ANALYSIS OF EMBANKMENT SLOPE STEEPNESS AND STABILITY

This paper describes the stability calculations of the most common road embankments slopes and their results using the modified Bishop method. By searching for the smallest possible effective angle of internal friction of the different slope steepness embankments, the possible different bases of the embankment, the weight of the embankment soil, the load caused by transport and the location of load application (shoulder) were evaluated. Analyzing the obtained calculation results, it was determined that at a slope of 1:2 (26.57°) steepness, to ensure slope stability, the calculated effective internal friction angle of the embankment soil should be φʹd ≥ 28.5°, and at a slope of 1:1.75 (29.74°) steepness – φʹd ≥ 29.8°. When the slope is 2:3 (33.69°) steepness, the stability of the slope cannot be guaranteed.

Analysis of Settlement Behaviour of Soft Ground Under Wide Embankment

An elastoplastic numerical model for calculating the consolidation settlement of wide embankment on soft ground is established using PLAXIS finite element software to investigate the settlement behaviour of soft ground under the wide embankment. The distribution rules are analysed and compared to narrow embankments, such as surface settlements of ground and embankment, lateral displacement of soft ground at the foot of embankment slope and excess pore pressure in soft ground. The influence rule of elastic modulus of soft ground on the settlement of soft ground under wide embankment is discussed. The results show that the settlement distributions of wide and narrow embankments on soft ground are “W” and “V” shapes, respectively. The maximum settlement of wide embankment is near the foot of the embankment slope, which is unequal to the settlement at the centreline of the embankment. The lateral displacement distribution rules of soft ground are both “belly” shaped at the foot of two types of embankments slope. However, the lateral displacement of the wide embankment is larger in each corresponding stage. During the construction period, the excess pore pressure in the soft ground under the wide embankment is much higher than that of the narrow embankment, so the post-construction consolidation time of the wide embankment is longer. Moreover, the macroscopic settlement rule of the wide embankment is still the same with the increase of elastic modulus of soft ground.

ANALISA STABILITAS LERENG DAN ALTERNATIF PERKUATAN TANAH PADA JALUR KERETA API CEPAT JAKARTA-BANDUNG MENGGUNAKAN APLIKASI PLAXIS 8.6

Abstrak: Masalah dalam perencanaan struktur jalan kereta seperti tinggi lereng embankment yang lebih dari sama dengan 6 m, tanah asli yang tergolong sedang lunak, dan merupakan daerah rawan terjadinya longsor merupakan alasan dilakukannya penelitian ini. Hal tersebut didukung oleh hasil uji lab tanah, kondisi geografis dan geologis Kabupaten Purwakarta berupa bukit dan lembah yang terbentuk dari endapan batuan sedimen dan aluvium vulkanik dengan kemiringan lahan 8-40%. Oleh karena itu penelitian ini bertujuan untuk mengetahui stabilitas lereng embankment berupa nilai safety factor pada jalur kereta cepat Jakarta-Bandung daerah konstruksi DK70+150.00 sampai DK70+181.88. Adapun analisis numerik yang dilakukan pada penelitian ini menggunakan program Plaxis 8.6 yang dikembangkan berdasarkan metode Finite Element dengan model Mohr-Coulomb. Proses analisis dengan menginput parameter material yang dibutuhkan berdasarkan Mohr-Coulomb. Hasil analisis berupa angka safety factor yang menunjukkan kondisi stabilitas suatu lereng embankment. Penambahan alternatif perkuatan lereng embankment berupa cerucuk (micropile), bronjong (gabion) dan geotextile sebagai upaya pencegahan adanya kelongsoran jangka pendek dan panjang pada lereng embankment yang tidak stabil. Hasil analisis lereng embankment kereta api cepat Jakarta-Bandung DK70+150 sampai DK70+181.88 kondisi eksisting sebesar ΣMSF 1,1565 (cek global) dan ΣMSF 1,0515 (cek dinamik gempa) yang artinya lereng dalam kondisi tidak stabil dan perlu penambahan alternatif perkuatan. Berdasarkan simulasi kombinasi alternatif perkuatan. Menunjukkan kombinasi alternatif perkuatan geotextile dengan micropile menghasilkan angka safety factor ΣMSF 1,8151 (cek stabilitas global) dan ΣMSF 1,6262 (cek stabilitas akibat beban dinamik gempa).Kata-kata kunci: stabilitas lereng embankment, Plaxis 8.6, safety factor, kereta cepat Jakarta-BandungAbstract: Problems in the design of the railway structure such as the embankment slope height of 6 m, the original soil which is classified as moderately soft, and is an area prone to landslides is the reason for conducting this research. This is supported by the results of soil lab tests, geographical and geological conditions of Purwakarta Regency in the form of hills and valleys formed from sedimentary rock deposits and volcanic alluvium with a slope of 8-40%. Therefore, this study aims to determine the stability of the embankment slope in the form of the safety factor value on the Jakarta-Bandung high-speed rail line in the construction area DK70+150.00 to DK70+181.88. The numerical analysis carried out in this study used the Plaxis 8.6 program which was developed based on the Finite Element method with the Mohr-Coulomb model. The analysis process by inputting the required material parameters based on Mohr-Coulomb. The results of the analysis are in the form of safety factor numbers which indicate the stability condition of an embankment slope. The addition of alternative reinforcement for embankment slopes in the form of micropile, gabion (gabion) and geotextile as an effort to prevent short and long term landslides on unstable embankment slopes. The results of the slope analysis of the Jakarta-Bandung high-speed rail embankment DK70+150 to DK70+181.88 existing conditions of MSF: 1.1565 (global check) and MSF: 1.0515 (earthquake dynamics check) which means the slope is in an unstable condition and needs additional alternative reinforcement. Based on the simulation of alternative reinforcement combinations. Showing the alternative combination of geotextile reinforcement with micropile produces a safety factor number MSF: 1.8151 (check global stability) and MSF: 1.6262 (check stability due to dynamic earthquake loads)..Keywords: embankment slope stability, Plaxis 8.6, safety factor, Jakarta-Bandung high-speed train

