Abstract
When the pipe jacking technology is applied in expansive formation, the soil around the pipe will easily absorb water from the slurry and expand to wrap up the pipe, producing an excessive pipe jacking force. A water-based slurry formula suitable for pipe jacking in expansive soil layer was proposed in this paper. Firstly, the key design points of pipe jacking slurry in expansive soil were put forward. Secondly, plant glue, potassium humate, Na-CMC, and graphite powder were chosen as treating agents to improve the slurry performance. The effect of addition levels of different treating agents on the funnel viscosity, filter loss, expansion ratio, friction coefficient and water dissociation rate of the slurry were tested. Thirdly, based on the results of single-factor tests, a water-based slurry formula suitable for pipe jacking in expansive soil was obtained. Finally, the slurry formula was applied in a practical pipe jacking project in expansive formation, and the jacking force was controlled well in the whole jacking process. The new water-based slurry is cheap and practical and has no pollution to environment. Furthermore, a simple and practical calculating method of the pipe jacking force was presented. The comparison of the calculated and measured pipe jacking force shows that the simple calculating method can estimate the jacking force well. Improving slurry performance to reduce jacking force in pipe jacking and predicting pipe jacking force accurately can help reducing the investment for counterforce wall and jacking system in pipe jacking engineering.
Highlights
When the pipe jacking technology is applied in expansive formation, the soil around the pipe will absorb water from the slurry and expand to wrap up the pipe, producing an excessive pipe jacking force
A water-based slurry formula suitable for pipe jacking in expansive soil layer was proposed in this paper
Plant glue, potassium humate, Na-CMC, and graphite powder were chosen as treating agents to improve the slurry performance. e effect of addition levels of different treating agents on the funnel viscosity, filter loss, expansion ratio, friction coefficient and water dissociation rate of the slurry were tested. irdly, based on the results of single-factor tests, a waterbased slurry formula suitable for pipe jacking in expansive soil was obtained
Summary
2.1. e Key Points of Slurry Formula Design. It is known that there are a large number of clay minerals in the expansive soil, especially the montmorillonite mineral. is will make the soil around the pipe absorb water from the slurry. e clay particles disperse into the gap between the pipe and the formation. en the gap size will get smaller, or even the formation will collapse to wrap up the pipe tightly, leading to the failure of pipe jacking. E funnel viscosity of thixotropic slurry is required to be ranged from 40 s to 65 s in general pipe jacking project In this range, it can ensure the slurry’s fluidity and fill the gap effectively but will not spread too much into the formation to result in surface deformation. Considering the particularity of the expansive soil and the high requirement for the lubricity in pipe jacking, some corresponding treating agents must be added into the slurry system. In addition to the good lubrication performance, the particles of the graphite powder can enter the microcracks in the formation to block the cracks, which can prevent the free water from slurry into the soil and reduce the hydration of the clay minerals. In addition to the good lubrication performance, the particles of the graphite powder can enter the microcracks in the formation to block the cracks, which can prevent the free water from slurry into the soil and reduce the hydration of the clay minerals. e general addition amount of graphite powder is about 0.5%–1%
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