Earthen Sites Research Articles

Quantitative Assessment of the Peeling on Earthen Heritage Sites Using on Improved Rank Sum Ratio

ABSTRACT The peeling disease has caused the volume of the earthen site to recede over the years, seriously jeopardizing the longevity of the earthen sites. Accurately evaluating the degree of development of peeling disease is the key to carrying out conservation work. This paper organically combines the Decision Making Trial and Evaluation Laboratory, the multi-correlation coefficient, and the anti-entropy weight method in a weighted average combination, and assigns weights to the weight indicators of the rank sum ratio method. The improved RSR evaluation method comprehensively, objectively, and accurately evaluates the degree of peeling disease development at 18 earthen sites in the arid region of northwest China. The results show that 2, 7, and 8 earthen sites have very high, high, and moderate grades of peeling disease development, respectively. Comparison of the evaluation results of the regression values of peeling features using ridge regression verifies the accuracy of the evaluation results of the improved rank sum ratio approach. The improved rank sum ratio method proposed in this paper for the development of peeling disease at earthen sites is a robust assessment system. It lays the foundation for conservationists of earthen sites to make conservation decisions in a scientific manner.

Evaluating the impact threshold of soluble salts on preservation of earthen site in Emperor Qin Shi Huang’s mausoleum

The recurrent crystallization and subsequent volumetric expansion of soluble salts pose significant risks to earthen sites, particularly those with archaeological remains on their surfaces. Therefore, timing interventions based on salt content is crucial. This study focuses on the effects of soluble salt content on the earthen site within the burial pits of the Qin Mausoleum, with a particular emphasis on defining safe salinity levels. A mixture of Na2SO4/NaCl salts in a 1:1 mass ratio was added to remodelled soil cakes, which were then aged in a climate chamber for several months. The area of salt expansion on the soil cakes’ surfaces was measured using a deep-focus microscope to assess damage. The results indicate a sudden increase in salt expansion when salinity exceeded 0.1%. Additionally, re-evaluations of these soil cakes years later allowed for the exploration of mechanisms and the feasibility of assessing soil surface expansion and friability at different stages of the earthen site’s lifecycle, including excavation and display. These findings provide preliminary scientific bases and novel methodologies for the further preventive conservation of heritage earthen sites.

Mapping the susceptibility to freeze-thaw deterioration and regionalization of freeze-thaw environments of earthen sites in China: A preliminary study

Earthen sites in China are widely exposed to freeze-thaw environments. There is a lack of knowledge about the spatial distribution patterns of freeze-thaw deterioration and environments, as well as preventive conservation strategies and subsequent refined research on the freeze-thaw deterioration of earthen sites. In this study, the freeze-thaw deterioration process of earthen sites was divided into two periods. Thirteen relevant factors were selected, and using the GIS-FAHP method, a susceptibility map for freeze-thaw deterioration of earthen sites in China was created. The Jenks Natural Breaks method was then employed to categorize the areas into five susceptibility levels: very low (24.6 %), low (18.2 %), moderate (24.2 %), high (18.2 %) and very high (14.8 %). Based on the susceptibility map, the three-level regionalization scheme for freeze-thaw environments of earthen sites in China was systematically developed, taking into account the differences in freeze-thaw deterioration susceptibility and natural landscape within the geomorphological units, and the environmental codes were assigned to third level small-regions. The freeze-thaw environments of earthen sites in China were finally divided into 5 major-regions, 20 sub-regions and 42 small-regions. The results showed that in the area east of the Heihe-Tengchong line, the susceptibility to freeze-thaw deterioration showed latitudinal correlation, and the susceptibility gradually increased from south to north; in the area west of the Heihe-Tengchong line, the susceptibility to freeze-thaw deterioration exhibited strong zonal characteristics. Among the provincial administrative units, Gansu Province and Xinjiang Uighur Autonomous Region have the most complex freeze-thaw environments, while Qinghai, Tibet, Sichuan and Heilongjiang Provinces have the harshest freeze-thaw environments. This study can support regional management and prevention of freeze-thaw deterioration and deterioration studies of earthen sites in China.

