Low Soil Strength Research Articles

Hydrated halloysite: the pesky stuff responsible for a cascade of landslides triggered by the 2018 Iburi earthquake, Japan

Coseismic landslides generated by strong earthquakes can substantially increase the devastation imposed on society and humanity, especially when such seismic events occur in unconsolidated pyroclastic fall deposits that are prone to destabilization. The catastrophic 2018 Hokkaido Eastern Iburi Earthquake triggered thousands of shallow liquefied landslides in pyroclastic fall deposits, 1 day after the passage of Typhoon Jebi. The landslides were highly mobile and had long runouts. We here report novel findings pertaining to distinctive properties of the widely distributed, weathered Plinian Ta-d tephra deposit from Tarumae volcano, and their impact on the spatial clustering of the Iburi landslides. Distribution of the landslides is positively correlated with the dispersal of Ta-d. Liquefaction occurred in the weathered Ta-d pumice, despite the absence of unconfined groundwater. The Ta-d pumice also has lower soil strength than other local pumice units. The volumetric soil moisture content of weathered Ta-d pumice is very high (>90%) and exceeds other soil layers, regardless of precipitation variation. The presence of hydrated halloysite was confirmed by X-ray diffraction. The halloysite enhances the shaking-triggered liquefaction, because it maintains weathered Ta-d pumice in a highly saturated and exceedingly loose state, even in the absence of unconfined groundwater. This is inconsistent with the traditional concept of liquefaction that generally occurs in sandy soils below the groundwater level.

Strength of frozen soils during thawing

More than a third of the Earth’s surface is subject to seasonal or prolonged soil frosts, and the recent warming of the climate requires revision of the construction standards in the conditions of permafrost because under heavy load in low-strength soils, there is a high risk of mobility of thawing rock and collapse of the construction structures, which is fraught with disastrous consequences. For design tasks it is necessary to know the behavior of frozen soils under certain changing conditions. This creates new requirements related to the degradation of permafrost and, as a result, the criteria for strength and stability of soils suitable for construction are changing. Calculation of loads during construction in the permafrost zone requires a special approach in each specific case, since it is impossible to make a single model in connection with the variety of soils and the history of their freezing. Soil typization does not give a clear picture at negative temperatures, since the transition “water-ice-water” in the soil changes the behavior of the grounds, and the unpredictability of climatic changes affecting this process greatly complicates the task. In the hydraulic laboratory of the RUDN University, a series of experiments was conducted for various types of soil subject to load, in order to determine the main parameters affecting the stability of soils during thawing, and to give approximate recommendations regarding the use of these soils as bases.

Sinkage control of North-West corner of Kolkata high court by consolidation grouting and stabilization using Drucstone chemical grout: A case study

The North-West corner of the Kolkata high court started developing cracks and showing signs of differential subsidence due to unstable soil conditions below its foundation. Investigations indicated that the brick foundation of the high court rested on backfilled material and low strength soil, which had now developed greater instability due to possible soil liquefaction as a result of the proximity of Hooghly River. Based on the damage monitoring of the structure, a two-phase grouting operation was executed at the N-W corner of the building which involved consolidation grouting below and surrounding the brick foundation, and curtain grouting around the corner periphery. The grouting operation was performed using Drucstone chemical grout, which is a two-component low-foaming polyurethane-based chemical, capable of substantially improving the properties of the deteriorated soil mass. This stopped the sinkage of the building completely, which was confirmed by deformation monitors installed throughout the N-W corner of the building. The settlement of the N-W corner was arrested at 19.48 mm depth, while the rate of settlement, which was initially 0.25 mm/day, was finally reduced to 0.015 mm/day and gradually arrested. This project also proved the effectiveness of Drucstone in such scenarios by showcasing its efficient soil improvement and consolidation properties indicated by an increase in soil cohesion by 90% and its shear modulus by 300%.

