| Summary: | 碩士 === 中原大學 === 土木工程研究所 === 86 === Silting is a serious problems in most of the reservoirs in Taiwan. Dredging is frequently conducted to remove soils deposited in the reservoirs. On the other hand, back-fill materials are in serious shortage for engineering constructions. Thus, use of the dredged soils as a back-fill material has presented a great solution to the treatment of dredged soils. This study focuses on the use of dredged soils to construct road embankment. Soil samples were taken from Bai-Ho reservoir for laboratory tests. The soil was classified as CL based on the USCS classification system. Compressibility characteristics of compacted soil and soil-cement were investigated by conducting both static and repeated loading consolidation tests.Portland cement (type 1) of 0, 3, 6, 12, and 18% were mixed with the soil to prepare specimens of 1.91 cm in height and 6.35 cm in diameter. The specimens were cured for 28 and 90 days before the consolidation tests. Other testing conditions include a constant pressure increment of 50 kPa for repeated loading under static pressures of 25, 50 ,and 100 kPa to give load increment ratios of 0.5, 1, and 2, respectively. Furthermore, periods of both 20 and 100 seconds were used for applying the repeated loads. Results of this study include: (1) ratio of secondary compression indexes between improved soil and unimproved soil changes with the magnitudes of effective stress. The ratio is at its minimum value for stresses near the preconsolidation pressure. For stresses larger than the preconsolidation pressure, the ratio gradually increases with the effective stress with cement content smaller than 6% and keeps constant with the effective stress with cement content higher than 6%;(2) the average degree of improvement in secondary compression increases with cement content and reaches a peak value of 0.3 at 6% cement content; (3) the value of Cα/Cc increases with cement content, and an equation is proposed for predicting the value of Cα/Cc; (4) settlement under repeated loading is primarily affected by load increment ratio and cement content;(5) a prediction model for settlement of embankment under repeated loading. In summary, results of this study show that the compressibility of the soft dredged soil is greatly reduced by mixing with cement. Therefore, application of the soil-cement as a construction material for road embankment and foundation back-fill is highly feasible.
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