Shear strength of the loess joint has significant influence on the stability of loess engineering with joints. “Joint” is the weak structural plane of loess, and its shear strength determines the stability of loess. In this study, a series of loess joint samples was collected from Binxian County, Liquan County, and Zichang County in Shaanxi Province. The shear strength of the loess joint was determined by means of the direct shear test. The influence of the water content on the shear strength parameters of the loess joint was investigated by means of tests. The results showed that initially the internal friction angle varied slightly with the water content but decreased very quickly as the water content surpassed the threshold value of 14 %. The relationship between shear strength and water content can be expressed as an exponential function. This study devised a new empirical formula that determines the peak internal friction angle by observing the effects of dry density, water content, shear strength, and joint surface morphology.
Generally, it is difficult to control the trench stability and panel joint permeability in the construction of a diaphragm wall. The high construction cost is inevitable because of the environmental pollution due to the slurry, waste of water consumption, and debris disposal treatment. A new technique, called the dry trenching diaphragm wall with self-guided double-rectangular-casing, is thereafter developed in the current study to avoid these problems. In this technique, two pieces of rectangular steel casing are driven in sequence and guided each other. The trench is made by squeezing into the soft soil. The panel alignment and straightness are assured without any joints due to the dry concrete pouring instead of the influences of the slurry. Compared to the regular diaphragm wall, the technique is an environment-friendly, less emissive and energy-conserved one by eliminating the slurry pollution with the low cost. It shows that the quality of panel connection is reliable, and the permeation-proof performance is superior with high efficiency in wall-forming due to non-joint interlocking.
In the existing flange occlusion technique, a borehole is formed by taking the soils from casing pipes. In the technique, super retarded time is used to extend the initial set time of pile concrete and to realize the occlusions between the piles by cutting the latter ones. However, this technique still has several inadequacies and will be examined in this paper. A fast soil extraction technique was thereafter developed for the soft soil. A novel occlusion pile, or occlusal cast-in-place pile with a whole-length casing and soil dragline, was developed to improve the existing technique. In this new technique, pile with convex boundary is cut and constructed in a sequential arrangement. Conventional concrete can be poured using an adoption of the casing connector and a fast soil-extraction patent. The single pile construction is 1-2 times higher in efficiency and much lower in cost compared with bored pile with the same section and length. Moreover, it shows in practice that this technique is reliable in bite quality and high both in waterproofing and in wall-forming efficiency.
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