Effect of Area Development on the Stability of Cut Slopes

AbstractMany natural slopes were subjected to change in geometry in order to make room for construction of infrastructures. This paper presents stability analysis of a natural slope subjected to cutting to make room for the development of factories in an industrial site. The analysis was performed for the most critical slope section and analysis was made in comparison to the case presented in literature. Data required for slope stability analysis were retrieved from relevant project report. The result shows that the stability of the slope decreases due to slope excavation and stabilization should be done in order to limit further reduction of shear strength due to yielding of soil mass. Analysis using circular failure surface such as Simplified Bishop is simple and is usually suitable for analysis of existing slope where there is no indication of incipient failure. However, pre-defined failure surface in Morgensten Price method is more useful if failure surface could be predicted based on slope assessment or when rectification work has been applied

Transient seepage and slope stability analysis for rainfall induced landslide: a case study

A transient seepage and slope stability analyses were carried out for a case of rainfall-induced landslide in Air Laya Indonesia . The landslide occurred in December 2002 on a dumping area of an open coal mining site. This study examined the mechanism causing the slope failure based on transient analysis between April 21, 2001 and December 1, 2002. The slope profile was simulated using a seepage analyzing tool, VADOSE/W and the soil properties were determined based on field and laboratory data. The saturation profile resulted from seepage analysis was exported to SLOPE/W for the slope stability evaluation. The results show that the main factor contributing to the landslide is the reduction of shear strength due to increase in soil moisture content impelled by the formation of tension cracks on the ground surface of the slope

Performance of ground improvement by precompression and vertical drain

Ground improvement is required when construction has to take place on geotechnically unsuitable material such as soft clay. This paper discusses the performance of ground improvement by pre-compression and vertical drain implemented for the construction of permanent campus of Universiti Malaysia Pahang (UMP) in Kuala Pahang, Pekan. The comparison was made in terms of engineering properties of the soil such as shear strength and compressibility characteristics before and after improvement and the achievement of criteria in terms of time and post construction settlement. The soil investigation showed that subsoil profile consisted of four layers whereby the thickness of compressible layer varies from 6 to 14 m. Settlement monitoring showed that the required pre-construction settlement was achieved in less than six months after the completion of ground improvement by pre-compression. Installation of the vertical in swampy area further reduced the consolidation time to about one month. The undrained shear strength (Su) of the soft compressible layer increased from 6 - 30 kPa to about 67 kPa while the compression index (Cc) decreased from about 0.2 - 0.6 to about 0.33. The coefficient of consolidation (Cv) of the soft soil layer decreases from 6m2/yr - 21m2/yr to about 2.11m2/yr - 3.64m2/yr due to compaction and consolidation process

Effectiveness of unsaturated drainage layer in water diversion under different rainfall conditions

The concept of capillary barrier principle is widely applied as lasting solution to rainfall infiltration in unsaturated soil slope. However, the performance of a capillary barrier system normally reduced as rainfall duration gets longer, due excessive rainfall infiltration. Therefore this paper uses numerical modeling approach to highlights the effectiveness of a capillary barrier system with unsaturated drainage layer at interface to improve its performance under three different rainfall conditions. The capillary barrier system was constructed using residual soil obtained within the compound of Universiti Teknologi Malaysia, Johor Bahru campus; with sand and gravel employed as unsaturated drainage layer. The system was subjected to rainfall intensities of 1 hour, 1 day and 7 days obtained from Intensity-Duration-Frequency (IDF) curve of Johor Bahru, Malaysia. The results show that high intensity short duration rainfall has less effect on eliminating soil matric suction completely, however the near surface matric suction was eliminated due to prolonged rainfall infiltration and a capillary barrier system constructed with gravel as unsaturated drainage layer is more effective in diverting the infiltrated water before breakthrough occurs under all the rainfall conditions

THE EFFECT OF SOIL STABILIZATION AND REINFORCEMENT ON THE STABILITY OF EMBANKMENT ON SOFT SOIL

The construction of toll roads in South Sumatra faces two problems. First, most of the road sections are built on soft soil deposits, so the soil must be improved to speed up consolidation process and to improve bearing capacity. Second, the embankment required to reach the design elevation of the toll road is quite high so that reinforcement is needed to improve slope stability. This paper contains the results of a study on the effect of soil improvement using PVD and vacuum pressure, installation of geotextile layers and pile at the toe of embankment slopes, on the stability of the embankment.  The analysis were carried out using data obtained from the construction of the Kayu Agung – Palembang toll road Section 1A, including geometry data, soil stratification, and configuration of PVD installation and soil reinforcement. Slope stability analysis was carried out using the Morgenstern & Price method which is integrated in SLOPE/W program. The results of the analysis show that the safe embankment height for the original soil condition is 3.5 m while the required height of embankment was 6 m. Analysis made for the 6 m high embankment using soil properties after ground improvement with PVD and vacuum pressure shows the FoS is still below 1.5. The presence of geotextile layers and pile improved the performance of the embankment and increased the FoS to 2.410. The slope is still in a safe condition with FoS of 1.762 after the construction of toll road and traffic load which induces a combined load of 35 kPa

