Increase In Soil Shear Strength Research Articles

How revegetation reinforces soil at early stage of restoration: A 6‐year field study in southwest China

AbstractBackground and aimsRestoring vegetation on hillslopes has been found to increase soil strength, thereby reducing the risk of soil erosion and shallow landslides. However, limited information is available on the temporal changes in root biomechanical traits and increased soil shear strength related to vegetation growth following restoration with different species.MethodsIn 2012, Symplocos setchuensis, Buxus megistophylla, and Cynodon dactylon were replanted in a forest gap in Jinyun Mountain, Beibei District, China, and studied over a 6‐year period. We measured root traits (root tensile strength, Young's modulus, cellulose content, and root density) and soil traits (cohesion and internal friction angle) at two soil depths (0–20 and 20–40 cm) for undisturbed and reconstituted samples.ResultsS. setchuensis was found to have the highest tensile strength and resistance to failure for root diameters <2 mm. With elapsed time, tensile strength and cellulose content decreased. Cohesion and root mechanical reinforcement of topsoil generally increased with time (+10% per year). Root chemical and mechanical effects contributed approximately 50% to soil reinforcement. C. dactylon had the fastest growth rate and reinforced the topsoil soil rapidly, whereas S. setchuensis exhibited a consistent increase in soil reinforcement during the study period and provided more deep roots that could reinforce subsoil.ConclusionChemical and mechanical effects almost equally contributed to soil reinforcement. Although the relative contributions varied for different species, the variation in each contribution sheds new light on the sustainable use of vegetation for mitigating shallow landslides in mountainous areas.

Comparison between mechanical and hydrological reinforcement effects of cultivated plants on shallow slope stability

Root reinforcement, provided by plants in soil, can be exerted by a mechanical effect, increasing soil shear strength for the presence of roots, or by a hydrological effect, induced by plant transpiration. No comparisons have been still carried out between mechanical and hydrological reinforcements on shallow slope stability in typical agroecosystems. This paper aims to compare these effects induced by sowed fields and vineyards and to assess their effects towards the shallow slope staibility. Root mechanical reinforcement has been assessed through Root Bundle Model-Weibull. Root hydrological reinforcement has been evaluated using an empirical relationship with monitored or modelled pore water pressure. Each reinforcement has been inserted in a stability model to quantify their impacts on susceptibility towards shallow landslides. Considering the same environment, corresponding to a typical agroecosystem of northern Italian Apennines, land use has significant effects on saturation degree and pore water pressure, influencing hydrological reinforcement. Root hydrological reinforcement effect is higher in summer, although rainfall-induced shallow landslides rarely occur in this period due to dry soil conditions. Instead, in wet and cold periods, when shallow landslides can develop more frequently, the stabilizing contribution of mechanical reinforcement is on average higher than the hydrological reinforcement. In vineyards, the hydrological reinforcement effect could be observed also during autumn, winter and spring periods, giving a contribution to slope stability also in these conditions. This situation occurs when plants uptake enough water from soil to reduce significantly pore water pressure, guaranteeing values of hydrological reinforcement of 1–3 kPa at 1 m from ground, in agreement with measured mechanical root reinforcement (up to 1.6 kPa). These results suggest that both hydrological and mechanical effects of vegetation deserve high regard in susceptibility towards shallow landslides, helping in selection of the best land uses to reduce probability of occurrence of these failures over large territories.

