A calibration test was done in order to measure its sensitivity coefficient by an improved soil test device.The experimental result shows that the soil pressure min-sensor made of the monocrystalline silicon（SPMMS）i...A calibration test was done in order to measure its sensitivity coefficient by an improved soil test device.The experimental result shows that the soil pressure min-sensor made of the monocrystalline silicon（SPMMS）is proved to be good linear,high precision and less that can fetch precise data in low pressure range even near by O point,which guarantees the reliability of the soil pressure test in geotechnical engineering.展开更多
Numerous incidents and failures of landslides in reservoir areas are attributed to water level fluctuations,which frequently induce cyclic changes in seepage pressure within the soil masses.Under such complex cyclic s...Numerous incidents and failures of landslides in reservoir areas are attributed to water level fluctuations,which frequently induce cyclic changes in seepage pressure within the soil masses.Under such complex cyclic seepage conditions,the hydro-mechanical behavior of sliding-zone soils may significantly differ from that observed under steady seepage conditions.However,the seepage characteristics and deformation behavior of sliding-zone soils experiencing cyclic seepage pressure are not yet fully understood.In this study,we conduct cyclic seepage pressure tests under isotropic consolidation to investigate the variation in hydraulic conductivity and volumetric strain of sliding-zone soils.The results show that the hydraulic conductivity of the sliding-zone soil samples fluctuatesunder cyclic seepage pressure,with the magnitude increasing as seepage pressure amplitude rises and decreasing with higher confiningpressure.Additionally,the volumetric strain of the sliding-zone soil samples exhibited notable fluctuationsunder cyclic seepage pressure,with the magnitude of the fluctuationsintensifying as the seepage pressure amplitude increased.The cumulative volumetric strain and irrecoverable volumetric strain of the samples are higher compared to those observed under steady seepage pressure.Subsequently,hysteresis loops are classifiedinto three types,each indicating distinct deformation characteristics.Finally,the micromechanism of sliding-zone soil under cyclic seepage pressure,considering the effect of physicochemical reactions on pore structure,is revealed to interpret better the intrinsic mechanism of seepage characteristics and deformation behavior.These findingsprovide a theoretical basis for further accurately evaluating reservoir landslide stability under fluctuatingwater levels.展开更多
Drought significantly constrains vegetation growth and reduces terrestrial carbon sinks.Currently,the spatiotemporal patterns and mechanisms of the differential impacts of soil and meteorological droughts on vegetatio...Drought significantly constrains vegetation growth and reduces terrestrial carbon sinks.Currently,the spatiotemporal patterns and mechanisms of the differential impacts of soil and meteorological droughts on vegetation productivity remain inadequately understood.In this study,we analyzed soil moisture(SM),vapor pressure deficit(VPD),and gross primary productivity(GPP)to investigate their spatiotemporal patterns and the combined effects on GPP over China.The results revealed that:(1)Soil drought and meteorological drought generally exhibited temporally synchronous trends across China.(2)GPP was predominantly affected by the combined and synchronous effects of both SM and VPD,although their effects displayed directional variability differences in certain regions.(3)SM demonstrated a greater relative importance on GPP than VPD across more than half of the regions in China,whereas deciduous broadleaf forests were the only vegetation type primarily affected by VPD.(4)Under the lag effects,both SM and VPD exhibited bidirectional Granger causality with GPP,with the interaction between VPD and GPP proving more pronounced than that of SM.Our research provides valuable insights into the mechanisms through which SM and VPD influence GPP,contributing to improved predictions vegetation productivity and implementing ecological restoration.展开更多
The article considers the impact of forestry machines on the soil of the cutting areas and presents the results of the impact of harvesters of different classes(middlesmall,middle and heavy)and configurations of wheel...The article considers the impact of forestry machines on the soil of the cutting areas and presents the results of the impact of harvesters of different classes(middlesmall,middle and heavy)and configurations of wheeled equipment and additional equipment on the soil of the cutting areas in the conditions of Kronoberg County(South of Sweden).Methods to reduce negative impact of wheeled harvesters on the soil of forests are proposed.The aim of the research is to assess the effect of the structural parameters of the wheel harvesters of different class on the soil of the cutting areas.Wheeled harvesters were loaded with 60 kN force.The results of experimental studies of the impact of wheeled harvesters on the forest soil are presented.Recommendations on the possibility of testing the results of research in the conditions of the rental base of the Western part of the North-Western Federal District of the Russian Federation are given.展开更多
When the electronic temperature sensor was incorporated into a system of soil water tension and the insidetube temperature was monitored in real time, it is concluded that the inside temperature increased by 26.9 ℃ a...When the electronic temperature sensor was incorporated into a system of soil water tension and the insidetube temperature was monitored in real time, it is concluded that the inside temperature increased by 26.9 ℃ and the inside pressure changed about 14.6 Kpa, when the pottery soil was replaced by the sealing plug. When the soil water was relatively stable in the experimental salvers, the in-side pressure stil varied regularly with the temperature. When the inside temperature increased by 22.2 ℃, the inside pressure varied about 7.4 Kpa. Through com-pensation calculation of the inside tension, the temperature in the warming and cooling periods was compensated, which was useful to correct the tension measurement errors induced from the changing temperature. When the measuring interval was 4 hours and the temperature difference was 18.1 ℃, the tension difference of both points was only 0.278 Kpa, compared to the difference up to 6.5 Kpa before compensation.展开更多
