In order to assess the performance of the embankment soil under various climate conditions during the period of service, the modulus behaviour of an unsaturated compacted soil is evaluated using the constant water con...In order to assess the performance of the embankment soil under various climate conditions during the period of service, the modulus behaviour of an unsaturated compacted soil is evaluated using the constant water content triaxial test. Since the water content measurement method is simple and economical and it is used widely in engineering, the soil suction is replaced by the water content and the relationship between the water content and the modulus is developed. The compacted samples are prepared with different compacted water contents, and samples with a similar water content subjected to drying or wetting procedures prior to the triaxial test are also investigated. The effect of the water content and the confining pressure on the modulus is analyzed. The results show that the modulus decreases with the increase in the water content and a power function can be proposed to quantitatively describe the relationship between the modulus and the water content in the range of the measured water content. The modulus increases with the increase in the confining pressure of the compacted soil. However, the effect of the water content on the modulus is more pronounced than that of the confining pressure. This research can be referenced for the compacted embankment soil assessment in-service period.展开更多
Loess soil deposits are widely distributed in arid and semi-arid regions and constitute about 10% of land area of the world.These soils typically have a loose honeycomb-type meta-stable structure that is susceptible t...Loess soil deposits are widely distributed in arid and semi-arid regions and constitute about 10% of land area of the world.These soils typically have a loose honeycomb-type meta-stable structure that is susceptible to a large reduction in total volume or collapse upon wetting.Collapse characteristics contribute to various problems to infrastructures that are constructed on loess soils.For this reason,collapse triggering mechanism for loess soils has been of significant interest for researchers and practitioners all over the world.This paper aims at providing a state-of-the-art review on collapse mechanism with special reference to loess soil deposits.The collapse mechanism studies are summarized under three different categories,i.e.traditional approaches,microstructure approach,and soil mechanics-based approaches.The traditional and microstructure approaches for interpreting the collapse behavior are comprehensively summarized and critically reviewed based on the experimental results from the literature.The soil mechanics-based approaches proposed based on the experimental results of both compacted soils and natural loess soils are reviewed highlighting their strengths and limitations for estimating the collapse behavior.Simpler soil mechanics-based approaches with less parameters or parameters that are easy-to-determine from conventional tests are suggested for future research to better understand the collapse behavior of natural loess soils.Such studies would be more valuable for use in conventional geotechnical engineering practice applications.展开更多
Seasonal development of soil microbial activity and bacterial biomass in sub-polar regions was investigated to determine the impacts of biotic and abiotic factors, such as organic matter content, temperature and moist...Seasonal development of soil microbial activity and bacterial biomass in sub-polar regions was investigated to determine the impacts of biotic and abiotic factors, such as organic matter content, temperature and moisture. The study was performed during spring thaw from three cultivated meadows and two non-cultivated forest sites near Alta, in northern Norway. Samples from all five sites showed increasing respiration rates directly after the spring thaw with soil respiration activity best related to soil organic matter content. However, distributions of bacterial biomass showed fewer similarities to these two parameters. This could be explained by variations of litter exploitation through the biomass. Microbial activity started immediately after the thaw while root growth had a longer time lag. An influence of root development on soil microbes was proposed for sites where microorganisms and roots had a tight relationship caused by a more intensive root structure. Also a reduction of microbial activity due to soil compaction in the samples from a wheel track could not be observed under laboratory conditions. New methodological approaches of differential staining for live and dead organisms were applied in order to follow changes within the microbial community. Under laboratory conditions freeze and thaw cycles showed a damaging influence on parts of the soil bacteria. Additionally, different patterns for active vs. non-active bacteria were noticeable after freeze-thaw cycles.展开更多
This study focuses on the saturated anisotropic hydraulic conductivity of a compacted lateritic clayey sandy soil. The effects of the molding water content and the confining stress on the anisotropic hydraulic conduct...This study focuses on the saturated anisotropic hydraulic conductivity of a compacted lateritic clayey sandy soil. The effects of the molding water content and the confining stress on the anisotropic hydraulic conductivity are investigated. The hydraulic conductivity is measured with a flexible-wall permeameter. Samples are dynamically compacted into the three compaction states of a standard Proctor compaction curve： the dry branch, optimum water content and wet branch. Depending on the molding water content and confining stress, the hydraulic conductivity may increase or decrease. In addition, the results indicate that, when the samples are compacted to the optimum water content, lower hydraulic conductivity is obtained, except at a confining stress equal to 50 kPa. The increase of the confining stress decreases the hydraulic conductivity for each of the evaluated compaction states. In the wet branch, horizontal hy- draulic conductivity is about 8 times higher than the vertical value. The anisotropic hydraulic conduc- tivities of the dry and wet branches decrease when the confining stress increases, and the opposite is observed in the optimum water content state.展开更多