Уменьшение колееобразования широкозахватных дождевальных машин

During the process of irrigation, when moving sprinklers across the field, the wheels of the run-ning supports create a track. As the number of passes increases, so does the depth of the track. At the end of the irrigation season, it can reach 0.3-0.45 m, lead to slipping wheels and excessive wa-tering. The intensity of the process of rutting and reducing the coupling properties of the running systems of sprinkler machines is further increased in the presence of free, not absorbed water, caus-ing the formation of runoff on the track. The greatest depth of the track by the end of the season in the last undercarriages occurs due to the increase in the intensity of irrigation and the diameter of the drops of sprinklers located at the end of the pipeline. The choice of running systems should be made taking into account the characteristics of irrigated surfaces, rational ratios of span lengths, di-ameters of pipelines and sprinkler arrangement schemes. The aim of the study is to consider the im-pact of the irrigation process on the bearing properties of the soil and the formation of a track. The article presents theoretical dependences for determining the depth and width of the track for two-wheeled and three-wheeled undercarriages of wide-grip sprinkler machines. Field studies were con-ducted on “Kuban-LK1M” (Cascade) and “CASCADE” sprinkler machines. The article presents the dependence of the track depth on the number of the undercarriages with a soil bearing capacity of 110-125 kPa. The research made it possible to determine the approximate zones of application of wheel systems, depending on the bearing capacity of the soil. Analysis of the data shows that it is advisable to equip sprinklers with narrow pneumatic wheels on soils of increased strength. On soils with low bearing capacity and significant irrigation rates from 600 m3 / ha - wide-profile pneumatic tires 18-24; 23-26, 21.3-24 for “Kuban-LK1”, “Kuban-LK1M” (KASKAD), KASKAD with a pro-file width of 0.30-0.54 m, including the installation of wider tires at the end part of the machines. In addition, in conditions of low soil strength, it is possible to use tires on sprinklers with smaller profile widths than the recommended ones, but for reduced span lengths or a reduced diameter of the water pipeline.

Geotechnical Problems Of The Foundation Of Road Embankments By The Bridge Structures

Abstract This work presents the geotechnical problems occurring in the interaction area between road embankments and the bridge structures in case a subsoil characterised by complex and complicated geological and engineering conditions. These significant problems that occur during the design, performance and exploitation of the abutment structures, are illustrated on the example of engineering practice in Lower Silesia, concerning a road embankment that constitutes access to the bridge. The results of numerical analyses concerning the process of consolidation of low-strength soils and their impact on the settlements of road embankment indicate the need to carry out such analyses also in the cases, when the soft soils occur in the direct geotechnical layer under the designed embankment. The Authors included in this article a discussion regarding other effective actions and solutions that can be used in the design and performance phase, leading to the elimination or reduction of problems concerning the connection of engineering structures with road embankments, which have been recurring for years, ultimately resulting in the improvement of quality, comfort and safety of road exploitation.

STRENGTH OF SOFT CLAY REINFORCED WITH 10 MM SINGLE CRUSHED COCONUT SHELL (CCS) COLUMN

Stone column can be used as a ground improvement technique where a portion of soft soil is replaced with granular material such as stone or sand. The benefit of using stone columns in low strength soil has been proven as an efficient method to improve the bearing capacity and reduce settlement of soft soils. This study aims to investigate the improvement in shear strength of soft clay by embedded with a single crushed coconut shell (CCS) column. The cost of soil improvement can be reduced because of CCS is a waste material. This paper was done by determining the physical and mechanical properties of kaolin and CCS as well as the effect of height penetration ratio of a single CCS column on shear strength characteristics. Unconfined Compression Test (UCT) was conducted for 4 batch kaolin samples including a control sample in order to determine the shear strength. Each batch involved four samples to find the accurate value. The research variables are the height of crushed coconut shell column which is 60 mm, 80 mm and 100 mm where the column penetration ratio is 0.60, 0.80 and 1.00 respectively. A total of 16 unconfined compression tests had been conducted on kaolin sample with dimensions of 50mm in diameter and 100 mm in height. The increment of shear strength by embedded with crushed coconut shell columns is 19.02 %, 34.76 % and 24.34 % for with 4 % area displacement ratio at column penetration ratio of 0.60, 0.80 and 1.00 respectively. From the results obtained, the relationship between shear strength increases is influenced by the height of the column. The maximum column height (full penetration) does not generate the highest strength and it proves that critical column length theory is true in this study.

