Hakki O. Ozhan

Use of Perforated Base Pedestal to Simulate the Gravel Subbase in Evaluating the Internal Erosion of Geosynthetic Clay Liners

When geosynthetic clay liners (GCLs) are placed over coarse-grained gravel subgrades, the permittivity of the GCLs may increase because of internal erosion. To simulate this condition, geosynthetic clay liners typically are placed over gravel and tested in the laboratory under high hydraulic heads. In this study, a perforated base pedestal was used instead of gravel. The base pedestal was designed to have circular voids to represent the voids of a uniform and rounded gravel subgrade. Results obtained from tests where natural gravel and a perforated base pedestal were used were compared. To verify the effectiveness of the new approach, two different geosynthetic clay liners were tested over two different gravel subgrades. Tests also were conducted using rounded, uniform, coarse-grained gravels to compare to the results of the tests with the perforated base pedestals. The void diameter of the perforated base pedestals was chosen to be approximately the same as the maximum void size between the gravel particles. Test results indicated that a perforated base pedestal with uniform voids simulated a rounded, uniform, coarse-grained gravel subgrade in terms of internal erosion. The hydraulic heads that caused internal erosion were similar when a perforated base pedestal or a rounded gravel subgrade was placed beneath a GCL. When the same GCL was used over a base pedestal or over a gravel subgrade with equivalent void size, the difference in hydraulic heads at failure did not alter more than 5 m, except for one comparison. For most of the tests, the performance of the GCL placed over the gravel subgrade was slightly better than that of the perforated base pedestal in terms of internal erosion. These results indicated that the proposed technique of using perforated subbase to simulate gravel remains conservative for the GCLs and gravel subgrades considered as part of this study.

FACTORS AFFECTING FAILURE BY INTERNAL EROSION OF GEOSYNTHETIC CLAY LINERS USED IN FRESHWATER RESERVOIRS

Geosynthetic clay liners (GCLs) are often used as lining materials for freshwater reservoirs. To irrigate agricultural land without depleting groundwater, surface water is stored in these artificial ponds. In this study, hydraulic conductivity tests were performed on GCLs placed in flexible-wall permeameters under hydraulic heads of up to 50 m in order to investigate the risk of internal erosion. In these tests, base pedestals made of Plexiglas with uniform circular voids were placed beneath the GCLs instead of a typical gravel subgrade. The voids in the base pedestal represented the voids between uniform rounded gravel particles. Different types of GCLs were tested. GCL-1 was reinforced using needle-punching technology whereas GCL-2, GCL-3 and GCL-4 were unreinforced GCLs that were assembled in the laboratory. The effects on internal erosion of the void size in the subbase; the geotextile component that was in contact with the subbase; the bentonite component, and the manufacturing process of the GCLs were investigated. Test results indicated that internal erosion was directly related to the void diameter of the base pedestal. The resistance of the needle-punched GCL to internal erosion was better than that of the unreinforced GCL. The degree of internal erosion was also related to the engineering properties of the geotextile in contact with the base pedestal. Higher tensile strength of the GCL reduced the possible potential for internal erosion within it. The type of bentonite did not have a significant effect on internal erosion.

Value and vulnerability assessment of a historic tomb for conservation.

Monumental tombs reflect various social, cultural, architectural, religious, economic, and engineering features of a community. However, environmental weathering, natural disasters, poor maintenance, vandalism, and misuse unfortunately pose serious threats to these cultural assets. Historic monuments are often exposed to the highest risk due to their vulnerability. The Ottoman-style Nişancı Hamza Paşa tomb located in Karacaahmet Cemetery, Istanbul, the largest and oldest public cemetery in Turkey, is a case in point. The tomb consisting of six granite columns and a brick dome supported by six arches was constructed in 1605. Cracks, material loss, and decay as a result of adverse environmental effects and past earthquakes are evident. Therefore, this paper analyses the overall value of the tomb with respect to its historical, communal, evidential, and aesthetic aspects. Using the finite element approach and data on the tombs material properties, a structural analysis under the self-weight and a time history analysis based on the earthquake ground motion data recorded in Duzce, Turkey, in November 1999 were conducted to encourage the conservation of this tomb and similar cultural heritage assets all over the world. The damage observed in the structure is congruent with the analysis results.

Design of a Geomembrane-Laminated Geosynthetic Clay Liner on the Slopes of a Mine Tailings Dam in Emet, Turkey