Deforestation of headwater in the Andes of Colombia is a historical process that has its origins in pre-Hispanic communities and in nineteenth and twentieth centuries, intensified by settlers and farmers. These lands ...Deforestation of headwater in the Andes of Colombia is a historical process that has its origins in pre-Hispanic communities and in nineteenth and twentieth centuries, intensified by settlers and farmers. These lands have been intended mainly to pasture cattle. Soil compaction, caused by the trampling of cattle, was evaluated in soils derived from volcanic ash (Andisols), with reference to values found for variables in undisturbed natural forests in the same region. The compared parameters were bulk density (Db), total porosity (α), soil resistance to penetration (Rp) and pore size distribution, analyzed by water retention curves (WRC). The grazed soils had significant differences with respect to the natural forest reference values: Db was 53.7% higher, α was reduced by 11.0% and Rp in the first 7.5 cm of the top soil was more than double, with an average increase of 275.2 to 527.2 kPa. The analysis indicated that compacted soils had relatively uniform reduction in distribution of macro, meso and micropores. It was concluded that deforestation followed by pasture land destination in steep headwaters generates significant compaction processes that can affect the infiltration, percolation and soil water storage, which would have important hydrological implications: augmentation of surface runoff and soil erosion, decreased the base flow and increased direct runoff. For this reasons, it is considered that forest restoration of headwaters is important for the maintenance of hydrological functions of large river systems.展开更多
With the advancement of agricultural mechanization,soil compaction has become a serious environmental problem.Soil compaction can increase soil bulk density and firmness,reduce porosity and permeability,and deteriorat...With the advancement of agricultural mechanization,soil compaction has become a serious environmental problem.Soil compaction can increase soil bulk density and firmness,reduce porosity and permeability,and deteriorate soil structure,ultimately inhibit sugar beet growth and reduce both root yield and sugar content.However,few farmers recognize the link between soil compaction and these adverse effects.Soil compaction has a cumulative effect,with significant differences observed in the vertical range of compaction accumulation.The most significant soil compaction occurs in the topsoil of 0-10 cm,and the influence depth can reach 70 cm,but it is small in deep soil,and the inflection point is at a soil depth of 10 cm.The degree of soil compaction is related to soil type,water content,tractor shaft load,tyre type,tyre pressure and operation speed,etc.Therefore,in the production process of sugar beet,it is advisable to avoid high-humidity operations,use low pressure tyres,reduce the number of tractor-units passes over the farmland,and implement agricultural and agronomic measures to minimize soil compaction.These practices will help protect the soil environment and ensure sustainable production of sugar beets.展开更多
[Objective] This study was conducted to explore the effects of deep loos- ening on soil structure and the activity of maize root system, to provide a theoreti- cal basis for the efficient and rational use of water res...[Objective] This study was conducted to explore the effects of deep loos- ening on soil structure and the activity of maize root system, to provide a theoreti- cal basis for the efficient and rational use of water resources. [Method] Three differ- ent loosening treatments for maize in ridges were performed in field trials as fol- lows： conventional ridge tillage, loosening the cm in spring （deep loosening in spring）, and depth of 30 cm in autumn （deep loosening in soils between rows to a depth of 30 oosening the soils between rows to a autumn）. Then the soil properties and the development of root system were measured to evaluate the effects of different loosening methods. [Result] Soil compactness was significantly reduced after deep loosening in spring, There were significant differences in soil compactness in 0-20 cm depth and soil bulk density in 0-40 cm depth between deep loosening in spring and deep loosening in autumn, deep loosening in spring and conventional ridge tillage. The soil water holding capacity was also significantly different between the two deep loosening treatments and conventional ridge tillage. Moreover, the root ac- tive absorption area of maize of deep loosening in spring was higher than that of conventionai ridge tillage. [Conclusion] Deep loosening can reduce soil compactness, bulk density, and improve soil water holding capacity, soil water content and the root activity of maize. Deep loosening in spring is better in soil improvement be- cause spring is closer to the growth period of crops than autumn. So, deep loosen- ing is conducive to the improvement of soil compactness and structure.展开更多
As agricultural mechanization is becoming more and more popular, soil compaction, on basis of agricultural machinery, has become a serious problem that can not be ignored. Soil compaction, which is caused by frequent ...As agricultural mechanization is becoming more and more popular, soil compaction, on basis of agricultural machinery, has become a serious problem that can not be ignored. Soil compaction, which is caused by frequent til age and large load in the field, may have different effects on various properties of soil. Soil com-paction may result in different conditions, such as increased soil density and the mechanical resistance, and decreased soil ventilation and the capacity of water holding and storage, but uptaking capacity of chemical elements is restricted. There-fore, soil compaction has some negative impacts on soil properties, physical y, chemical y, or biological y, as wel as plant growth. This research analyzed the cause and the harm of soil compaction in recent years, and some effective mea-sures were proposed to improve soil compaction, in order to reduce the extent of soil compaction caused by agricultural machinery.展开更多
The paper presents two case studies that provide information on the process of homogenization of initially heterogeneous clay barriers and seals. The first case is the canister retrieval test performed in the Asp0 Har...The paper presents two case studies that provide information on the process of homogenization of initially heterogeneous clay barriers and seals. The first case is the canister retrieval test performed in the Asp0 Hard Rock Laboratory （Sweden）. The heterogeneity arises from the use of a combination of blocks and pellets to construct the engineered barrier. The degree of homogenization achieved by the end of the tests is evaluated from data obtained during the dismantling of the test. To assist in the interpretation of the test, a fully coupled thermo-hydro-mechanical （THM） analysis has been carried out. The second case involves the shaft sealing test performed in the HADES underground research laboratory （URL） in Mol （Belgium）. Here the seal is made up of a heterogeneous mixture of bentonite pellets and bentonite powders. In addition to the full scale test, the process of homogenization of the mixture has also been observed in the laboratory using X-ray tomography. Both field test and laboratory tests are successfully modelled by a coupled hydro-mechanical （HM） analysis using a double structure constitutive law. The paper concludes with some considerations on the capability of highly expansive materials to provide a significant degree of homogenization upon hydration.展开更多