РЕШЕНИЕ ЗАДАЧИ О РАСШИРЕНИИ СФЕРИЧЕСКОЙ ПОЛОСТИ В СРЕДЕ С УСЛОВИЕМ ПЛАСТИЧНОСТИ МОРА - КУЛОНА - ТРЕСКА

An analytical solution of the one-dimensional problem of a spherical cavity expanding at a constant velocity from a point in a space occupied by a plastic medium has been obtained. Impact compressibility of the medium is described using linear Hugoniot's adiabat. Plastic deformation obeys the Mohr - Coulomb yield criterion with constraints on the value of maximum tangential stresses according to Tresca's criterion. In the assumption of rigid-plastic deformation (the elastic precursor being neglected), incompressibility behind the shockwave front and the equality of the propagation velocities of the fronts of the plastic wave and the plane shockwave defined by linear Hugoniot's adiabat, a boundary-value problem for a system of two first-order ordinary differential equations for the dimensionless velocity and stress depending on the self-similar variable is formulated. A closed-form solution of this problem has been obtained in the form of a stationary running wave - a plastic shockwave propagating in an unperturbed half-space. This solution is a generalization of the earlier obtained analytical solution for a medium with the Mohr - Coulomb plasticity condition. The effect of constraining the limiting value of maximal tangential stresses on the distribution of dimensionless stresses behind the shockwave front has been examined. Formulas for determining the range of cavity expansion velocities, within which a simple solution for a medium with Tresca's plasticity condition is applicable, have been derived. The obtained solution can be used for evaluating resistance to high-velocity penetration of rigid strikers into low-strength soil media.

Low-Strength Substrates and Anthropogenic Soils in Transportation Engineering

Abstract Road embankments, especially their slopes’ surfaces, must fulfil all the requirements concerning the exploitation criteria after the completion of construction works. This is very important while constructing or modernizing the embankments, based on the substrate including low-strength soils as well as in simple ground conditions (most convenient). The last dozen or so years of intensive construction of transport infrastructure have shown how big is the problem of ensuring the required volumes of qualified soil material for the construction of road embankments or the modernization of railway embankments. The depleting deposits of natural and easily accessible soils for the construction of embankments result in the need to use anthropogenic soils, for example, in the form of aggregates from the recycling of construction waste and other locally available waste materials, usually in the form of slag and ashes from the combined heat and power plants. In such cases, there’s a need to treat transportation earth structures individually in the scope of designing and quality control, because there are no applicable standard provisions in this scope. This work indicates some of these important contemporary problems of transport engineering, occurring in newly built and modernized road objects, such as the stability of road embankments based on a low-strength substrate, use of anthropogenic soils and materials originating from the recycling of concrete surfaces for the construction of road embankments.

Effects of Waste Glass Powder on the Geotechnical Properties of Loose Subsoils

Foundation soils are most affected by different problems when it comes to the loose soil having low shear strength and bearing capacity. Failure of the soil with settlement and shear arises when the shear stresses in the soil exceed the limit. This study is keen to observe the effects of utilization of waste broken glass in the enhancement of Geotechnical properties of soil by performing different laboratory tests. Collection of the soil sample from was concluded from Pabbi, Peshawar, KPK, and Pakistan, which is a low strength soil, are also being called soft soil having low bearing capacity. Furthermore, this particular soil was needed to be enhanced. The physical, chemical and engineering properties of virgin soil were contemplated and the soil was treated with added substances of Glass Powder to stabilize the local soil. Addition of Glass Powder was finished in different proportions that are 4%, 8% and 12% etc. Performance of different tests as Gradation, Specific Gravity, Standard Proctor compaction, Atterberg Limits, Direct Shear, CBR and so forth were done. The results were concluded, based on the Glass Dust stabilization analysis. It was obtained that pulverized glass can be effectively used as a soil stabilizer as mainly the strength characteristics were observed to be valeted. The Results showed that the gradation of soil is narrow from the particle size analysis. Plasticity index (P.I), Liquid limit (L.L) and plastic limit (P.L) were decreased with the addition of Glass powder. The reason behind decreasing P.I is maybe the fact that the Glass powder is cohesionless. Ideal percentage of Glass Powder as a stabilizer is 8%. Such improvements included an achievement of the highest CBR obtained at the 4%, 8% and 12% of powdered glass content. The reason is that the glass is pozzolanic material when blended with soil gives additional strength. The achievement of the increasing rate of the values of angle of internal friction on 4% and 8% and decreasing rate of values obtained at 12% powdered glass substances. Cohesion rate decreases up to 8% and starts increasing at 12%. Maximum dry density increasing as the density of glass is higher than such soil and Optimum moisture content (OMC) is decreasing because of low absorption capacity of glass. The study showed that the best stabilizer for the case study (Pabbi, Peshawar) is the Glass Powder and the optimum dose is 8 %.

