Lower Void Ratio Research Articles

Study on geotechnical characteristics of marine soil at Hong Kong–Zhuhai–Macao tunnel

The Hong Kong–Zhuhai–Macao Bridge (HZMB) immersed tunnel is part of the HZMB, connecting three vibrant cities and crossing the Lingding Sea in South China. It is at the west channel of the Pearl River Estuary and the Tonggu West Channel. The stratum in this area includes deep soft soil with large differences in soil distribution. Based on geotechnical investigation data on marine soil at the HZMB tunnel, the spatial distribution of physical and mechanical properties of deposit soils was statistically analyzed. A field investigation revealed that deposit soils could be subdivided into four strata: Holocene marine deposit stratum, late Upper Pleistocene continental, mid Upper Pleistocene marine alluvial deposit, and early Upper Pleistocene alluvial deposit stratum. Field and laboratory test results indicate that Holocene marine deposit soils had a high water content (42.5% < < 81.2%), large void ratio (1.21 < < 2.43), flow-plastic state ( > 1), high compressibility ( < 5 MPa), low shear strength (2.5 kPa < < 28.5 kPa), and low bearing capacity (58.9 < < 120 kPa); therefore, they could not be used as a natural foundation. The late, mid, and early Upper Pleistocene continental deposit strata had low water content (1.5% < < 40.5%), high bearing capacity ( > 120kPa), low void ratio (0.41 < < 1.24), and low flow-plastic to liquid state ( < 0.95), Additionally, the results of regression analysis showed that the compression ratio was positively correlated with natural water content. Finding from field and laboratory tests provide a basis for immersed tunnel design and construction.

Determining material characteristics of “Rammed Earth” using Non-Destructive Test methods for structural design

One of the ancient construction materials used for wall construction includes the use of locally available soil (basic earth) stabilized with cement. Driven by the need to source locally available materials in remote communities and to reduce the carbon footprint arising from hauling of materials over long distances, the use of the rammed earth (RE) technology is regaining popularity.In this study, the rebound hammer values, corresponding to compressive strength of the RE material demonstrated a positive trend with aging. Further, the application of two different ramming head diameters (15.24 cm vs. 7.62 cm diameter) for compaction, revealed that the smaller head results in higher density, lower void ratio, higher compressive strength and better compaction near the end corners of the tested wall.The compressive strength of the material calculated using rebound hammer, showed a positive effect when cement was substituted with 15% of industrial waste additives. Interestingly, the same mix reported 23% higher strength when exposed to wetting-drying cycles as compared to a reference mix under ambient conditions. Overall, the exposure of the specimens to alternating wetting and drying cycles presented a positive impact on the strength of the RE material. Furthermore, the pulse speed recorded by using Ultrasonic pulse velocity equipment revealed a similar trend for the RE material with and without additives when compared to same exposure conditions. On the other hand, uni-axial compressive test results on cylindrical specimens illustrated 34% higher strength for sample prepared without any industrial additive on exposure to wet-dry cycle, while the sample with 15% additives reported 25% increased strength under ambient conditions. The experimental results also highlighted the significance of more lifts on the resulting strength of the material. Therefore, the findings of this paper present useful baseline data for RE that can be used when comparing tests conducted on existing RE structures made of similar materials.

Effect of silica fumes on fluidity of UHPC: Experiments, influence mechanism and evaluation methods

Abstract Silica fumes are adopted to densify the microstructure in UHPC, which has an obvious effect on fluidity of UHPC. It is still unclear to explain the influence mechanism of silica fume with different material properties on fluidity of UHPC systematically. In this paper, based on analytic hierarchy process (AHP), a new evaluation method of fluidity for UHPC is proposed through analyzing materials properties of silica fumes. In order to obtain the judgment matrixes of criteria in the evaluation method, five types of silica fumes are selected as mineral admixtures to measure fluidity of UHPC. Compressive packing model (CPM) is adopted to calculate the real packing density of silica fume-cement system. Moreover, influence mechanism and effect factors of silica fumes on fluidity of UHPC are explored. The results indicate that low void ratio, high packing density, wide particle size span and low carbon content can increase the fluidity of UHPC through enhancing “ball effect” and “plasticizing effect”. Finally, the judgment matrixes of criteria in the evaluation method are developed by quantifying the effect factors, and evaluation methods can be adopted to evaluate the fluidity of UHPC with various silica fumes accurately.

