^{p}$ ).