Study of Engineering Behavior of Coal Mine Waste Generated From Barapukuria Coal Mine As Road Subgrade

This study is focused on the possibility of using coal mine wastes as a replacement for conventional road subgrades. Various laboratory tests carried out on fresh coal mine waste collected from Barapukuria Coal Mine (Located at Dinajpur, Bangladesh) showed that, it behaves like low strength soil with 0.71% CBR and 18.74% plasticity index which is unsuitable for engineering utilization. Later, fine sand and cement were added with the waste. Three different cement proportion were tested (5%, 8% and 10% of total weight) keeping a constant sand proportion (20% of total weight). The unconfined compression strength and CBR value were found to increase greatly. Analyzing the test results, waste mixed with 8% cement and 20% sand showing 27.44% CBR and 9.09% plasticity index was found to be effective for using as subgrade. Chemical analysis of waste detected the presence of lead as 0.026 ppm which may cause groundwater contamination.

Reclamation of acid sulphate soils in paddy cultivation area with organic amendments

A soft soil is distinguished by high compressibility and low strength. It is formed in acid sulphate soil under a zero or low pressure gradient as an incompletely consolidated fine grain medium. The problem is related to the presence of weak hardpan structure that permits the soil to experiencing continuous wet condition. The objective of study was to examine closely the effects of addition of organic soil amendment namely Hasil Tani Organic Compound (HTOC) to soft soil in order to enhance its quality and strength. The study was carried out in paddy soils of Muda Agricultural Development Authority (MADA) Alor Senibong Kedah, Malaysia. High water content of soft soil caused low soil strength, which delayed the formation of hardpan layer. The application of HTOC could increase soil strength and reduce water content. After being treated with HTOC, soil strength has increased from 0.22 MPa to 0.70 MPa and organic matter content increased from 3.19% to 7.07%. Whilst, exchangeable sodium percentage (ESP) has decreased from 21% to 5% and soil water content decreased from 40.11% to 24.38%. As whole, the application of HTOC product could improve soft soil in study area.

Root Tip Shape Governs Root Elongation Rate under Increased Soil Strength

Increased soil strength due to soil compaction or soil drying is a major limitation to root growth and crop productivity. Roots need to exert higher penetration force, resulting in increased penetration stress when elongating in soils of greater strength. This study aimed to quantify how the genotypic diversity of root tip geometry and root diameter influences root elongation under different levels of soil strength and to determine the extent to which roots adjust to increased soil strength. Fourteen wheat (Triticum aestivum) varieties were grown in soil columns packed to three bulk densities representing low, moderate, and high soil strength. Under moderate and high soil strength, smaller root tip radius-to-length ratio was correlated with higher genotypic root elongation rate, whereas root diameter was not related to genotypic root elongation. Based on cavity expansion theory, it was found that smaller root tip radius-to-length ratio reduced penetration stress, thus enabling higher root elongation rates in soils with greater strength. Furthermore, it was observed that roots could only partially adjust to increased soil strength. Root thickening was bounded by a maximum diameter, and root tips did not become more acute in response to increased soil strength. The obtained results demonstrated that root tip geometry is a pivotal trait governing root penetration stress and root elongation rate in soils of greater strength. Hence, root tip shape needs to be taken into account when selecting for crop varieties that may tolerate high soil strength.