A two-year experiment was carried out on the effect of sprinkler irrigation on the topsoil structure in a winter wheat field. A border-irrigated field was used as the control group. The total soil porosity, pore size ...A two-year experiment was carried out on the effect of sprinkler irrigation on the topsoil structure in a winter wheat field. A border-irrigated field was used as the control group. The total soil porosity, pore size distribution, pore shape distribution, soil cracks and soil compaction were measured. The sprinkler irrigation brought significant changes to the total soil porosity, capillary porosity, air-filled porosity and pore shape of topsoil layers in comparison with the border irrigation. The total porosity and air-filled porosity of the topsoil in the sprinkler irrigation were higher than those in the border irrigation. The changes in the air-filled and elongated pores were the main reasons for the changes in total porosity. The porosities of round and irregular pores in topsoil under sprinkler irrigation were lower than those under border irrigation. Sprinkler irrigation produced smaller soil cracks than border irrigation did, so sprinkler irrigation may restrain the development of macropore flow in comparison with border irrigation. The topsoil was looser under sprinkler irrigation than under border irrigation. According to the conditions of topsoil structure, it is preferable for crops to grow under sprinkler irrigation than under border irrigation.展开更多
The widespread contamination of soils and aquifers by non-aqueous phase liquids （NAPL）, such as crude oil, poses serious environmental and health hazards globally. Understanding the infiltration characteristics of N...The widespread contamination of soils and aquifers by non-aqueous phase liquids （NAPL）, such as crude oil, poses serious environmental and health hazards globally. Understanding the infiltration characteristics of NAPL in soil is crucial in mitigating or remediating soil contamination. The infiltration characteristics of crude and diesel oils into undisturbed loessal soil cores, collected in polymethyl methacrylate cylindrical columns, were investigated under a constant fluid head （3 era） of either crude oil or diesel oil. The infiltration rate of both crude and diesel oils decreased exponentially as wetting depth increased with time. Soil core size and bulk density both had significant effects on NAPL infiltration through the undisturbed soil cores; a smaller core size or a greater bulk density could reduce oil penetration to depth. Compacting soil in areas susceptible to oil spills may be an effective stratage to reduce contamination. The infiltration of NAPL into soil cores was spatially anisotropic and heterogeneous, thus recording the data at four points on the soil core is a good stratage to improve the accuracy of experimental results. Our results revealed that crude and diesel oils, rather than their components, have a practical value for remediation of contaminated loessal soils.展开更多
The compaction and stress generation on terrain were always investigated based on empirical approaches or testing methods for tire/soil interaction.However,the analysis should be performed for various tires and at dif...The compaction and stress generation on terrain were always investigated based on empirical approaches or testing methods for tire/soil interaction.However,the analysis should be performed for various tires and at different soil strengths.With the increasing capacity of numerical computers and simulation software,finite element modeling of tire/terrain interaction seems a good approach for predicting the effect of change on the parameters.In this work,an elaborated 3D model fully complianning with the geometry of radial tire 115/60R13 was established,using commercial code Solidwork Simulation.The hyper-elastic and incompressible rubber as tire main material was analyzed by Moony-Rivlin model.The Drucker-Prager yield criterion was used to model the soil compaction.Results show that the model realistically predicts the laboratory tests outputs of the modeled tire on the soft soil.展开更多
Ground subsidence is an emerging geological hazard in Baotou,Inner Mongolia.Four areas of Baotou with relatively large subsidence range and rate were selected for analysis.Focusing on investigation of ground subsidenc...Ground subsidence is an emerging geological hazard in Baotou,Inner Mongolia.Four areas of Baotou with relatively large subsidence range and rate were selected for analysis.Focusing on investigation of ground subsidence using PS-In SAR technology,a total of 43 frames of ALOS PALSAR images yielded a SAR data span from December 2006 to January 2011,allowing ground subsidence scope,subsidence velocity,time-series deformation to be obtained.Major causes and influencing factors of the ground subsidence are closely related to soft soil consolidation and compaction and the decrease in the level of groundwater caused by increased development and utilization of groundwater.展开更多
The mechanical properties of granitic residual soils vary with depth due to changes in soil type and heterogeneity caused by weathering.The purpose of this study was to relate the spatial variation of particle-size di...The mechanical properties of granitic residual soils vary with depth due to changes in soil type and heterogeneity caused by weathering.The purpose of this study was to relate the spatial variation of particle-size distribution(PSD)of granitic soils with soil shrinkage parameters using multifractal theory.The heterogeneity of PSD and pedogenic processes were depicted in detail by multifractal dimensions.The PSD generally increased with the increase of profile depth in accordance with the variation of single fractal dimension(D)ranging from 2.45 to 2.65.The shrinkage limit was greatly influenced by the multifractal dimension parameters,including information dimension(D1)and capacity dimension(D0)(Adjusted R2=0.998,P<0.01),and the maximum linear extensibility(κv)was determined by spectral width(?α)and bulk density,with the latter explaining 89%of the total variance ofκv(P<0.01).Soil shrinkage characteristic curve was fitted by the modified logistic model(R2>0.97,root sum of squares<0.1),and the water variation corresponding to the maximum change rate of linear extensibility was determined by the silt content(R2=0.81,P<0.01).Overall,the shrinkage of granitic soils was primarily influenced by PSD and soil compactness.展开更多
