Average Dry Density Research Articles

Analysis of the mechanical effects and influencing factors of cut-fill interface within loess subgrade

Cut-fill interfaces within the loess subgrade tend to form potential failure surfaces, controlling the mechanical properties of cut-fill engineering. Focusing on the cut-fill interface, extensive laboratory tests in this research show the performance of interfacial mechanical properties under various test conditions, revealing interface effects and exploring the impact of different factors on these effects. The results indicate that the interface strengthens the friction angle of soil but weakens cohesion, especially impacting the cohesion, thereby reducing the shear strength of soil. The increase in dry density diminishes the enhancement effect on friction angle caused by the interface while amplifying the degradation effect on cohesion. Elevated water content has a weak influence on the enhancement effect of friction angle but diminishes the degradation effect of cohesion. Load doesn't change the impact of dry density on the interface effect but amplifies the impact of water content. The impact of various factors on interfacial shear strength manifests as follows: load > average dry density > water content. The interaction among these factors demonstrates average dry density + load > water content + load > average dry density + water content. The study indicates that the construction of loess subgrades based on the standard of maximum dry density and optimum water content may not align with the conditions required for achieving optimal stability at the cut-fill interface. These research findings reveal the crucial role of various factors in comprehensive impact of interfacial effect, offering essential support for ensuring the stability of cut-fill interfaces.

Research on the possibility of manufacturing aerated-foam concrete with a variatropic structure based on aluminum powder and eabassoc foaming agent

This article presents some experimental research results on the composition and properties of aerated-foam concrete with a variable structure using available materials in Vietnam. To obtain concrete products containing anisotropic pores from the central area to the periphery, this study proposed fabricating cubic wooden molds with four perforated mold walls. The diameter of the pores is 1.5 mm and the distance between these pores is 10 mm. The pre-punching of hollow holes in the four mold wall panels is to remove excess gas and liquid phases during the setting and solidification process and form the internal variable structure of the air-foam concrete product. Experimental research results have shown that it is possible to produce anisotropic aerated-foam concrete with an average dry density of about 1459 kg/m3; the average compressive strength at the ages of 7 days, 14 days, and 28 days are 18.2 MPa; 21.2 MPa and 28.7 MPa, respectively. Besides, this study also compares the properties of anisotropic aerated-foam concrete with conventional foam concrete and aerated concrete. The obtained results show that the physical and mechanical properties of aerated-foam concrete with the variable structure are better than conventional foam concrete and aerated concrete with the same density.

Heated fibre-optic cable installed in compacted bentonite layers: numerical evaluation of influences of the compaction-induced variability on thermal conductivity estimation

Active heating of fibre-optic (FO) cable combined with distributed temperature sensing has been applied as a quality control tool for emplacing granulated bentonite buffer. For calibrating the tool, the FO cable is installed in specimens with known dry densities. Layer-by-layer compaction is often employed to prepare the specimens. Although the average dry density is guaranteed, some studies report possible variations in the dry density within a layer. In this study, heat transfer from a heated FO cable installed in granulated bentonite with different compaction-induced variabilities was numerically simulated. The reference case used homogeneous bentonite with an average dry density of 1.5 g cm −3 . For three other cases the granulated bentonite was filled in two, three and four layers, respectively, each of which had a distinct dry density gradient ranging from 1.3 to 1.7 g cm −3 . For each case, the FO cable placed at the centre of the container was numerically heated, and the thermal conductivity was calculated using temperature changes. In the cases where the FO cable was placed on the layer interface at which the dry density was discontinuous, the calculated apparent thermal conductivity was found to have been underestimated with an error of as much as 4%. In the other two cases, the thermal conductivities obtained were nearly identical to those corresponding to the average dry density. The influence of the compaction-induced variability in the dry density was found to be insignificant and the estimated thermal conductivity was essentially that of the bentonite represented by its average dry density. Thematic collection: This article is part of the Sustainable geological disposal and containment of radioactive waste collection available at: https://www.lyellcollection.org/topic/collections/radioactive

