Engineering Properties of Unstabilized Rammed Earth with Different Clay Contents

The physical and mechanical properties of unstabilized rammed earth with different clay contents were studied, which could provide a theoretical basis for the understanding of mechanical properties of unstabilized rammed earth and improve the construction design method and specification of RE buildings for sustainable development. The experimental results show that clay content has significant influences on the engineering properties of unstabilized rammed earth. For the fine-grained soil, the liquid limit, plastic limit and plasticity index increase gradually with the increase of the clay content. The influence of clay content on the optimum moisture content compared with the maximum dry density is more significant. The mechanical properties of unstabilized rammed earth are significantly affected by the clay content. There exist good linear relationships, which can be used for the mutual verification or calculation among the mechanical properties. An empirical model of unconfined compression strength with the FA/CA ratio as the main parameter is established, and the UCS may obtain the maximum with a FA/CA ratio of 5.77.

Investigation of effects of clay content on F-Ф relationship by Lattice gas automation using digital rock model

The Lattice Gas Automation （LGA） method, which is improved by introducing a reflection coefficient for the border between phases to show its effect on current path, is used in this paper to simulate the current flow in digital rock for investigating the effects of clay content and clay distribution types on the relationship between formation factor（F） and rock porosity（φ）. The digital rock model is constructed by simulating a natural deposit of matrix particles with different shapes and radius. Based on the simulation results, it was found that both dispersed clay and laminated clay can lead to a non-Archie relationship of F-φ. The non-Archie effect of laminated clay on the F-φ relationship was more significant than that of dispersed clay. Moreover, a realistic model is developed in this work for quantitatively describing the effect of clay content （Denoted as Vsh） on parameters a and m. These study results have further demonstrated the validity of LGA in study of electrical transport properties at a pore scale.

Effects of irrigation water regime, soil clay content and their combination on growth,yield,and water use efficiency of rice grown in South China

To investigate the effect of irrigation regime,soil clay content and their combination on growth,yield,and water productivity of rice,a shelter experiment was conduct using Randomized Complete Block Design(RCBD)with a factorial arrangement of treatments with four replications.Irrigation regime was the main treatment investigated,set in three levels as R(30 mm-100%)(100%of saturation and 30 mm flooded),R(30 mm-90%)(90%of saturation and 30 mm flooded)and R(30 mm-70%)(70%saturation and 30 mm flooded),respectively.The sub-treatment was soil type,set in three levels as 40%,50%and 60%clay content,respectively.Results showed that irrigation regime and soil clay content had significant effects on growth,yield and water productivity of rice.However,their combination showed no significant impact on panicles number,root biomass,harvest index and irrigation water productivity.Higher soil clay content results in increase in growth,yield,and water productivity of rice.The total water consumption during R(30 mm-100%)was higher than that during R(30 mm-90%)and R(30 mm-70%)because the latter two saturation levels led to the cracking of soil and decrease of total number of irrigations.Cracks were consistently getting more serious with the reduction in soil water content and the increase in soil clay content.Cracks in soil will preferentially become the major routes of water losses,thus water percolation during R(30 mm-70%)was higher than that during R(30 mm-90%)and R(30 mm-100%)after each irrigation event.The total water use under R(30 mm-70%)exceeded the water consumption under R(30 mm-90%)due to the great amount of soil cracking as well as the excessive volume of standing water depth.Considering water consumption and grain yield,the following conclusion can be reached:(i)The reduction in water consumption was greater than the reduction in grain yield in the case of drying soil 10%below saturation before reflooding.(ii)The reduction in water consumption was less than the reduction in grain yield in the case of drying soil 30%below saturation before reflooding;(iii)The increase in water use was greater than the increase in grain yield in the case of maintaining soil moisture at 100%of saturation before reflooding.Therefore,the water use efficiency was recorded in the order of R(30 mm-90%)>R(30 mm-100%)>R(30 mm-70%).

Modeling Virgin Compression of Reconstituted Clay at Different Initial Water Contents

The observations on compressibility of reconstituted clays show that the compression line with a higher initial water content lies above the compression line with a lower initial water content for a given clay. Hence there exists additional void ratio due to initial water contents among virgin compression lines（VCLs） of reconstituted clays. In this paper, the difference in void ratio caused by different initial water contents is investigated based on the empirical equation proposed by Liu and Carter（2000） for describing the differential void ratio at the same stress between natural and reconstituted clays. The mechanism of compressibility of reconstituted clays, when the stress level is larger than the remolded yield stress, is also discussed.

