Soil disturbance evaluation of soft clay based on stress-normalized smallstrain stiffness

Soil disturbance includes the change of stress state and the damage of soil structure.The field testing indices reflect the combined effect of both changes and it is difficult to identify the soil structure disturbance directly from these indices.In the present study,the small-strain shear modulus is used to characterize soil structure disturbance by normalizing the effective stress and void ratio based on Hardin equation.The procedure for evaluating soil sampling disturbance in the field and the further disturbance during the subsequent consolidation process in laboratory test is proposed,and then validated by a case study of soft clay ground.Downhole seismic testing in the field,portable piezoelectric bender elements for the drilled sample and bender elements in triaxial apparatus for the consolidated sample were used to monitor the shear wave velocity of the soil from intact to disturbed and even remolded states.It is found that soil sampling disturbance degree by conventional thin-wall sampler is about 30%according to the proposed procedure,which is slightly higher than that from the modified volume compression method proposed by Hong and Onitsuka(1998).And the additional soil disturbance induced by consolidation in laboratory could reach about 50%when the consolidation pressure is far beyond the structural yield stress,and it follows the plastic volumetric strain quite well.

Effects of self-healing biomimetic subsoiler on tillage resistance, wearcorrosion performance and soil disturbance morphology under different soil types

Subsoiling has been widely used all over the world as an important operation method of no-tillage farming.For energy-saving and life-extension,the tillage resistance and wear-corrosion of subsoilers have attracted wide attention.In this study,the tillage resistance,soil disturbance,wear and corrosion of subsoiler with S-T-SK-2#biomimetic structures(S means subsoiler;T means tine;SK means shank;2#,h/s=0.57,h=5 mm andα=45°.)and self-healing coating under two seasons,two locations with different soil properties(black loam and clay soil)and subsoiling speeds(2 km/h and 3.6 km/h)were investigated.The soil moisture content and compactness affected the tillage resistance and wear-corrosion.The tillage resistance and degree of corrosion on all subsoilers were much larger in clay soil than that in black loam soil.Compared with S-T-SK-2#,the tillage reduction rate of C-S-T-SK-2#(S-T-SK-2#with self-healing coating)was up to 14.32%in clay soil under the speed of 2 km/h.The significance tests of regression equation results showed that subsoiler type and soil properties had a significant impact on soil disturbance coefficient,swelling of total soil layer,bulkiness of the plough pan.It is of a guiding significance for the analysis of soil disturbance.Synergism mechanism of subsoiler coupling with biomimetic structures and self-healing coating was analyzed in following.It depicted the guiding effect of biomimetic structure and the shield function of self-healing coating,resulting in anticorrosion and wear resistance of subsoiler.

Predicting 3D forces of disc tool and soil disturbance area using fuzzy logic model under sensor based soil-bin

A knowledge-based fuzzy logic model was developed on experimental data and used to predict the draft,side and vertical forces and soil disturbance area by disc tillage tool operation.The laboratory research work was conducted to evaluate the performance of the disc tool at three working speeds(1.25 m/s,1.98 m/s and 2.47 m/s,respectively)and depths(0-5 cm,5-10 cm and 10-15 cm,respectively)on paddy soil under soil-bin environment.Further,draft(Fx),side(Fz)and vertical(Fy)forces of disc and soil disturbance area were assessed and predicted towards working speeds and depths.A fuzzy prediction model with two input variables(speed and depth)and four output variables was developed and the Mamdani inference approach was used.Draft,side and vertical forces of disc and soil disturbance area were positively responded 0.97,0.95 and 0.84 and 0.99,respectively.The prediction results showed a close relationship between measured and predicted data.Similarly,the measured and predicted results revealed that the draft,side,vertical forces,and soil disturbance area slightly increased,while increasing the speed and depth of the disc tool.Furthermore,disc forces and soil disturbed area were highly significant(p<0.05)for higher speed towards depth.It was concluded that the fuzzy model may be introduced for predicting the disc forces and soil disturbance area during the disc tillage tool operation with high accuracy.

Effect of Soil Transplantation to Abandoned Paddy Field on the Conservation of Threatened Hydrophyte Species

Threatened or near threatened hydrophytes, Ottelia alismoides, Monochoria korsakowii, Najas graminea, Najas minor and Chara braunii, appeared in an inundated paddy field after the 2011 Tohoku-oki Tsunami in Japan. Due to the reconstruction of roads and agricultural restoration efforts implemented following the disaster, the top soil of the paddy field was transplanted to another abandoned paddy field in 2014 to avoid extirpation of the aforementioned species. We then conducted vegetation surveys in July and September from 2014 to 2016. Monochoria korsakowii appeared at the transplantation site from 2014 to 2016, forming a large community in 2016. The volume of this species was significantly higher than that in July 2014 and 2015. Although Ottelia alismoides and Chara braunii appeared in 2014, they were not observed in 2015. Najas graminea and Najas minor were not observed during the vegetation survey, and Salvinia natans and Alisma plantago-aquatica newly appeared at the transplantation site. Our findings suggest that transplantation of surface soil and the seed bank therein to an abandoned paddy field is well suited for the conservation of hygrophytes such as Monochoria korsakowii, Ottelia alismoides and Chara braunii. Preventing disturbances that suppress the growth of herbaceous perennial plants is considered necessary for maintaining the habitats of threatened plant species.