Field Test Study of Performance of Bored Piles in Collapsible Loess

Bored piles comprise an advanced pile foundation technology that has the advantages of high bearing capacity, fast construction speed, stable construction technology, and no noise or mud pollution. To study the applicability of bored piles to collapsible loess sites, the compaction effect and load-bearing characteristics of bored piles before and after immersion were studied via a full-scale field test combined with the theory of hole expansion. The results indicate that when the pile spacing is 1.0, 1.25, and 1.5 m, the average dry density of the soil between piles increases by 23.8%, 18.5%, and 3.1%, respectively, compared with that of untreated foundation soil. When bored piles are used to treat deep collapsible loess foundations, the reasonable pile spacing to eliminate the collapsibility of the loess foundation is 2.5 times the pile diameter. It is feasible to estimate the effective compaction range using the pore expansion theory, and the effective compaction coefficients of similar sites are given. The positive friction of bored piles in the collapsible loess area is more than 95.5 kPa, which increases by more than 48.5% compared with that of non-extruded piles. Therefore, the bearing capacity of a single pile is significantly improved, and it is an effective treatment method for collapsible loess areas. Under immersion, the pile side negative friction did not change significantly with a pile diameter of approximately 27 kPa, and the increase was approximately 14% compared with that of non-extruded piles. Consequently, to avoid the adverse effects of negative friction resistance on the bearing capacity of pile foundations and to fully utilize the technical advantages of bored piles, it is necessary to eliminate or partially eliminate site collapsibility before applying bored piles. The results can provide experimental support and theoretical guidance for the popularization and application of screw–squeeze piles in deep, collapsible loess areas.

Aerated Concrete with Geopolymer Binder from Technogenic Waste

Aerated concrete is a material widely used in Vietnam due to several advantages over heavy concrete. This article presents some results of experimental studies of the properties of aerated concrete produced using geopolymer binder from industrial waste generated in large quantities in Vietnam. The raw materials used included thermal power plant fly ash, blast furnace slag, ceramic powder, aluminum powder and an activating alkaline solution consisting of aqueous solutions of sodium hydroxide and sodium metasilicate. Testing of aerated concrete samples of the developed compositions was carried out in accordance with current Russian and Vietnamese standards. Experimental results confirmed the possibility of producing aerated concrete with a geopolymer binder based on large-tonnage technogenic waste, with an average dry density of less than 1600 kg/m3 and a compressive strength at the age of hardening of 28 days of 18.8–27.9 MPa. At the same time, aerated concrete containing 0.456 kg/m3 of aluminum powder and 50% wt. showed the greatest strength. blast furnace slag in the composition of the geopolymer binder, with a ratio of activating alkaline solution and active mineral additives equal to 0.4.

Compaction-induced variability in the 80/20 sand-bentonite mixture: Spatial variation in dry density at different scales in the laboratory and large-scale gas seal test

Sand-bentonite (SB) mixtures are considered as backfill materials for sealing designated sections of nuclear waste repositories. The dry density of the SB mixture is the crucial parameter for the quality control during emplacement because it strongly controls the hydraulic and mechanical properties. Backfilling of an SB mixture is often performed layer by layer by keeping track of the average dry density of each layer. The compaction is typically done in a dynamic manner leading to more compaction near the compaction surface. In this study, an SB mixture with 80% sand and 20% bentonite was compacted in the laboratory by static and dynamic procedures to a height of 10 cm and the dry density profile was characterized by destructive slicing and microfocus X-ray CT imaging. When dynamically compacted, a distinct dry density gradient was identified. The variation in the dry density identified by the slicing was as much as 0.4 g/cm3 which leads to hydraulic conductivity variation by a factor of 4.8. The SB seal emplaced in the large-scale gas seal test (GAST) for demonstrating the effective functioning of the gas permeable seals was also analyzed to identify if any variability was present at the field scale. The samples collected from the top 2 cm of each 10 cm-thick horizontal layers yielded a higher overall average by 0.06 g/cm3 than the average of the mass balance method. In conjunction with the laboratory studies, it was implied that sampling results, if only collected from the very top few centimeters of the layers, could lead to an overestimation in the global dry density. Overall, the results with different methods at different scales indicated that the dynamic compaction-induced variability within a single layer was more pronounced than the variability in the larger scales detected in the mass balance and sampling methods.

