The Ratu Boko site is a cultural heritage that has a high historical value and located about 30 kilometers to the east of Yogyakarta. Instability of the slope occurred due to the Yogyakarta earthquake in 2006, and it was indicated by the occurrence of cracks in the resto building that built on the top of the hill. The first reinforcement of the columns and foundations of the outside building was used a reinforced concrete that built-in 2012. The similar reinforcement on the inside building column and foundation was finished in 2017. In this research the displacement of the reinforced foundation, and slope stability generally both in safety factor and deformation were evaluated. The deformation and displacement analysis of the foundation were solved using Finite Element Analysis. On the other hand, for the safety factor of the slope, Limit Equilibrium Method was used. The simulation is divided into several stages, starting from the existing condition, after the first and second reinforcement, and also after increasing load due to development plan. Based on the numerical simulation, the horizontal displacement on the foundation of Plaza Andrawina decreases after the first and second reinforcement was installed. The horizontal displacement is significantly decreased in both foundations for 9.44 mm and 8.03 mm. Furthermore, the safety factor of the slope increases after the first and second reinforcement was installed. The slope safety factor using a maximum acceleration of 0.30g is 1.318. These obtained results are relatively safe from slope failures

The effect of soil disturbance on the shear strength of black volcanic ash soil was investigated using a constant volume direct shear apparatus. Disturbance of soil structure was considered as the pore size distribution which obtained from the soil-water characteristic curve (SWCC). The disturbed sample was used as a representation of soil structure disturbance due to earthquake shakes. A series of cyclic tests were conducted under unsaturated and saturated samples. It was found that the undisturbed samples exhibit a unimodal pore structure, and the disturbed samples indicate to a bimodal pore structure. Since the pore structure of the disturbed sample is unstable, the degradation index value is higher than that of the undisturbed sample and increases with the increasing number of cycles. In other words, the cyclic normalized vertical stress of disturbed samples degrades faster. Furthermore, the degradation index value in the normallyconsolidated samples was found to be larger than the overconsolidated. It might be attributed to increasing of the pore water pressure during shearing. Where in the over-consolidated samples is lower than normally-consolidated. On the other hand, the normalized shear stress of unsaturated samples, it is slightly larger due to the suction forces in the total strength of soils.

Through this paper, three main approaches were adopted to evaluate the effectiveness of waste paper ash (WPA) for stabilization on clay soil. First, the physical properties of mixing soil were studied. Furthermore, the swelling potential of mixing soil with different percentage was also discussed. Finally, the compressive strength using unconfined compressive strength (UCS) apparatus was evaluated. It was found that after mixing with waste paper ash (WPA), the percentage of soil passing sieving number 200 and plasticity index reduces by increasing of the waste paper ash (WPA) percentage. It might be attributed to the bonding of the chemical content of waste paper ash (WPA) to the soil particles. In addition, the swelling potential slightly reduces by increasing of waste paper ash (WPA) percentage. Furthermore, the compressive strength increases with waste paper ash (WPA) 5% and 10%.

The mechanical behaviour of unsaturated undisturbed black volcanic ash soils was investigated using a constant volume direct shear apparatus. A series of static and cyclic tests were conducted under unsaturated and saturated samples. The cyclic test under two patterns were adopted. First type of pattern, cyclic one-sided shearing was applied. For the second type, two-sided shearing was conducted. For further understanding of the chemical content and microstructure, X-Ray Fluorescence analysis (XRF) and Scanning Electron Microscope (SEM) were evaluated. It was found that, under static shearing, the unsaturated sample exhibits a higher apparent cohesion and friction angle in comparison to the saturated sample. The normalized vertical stress under one-sided cyclic shearing in both overconsolidated and normally consolidated samples rapidly reduced at the beginning of shearing. This might be attributed to increase of the pore water pressure during shearing. Furthermore, there is a significant difference between the normalized shear stress under cyclic one-sided and two-sided shearing. For the two-sided cyclic shearing test, the normalized shear stress value is higher than the one-sided cyclic shearing test. In addition, the normalized shear stress under unsaturated condition is significantly larger. This can be related to the suction forces to the total strength of soils. The main chemical content of the black volcanic ash soil is allophane. Further, the microstructure of the black volcanic ash changes due to shearing. For the overconsolidated sample, particles of soil more severe damage than normally consolidated sample.