This study investigated the distribution pattern of biological soil crust （BSC） in Artemisia ordosica communities in Mu Us Sandy Land. Three experimental sites were selected according to grazing pressure gradient. I...This study investigated the distribution pattern of biological soil crust （BSC） in Artemisia ordosica communities in Mu Us Sandy Land. Three experimental sites were selected according to grazing pressure gradient. In each experimental site, the total vegetation cover, A. ordosica cover, BSC cover, litter-fall cover, BSC degree of fragmentation, BSC thickness and soil properties were investigated in both fixed and semi-fixed sand dunes and simultaneously analyzed in the laboratory. The results showed that at the same grazing pressure, BSC cover and composition were significantly affected by the fixation degree of sand dunes. In addition, BSC cover in the fixed sand dunes was 83.74% on average, whereas it is proportionally dominated by 28% mosses, 21% lichens, and 51% algae. Meanwhile, BSC cover in the semi-fixed sand dunes was 23.54% on average, which is proportionally domi- nated by 6.3% mosses, 2.5% lichens, and 91.2% algae. Fine sand, organic matter, and total nitrogen （N） contents in the fixed sand dunes were all significantly higher than those in the semi-fixed sand dunes. Litter-fall cover de- creased along the grazing pressure gradient, whereas BSC fragmentation degree increased. Fine sand content decreased along with the increase of grazing pressure, whereas medium sand content increased in both fixed and semi-fixed dunes. The organic matter and total N contents in the no grazing site were significantly higher than those in light and normal grazing sites. However, there were no significant differences between the light and normal grazing sites. In addition, there were also no significant differences in BSC thickness between the light and normal grazing sites in the fixed sand dunes. However, a significant decrease was observed in both BSC cover and thick- ness in the normal grazing site. The BSC in the semi-fixed dunes was more sensitive to disturbance.展开更多
Cyclic triaxial tests and numerical analyses were undertaken, in order to evaluate the wave-induced pore water pressure in seabed sediments in the Hangzhou Bay. The cyclic triaxial tests indicate that the rate of pore...Cyclic triaxial tests and numerical analyses were undertaken, in order to evaluate the wave-induced pore water pressure in seabed sediments in the Hangzhou Bay. The cyclic triaxial tests indicate that the rate of pore water pressure generation in cohesive soils decreases with time, and the development of the pore water pressure can be represented by a hyperbolic curve. Numerical analyses, taking into account the generation and dissipation of pore water pressure simultaneously, suggest that the pore water pressure buildup in cohesive soils may increase with time continuously until the pore water pressure ratio approaches to 1, or it may decrease after a certain time, which is controlled by drain conditions. These phenomena are different from those in sands. For waves with a retum period of 100 a in the Hangzhou Bay, if the wave duration is more than 60 h, then the pore water pressure ratio will be close to 1 and soil fabric failure will take place.展开更多
This paper aims to reveal the depth distribution law of non-limit passive soil pressure on rigid retaining wall that rotates about the top of the wall(rotation around the top(RT) model). Based on Coulomb theory, the d...This paper aims to reveal the depth distribution law of non-limit passive soil pressure on rigid retaining wall that rotates about the top of the wall(rotation around the top(RT) model). Based on Coulomb theory, the disturbance degree theory, as well as the spring-element model, by setting the rotation angle of the wall as the disturbance parameter, we establish both a depth distribution function for sand and a nonlinear depth distribution calculation method for the non-limit passive soil pressure on a rigid retaining wall under the RT model, which is then compared with experiment. The results suggest that under the RT model: the non-limit soil pressure has a nonlinear distribution; the backfill disturbance degree and the lateral soil pressure increase with an increase in the wall rotation angle; and, the points where the resultant lateral soil pressure acts on the retaining wall are less than 2/3 of the height of the wall. The soil pressure predicted by the theoretical calculation put forward in this paper are quite similar to those obtained by the model experiment, which verifies the theoretical value, and the engineering guidance provided by the calculations are of significance.展开更多
This paper describes a systematic study on the fundamental features of seismic soil pressure on underground tunnels, in terms of its magnitude and distribution, and further identifi es the dominant factors that signif...This paper describes a systematic study on the fundamental features of seismic soil pressure on underground tunnels, in terms of its magnitude and distribution, and further identifi es the dominant factors that signifi cantly infl uence the seismic soil pressure. A tunnel embedded in water-saturated poroelastic half-space is considered, with a large variety of model and excitation parameters. The primary features of both the total soil pressure and the pore pressure are investigated. Taking a circular tunnel as an example, the results are presented using a fi nite element-indirect boundary element(FE-IBE) method, which can account for dynamic soil-tunnel interaction and solid frame-pore water coupling. The effects of tunnel stiffness, tunnel buried depth and input motions on the seismic soil pressure and pore pressure are also examined. It is shown that the most crucial factors that dominate the magnitude and distribution of the soil pressure are the tunnel stiffness and dynamic soil-tunnel interaction. Moreover, the solid frame-pore water coupling has a prominent infl uence on the magnitude of the pore pressure. The fi ndings are benefi cial to obtain insight into the seismic soil pressure on underground tunnels, thus facilitating more accurate estimation of the seismic soil pressure.展开更多
In this study consecutive consolidated isotropically drained triaxial tests for the coefficient of earth pressure at rest(K_0) were carried out to investigate its rules of evolution as well as its strength characteris...In this study consecutive consolidated isotropically drained triaxial tests for the coefficient of earth pressure at rest(K_0) were carried out to investigate its rules of evolution as well as its strength characteristics for normal,consolidated saturated silt under high pressure.The tests results indicate that:1) for normal,consolidated saturated silt,K_0 values increase as the consolidation stress increases at high pressure levels,while the nonlinear characteristics of K_0 are inconspicuous compared to cohesive soils;2) the Jaky and Roscoe equations,used to calculate K_0,are only suitable for certain soils,but cannot represent these values for normal, consolidated saturated silt due to the variation in bilinear strength at high pressure;and 3) there are close relations between the nonlinear characteristics of K_0 and the void ratio,measured in the tests.Both share the same functional form while under pressure. Based on our experimental results,we developed an empirical linear model to interpret the rules of nonlinear variation for the coefficient of earth pressure at rest.展开更多