The Effect of Addition Superplasticizer (Sikament-LN) with Variation of Percentage on Compressive Strength Foamed Mortar Lightweight Materials

The foamed mortar (morbus) lightweight material consists of a mixture of sand, cement, water, and liquid foam (foam agent), which can improve the mechanical properties of clay soil and increase its bearing capacity. This research uses various variations of superplasticizer mixtures, namely by adding additional ingredients in the form of sikament-LN which will increase compressive strength by up to 40% at 28 days. This research needs to be carried out to determine the effect of sikament-LN on increasing the compressive strength of foamed mortar. The percentages of the sikament-LN mixture were 0.5%, 0.75%, 1%, and 1.25% with ages of 7, 14, and 28 days, each of which made 3 test objects in 4 variations of the mixture. The research results showed that the addition of sikament-LN to the 1.25% mixture did not meet the requirements because it produced a flowability of 23.5 cm and the mixture experienced a shrinkage of > 20% when placed in a cylindrical mold. All foamed mortar specimens experienced an average dry density increase of 1.994% at a curing age of 7 to 14 days and an average dry density increase of 4.044% at a curing age of 7 to 28 days. In a mixture of 0.5%, 0.75%, and 1%, at 28 days the maximum compressive strength value obtained was 841,667 kPa (more than the required 800 kPa). For the sikament-LN mixture, a maximum of 1% of the cement weight is recommended so that the hardening process occurs in the foamed mortar test object.

Performance of screw piles in thick collapsible loess

The bearing capacity of the composite foundation would be significantly increased by the squeezing effect of soil displacement screw pile. To investigate the effect of soil displacement screw pile treatment on the large-thickness collapsible loess foundation, full-scale field tests and pore expansion theory were used to compare the physical and mechanical properties of the soil around the pile before and after soil displacement screw pile treatment. It was found that the maximum influence range of a single pile in loess foundation was 3D, and the effective influence range was 2.5D. Compared with natural foundation, the average dry density of soil between two and three piles increased by 23 % and 15 %, and the compression coefficient decreased by 57 % and 38 %, respectively, when the pile spacing was 2.0D and 2.5D. The collapsibility coefficient and self-weight collapsibility of soil between two and three piles were far less than 0.015 when the pile spacing was less than or equal to 2.5D. The soil deformation caused by compaction was mainly plastic deformation. The plastic zone radius calculated by pore expansion theory can be used to estimate the compaction range of soil displacement screw piles in large-thickness loess regions. When the pile spacing was 2D and 2.5D, compared with the natural foundation, the characteristic values of soil bearing capacity between piles increased by 60 % and 30 %, that soil displacement screw pile of plain soil composite foundation increased by 220 % and 200 %, and that of plain concrete soil displacement screw pile increases by 450 % and 400 %, respectively. It shows that a soil displacement screw pile can significantly increase the bearing capacity of a large-thickness collapsible loess foundation. When the area replacement rate was 0.145–0.23, the pile-soil stress ratio of soil displacement screw piles in large-thickness collapsible loess region ranged from 2.6 to 4.7.

THERMAL INSULATION PERLITE CONCRETE GRADES D150 and D200

The article presents the results of research on the development of compositions and the study of the physico-mechanical properties of particularly light perlite concrete. It has been found that the use of foam makes it possible to dramatically increase the volume of cement dough, which makes it possible to mix the solution with brittle, weakly strong grains of expanded perlite sand. As a result of experimental studies, perlite concrete was obtained with an average dry density of 150-200 kg/m3, compressive strength of 0.32-0.43 MPa, thermal conductivity coefficient of 0.048-0.052 W / (m · ° C). The plates are designed for thermal insulation of residential and public buildings. In the conditions of Almaty, with a plate thickness of 10 cm, the required thermal protection of external structures of buildings is provided.

