The resistance of a fill dam against seepage is a critical element in judging whether it is unstable or hazardous, and accordingly whether an excessive quantity of leaking water has occurred or whether soil particles are contained in the water leakage, etc. This is normally monitored after the installation of a measuring device that is used for the quantity of a water leakage in the downstream reaches of the dam body. In reality, however, the safety management aspect against water leakage is not easy because the current methods of measuring the quantity of water leakage are sometimes inaccurate as a result of being affected by rainfall or by the groundwater, etc. through the foundational ground or the surrounding mountainous area. Using two-dimensional (2D) numerical analysis that covers the largest section of the dam body, a process is generally performed when evaluating its stability against seepage. The quantity of seepage is first obtained by assuming that its bottom topography is in the simple form of a rectangle, it is then calculated by reflecting its sectional shape during this process of analyzing the seepage quantity. Considering that various forms of dams are being constructed on various types of ground, thanks to more recent technological advances, it is judged more appropriate to draw a conclusion by means of the results on reflecting the realistic shape and topographical conditions of the dam body through three-dimensional (3D) numerical analysis. Therefore, this study intends to present a method designed to carry out safety management by evaluating the correct quantity of water leakage that passes only through the dam body, having excluded other factors that include the amount of rainfall through the three-dimensional finite element method (3D FEM) analysis.

View full abstract

Suffusion is the phenomenon that fine particles are detached from the solid matrix by seepage flow and are transported through the pores formed by coarse particles in the ground. This may cause deterioration of soil structures and, in the worst case, resulting in failure of the soil structures. In this paper, to examine the seepage-induced suffusion process in embankments, a series of physical model tests on seepage-induced suffusion on small-scale model embankments are presented. Binary mixtures consist of two Silica sands (Silica No.3 and No.8), having different dominant particle sizes, were used for the model embankment. The spatial extent of erosion-induced fines content variation is discussed through sieve analyses on subdivided areas of the model embankment after seepage testing. In particular, effects of seepage duration and unsteady seepage flow on soil erodibility and migrating of fines in embankments are discussed. The results of these experiments show that the temporal suffusion development under the steady seepage flow depends on balance between dislodgement of erodible fines from embankment and its deposition into the base in the early stage. After a certain elapsed time, suffusion may develop backward along the phreatic surface from downstream in the embankment. It was also observed that the erodible fines may not only move laterally by seepage flow but also move vertically due to the gravitational force and are deposited in the base. This deposition of the fines resulted in the expansion of the fine-rich region in the base and may have caused decrease in the nominal hydraulic conductivity of the embankment. When the unsteady seepage flow was adopted, changes in the spatial distribution of fine fraction were exaggerated and the downward movement of the fines became prominent.

View full abstract

In this study, the generation process of the phreatic surface within a river levee is investigated through soil/water/air coupled simulation. Here, the effects of river level fluctuation and rainfall on changes in soil moisture distribution within a river levee are considered. The constitutive model proposed by Ohno et al.1) is formulated to the initial and boundary value problems in accordance with Borja’s multi phases’ concept and is used for simulation. Consequently, it is first found that high groundwater level is maintained for ground consisting of low permeability and high soil water retentivity. Moreover, it is found that the fluctuation of river level directly influences the phreatic surface, and that, in contrast, the effect of rainfall appears after a time lag.

View full abstract

Tropical residual soils derived from in-situ weathering and decomposition of parent rocks which has not been transported from its original location are mostly found in Indonesia. They have been used widely as clay core and homogenous embankment dams in Indonesiafrom long time ago, usage example as in Cipanunjang dam which built in 1927. Hydraulic fracturing may occur in the upstream face of clay core of rockfill dam in case the vertical effective stress in the core is reduced to levels that are small enough to allow tension fracture to occur. Pore water pressure in the core will also increase during impounding, and this will further reduce the effective stress in the core. Wedging due to water pressure may crack the upstream face of the clay core. This phenomenon was known as hydraulic fracturing in the rock fill dams. This paper present the investigation on the resistant of the tropical residual soils as clay core from 5 major dams in Indonesia against hydraulic fracturing. Soil samples are taken from the borrow pits and the clay mineral composition was obtained by x-ray diffraction test. The soil samples then modeled into six different fine content (q<0.075mm); there are 30%, 40%, 50%, 60%, 70%, and 80%. Hydraulic fracturing in the clay core of rock fill dam can be modeled in the laboratory using hydraulic fracturing test apparatus. The soil specimens are compacted hollow cylinder with outer diameter of 104 mm, the height was 120 mm, while the inner diameter was 18 mm. Hydraulic fracturing tests were carried out in the variation of three (3) initial stress states and also three (3) compaction moisture contents. The test results indicated that the clay core which have greater halloysite clay mineral may have greater resistant against hydraulic fracturing, while the clay core which compacted at wet sides may have greater resistant against hydraulic fracturing.

View full abstract

This study has investigated sensitivities of input parameters in stability analysis of embankments to safety factor Fs based on experimental deign. In addition to the geotechnical parameters, parameters about geometry such as height, width, and slope gradient of embankments were also considered in the analysis. This study applied regression analysis based on orthogonal design to the sensitivity analysis. The geotechnical parameters required for the stability analysis were used in the sensitivity analysis, and the sensitivity of these parameters to Fs were investigated. The results of the sensitivity analysis showed that the parameters about geometry of embankments such as height and slope gradient are more sensitive to Fs, although the parameters about hydraulic characteristics of embankment material are less sensitive to the Fs.

View full abstract

Failure of dams could lead to not only severe economic loss but also human casualties. Breaching analysis is therefore an important component in the risk assessment of dam safety. Traditionally the breaching process is often characterized by the breach parameters including the breach geometry and hydrograph. Over the decades, a large variety of empirical formulas have been proposed on the basis of different dam failure databases to predict the parameters. In most cases, the goodness-of-fit criteria (e.g., minimizing the sum of squares of the fitting errors) remains the only measure of the formula suitability. It may therefore lead to the use of over-complicated formula due to its higher capability of fitting. In this paper, the Bayesian probabilistic approach is used to revisit the problem. The study concludes a set of empirical formulas for the dam breach parameters which are well-balanced between formula fitting capacity and complexity.

View full abstract

The ground destabilization that results from internal erosion involving soil particle effluxes can result in piping displacements and seepage-related levee failures. While such erosion can be evaluated by using Kenney’s Filter Index and particle size distributions, the relationship between ground destabilization and soil particle outflow has not yet been elucidated. In this study, we intend to clarify this internal erosion mechanism through two experiments. The primary conclusions of these experiments are as follows: (1) Since differences in soil particle distribution cause the efflux of soil particles and result in hydraulic conductivity changes, seepage-related soil failures that involve unstable soil particle distribution cannot be evaluated by Terzaghi’s critical hydraulic gradient. (2) Soil porosity changes that occur during the efflux of soil particles can be measured using a dielectric constant-type soil water meter.

View full abstract