Effect of In Situ Polymerization of Super Absorbent Polymers on the Protection of Earthen Heritage Sites in Semi-Arid Regions

As precious cultural heritage, earthen sites are susceptible to various natural factors, leading to diverse forms of degradation. To protect earthen sites, the effects of super absorbent polymers (SAPs) on soil water retention, physical properties, and color compatibility at different concentrations were studied. After applying SAP treatment to an earthen site with different degrees of weathering, we drew the following conclusions. SAP-2 improved soil water retention capacity, increased soil water content, and slowed down the precipitation of soluble salts. At the same time, SAP-2 had the least effect on soil color difference and reduced the development of cracks by filling soil pores and enhancing the cohesion between soil particles, thus giving the earthen sites better weathering resistance. Therefore, the results provide a useful reference for the surface cracking of earthen sites in semi-arid areas and the degradation caused by flaking and block spalling.

Characterization on Flaking of Rammed Earthen Sites Using SMO Algorithm and Surface Topography Analysis: A Case Study of Jiaohe Ruins

There are a large number of rammed earthen sites in northwest China. For thousands of years, earthen sites have developed a series of deterioration types that include surface weathering, sapping, cracks, collapses, gullies, and so on. Surface weathering is a highly destructive type of soil deterioration which erodes the sites all the time. Flake peeling (flaking) is one of the main manifestations of weathering. In order to prevent flaking more scientifically and efficiently, it is necessary to quantitatively evaluate its development stage and degree. In this article, the Vajra Pagoda of Jiaohe Ruins was selected as the research area, and we explored how to use GIS to analyze the surface topography of 3D scanning data. Meanwhile, using the sequential minimum optimization (SMO) algorithm, the authors effectively identify the crust and original wall (wall outcroppings following the detachment of crust) in the evolution of flaking. Finally, the 3D roughness of the four facades was calculated. The calculations show that the roughness parameters D and R s can well characterize the development of flaking. In a period of flaking development, the change rule of D and R s first increases and then decreases. This study proves that it is feasible to quantify the development degree of flaking employing morphological characteristic parameters. Furthermore, the results of the study provide a basis for determining the degree of deterioration of the sites in future heritage management efforts, leading to more rational and efficient conservation.

Plant investigation and the impact on earthen site soil properties in the east city wall of the Sanxingdui site

In southern China, vegetation on exposed earthen sites serves not only to mitigate erosion but also alters their visual appearance, leading to biodeterioration. However, how plants influence the properties of earthen sites is virtually unknown. This study undertook an ecological investigation of the original habitat in the east city wall of the Sanxingdui site, analyzing its soil properties and investigating plant-soil interactions. Research findings indicate that existing plant communities are not conducive to biodiversity nor site presentation. Plants exert a direct influence within a vertical range extending 0–40 cm beneath the site; root content correlates negatively with soil pH value but positively with organic matter content. The herbaceous community (E-2 and E-3) exhibits higher clay content than the arbor community (E-1) within this range. The above conclusions exhibit statistical significance. This study offers a scientific elucidation of the ecological parameters governing plant communities concerning the conservation of earthen sites, and provides an initial influence range of plant communities and biodegradation on the east city wall of the Sanxingdui sites, thereby revealing the technical potential for employing plants as a soft capping for earthen sites in the open air from the function method.

Enhanced Water Resistance of TiO2-GO-SMS-Modified Soil Composite for Use as a Repair Material in Earthen Sites.

