| Summary: | 碩士 === 國立臺灣科技大學 === 營建工程系 === 92 === Jet grouting method is usually used to improve soft clay associated with deep excavation. The purpose of this study is to investigate the failure behavior and strength characteristics of the composite soil specimen consisted of soft clay and treated material by changing the stress path and the improvement ratio. The test results are used to evaluate and verify the empirical formulas that are commonly used to estimate the equivalence strength of the composite soil. Finally, methods are developed to reasonably estimate the equivalent strength of the composite soil element subjected to various stress paths.
Results from the true triaxial test indicate that (1) the grout piles in the composite soil specimen exhibit apparent shear fissures for stress path angles (θ) of 0 , 30 , and 60 . The grout piles exhibit apparent tension fissures for stress path angles of 90 , 120 , 150 , and 180 . (2)For the stress path angles of 0 , 30 and60, the composite soil specimens exhibit axial compression failure. For the stress path angles of 120 and 150 , the composite soil specimens exhibit lateral compression failure. For stress path angles of 90 and 180 , the composite soil specimens exhibit tension failure. (3)When using the axial compression equivalence strength formula to evaluate the strength, the strength is increased linearly as the improvement ratio increases. However, the strength increase tendency of the test results is like a natural log curve. Thus, the formula can’t evaluate the axial compression strength accurately, especially for tests of higher improvement ratio. (4) The axial tension equivalence strength formula can evaluate the strength accurately. (5) The equivalent strength formulas developed in this study can predict test results accurately. The average errors of the predictions are less than 4%.
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