The paper discusses the development of a numerical method for a multi-braced excavation to estimate strut forces. Two different software were used in the proposed method. Equivalent strut forces were calculated by plane strain analysis on Plaxis 2D. The number of Etabs models built corresponds to the number of strut levels. Loads acting on waler beams in these structural models were derived from the results of equivalent strut forces on the Plaxis 2D model. The results of the proposed method were compared with those of a full 3D analysis. This method ensures the force equilibrium with an error of less than 5% as compared with the total strut forces in the 3D calculation. Due to the corner effect not take into account, the corner strut internal forces in the proposed method are usually larger than those in the 3D analysis, while the internal forces of the middle struts seem to be the opposite. Although the differences have a wide variation, the average error is 35%. However, the results from the proposed method are conservative. The proposed method is useful for practicing engineers, especially in the primary design stage of multi-braced excavation with a complex-shaped plan.
This paper presents a series of laboratory tests to determine the shear strength and interface shear strength of cement-treated silty soil under consolidated and drained conditions. The test variables include the effective normal stress, cement content, and curing period. Experimental results indicated that the effective shear strength and interface shear strength of cement-treated soil specimens increased significantly as the cement content increased. After 28 days, the average shear strength ratio increased from 1.28 to 2.4, and the average interface efficiency factor improved from 1.15 to 1.55 as the cement content increased from 3% to 10%. It resulted from an increase in grain size and the fraction of sand-sized particles in the treated soils, approximately in two-time increments for the specimens treated with 10% cement content after 28 days of curing. In addition, the peak and residual values of the shear strength and interface shear strength of the cement-treated soil specimens were determined to assess their brittle behavior under high shear deformation. Last, two new empirical models are introduced herein. The first power equation is to predict the shear strength ratio of cement-treated soil at 28 days of curing using the soil-water/cement content ratio. The other proposed model is useful for assessing the rate of shear strength and interface shear development of cement-treated soil specimens within 56 days of curing.
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