Most earthen sites are located in open environments eroded by wind and rain, resulting in spalling and cracking caused by shrinkage due to constant water absorption and loss. Together, these issues seriously affect the stability of such sites. Gypsum-lime-modified soil offers relatively strong mechanical properties but poor water resistance. If such soil becomes damp or immersed in water, its strength is significantly reduced, making it unviable for use as a material in the preparation of earthen sites. In this study, we achieved the composite addition of a certain amount of sodium methyl silicate (SMS), titanium dioxide (TiO2), and graphene oxide (GO) into gypsum-lime-modified soil and analyzed the microstructural evolution of the composite-modified soil using characterization methods such as XRD, SEM, and EDS. A comparative study was conducted on changes in the mechanical properties of the composite-modified soil and original soil before and after immersion using water erosion, unconfined compression (UCS), and unconsolidated undrained (UU) triaxial compression tests. These analyses revealed the micro-mechanisms for improving the waterproof performance of the composite-modified soil. The results showed that the addition of SMS, TiO2, and GO did not change the crystal structure or composition of the original soil. In addition, TiO2 and GO were evenly distributed between the modified soil particles, playing a positive role in filling and stabilizing the structure of the modified soil. After being immersed in water for one hour, the original soil experienced structural instability leading to collapse. While the water absorption rate of the composite-modified soil was only 0.84%, its unconfined compressive strength was 4.88 MPa (the strength retention rate before and after immersion was as high as 93.1%), and the shear strength was 614 kPa (the strength retention rate before and after immersion was as high as 96.7%).

Revamp of the eco-friendly grouting materials by mixing basalt fiber for earthen sites conservation: Compressive performance and constitutive models

Reinforcement techniques, including anchorage and sealing with grout, are frequently employed to protect earthen sites and minimize the impact of fissures, the effectiveness of these approaches relies heavily on the mechanical properties of grout. To enhance the strength and ductility of the conventional grout, an eco-friendly composite grouting material mixture basalt fibers of varying lengths and contents is prepared. The DIC-based UCS tests were conducted to evaluate its compressive performance. Constitutive models of the basalt fiber-reinforced grout, including elastic perfectly-plastic (EPP) and median nonlinear (MNL) constitutive models, were established respectively based on the equal energy rule and cross-sectional data analysis for simplification application and precision evaluation purposes. The results show that the mixture of basalt fibers resulted in a distinct semi-brittle failure mode for the grout, with a significant increase in its compressive strength, ductility, compressive fracture energy, and residual bearing capacity. However, the elastic modulus will be lower when the fibers are relatively longer. Considering the differences in the relations between performance parameters and fiber content, and length, the highest compressive strength was reached at the fiber length of 6 mm and the content of 0.2 wt%, while maximum ductility was achieved at 18 mm and 0.4 wt%. The fracture energy exhibits an approximate positive correlation with fiber content. In addition, the EPP and MNL constitutive models can effectively characterize the compressive mechanical behavior of semi-brittle materials to satisfy different requirements on the precision of engineering analysis. This study contributes valuable insights into the development of high-ductility grouting materials of earthen sites, and the establishment of constitutive models for semi-brittle materials.

Effects of superplasticizer on properties of calcined ginger nuts-based grouting material for earthen site cracks

Grout injection is an effective technique for repairing cracks in earthen sites. This study aims to address the challenges of Calcined Ginger Nuts (CGN)-based grout and enhance its engineering performance by investigating the compatibility of different superplasticizers. We examined the effects of Polycarboxylate Superplasticizer (PCE) and Naphthalene Superplasticizer (PNS) on the properties of CGN-based grout, focusing on fluidity, rheological properties, mechanical strength, volume stability, color difference, and pore structure. The engineering applicability of the optimized CGN-based grout with superplasticizers was assessed using COMSOL Multiphysics. The results show that fluidity increased with higher dosages of PCE and PNS. The grout containing these superplasticizers behaved as a shear-thinning fluid, following the power law model. Specifically, the consistency coefficient of grout with 0.5 wt% PCE and PNS decreased by 39.73% and 64.83%, respectively. Additionally, 2.9 wt% PCE and PNS reduced volume shrinkage rate by 6.86% and 6.27%, respectively. Initially, increasing the dosage of PCE and PNS improved compressive and flexural strength, but these properties later declined. XRD analysis revealed that PNS above 1.1 wt% and PCE weakened the hydration reaction, while both superplasticizers promoted carbonation. Mercury Intrusion Porosimetry (MIP) showed that 1.1 wt% PCE and PNS reduced the proportion of capillary pores by 13.79% and 10.11%, respectively. Based on these findings, 0.5 wt% PNS demonstrated the best compatibility with CGN-based grout, whereas PCE showed poor compatibility. Numerical simulations using COMSOL Multiphysics confirmed that 0.5 wt% PNS provided superior grouting effectiveness. Therefore, the CGN based grout with 0.5wt% PNS demonstrates excellent engineering performance and applicability. This study offers valuable insights into optimizing CGN-based grout for the preservation of earthen sites.

