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Since 2006, with the implementation of a series of national research projects in the field of earthen site conservation, the Chinese theoretical foundation and technological conservation system for the protection of earthen sites in arid environments has gradually formed. However, there are some global problems such as an unclear relationship between characteristics of diseases on sites and their existing environment, unclear deterioration mechanisms under multi-field coupling, immature stability control technology under dynamic loading, the poor suitability of protection process quality assessment equipment, and a lack of systematic research on comprehensive protection synergy mechanisms. On the basis of summarizing the research achievements in the field of earthen site conservation in China for more than 30 years, and a large number of practical experiences in earthen site reinforcement engineering, this paper expounds the multi-field coupling characteristics of earthen site construction technology, the climatic environment, and dynamic loading and protection measure activities, clarifies the main characteristics of the protection of earthen sites in China at present, puts forward the key scientific and technical problems existing in the conservation of earthen sites, constructs a picture of the research on the conservation of earthen sites under the action of multi-field coupling, and discusses the protection projects of earthen sites under different environments. We hope the technological system can provide support for the transformation of earthen site conservation from the rescuing conservation stage to the stage of both rescuing and preventive conservation, and move the foundation of earthen site conservation towards the stage of preventive protection. [ABSTRACT FROM AUTHOR]

As a world-renowned heritage site, the Ming Great Wall in Qinghai Province, is an example of an earthen site that is seriously threatened by a series of deterioration. Its damage assessment is the precondition for further protection planning and implementation, but related research was found to be scant. To fill this gap, we explore to study its damage assessment by applying Fuzzy-AHP and AHP-TOPSIS to determine the damage assessment levels for 18 earthen sites selected from Qinghai Province, combined with their occurrence environment, engineering properties of rammed earth, deterioration characteristics, and building technologies. After obtaining and comparing results, the AHP-TOPSIS is indicated to be much closer to the real damage conditions. Therefore, this method is proved to be more suitable for the damage assessment of earthen sites in Qinghai Province. This study also holds the potential application of the AHP-TOPSIS in the damage assessment for other earthen sites in Northwest China. [ABSTRACT FROM AUTHOR]

Calcined ginger nut (CGN) has been applied in grouting mortars for anchoring unstable earthen sites, but the lack of scientific research limits its application. In this study, CGN-based grouts admixed with fly ash (F), quartz sand (S), or both are evaluated. To explore the optimal mixture ratios, three types of mixing groups (five proportion gradients in each group) are established. All the grout specimens are buried and maintained outdoors, and their physical (shrinkage rate, density, elastic wave velocity, and permeability) and mechanical properties are continuously examined over 180 days. The solidification processes at different ages are simultaneously observed by means of scanning electron microscopy (SEM) images. The results indicate that the physical properties of grouts are influenced significantly by initial moisture content but then remain steady for approximately 15 days. Quartz sand can effectively reduce the shrinkage rate of grouts as well as adjust their density and permeability, and might be considered as an ideal mixing material for CGN. In the solidification process, grouts are rapidly solidified after the initial hydration reaction, and the carbonation reaction in the later stage constantly improves their mechanical strength, with physical properties kept relatively stable. SEM images show fly ash and quartz sand particles are cemented by CaCO 3 crystals. Through comprehensive comparison, the grouts with the mass ratio of CGN and S at 1:1 are found to better satisfy requirements that grouts should be compatible with earthen sites. [ABSTRACT FROM AUTHOR]

• Sticky rice can inhibit the carbonation reaction of lime-treated soil. • The outer part of the sample had a higher carbonation than the inner part. • Binding and inhibition effects of sticky rice adjusted strength of lime-treated soil. Earthen sites with important historical, artistic, social, cultural, and scientific values have suffered serious damage due to long-term influences from various natural factors. The sticky rice and lime composite shows the potential to be applied to the protection of earthen sites. The carbonation of lime has a significant impact on the engineering properties of earthen sites. The main purpose of this study is to investigate the effect of sticky rice on the carbonation reaction of lime-treated soil in earthen sites. The results indicated that sticky rice can inhibit the carbonation reaction of lime, resulting in a reduced calcium carbonate content. The inhibition effect of sticky rice on carbonation reaction of lime could be attributed to the limitation of gaseous water and CO 2 gas diffusion. Sticky rice had both binding effect and inhibition effect on lime-treated soil, and its mechanical properties depended on the dominant effect after these effects cancelled each other. When the lime content was ≤6%, the addition of sticky rice can increase the strength of soil. When the lime content was >6%, however, the addition of sticky rice resulted in a decrease in strength. In addition, the carbonation of the outside of the cylindrical sample was higher than that of the inside. These findings can increase the understanding of protecting earthen sites with sticky rice and lime composite, and optimize the application of sticky rice and lime composite. [ABSTRACT FROM AUTHOR]

In this study, calcined ginger nuts (CGN) grouts admixed by fly ash (F) and quartz sand (S) was investigated on its suitability for anchoring use in earthen sites. According to requirement for the consistency of grout, the mix proportions were determined with 0.45 for CGN_F, 0.33 for CGN_S and 0.35 for CGN_F_S, by mass, to study their physical and mechanical property and durability. Test results indicated that use of fly ash can prolong the initial setting time of grout and admixture by fly ash and quartz sand leaded to lowest density and shrinkage, higher porosity, and highest strength. Accelerated aging tests indicated that admixture by fly ash led to a high resistance to fluctuation of temperature and humidity, sulfate attack and alkali environment; meanwhile, admixture by quartz sand resulted in high resistance to freeze-thaw action and water environment. As a compromise, CGN_F_S can get predominant durability. The paper shows that CGN_F_S grout is basically compatible to earthen sites and suitable for anchoring use in the conservation of earthen sites in terms of workability and durability. [ABSTRACT FROM AUTHOR]