Wood extraction by heavy machinery has always been associated with soil disturbance in mountain forests,and the degree of soil degradation is influenced by several factors,including site and soil characteristics,soil ...Wood extraction by heavy machinery has always been associated with soil disturbance in mountain forests,and the degree of soil degradation is influenced by several factors,including site and soil characteristics,soil moisture,type of equipment used,and number of machine passes.The effects of ground-based skidding operations on the physical properties of soils with different texture were evaluated at different levels of traffic frequency and trail gradient at two sites in an Iranian temperate forest.The treatments included combinations of three different traffic frequencies(3,8,and 14 passes of a rubber-tired cable skidder),three levels of trail gradient(<10%,10%–20%,and>20%) and two soil texture classes,clay loam(Site 1) and sandy loam(Site 2).The average gravimetric soil moisture at the time of skidding was 23%(Site 1) and 20%(Site 2).The average dry bulk density and total porosity of the undisturbed soil(control) were0.71 g cm-3 and 73.3% at Site 1(clay loam) and 0.86 g cm-3and 59.1% at Site 2(sandy loam),respectively.At site 1(fine-textured soil),rutting began after three passes of the skidder,whereas at site 2(coarse-textured soil),rutting occurred only after eight passes.Independent of the traffic frequency and trail gradient,machine impact on the fine-textured soil caused greater increases in bulk density and rut depth compared to that on the coarse-textured soil.After three skidder passes and independent from trail gradients,dry bulk density at Site 1 increased by 54.8% compared to that of the undisturbed control,and the increase was 45.5% at Site 2.Therefore,medium to fine-textured soils are more susceptible to compaction than coarse-textured soils.Such soils,especially when moist,should be protected using brush mats created from harvesting residues during the forest processing phase.展开更多
A study was conducted to investigate the effects of skid trail slope and traffic levels on soil disturbances at two soil depths （0--10 and 10-20 cm）. The treatments were set at four traffic levels （2, 7, 12 and 20...A study was conducted to investigate the effects of skid trail slope and traffic levels on soil disturbances at two soil depths （0--10 and 10-20 cm）. The treatments were set at four traffic levels （2, 7, 12 and 20） two slope classes （〈20% and 〉20%） and two soil depths （0-10 and 10-20 cm）. Results show that skidder traffic, longitudinal slope and soil depth have significant effect on soil bulk density in skid trail. Compari- son of average soil bulk density in different traffic levels shows that there are significant differences in average bulk density between different traffic levels and control （p〈0.05）. The average bulk densities in different slopes and soil depths are significantly increased with increase in traffic levels, maximized at 12 passes （p〈0.05）, but there are no significant differences between 12 and 20 passes. The interaction effects between traffic and soil depth are significant （F005,3=0.109, p〈0.001）. For all traffic treatments, there are significant differences in soil moisture con- tent between the two slope classes and the two depths （p〈0.001）. However, the interaction effects between traffic levels and slope classes are not significant （p 〉0.05）, although skidder traffic and slope affected soil moisture content.展开更多
Soil drying may induce a number of stresses on crops. This paper investigated maize（Zea mays L.） root growth as affected by drought and soil penetration resistance（PR）, which was caused by soil drying and tillage ...Soil drying may induce a number of stresses on crops. This paper investigated maize（Zea mays L.） root growth as affected by drought and soil penetration resistance（PR）, which was caused by soil drying and tillage in a clayey red soil. Compared with conventional tillage（C） and deep tillage（D）, soil compaction（P） and no-till（N） significantly increased soil PR in the 0-15 cm layer. The PR increased dramatically as the soil drying increased, particularly in soil with a high bulk density. Increased soil PR reduced the maize root mass density distribution not only in the vertical profile（0-20 cm） but also in the horizontal layer at the same distance（0-5, 5-10, 10-15 cm） from the maize plant. With an increase in soil PR in pots, the maize root length, root surface area and root volume significantly decreased. Specifically, the maize root length declined exponentially from 309 to 64 cm per plant with an increase in soil PR from 491 to 3 370 k Pa; the roots almost stopped elongating when the soil PR was larger than 2 200 k Pa. It appeared that fine roots（〈2.5 mm in diameter） thickened when the soil PR increased, resulting in a larger average root diameter. The average root diameter increased linearly with soil PR, regardless of soil irrigation or drought. The results suggest that differences in soil PR caused by soil drying is most likely responsible for inconsistent root responses to water stress in different soils.展开更多
Determining the physical and mechanical properties of soil and its behavior for engineering projects is essential for road construction operations. One of the most important principles in forest road construction, whi...Determining the physical and mechanical properties of soil and its behavior for engineering projects is essential for road construction operations. One of the most important principles in forest road construction, which is usually neglected, is to avoid mixing organic matter with road materials during excavation and embankment construction. The current study aimed to assess the influence of organic matter on the physical properties and mechanical behaviors of forest soil and to analyze the relation between the amount of organic matter and the behavior of forest soil as road material. A typical soil sample from the study area was collected beside a newly constructed roadbed. The soil was mixed with different percentages of organic matter（control treatment, 5, 10, and 15% by mass） and different tests including Atterberg limits, standard compaction, and California bearing ratio（CBR） tests were conducted on these different soil mixtures. The results showed that soil plasticity increased linearly with increasing organic matter.Increasing the organic matter from 0%（control） to 15%resulted in an increase of 11.64% of the plastic limit and 15.22% of the liquid limit after drying at 110 ℃. Also,increasing the organic matter content reduced the soil maximum dry density and increased the optimum moisture content. Increasing the organic matter from 0 to 15% resulted in an increase of 11.0% of the optimum moisture content and a decrease of 0.29 g/cm;of the maximum dry density. Organic matter decreased the CBR, which is used as the index of road strength. Adding 15% organic matter to the soil resulted in a decrease of the CBR from 15.72 to 4.75%. There was a significant difference between the two drying temperatures（60 and 110 ℃） for the same organic matter mixtures with lower water content values after drying at 60 ℃. The results revealed the adverse influence of organic matter on soil engineering properties and showed the importance of organic matter removal before excavation and fill construction.展开更多