We evaluated the potential use of a geomembrane-laminated geosynthetic clay liner (GCL) along the slopes of a boric acid tailings dam in Emet, Turkey. Even though a compacted clay liner (CCL) had been used at the bottom of the tailings dam, it was not possible to place a CCL along the slopes of the dam due to their steepness. Triaxial permeability tests were conducted on the base GCL without a geomembrane and the results indicated that although the volumetric flow through a cross section of the GCL was measured to be very low initially, it increased after a while due to the interaction of the bentonite in the GCL and the mine leachate. For this reason, using a geomembrane-laminated GCL along the steep slopes was found to be an appropriate solution. The mechanical properties of the barrier material were evaluated by performing a parametric study, including a slope stability analysis and an anchorage design for the geomembrane-laminated GCL. Based on the results, a geomembrane-laminated GCL with appropriate mechanical and hydraulic properties was chosen.ZusammenfassungBewertet wird der mögliche Einsatz einer geosynthetischen folieverstärkten Tondichtung (GCL) in Böschungsbereichen des Borsäure-Schlammteiches von Emet, Türkei. Im Gegensatz zur Aufstandsfläche des Schlammteiches, die mit einer mineralischen Abdichtung (CCL) versehen wurde, gelang es auf deren Böschungen aufgrund zu steiler Neigungen nicht, eine ebensolche Abdeckung einzubauen. An der mineralischen Basisabdichtung durchgeführte Triaxialtests zeigten, dass sich deren anfänglich geringe Durchflussmengen nach einer gewissen Zeit erhöhten, was auf die Alteration des Bentonits unter Sickerwassereinfluss zurückgeführt wird. Daher erschien die Verwendung einer folieverstärkten Tondichtung in den Böschungsbereichen als geeignete Lösung. Die mechanischen Eigenschaften der Barrierematerialien wurden mittels Parameterstudie bewertet, welche eine Standsicherheitsanalyse sowie eine Einbaurichtlinie für die geosynthetische folieverstärkte Tondichtung (GCL) einschließt. Auf Grundlage der hierbei erzielten Ergebnisse wurde eine GCL mit hinreichenden mechanischen und hydraulischen Eigenschaften ausgewählt.ResumenEvaluamos el potencial uso de un revestimiento de arcilla geosintético laminado con geomembrana (GCL) a lo largo de las laderas de un dique de relaves de ácido bórico en Emet, Turquía. A pesar de que se había utilizado un revestimiento de arcilla compactada (CCL) en el fondo de la presa de relaves, no fue posible colocar un CCL a lo largo de las laderas de la presa debido a su inclinación. Se realizaron pruebas de permeabilidad triaxial en GCL sin geomembrana y los resultados indicaron que aunque el flujo volumétrico a través de una sección transversal de GCL se midió inicialmente como muy bajo, aumentó después de un tiempo debido a la interacción de la bentonita en el GCL y el lixiviado de la mina. Por esta razón, el uso de GCL laminado con geomembrana a lo largo de las pendientes pronunciadas era una solución apropiada. Las propiedades mecánicas del material de barrera se evaluaron mediante la realización de un estudio paramétrico, que incluye un análisis de estabilidad de taludes y un diseño de anclaje para GCL laminado con geomembrana. En base a los resultados, se eligió un GCL laminado con geomembrana con propiedades mecánicas e hidráulicas adecuadas.抽象评价了沿Emet(土耳其)硼酸尾矿坝坡面铺设多层土工膜膨润土垫层(GCL)的可行性。虽然尾矿坝底已经铺设夯实粘土层(CCL),但急倾斜坡面无法使用CCL。试验了膨润土垫层(GCL)的三轴渗透性能;结果显示,虽然穿过GCL断面的初始容积流很小,但GCL中斑脱土与淋滤液的反应却使容积流很快增大。发现多层土工膜膨润土垫层(GCL)为较好的解决方法。通过坡体稳定性分析和多层土工膜膨润土垫层(GCL)锚固设计,评价了防渗材料的力学性质。据此,确定了多层土工膜膨润土垫层(GCL)的合理力学和水力学性质参数。

Katyonik Polimer Katkılı Geosentetik Kil Örtülerin Farklı Tuz Çözeltileri ile Etkileşimi

Geosentetik kil ortu (GKO), dusuk hidrolik iletkenligi sayesinde atik depolama alanlarinda bariyer ozelligi ile kullanilan bir kaplama malzemesidir. Bu calismada, GKO’nun bentonit bilesenine sirasiyla kutlece %0.5, %1 ve %2 oranlarinda katyonik polimer eklenmis ve uc eksenli hidrolik iletkenlik ile serbest sisme deneyleri yapilarak GKO’nun sirasiyla 0.1 M KCl, 0.5 M KCl ve 0.1 M MgCl 2 tuz cozeltilerinde hidrolik performansi irdelenmistir. Sonuc olarak GKO’ye 0.1 M KCl cozeltisinde %0.5 katyonik polimer eklenmesi, hidrolik iletkenligi yaklasik 0.13 katina, 0.5 M KCl ile 0.1 M MgCl 2 cozeltilerinde ise %1 katyonik polimer eklenmesi, hidrolik iletkenligi sirasiyla yaklasik 0.18 ve 0.08 katina dusurerek gerekli hidrolik performansi saglamistir. GKO’ye daha fazla polimer eklemek, hidrolik iletkenligi ya degistirmemis ya da artirmistir. GKO’nun sisme indeksi de %2 miktarina kadar katyonik polimer eklenmesi sonucunda artmistir. Katyonik polimerin hidrolik iletkenlik uzerindeki etkileri polimer-bentonit-tuz cozeltisi arasindaki elektrostatik kuvvetler ile, sisme indeksi uzerindeki etkileri ise difuz cift tabaka ile iliskilendirilmistir. Tuz cozeltilerinin konsantrasyonunu ve katyon degerligini artirmak ise hidrolik iletkenligi artirip sisme indeksini azaltmistir. Deney sonuclarina gore kullanilan katyonik polimer, GKO’nun hidrolik ozelliklerini iyilestirerek tuz cozeltilerinde yeterli hidrolik performansta kullanimini saglamistir.