Forensic Analyses and Rehabilitation of a Failed Highway Embankment Slope in Texas

A comprehensive investigation was designed and conducted to identify the potential causes of failure of a highway embankment slope in Texas and evaluate the effectiveness of lime treatment to rehabilitate the failed slope. Highway slopes built with high plasticity clays often experience shallow slope failures after exposure to repeated wet–dry weathering cycles. Lime stabilization generally reduces the swell–shrink potential, enhances the engineering properties of problematic clayey soils, and can potentially prevent surficial slope failures. However, exposure to wet–dry cycles can negate some of the benefits of lime treatment and therefore a study was conducted to address the use of this lime treatment to stabilize embankment slopes. Extensive laboratory tests were conducted to study the effect of weathering cycles on the degradation of hydro-mechanical properties of untreated and lime-treated soils. Rainfall-induced slope stability analyses were performed to investigate the probable causes of slope failure and evaluate the stability of lime-treated surficial slope. The optimum stabilizer dosage and treated layer thickness required for the slope rehabilitation were determined based on laboratory tests and numerical analysis results. The stability analysis results indicate that the degradation of surficial soil’s hydro-mechanical properties and the development of a perched water table during prolonged rainfall possibly caused the slope failure. The post-treatment increase in shear strength properties, reduction in moisture fluctuations recorded by embedded moisture sensors, and the presence of newly installed underlying drains are expected to prevent recurrence of surficial slope failures. Salient results from this study are covered in this paper.

Slope stability estimation of the «earth bed – road dressing» system with disturbed structure

Off-standard soil-geological systems stability assessing issues under complex conditions is being discussed in this article. Modern methods and tools analytical review for assessing the embankment slope stability was performed here. Embankment work peculiarities in the areas of the permafrost soil spread were discussed in this paper. Special attention is paid to the embankments stability issue on a thawed foundation. The design features of the embankments on permafrost soils with the frozen soils preservation or partial thawing have been studied here. Two variations of sliding surface design-level static circuit are presented in this paper: base – earth bed and base – earth bed – road dressing. The main reasons that lead to the soil slopes stability loss of soil slopes are presented here. Based on the field research results, the embankment soil stress-related characteristics and the earth bed base were determined. Those results became the basis for embankment slope stability mathematical modeling and assessment. In software packages, GeoStab (demo) and Geo5 (educational license), based on the finite element method and the field research results, digital embankment models were built on a weak foundation. The «earth bed – road dressing» system stability calculation under the standard uniformly distributed load has been performed. Two system strengthening options are proposed to increase its stability: reinforcement with soil anchors and geosynthetic materials. The hypothesis sufficiency about the influence of the pavement road dressing state on the embankment stability was also tested here. Two models of the system and the base – earth bed – road dressing are discussed: without cracks on the track and with cracks on the track. It has been elucidated that coating imperfection affects the system stability only in the presence of medium or larger strength earthquakes. Recommendations for strengthening the embankment slopes operating in difficult soil-geological conditions were given in this article.