As important methods to guide the field soil compaction,the standard and modified Proctor tests for laboratory compaction have remained unchanged for decades,which should be improved to better understand the compactio...As important methods to guide the field soil compaction,the standard and modified Proctor tests for laboratory compaction have remained unchanged for decades,which should be improved to better understand the compaction process and the properties of soils.In this study,an accelerometer was installed on a Marshall impact compactor to capture the dynamic response of three types of soils during compaction.The experimental test results indicated that the acceleration curve for each blow gradually evolved to a stable pattern following the progress of compaction,and the impact and gyratory locking points were linearly related with coefficient of determination R2equal to 0.59.The impact compaction curve could be further constructed by filtering the structural resonance,which can be used to quantify the compactability of soil materials.Although each type of soil had a unique set of compaction curves,the slope and value of compaction curve altered accordingly as the moisture content changed for the same soil.In addition,the average acceleration value at the final compaction stage could serve as the target value of soil stiffness.展开更多
基金The Natural Science Foundation of Jiangsu Province(No. BK2011618)
文摘In order to assess the performance of the embankment soil under various climate conditions during the period of service, the modulus behaviour of an unsaturated compacted soil is evaluated using the constant water content triaxial test. Since the water content measurement method is simple and economical and it is used widely in engineering, the soil suction is replaced by the water content and the relationship between the water content and the modulus is developed. The compacted samples are prepared with different compacted water contents, and samples with a similar water content subjected to drying or wetting procedures prior to the triaxial test are also investigated. The effect of the water content and the confining pressure on the modulus is analyzed. The results show that the modulus decreases with the increase in the water content and a power function can be proposed to quantitatively describe the relationship between the modulus and the water content in the range of the measured water content. The modulus increases with the increase in the confining pressure of the compacted soil. However, the effect of the water content on the modulus is more pronounced than that of the confining pressure. This research can be referenced for the compacted embankment soil assessment in-service period.
基金the Chinese Scholarship Council,which funded her Joint Ph D research programthe support from Natural Sciences and Engineering Research Council of Canada(NSERC)for his research programsthe Chinese Ministry of Science and Technology for supporting his research program(grant No.2014CB744701)
文摘Loess soil deposits are widely distributed in arid and semi-arid regions and constitute about 10% of land area of the world.These soils typically have a loose honeycomb-type meta-stable structure that is susceptible to a large reduction in total volume or collapse upon wetting.Collapse characteristics contribute to various problems to infrastructures that are constructed on loess soils.For this reason,collapse triggering mechanism for loess soils has been of significant interest for researchers and practitioners all over the world.This paper aims at providing a state-of-the-art review on collapse mechanism with special reference to loess soil deposits.The collapse mechanism studies are summarized under three different categories,i.e.traditional approaches,microstructure approach,and soil mechanics-based approaches.The traditional and microstructure approaches for interpreting the collapse behavior are comprehensively summarized and critically reviewed based on the experimental results from the literature.The soil mechanics-based approaches proposed based on the experimental results of both compacted soils and natural loess soils are reviewed highlighting their strengths and limitations for estimating the collapse behavior.Simpler soil mechanics-based approaches with less parameters or parameters that are easy-to-determine from conventional tests are suggested for future research to better understand the collapse behavior of natural loess soils.Such studies would be more valuable for use in conventional geotechnical engineering practice applications.
文摘Seasonal development of soil microbial activity and bacterial biomass in sub-polar regions was investigated to determine the impacts of biotic and abiotic factors, such as organic matter content, temperature and moisture. The study was performed during spring thaw from three cultivated meadows and two non-cultivated forest sites near Alta, in northern Norway. Samples from all five sites showed increasing respiration rates directly after the spring thaw with soil respiration activity best related to soil organic matter content. However, distributions of bacterial biomass showed fewer similarities to these two parameters. This could be explained by variations of litter exploitation through the biomass. Microbial activity started immediately after the thaw while root growth had a longer time lag. An influence of root development on soil microbes was proposed for sites where microorganisms and roots had a tight relationship caused by a more intensive root structure. Also a reduction of microbial activity due to soil compaction in the samples from a wheel track could not be observed under laboratory conditions. New methodological approaches of differential staining for live and dead organisms were applied in order to follow changes within the microbial community. Under laboratory conditions freeze and thaw cycles showed a damaging influence on parts of the soil bacteria. Additionally, different patterns for active vs. non-active bacteria were noticeable after freeze-thaw cycles.
文摘This study focuses on the saturated anisotropic hydraulic conductivity of a compacted lateritic clayey sandy soil. The effects of the molding water content and the confining stress on the anisotropic hydraulic conductivity are investigated. The hydraulic conductivity is measured with a flexible-wall permeameter. Samples are dynamically compacted into the three compaction states of a standard Proctor compaction curve： the dry branch, optimum water content and wet branch. Depending on the molding water content and confining stress, the hydraulic conductivity may increase or decrease. In addition, the results indicate that, when the samples are compacted to the optimum water content, lower hydraulic conductivity is obtained, except at a confining stress equal to 50 kPa. The increase of the confining stress decreases the hydraulic conductivity for each of the evaluated compaction states. In the wet branch, horizontal hy- draulic conductivity is about 8 times higher than the vertical value. The anisotropic hydraulic conduc- tivities of the dry and wet branches decrease when the confining stress increases, and the opposite is observed in the optimum water content state.
