A Study on the Durability of Dispersive Soils Improved by Alum in Western Jilin Province of China

Dispersive soil, which has the characteristics of low erosion resistance and high dispersibility in water, is the main reason for the channel slope failure that happened in the planning area of the Western Alkaline Treatment project in Jilin Province. Therefore, the study focused on the improvement of dispersive soil. In this research, pinhole test and crumb test were conducted on the soil under varying percentages of alum (1%, 1.5%, 2%, 2.5%, and 3%). Results indicated that alum can reduce the dispersivity of soil distinctly, and the optimal content of alum was 2.5%. This research also investigated the durability of 2.5%-alum-improved dispersive soil for dispersibility under the condition of freeze-thaw cycle. The soil samples with 2.5% alum content were subjected to pinhole test, crumb test, double hydrometer test, and percentage of exchangeable sodium ion test under the different number of freeze-thaw cycles. The results showed that the 2.5%-alum-improved soil was unaffected by the number of freeze-thaw cycles, which illustrated that alum can be used to improve soil dispersivity in engineering practice.

Avaliação do uso do agregado reciclado da construção civil como barreira hidráulica em camadas de coberturas de aterros sanitários

As camadas de cobertura de aterro sanitário têm a função de impedir a entrada de líquidos bem como evitar a saída de gases. Geralmente são construídas com solos argilosos compactados e de baixa condutividade hidráulica. Neste sentido, esta pesquisa tem como objetivo avaliar a viabilidade do uso de misturas resíduos da construção e demolição (RCD) com solo, para ser utilizado como barreira hidráulica em cobertura final de aterros sanitários. Para isso, foi utilizado um solo argiloso de uma antiga área de extração de saibro desativada a mais de 30 anos, em uma encosta localizada na Ilha de Itamaracá-PE, Região Metropolitana do Recife (RMR). As misturas utilizadas foram de 10%, 30% e 50 % de solo e RCD. O programa de investigação contou com ensaios de caracterização física, mecânica e mineralógica, além de ensaios de erodibilidade. Nos ensaios de caracterização física, o solo foi classificado com uma argila de alta plasticidade e o RCD como um material arenoso, cuja adição ao solo provocou uma diminuição do teor de finos do solo até chegar numa argila medianamente plástica, resultados esses, confirmados nos ensaios de Limites de Atterberg. As condutividades hidráulicas saturadas dos solos e das misturas foram da ordem de 10-9m/s. Os parâmetros de resistência à compressão simples das misturas foram superiores à resistência máxima do solo, tendo alcançado o seu maior valor na mistura de 30%. Quanto à erodibilidade os ensaios de crumb test e pinhole test indicaram que o solo estudado não apresenta tendência erodível. O acréscimo de RCD diminui a expansibilidade do solo. Desta forma, conclui-se que mistura deste solo específico da região com o RCD é viável para utilização como barreira hidráulica, sendo a mistura de 50% a que apresentou os melhores resultados.

Evaluation of erosion characteristics of soils using the pinhole test

This paper investigates the erosion characteristics of soils using the pinhole test. The tests were conducted with two undisturbed clay samples and five disturbed sandy soil samples. Based on the pinhole test results, a process to analyze the critical shear stress and erosion rate was proposed. The result indicates that the particle size distribution and coefficient of uniformity of soils are significant factors that affect the erosion characteristics of the soil. Samples with a grain size ranging from 0.2 to 0.6 mm is most susceptible to soil erosion. The erosion coefficients can be used to distinguish between the low erodible soils (ND3 and ND4) and high erodible ones (D1 and D2). Furthermore, it is interesting to note that the critical shear stress might be used as an identification parameter for erosion characteristics of the soil: τc > 3.5 Pa (ND3), 3.0 Pa < τc < 3.5 Pa (D2), and τc < 3.0 Pa (D1).

Rethinking the Water Leak Incident of Tunnel LUO09 to Prepare for a Challenging Future

Incident often occurs while deepening excavation pit and/or tunnelling underground pipelines although serious attention from practitioners, engineers, and scientists has received. Prevention and mitigation of incident have thus been deemed to be the key in developing sustainable infrastructure in urban areas. This study analyses and discusses an extensive water leak incident taken place throughout the parallel tunnels LUO09 construction in the soft alluvial deposits in Kaohsiung, Taiwan. Dumping sand bags and quick-set cement intervened the incident but in vain. The water leak incident is initiated by the piping. The existing vehicle underpass causes the jet-grout columns installed not exactly in the plumb. Their overlapping is estimated to be less than the design value of 60 cm, and some seepage-prone weak zones are thus developed. The measured hydraulic gradient being equal to 12.1 and existence of seepage-prone weak zones are deemed as the main cause initiating the water leak incident. The pinhole test results highlight not only the nonplastic nature of the Kaohsiung silt but also its vulnerability to piping under large hydraulic gradients. Some bullet points that indicate what engineers should do or avoid are learned and summarised.

Cambio en las propiedades geotécnicas de un suelo sometido a ignición en laboratorio

Las zonas tropicales son regiones sometidas a ambientes cálidos, y sus suelos, en especial en aquellas áreas cubiertas de vegetación, pueden estar expuestos a eventos como los incendios. Las altas temperaturas que se pueden alcanzar en estos eventos causan variaciones en algunas de las propiedades geotécnicas de los suelos, influenciando el comportamiento del material, y pueden dar origen a procesos erosivos, que en muchos casos preceden a movimientos en masa. El siguiente artículo expone lo que ocurre en un suelo sometido a un proceso de ignición en el laboratorio, analizando las variaciones en algunas propiedades físicas (contenido de humedad, límites de Atterberg, gravedad específica y granulometría), químicas (pH y capacidad de intercambio catiónico), mineralógicas, estructurales y mecánicas (succión, desagregación y pinhole test); mostrando claramente que el material se torna más ácido con mayor relación de vacíos, menor capacidad de intercambio catiónico, menor cantidad de caolinita, plasticidad y succión, y variación en su textura, con un consecuente aumento en la erodabilidad.

Studies on a Novel Qualification Method of Silicon Nitride Layer

In wafer fabrication, a silicon nitride (Si3N4) layer is widely used as passivation layer. To qualify the passivation layers, traditionally chemical recipe PAE (H3PO4+ HNO3) is used to conduct passivation pinhole test. However, it is very challenging for us to identify any pinholes in the Si3N4 layer with different layers underneath. For example, in this study, the wafer surface is Si3N4 layer and the underneath layer is silicon substrate. The traditional receipt of PAE cannot be used for passivation qualification. In this paper, we will report a new recipe using KOH solution to identify the pinhole in the Si3N4 passivation layer.