Investigating spatial and temporal variations of soil moisture content in an arid mining area using an improved thermal inertia model

Mining operations can usually lead to environmental deteriorations. Underground mining activities could cause an extensive decrease in groundwater level and thus a dramatic variation in soil moisture content（SMC）. In this study, the spatial and temporal variations of SMC from 2001 to 2015 at two spatial scales（i.e., the Shendong coal mining area and the Daliuta Coal Mine） were analyzed using an improved thermal inertia model with a long-term series of Landsat TM/OLI（TM=Thematic Mapper and OLI=Operational Land Imager） data. Our results show that at large spatial scale（the Shendong coal mining area）, underground mining activities had insignificant negative impacts on SMC and that at small spatial scale（the Daliuta Coal Mine）, underground mining activities had significant negative impacts on SMC. Trend analysis of SMC demonstrated that areas with decreasing trend of SMC were mainly distributed in the mined area, indicating that underground mining is a primary cause for the drying trend in the mining region in this arid environment.

Effects of Soil-Cement Stabilization on the Index Properties of Subgrades of Three Selected Roads in the Niger Delta Region of Nigeria

In this study, the impact of soil-cement stabilization on the index properties of the subgrade of roads was investigated. Efforts were on the means of improving the bearing capacity of the subgrade of a flexible pavement structure. Three selected roads (Ogbia-Nembe, section of the East-West Road and section of Port Harcourt-Aba Road) in the Niger Delta Region of Nigeria were examined to determine the effect of sand-cement stabilization on the compaction index property of their undisturbed subgrade and the optimal ratio of soil-cement on the expansive soils at which the California Bearing Ratio (CBR) is optimized. Disturbed soil samples were collected from twenty trial pits on each of the three study roads using a hand ulger and tested for their respective compaction index properties. It was discovered that their California Bearing Ratio (CBR) was very low. Some of the collected specimen materials were stabilized with varying percentages of soil-cement contents ranging from 6% - 14% in order to ascertain its effects on the compaction index properties of the sample soils. Results of the various stabilization test procedures show that: Stabilization of the soil using Soil-Cement Stabilization affected the Compaction Index properties of the soil and further improved the California Bearing Ratio (CBR). On the Ogbia-Nembe Road;Soil-Cement stabilization improved the CBR and is optimized at a 10% sand-cement ratio with optimum moisture content ranging from 6.2% - 14%, maximum dry density ranges from 1700 - 1780 kg/m3, yielding an average CBR of 42.7% for soaked samples. On the section of East-West Road from Eleme Junction to Etteh Junction;Soil-Cement stabilization improved the CBR and is optimized at a 14% sand-cement ratio with optimum moisture content ranging from 6.2% - 14.2%, maximum dry density ranges from 1660 - 1800 kg/m3, yielding an average CBR of 43.9% for soaked samples. On the section of Port Harcourt-Aba Express Road from Eleme Junction to Osisioma Junction;Soil-Cement stabilization improved the CBR and is optimized at a 12% sand-cement ratio having an optimum moisture content ranging from 5.4% - 17.3%, maximum dry density ranges from 1610 - 1740 kg/m3, and an average California Bearing Ratio for soaked samples at 40%.

Soil Microstructure Evolution and Macro Deformation Mechanism for Controlling Construction Disturbance in Shanghai Soft Soil

Abundant practical evidences have indicated that the soil progressively loses its structural configuration under construction disturbance and this can result in long-term macro deformation.The fundamental understanding of soil microstructure evolution subject to construction disturbance is necessary for controlling disturbance in excavation projects and minimizing ground settlement.The microstructure of Shanghai soft soil is investigated in this study.The laboratory isotropic compression tests are respectively performed on the virgin soil and the reconstructed Shanghai soft soil to investigate the macro deformation of soil under disturbance.Discrete element method model is used to study the micro particle level responses of soil under disturbance.The laboratory tests and numerical simulations provide theoretical basis for construction disturbance mitigation to ensure safety and stability of excavation projects.