文摘Deforestation of headwater in the Andes of Colombia is a historical process that has its origins in pre-Hispanic communities and in nineteenth and twentieth centuries, intensified by settlers and farmers. These lands have been intended mainly to pasture cattle. Soil compaction, caused by the trampling of cattle, was evaluated in soils derived from volcanic ash (Andisols), with reference to values found for variables in undisturbed natural forests in the same region. The compared parameters were bulk density (Db), total porosity (α), soil resistance to penetration (Rp) and pore size distribution, analyzed by water retention curves (WRC). The grazed soils had significant differences with respect to the natural forest reference values: Db was 53.7% higher, α was reduced by 11.0% and Rp in the first 7.5 cm of the top soil was more than double, with an average increase of 275.2 to 527.2 kPa. The analysis indicated that compacted soils had relatively uniform reduction in distribution of macro, meso and micropores. It was concluded that deforestation followed by pasture land destination in steep headwaters generates significant compaction processes that can affect the infiltration, percolation and soil water storage, which would have important hydrological implications: augmentation of surface runoff and soil erosion, decreased the base flow and increased direct runoff. For this reasons, it is considered that forest restoration of headwaters is important for the maintenance of hydrological functions of large river systems.
基金Supported by China Agriculture Research System(Sugar Crops)of Ministry of Agriculture and Rural Affairs and Ministry of Finance(CARS-170601)Natural Science Foundation of Heilongjiang Province(C201239).
文摘With the advancement of agricultural mechanization,soil compaction has become a serious environmental problem.Soil compaction can increase soil bulk density and firmness,reduce porosity and permeability,and deteriorate soil structure,ultimately inhibit sugar beet growth and reduce both root yield and sugar content.However,few farmers recognize the link between soil compaction and these adverse effects.Soil compaction has a cumulative effect,with significant differences observed in the vertical range of compaction accumulation.The most significant soil compaction occurs in the topsoil of 0-10 cm,and the influence depth can reach 70 cm,but it is small in deep soil,and the inflection point is at a soil depth of 10 cm.The degree of soil compaction is related to soil type,water content,tractor shaft load,tyre type,tyre pressure and operation speed,etc.Therefore,in the production process of sugar beet,it is advisable to avoid high-humidity operations,use low pressure tyres,reduce the number of tractor-units passes over the farmland,and implement agricultural and agronomic measures to minimize soil compaction.These practices will help protect the soil environment and ensure sustainable production of sugar beets.
基金Supported by National Maize Industry Technology System(CARS-02-38)Science and Technology Development Project of Jilin Province(LFGC14308)Special Fund for Scientific Research in the Public Interest(201303125-03)
文摘[Objective] This study was conducted to explore the effects of deep loos- ening on soil structure and the activity of maize root system, to provide a theoreti- cal basis for the efficient and rational use of water resources. [Method] Three differ- ent loosening treatments for maize in ridges were performed in field trials as fol- lows： conventional ridge tillage, loosening the cm in spring （deep loosening in spring）, and depth of 30 cm in autumn （deep loosening in soils between rows to a depth of 30 oosening the soils between rows to a autumn）. Then the soil properties and the development of root system were measured to evaluate the effects of different loosening methods. [Result] Soil compactness was significantly reduced after deep loosening in spring, There were significant differences in soil compactness in 0-20 cm depth and soil bulk density in 0-40 cm depth between deep loosening in spring and deep loosening in autumn, deep loosening in spring and conventional ridge tillage. The soil water holding capacity was also significantly different between the two deep loosening treatments and conventional ridge tillage. Moreover, the root ac- tive absorption area of maize of deep loosening in spring was higher than that of conventionai ridge tillage. [Conclusion] Deep loosening can reduce soil compactness, bulk density, and improve soil water holding capacity, soil water content and the root activity of maize. Deep loosening in spring is better in soil improvement be- cause spring is closer to the growth period of crops than autumn. So, deep loosen- ing is conducive to the improvement of soil compactness and structure.
文摘As agricultural mechanization is becoming more and more popular, soil compaction, on basis of agricultural machinery, has become a serious problem that can not be ignored. Soil compaction, which is caused by frequent til age and large load in the field, may have different effects on various properties of soil. Soil com-paction may result in different conditions, such as increased soil density and the mechanical resistance, and decreased soil ventilation and the capacity of water holding and storage, but uptaking capacity of chemical elements is restricted. There-fore, soil compaction has some negative impacts on soil properties, physical y, chemical y, or biological y, as wel as plant growth. This research analyzed the cause and the harm of soil compaction in recent years, and some effective mea-sures were proposed to improve soil compaction, in order to reduce the extent of soil compaction caused by agricultural machinery.
基金co-funded by ANDRA,CIEMAT,ONDRAF-NIRAS and the European Commission (EC contracts FIKWCT-2000-00010 and STRP-036458)The support of the Spanish Ministry of Science and Innovation trough grant BIA2011-27217 is also gratefully acknowledged
文摘The paper presents two case studies that provide information on the process of homogenization of initially heterogeneous clay barriers and seals. The first case is the canister retrieval test performed in the Asp0 Hard Rock Laboratory （Sweden）. The heterogeneity arises from the use of a combination of blocks and pellets to construct the engineered barrier. The degree of homogenization achieved by the end of the tests is evaluated from data obtained during the dismantling of the test. To assist in the interpretation of the test, a fully coupled thermo-hydro-mechanical （THM） analysis has been carried out. The second case involves the shaft sealing test performed in the HADES underground research laboratory （URL） in Mol （Belgium）. Here the seal is made up of a heterogeneous mixture of bentonite pellets and bentonite powders. In addition to the full scale test, the process of homogenization of the mixture has also been observed in the laboratory using X-ray tomography. Both field test and laboratory tests are successfully modelled by a coupled hydro-mechanical （HM） analysis using a double structure constitutive law. The paper concludes with some considerations on the capability of highly expansive materials to provide a significant degree of homogenization upon hydration.