Investigation of the emplacement dry density of granulated bentonite mixtures using dielectric, mass-balance and actively heated fiber-optic distributed temperature sensing methods

Granulated bentonite mixture (GBM) is considered to be one of the key elements of the engineered barrier system in the Swiss concept for disposal of spent fuel/vitrified high-level waste. To demonstrate the full-scale emplacement of GBM using a prototype backfilling machine consisting of five screw feeders, an 8-m-long mock-up tunnel in a warehouse and a 50-m-long tunnel in the Mont Terri rock laboratory were backfilled. To ensure the successful emplacement of the GBM in these tests, attempts were made to quantify the dry density of the GBM using conventional mass-balance averaging as well as tools based on dielectric and heated fiber-optic methods. In the mock-up test, the dry density was measured using a set of dielectric tools installed through the tunnel wall. Heterogeneity over the tunnel cross-section was captured, with a general trend towards higher dry density near the screw feeders and lower values near the tunnel wall and crown areas. The in-situ tunnel backfilling in the Mont Terri rock laboratory was performed in twelve steps and the section-wise average dry densities along the tunnel showed a longitudinal variation. Nonetheless, both mock-up and in-situ backfilling tests showed that the overall average dry density exceeded the target value of 1,450 kg/m3. The fiber-optic method involved actively heating the fiber-optic cable installed near the GBM-shotcrete interface at the crown of the tunnel. The GBM dry density profile along the cable was estimated based on the temperature responses. The estimated dry density near the tunnel crown indicated longitudinal variations and was generally lower, which was consistent with the results of the mock-up test. The three methods provided the GBM dry density at different locations with different spatial resolutions. However, the combined results demonstrated that GBM backfilling met engineering and safety-relevant requirements.

Utilization of Dredged River Sediment in Preparing Autoclaved Aerated Concrete Blocks

In this study, the dredged river sediment, soft texture and fine particles, is mixed with other materials and transformed into eco-friendly autoclaved aerated concrete (hereinafter referred to as AAC) blocks. The results indicated the bricks produced under the conditions of 30%–34% dredged river sediment, 24% cement, 10% quick lime, 30% fly ash, 2% gypsum and 0.09% aluminum powder with 0.5 water to material ratio, 2.2 MPa autoclave pressure and 6 h autoclave time, the average compressive strength of 4.5 MPa and average dry density of 716.56 kg/m³ were obtained, the two parameters (strength & density) both met the requirement of national industry standard. At the same time, the contents of dredged river sediment, cement, lime, fly ash, gypsum and aluminum powder were 15%, 48%, 20%, 15%, 2% and 0.09%, respectively, and the non-AAC block made of 0.5 water to material ratio, the average compressive strength of 3.1 MPa and average dry density of 924.19 kg/m³ were obtained, the two parameters (strength & density) also met the requirement of national industry standard. In addition, the AAC block’s phase composition and morphology were micro-analyzed by SEM and XRD, the main substances in AAC block were found to be tobermorite and CSH, Among them, the chemical bond between Si-O-Si and Al-O-Al is broken, Al-O-Si is regenerated, Al substituted tobermorite with better strength is formed, and the compressive strength of AAC is further improved.

The effect of compaction and microbial activity on the quantity and release rate of water-soluble organic matter from bentonites

