Study on Strength and Permeability of Silt Soils Improving by Tung Oil and Sticky Rice Juice

Abstract

Tianluoshan site (5000∼2500 BC), which belongs to the Hemudu culture, has suffered damages from the hydraulic effect like other Chinese earthen sites in moist circumstance. Tung oil and sticky rice juice, as Chinese traditional building materials, were chosen as the additives in this study. Tung oil has the property of good waterproofness, fast dry-up, and quick film-forming by oxidation. Sticky rice juice has the advantage of high glutinousness, good tenacity, and low expandability. The study is to figure out the best performing mixture of tung oil and sticky rice juice to decrease the permeability of soil and increase its strength to facilitate excavations at archeological sites enlarging the display of layers of cultures. Meanwhile, the color of the site soil after reinforcement must be maintained for a long time. From the direct shear tests and the falling head test of 9 specimens mixed in different mass ratios, it was confirmed that the optimal mass ratio of the tung oil, the sticky rice juice, and the soil was 5 : 10 : 85. The treated soil specimen of the optimal mass ratio had the largest increment of shearing strength. The self-standing height of the vertical soil wall increases correspondingly from 2.63 m to 6.18 m, which could enlarge the step height when excavating a deep earthen site and extend the display height at the protection stage. The treated soil at the optimal mass ratio also showed the largest decrement of permeability coefficient from 1.257 × 10−5 cm/s of the untreated soil to 1.627 × 10−6 cm/s, which could reduce the hydraulic effect to the soil. The microstructures of the 9 specimens in different mass ratios were observed by SEM. The results showed that the glutinousness of sticky rice juice could cohere soil particles together, and the tung oil could then form oxidation film wrapping around the particle groups. In order to meet the aesthetic requirements of earthen sites conservation, the surface color contrast tests were used to measure the color change induced by the two additives. The surface contrast tests showed that the treated soil at the optimal mass ratio had the minimum variation of the surface, which could satisfy the basic requirements of earthen sites protection.