基金Supported by the National Natural Science Foundation of China (No.50679077)the Knowledge Innovation Programof the Chinese Academy of Sciences (No.KSCX2-YW-N-003)the National Key Technology R&D Program of China(No.2007BAD87B05)
文摘A two-year experiment was carried out on the effect of sprinkler irrigation on the topsoil structure in a winter wheat field. A border-irrigated field was used as the control group. The total soil porosity, pore size distribution, pore shape distribution, soil cracks and soil compaction were measured. The sprinkler irrigation brought significant changes to the total soil porosity, capillary porosity, air-filled porosity and pore shape of topsoil layers in comparison with the border irrigation. The total porosity and air-filled porosity of the topsoil in the sprinkler irrigation were higher than those in the border irrigation. The changes in the air-filled and elongated pores were the main reasons for the changes in total porosity. The porosities of round and irregular pores in topsoil under sprinkler irrigation were lower than those under border irrigation. Sprinkler irrigation produced smaller soil cracks than border irrigation did, so sprinkler irrigation may restrain the development of macropore flow in comparison with border irrigation. The topsoil was looser under sprinkler irrigation than under border irrigation. According to the conditions of topsoil structure, it is preferable for crops to grow under sprinkler irrigation than under border irrigation.
基金supported by the Innovation Team Pro-gram of Chinese Academy of Sciencesthe Program for Innovative Research Team in University (No IRT0749)
文摘The widespread contamination of soils and aquifers by non-aqueous phase liquids （NAPL）, such as crude oil, poses serious environmental and health hazards globally. Understanding the infiltration characteristics of NAPL in soil is crucial in mitigating or remediating soil contamination. The infiltration characteristics of crude and diesel oils into undisturbed loessal soil cores, collected in polymethyl methacrylate cylindrical columns, were investigated under a constant fluid head （3 era） of either crude oil or diesel oil. The infiltration rate of both crude and diesel oils decreased exponentially as wetting depth increased with time. Soil core size and bulk density both had significant effects on NAPL infiltration through the undisturbed soil cores; a smaller core size or a greater bulk density could reduce oil penetration to depth. Compacting soil in areas susceptible to oil spills may be an effective stratage to reduce contamination. The infiltration of NAPL into soil cores was spatially anisotropic and heterogeneous, thus recording the data at four points on the soil core is a good stratage to improve the accuracy of experimental results. Our results revealed that crude and diesel oils, rather than their components, have a practical value for remediation of contaminated loessal soils.
文摘The compaction and stress generation on terrain were always investigated based on empirical approaches or testing methods for tire/soil interaction.However,the analysis should be performed for various tires and at different soil strengths.With the increasing capacity of numerical computers and simulation software,finite element modeling of tire/terrain interaction seems a good approach for predicting the effect of change on the parameters.In this work,an elaborated 3D model fully complianning with the geometry of radial tire 115/60R13 was established,using commercial code Solidwork Simulation.The hyper-elastic and incompressible rubber as tire main material was analyzed by Moony-Rivlin model.The Drucker-Prager yield criterion was used to model the soil compaction.Results show that the model realistically predicts the laboratory tests outputs of the modeled tire on the soft soil.
文摘Ground subsidence is an emerging geological hazard in Baotou,Inner Mongolia.Four areas of Baotou with relatively large subsidence range and rate were selected for analysis.Focusing on investigation of ground subsidence using PS-In SAR technology,a total of 43 frames of ALOS PALSAR images yielded a SAR data span from December 2006 to January 2011,allowing ground subsidence scope,subsidence velocity,time-series deformation to be obtained.Major causes and influencing factors of the ground subsidence are closely related to soft soil consolidation and compaction and the decrease in the level of groundwater caused by increased development and utilization of groundwater.
基金supported by the National Natural Science Foundation of China(Nos.41807065 and 41630858)
文摘The mechanical properties of granitic residual soils vary with depth due to changes in soil type and heterogeneity caused by weathering.The purpose of this study was to relate the spatial variation of particle-size distribution(PSD)of granitic soils with soil shrinkage parameters using multifractal theory.The heterogeneity of PSD and pedogenic processes were depicted in detail by multifractal dimensions.The PSD generally increased with the increase of profile depth in accordance with the variation of single fractal dimension(D)ranging from 2.45 to 2.65.The shrinkage limit was greatly influenced by the multifractal dimension parameters,including information dimension(D1)and capacity dimension(D0)(Adjusted R2=0.998,P<0.01),and the maximum linear extensibility(κv)was determined by spectral width(?α)and bulk density,with the latter explaining 89%of the total variance ofκv(P<0.01).Soil shrinkage characteristic curve was fitted by the modified logistic model(R2>0.97,root sum of squares<0.1),and the water variation corresponding to the maximum change rate of linear extensibility was determined by the silt content(R2=0.81,P<0.01).Overall,the shrinkage of granitic soils was primarily influenced by PSD and soil compactness.
