Earthquake and rainfall-induced landslide hazard assessment of Kutupalong Rohingya camp using meteorological and geological information

Abstract

Kutupalong Rohingya camp is one of the largest humanitarian shelters for conflict-fled people. The camp area is susceptible to landslide hazards because of being situated in dynamic tectonic settings and meteorological conditions. Hence, the study aims to assess the earthquake and rainfall-induced landslide hazards in the camp for the worst-case scenario. The landslide triggering parameters (topographic, soil physical property, and contributing factors) are designed in the study to identify the hazard-prone areas through the factor of safety computation. The topographic parameters are prepared by combining field investigation and remote sensing-based information. The soil physical properties are modeled in two ways to account for their uncertainties: normal probabilistic distribution and interpolation-based spatial distribution. The contributing factors (i.e., earthquake and rainfall) have been assessed using the probabilistic approach. The Peak Ground Acceleration (PGA) exceedance of 50, 75, 100, 200, and 475 years return periods are applied in the factor of safety calculation for earthquake-induced landslides. The rainfall intensities of 50 and 75 years return periods are combined with the PGA exceedance of the respective years to assess the earthquake and rainfall-triggered landslide-prone areas. The factor of safety has been measured following two methods: Monte-Carlo simulation and direct estimation method. Multiple scenarios (rainfall with the duration of 1, 2, and 3 days) are also considered to estimate the landslide-prone areas in these models. The study findings are finally validated against field investigation-based landslide inventory with more than 85% accuracy at a 90% confidence interval.

Appendix 1

The weight of the block QRST:

$$w = \gamma bH$$

(8)

where, $\gamma = {\text{unit weight of soil}}$, H = Thickness of soil.

Height of water table above failure surface = $h$

$${\text{Weight}}\,{\text{of}}\,{\text{water}} = w_{w} = \gamma_{w} bh$$

(9)

[$\gamma_{w}$ is the density of water].

Normal component of water weight, $Pw = \gamma_{w} bh{\text{cos}} \alpha$

$${\text{Pore}}\,{\text{pressure}}\,{\text{on}}\,{\text{QR}},\,u = \frac{Pw}{{QR}} = \frac{{\gamma_{w} bh{\text{cos}} \alpha }}{{\frac{b}{{{\text{cos}} \alpha }}}} = \gamma_{w} h{\text{cos }}^{2} \alpha$$

(10)

Earthquake loading is expressed as $kw$, where seismic coefficient, k is multiplied by soil weight $w$ which is working on the horizontal direction.

Forces perpendicular to slip plane:

$$\begin{aligned} N & = \,W {\text{cos}} \alpha {-} kW {\text{sin}} \alpha \\ N & = \,\gamma bH{\text{cos}} \alpha - k\gamma bH {\text{sin}} \alpha \quad \left[ {{\text{From}} \left( 8 \right)} \right] \\ \end{aligned}$$

Forces parallel to the slip plane:

$$\begin{aligned} T & = \,W {\text{sin}} \alpha + kW {\text{cos}} \alpha \\ T & = \,\gamma bH {\text{sin}} \alpha + k\gamma bH {\text{cos}} \alpha \quad \left[ {{\text{From}} \left( 8 \right)} \right] \\ \end{aligned}$$

$${\text{Shear}}\,{\text{stress}},\,\tau = \frac{T}{QR} = \frac{{\gamma bH {\text{sin}} + k\gamma bH{\text{cos}}\alpha }}{{\frac{b}{{{\text{cos}} \alpha }}}} = \gamma H {\text{sin}}\alpha {\text{cos}}\alpha + k\gamma H{\text{cos}}^{2} \alpha$$

(11)

$${\text{Normal}}\,{\text{stress}},{\upsigma }_{n} = \frac{N}{QR} = \frac{{ \gamma bH{\text{cos}} \alpha - k\gamma bH{\text{sin}}\alpha { }}}{{\frac{b}{{{\text{cos}}\alpha }}}} = \gamma H{\text{cos}}^{2} \alpha - k\gamma H{\text{sin}}\alpha {\text{cos}}\alpha$$

(12)

$$\begin{aligned} {\text{Factor}}\,{\text{of}}\,{\text{Safety}},FS_{ps} & = \frac{{{\text{Resisting}}\,{\text{Force}}}}{{{\text{Driving}}\,{\text{force}}}} = \frac{{c + \left( {{\upsigma }_{n} - u} \right){\text{tan}}\emptyset }}{\tau } = \frac{{c + \left( {\gamma H{\text{cos}}^{2} \alpha - k\gamma H{\text{sin}}\alpha {\text{cos}}\alpha - \gamma_{w} h{\text{cos}} ^{2} \alpha } \right){\text{tan}}\emptyset }}{{\gamma H{\text{sin}}\alpha {\text{cos}}\alpha + k\gamma H{\text{cos}}^{2} \alpha }} \\ & = \frac{{c + \left( {\gamma H - \gamma_{w} h} \right){\text{cos }}^{2} \alpha {\text{tan}}\emptyset - k\gamma H{\text{sin}}\alpha {\text{cos}}\alpha {\text{tan}}\emptyset }}{{\gamma H{\text{sin}}\alpha {\text{cos}}\alpha + k\gamma H{\text{cos}}^{2} \alpha }} \\ \end{aligned}$$