Pullout resistance of a soil nail is a critical parameter in design and analysis for geotechnical engineers. Due to the complexity of field conditions, the pullout behaviour of cement grouted soil nail in field is not...Pullout resistance of a soil nail is a critical parameter in design and analysis for geotechnical engineers. Due to the complexity of field conditions, the pullout behaviour of cement grouted soil nail in field is not well investigated. In this work, a number of field pullout tests of pressure grouted soil nails were conducted to estimate the pullout resistance of soil nails. The effective bond lengths of field soil nails were accurately controlled by a new grouting packer system. Typical field test results and the related comparison with typical laboratory test results reveal that the apparent coefficient of friction （ACF） decreases with the increase of overburden soil pressure when grouting pressure is constant, but increases almost linearly with the increase of grouting pressure when overburden pressure （soil depth） is unchanged. Water contents of soil samples at soil nail surfaces show obvious reductions compared with the results of soil samples from drillholes. After soil nails were completely pulled out of the ground, surface conditions of the soil nails and surrounding soil were examined. It is found that the water content values of the soil at the soil/nail interfaces decrease substantially compared with those of soil samples extracted from drillholes. In addition, all soil nails expand significantly in the diametrical direction after being pulled out of ground, indicating that the pressurized cement grout compacts the soil and penetrates into soil voids, leading to a corresponding shift of failure surface into surrounding soil mass significantly.展开更多
An opened bottom cylinder is a large-diameter cylinder placed on a rubber base or embedded in a soil foundation. The settlement of such a cylinder differs greatly from that of a closed bottom cylinder and so does the ...An opened bottom cylinder is a large-diameter cylinder placed on a rubber base or embedded in a soil foundation. The settlement of such a cylinder differs greatly from that of a closed bottom cylinder and so does the distribution of inner soil pressure over the opened bottom cylindrical structure. Through investigation of the settlement and the inner soil pressure on the opened bottom cylinder by model experiments, the interactions among the filler inside the cylinder, subsoil and cylinder are analyzed. The adjusting mechanism of friction resistance between the inner filler and the wall of the cylinder during overturning of the cylinder is discussed. Based on the experimental study, a method for calculating the inner soil pressure on the cylindrical structure under axisymmetric loading or non- axisymmetric (with lateral) loading is proposed in this paper. Meanwhile, the effective anti-overturning ratio of the opened bottom cylinder is derived.展开更多
This paper presents experimental studies on a compacted expansive soil,from Nanyang,China for investigating the at-rest lateral earth pressureσL of expansive soils.The key studies include(i)relationships between the...This paper presents experimental studies on a compacted expansive soil,from Nanyang,China for investigating the at-rest lateral earth pressureσL of expansive soils.The key studies include(i)relationships between theσL and the vertical stressσV during soaking and consolidation,(ii)the influences of initial dry densityρd0 and moisture content w 0 on the vertical and lateral swelling pressures at no swelling strain(i.e.σV0 andσL0),and(iii)evolution of theσL during five long-term wetting-drying cycles.Experimental results demonstrated that the post-soakingσL-σV relationships are piecewise linear and their slopes in the passive state(σL>σV)and active state(σL<σV)are similar to that of the consolidationσL-σV relationships in the normal-and over-consolidated states,respectively.The soakingσL-σV relationships converge to the consolidationσL-σV relationships at a thresholdσV where the interparticle swelling is restrained.TheσL0 andσV0 increase monotonically withρd0;however,they show increasing-then-decreasing trends with the w 0.The extent of compaction-induced swelling anisotropy,which is evaluated byσL0/σV0,reduces with an increase in the compaction energy and molding water content.TheσL reduces over moisture cycles and the stress relaxation in theσL during soaking is observed.An approach was developed to predict the at-rest soakingσL-σV relationships,which requires conventional consolidation and shear strength properties and one measurement of theσL-σV relationships during soaking.The proposed approach was validated using the results of three different expansive soils available in the literature.展开更多
It is well known that soilewater characteristic curve （SWCC） plays an important role in unsaturated soil mechanics, but the measurement of SWCC is inconvenient. In laboratory it requires days of testing time. For fi...It is well known that soilewater characteristic curve （SWCC） plays an important role in unsaturated soil mechanics, but the measurement of SWCC is inconvenient. In laboratory it requires days of testing time. For fine-grained clays, it may last for a couple of months using pressure plate tests. In this study, the effects of sample dimensions and shapes on the balance time of measuring SWCCs using pressure plate tests and the shape of SWCCs are investigated. It can be found that the sample dimensions and shapes have apparent influence on the balance time. The testing durations for circular samples with smaller diameters and annular samples with larger contact area are significantly shortened. However, there is little effect of sample dimensions and shapes on the shape of SWCCs. Its mechanism is explored and discussed in details through analysing the principle of pressure plate tests and microstructure of the sample. Based on the above findings, it is found that the circular samples with smaller dimensions can accelerate the testing duration of SWCC using the pressure plate.展开更多
The effect of test methods and stress paths on the experimental value of the coefficient of earth pressure at rest, K0, was investigated under high pressures. The results indicate that the rigid pressure chamber and f...The effect of test methods and stress paths on the experimental value of the coefficient of earth pressure at rest, K0, was investigated under high pressures. The results indicate that the rigid pressure chamber and flexible lateral confining pressure medium method gives a stress ratio at the initial stage that is not the real K0. Moreover, K0 increases during the loading process becoming greater at high pressures. In the unloading process, however, K0 increases only at the initial stage but decreases thereafter. In addition, the incremental magnitude definition, K0=dσ3/dσ1, gives higher values than the total magnitude definition, K0=σ3/σ1, under loading. This is also true during initial stages of unloading. The experiment results also indicate that earth pressure at rest in deep and thick soils can be estimated by a power function of axial and confining pressures. It is necessary to choose the appropriate Kn to avoid some accidents.展开更多
