This paper presents the performance of PVD and vacuum consolidation as ground improvement method at the construction of Kayu Agung – Palembang Toll Road. The analysis was based on observation data ...collected between STA 00+000 and STA 09+000. The PVD was installed to a depth where the conus resistance of 80 kPa was achieved. Thus, the length of PVD varies from 5 to 13 m while the actual depth of clay deposit could reach 20 m. As many as 42 settlement plate data were collected and analyzed using Asaoka method to obtain the predicted final settlement, the coefficient of consolidation and the time to reach 90% degree of consolidation. The results were compared with the duration of vacuum consolidation application and the recorded settlement when the vacuum pressure was stopped i.e., when settlement plate recorded no differential settlement in three readings. The duration of vacuum consolidation application generally longer than the t90 predicted by the method and the actual settlement was larger than the predicted final settlement. This study concluded that the variation of the t90 and the magnitude of settlement at t90 have close relationship with the length of PVD and the condition of the soil layer.
Existing design methods of a reinforced-soil retaining wall were established for walls with cohesionless soil backfill. However, local soil has been used widely in the construction of such a wall for ...economic reasons. Laboratory and numerical studies have pointed out the merit of using cohesive backfill in association with geosynthetic reinforcement. Since the compacted soil was in an unsaturated condition during the construction of the reinforced wall, the apparent cohesion derived from both soil mineralogy and suction could contribute to the stability of the wall. This paper considers methods to include the suction contribution to the existing design guidelines based on slope stability analysis, i.e. simplified method and simplified stiffness method. The analyses were carried out on a case study of geosynthetics reinforced soil retaining wall. Results show that the contribution of suction as part of cohesion existing in the cohesive backfill could be considered for the stability analysis of reinforced soil retaining walls using the available design guidelines.
This paper presents results of saturated and unsaturated stability analysis of typical residual slopes subjected to rainfall infiltration corresponds to 50 years rainfall return period. The slope ...angles considered were 45° and 70°. The saturated stability analyses were carried out for original and critical ground water level commonly considered by practicing engineer. The analyses were conducted using limit equilibrium method. Unsaturated stability analyses used combination of coupled stress–pore-water pressure analysis to evaluate the effect of rainfall infiltration on the deformation and transient pore-water pressure on slope stability. Slope stability analyses were performed at some times during and after rainfall infiltration. Results show that the critical condition for slope made by sandy material was at the end of rainfall while for clayey material was at some specified times after the rainfall ceased. Unsaturated stability analysis on sandy soil gives higher factor of safety because the soil never reached saturation. Transient analysis using unsaturated soil concept could predict more critical condition of delayed failure of slopes made up of clayey soil.
Demolition of old buildings to create space for new development resulted in the near surface soil (topsoil) to be mixed with particles derived mostly from concrete wastes. This condition could affect ...the infiltration capacity and surface runoff, therefore, storm-water management of the area. This paper presents results of study on the effect of concrete waste particles on the hydraulic properties and infiltration capacity of the topsoil. Laboratory tests were performed to compare the hydraulic properties of the topsoil and the mixture of topsoil and concrete particles. Laboratory infiltration column test was performed on the mixture to evaluate its infiltration capacity. Results from the laboratory tests indicated that the presence of particles from concrete waste decreased the water-holding capacity and permeability, thereby the infiltration capacity of the ground surface. The results were supported by numerical analysis performed using the same material and boundary conditions as the column test. Parametric study was performed on both the topsoil and the mixture to extend the results of infiltration test to different materials under different ranges of rainfall intensity. The parametric study showed that the presence of concrete particles increased the run-off and the effect increased as the rainfall intensity increased. Therefore, the increase in runoff coefficient should be considered for the storm-water management when the near surface soil is mixed with concrete waste.
The western part of South Sumatra Province is situated near Bukit Barisan. Therefore, the topography is characterized by hills and mountains. This condition makes the area vulnerable to ground ...movement. Information on the risk level and type of ground movement is very important for the region's development. This paper presents the mapping of risk level and type of ground movement along the national road system in South Sumatra Province. The map was developed based on slope condition data collected and tabulated in the Slope Management System developed by the Ministry of Public Works based on several parameters. These parameters were processed and analyzed using ArcGIS software. The risk level is classified as low, medium, high, and very high. The type of ground movement is categorized as debris flow, rock fall, slope failure, rock mass failure, embankment failure, rotation failure, and translation failure. The study uses data from 2018 and 2021. Results show that most ground movement on road segments 36, 37, 38, 18, 19, and 21 is slope failure. The map suggests an increase in the number and level of risk of slope failures from 28 in 2018 to 45 in 2021. The map could be used as preliminary information but not as a replacement for slope surveys and investigations.