基金financially supported by University of Guilan, Iran
文摘Wood extraction by heavy machinery has always been associated with soil disturbance in mountain forests,and the degree of soil degradation is influenced by several factors,including site and soil characteristics,soil moisture,type of equipment used,and number of machine passes.The effects of ground-based skidding operations on the physical properties of soils with different texture were evaluated at different levels of traffic frequency and trail gradient at two sites in an Iranian temperate forest.The treatments included combinations of three different traffic frequencies(3,8,and 14 passes of a rubber-tired cable skidder),three levels of trail gradient(<10%,10%–20%,and>20%) and two soil texture classes,clay loam(Site 1) and sandy loam(Site 2).The average gravimetric soil moisture at the time of skidding was 23%(Site 1) and 20%(Site 2).The average dry bulk density and total porosity of the undisturbed soil(control) were0.71 g cm-3 and 73.3% at Site 1(clay loam) and 0.86 g cm-3and 59.1% at Site 2(sandy loam),respectively.At site 1(fine-textured soil),rutting began after three passes of the skidder,whereas at site 2(coarse-textured soil),rutting occurred only after eight passes.Independent of the traffic frequency and trail gradient,machine impact on the fine-textured soil caused greater increases in bulk density and rut depth compared to that on the coarse-textured soil.After three skidder passes and independent from trail gradients,dry bulk density at Site 1 increased by 54.8% compared to that of the undisturbed control,and the increase was 45.5% at Site 2.Therefore,medium to fine-textured soils are more susceptible to compaction than coarse-textured soils.Such soils,especially when moist,should be protected using brush mats created from harvesting residues during the forest processing phase.
文摘A study was conducted to investigate the effects of skid trail slope and traffic levels on soil disturbances at two soil depths （0--10 and 10-20 cm）. The treatments were set at four traffic levels （2, 7, 12 and 20） two slope classes （〈20% and 〉20%） and two soil depths （0-10 and 10-20 cm）. Results show that skidder traffic, longitudinal slope and soil depth have significant effect on soil bulk density in skid trail. Compari- son of average soil bulk density in different traffic levels shows that there are significant differences in average bulk density between different traffic levels and control （p〈0.05）. The average bulk densities in different slopes and soil depths are significantly increased with increase in traffic levels, maximized at 12 passes （p〈0.05）, but there are no significant differences between 12 and 20 passes. The interaction effects between traffic and soil depth are significant （F005,3=0.109, p〈0.001）. For all traffic treatments, there are significant differences in soil moisture con- tent between the two slope classes and the two depths （p〈0.001）. However, the interaction effects between traffic levels and slope classes are not significant （p 〉0.05）, although skidder traffic and slope affected soil moisture content.
基金supported by the National Natural Science Foundation of China (41271240)
文摘Soil drying may induce a number of stresses on crops. This paper investigated maize（Zea mays L.） root growth as affected by drought and soil penetration resistance（PR）, which was caused by soil drying and tillage in a clayey red soil. Compared with conventional tillage（C） and deep tillage（D）, soil compaction（P） and no-till（N） significantly increased soil PR in the 0-15 cm layer. The PR increased dramatically as the soil drying increased, particularly in soil with a high bulk density. Increased soil PR reduced the maize root mass density distribution not only in the vertical profile（0-20 cm） but also in the horizontal layer at the same distance（0-5, 5-10, 10-15 cm） from the maize plant. With an increase in soil PR in pots, the maize root length, root surface area and root volume significantly decreased. Specifically, the maize root length declined exponentially from 309 to 64 cm per plant with an increase in soil PR from 491 to 3 370 k Pa; the roots almost stopped elongating when the soil PR was larger than 2 200 k Pa. It appeared that fine roots（〈2.5 mm in diameter） thickened when the soil PR increased, resulting in a larger average root diameter. The average root diameter increased linearly with soil PR, regardless of soil irrigation or drought. The results suggest that differences in soil PR caused by soil drying is most likely responsible for inconsistent root responses to water stress in different soils.
基金financially supported by the University of Tehran
文摘Determining the physical and mechanical properties of soil and its behavior for engineering projects is essential for road construction operations. One of the most important principles in forest road construction, which is usually neglected, is to avoid mixing organic matter with road materials during excavation and embankment construction. The current study aimed to assess the influence of organic matter on the physical properties and mechanical behaviors of forest soil and to analyze the relation between the amount of organic matter and the behavior of forest soil as road material. A typical soil sample from the study area was collected beside a newly constructed roadbed. The soil was mixed with different percentages of organic matter（control treatment, 5, 10, and 15% by mass） and different tests including Atterberg limits, standard compaction, and California bearing ratio（CBR） tests were conducted on these different soil mixtures. The results showed that soil plasticity increased linearly with increasing organic matter.Increasing the organic matter from 0%（control） to 15%resulted in an increase of 11.64% of the plastic limit and 15.22% of the liquid limit after drying at 110 ℃. Also,increasing the organic matter content reduced the soil maximum dry density and increased the optimum moisture content. Increasing the organic matter from 0 to 15% resulted in an increase of 11.0% of the optimum moisture content and a decrease of 0.29 g/cm;of the maximum dry density. Organic matter decreased the CBR, which is used as the index of road strength. Adding 15% organic matter to the soil resulted in a decrease of the CBR from 15.72 to 4.75%. There was a significant difference between the two drying temperatures（60 and 110 ℃） for the same organic matter mixtures with lower water content values after drying at 60 ℃. The results revealed the adverse influence of organic matter on soil engineering properties and showed the importance of organic matter removal before excavation and fill construction.
文摘As important methods to guide the field soil compaction,the standard and modified Proctor tests for laboratory compaction have remained unchanged for decades,which should be improved to better understand the compaction process and the properties of soils.In this study,an accelerometer was installed on a Marshall impact compactor to capture the dynamic response of three types of soils during compaction.The experimental test results indicated that the acceleration curve for each blow gradually evolved to a stable pattern following the progress of compaction,and the impact and gyratory locking points were linearly related with coefficient of determination R2equal to 0.59.The impact compaction curve could be further constructed by filtering the structural resonance,which can be used to quantify the compactability of soil materials.Although each type of soil had a unique set of compaction curves,the slope and value of compaction curve altered accordingly as the moisture content changed for the same soil.In addition,the average acceleration value at the final compaction stage could serve as the target value of soil stiffness.