Swelling bentonites, planned to be installed around spent nuclear fuel canisters made of copper/cast iron in geological repositories, contain organic matter. Organic matter can act as substrates for microorganisms, such as sulfate-reducing microorganisms (SRM), which produce sulfide, a copper corrosion agent. Thus, it is important to study the quantity and release rate of organic matter from bentonites. In this study, the soluble organic matter (sOM) quantity of three bentonites (Wyoming, Indian, and Bulgarian) determined by dynamic leaching assays was originally 85, 16 and >163 mg kg−1, respectively. To assess the effect of simulated repository conditions on the quantity and release rate of bentonite sOM, the original bentonites were compacted to an average dry density of 1314–1368 kg m−3 and connected to sand layers in anaerobic cell systems. The sand layers were either inoculated or uninoculated with microorganisms. Afterwards, the cells were operated on for 12–15 months. As shown by postmortem dynamic leaching assays, the bentonite sOM quantities either increased (Indian and Bulgarian) or decreased (Wyoming) relative to the initial sOM quantities in original bentonites. The release rate of sOM increased in all bentonites in comparison with the original bentonites, and the increase was higher for the bentonites of the inoculated cells than for the uninoculated cells. The findings suggest that the interaction of the microorganisms with the bentonites increased the quantity and/or release rate of the bentonite sOM. Compaction of the bentonites, leading to changes in the mineral size and microstructure of bentonites, was also hypothesized to affect the amount of sOM released. Additional processes (e.g., diffusive transport) might also be relevant for the release of sOM from bentonites, but they were beyond the scope of this study. The present study represents an advance in the understanding of the effect of different possible repository conditions on the quantity and role of bentonite sOM as a source of substrates for the microbial community, especially considering the sulfide-producing SRM.

The Healing Process of the Joints between Buffer Material Blocks and the Influence on Solute Migration

A set of thermo-hydro-mechanical coupling control equations was established, and the healing process of the joints between Gaomiaozi bentonite (GMZ01) buffer material blocks and the influence of the joint parameters were numerically simulated. The calculations consider the effect of joints on solute migration, the permeability and thermal conductivity of the buffer material, and the evolution of the healing effect. The effects of the joint design parameters, including the type, number, width, splicing form, and average dry density of the joint, are investigated. Studies show that, under an external water head, the joints will become hydraulic priority channels due to their higher permeability, which will shorten the saturation time of the blocks. As the bentonite gradually saturates, the swelling force compresses the joint material. This action improves the overall uniformity of the buffer material and reduces the priority channel effect. Meanwhile, the final average permeability and diffusion coefficient of the buffer material are found to mainly depend on the average dry density of the buffer material. The higher the average dry density of the buffer material is, the lower the final average permeability and diffusion coefficient are, whereas the distribution of joints and the block splicing are less affected by the average dry density of the buffer material. The findings of this study can provide a reference for the design of bentonite buffer material blocks in the repository.

Permanent deformation analysis of base layers with recycled material: Effect of density and stress level

Full-depth reclamation techniques present numerous advantages for pavement rehabilitation strategies. The recycling process produces a thick layer of stabilized or unstabilized reclaimed materials, which is used as a new base layer of RAP aggregates. The compaction of the unstabilized thick layer is critical for adequate permanent deformation behaviour of the reclaimed layer. In some agencies, the smooth drum compaction is often used directly after the recycling process to compact the reclaimed materials. Previous studies demonstrated the challenges associated with adequate densification of the thick reclaimed layer through its whole thickness, leaving among other a material with a vertical density gradient. In that context, this study was designed to quantify the effect of the degree of compaction on the permanent deformation behaviour using cyclic triaxial tests. Granite and limestone aggregates were mixed with RAP in order to obtain mixes with 50% RAP, and each blend was tested using a permanent deformation test procedure at four different degree of compaction. One of the tested degree of compaction was a varying compacted density over the sample height. It was found that the analysis of this particular sample performance could be done on the basis of the average dry density of the sample. The shakedown ranges of each sample were analyzed with respect to stress ratio and degree of compaction. The behaviour for each type of mix was also similar. A generalized model was therefore proposed allowing to predict the range of permanent deformation behaviour knowing stress level and the degree of compaction. The general model between shakedown range and a relative stress ratio is based on a shift factor linking the effect of stress and density. Limit states were also defined for the possible ranges of behaviour with respect to the degree of compaction.