Clayshale Stabilization Using Liquid Calcium Carbonate to Increase Soil Shear Strength

Clayshale is a material that often causes various stability and bearing capacity problems in geotechnical engineering structures because it tends to weather and slake relatively quickly. This causes clayshale to be often not used during construction. Therefore, it is necessary to stabilize the clayshale. This study aims to determine the effect of adding variations in the levels of liquid calcium carbonate to the clayshale shear parameters. Physical and mechanical properties were tested on the original remoulded clayshale and samples with additional variations of 1M and 2M liquid CaCO3. Based on laboratory testing, the original clayshale samples had LL values of 37.9%, PL 14.6%, IP 23.3%, Gs 2.617, OMC 13.67%, γdry 1.762 gr/cm3. The addition of CaCO3 has been proven to increase the Gs value and reduce the plasticity index of the clayshale. After the Triaxial UU test, the clayshale sample in remoulded condition has a c value of 0.171 kg/cm2 and φ 8.33°. While the clayshale sample with 2M CaCO3 substitution as much as 80% OMC value which has been cured for three days increased the most optimum c and φ values, respectively 0.289 kg/cm2 and 11.13°. This shows that the addition of liquid CaCO3 can be used as a clayshale stabilization agent because it can increase the value of the shear parameter and improve the clayshale properties.

A Critical Review on the Feasibility of Synthetic Polymers Inclusion in Enhancing the Geotechnical Behavior of Soils.

Polymers have attracted widespread interest as soil stabilizers and are proposed as an ecologically acceptable means for enhancing the geotechnical properties of soils. They have found profound applications in diverse fields such as the food industry, textile, medicine, agriculture, construction, and many more. Various polymers are proven to increase soil shear strength, improve volume stability, promote water retention, and prevent erosion, at extremely low concentrations within soils through the formation of a polymer membrane around the soil particles upon hydration. The purpose of this work is to provide an overview of existing research on synthetic polymers for soil improvement. A fundamental evaluation of many synthetic polymers used in soil stabilization is provided, Furthermore, the impact of different polymer types on the geotechnical parameters of treated soil was assessed and compared. Limiting factors like polymer durability and the effect of changing climatic conditions on the engineering behavior of the polymer-treated soils have been critically reviewed. The dominant mechanisms responsible for the alteration in the behavior of polymer-soil admixture are reviewed and discussed. This review article will allow practicing engineers to better understand the intrinsic and extrinsic parameters of targeted polymers before employing them in real-field scenarios for better long-term performance.

Stability Evaluation of Reinforced Slope Soil with Vetiver Grass against Erosion and Landslides Hazards by Using Finite Element Method

This work studied slopes with different geometric situations. The purpose is to select types of soil for embankment construction to stabilise the site by using nearby accessible filling materials. Then, PLAXIS-2D software was used including five (6) phases of sequential calculation such as soil, structure, mesh generation, conditions of flow and construction stage and the use of Vetiver grass for embakment stability reinforcement. Choices were made on soil properties, loading, water table effect, embankment geometry and reinforcement actions of vetiver grass. The method is based on using diverse filling materials and varied slope gradients with different heights. So, the slope analyse involves homogeneous soils, in addition to slope section by various soils strata. Results obtained showed that the increase in soil shear strength is related to the mechanical effects of vetiver roots and make the soil able to resist shear stress due to the presence of roots density within the soil mass and the root tensile strength. It is also noticed that the soil suction effects and roots reinforcement increased the apparent cohesion of the soil, showing an important role played by vetiver grass in stabilising shallow-seated slopes failure with significant effect on slopes stability.

Fragmentation of soil-root complexes in sloping landscapes during tillage and soil translocation