Experimental study on sand production and coupling response of silty hydrate reservoir with different contents of fine clay during depressurization

To further understand the characteristics of clay and sand production(hereafter collectively referred to as sand production)and to provide optimization designs of sand control schemes are critical for gas production from clayey silt natural gas hydrate reservoirs in the South China Sea.Thus,gas-water-sand production behavoirs and coupling reservoir subsidence characteristics before,during,and after hydrate dissociation of the clayey silt hydrate reservoirs with different clay contents(5%,10%,15%,20%,25%,and 30%)have been studied through a self-developed experimental system.The results show that with the increase of clay content,the total mass of sand production first increases and then decreases,and it reaches maximum when the clayey content is 20%.The sand production is the lowest before hydrate dissociation and increases significantly during hydrate dissociation,which mainly occurs in the high-speed gas and water production stage at the beginning of hydrate dissociation.After hydrate dissociation,the sand production decreases significantly.During the whole depressurization process,the clay and free sand particles generally move to the sand outlet due to the fluid driving force and overlying stress extrusion.However,for conditions of high clay contents,those particles fail to pass through the sand control screen and gradually accumulate and block the screen by forming a mud cake,which greatly reduce the permeability of the screen and limite sand production as well as gas and water production.Our research lays a foundation for sand production prediction and sand control scheme selection during gas recovery from clayey silty hydrate reservoirs that greatly need to consider a balance between sand control and gas productivity.

Study on strength properties and soil behaviour type classification of Huanghe River Delta silts based on variable rate piezocone penetration test

Fine-grained silt is widely distributed in the Huanghe River Delta(HRD)in China,and the sedimentary structure is complex,meaning that the clay content in the silt is variable.The piezocone penetration test(CPTu)is the most widely approved in situ test method.It can be used to invert soil properties and interpret soil behavior.To analyse the strength properties of surface sediments in the HRD,this paper evaluated the friction angle and its inversion formula through the CPTu penetration test and monotonic simple shear test and other soil unit experiments.The evaluation showed that the empirical formula proposed by Kulhawy and Mayne had better prediction and inversion effect.The HRD silts with clay contents of 9.2%,21.4%and 30.3%were selected as samples for the CPTu variable rate penetration test.The results show as follows.(1)The effects of the clay content on the tip resistance and the pore pressure of silt under different penetration rates were summarized.The tip resistance Q_t is strongly dependent on the clay content of the silt,the B_(q)value of the silt tends to 0 and is not significantly affected by the change of the CPTu penetration rate.(2)Five soil behavior type classification charts and three soil behavior type indexes based on CPTu data were evaluated.The results show that the soil behavior type classification chart based on soil behavior type index ISBT,the Robertson 2010 behavior type classification chart are more suitable for the silty soil in the HRD.

Effect of Methylene Blue (MB)-value of Manufactured Sand on the Durability of Concretes

The relation between the methylene blue （MB） value of MS and its limestone powder content and clay content was investigated. The effects of MB values ranging from 0.35 to 2.5 on the workability of fresh concrete, the mechanical properties, the resistance to freezing as well as the resistance to chlorine ion permeation of the hardened concrete were all investigated. The experimental results showed that the MB value had no correlation with the limestone powder content of MS, while it was directly related to the clay content. With an increase of MB value, concrete workability decreased, as did the flexural and 7-day compressive strengths, however, the 28-day compressive strength was not affected. Furthermore, influence of MB value on concretes of different strength levels was different. For low-strength concretes, an increase of MB value could improve its impermeability, but this was not the case for high-strength concretes. Instead, their resistance to chloride ion permeability decreased slightly. However, even a slight increase in MB value remarkably accelerated freeze-thaw damage of MS concrete. It was thus concluded that the critical MB value of 1.4 would not cause significant deterioration in the performance of MS concretes.

Linkage of microbial living communities and residues to soil organic carbon accumulation along a forest restoration gradient in southern China