• The protective effects of sticky rice and lime composite are evaluated. • The relationship between macroscopic properties and microstructure is established. • The feasibility of protecting earthen sites with sticky rice and lime is discussed. Earthen sites have important historical, artistic, social, cultural, and scientific values. However, due to the extreme natural environment, they have suffered serious damage. The sticky rice and lime composite is one of the most important technological inventions in Chinese architectural history, which is an alternative material for the protection of earthen sites. In the past, the mechanical and microscopic properties of sticky rice and lime composite as binding material have been discussed. However, these properties are not sufficient to evaluate the feasibility of protecting earthen sites with sticky rice and lime composite. In this study, 25 groups of soil samples were prepared at five different lime contents (i.e. 0%, 3%, 6%, 9% and 12% by dry weight of sample) and five different sticky rice contents (i.e. 0.0%, 0.5%, 1.0%, 1.5% and 2.0% by dry weight of sample), and several important characteristics of the samples such as drying shrinkage, colour difference, surface hardness, unconfined compressive strength (UCS), and water vapour permeability are investigated comprehensively. Scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) were used to study the microstructure of samples. Then, the feasibility of protecting earthen sites with sticky rice and lime composite was systematically evaluated. The results indicate that the effectiveness of sticky rice and lime composite is better than that of their individual application. The optimal formula is 6% lime and 0.5% sticky rice for the protection of earthen sites when above indicators are compared. The surface fractal dimension builds bridges between microstructure and macroscopic properties of the soil with sticky rice and lime. Surface hardness and UCS are positively related to the surface fractal dimension, while water vapour permeability is negative related to the surface fractal dimension. This research further provides insights into the potential application of traditional Chinese inorganic–organic composite for protecting earthen sites in arid and semi-arid regions of northwest China. [ABSTRACT FROM AUTHOR]

• The development difference of scaling off on the sunward side and nightside of earthen sites was revealed. • The new indicators of salt migration gradient (SMG) and normalized shrinkage rate (NSR) were proposed. • The mechanism of salt difference and heterogeneous shrinkage on different building orientations were indicated. • Environmental monitoring was comprehensively analysed to explain the development difference of scaling off on different building orientations. Scaling off is one of the most representative deterioration types of earthen sites, severely causing their damage with a characteristic binary structure consisting of the crusted and loose layers. Exploring the development cause of scaling off is the key premise for targeted protection of earthen sites. Thus far, numerous researchers focused on environmental and rammed earth factors; however, the development difference of scaling off on different building orientations has not been studied. Therefore, this study aims to reveal the development difference of scaling off on the sunward side and nightside of earthen sites. In this study, 15 earthen sites situated in NW, China, are chosen and the scaling off is investigated in the field to collect characteristic values of the binary structure of scaling off on two sides of the wall. Subsequently, the previous built-up evaluation system is applied to calculate the development degree of scaling off to show its discrepancy rate (DR) on distinct building orientations. Additionally, the samples of rammed earth in different layers are collected and indoor geotechnical tests are performed to obtain the evaluation indicators. Combined with the binary structure and rammed earth properties, the salt differentiation and heterogeneous shrinkage of soils in different layers are quantificationally reflected. Finally, the temperature and humidity of three representative earthen sites are monitored for 24 h after rainfall. By analysing the environmental change, the greater amplitude of environmental change for the sunward side is found; this is an important driving force for salt migration, which leads to the difference in binary structures. This study reveals the development difference of scaling off on the sunward side and nightside from the quantitative perspective, which supplements current research contents on characteristics and mechanism of earthen sites deteriorations, beneficial to their further protection work. [Display omitted] [ABSTRACT FROM AUTHOR]

• The morphological characteristics of BSCs on the earthen sites were analyzed. • We obtained the mechanical properties of BSCs on the earthen sites. • The research strategy to determine the effect of plant development in the surface layers of the earthen sites was proposed. Earthen sites are cultural and have rich historical significance. However, most earthen sites have been damaged or even destroyed during historic preservation. To reduce the damage caused by rain, snow erosion, freezing and thawing, these sites should be protected using vascular plant capping technology, which has great research value and application prospects. However, the effect of biological soil crusts (BSCs) on the shallow surfaces of these sites is scarcely understood. Therefore, this study aimed to explore the soil consolidation characteristics of BSCs on the shallow surfaces of earthen sites through laboratory experiments. First, the species, morphology and geometric characteristics of BSCs were studied using observation with a high–resolution digital microscope and analyses of the fractal and topological dimensions of rhizoids. The results showed that the dominant population of BSCs was composed of Didymodon vinealis , and the rhizoid type exhibited herringbone architecture. In addition, the effect of rhizoid anchoring was greater than that of rhizoid wedging. Second, the mechanical properties of the soil consolidation of the rhizoid–soil composite were investigated using tensile strength tests of single rhizoids and shear strength tests of rhizoid–soil composites. It was concluded that moss rhizoids could improve the shear strength of the surface soil. Additionally, the surface roughness of the rhizoids affected their anchorage characteristics. Finally, we discussed the disadvantages of generally classifying plants as "potentially harmful", and emphasized the necessity of constructing a heterogeneous research model highlighting specific environmental factors, plants, and earthen sites. [ABSTRACT FROM AUTHOR]