Use of agar biopolymer to improve the shear strength behavior of sabarmati sand

Loose saturated sandy soils are low shear strength soils, which are also prone to liquefaction under earthquake conditions. Many soil treatment techniques using admixers are available such as cement, chemical grouts, epoxy, acrylamide, phenoplast, polyurethane, etc. However, these admixtures have negative impact on environment or ecosystem. In the current research, the agar biopolymer has been chosen to strengthen the loose saturated Sabarmati soil (cohesionless soil) due to its gel forming capability and environment friendly nature. Sabarmati soil has been treated using different concentration of agar biopolymer (0.5, 1, 2, and 3%) at different curing time (4hrs, 8hrs, 1, 3, and 7 days). A series of shear strength tests has been performed on Sabarmati soil before and after its treatment to evaluate its shear stress behavior at different agar content and curing time. The settlement behavior of treated soil has been evaluated by obtaining vertical displacement during its shear deformation, which showed significant decrease in settlement of soil after its treatment. The agar treatment technique has also been evaluated for its applicability in moisture exposed region by performing shear strength tests on treated soil after water soaking, which exhibited small reduction in the shear strength of treated soil after moisture absorption.

Submergence and Herbivory as Divergent Causes of Marsh Loss in Long Island Sound

Tidal marsh degradation has been attributed to a number of different causes, but few studies have examined multiple potential factors at the same sites. Differentiating the diverse drivers of marsh loss is critical to prescribing successful interventions for conservation and restoration of this important habitat. We evaluated two hypotheses for vegetation loss at two marshes in Long Island Sound (LIS): (1) marsh submergence, caused by an imbalance between sea-level rise and marsh accretion, and (2) defoliation associated with herbivory by the purple marsh crab, Sesarma reticulatum. At our western LIS site, we found no evidence of herbivory: crabs were scarce, and crab-exclusion cages provided no benefit. We attribute degradation at that site to submergence, a conclusion supported by topographic and hydrologic data showing that loss of vegetation occurred only in wetter parts of the marsh. In contrast, at our central LIS site, our observations were consistent with herbivory as a driving force: There were substantial populations of Sesarma, crab-exclusion cages allowed plants to thrive, and vegetation loss took place across a variety of elevations. We also analyzed soil conditions at both sites, in order to determine the signatures of different degradation processes and assess the potential for restoration. At the submergence site, unvegetated soils exhibited high bulk density, low organic content, and low soil strength, posing significant biogeochemical challenges to re-colonization by vegetation. At the herbivory site, unvegetated soils had a characteristic “riddled-peat” appearance, resulting from expansion and erosion of Sesarma burrow networks. The high redox potential and organic content of those soils suggested that revegetation at the herbivory site would be likely if Sesarma populations could be controlled before erosion leads to elevation loss.

Vertical drainage capacity of new electrical drainage board on improvement of super soft clayey ground

As an advanced polymer composites electro-kinetic geosynthetics, the electro-osmotic vertical drainage (EVD) board could drain water quickly and accelerate consolidation process. However, the drainage rate was mainly impacted by the vertical drainage capability. Therefore, vertical drainage capability at the top of EVD board was theoretically analyzed. Basic requirements for drainage at the top of the board were summed up, as well as the formula of anode pore pressure when losing the vertical drainage capability. Meanwhile, a contrast test on the top and bottom drainage capacities was conducted. In use of the advanced EVD board, the voltage potential and pore pressure of anode were measured. Moreover, the derived formulas were verified. The result shows that the decrease of electric force gradient had an observable impact on the drainage capability. There was nearly no difference between the energy consumption for the two drainage methods. Although a little less water was discharged, the top drainage method had more advantages, such as high initial drainage velocity, few soil cracks, low anode water content and high soil strength. All of these show that the super soft soil ground could be consolidated quickly in use of the advanced EVD board through the top drainage. The top drainage method could efficiently improve the drainage effect, decrease the energy consumption and speed up the project proceeding.