Seepage and slope stability are important problems analyzed in geotechnical engineering. Conventionally, the analysis is performed in conditions where the soil is intact. However, near-surface soil ...is subjected to various conditions that lead to heterogeneity, for example, the presence of cracks in clay, relics in weathered rock, and plant roots. The presence of cracks and other forms of heterogeneity on the near-surface layer increases the rainfall infiltration into the slope and changes the pore water pressure distribution accordingly. Water infiltration increases the pore water pressure, raises groundwater level, and decreases the matrix suction of unsaturated soils - which is a critical factor for the stability of slopes. This study aims to evaluate the effect of varying permeability of near-surface soil on the rainwater infiltration to slope and, subsequently, the safety factor. In this case, the near-surface soil is modeled as a layer with higher permeability. Numerical analysis performed in this study using SEEP/W and SLOPE/W indicated that considering this condition results in a higher safety factor of the slope because the higher permeability resulting from heterogeneity helps dissipate pore water pressure, which is critical in maintaining the slope stability during heavy rainfall.
The formation of residual soil of Grade V and Grade VI due to tropical weathering process introduces small hydraulic heterogeneities in the soil mantle which greatly alter the suction distribution ...during rainfall infiltration, and hence the stability of the residual soil slopes. This paper presents field evidences of suction distributions in a heterogeneous residual soil slope. Several modeling approaches were attempted to simulate the observation by considering the presence of thin layer of Grade VI, the variation in the hydraulic conductivity of Grade V layer as well as the effect of evaporation. The soil hydraulic heterogeneity in Grade V layer was modeled by adopting continuum method, in which the residual soil was subdivided into three zones of average hydraulic conductivities. The analysis results show that the presence of thin layer of Grade VI residual soil and the relict discontinuities in Grade V soil must be considered in the analysis as these features introduced permeability disparity and thus a natural capillary barrier effect that limited the downward movement of infiltrated rainwater even during the exceptionally wet condition. The results also show that the inclusion of evaporation effect provided a better prediction to the suction distributions during wet condition than dry condition.
► Modeling of heterogeneous residual soil slope. ► Comparisons between field and simulated suctions. ► Soil heterogeneity introduces permeability disparity and natural capillary barrier. ► Simulations with evaporation effect showed better results during wet condition.
In the common practice of geotechnical design, the state of soil is considered fully saturated, while recent examples show the importance of the consideration of unsaturated conditions as well due to ...the location of the groundwater table at deeper levels. However, it is problematic to design a foundation and calculate bearing capacity as the internal stress in unsaturated conditions needs to be quantified. The mechanics of unsaturated soils are critical in geotechnical engineering, especially when the case of the foundation design is required. This study aims to investigate the influence of suction on the shaft capacity of pile foundations based on the data obtained from in situ and laboratory testing. The three modified methods (i.e., modified α, β, and λ) were implemented in this study in order to calculate the shaft capacity of the pile foundation incorporating unsaturated soil mechanics principles. In addition, the effect of varying matric suction on shaft capacity was discussed. The results of obtained changes show the importance of rain infiltration in the design of piles in unsaturated conditions. It can be concluded that the most conservative method is found to be the modified β method in designing pile foundations incorporating the suction changes due to rainwater infiltration. However, cost optimization shall be considered while choosing the method for the design. As for the increase in GWT, the modified λ method depicted the most conventional behavior. The possible rain infiltration decreases matric suction, mostly in the upper layers.
Many 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.
Compressibility and cracking potential are two main problems commonly associated with clay soils. Previous studies have proven that lime is useful in improving the shear strength and compressibility ...of clay. However, it also increases the brittleness of the soil, leading to a higher potential for crack formation when subjected to repetitive wetting and drying cycles. The present study attempted to explore the potential of using an ancient construction material, namely glutinous rice slurry, to improve the compressibility and cracking potential of pure kaolin and lime-treated kaolin. The lime concentration was fixed at 10%, while the glutinous rice slurry was prepared at concentrations of 2%, 4%, 6%, and 8%. The soil samples were subjected to Atterberg limit tests, 1D consolidation tests, and desiccation tests. The results showed that the lime-treated kaolin yielded the most improved plasticity behavior (the plasticity index was reduced from 17.9 to 7.8). The compressibility of the kaolin was best improved by adding 2% of glutinous rice slurry only. The compression index of the soil was successfully reduced from 0.158 to 0.079. The desiccation test indicated that the lime-treated kaolin showed a great tendency towards large crack formation, while the glutinous rice slurry-improved kaolin exhibited a great tendency towards swelling/shrinkage when subjected to repetitive wetting and drying cycles. The kaolin treated with 10% lime and 2% glutinous rice slurry showed the greatest resilience towards crack formation. Despite the fact that the combination of lime and glutinous rice slurry did not yield the greatest improvement in soil compressibility, the glutinous rice slurry was capable of neutralizing the brittleness caused by lime, while creating strong bonds in the soil to resist surface tension, shrink and swell behavior, and reduce soil compressibility. The compression index of the glutinous rice slurry-improved lime-treated kaolin was 25% lower than that of the pure kaolin.
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