It is well known that roots play a significant role in reducing water erosion in soil, yet few studies have reported the influence of crop roots on soil translocation induced by tillage in sloping fields. To examine the relationship between soil-root complexes (i.e., complexes of wheat roots and soil) and soil redistribution caused by tillage, a series of tillage experiments were carried out on bare soil and areas of wheat sown by drilling ( DS ) and nesting ( NS) using nine slopes with gradients varying from 0.19 to 0.32 m m −1 . The magnetic tracing technique was used to determine soil translocation rates under hoeing tillage in sloping landscapes in response to soil-root complexes and bare soil. The results indicated that mean displacement distance for DS and NS in the downslope direction was 0.15 m and 0.16 m, respectively. This was much shorter than that of bare soil which was 0.26 m. Mean tillage erosion rates ranged from 14.58 to 19.15 Mg ha −1 per tillage pass for DS and 13.90 –21.10 Mg ha −1 per tillage pass for NS , while reached 31.23–36.31 Mg ha −1 per tillage pass for bare soil. Tillage transport coefficients ( k 3 and k 4 ) were 6.31 and 106.46 kg m −1 per tillage pass for DS , 6.58 and 118.68 kg m −1 per tillage pass for NS , and 28.12 and 151.07 kg m −1 per tillage pass for bare soil, respectively. A significant difference in cohesive force ( C ) was found between DS ( NS ) and bare soil ( P < 0.05), thereby resulting in an increase in the soil shear strength of soil-root complexes. Compared with those of bare soil, the soil fractal dimension of soil-root complexes decreased significantly due to an increase in the percentage of coarse clods (>100 and 100–80 mm) and a decrease in the percentage of fine clods (50–20 and < 20 mm). Mean soil displacement distance caused by tillage displayed a negative relationship with C and wheat root traits (the root density, the root length density, and the root area ratio) within the hilly landscape of soil-root complexes ( P < 0.05), implying that wheat roots played a crucial part in soil translocation and soil fragmentation during hoeing tillage. Our study revealed that soil-root complexes markedly reduce the soil downslope transfer process during tillage and prevent the break-up of large clods by tillage implements on sloping farmland. • Wheat root attenuated the mechanical breakage of clods during tillage operation. • Root systems increase soil shear strength and reduce fragmentation of soil clods. • Displacement distance for soil-root complexes was smaller than that for bare soil. • Tillage erosion decreased with increasing structure stability and cohesive force.

Root traits of crop species contributing to soil shear strength

Roots of annual species would be able to conserve soil properties during traffic induced compaction. The objective of this study was to determine and compare root traits and soil shear strength for three crop species with contrasted root types and morphological traits to see if roots of annual species are able to increase soil shear strength and thus explain the soil properties conservation. The experiment was performed under controlled conditions in steel cylinders containing a repacked loamy sand, with initial dry bulk density of 1.2 g cm−3 and that was kept moist. Soil shear strength parameters, i.e. cohesion and angle of internal friction, were determined from direct shear tests for soil cores at a soil matric potential of −10 kPa (i.e. water content at field capacity). The direct shear tests were performed with six external normal stress levels (25, 34, 44, 63, 83 and 93 kPa) and at a constant shear rate of 3 mm.min−1, and applying Mohr Coulomb equation. The difference of root type, root length density, root density, specific root length and root dry matter content among crop species was not related to a difference in soil shear strength. The root volume density was the main trait involved in both soil cohesion and the angle of internal friction. This study highlights the effect of roots of annual crop species on soil shear strength by comparing their root traits to the apparent cohesion of soil core where they grow. Vicia faba would be a good candidate to improve soil shear strength for soil conservation. This study constitutes a step towards improving the understanding of plants’ effects on soil shear strength with regards to selecting species and designing cropping systems for soil conservation.

FUNCTION OF INTERCEPTION, EVAPOTRANSPIRATION AND ROOT REINFORCEMENT OF PLANT ON SLOPE STABILIZATION

The ability of plants to carry out the functions of interception, evapotranspiration and root reinforcement provides an effective and contributes to an increase in slope stability. Canopy has a role in the process of interception related to the reduction of amount the infiltrated water and the rapid fulfilment of soil moisture. Through the evapotranspiration mechanism, plants can reduce pore water pressure in the soil so that the trigger force for landslides can be reduced and the soil will be more stable. The roots mechanically strengthen the soil, through the transfer of shear stresses in the soil into tensile resistance in the roots. Roots also bind soil particles and increase surface roughness, thereby reducing the process of soil displacement or erosion. There is a positive relationship between the density of the tree canopy with the value of rainfall interception, evapotranspiration with a decrease in pore water pressure in the soil and the ability of root anchoring and binding with an increase in soil shear strength, indicating that the function of interception, evapotranspiration and strengthening of plant roots have a positive effect on increasing slope stability. Plants selection that considers the level of interception, the rate of evapotranspiration and root reinforcement by adjusting environmental and slopes conditions will determine the success of slope stabilization efforts by vegetative methods.Keywords : interception, evapotranspiration, root reinforcement, slope stabilization.