Techno-Financial Analysis of Energy Access through Hybrid System with Solar PV under the Various Rural Community Models for State of Uttarakhand, India

Uttarakhand state comes under special category state where approximately 69.45% population lived in rural area under the population density with varied range of 37 to 607 persons per sq.km. Although Uttarakhand is having per capita consumption of 1112.29 kWh which is higher than national average per capita consumption of 779 kWh as till date, but remote communities, villages are not able to access clean, cheep and good quality of energy due to uneven terrain, lack of proper transmission & distribution lines [1]. 100% villages are electrified under the RGGVY scheme as per the Ministry of Power Government of India, but due to poor loading of transformer, lack of grid infrastructure and natural calamities, remote house owners are not able to get good quality of power thus affect the livelihood and source of income generation in various means [2]. As Uttarakhand state having future plans to be make state energy sufficient and energy access to all by year 2016-2017, so major ground level initiative have been taken by Government of Uttarakhand. The government of Uttarakhand has incorporated innovative business model to provide good quality of power with non-conventional energy source. Under the initiative invlovement of local people and village level, panchayats have ownership and responsibility to operate these clean energy business model to improve livelihood in remote hilly places of Uttarakhand. Under this analysis, five different type of community models are categorized as Community 1, Community 2, Community 3, Standalone 1 & Standalone 2 for rural &remote communities based on number of unclustered households with the distance covered between 200 m to 20 km, and electrical loads i.e. lighting, fan, mobile chargers, television along with time of day energy consumption patterns. These community models are for remote hilly location where grid integration and distribution lines are not feasible to built due to hilly terrain, low soil strength and huge expenses for expanding power cables for supplying good quality power. The preliminary studies and simulations has been done in HOMER tool by considering the various composite source of power, i.e. Solar PV with battery bank, Solar PV with battery Bank & Generator, and Solar PV along with DG. These three hybrid source of power generation with Solar PV as base source under five different community models, the techno-commercial feasibility has been analyzed in terms of load sharing proposition with Solar PV and battery, DG, Energy production through PV, load consumption per year, Excess and unmet energy monitoring, battery sizing to meet the load during nights, DG operation when the solar energy not available due to weather condition and non availability of sunshine in night. Financial feasibility has been examined in terms of levelized cost of energy, cost summary and O&M cost per year of three integrated sources of energy generation with Solar PV under each community model. Solar PV power plant , which is the best renewable source of energy to cater energy access issue in remote hilly places. The Uttarakhand receives good amout of daily average radiation level of 5.14 - 5.50 kWh/m2/day. Financial feasible community models for different hilly region based on their energy consumption need to be implemented with the help of local community by providing ownership to local people, panchayat, for it not only caters energy access issue but also provides clean, cheep, uninterruptable energy and improves livelihood standard to locals by engaging them into operation maintenance and tariff or rent collection. The study shows that Solar PV power plant with battery bank is the optimal solution considering life cycle cost of hybrid system. It is feasible due to low operation and maintenance cost, price declination of battery and Solar PV module, battery prices at time of replacement.

Using Electrical Resistivity Tomography (ERT) as a tool in geotechnical investigation of the substrate of a highway

Abstract Geological and geotechnical engineering field tests, like structure drillings and dynamic (DPL, DPSH) or static probing (CPT), are considered for a fundamental source of information about soil and water environments. Since Eurocode 7 has been introduced, it has become more common to use also dilatometers (DMT) or pressure meters (PMT). Results obtained using all the mentioned tests are always of a discrete nature - information is provided in certain points in the field. However, they determine the basis for creating spatial models of geological structure and geotechnical condi- tions of a substratum. The range and number of investigations conducted (including drilling, probing and laboratory tests) influence precision, in which a geological structure is identified and thus, also affect probability of compatibility between spatial model and real geological conditions of a substratum. In the paper, results of non-invasive electrical resistivity tomography (ERT) method are presented, comprising 2-dimensional image of a soil medium resistance. Electrical resistance is a parameter that reflects diversification of a soil medium, considering its lithological aspect. In addition, when combined with drilling results, it can be used to accurate determination of boundaries between soil layers. Carrying out of ERT tests in the field during expressway construction contributed to identification of weak, low-strength soils like organic soils (peat, aggradated mud) and of soft consistency cohesive soils. These kinds of soil are the main cause for unacceptable deformations appearing in the new road engineering structure.