EFFECT OF CHANGING IN FREE WATER LEVEL ON THE STABILITY OF RIVER EMBANKMENT

The construction of Levee or river embankment is one method adopted for flood control in Palembang. The stability of the embankment is affected by water seepage inside the embankment due to several factors including rainfall as well as the repeated rise and fall of water surface in the sea due to gravity of moon and sun. Palembang is located 106 km from the east coast of Sumatra, thus the free water surface in Musi river and its tributaries is affected by the sea level. The stability of the levee is affected by the repeated change in the water level which induces changing seepage direction. This paper discusses the stability of levees constructed along Sungai Lacak, one of Musi river tributaries. In this case the stability of the existing levees was evaluated for different conditions of free water level i.e. normal, low tide and high tide. Analysis was also conducted for the case when the levee was constructed following the guidance in Standard Nasional Indonesia (SNI 1724-2015) and Guidelines of Public Work Department (2017). Improvement on the stability was obtained if the embankment was to be rebuilt according to the specification given in the standard. The presence of riprap protects the embankment from the effect of changing seepage direction due to the rise and fall of water level, thus increased the safety factor of the ideal levee during high tide from 1.270 to 2.325

Block model approach for analysis of rock bench stability in open pit mines

Wedge failure analysis conventionally adopted for the design of global angle of open pit mines is not always applicable when the area consists of jointed rock benches. In this analysis, the unstable wedge is assumed intact while, in fact, the rock bench consists of an assemblage of blocks generated by the intersections of well-defined discontinuities. Block model approach adopted in Resoblok provides an alternative solution for the design and stability analysis of a rock bench. The model analyzes the stability of individual block by limit equilibrium method while the discontinuity aspect is considered statistically based on geometrical modelling of the individual fractured rock mass. This paper presents the stability analysis of five rock benches from two mining sites. The analysis shows that Resoblok model provides a good indication of the distribution, the number and the volume of unstable blocks; therefore, it is useful for the design of open pit mines. The result of this study is in good agreement with field observation

Long term compression behavior of fibrous peat

This paper discusses a long term compression behavior of fibrous peat, analyzed based on data obtained from consolidation test performed in Rowe cell with excess pore water pressure measurement. The preliminary test results show that the peat used in this study is classified as fibrous peat with low to medium degree of decomposition and of very high organic and fiber contents which are typical of peat found in Peninsular Malaysia. The results of consolidation test show that the fibrous peat has a high compressibility with primary compression index of 3.15 and significant secondary compression stage which is not constant with the logarithmic of time. The secondary compression started as early as 65% degree of primary consolidation. The study showed that the consolidation test with pore water pressure measurement using Rowe cell is advantageous because it enables the observation of the large deformation and better assessment of the long term compression behavior of fibrous peat. The separation of primary and secondary consolidation is very important for the evaluation of long term compressibility behavior of fibrous peat

The study on the development of saturation profile in soil slope

This study was carried out to investigate the mechanisms involved in the development of saturation profiles in soil. A series of laboratory tests were conducted to monitor the saturation profiles in four types of soil under various rainfall conditions. The understanding in saturation profile is essential to predict the shear strength of soil, particularly for slope stability problem. The study showed that the saturation profile in soil could be effectively monitored through a fabricated soil column model. The effect of rainfall pattern on the saturation profile of coarse-grained soil is relatively insignificant. Conversely, the saturation profile in fine-grained soil could be significantly altered when the soil is subjected to a prolonged rainfall. It is believed that the findings from the present study could lead to better understanding of saturation profile in soil, and subsequently contributing efforts in mitigating rainfall-induced slope failure

PERISI: a computer program for preliminary evaluation of rainfall-induced slope instability

This paper introduces a computer program PERISI stands for Preliminary Evaluation of Rainfall-Induced Slope Instability. The program was developed by utilizing the concept of extreme rainfall and unique relationships between rainfall characteristics, hydraulic conductivity, suction, and water content of unsaturated soil to evaluate the minimum suction distribution in soil. The outcome of the program is the factor of safety of soil slope in the critical condition as compared to normal condition