Tillage force and disturbance characteristics of different geometric-shaped subsoilers via DEM

With the increased use of agricultural machinery in field operations,soil compaction has become increasingly severe,and the plough pan has become deeper.Subsoiling is an excellent way to address this problem.However,it is limited by high energy consumption,which is closely related to tillage force.To investigate the effect of the geometric shape of shanks and tines on tillage force and soil disturbance in loam,a layered soil model in accordance with the actual conditions was established and five different subsoilers were simulated via discrete element modeling.The results indicated that the shank impacted soil disturbance and tine impacted tillage force.The draft force of curved shank and chisel tine was 8%less than that of the straight shank and sweep tine.The straight shank and sweep tine produced a larger furrow profile and a higher furrow width.The subsoiler with curved shank and chisel tine(C-C)exhibited the lowest specific resistance(12.87,17.52,19.46 and 21.18 kN/m^2 in the 30,35,40 and 45 cm tillage depth,respectively)considering the draft force and soil disturbance characteristics.Hence,these results will facilitate in the selection of a suitable subsoiler and design of new subsoilers with lower energy consumption requirements for loam areas worldwide.

Study of Spudcan Reinstallation Near Existing Footprint in Soft Clay

Spudcan extraction leaves a footprint and disturbed soil surrounding the footprint,which introduces uncertainty and complexity in the spudcan−footprint interaction during spudcan reinstallation.This paper reports large deformation from finite element results of spudcan reinstallation near the footprint considering the effect of soil disturbance.Three stages are proposed based on the failure mechanisms of a spudcan reinstalled in disturbed soil and undisturbed soil.Besides,the effects of soil disturbance on the position of the maximum horizontal force and moment are discussed.It could be found that the critical offset distance in the disturbed case is larger than that in the undisturbed case.In addition,the maximum horizontal force and moment occur at different depths in the disturbed case and undisturbed case.A critical area is proposed based on the analyses,which could be useful for determining the position of the maximum horizontal force and moment in practical design.

Disturbed state concept as unified constitutive modeling approach

A unified constitutive modeling approach is highly desirable to characterize a wide range of engineeringmaterials subjected simultaneously to the effect of a number of factors such as elastic, plastic and creepdeformations, stress path, volume change, microcracking leading to fracture, failure and softening,stiffening, and mechanical and environmental forces. There are hardly available such unified models. Thedisturbed state concept （DSC） is considered to be a unified approach and is able to provide materialcharacterization for almost all of the above factors. This paper presents a description of the DSC, andstatements for determination of parameters based on triaxial, multiaxial and interface tests. Statementsof DSC and validation at the specimen level and at the boundary value problem levels are also presented.An extensive list of publications by the author and others is provided at the end. The DSC is considered tobe a unique and versatile procedure for modeling behaviors of engineering materials and interfaces. 2016 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. This is an open access article under the CC BY-NC-ND license

Effects of key design parameters of tine furrow opener on soil seedbed properties

The structural parameters of tine furrow openers have significant effects on soil property of seed furrow in no-till planting,thereby affecting crop growth and yields.In order to analyze the effects of key parameters of tine furrow openers on soil properties(soil bulk density,soil water-stable aggregates(WSA),and soil disturbance)of the surface soil layer of 0-10 cm and surface straw disturbance,the tine furrow openers with different structural parameters,including cutting edge thickness,cutting edge curve,penetration clearance angle and rake angle,were designed and tested under no-till conditions.Orthogonal test and single factor test were performed to analyze the effects of different parameters.Results showed that the rake angle,cutting edge thickness and cutting edge curve had significant effects on cross-sectional area of furrow(Af)and disturbance of surface straw;the rake angle had a significant effect on soil bulk density.Soil types and operating depth had significant effects on soil disturbance caused by tine furrow openers.The concave type tine furrow opener produced the lowest soil disturbance and soil bulk density of seed furrow,the highest surface straw disturbance and the greatest content of WSA(>0.5 mm).With increasing rake angles of tine furrow opener,the width of seedbed(Wsb)and the Af decreased first and then increased,respectively,while the width of soil throw(Wst)and the height of ridge(Hr)increased.The Wsb and Af created by tine furrow opener with 60°rake angle were significantly lower than that with others,respectively.The tine furrow opener with rake angle ranged from 45°to 60°created the lowest soil bulk density.As the penetration clearance angle increased,the content of WSA(>0.5 mm)decreased,but the effect of penetration clearance angle on the content of WSA(<0.5 mm)was not significant.The cutting edge thickness(<2 mm)had no significant effects on soil properties of seedbed.This study could provide a reference for optimal design of the tine furrow opener to create more suitable seedbed environment,and promote the application of the light no-till planters.