Background:Forest restoration has been considered an effective method to increase soil organic carbon(SOC),whereas it remains unclear whether long-term forest restoration will continuously increase SOC.Such large uncertainties may be mainly due to the limited knowledge on how soil microorganisms will contribute to SOC accumulation over time.Methods:We simultaneously documented SOC,total phospholipid fatty acids(PLFAs),and amino sugars(AS)content across a forest restoration gradient with average stand ages of 14,49,70,and>90 years in southern China.Results:The SOC and AS continuously increased with stand age.The ratio of fungal PLFAs to bacterial PLFAs showed no change with stand age,while the ratio of fungal AS to bacterial AS significantly increased.The total microbial residue-carbon(AS-C)accounted for 0.95-1.66% in SOC across all forest restoration stages,with significantly higher in fungal residue-C(0.68-1.19%)than bacterial residue-C(0.05-0.11%).Furthermore,the contribution of total AS-C to SOC was positively correlated with clay content at 0-10 cm soil layer but negatively related to clay content at 10-20 cm soil layer.Conclusions:These findings highlight the significant contribution of AS-C to SOC accumulation along forest restoration stages,with divergent contributions from fungal residues and bacterial residues.Soil clay content with stand age significantly affects the divergent contributions of AS-C to SOC at two different soil layers.

Key geological factors controlling the estimated ultimate recovery of shale oil and gas: A case study of the Eagle Ford shale, Gulf Coast Basin, USA

Based on 991 groups of analysis data of shale samples from the Lower Member of the Cretaceous Eagle Ford Formation of 1317 production wells and 72 systematic coring wells in the U.S. Gulf Basin, the estimated ultimate recovery(EUR) of shale oil and gas of the wells are predicted by using two classical EUR estimation models, and the average values predicted excluding the effect of engineering factors are taken as the final EUR. Key geological factors controlling EUR of shale oil and gas are fully investigated. The reservoir capacity, resources, flow capacity and fracability are the four key geological parameters controlling EUR. The storage capacity of shale oil and gas is directly controlled by total porosity and hydrocarbon-bearing porosity, and indirectly controlled by total organic carbon(TOC) and vitrinite reflectance(Ro). The resources of shale oil and gas are controlled by hydrocarbon-bearing porosity and effective shale thickness etc. The flow capacity of shale oil and gas is controlled by effective permeability, crude oil density, gas-oil ratio, condensate oil-gas ratio, formation pressure gradient, and Ro. The fracability of shale is directly controlled by brittleness index, and indirectly controlled by clay content in volume. EUR of shale oil and gas is controlled by six geological parameters: it is positively correlated with effective shale thickness, TOC and fracture porosity, negatively correlated with clay content in volume, and increases firstly and then decreases with the rise of Ro and formation pressure gradient. Under the present upper limit of horizontal well fracturing effective thickness of 65 m and the lower limit of EUR of 3×10^(4) m^(3), when TOC<2.3%, or Ro<0.85%, or clay content in volume larger than 25%, and fractures and micro-fractures aren’t developed, favorable areas of shale oil and gas hardly occur.

Preliminary Study on Loess Slumping Hazard between Northern Shaanxi and Western Shanxi along the Line of West-East Gas Transportation Project

The loess slumping hazard is a special type of slope failures in the northern area of loess plateau of China. The characteristics of paroxysm and high frequency of the hazard always lead to ruin of cave houses, as well as a high human casualties. The hazard is also seriously harmful to railways, highroads and long transporting pipelines. With the mechanisms of both landslide and falling, as well as the forming process of sliding followed by collapses, loess slumping is used to be treated as landslide or falling. Based on field investigations and lab analyses of the loess between Jingbian County of Shaanxi Province and Puxian County of Shanxi Province along the line of west east gas transportation project which is 300 km long, it is discovered that the hazards of loess slumping are controlled by the content of clay, which lead to their obvious regional properties: the area with a content of clay (<0.005 mm) less than 10 %, called sand loess area, is a seriously developing area of slumping; the area with a content of clay between 10 % and 20 %, called typical loess area, is a medium developing area of slumping; the area with a content of clay more than 20 %, called clay loess area, is a non developing area of slumping. Based on research of the formation mechanism and formation conditions of the loess slumping hazards, some corresponding engineering countermeasures are suggested in this paper.

Pore shrinkage capacity of Shajiang black soils(Vertisols)on the North China Plain and its influencing factors