Water conveyance tunnels usually experience high internal water pressures and complex soil conditions.Therefore,shield tunnels with double-lining structure have been adopted because of their high bearing capacity.The ...Water conveyance tunnels usually experience high internal water pressures and complex soil conditions.Therefore,shield tunnels with double-lining structure have been adopted because of their high bearing capacity.The effect of the interface between the segmental and inner linings on the bearing capacity has been widely investigated;however,the effect of soil on the internal water pressure bearing capacity has not been emphasized enough.Therefore,in this study,model tests and an analytical solution are presented to elucidate the effect of soil on the internal water pressure bearing capacity.First,model tests are conducted on double-lining models under sandy soil and highly weathered argillaceous siltstone conditions.The internal force and earth pressure under these different soil conditions are then compared to reveal the contribution of soil to the internal water pressure bearing capacity.Following this,an analytical solution,considering the soil–double-lining interaction,is proposed to further investigate the contribution of the soil.The analytical solution is verified with model tests.The analytical solution is in good agreement with the model test results and can be used to evaluate the mechanical behavior of the double-lining and soil contribution.The effect of soil on the bearing capacity is found to be related with the elastic modulus of the soil and the deformation state of the double-lining.Before the double-lining cracks,the sandy soil contributes 3.7%of the internal water pressure but the contribution of the soil rises to 10.4%when it is the highly weathered argillaceous siltstone.After the double-lining cracks,the soil plays an important role in bearing internal water pressure.The soil contributions of sandy soil and highly weathered argillaceous siltstones are 10.5%and 27.8%,respectively.The effect of soil should be considered in tunnel design with the internal water pressure.展开更多
Impact compression tests on frozen soil samples with different freezing temperatures and subjected to passive confined pressure were performed using a split Hopkinson pressure bar at different loading strain rates.The...Impact compression tests on frozen soil samples with different freezing temperatures and subjected to passive confined pressure were performed using a split Hopkinson pressure bar at different loading strain rates.The three-dimensional stress-strain curves of the frozen soil samples under the corresponding conditions were obtained.The experimental results showed that,when the frozen soil was loaded to its elastic limit,shear failure occurred,the bearing capacity of pore ice was lost,and the thawed soil functioned as the main stress-bearing body.Nevertheless,the capacity of frozen soil to withstand hydrostatic pressure continued to increase.The dynamic mechanical properties of the frozen soil under passive confined pressure were observed to be strongly related to the loading strain rate and freezing temperature.As the loading strain rate increased,the secant modulus,elastic modulus,and strength(including the shear strength)of the frozen soil increased,whereas its Poisson^ratio and coefficient of lateral pressure decreased.As the freezing temperature decreased,the secant modulus,elastic modulus,and shear strength of the frozen soil increased;however,its Poisson5s ratio and coefficient of lateral pressure decreased.When the frozen soil was subjected to impact loading under passive confined pressure,energy dissipation occurred due to plastic deformation,mesoscopic damage evolution,and ice-water phase transition.When shear failure occurred,the absorption energy per unit volume of frozen soil increased as the freezing temperature decreased and the loading strain rate increased.展开更多
In order to clarify the damage mechanism of the subway structure, the dynamic soil-structure interaction and the dynamic forces acting on the structure, a series of shaking table tests and simulation analyses were per...In order to clarify the damage mechanism of the subway structure, the dynamic soil-structure interaction and the dynamic forces acting on the structure, a series of shaking table tests and simulation analyses were performed. The seismic response of the structure and the dynamic forces acting on the structure due to sinusoidal and random waves were investigated with special attention to the dynamic soil-structure interaction. The result shows that the compression seismic soil pressures and extension seismic soil pressures simultaneously act on the sidewalls, and big shear stress also acts on the ceiling slab due to horizontal excitation. The seismic soil pressure could be approximated to hyperbola curve, and reached a peak value with increase of the shear strain of the model ground. In addition, a slide and exfoliation phenomenon between the structure and the surrounding ground was simulated, using the nonlinear analyses. The foundation is provided for amending the calculation method of seismic soil pressure and improving the anti-earthquake designing level of underground structure.展开更多
An investigation is made on the soil pressure in a nine cabin opened bottom elliptical barrel structure. The calculation models using the penetration of negative pressure method have been developed. The first calculat...An investigation is made on the soil pressure in a nine cabin opened bottom elliptical barrel structure. The calculation models using the penetration of negative pressure method have been developed. The first calculation model is is for the construction stage involving three zones, namely, passive, transitional, and active established for the soil pressure in cabins. The other calculation model is based on the use stage, with the two （passive and active） zones for the soil pressure in cabins. The height of zones and the theoretical analytical solutions of inner soil pressure are derived. The analytical formulas of the models are proved using the finite element method and experimental data, and the formulas are analyzed in the inner soil pressure in the same condition. The calculation models can be used for other multi-position structural design or construction.展开更多
文摘A calibration test was done in order to measure its sensitivity coefficient by an improved soil test device.The experimental result shows that the soil pressure min-sensor made of the monocrystalline silicon（SPMMS）is proved to be good linear,high precision and less that can fetch precise data in low pressure range even near by O point,which guarantees the reliability of the soil pressure test in geotechnical engineering.
