Geological and soil engineering properties of shallow landslides occurring in the Kutupalong Rohingya Camp in Cox’s Bazar, Bangladesh

The Forcibly Displaced Myanmar Nationals (FDMN), historically known as ‘Rohingya’ who fled the 2017 ethnic atrocities and genocide in the Northern Rakhine State of Myanmar, took shelter in Cox’s Bazar District of Bangladesh. The camp network, known as Kutupalong Rohingya Camp (KRC), is situated in the tectonically active tertiary hilly terrain. The KRC has been experiencing hydrometeorological hazards, where landslides are frequent. This study investigated the slopes’ geological condition, engineering properties and human interventions, which influence the landslides. The exposed slopes were relatively high (> 10 m) and steep ranging from 40° to 60° that have numerous polygonal tension cracks and fissures. From the geological and geotechnical aspects, there are three successive units of slope materials: (1) residual soils of sandy silt with clay, (2) highly weathered silty sandstones and (3) shale/clay with silt and fine sand intercalations at the bottom of the slopes. Field observations revealed that most slope failures occurred in the residual soil and weathered silty sandstone units. The residual soils have a bulk density of 1.49–1.97 g/cm3, a liquid limit of 25–48%, a plasticity index of 5–16% and an undrained shear strength of 23–46 kPa. The silty sandstones have a bulk density of 1.44–1.94 g/cm3, an internal friction angle of 34°–40° and a cohesion of 0.5–13 kPa. The mineralogical composition determined by the X-ray diffraction shows low clay mineral content, which does not affect landslides. However, the slope geometry, low shear strength with strain softening properties and torrential rainfall accompanied by anthropogenic factors cause numerous landslides every year. This study will help take proper mitigation and preparedness measures for slope protection in the KRC area and surroundings.

An assessment of the urban water footprint and blue water scarcity: A case study for Van (Turkey)

Today, most of the world’s population faces water scarcity, while global warming, urbanization, industrialization and population increases continue to increase the severity of the pressure on water resources. Management of water resources plays a key role in the sustainability of agricultural production. The water footprint (WF) is different in comparison to other water statistics because it takes direct and indirect water consumption into account, and helps in the management of water resources. Within this context, the WF of Van province, which is Turkey’s most easterly located arid region, was calculated from 2004 to 2019. The study area covers lake Van, which is Turkey's largest lake, and the Van basin with an area of 23.334 km2 and a population of 1.136.757 (2019). In the calculations, crop (WFcrop), livestock (WFlivestock), and domestic and industrial water footprints (WFdomestic+industrial) were evaluated separately, and blue and green water footprints (WFblue and WFgreen) were analyzed in detail. According to the results, the average WF of Van province was found to be 8.73 billion m3 year-1. Throughout the province, 87.6% of the WF is composed of WFcrop, 4.9% is WFlivestock and 7.5% is WFdomestic+industrial. Of the WFcrop, 62.5% depends on WFblue, i.e., freshwater. Most of the WFlivestock consisted of dairy cattle (49%) and sheep (38%). The average WFdomestic+industrial for 2004 to 2019 was 0.64 billion m3 year-1. The average per capita water footprint of Van province was found to be 889.9 m3 year-1 capita-1. In addition, the province is classified as severe water scarcity (257%). This study is one of the first province-based calculations of WF in Turkey and is the first study to bring a different aspect to published literature by including residual soil moisture from the winter months. As a result of this study, the WFblue of the WFcrop is above the worldwide average and should be reduced by changing the crop pattern or synchronizing the planting and harvest dates of the crops to a period that benefits from precipitation. In addition, this study is expected to contribute to new studies for calculating the provincial scale WF and will have positive effects on agricultural planning, water allocation and the sustainability of water resources.

Numerical Analysis of Slope Stability Due to Excavation of Diversion Tunnel at Pamukkulu Dam Site, Indonesia