모래의 입도분포와 세립분 함유량에 따른 액상화 저항특성 비교

The liquefaction phenomenon occurs when the groundwater is pumped up through the top of sediments as the pore pressure increases due to the earthquake. There have been many studies on the loose sandy soils and various samples through repeated triaxial compression tests and shaking table tests, but there have been few studies on the effects of particle size distributions and the fine contents of sand on the liquefaction of sand. In this study, the undrained repeated triaxial compression tests were performed on sands with different particle size distributions, confining pressures, relative densities, and deviatoric stresses. The results of analysis showed that, with increasing relative density, SW(Well-graded sand) samples had higher liquefaction strength than SP(Poor-graded sand) samples. This is due to the lower void ratio of sand in SW samples than in SP samples. It was also found that the liquefaction strength decreased with a high fine content due to he rapid destruction of the filling of fine particles between the soil particles, leading to lower liquefaction strength.

Time-dependent behaviour of sand with different fine contents under oedometric loading

To characterize the effects of creep, strain rate, and relaxation in granular soils, different sands have been studied under oedometric loading. The tests were analysed in the framework of the isotache concept. The results show increasing creep rates with increasing vertical stresses and a strong reduction of the creep rate upon unloading. A lower void ratio leads to less creep. Evaluation of the ratio Cα/Cc, where Cα is the creep coefficient and Cc is the compression index, demonstrates considerable deviation from a constant soil-specific value for the sands. With increasing fine content, however, a constant soil-specific ratio has been found for a silty sand. In strain rate–controlled tests, a sand with low and a sand with significant content of nonplastic fines were compared. Constant rate of strain tests displayed practically no strain rate dependency for the sand with little fines and a well visible strain rate dependency for the very silty sand. Tests with stepwise change of strain rate showed non-isotache behaviour for the sand with little fines and isotache behaviour for the other. Stress-relaxation tests displayed an isochronous behaviour. The analysis of the three viscous effects in sands showed they cannot altogether be mathematically described in the framework of the isotache concept. A new compression model for the creep behaviour of sands is presented.

Evaluation of dynamic properties of calcareous sands in Egypt at small and medium shear strain ranges

Calcareous sand deposits are widely distributed along the shoreline of Mediterranean Sea in Egypt; known as the North Coast area, which covers promising areas for industrial and touristic activities. An experimental study was conducted to evaluate the shear modulus and damping ratio at small and medium shear strain ranges of sands procured from two districts along the North Coast using fixed-free resonant column apparatus. In addition, flexural and constrained moduli, flexural damping ratio, and Poisson's ratio were estimated. Effects of effective confining stress, void ratio, and saturation condition (saturated versus dry) on evaluated dynamic properties were investigated. The maximum shear modulus increased with increasing the effective confining stress exponentially with relatively high exponent values compared to those reported for siliceous sands. The effect of void ratio on shear modulus was more pronounced at low void ratios and maximum shear modulus increased as the void ratio decreased. Dry cemented sands characterized with their irregular and rough particles showed lower maximum shear moduli and higher stress exponents compared to saturated sands. Natural cementation was found to indirectly influence the dynamic properties of sands as it alters the inter-particle properties.

English

Vertisols are widespread in North Cameroon, but are undercultivated due to difficulties linked to their shrink-swell behaviour under different moisture conditions. Eighteen vertisol samples from five profiles representative of the studied area (Benue floodplain in North Cameroon) were studied to establish a relationship between moisture and physico-chemical characteristics and supplement data for planning sustainable agricultural management. The main results revealed that the soils are deep, dark grey, heavy clayey, with high coefficients of linear extensivity, low organic matter and low electrical conductivity. At field capacity, they showed a very low bulk density, high porosity and a high void ratio. Oven-dry soils exhibited very high bulk density, very low porosity and very low void ratio. This high reversibility of properties with changing moisture content is related to high smectitic mineralogy. The moisture properties revealed very high water-holding capacity, very high available water and very high readily available water. Most of the physico-chemical characteristics correlated well with the moisture parameters. The principal component analysis revealed a reduction of 17 initial variables to two principal components (PC1 and PC2) explaining over 70% of the total variance. The PC1 clustered 12 soil and soil moisture variables indicating strong correlation between moisture and physicochemical properties. Management practices for crop production must be primarily directed at moisture control. Key words: Vertisols, soil moisture, soil suction, land evaluation, Benue floodplain.