基金supported by the NSFC Key Projects of International Cooperation and Exchanges(No.42020104006)the National Key Research and Development Program of China(No.2023YFC3007004).
文摘Numerous incidents and failures of landslides in reservoir areas are attributed to water level fluctuations,which frequently induce cyclic changes in seepage pressure within the soil masses.Under such complex cyclic seepage conditions,the hydro-mechanical behavior of sliding-zone soils may significantly differ from that observed under steady seepage conditions.However,the seepage characteristics and deformation behavior of sliding-zone soils experiencing cyclic seepage pressure are not yet fully understood.In this study,we conduct cyclic seepage pressure tests under isotropic consolidation to investigate the variation in hydraulic conductivity and volumetric strain of sliding-zone soils.The results show that the hydraulic conductivity of the sliding-zone soil samples fluctuatesunder cyclic seepage pressure,with the magnitude increasing as seepage pressure amplitude rises and decreasing with higher confiningpressure.Additionally,the volumetric strain of the sliding-zone soil samples exhibited notable fluctuationsunder cyclic seepage pressure,with the magnitude of the fluctuationsintensifying as the seepage pressure amplitude increased.The cumulative volumetric strain and irrecoverable volumetric strain of the samples are higher compared to those observed under steady seepage pressure.Subsequently,hysteresis loops are classifiedinto three types,each indicating distinct deformation characteristics.Finally,the micromechanism of sliding-zone soil under cyclic seepage pressure,considering the effect of physicochemical reactions on pore structure,is revealed to interpret better the intrinsic mechanism of seepage characteristics and deformation behavior.These findingsprovide a theoretical basis for further accurately evaluating reservoir landslide stability under fluctuatingwater levels.
基金National Key Research and Development Program,No.2021xjkk0303。
文摘Drought significantly constrains vegetation growth and reduces terrestrial carbon sinks.Currently,the spatiotemporal patterns and mechanisms of the differential impacts of soil and meteorological droughts on vegetation productivity remain inadequately understood.In this study,we analyzed soil moisture(SM),vapor pressure deficit(VPD),and gross primary productivity(GPP)to investigate their spatiotemporal patterns and the combined effects on GPP over China.The results revealed that:(1)Soil drought and meteorological drought generally exhibited temporally synchronous trends across China.(2)GPP was predominantly affected by the combined and synchronous effects of both SM and VPD,although their effects displayed directional variability differences in certain regions.(3)SM demonstrated a greater relative importance on GPP than VPD across more than half of the regions in China,whereas deciduous broadleaf forests were the only vegetation type primarily affected by VPD.(4)Under the lag effects,both SM and VPD exhibited bidirectional Granger causality with GPP,with the interaction between VPD and GPP proving more pronounced than that of SM.Our research provides valuable insights into the mechanisms through which SM and VPD influence GPP,contributing to improved predictions vegetation productivity and implementing ecological restoration.
文摘The article considers the impact of forestry machines on the soil of the cutting areas and presents the results of the impact of harvesters of different classes(middlesmall,middle and heavy)and configurations of wheeled equipment and additional equipment on the soil of the cutting areas in the conditions of Kronoberg County(South of Sweden).Methods to reduce negative impact of wheeled harvesters on the soil of forests are proposed.The aim of the research is to assess the effect of the structural parameters of the wheel harvesters of different class on the soil of the cutting areas.Wheeled harvesters were loaded with 60 kN force.The results of experimental studies of the impact of wheeled harvesters on the forest soil are presented.Recommendations on the possibility of testing the results of research in the conditions of the rental base of the Western part of the North-Western Federal District of the Russian Federation are given.
基金Supported by Jiangsu Agricultural Self-innovation Fund[CX(13)3031]~~
文摘When the electronic temperature sensor was incorporated into a system of soil water tension and the insidetube temperature was monitored in real time, it is concluded that the inside temperature increased by 26.9 ℃ and the inside pressure changed about 14.6 Kpa, when the pottery soil was replaced by the sealing plug. When the soil water was relatively stable in the experimental salvers, the in-side pressure stil varied regularly with the temperature. When the inside temperature increased by 22.2 ℃, the inside pressure varied about 7.4 Kpa. Through com-pensation calculation of the inside tension, the temperature in the warming and cooling periods was compensated, which was useful to correct the tension measurement errors induced from the changing temperature. When the measuring interval was 4 hours and the temperature difference was 18.1 ℃, the tension difference of both points was only 0.278 Kpa, compared to the difference up to 6.5 Kpa before compensation.