Quantification of mechanical strength and sliding stability of an artificial water catchment (Chicken Creek)

Natural shear forces due to gravity along inclined terrain surfaces are controlled by the inclination of the terrain, material composition and its mechanical properties, stratification and hydraulic stress states. Both shear forces and shear strength under a given inclination of the terrain surface strongly depend on the interaction between mechanical and hydraulic stresses. These internal conditions as well as the interactions between these various components are fundamentals in all nonplanar regions under arable, forest or grassland management and they dominate also under various geoscientific aims. Generally, soil creep is a slow soil movement downslope under gravity. It can occur even on gentle slopes when the shear forces exceed the shear strength of the soil. Deposited material on slopes is more sensitive to such movements than well-developed soils due to the absence of a pronounced soil structure, site and management dependent hydraulic properties and functions, which results in low soil strength.We applied the described measurements and the modelling approaches to investigate and to analyse the stability of an artificially constructed water catchment (Chicken Creek) in the mining district of Cottbus/Germany, where glacial sand was deposited above a clay layer with an inclination of about 3.5%. At the lower part of the catchment, an impermeable barrier (clay wall) was positioned transversally to the main slope. Mechanical and hydraulic parameters of the soil layers were determined on soil samples taken from the field site. The measured values were inserted as input parameters for the finite element model (Plaxis 2D) to simulate soil movements and their effect on the stability of the catchment. The obtained results showed that the kind of construction negatively affected the physical low soil strength (low pre-compression stress) although the bulk density was very high (1.7–1.9g/cm3 for the sandy material). Hydraulic conductivity revealed a significant anisotropy with higher hydraulic conductivity values in the horizontal direction. Furthermore, finite element results showed that the design of the newly formed landscape remains weak concerning mass movements too. The high water table in the sandy material in conjunction with low soil strength enhances the downslope movement and increases the shear stress near the clay wall at the lower end of the slope, which finally results in soil creep processes.These results also proof that such geotechnical and modelling approach is also suitable to validate or to predict mass movements and the internal processes responsible for these internal mass erosion.

Stability Analysis of Soft Soil Foundation Excavation of Underground Station in Coastal Area of Tianjin

The marine sedimentary strata are spread in coastal area of Tianjin. Due to low soil strength, high underground water level and strong soil plasticity flow, instability accidents happened frequently in soft soil area. In the foundation excavation of underground station, because of stress release and change in ground water level, the differential settlement of surrounding buildings, ground crack and deformation of underground pipeline will happen. The stability of surrounding rocks in the foundation excavation of underground station has been calculated and analyzed by using numerical simulation method. The Surrounding soil deformation of foundation pit has been gotten to analyze.

Root hair length and rhizosheath mass depend on soil porosity, strength and water content in barley genotypes

Selecting plants with improved root hair growth is a key strategy for improving phosphorus-uptake efficiency in agriculture. While significant inter- and intra-specific variation is reported for root hair length, it is not known whether these phenotypic differences are exhibited under conditions that are known to affect root hair elongation. This work investigates the effect of soil strength, soil water content (SWC) and soil particle size (SPS) on the root hair length of different root hair genotypes of barley. The root hair and rhizosheath development of five root hair genotypes of barley (Hordeum vulgare L.) was compared in soils with penetrometer resistances ranging from 0.03 to 4.45 MPa (dry bulk densities 1.2-1.7 g cm(-3)). A "short" (SRH) and "long" root hair (LRH) genotype was selected to further investigate whether differentiation of these genotypes was related to SWC or SPS when grown in washed graded sand. In low-strength soil (<1.43 MPa), root hairs of the LRH genotype were on average 25 % longer than that of the SRH genotype. In high-strength soil, root hair length of the LRH genotype was shorter than that in low-strength soil and did not differ from that of the SRH genotype. Root hairs were shorter in wetter soils or soils with smaller particles, and again SRH and LRH did not differ in hair length. Longer root hairs were generally, but not always, associated with larger rhizosheaths, suggesting that mucilage adhesion was also important. The root hair growth of barley was found to be highly responsive to soil properties and this impacted on the expression of phenotypic differences in root hair length. While root hairs are an important trait for phosphorus acquisition in dense soils, the results highlight the importance of selecting multiple and potentially robust root traits to improve resource acquisition in agricultural systems.