What Makes Cow-Dung Stabilised Earthen Block Water-Resistant

The water-resistance of cow-dung has made it a widely used stabiliser in traditional earthen structures in several Asian and African countries. Multiple studies have shown an improvement in water-resistance with the addition of cow-dung, but none provides insight into this behaviour. The present study investigates the water-resistance behaviour of cow-dung stabilised earthen blocks through an extensive experimental programme to identify and characterise the components of cow-dung responsible for its water-resistance. Fresh cow-dung was collected and separated into fibres (>63 μm), medium-sized microbial aggregates (1-63 μm) and small-sized microbial aggregates (0.5-7 μm). Each component was mixed with soil and samples were prepared at different water contents (optimum water content corresponding to the highest dry density and water content higher than optimum) and compacted with 2.5 MPa force to prepare compressed blocks. The water-resistance of these blocks was evaluated through the immersion and modified drip/rain test. It was found that the small-sized microbial aggregates are almost entirely responsible for water-resistance behaviour of cow-dung stabilised earthen blocks. Small-sized microbial aggregates were further characterised by gas chromatography, mercury intrusion porosimetry, N2- BET surface area, zeta potential measurement and electron microscopy. The results indicate that the small-sized microbial aggregates are composed of clay-sized negatively charged particles that are rich in fatty acids. The hydrophobicity of these particles is hypothesised to be responsible for water-resistance behaviour. These insights are further used to produce stabilised blocks that performed at least 30 times better than the unstabilised blocks in both water-resistance tests. The study concludes with practical recommendations for the use of wet cow-dung over dry cow-dung and a reduction of fibre content to increase the water-resistance of earthen blocks.

Overcoming the Perceptual Gap: Worldwide Perceived Comfort Survey of Earthen Building Experts and Homeowners

Earthen building materials are a critical future for sustainable construction because they are locally available, minimally processed, and waste-free. However, despite their advantages, earthen materials still face challenges for comprehensive implementation. First, their technical data vary significantly, making it challenging to quantify their true performance for different climates and environmental contexts. Second, people mistakenly perceive these materials as low-tech and poor in their performance. Lastly, building codes and standards do not comprehensively represent these materials worldwide. This work identifies perceptual barriers that hold back the broader implementation of earthen materials in order to ascertain possible solutions and assess the performance of earthen buildings and perceived comfort among primary resources such as practicing professionals and people who live in earthen houses. The results of an online survey of 126 earthen building experts and homeowners are presented, providing important insights regarding a range of barriers to, and motivating factors for, the implementation of earthen materials, as well as design and thermal performance aspects of existing earthen homes. The results of the surveys show that, of the various earthen building techniques, light straw clay requires the lowest maintenance, and construction of adobe and/or clay plaster encountered the least barriers to implementation. The energy performance of existing earthen homes show that all types of earthen materials reduce the need for cooling, in all climate zones. Insulation over earthen walls was shown to increase occupants’ perceived comfort levels, but only slightly. Additional results provide significant recommendations for future research on thermal performance and comfort guidelines for earthen structures. This study contributes to the development of environmental and policy measures that could be used by policymakers by synthesizing technical and environmental data and by identifying means of improving the perception of natural building.

Lateral Ground Spread at Kausaltar, Kathmandu that Appeared in the 2015 Gorkha Earthquake

The April 25, 2015 Gorkha earthquake jolted the central region of Nepal causing extensive damage to buildings and earthen structures in both mountainous and urban areas of Nepal. Kathmandu-Bhaktapur road, one section of the Araniko Highway, crosses a small valley in the center of the Kathmandu Basin with an embankment. This embankment and adjacent area were deformed in the earthquake. To examine the cause of this ground deformation, several in-situ tests such as micro-tremor measurements, standard penetration tests (SPT), multi-channel analyses of surface waves (MASW), and C 14 dating were conducted. These tests show that a silty sand layer with low plasticity has most likely been liquefied 5 to 8 meters underground. It is also shown that groundwater lowering using existing wells can decrease the liquefaction-prone area by 81%.

Fragility Curves for Slope Stability of Geogrid Reinforced River Levees

When constructing flood protection structures such as river levees, oftentimes due to various factors engineers must design composite structures, i.e., reinforced earthen structures which comply with all the stability criteria. The most common way of reinforcing such structures is the usage of geosynthetics, or mostly geogrids when talking about stability. Since geosynthetics are man-made materials produced in a controlled environment and go through quality control measures, their characteristics contain a negligible amount of uncertainty compared to natural soils. However, geosynthetic handling, their installation in the levee, and their long-term degradation can all have significant effects of variable magnitude on geosynthetic characteristics. These effects and their variability can be considered as random variables, which can then be used in probabilistic analyses together with soil properties. To investigate the effects of the geogrid’s resistance variability on slope stability compared to soil properties variability, probabilistic analyses are conducted on a river levee in northern Croatia. It is found that the geogrid’s variability generally has very little effect on the total uncertainty compared to the friction angle’s variability, but out of the three geogrid layers used the top grid has the most influence.