Petrographical and geophysical investigation of the Ecca Group between Fort Beaufort and Grahamstown, in the Eastern Cape Province, South Africa

Abstract The outcrop of the Ecca Group in the Eastern Cape Province was investigated in order to reveal petrographic and geophysical characteristics of the formations that make up the group which are vital information when considering fracking of the Karoo for shale gas. The petrographic study reveals that the rocks of the Ecca Group are both argillaceous and arenaceous rock with quartz, feldspar, micas and lithics as the framework minerals. The sandstones are graywackes, immature and poorly sorted, thus giving an indication that the source area is near. The observed heavy minerals aswell as the lithic grains signify that the minerals are of granitic, volcanic and metamorphic origin. The porosity result shows that of all the formations that make up the Ecca Group, the Whitehill Formation is the most porous with an average porosity of about 2.1% and also least dense with an average dry density of about 2.5 g/cm3. The least porous unit is the Ripon Formation with porosity of about 0.8% but has the highest dry density of approximately 2.8 g/cm3. The magnetic map shows some ring-like structures which coincide with dolerites that were mapped in the field. As revealed by the depth slices result, dolerite intrusions are pervasive in the northern part of the study area, extending to a depth of about 6000 m below the ground surface. The appearance of dolerite intrusions at the targeted depth (3000 - 5000 m) for gas exploration could pose a serious threat to fracking of the Karoo for shale gas.

Fabrication and Properties of Glass Fibre Reinforced Fly Ash-Cement Roofing Tiles

In this study Glass fibre reinforced fly ash -cement roofing tiles were fabricated using three different forms of coal fly ash (CFA) such as CFA as it is, CFA particle sizes below 75μm and below 45μm.The separated CFA was used to replace cement 30% by the weight and those matrices were reinforced by Alkali Resistant (AR) glass fibres adding 1% and 2% by weight.The corrugated roof tiles have dimensions of 490×250×8mm and they were hand cast using ordinary vibration. Physical and mechanical tests were performed after 28 days of aging. The tiles were tested in accordance with SLS 1189. Transverse strength increased with increasing fibre percentage. Further, the transverse strength decreased with decreasing CFA particle size. Highest characteristic transverse strength was observed in the CFA as it is sample which is 1650N and the lowest from CFA below 45µm particle size sample which is 1240N. However, all the samples satisfy the strength requirement which is 230N. High water absorption was observed in all the samples which is around 20%.The dry density was ranged in between 1.62-1.68g/cm3 .The lowest average dry density was observed in CFA as it is samples whereas CFA below 75μm particle size and CFA below 45μm particle size samples showed similar density values. The dry density of tile samples is in comparable with the dry density of asbestos cement sheets (≈1.63g/cm3) and the characteristic transverse strength is in comparable with Calicut clay tiles (1000-2000N) in Sri Lanka. Therefore, glass fibre reinforced fly ash-cement roofing tiles are promising substitute for asbestos roofing sheets.

Experimental studies on cement stabilized masonry blocks prepared from brick powder, fine recycled concrete aggregate and pozzolanic materials

This experimental work deals with the assessment of strength and water absorption characteristics of cement stabilized masonry block (CSMB) units made with brick powder (BP) and fine recycled concrete aggregate (FRCA) along with pozzolanic materials such as silica fume (SF), fly ash (FA) and ground granulated blast furnace slag (GGBS) as partial replacement for cement. The basic tests such as, dry density, 28 days wet compressive strength, water absorption and rate of moisture absorption are performed on CSMB units of size 190×90×90mm. The correction factors that are available in the literature, with respect to fired clay bricks and compressed earth blocks, so as to account for the confinement of specimens by platen restraints at the ends are used to assess the uniaxial strength of CSMB units. The corrected average values of wet compressive strength of CSMB units at 28 days are found to meet the minimum requirement of 3.5MPa. The percentage of water absorption is found to be higher, but, still within permissible limit of 18% by weight. The average dry density is also found to meet the minimum requirement of 1750kg/m3. The rate of moisture absorption with time is found to follow an exponential trend.