Different pore sizes present different pore shrinkage capacities in a nonrigid soil.However,the shrinkage capacities of different pore sizes and their influencing factors are not clear.We aimed to quantify the shrinkage capacities of different pore sizes(large pores,>50μm;medium pores,0.2-50μm;fine pores,<0.2μm)and determine how soil properties impact soil shrinkage capacity at the regional scale.Two sampling transects from west to east(360 km long,35 samples)and from north to south(190 km long,29 samples)were selected to investigate soil shrinkage capacity and physicochemical properties of at0-20 cm depth in the Vertisol(locally known as Shajiang black soil)region of the North China Plain.The results showed that soil total shrinkage capacity,indicated by the coefficient of linear extensibility(COLE),had a mean value of 0.041-0.051 in the west-east and north-south transects.Large pores had higher pore shrinkage index(PSI)values(0.103-0.109)than medium(0.077-0.096)and fine(0.087-0.091)pores.The PSI of fine pores showed a fluctuating increasing trend from northwest to southeast,and the fine pore shrinkage capacity determined the COLE(r^(2)=0.789,P<0.001).The PSI of large pores had a significant relationship with soil bulk density(r=0.281,P<0.05)and organic carbon(r=-0.311,P<0.05),whereas those of medium and fine pores were correlated with soil clay content(r=0.381 and 0.687,respectively,P<0.001).In addition,the PSI of fine pores was also correlated with montmorillonite content(r=0.387,P<0.01).It can be concluded that the PSI of large pores is related to anthropogenically influenced soil properties with low stability,whereas those of medium and fine pores are related to pedogenic properties.The high variability in anthropogenic and pedogenic factors explains the spatial pattern of Vertisol shrinkage capacity on the North China Plain.

Monitoring and predicting the soil water content in the deeper soil profile of Loess Plateau,China

Estimation of soil water content(SWC)in deep soil profiles is of crucial importance for strategic management of water resource for sustainable land use in arid and semi-arid zones,as well as for soil and water conservation.Soil properties have a very important effect on SWC.This study aimed to analyze the influence of soil particle size on SWC,for the first time using soil particle size to estimate SWC in deep soil profiles.SWC was measured mainly in farmland,natural grasslands and plantations of Caragana from the surface to more than 20 m depth.The same soil samples were also tested for particle size.The results show that the soil desiccation is formed in the caragana forest in 3–18 m soil layers,but almost no formation in 18–24 m layers;water content of farmland and grassland is different in all soil profiles although they are both shallow rooted plants.Correlation analysis indicated that SWC could be well predicted by clay content and the close correlation between SWC and clay content yielded a coefficient of determination(R^(2))of 0.82 and 0.72,respectively,for farmland and grassland.After multiple regression analysis,a regression model was built using SWC,clay content and sand content data,giving R^(2)=0.66.The model provided reliable estimates of SWC profile based on textural class.This can assist in estimating water depletion by vegetation,by comparing moisture of farmland and grassland soils with that of plantation forests,and in selecting sustainable land use of arid land.

Experimental study on calculation model of labyrinth emitter discharge under subsurface drip irrigation

For different texture of soils,the grain composition is different with significant changes.Since the emitter of subsurface drip irrigation(SDI)is buried in the soil,emitter discharge is influenced by soil properties.An experiment was conducted to investigate the relationship between the soil properties with emitter working pressure and emitter discharge of SDI.Selecting three different grain composition soils,and emitter working pressure,as well as soil clay content,soil bulk density and initial soil moisture content respectively as influence factors of emitter discharge of SDI,the experimental scheme was gained by uniform design.A calculation model for determination of the SDI emitter discharge was established by regression analysis with the first two kinds of soil test data,and its reliability was verified by the third kind of soil test data.The model is simple with high accuracy,easy to use,and lays the foundation to study hydraulic elements of SDI field network,especially taking the soil clay content as an influencing factor has widened the scope of application of the model.The achievement is of great significance for design and management of SDI.

Spatial Variation of Hydraulic Conductivity Categories in a Highly Heterogeneous Aquifer： A Case Study in the North China Plain (NCP)

Compared with research on spatial variation of hydraulic conductivity（K）, less effort has been made researching different grades of K value in the North China Plain（NCP）. In this study, 3D spatial distribution models of different grades of K were established by considering the effects of clay fraction content and uniformity coefficient（Cu）. The K value can be divided into five grades： very low, low, permeable, high, and very high groups. The volume percentages of these clusters were 3.06%, 36.01%, 55.70%, 4.82%, and 0.41% for the first aquifer; 0.016%, 9.56%, 88.25%, 2.16%, and 0.014% for the second aquifer; and 0.04%, 17.74%, 84.21%, 0.001%, and 0.01% for the third aquifer. It is concluded that the high and very high K values are fully affected by burial depth and that the very low, low, and permeable K values are mainly controlled by depositional environment and are partially influenced by burial depth. The burial depth became the main influencing factor only within the same depositional environment, causing the overall K to decrease with depth. The variations of very low, low, permeable, high, and very high categories of K values with depth are described in this study. This can provide useful information for non-technical decision makers to achieve sustainable development of deep groundwater resources.