Numerical study on percolation and dam slope’s stability of impermeable wall composed by clay and concrete for earth-rock dam

In order to study the percolation and dam slope’s stability of an impermeable wall composed by clay and concrete for earth-rock dam, the steady seepage field of a reservoir in Jiangxi is numerically simulated by using finite element method based on the basic principles of saturated and unsaturated seepage under different ratios of clay to concrete. The results of the flow field of steady seepage are carried out and the dam slope’s stability is analyzed. We found relatively minor impacts of concrete proportion on the discharge of seepage per unit width and the dam slope’s stability. In this study, the impermeability performance of the impermeable wall is concerned. The results showed that impermeable effect of the impermeable wall has not obviously changed if the concrete proportion is below 0.43. When the proportion of concrete exceeds 0.43, the anti-seepage effect of the impermeable wall begins to change significantly. Besides, when the proportion of concrete reaches 1.0, the reduction of water level at front and behind impermeable wall, the discharge of seepage per unit width, and the safety factor of the Bishop method are all infinitely close to the value of the best anti-seepage performance and the most stable state of the dam slope.

KAJIAN PEMBUATAN TANGGUL SEBAGAI ALTERNATIF PENANGGULANGAN BANJIR PADA SUNGAI Kr. PANDRAH KABUPATEN BIREUEN

Kawasan sekitar sungai Kr. Pandrah merupakan kawasan yang setiap lima tahun sekali mengalami banjir. Banjir terbesar Q tersebut telah digolongkan sebagai bencana alam, baru saja terjadi pada akhir tahun 2006 yang telah merusakkan harta benda masyarakat disekitar kawasan pandrah. Untuk itu diperlukan suatu kajian untuk T mendapatkan alternatif penanggulangan perluapan banjir sehingga dapat menyelamatkan musibah yang rutin terjadi setiap lima tahun. Berdasarkan data survey dan informasi dari beberapa narasumber serta analisis yang dilakukan terhadap kondisi eksisting yang ada bahwa banjir tertinggi ± 0,60 m, dengan menggunakan program HAC-RAS diperoleh debit terbesar 350 m3/dt. Penampang sungai dimodifikasi menjadi penampang majemuk dengan lebar sungainya tetap berdasarkan lebar yang ada. Lebar bantaran kiri dan kanan 5 meter dari tebing sungai dan lebar puncak tanggul 3 meter dengan kemiringan 1 : 1 Perhitungan stabilitas tanggul dilakukan dengan menggunakan program Geo-Slope metoda Bishop cara Grid and Radius diperoleh faktor keamanan pada masa pembangunan hilir 2,146, pembangunan hulu 2,143, Steady seepage hilir 1,667, steady seepage hulu 1,183, Rapid drow down hulu 1,597 dan Rapid drow down hilir 1,682.Kata-kata kunci: tinggi banjir, elevasi tanggul banjir, stabilitas tanggul

One-Dimensional Vacuum Steady Seepage Model of Unsaturated Soil and Finite Difference Solution

Vacuum tube dewatering method and light well point method have been widely used in engineering dewatering and foundation treatment. However, there is little research on the calculation method of unsaturated seepage under the effect of vacuum pressure which is generated by the vacuum well. In view of this, the one-dimensional (1D) steady seepage law of unsaturated soil in vacuum field has been analyzed based on Darcy’s law, basic equations, and finite difference method. First, the gravity drainage ability is analyzed. The analysis presents that much unsaturated water can not be drained off only by gravity effect because of surface tension. Second, the unsaturated vacuum seepage equations are built up in conditions of flux boundary and waterhead boundary. Finally, two examples are analyzed based on the relationship of matric suction and permeability coefficient after boundary conditions are determined. The results show that vacuum pressure will significantly enhance the drainage ability of unsaturated water by improving the hydraulic gradient of unsaturated water.

Stochastic analysis of steady seepage underneath a water-retaining wall through highly anisotropic porous media

Steady seepage is determined by a head drop upstream/downstream of a water-retaining wall. Due to its erratic variations, hydraulic log-conductivity $Y=\ln K$ is modelled as a stationary random space function (RSF). We deal with a highly anisotropic porous formation, i.e. an axisymmetric medium where the horizontal correlation integral scale of $Y$ is much larger than the vertical one. The goal of computing the resulting flow field within a stochastic framework is complicated by non-uniformity of the mean flow. Simple (closed-form) expressions for the correlation functions of the flow variables as well as the mean head are derived. We use these results to quantify the impact of spatial variability of $Y$ upon the probability that the exit volumetric flow rate downstream of the wall is greater than that obtained by regarding the formation as homogeneous (with constant hydraulic conductivity). In particular, we show that the spatial variability of $Y$ may lead to predictions (and consequently to design choices) which significantly differ from those achieved by regarding the porous formation as homogeneous.