This paper presents the experimental study of liquefaction potential for sandy soil in Prambanan Area, Yogyakarta, Indonesia, which underwent liquefaction due to the Mw 6.3 Jogja Earthquake on May 27, 2006. Shaking table tests considering the variation of acceleration and shaking duration were performed to investigate the liquefaction potential of sand. The liquefaction time stages including time to start liquefaction, time to start pore pressure dissipation, and liquefaction duration were observed. The percentage of liquefaction duration increase, the excess pore water pressure ratio and the required time to generate liquefaction, and the effect of applied acceleration to cyclic stress ratio, were also presented. The results showed that the sand could undergo liquefaction under the variation of dynamic load. The variation of dynamic load significantly influenced the time stages of liquefaction, the increase of liquefaction duration percentage and cyclic stress ratio. The results also exhibited that the larger applied acceleration and the longer shaking duration means the longer liquefaction duration and the larger liquefaction potential. In general, the result could bring the recommendation to the liquefaction countermeasure for Prambanan Area.

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The shear strength parameters of the soil is the key engineering property required for the design of geotechnical structures and stability analysis. The shear strength of an unsaturated soil is controlled by matric suction. This research examined the effect of matric suction on the shear strength behavior of sandy clay using a series of experimental tests in the laboratory. The contact filter paper method was used to measure matric suction and the SoilVision knowledge-based system was used to give an approximation of the entire soil water characteristic curve (SWCC). The shear strength of the unsaturated sandy clay was examined using a series of unconsolidated undrained (UU) triaxial tests to identify the relationship between shear strength, cohesion, internal friction angle, and matric suction. The result shows that the shear strength of the soil increases as matric suction increases. It was found that when the matric suction is smaller than air entry value (AEV), the shear strength of the soil increases as matric suction increases and the increment is linear because the soil is in saturated conditions. At a certain matric suction value (on soil samples occurred at 40-600 kPa matric suction values), there is a significant increase in the shear strength of soil associated with the inter-particle force produced due to negative pore water pressure. Furthermore, at a high matric suction, the relationship between shear strength and matric suction tend to be stable as in a low water content, the matric suction is not transmitted effectively to the contact point of soil particles.

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Sloof yang menghubungkan dua kolom selama ini diperhitungkan sebagai balok ikat (tie beam) agar kolom tidak bergeser. Sloof diasumsikan menggantung atau tidak bertumpu di atas tanah. Sehingga sloof murni sebagai pengikat antar dua kolom. Namun, kenyataan di lapangan sloof bertumpu di atas tanah atau di atas pasangan batu. Oleh karena itu sloof akan menerima beban vertikal dari bangunan. Desain sloof perlu diubah karena kondisi ini. Analisis dilakukan dengan menggunakan program SAP2000. Tanah dan pasangan batu dimodelkan sebagai spring dengan input parameter modulus reaksi tanah dasar (k s ). Hasil analisis menunjukkan bahwa penurunan fondasi telapak pada kondisi sloof bertumpu di atas tanah atau di atas pasangan batu lebih kecil dibandingkan kondisi sloof menggantung. Selisih penurunan rata-rata sekitar 26%. Beda penurunan dan angular distortion antara dua kolom menjadi lebih kecil ketika sloof bertumpu di atas tanah atau di atas pasangan batu dibandingkan kondisi sloof menggantung. Momen lapangan yang bekerja pada sloof menggantung adalah positif sedangkan momen tumpuan adalah negatif. Sebaliknya, momen lapangan yang bekerja pada sloof bertumpu di atas tanah maupun di atas pasangan batu adalah negatif, sedangkan momen tumpuan adalah positif.