Rising damp in heritage sites under urban expansion: A comprehensive case study of the Jinsha Earthen Site

Rising damp poses a significant threat to cultural heritage, yet its dynamics within actual heritage sites remain inadequately understood, particularly regarding its evolution and the impact of urbanization. The Jinsha Site, an earthen site from the Shang periods, is primarily composed of silt, with a layer of sand beneath and pebbles at the bottom, making it susceptible to rising damp. This study investigates the Jinsha Site as a case, monitoring soil water content and electrical conductivity, tracking changes in groundwater, precipitation, and river water levels, and investigating the relationship between urbanization and rising damp. The study aims to understand the process, causes, and influencing factors of rising damp and evaluate previous preservation strategies. The findings indicate that groundwater level in the sand layer trigger dampness, whereas the pebble layer exhibits dryness. Urban construction from 2006 to 2013 and 2014–2017 caused fluctuating groundwater levels, leading to repeated transitions between dryness and dampness at the site. Rainfall and river levels have negligible effect; even rainfall exceeding 100 mm (frequency <0.0056) only raises groundwater levels by approximately 1 m and increases water content by less than 2 % for a brief duration, typically less than half a month. The 2022 groundwater pumping strategy effectively maintained levels beneath the pebble layer (506 m), decreasing moisture by 12.71 % and conductivity by 0.27 dS/m. This study reflects on previous protection effortsand offers evidence-based strategies for heritage conservation amidst urban expansion.

Vascular plants and biocrusts ameliorate soil properties serving to increase the stability of the Great Wall of China

The Great Wall, as a World Heritage Site, is constructed with rammed earth and is currently facing the threat of erosion from wind and rain. Vascular plants and biocrusts are the main coverings of the Great Wall, and their role in mitigating soil erosion has attracted increased amounts of attention; however, the understanding of their underlying mechanisms is limited. Here, we conducted an extensive survey of vascular plants, biocrusts, soil properties (soil organic and inorganic binding materials, aggregates, and texture), soil aggregate stability, and soil erodibility at the top of the Great Wall in four different defensive zones in Northwest China. Vascular plants covered 13.6 % to 63.9 % of the tops of the Great Wall, and their rich diversity was mainly derived from perennial herbs. Moss, lichen, and cyanobacterial crusts collectively covered 36.3 % to 67.8 % of the top of the Great Wall. Redundancy analysis and structural equation modeling revealed that the synergistic effects of vascular plants and biocrusts enhanced soil aggregation stability (including geometric mean diameter, GMD; water-stable macroaggregate content, R) by increasing the accumulation of soil organic carbon (SOC), amorphous iron oxide (Feo), and amorphous alumina (Alo) and promoting the formation of macroaggregates (ASD>0.25 mm) and microaggregates (ASD0.053-0.25 mm). Furthermore, soil erodibility was primarily influenced negatively by the synergistic promotion of SOC accumulation by vascular plants and biocrusts and positively by the reduction in soil sand (PSD>0.05 mm) content by biocrusts. Our work highlights the mechanisms and importance of vascular plants and biocrusts as natural covers for altering the intrinsic properties of soil for the protection of the Great Wall. These findings provide reliable theoretical support for the protection of the Great Wall from erosion by vascular plants and biocrusts and offer new insights for the conservation of global earthen sites and similar wall habitats.