Improving the structure and mechanical properties of loess by acid solutions – An experimental study

The structure of loess is the primary cause of loess-related disasters, such as collapse, seismic subsidence, and liquefaction. To improve the pore structure of loess more effectively, chemical methods are preferred over conventional physical methods. It is found that acidic solutions can readily dissolve the salt crystal cement composed of CaCO3 and other soluble salts in loess, thereby easily and thoroughly destroying the macropores of loess and resulting in a new, superior structure with improved mechanical properties. A series of laboratory tests was performed to investigate and compare the structural and mechanical properties of natural collapsible loess and loess treated with acid (LTA). Scanning electron microscopy (SEM) analysis revealed that the well-spaced granules with point contacts of natural loess were transformed into cemented interlocking amorphous grain modes in LTA. Compression and collapsibility tests proved that the pore structure of the loess was easily destroyed and improved by the addition of an acid solution, and the resulting LTA was more resistant to single and multiple collapse events than the natural loess. Static triaxial tests confirmed that the enhancement of the original cohesion force and curing cohesion force among soil particles improved the shear strength of LTA. Dynamic triaxial tests showed that, because of a lower void ratio (e) than the natural loess, LTA had a better seismic performance as well as a lower likelihood of liquefaction. The new acid-addition presoaking method is shown effective in improving mechanical properties of loess. The implication of this finding is significant for the construction in the loess deposits. The results also provide a valuable reference for studies on construction in loess polluted with acidic wastewater.

A Lumped Bubble Capacitance Model Controlled by Matrix Structure to Describe Layered Biogenic Gas Bubble Storage in Shallow Subtropical Peat

AbstractMethane (CH4) accumulates in the gaseous phase in peat soils, being released to the atmosphere at rates higher than those for diffusion and plant‐mediated pathways. An understanding of the mechanisms regulating gas bubble storage in peat remains incomplete. We developed a layered capacitance model to compare the bubble storage ability of peat over different depths. A peat monolith (0.395 m × 0.243 m × 0.247 m) was collected from the U.S. Everglades and kept submerged for 102 days from a condition of minimum bubble storage to bubble saturation. Time‐lapse electromagnetic wave velocity and power spectrum data were used to estimate changes in both gas content and relative average dimensions of stored bubbles with depth. Bubble capacitance, defined as the increase in volumetric gas content (m3 m−3) divided by the corresponding pressure (Pa), ranges from 3.3 × 10−4 to 6.8 × 10−4 m3 m−3 Pa−1, with a maximum at 5.5 cm depth Bubbles in this hotspot were larger relative to those in deeper layers, while the decomposition degree of the upper layers was generally smaller than that of the lower layers. X‐ray computed tomography on peat sections identified a specific depth with a low void ratio, and likely regulating bubble storage. Our results suggest that bubble capacitance is related to (1) the difference in size between bubbles and peat pores, and (2) the void ratio. Our work suggests that changes in bubble size associated with variations in water level driven by climate change will modify bubble storage in peat soils.

The physicochemical properties and microstructural characteristics of peat and their correlations: reappraisal

ABSTRACT The accumulation of organic matter in the form of plant remains at the various stages of decomposition results in the formation of peat. A very low land, water logged and excessive rainfall regions are the highest places of its occurrence. The presence of organic matter plays a major role in governing physicochemical and engineering properties of peat. The wide spatial variations in inherent properties of peat contribute high water content, low shear strength, high compressibility and high void ratio. The exploration of peatland has been done by the various researchers in many places across the world; however, in India, proper knowledge on peatland periphery is still obscure. This article highlights brief information on physicochemical properties of Northeast-Indian peat. Further, an extensive literature review is also carried out on physicochemical and engineering, microstructural and thermal characteristics of peat in worldwide and their various classification systems. The correlations developed based on present study and literature data on physical properties of peat are also presented.

An updating void ratio model for large deformation simulation of geogrid-granular strip anchors plates

A modeling approach to investigate the complex behavior of granular trench and reinforcement system is presented in this paper. For this purpose experimental and numerical investigations have been carried out on the behavior of pullout resistance of an embedded strip anchor with and without geogrid reinforcement layers at stabilized loose and dense sand using a granular. Different parameters have been considered, such as number of geogrid layers, embedment ratios, relative density of soil and height ratios of granular trench. For sand and granular trench the CANAsand constitutive model were utilized to investigate failure mechanism and the associated rupture surfaces in the analysis. The obtained results indicate that, when soil was improved with the granular-geogrid trench, the uplift force significantly increased. The ultimate uplift capacity of anchor plate and the variation of surface deformation for all the tests indicated a close agreement between the experimental and numerical models. Also, numerical results show that larger deformations at ultimate pullout load are associated with high void ratios whereas smaller deformations are related with low void ratios.