Saturation of barrier materials under thermal gradient

Two different sealing materials–a granulate of MX-80 bentonite pellets (B) and a 65/35 sand/MX-80 bentonite mixture (S/B)–were tested in cylindrical cells to analyse the effect of heating and hydration on the spatial distribution of temperature and humidity inside them. The 50-cm long columns were heated on their base to 140°C while Pearson water was supplied through their upper surface at a very low pressure. The aim of the tests was to simulate in the laboratory the conditions of the two barrier materials used in a large-scale in situ test (the HE-E, performed at the Mont Terri Underground Laboratory), reproducing the engineered barrier of an underground repository of nuclear waste. The S/B cell was dismantled after three years of operation, whereas cell B has been running for four years.The temperature distribution was very dependent on the geometry of the experimental setup and on the thermal conductivities, not only of the sealing materials, but also of the different components of the cells. The changes in thermal conductivity of the sealing materials because of the changes in water content affected the heat conduction and hence the temperatures inside the columns. Heat dissipation through the bottom of the cells seems to be a relevant process.The two materials have very different gas and liquid permeabilities, as well as water retention capacity, and this conditioned the water redistribution in the vapour phase triggered by heating as well as the liquid water intake, which were both much more restricted in the bentonite pellets. Convection cells probably formed near the heater, since evidences of soluble species transport and their precipitation in the area were found.The good consistency of column S/B upon dismantling indicated that, despite the low percentage of bentonite in the mixture and the low average dry density, the bentonite was able to swell and give the mixture a cohesive texture, even though the high salinity of the saturation water probably reduced the swelling capacity and increased the hydraulic conductivity of the material.

Explanation of Dry Density Distribution Induced by Compaction through Soil/Water/Air Coupled Simulation

Most onshore earth structures, such as earthen dams, embankment, and river levees, are constructed by compaction. Transportation geotechnics also includes construction of compacted earth structures, such as road and railway embankment. Optimum compaction can increase shear strength, while decreasing compressibility and permeability of earth structures. For this reason, compaction has been used for earthworks since the dawn of times. Generally, a series of lab compaction tests is conducted to obtain a compaction curve before constructing these structures. The shape of the compaction curve, which determines the maximum dry density at the optimum water content, is very important in the design and construction of structures. However, it is difficult to control compaction quality on the basis of lab tests alone, as soil materials are inhomogeneous. Furthermore, there are differences in the compaction methods used in lab tests and at construction sites. Therefore, it is necessary to explain the mechanisms of compaction in the framework of soil mechanics. In this study, compaction of earthworks is simulated in a similar way. The effect of compaction layer thickness and the number of compaction layers on the distribution of dry densities in an earth structure was investigated through soil/water/air coupled simulation. Consequently, it was found that multi-layered compaction can create a gap in the dry density between two layers and that this gap can be reduced by thinner layer compaction. On the other hand, though the average dry density in a compacted earth structure can be increased by increasing the number of compacted layers, some gap between compaction layers was inevitable. Through these findings, this study contributes to the performance design of compacted earth structures.

Quasi-static and dynamic nanoindentation to determine the influence of thermal treatment on the mechanical properties of bamboo cell walls

Abstract Bamboo was thermally treated at 180°C and 200°C, and the micromechanical properties of its cell walls were investigated by means of quasi-static and dynamic nanoindentation experiments. With increasing treatment temperatures, the average dry density and mass of the bamboo decreased, whereas the already reduced elastic modulus at 180°C of the fiber cell walls did not change, but the hardness showed increasing tendencies. Dynamic nanoindentation revealed reduced storage modulus ( E ′ r ) $({E'_{\rm{r}}})$ and loss modulus ( E ″ r ) $({E''_{\rm{r}}}\,)$ for the thermotreated bamboo cell walls compared with the untreated bamboo fibers in all frequency regions. Moreover, E ′ r , E ″ r , ${E'_{\rm{r}}},{\rm{ }}{E''_{\rm{r}}},$ and loss tangent (tan δ) of treated bamboo decreased with increasing treatment temperature.