Discrete element simulations and experiments of soil-winged subsoiler interaction

Understanding soil disturbance behaviors under the impact of the winged subsoiler is critical for designing or optimizing the winged subsoiler(a primary subsoiling tool).In this study,a soil-winged subsoiler interaction model was developed and the effects of winged subsoiler on soil disturbance behaviors were investigated using the discrete element method(DEM)simulations and lab soil-bin tests.The results showed that wings mainly affected the disturbance range and fragmentation degree of soil above them.The draught forces of share section(SS),arc section in the hardpan(ASHP),arc section in the top layer(ASTL)and line section(LS)were accounted for 69.53%,25.22%,4.73%and 0.52%of the total draught force of winged subsoiler;the lateral disturbance range from high to low of the soil at different depths followed the ranking:top layer(TL),hardpan disturbed by arc section(HDAS)and hardpan disturbed by share section(HDSS).Wings had the greatest influence on the draught force of ASHP.Adding wings to an arc-shaped subsoiler increased the disturbance areas of HDAS,TL and HDSS by 47.52%,7.74%and 4.59%,respectively,but meanwhile increased the total draught force by 36%.Compared with a non-winged subsoiler,winged subsoiler had higher soil looseness(15.83%),soil disturbance coefficient(58.59%),furrow width(448.65 mm)and soil disturbance area ratio(0.3835),but poorer soil surface flatness(19.79 mm)and lower soil loosening efficiency(39.35 mm²/N).This study provided critical information for optimizing winged subsoilers on aspects of improving soil loosening effectiveness and reducing draught force.

Combined effects of soil texture and machine operating trail gradient on changes in forest soil physical properties during ground-based skidding

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.

Effects of tilt angle of disk plough on some soil physical properties, work rate and wheel slippage under light clay soil

Standard Disk Plough(SDP)is the integral element of traditional farming system in Middle and Northern Sudan.In SDP,the tilt angle between the planes of the cutting edge of the disk which is inclined to a vertical line may be altered according to the field conditions.Tractor drivers usually use an angle close to maximum in order to decrease the tillage depth,consequently decreasing power requirements,without considering the tillage quality and the impact on the soil properties.This experiment was conducted at the College of Agricultural Studies farm of Sudan University of Science and Technology to study the effects of three tilt angles(15°,20°and 25°)on soil bulk density,mean weight diameter,wheel slippage,work rate(or effective field capacity)and soil volume disturbed using mounted disk plough.The nature of soil on the farm found to be light clay.The theoretical forward speed was maintained at 6 km/h.The results showed that increasing tilt angle of the plough significantly(p<0.05)increased the bulk density,mean weight diameter and field capacity while significantly decreasing the tractor wheel slippage and soil volume disturbance.

Stalk cutting mechanism of no-tillage planter for wide/narrow row farming mode

A no-tillage planter of narrow row spacing was designed according to the agronomic requirements of wide/narrow row farming mode in the black soil region of Northeast China.Due to the narrow spacing of the seeder unit,a gear-tooth stalk cutting mechanism was designed in order to prevent residues from blocking the planter.The basic parameters,number and edge curve of the stalk cutting blade were designed and optimized.Three-factor and three-level combined orthogonal experiments were conducted using the factors of working speed(1.12 m/s,1.57 m/s and 2.02 m/s),tillage depth(75 mm,90 mm and 105 mm)and cutter spacing(15 mm,30 mm and 45 mm),which significantly affected stalk cutting rate and soil disturbance rate.The optimal combination is the working speed of 1.62 m/s,tillage depth of 92 mm and cutter spacing of 35 mm.Under this condition,the stalk cutting rate is more than 90%and soil disturbance rate is 7.5%-12.0%.The performance of the new no-tillage planter was tested by using the above parameters.The results showed that the no-tillage planter of narrow row spacing came up to the relevant national standards in China.

Ecological role of the giant root-rat(Tachyoryctes macrocephalus)in the Afroalpine ecosystem

Rodents with prevailing subterranean activity usually play an important role in the ecosystems of which they are a part due to the combined effect of herbivory and soil perturbation.This is the case for the giant root-rat Tachyoryctes macrocephalus endemic to the Afroalpine ecosystem of the Bale Mountains,Ethiopia.We studied the impact of root-rats on various ecosystem features within a 3.5-ha study locality dominated by Alchemilla pasture,which represents an optimal habitat for this species,in 2 periods of a year.The root-rats altered plant species composition,reducing the dominant forb,Alchemilla abyssinica,while enhancing Salvia merjame and a few other species,and reduced vegetation cover,but not the fresh plant biomass.Where burrows were abandoned by root-rats,other rodents took them over and A.abyssinica increased again.Root-rat burrowing created small-scale heterogeneity in soil compactness due to the backfilling of some unused burrow segments.Less compacted soil tended to be rich in nutrients,including carbon,nitrogen and phosphorus,which likely affected the plant growth on sites where the vegetation has been reduced as a result of root-rat foraging and burrowing.