ASSESSMENT OF MIX PROPORTIONS FOR DEVELOPING LIGHTWEIGHT CEMENTITIOUS COMPOSITES WITH WOOD WASTES

ABSTRACT The main objective of this work was to assess mix proportions for developing lightweight cementitious composites, manufactured with Eucalyptus grandis sawdust. Different wood:cement, water:cement and admixture:cement ratios were used to evaluate physical (water absorption, void ratio and density) and mechanical (compressive strength, static and dynamic modulus of elasticity) properties of the cement-wood composites. Results shows that, bulk density is directly proportional to the compressive strength and elastic modulus, and inversely proportional to the percentage of timber, considering composites with same water:cement ratio, without superplasticizer. The performance of the cement-wood composites, regarding mechanical properties, can be improved if superplasticizer is used to increase paste fluidity. Higher values of bulk density are related to lower void ratio and water absorption and higher compressive strength and modulus of elasticity.

Assessment of non-uniform deformation during consolidation with lateral drainage using Particle Image Velocimetry (PIV)

This paper experimentally investigates the lateral deformation characteristic of clay under consolidation with lateral drainage. A transparent consolidation test device was developed to obtain photo images of the soil specimen during lateral drainage consolidation. Particle Image Velocimetry (PIV) was applied to quantify the displacements within the entire clay specimen, and subsequently, the strains and void ratio fields were computed through the moving least square method. The results of the PIV showed complex lateral deformation characteristics depending on the degree of consolidation and the locations. The lateral deformation induced a lower void ratio, and consequently, permeability near the vertical drain compared to the average values of the entire specimen. Additionally, the non-uniformity of the effective stress state, and hence of the soil stiffness, was verified with the total stress measurements.

A Multichip Phase-Leg IGBT Module Bonded by Pressureless Sintering of Nanosilver Paste

This paper presents the design, development, and optimization of large-area die attachment by pressureless sintering of nanosilver paste. With the proposed die attachment, a high power 1200 V/150 A insulated-gate-bipolar-transistor (IGBT) module is fabricated using large-area IGBT ( ${12.56 \times 12.56}$ mm2) and diode ( ${6.3 \times 6.3}$ mm2) chips. The average die-shear strength of higher than 30 MPa can be obtained with the low void ratio of 1.8%. The electrical characteristics of the IGBT module using pressureless sintered nanosilver paste have been measured and compared with the commercial one using soldered Sn5Pb92.5Ag2.5. Test result shows that this IGBT module has identical static and dynamic characteristics as the commercial one. Therefore, the pressureless sintered nanosilver could be used as an alternative to high-lead solder in power module manufacturing, especially in assembling SiC- or GaN-based devices for high temperature applications.

Effects of void ratio and grain size distribution on water retention properties of compacted infilled joint soils

The effects of the initial void ratio and the grain size distribution (GSD) on the water retention properties of a compacted infilled joint soils from Beihetan (China) were investigated. Three initial void ratios (0.3, 0.4, and 0.5) and three GSDs were selected based on the in situ soil states. A total of nine drying water retention curves (WRCs) was established with the filter paper method. The microstructure of the specimens was also studied to better understand the water retention properties. It was found that the denser samples underwent smaller volume changes, and that the volumetric strain increased with the increasing clay size fraction. The void ratio had a significant effect on the WRCs in terms of the degree of saturation; however, the WRCs were independent of the void ratio in terms of the gravimetric water content. In terms of the degree of saturation, the WRCs were seen to shift upwards with the increase in clay size fraction, indicating an increase in the water retention capacity. The results from mercury intrusion porosimeter (MIP) tests revealed that the difference in the inter-aggregate pores is the main reason for the different shapes of the WRCs. Moreover, the infilled joint soils with lower void ratios and coarser particles were found to be more suitable for MIP-based evaluations of water retention properties.