An approach based on P-wave velocity for grouting effectiveness evaluation in earthen sites

Grouting technology is the primary method for repairing cracks in earthen sites. However, there has been a long-standing lack of effective methods for evaluating grouting effectiveness. This paper proposes a field evaluation method based on P-wave velocity. This method explicitly discusses two scenarios where the P-wave velocity of the grout is either higher or lower than that of the soil, using the depth ℎ of the “hypothetical crack” as the evaluation indicator. The experimental results indicate that specimens with 20% and 40% defects show increases in ℎ values of 0.0113 m and 0.0166 m, respectively. Laboratory tests have demonstrated that this method can accurately evaluate grouting effectiveness and is not affected by the P-wave velocity of the soil. The application of this evaluation method to three typical earthen sites resulted in more reliable and easily quantifiable evaluation outcomes. By considering the width of grout, the method provides a more intuitive comparison of reparation effectiveness. The study demonstrates the feasibility of the proposed method, thereby facilitating effective crack reparation in earthen sites.

Experimental and Numerical Investigation on Group Anchor Performance of Wooden Bolts in Rammed Earthen Sites

ABSTRACT Challenges remain in understanding the interaction mechanisms and influencing factors of multi-anchor systems. To investigate this matter, this study conducted nine full-scale model experiments examining the pulling resistance and failure modes of wood bolts embedded in rammed earth. These experiments varied bolt numbers (2, 3, 4), spacings (500 mm, 1000 mm, 1500 mm), and embedment depths (200 mm, 300 mm, 400 mm). Key factors and their levels for the group anchoring effect in the model tests were determined through orthogonal analysis. Among these factors, embedment depth exerted the most significant influence on pulling resistance, followed by bolt spacing and number. Furthermore, a numerical simulation method for wooden anchor group systems was developed using the “contact surface” element in FLAC 3D finite difference simulation software. This method considered factors such as bolt number, spacing, edges, embedment depth, and the layered nature of the compacted soil. It analyzed stress distribution and transmission laws across various interfaces within the anchoring system and the compacted soil, thereby supplementing and expanding upon the findings of the model experiments. These findings enhance understanding of the complex interplay between multi-anchor systems and soil, providing a scientific foundation for analyzing mechanical behavior in similar anchoring applications.

Natural Capping Enhancing the Resilience of Earthen Heritage Under Rainfall Impacts

ABSTRACT Soft capping has proven effective in enhancing masonry ruins in humid regions. To-date, there are limited studies on the use of soft capping for earthen heritage in arid and semi-arid regions. Considering the diverse climatic conditions and the presence of vegetation on the Northern China earthen sites, there is an urgent need to study the effect of these vegetations on earthen heritage sites. As the plant species used in the previous studies are mainly based on artificial selection, we propose to use native plant species that are typically found in the study site and define the application of native plant species as ‘natural capping’. Taking the Ming dynasty Shanxi Great Wall sections as case study, four scale-down rammed earth test walls were subjected to rainfall tests under four patterns of rainfall once. Results showed that native plants excel in Northern climates. Under moderate rainfall, the moisture at the wall head of natural capping walls is nearly constant. However, when subjected to heavy and extreme rainfall, natural capping walls reduced inner wall moisture infiltration by 5.56%–7.52% and material loss by 58.24%–75.04%. Post-rainfall monitoring demonstrated that natural capping has sustainable benefits for temperature and moisture reduction in summer.