基金Funding was provided by the National Key Technology R&DP rogram (2012BAD16B01)the Special Research Program for Public-welfare Forestry of China (201104077)the National Natural Science Foundation of China (31170667)
文摘This study investigated the distribution pattern of biological soil crust （BSC） in Artemisia ordosica communities in Mu Us Sandy Land. Three experimental sites were selected according to grazing pressure gradient. In each experimental site, the total vegetation cover, A. ordosica cover, BSC cover, litter-fall cover, BSC degree of fragmentation, BSC thickness and soil properties were investigated in both fixed and semi-fixed sand dunes and simultaneously analyzed in the laboratory. The results showed that at the same grazing pressure, BSC cover and composition were significantly affected by the fixation degree of sand dunes. In addition, BSC cover in the fixed sand dunes was 83.74% on average, whereas it is proportionally dominated by 28% mosses, 21% lichens, and 51% algae. Meanwhile, BSC cover in the semi-fixed sand dunes was 23.54% on average, which is proportionally domi- nated by 6.3% mosses, 2.5% lichens, and 91.2% algae. Fine sand, organic matter, and total nitrogen （N） contents in the fixed sand dunes were all significantly higher than those in the semi-fixed sand dunes. Litter-fall cover de- creased along the grazing pressure gradient, whereas BSC fragmentation degree increased. Fine sand content decreased along with the increase of grazing pressure, whereas medium sand content increased in both fixed and semi-fixed dunes. The organic matter and total N contents in the no grazing site were significantly higher than those in light and normal grazing sites. However, there were no significant differences between the light and normal grazing sites. In addition, there were also no significant differences in BSC thickness between the light and normal grazing sites in the fixed sand dunes. However, a significant decrease was observed in both BSC cover and thick- ness in the normal grazing site. The BSC in the semi-fixed dunes was more sensitive to disturbance.
基金This work was supported by the National Natural Science Foundation of China under the contract Nos 10372089 and 40476032.
文摘Cyclic triaxial tests and numerical analyses were undertaken, in order to evaluate the wave-induced pore water pressure in seabed sediments in the Hangzhou Bay. The cyclic triaxial tests indicate that the rate of pore water pressure generation in cohesive soils decreases with time, and the development of the pore water pressure can be represented by a hyperbolic curve. Numerical analyses, taking into account the generation and dissipation of pore water pressure simultaneously, suggest that the pore water pressure buildup in cohesive soils may increase with time continuously until the pore water pressure ratio approaches to 1, or it may decrease after a certain time, which is controlled by drain conditions. These phenomena are different from those in sands. For waves with a retum period of 100 a in the Hangzhou Bay, if the wave duration is more than 60 h, then the pore water pressure ratio will be close to 1 and soil fabric failure will take place.
基金financially supported by the National Natural Science Foundation of China (No.51274192)Jiangsu Key Laboratory of Environmental Impact and Structural Safety in Engineering Open Foundation of China (No.JSKL2014K12)Jiangsu Ordinary University Graduate Students Research and Innovation Project of China (No.KYLX-1392)
文摘This paper aims to reveal the depth distribution law of non-limit passive soil pressure on rigid retaining wall that rotates about the top of the wall(rotation around the top(RT) model). Based on Coulomb theory, the disturbance degree theory, as well as the spring-element model, by setting the rotation angle of the wall as the disturbance parameter, we establish both a depth distribution function for sand and a nonlinear depth distribution calculation method for the non-limit passive soil pressure on a rigid retaining wall under the RT model, which is then compared with experiment. The results suggest that under the RT model: the non-limit soil pressure has a nonlinear distribution; the backfill disturbance degree and the lateral soil pressure increase with an increase in the wall rotation angle; and, the points where the resultant lateral soil pressure acts on the retaining wall are less than 2/3 of the height of the wall. The soil pressure predicted by the theoretical calculation put forward in this paper are quite similar to those obtained by the model experiment, which verifies the theoretical value, and the engineering guidance provided by the calculations are of significance.
基金Supported by:National Natural Science Foundation of China under Grant No.51978462
文摘This paper describes a systematic study on the fundamental features of seismic soil pressure on underground tunnels, in terms of its magnitude and distribution, and further identifi es the dominant factors that signifi cantly infl uence the seismic soil pressure. A tunnel embedded in water-saturated poroelastic half-space is considered, with a large variety of model and excitation parameters. The primary features of both the total soil pressure and the pore pressure are investigated. Taking a circular tunnel as an example, the results are presented using a fi nite element-indirect boundary element(FE-IBE) method, which can account for dynamic soil-tunnel interaction and solid frame-pore water coupling. The effects of tunnel stiffness, tunnel buried depth and input motions on the seismic soil pressure and pore pressure are also examined. It is shown that the most crucial factors that dominate the magnitude and distribution of the soil pressure are the tunnel stiffness and dynamic soil-tunnel interaction. Moreover, the solid frame-pore water coupling has a prominent infl uence on the magnitude of the pore pressure. The fi ndings are benefi cial to obtain insight into the seismic soil pressure on underground tunnels, thus facilitating more accurate estimation of the seismic soil pressure.
基金Financial support for this work,provided by the National Natural Science Foundation of China (No.50534040)the Project of the Science and Technology Ministry of China(No.2006BAB16B01)the Post Graduate Research Project of Jiangsu Province (No.CX08B_103Z),
文摘In this study consecutive consolidated isotropically drained triaxial tests for the coefficient of earth pressure at rest(K_0) were carried out to investigate its rules of evolution as well as its strength characteristics for normal,consolidated saturated silt under high pressure.The tests results indicate that:1) for normal,consolidated saturated silt,K_0 values increase as the consolidation stress increases at high pressure levels,while the nonlinear characteristics of K_0 are inconspicuous compared to cohesive soils;2) the Jaky and Roscoe equations,used to calculate K_0,are only suitable for certain soils,but cannot represent these values for normal, consolidated saturated silt due to the variation in bilinear strength at high pressure;and 3) there are close relations between the nonlinear characteristics of K_0 and the void ratio,measured in the tests.Both share the same functional form while under pressure. Based on our experimental results,we developed an empirical linear model to interpret the rules of nonlinear variation for the coefficient of earth pressure at rest.