Compressibility, grain breakage and time-dependent behavior of gap-graded aggregates of sugar cubes

The results of a simple and alternative, yet powerful, procedure to experimentally investigate particle breakage behavior are presented in this paper. One-dimensional compression tests on a crushable granular and gap-graded material (aggregates of sugar cubes) are described and discussed. Sugar parallelepipedic (27.4×17.6×12.2mm) cubes are compacted aggregations of welded sugar crystals having a mean size of 0.45mm. Two different geometric arrangements, having widely different initial void ratios (0.2 and 0.8) were tested. The lower void ratio corresponded to ordered piling arrangements, while the higher ratio corresponded to disordered piling arrangements. Vertical stresses up to a maximum of 640kPa were applied and grain size distributions (gsd) were obtained after the loading process. Identical gsd shapes of two S-shaped curves were obtained at the maximum vertical stresses for both ordered and disordered arrangements, underlying the gsd attractor concept associated with highly stressed aggregates irrespective of the initial state. Two breakage mechanisms were identified in the loading process, namely, comminution and splitting crushing. The time-dependent behavior was also studied based on creep tests lasting a maximum of 157.5 days. It was found that creeping could be explained by a delayed grain breakage process.

Pressureless sintering of nanosilver paste at low temperature to join large area (≥100 mm2) power chips for electronic packaging

We achieve robust bonding of large area power chip (≥100mm2) based on pressureless sintering of silver particles at low temperature, i.e., 250°C. The particle size of silver ranges from 0.02 to 2µm and most organics can be evaporated rapidly from 70°C to 180°C. It is not necessary for metallic bond to be formed entirely by silver nanoparticles. Instead, silver microparticles also can rapidly grow up and aggregated together by atom diffusion from the silver nanoparticles. This point of view leads to a new way to bond the large area chips without additional pressure. The sintered silver joint shows high shear strength, low porosity, high thermal conductivity, and low void ratio.

Engineering Properties of Soils on Boubyan Island in Kuwait

To full understand engineering properties of soils on Boubyan island in Kuwait, some in-situ tests were performed along the highway and railway line, meanwhile some laboratory tests for soil samples from the different depth. It was concluded that its properties was low void ratio, low moisture content, low plasticity, low sensitivity, low permeability and high salt content. The soil classification belonged to CL and Marine-chloride-highly saline-soil.

Effect of fines content and void ratio on the saturated hydraulic conductivity and undrained shear strength of sand–silt mixtures

The hydraulic conductivity represents an important indicator parameter in the generation and redistribution of excess pore pressure of sand–silt mixture soil deposits during earthquakes. This paper aims to determine the relationship between the undrained shear strength (liquefaction resistance) and the saturated hydraulic conductivity of the sand–silt mixtures and how much they are affected by the percentage of low plastic fines (finer than 0.074 mm) and void ratio of the soil. The results of flexible wall permeameter and undrained monotonic triaxial tests carried out on samples reconstituted from Chlef river sand with 0, 10, 20, 30, 40, and 50 % non-plastic silt at an effective confining pressure of 100 kPa and two initial relative densities (D r = 20, 91 %) are presented and discussed. It was found that the undrained shear strength (liquefaction resistance) can be correlated to the fines content, intergranular void ratio and saturated hydraulic conductivity. The results obtained from this study reveal that the saturated hydraulic conductivity (k sat) of the sand mixed with 50 % low plastic fines can be, in average, four orders of magnitude smaller than that of the clean sand. The results show also that the global void ratio could not be used as a pertinent parameter to explain the undrained shear strength and saturated hydraulic conductivity response of the sand–silt mixtures.

Swelling Pressures of some initially Saturated and Compacted Saturated Bentonites

The swelling pressures of several bentonites (Bentonite S-2, Febex, Calcigel, Montigel, Kunigel, Kunigel V1, Na-Kunigel, Alaska, Ca-Fourges, MX80, Na-Ca MX80, Ca-Wyoming, and Na- Wyoming) were determined from the Gouy-Chapman diffuse double layer theory. Many of these bentonites have been considered as barrier and backfilling materials for the underground storage of nuclear waste in various countries. The theoretical swelling pressures were then compared with the reported experimental swelling pressures for both initially saturated and compacted saturated samples. Qualitative agreements between the theoretical predictions and the experimental results were noted for all the bentonites studied. However, it was noted that at low dry densities or high void ratios, the theory generally predicted higher swelling pressures with the reverse trend at high dry densities or low void ratios. The lesser magnitude of experimental swelling pressures at higher void ratios can possibly be attributed to the formation of clay domains. Such behaviour also supports the fact that the effects of counterion crowding near the surfaces of the clay platelets are to reduce the surface charge and the electric potential at the Gouy-Stern plane. At smaller void ratios, the overlapping of the Stern layers of adjacent clay platelets influenced the swelling pressures. In this case, much stronger swelling pressures were exhibited by the bentonites.