Numerical and experimental modeling of geomechanical behavior of partially saturated soils

The Barcelona Basic Model (BBM) has been implemented in a finite difference-based computer program to simulate the behavior of unsaturated soils subjected to wetting. The BBM implementation was verified using analytical solutions, and the proposed model has been used to simulate the response of a compacted embankment under complete saturation and suction induced conditions. Numerical analyses indicate that considerable amount of total and differential settlements could develop at the top surface of the embankment. BBM is executed into FLAC2D extending a defined module for modified Cam Clay (MCC) and has been set up an analytical solution for suction-dependent stress and strain. Evaluating the effect of anisotropy and nonlinear apparent tensile strength in unsaturated soils, a modification to BBM formulation has been proposed and optimized by developing numerical analyses to reduce the size of elastic region of loading collapse (LC) curve. Then, an experimental study in the literature is investigated by utilizing comparative curves from BBM and modified BBM indicating well agreement with natural circumstances. As a result of the work presented in this research, finite difference codes with BBM and modified BBM has the capability of simulating the real behavior and is operational being applied to problems associated with earthen structures in unsaturated or partially saturated of expansive soils as a three-phases medium.

HISTORICAL HERITAGE AS A CULTURAL RESOURCE. INTEGRATION OF THE NEW OBJECT INTO THE STRUCTURE OF A UNIQUE ARCHITECTURAL COMPLEX IN LALIBELA, ETHIOPIA. TECHNOLOGICAL AND ENVIRONMENTAL ASPECTS

The study is based on the material from an experiment on the renovation of a historical heritage complex in Lalibela, Ethiopia. The unique properties of rock architecture of churches created in the structure of rocky massifs, starting from the X and XI centuries, are supplemented by the specifi c character of folk construction of adjacent sett lements, using the technology of earthen structures. An important factor in the ongoing experiment to study the complex and (also to)build a hotel, the object of a developing tourist infrastructure, is the careful study of traditional technologies and environmental aspects, including climatic characteristics of the area, sources of energy supply, and relationships with the local community.

Paleoclimatic reconstructions based on the study of structures of large kurgans of the Bronze Age and soils buried under different structures for the steppe zone of Russia

<p>Geoarchaeological studies of soils buried under burial mounds (kurgans) and materials of kurgan structures make it possible to solve a wide range of scientific problems. In the steppe zone of Russia, such studies are carried out in order to determine and compare the composition of buried soils and materials of kurgan structures, as well as to study the structure of earth monuments and to obtain data on the technology used by ancient people for their building.</p><p>We carried out geoarchaeological studies in two key areas: in Krasnodar (kurgan Beisuzhek 9) and Stavropol (kurgan Essentuksky 1) regions. For each object, the particle-size distribution and physicochemical properties of the earthen materials of the kurgans and buried soils were investigated.</p><p>Kurgan Essentuksky 1 was built in the second quarter of the 4th millennium BC (Maykop culture) according to a single plan in a short time (several decades). The kurgan with a height of 5.5-6.0 m and a diameter of 60 m consisted of four earthen and three stone structures. The earthen structures consisted of alternating layers of dark, slightly compacted humified and light dense carbonate-rich material that were taken from buried soils, i.e. dark material from the Ahkb and AhBkb horizons, and light material from the B1kb horizon. This is confirmed by similar changes in the physicochemical properties of paleosols and overlying kurgan structures. A decrease in the organic carbon content and an increase in the content of calcium carbonate, values of pH<sub>H2O</sub> and magnetic susceptibility from the first to the fourth paleosols predetermined similar changes in the materials from the first to the fourth earthen structures (from the center to the periphery of the kurgan).</p><p>In the Beysuzhek 9 kurgan, three earthen structures of different ages were identified: the first and the second - the middle of the 2nd millennium BC (Novotitorovsk culture), the third construction - the beginning of the 2nd millennium BC (Catacomb culture). Each of the subsequent structures overlapped and went beyond the boundaries of the previous one: the second overlapped the first and also untouched soil next to the first; and the third overlapped the second completely and also overlapped previously uncovered soil next to the second structure. The height of the kurgan was more than 4 m, the diameter - about 100 m. The material of each structure was a soil mass from the middle horizons of the buried soils, most likely the Bkb horizon. Samples from the kurgan structures were taken from one column in the middle of the central baulk. Physicochemical analysis of paleosols and earthen structures overlying them showed a decrease in the content of organic carbon and magnetic susceptibility, an increase in the content of carbonate carbon and pH<sub>H2O</sub> from the center to the periphery of the kurgan.</p><p>According to the results of the physicochemical properties of paleosols and materials of both key areas in the second half of the 4th millennium BC there was a climate change in the study region - the average annual temperatures increased and the amount of precipitation decreased.</p>

Bottom Sediments from a Dam Reservoir as a Core in Embankments—Filtration and Stability: A Case Study

A possibility of using bottom sediments from dam reservoirs in earth structures was considered. Sediments from the Rzeszow reservoir (Poland) were used as research material, which, according to geotechnical standards, were classified as low permeable silt with high organic content. As fine, cohesive soil with a low coefficient of permeability, the sediments can be used in sealing elements of hydraulic engineering embankments. In order to verify the suitability of the sediments, stability and filtration calculations were carried out for embankments with a sealing in the form of a core made of the sediments. It was stated that by using a core made of sediments, the volume of seepage on the downstream side during continuous or variable backwater was significantly lower in relation to an embankment without a core, and the phreatic line did not extend to the downstream slope. It is estimated that, in the case of a planned dredging in Rzeszow Reservoir, the amount of dredged sediment would exceed 1.5 million m3, and therefore, the possibility of their economic use is essential. The search for materials that could replace natural soil in earthen structures is an important issue from both the ecological and economic points of view.