Experimental study on improving the performance of imitation earthen site soil in carbon dioxide environment

This study aims to explore the performance of lime-treated soil for repairing the lime soil of the earthen city wall of Kaifeng and to standardize the construction technology of lime-treated soil. The research comprehensively considered factors such as carbonation time, lime particle size, aging conditions, and lime content, and conducted various tests and analyses including triaxial mechanical properties, surface crack analysis, particle size distribution, pH measurement, composition analysis, and electron microscopy on different samples. The results indicate that the significant effect of high-concentration CO2 carbonation enhances the chemical reactions of lime soil, and an appropriate carbonation process can strengthen the bonding and density between soil particles. Under the maintenance condition of 5 % CO2, with increasing carbonation time, the crack ratio, average crack length, and average crack width of the samples decreased. Cohesion and internal friction angle of the samples exhibited an initial increase followed by a decrease, while shear strength of the samples increased by 22.93 %–75.09 %. The lime particle size has a critical impact on the formation of cracks in lime soil. With increasing lime particle size, the crack ratio, average crack length, and average crack width of the samples increased. Cohesion and internal friction angle of the samples gradually increased with increasing lime content. The increase in crack ratio, average crack length, and average crack width during natural curing of lime-treated soil samples was proportional to the lime content. Appropriate carbonation time, smaller lime particle size, and curing conditions with 5 % CO2 contribute to improving the particle size distribution of lime-treated soil samples, reducing surface cracks, and enhancing performance. However, prolonged carbonation may lead to larger lime particle size, resulting in rough and loose particles, disorganized arrangement of CaCO3 crystals, and the inability to form a cross-linked network skeleton, causing a reduction in shear strength of the samples. These research findings provide important theoretical basis and construction technology guidance for the application of lime-treated soil combined with CO2 carbonation in repairing earthen city walls.

Sustainable and Collaborative Solutions for the Long-term Care of Heritage Earthen Sites in Seismic Areas in Peru

ABSTRACT The challenges posed by conserving historical earthen structures in seismic-prone regions prompted the initiation of the Seismic Retrofitting Project (SRP) by the Getty Conservation Institute (GCI) and the Ministry of Culture of Peru. Since 2009, the SRP has aimed to enhance the structural performance and safety of historic earthen buildings while preserving their historical fabric by combining traditional techniques, local materials, and technical expertise with advanced computational tools. The project has focused on four Peruvian earthen buildings as case studies, including the seventeenth-century adobe church of Kuñotambo. An intervention was carried out between 2016 and 2019 by the regional branch of the Ministry of Culture in Cusco based on techniques developed by the SRP. The GCI is now working on a monitoring and maintenance plan for the site, collaborating with local stakeholders, including the Ministry of Culture of Peru in Cusco, the Archdiocese of Cusco, and the community of Kuñotambo. This paper primarily discusses the practical aspects of on-site monitoring, including the tools and techniques used to track changes in the building and its decorated surfaces. It also outlines the implementation of a structural health monitoring system and the development of capacity-building activities for Latin American engineers. The overarching goal is to provide a sustainable framework for the long-term preservation of historic earthen structures in seismic-prone regions, highlighting the importance of community involvement and multidisciplinary collaboration.

Study on the salt-dissipating and settlement-preventing performance of composite modified cushion layers in the roof-propping body of earthen sites' basal sapping zone

Cushion layer replacement is currently an important method for preventing and treating salinized deterioration in the earthen sites' basal sapping zone. The water resistance, salt-dissipating property, and load-bearing capacity are key indicators for evaluating the effectiveness of capping replacement. In this study, gravel is an inorganic admixture for the calcareous soil base material. Prepared 19 soil samples through the cross-combination of gravel with three types of organic binders. These samples were subjected to tests on wave velocity, volume shrinkage, permeability, capillary rise, and consolidation. The suitability of the composite materials for reinforcing the rammed earth heritage capping layers was further studied using the AHP-CRITIC-TOPSIS method. The results show that: (1) The wave velocity and volume shrinkage rate of the samples increased over time and reached stability after 7 days. Moreover, the water resistance, salt dissipation, and load-bearing capacity of the samples were significantly enhanced; (2) Comprehensively evaluating the suitability of the composite materials for the capping layers in the earthen sites' basal sapping zone using six indicators: wave velocity, volume shrinkage rate, permeability coefficient, capillary water absorption rate, compression coefficient, and final settlement, it was found that the SMS-S: G7:3 mixture showed the best suitability. This study provides a reliable theoretical basis for the restoration of earthen sites in the arid areas of Northwest China.