基金Foundation item： Project（NTF 12015） supported by the Scientific Research Foundation for Talent of Shantou University, China Project（PolyU 5320107E） supported by the Research Grants Committee General Research Fund, China
文摘Pullout resistance of a soil nail is a critical parameter in design and analysis for geotechnical engineers. Due to the complexity of field conditions, the pullout behaviour of cement grouted soil nail in field is not well investigated. In this work, a number of field pullout tests of pressure grouted soil nails were conducted to estimate the pullout resistance of soil nails. The effective bond lengths of field soil nails were accurately controlled by a new grouting packer system. Typical field test results and the related comparison with typical laboratory test results reveal that the apparent coefficient of friction （ACF） decreases with the increase of overburden soil pressure when grouting pressure is constant, but increases almost linearly with the increase of grouting pressure when overburden pressure （soil depth） is unchanged. Water contents of soil samples at soil nail surfaces show obvious reductions compared with the results of soil samples from drillholes. After soil nails were completely pulled out of the ground, surface conditions of the soil nails and surrounding soil were examined. It is found that the water content values of the soil at the soil/nail interfaces decrease substantially compared with those of soil samples extracted from drillholes. In addition, all soil nails expand significantly in the diametrical direction after being pulled out of ground, indicating that the pressurized cement grout compacts the soil and penetrates into soil voids, leading to a corresponding shift of failure surface into surrounding soil mass significantly.
文摘An opened bottom cylinder is a large-diameter cylinder placed on a rubber base or embedded in a soil foundation. The settlement of such a cylinder differs greatly from that of a closed bottom cylinder and so does the distribution of inner soil pressure over the opened bottom cylindrical structure. Through investigation of the settlement and the inner soil pressure on the opened bottom cylinder by model experiments, the interactions among the filler inside the cylinder, subsoil and cylinder are analyzed. The adjusting mechanism of friction resistance between the inner filler and the wall of the cylinder during overturning of the cylinder is discussed. Based on the experimental study, a method for calculating the inner soil pressure on the cylindrical structure under axisymmetric loading or non- axisymmetric (with lateral) loading is proposed in this paper. Meanwhile, the effective anti-overturning ratio of the opened bottom cylinder is derived.
基金sponsored by the National Natural Science Foundation of China(Grant Nos.52378365 and 52179109)Jiangsu Province Excellent Postdoctoral Program(Grant No.2023)China Scholarship Council-University of Ottawa Joint Scholarship.
文摘This paper presents experimental studies on a compacted expansive soil,from Nanyang,China for investigating the at-rest lateral earth pressureσL of expansive soils.The key studies include(i)relationships between theσL and the vertical stressσV during soaking and consolidation,(ii)the influences of initial dry densityρd0 and moisture content w 0 on the vertical and lateral swelling pressures at no swelling strain(i.e.σV0 andσL0),and(iii)evolution of theσL during five long-term wetting-drying cycles.Experimental results demonstrated that the post-soakingσL-σV relationships are piecewise linear and their slopes in the passive state(σL>σV)and active state(σL<σV)are similar to that of the consolidationσL-σV relationships in the normal-and over-consolidated states,respectively.The soakingσL-σV relationships converge to the consolidationσL-σV relationships at a thresholdσV where the interparticle swelling is restrained.TheσL0 andσV0 increase monotonically withρd0;however,they show increasing-then-decreasing trends with the w 0.The extent of compaction-induced swelling anisotropy,which is evaluated byσL0/σV0,reduces with an increase in the compaction energy and molding water content.TheσL reduces over moisture cycles and the stress relaxation in theσL during soaking is observed.An approach was developed to predict the at-rest soakingσL-σV relationships,which requires conventional consolidation and shear strength properties and one measurement of theσL-σV relationships during soaking.The proposed approach was validated using the results of three different expansive soils available in the literature.
基金supported by the National Natural Science Foundation of China (Grant No. 10872210)the State Key Laboratory of Geomechanics and Geotechnical Engineering (Grant No. Y11002)
文摘It is well known that soilewater characteristic curve （SWCC） plays an important role in unsaturated soil mechanics, but the measurement of SWCC is inconvenient. In laboratory it requires days of testing time. For fine-grained clays, it may last for a couple of months using pressure plate tests. In this study, the effects of sample dimensions and shapes on the balance time of measuring SWCCs using pressure plate tests and the shape of SWCCs are investigated. It can be found that the sample dimensions and shapes have apparent influence on the balance time. The testing durations for circular samples with smaller diameters and annular samples with larger contact area are significantly shortened. However, there is little effect of sample dimensions and shapes on the shape of SWCCs. Its mechanism is explored and discussed in details through analysing the principle of pressure plate tests and microstructure of the sample. Based on the above findings, it is found that the circular samples with smaller dimensions can accelerate the testing duration of SWCC using the pressure plate.