Located in the Takalar Regency of South Sulawesi Province, the Pamukkulu Dam is planned to use a tunnel type as its diversion structure. One of the critical parts in the tunnel construction is the stability of portal slopes. This research aimed to estimate the effect of tunnel excavation on the stability of the portal inlet and outlet slopes under static and earthquake loads by using the finite element method. The slope stability analyses were carried out under conditions of prior to and after tunnel excavation. The input parameters used were laboratory test results in the forms of index properties and mechanical properties taken from rock core drilling samples, completed with the rock mass quality parameters based on the Geological Strength Index (GSI) classification. The Mohr-Coulomb failure criterion was used to model strength of the soil, while the Generalized Hoek-Brown failure criterion was used to model strength of the rocks. The results of rock cores analysis using the GSI method showed that the inlet tunnel slope consisted of four types of materials, namely residual soil, fair quality of basalt lava, good quality of basalt lava, and very good quality of basalt lava. Meanwhile, the outlet portal slope consisted of three types of materials, namely residual soil, good quality basalt lava, and very good quality basalt lava. The calculated horizontal seismic coefficient for the pseudo-static slope stability analysis was 0.0375. The analysis results of slope stability in the Y1 inlet section had a critical Strength Reduction Factor (SRF) value of 2.35 in a condition prior to the tunnel excavation and a critical SRF value of 2.34 after the tunnel excavation. The Y2 outlet section had a critical SRF value of 13.27 in a condition before tunnel excavation and a critical SRF value of 5.55 after the tunnel excavation. The earthquake load addition at the Y1 inlet section showed a critical SRF value of 2.05, both before and after the tunnel excavation. The Y2 outlet section showed a critical SRF value of 11.49 before the tunnel excavation and a critical SRF value of 5.54 after the tunnel excavation. The numerical analysis results showed that earthquake load reduced critical SRF values of the slopes. At the Y1 inlet section, the tunnel excavation did not have a significant effect on slope stability. It was demonstrated by an extremely small decrease in a critical SRF value of 0.43% for a condition without an earthquake load and an unchanged critical SRF in a condition with an earthquake load. At the Y2 outlet section, the tunnel excavation had a more significant effect on the slope stability. It was exhibited by the decrease in the critical SRF value of 58.18% in a condition without an earthquake load and a decrease in the critical SRF value of 51.78% in a condition with an addition of an earthquake load. However, the analysis of slope stability for both sections showed that all design slopes were above the required allowable safety factor value.

Small strain stiffness for granite residual soil: effect of stress ratio

Most previous studies have focused on the small strain stiffness of sedimentary soil while little attention has been given to residual soils with different properties. Most studies also neglected the effects of the deviator stress, which is extensively involved in civil engineering. This note considers the effects of the deviator stress on the small-strain stiffness of natural granite residual soil (GRS) as established from resonant column tests performed under various stress ratios. Although increasing the stress ratio results in a greater maximum shear modulus for both natural and remolded residual soils, remolded soil is more sensitive to changes in the stress ratio, which highlights the effects of soil cementation. The data herein offers new insights to understand the stiffness of residual soil and other weathered geomaterials.

A two layer soil moisture model for estimating crop evapotranspiration and runoff

In the present study, a two layer model has been proposed to estimate evapotranspiration, soil moisture storage and runoff. For this purpose soil profile has been assumed to be composed of two layers : the top layer having a fixed field capacity of 100 mm and the underlying layer having field capacity depending on the soil texture. Normal values of rainfall and potential evapotranspiration have been used in the study. The model, applied to kharif and rabi seasons furnishes crop evapotranspiration period when soil in two layers reach wilting point and surface runoff and its duration. The model developed has been applied to 411ocations representing most of the soil types found in India. The analysis revealed that lowest ET is seen over Himalayan foothills and northeast India in kharif and rabi seasons. Enough residual soil moisture is available to the crops at the end of kharif season over NE India; most of it being in the top layer. Eastern India record largest runoff of 800-1000 mm. Arid to semi-arid region in NW India does not seem to experience much runoff.

Cropping potential or the red-laterite-gravelly belt of West Bengal based on moisture availability index and soil characteristics

Crop potential has been brought out over the red-laterite-gravelly belt of West Bengal using Moisture Availability Index (MAI) and broad soil information. MAI indicates that a crop of 15. 18-20 and 22-24 weeks. duration at 80%, 50% and 30% probability levels respectively maybe raised from this belt. In most of the stations of the belt, rice could be raised in eight out of every ten years without encountering much waterstress period. At lower probability levels. after rice, pulses like gram. tur and lentil and oilseeds like rapeseed and mustard may be raised based on residual soil moisture. In low rainfall years sorghum. groundnut, maize could be introduced in place of rice in the kharif season. Emphasis should also be given on agro-forestry and horticultural crops for increasing and stabilizing agricultural production.

Shear Strength Deterioration of Compacted Residual Soils under a Wind Turbine due to Drying-Wetting Cycles and Vibrations

The soil beneath a wind turbine withstands not only environmental impacts but also continuous vibrations transmitted from the superstructure. This paper presents an experimental study of the deterioration characteristics of shear strengths of residual soils affected by drying-wetting cycles and continuous vibrations. A series of triaxial tests were performed on compacted residual soil specimens after various drying-wetting cycles and vibrations. The influences of drying-wetting cycles and vibrations on the shear strengths of residual soils with different compaction degrees were analyzed. The results demonstrate that the shear strength and cohesion of compacted residual soils decreased as the number of drying-wetting cycles increased, and they tended to be stable after three drying-wetting cycles. The angle of internal friction decreased linearly with the reduction of compaction degree but was generally not affected by drying-wetting cycles. The shear strength of compacted residual soils also decreased because of continuous vibrations. After 10000 vibrations, the strength was stabilized gradually. Both the cohesion and angle of internal friction showed dynamic attenuation phenomenon. Finally, a modified Mohr–Coulomb strength equation considering the effects of drying-wetting cycles and vibrations was established. This equation could be used to predict the shear strength of compacted residual soils and further estimate the embedded depth of wind turbine foundations.