The effects of herbs on the runoff and sediment-producing mechanism in Jinyang Ancient City

Abstract To study the effects of herbs on the runoff and sediment producing mechanism of Jinyang Ancient City, this study used the method of field artificial rainfall experiments to compare the earthen sites slope effects on the runoff producing, sediment producing, and soil infiltration of the plant slope surface in different periods. The conclusions are as follows. The phenomenon of petrichor was related to the withered herb coverage on the surface of the slope. The fluctuation amplitude of the soil volume moisture content was related to its distance to the surface. The runoff producing effects of different slopes were in descending order of Bare Soil slope, Fresh Herbs slope, and Withered Herbs slope. The sediment producing effects were in descending order of Bare Soil slope, Withered Herbs slope, and Fresh Herbs slope. The sediment yield intensity was positively correlated with runoff intensity, but its variation peak lagged slightly behind the latter. The runoff intensity and sediment yield was influenced by the dual effects of rainfall intensity and rainfall time, and sometimes the impact of rainfall time was higher than that of rainfall intensity. A research assistance in can be hopefully provided in this study on protecting earthen sites from rainfall erosion through plant covering.

Research on Calculation of Porosity of Rammed Soil in Pingyao City wall (China) Based on Scanning Electron Microscope Images

ABSTRACT Porosity is an important parameter that affects the deformation, mechanical properties, and constitutive relationships of soil structures. It can be used as an important basis for deterioration research and safety assessment in the field of earth site protection. By collecting scanning electron microscope images (SEM) of the rammed earth of the ancient city wall of Pingyao, a world cultural heritage, and using software such as ImageJ and MATLAB to analyze the characteristics of the images from two-dimensional and three-dimensional perspectives, the relationship between threshold and porosity was studied and summarized. It was found that using the Boltzmann function eigenvalue as the control threshold can well characterize the two-dimensional porosity of soil. Using the idea of integration, the binary slice images with different thresholds are simplified and accumulated to construct a three-dimensional image porosity calculation model. Write a three-dimensional pore characteristic parameter program to extract the statistical image grayscale information and perform normal fitting. Based on the probability interval of the image grayscale distribution, calculate the threshold interval that can effectively reflect the three-dimensional pore characteristics of the soil. This research has important theoretical and practical significance for the protection research of earthen sites.

Impact of soil density on biomineralization using EICP and MICP techniques for earthen sites consolidation

Enzyme-induced calcium carbonate precipitation (EICP) and microbially-induced calcium carbonate precipitation (MICP) techniques represent emerging trends in soil stabilization. However, the impact of soil density on biomineralization, particularly in historical earthen sites, remains unclear. This study compares the consolidation effects of EICP and MICP on cylindrical samples (10 cm × 5 cm) with three densities (1.5 g/cm3, 1.6 g/cm3, and 1.7 g/cm3) derived from the soil near the UNESCO World Cultural Heritage Site of Suoyang Ancient City, Gansu Province, China. Results showed that calcium carbonate production increased across all densities through bio-cementation, with higher densities producing more calcium carbonate. MICP-treated specimens exhibited larger increases in calcium carbonate production compared to those treated with EICP. Specimens with a density of 1.7 g/cm³ showed a wave velocity increase of 3.26% (EICP) and 7.13% (MICP), and an unconfined compressive strength increase of 8% (EICP) and 26% (MICP). These strength increases correlated with the generation of calcium carbonate. The findings suggest that biomineralization can be effectively utilized for in situ consolidation of earthen sites, emphasizing the importance of considering soil density in biologically-based conservation technologies. Furthermore, MICP shows potential advantages over EICP in providing stronger, compatible and more sustainable soil reinforcement.