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Water-salt migration is an important reason for the development of basal erosion which seriously threatens the conservation of earthen sites. Studies in cutting-off or redirection of the water-salt migration path become vital. Polyvinyl alcohol (PVA) composite soil with extreme hydrophobicity shows the potential as the cushion layer with the damp-proof function, but the feasibility of preventing basal erosion based on the PVA cushion layer still lacks verification. In this study, for the embedded and non-embedded PVA cushion layers, water-salt distribution and morphology of earthen wall after repeated injection of salt solution were compared. The results showed that PVA cushion layer changed the water-salt migration path and promoted the accumulation of soluble salt on the ground outside the wall rather than the bottom of cushion layer, which effectively prevented basal erosion. A numerical model based on HYDRUS-2D confirmed that a partial laying of hydrophobic cushion layer under the wall cannot effectively prevent the water-salt migration, and a full laying of cushion layer should be adopted to prevent basal erosion. The cushion layer was recommended to extend towards the direction of the earthen wall instead of towards the sides, which also resisted the destructive effects of sand-driving wind and runoff erosion. • Basal erosion caused by water-salt migration is directly confirmed. • Water-salt distribution for models with/without PVA cushion layer is explored. • PVA cushion layer can inhibit basal erosion. • Reasonable laying modes of the hydrophobic cushion layer is presented. [ABSTRACT FROM AUTHOR]

Grottoes are widely distributed along the ancient Silk Road in Northwest China, and wall paintings are among the most precious cultural relics in these grottoes. On-site investigation of some grottoes has revealed that these wall paintings are painted on earthen plaster and that most of them have a double-layer structure of plaster, i.e., a base coarse plaster layer (with wheat straw added) and a surface fine plaster layer (with hemp fibers added). Meanwhile, studies regarding the improvement in shrinkage and cracking behaviors via ancient plaster craftsmanship have been scarce. To investigate the specific effects of different material compositions on the shrinkage and cracking properties of plaster during desiccation, a series of laboratory shrinkage and cracking tests is conducted on plaster specimens composed of Dengban clay and quartz sand, vegetal fibers, and a potential restoration material (i.e., calcined ginger nut), respectively. The results show that adding sand and vegetal fibers can significantly increase the shrinkage limit of Dengban clay and inhibit its volume shrinkage and that vegetal fibers play an important role in the inhibition of surface cracking on plaster. Sand inhibits shrinkage by forming a skeleton in soil and reducing the formation of primary cracks. Fibers inhibit soil shrinkage by overcoming the suction between soil particles and preventing the formation of primary cracks. However, wheat straw cannot deform with the shrinkage of soil (e.g., hemp fibers); consequently, many subcracks appear around the wheat straw on the surface of coarse plaster. As a typical lime-based restoration material, calcined ginger nut paste presents slight shrinkage and a low surface crack ratio during desiccation, which demonstrates its good application prospect in plaster restoration. • Different types of plaster specimens are prepared based on the original composition. • Sand and vegetal fibers can significantly increase the shrinkage limit of Dengban clay. • Vegetal fibers are more effective in inhibiting surface cracking. • Calcined ginger nut paste shows slight shrinkage and a low surface crack ratio during drying. [ABSTRACT FROM AUTHOR]

Coastal loess is a special loess deposit that is distributed around the Bohai Sea. The primary objective of this study was to investigate the physical index, mineralogical characteristics and collapse potential of coastal loess. The secondary objective was to survey the effect of fine silt particles (particle size 5–10 μm, 6.64–7.64φ) on the collapse process. We tested the specific gravity, moisture content, dry density, Atterberg limits, grain size distribution, mineralogy, and collapsibility characteristics in a laboratory; generated scanning electron microscopy (SEM) images; and performed Mercury intrusion porosometry (MIP) tests. The results of this investigation indicated that coastal loess has a moderately severe collapse potential. The collapsibility coefficient decreases with an increase in the initial water content; it initially increases and then decreases with an increase in vertical pressure. As revealed by the MIP test, the collapse produces a smaller porosity, and the middle pores are primarily responsible for the collapse. The relationship of the collapsibility coefficient and particles with a diameter < 10 μm reveals that fine silt particles (particle size 5–10 μm, 6.64–7.64φ) and clay particles (particle size < 5 μm, >7.64φ) have the same tendency in terms of their effect on collapse. These results and analyses are important to improve the engineering construction safety in coastal zone loess areas and achieve a better understanding of loess properties compared with loess from a typical loess-paleosol section. • Surveyed the particle and pore size distribution, Atterberg limits and mineralogical characteristics of Coastal loess. • Obtained the collapsibility of Coastal loess, and proposed the relationship between collapsibility coefficient and micro indexes based on the results of SEM and MIP tests. • Discussed the effect of fine silt particles (5-10 μm) on the collapse process. [ABSTRACT FROM AUTHOR]

Abstract: A series of ring-shear tests was conducted on saturated loess to investigate the effects of NaCl concentration in pore water and desalinization on the shear behavior under undrained conditions. The loess samples were taken from the ground surface of a frequently active landslide in China, were saturated by de-aired, distilled water with different concentrations of NaCl, and then were sheared undrained. After that, the samples were retrieved, remolded, re-set into the shear box, and re-saturated by passing through de-aired, distilled water such that the samples were desalinized, and then were sheared undrained again. Through comparing the undrained shear behavior, the effects of NaCl in the pore-water and desalinization on the undrained shear behavior of loess were examined. The results showed that the variation of NaCl concentration in pore water can strongly affect the shear behavior of saturated loess. Both the peak shear strength and steady-state strength increased with increase of NaCl concentration until a certain value, after which they decreased with further increase of NaCl concentration. Meanwhile, the peak shear strength and steady-state strength of the desalinized samples recovered to those of the original sample; hence, the effects of salinization are reversible. These findings may be of practical importance to better understand the repeated occurrence of some irrigation-induced loess landslides in China. [Copyright &y& Elsevier]