基金Projects 50534040 supported by the National Natural Science Foundation of ChinaBK2007040 by the Natural Science Foundation of Jiangsu ProvinceCX08B_103Z by the Post Graduate Research Projects of Jiangsu Province
文摘The effect of test methods and stress paths on the experimental value of the coefficient of earth pressure at rest, K0, was investigated under high pressures. The results indicate that the rigid pressure chamber and flexible lateral confining pressure medium method gives a stress ratio at the initial stage that is not the real K0. Moreover, K0 increases during the loading process becoming greater at high pressures. In the unloading process, however, K0 increases only at the initial stage but decreases thereafter. In addition, the incremental magnitude definition, K0=dσ3/dσ1, gives higher values than the total magnitude definition, K0=σ3/σ1, under loading. This is also true during initial stages of unloading. The experiment results also indicate that earth pressure at rest in deep and thick soils can be estimated by a power function of axial and confining pressures. It is necessary to choose the appropriate Kn to avoid some accidents.
基金the Innovation Program of Shanghai Municipal Education Commission(No.2019-01-0700-07-456 E00051)the National Natural Science Foundation of China(Nos.51978517,52090082,and 52108381)the Shanghai Science and Technology Committee Program(Nos.21DZ1200601 and 20DZ1201404)。
文摘Water conveyance tunnels usually experience high internal water pressures and complex soil conditions.Therefore,shield tunnels with double-lining structure have been adopted because of their high bearing capacity.The effect of the interface between the segmental and inner linings on the bearing capacity has been widely investigated;however,the effect of soil on the internal water pressure bearing capacity has not been emphasized enough.Therefore,in this study,model tests and an analytical solution are presented to elucidate the effect of soil on the internal water pressure bearing capacity.First,model tests are conducted on double-lining models under sandy soil and highly weathered argillaceous siltstone conditions.The internal force and earth pressure under these different soil conditions are then compared to reveal the contribution of soil to the internal water pressure bearing capacity.Following this,an analytical solution,considering the soil–double-lining interaction,is proposed to further investigate the contribution of the soil.The analytical solution is verified with model tests.The analytical solution is in good agreement with the model test results and can be used to evaluate the mechanical behavior of the double-lining and soil contribution.The effect of soil on the bearing capacity is found to be related with the elastic modulus of the soil and the deformation state of the double-lining.Before the double-lining cracks,the sandy soil contributes 3.7%of the internal water pressure but the contribution of the soil rises to 10.4%when it is the highly weathered argillaceous siltstone.After the double-lining cracks,the soil plays an important role in bearing internal water pressure.The soil contributions of sandy soil and highly weathered argillaceous siltstones are 10.5%and 27.8%,respectively.The effect of soil should be considered in tunnel design with the internal water pressure.
基金funded by the National Natural Science Foundation of China(Grant Number 51778437).
文摘Impact compression tests on frozen soil samples with different freezing temperatures and subjected to passive confined pressure were performed using a split Hopkinson pressure bar at different loading strain rates.The three-dimensional stress-strain curves of the frozen soil samples under the corresponding conditions were obtained.The experimental results showed that,when the frozen soil was loaded to its elastic limit,shear failure occurred,the bearing capacity of pore ice was lost,and the thawed soil functioned as the main stress-bearing body.Nevertheless,the capacity of frozen soil to withstand hydrostatic pressure continued to increase.The dynamic mechanical properties of the frozen soil under passive confined pressure were observed to be strongly related to the loading strain rate and freezing temperature.As the loading strain rate increased,the secant modulus,elastic modulus,and strength(including the shear strength)of the frozen soil increased,whereas its Poisson^ratio and coefficient of lateral pressure decreased.As the freezing temperature decreased,the secant modulus,elastic modulus,and shear strength of the frozen soil increased;however,its Poisson5s ratio and coefficient of lateral pressure decreased.When the frozen soil was subjected to impact loading under passive confined pressure,energy dissipation occurred due to plastic deformation,mesoscopic damage evolution,and ice-water phase transition.When shear failure occurred,the absorption energy per unit volume of frozen soil increased as the freezing temperature decreased and the loading strain rate increased.
文摘In order to clarify the damage mechanism of the subway structure, the dynamic soil-structure interaction and the dynamic forces acting on the structure, a series of shaking table tests and simulation analyses were performed. The seismic response of the structure and the dynamic forces acting on the structure due to sinusoidal and random waves were investigated with special attention to the dynamic soil-structure interaction. The result shows that the compression seismic soil pressures and extension seismic soil pressures simultaneously act on the sidewalls, and big shear stress also acts on the ceiling slab due to horizontal excitation. The seismic soil pressure could be approximated to hyperbola curve, and reached a peak value with increase of the shear strain of the model ground. In addition, a slide and exfoliation phenomenon between the structure and the surrounding ground was simulated, using the nonlinear analyses. The foundation is provided for amending the calculation method of seismic soil pressure and improving the anti-earthquake designing level of underground structure.
基金supported by Open Fund Project of Hunan Province Research Center for Safety Control Technology and Equipment of Bridge Engineering(Changsha University of Science&Technology)(No.13KC05)
文摘An investigation is made on the soil pressure in a nine cabin opened bottom elliptical barrel structure. The calculation models using the penetration of negative pressure method have been developed. The first calculation model is is for the construction stage involving three zones, namely, passive, transitional, and active established for the soil pressure in cabins. The other calculation model is based on the use stage, with the two （passive and active） zones for the soil pressure in cabins. The height of zones and the theoretical analytical solutions of inner soil pressure are derived. The analytical formulas of the models are proved using the finite element method and experimental data, and the formulas are analyzed in the inner soil pressure in the same condition. The calculation models can be used for other multi-position structural design or construction.