Soil solution composition affects microstructure of tropical saline alluvial soils in semi-arid environment

The remediation of soils stressed by salinity improves soil quality for food production. However, information on how remediation techniques affect microstructural stability/elasticity and resistance is lacking. Hence, the objective of this study was to characterize the microstructure of saline alluvial soils from a semi-arid environment, and to evaluate how the techniques of leaching soil and Na+ substitution by other cations affect the microstructure strength and elasticity evaluated by rheological techniques. Homogenized soil of sixteen horizons of four salinized soil profiles (an Abruptic Solonetz, a Eutric Gleysol, and two Hypereutric Planosols) were collected in Northeast of Brazil. Each horizon was analyzed separately in a completely randomized design, with three replications. The treatments corresponded to soils saturated with 1 × 10−4 mol m−3 of KCl (+K), CaCl2 (+Ca) or MgCl2 (+Mg), leaching of salts (LS) by successive leaching with alcohol 60%, and untreated soil (control). The soils were submitted to an amplitude sweep test with controlled strain in a compact modular rheometer. The obtained variables were strain and stress at the end of the linear viscoelastic interval (LVR) (γLVR and τLVR, respectively), strain (γYP) and stress (G’YP) at the yield point, shear stress (τmax), and integral Z (Iz). The rheological properties varied greatly between the horizons of the same soil profile. The LS increased γLVR compared to control, while the saturation with cations caused reduction in γLVR, especially in soils of higher clay content. The saturation with saline solution increased γYP and Iz, with greater effect in + K treatment. Both leaching of salts and cation saturation increased soil shear strength at the end of the LVR and at the yield point. Leaching of salts caused destabilization of soil microstructure, which is an important finding that needs to be addressed by measures accompanying remediation of salinized soils to maintain soil physical quality.

Analisis Kuat Geser Tanah Lempung menggunakan Kapur dan Petrasoil

Several studies have added lime, fly ash, or gypsum to clay soils to increase the shear strength of relatively low clay soils. The addition of lime and petrasoil as solvents in water was carried out in this study, where petrsoil is often used in Indonesian road construction works. This study aims to obtain the effect of adding lime and petrasoil to the shear strength of clay. The tests consists of the index properties, seive analysis, atterberg limits, soil compaction, and shear strength testing, based on SNI and ASTM. Mixed variations consist of 6, namely: (i) soil + petrasoil; (ii) soil + 10% lime + petrasoil; (iii) soil + 15% lime + petrasoil; (iv) soil + 20% lime + petrasoil; (v) soil + 10% lime + water; (vi) soil + water; all variations without ripening. The test results showed an increase in the value of soil cohesion in the addition of petrasoil and lime variations of 20%, amounting to 50.94. While the angle of shear of the soil increased with the addition of lime at a variation of 10% both with water and with petrasoil, which amounted to 35.10. This shows an increase in soil shear strength with the addition of petrasoil and lime to the soil.

Experimental Investigation of Root Tensile Strength for Slope Stabilization

Bioengineering approaches provide cost-effective ways to protect slopes against surface erosion and shallow mass movements. Indeed, vegetation is an excellent way to control slope erosion and instability of slopes. Plants play an active role both on the surface, protecting and holding soil particles, and at deeper layers, reducing pore pressure and increasing soil shear strength. The use of vegetation is particularly appropriate where soil conservation measures are needed. In the paper, a series of laboratory tests are described, together with the equipment used, to better understand plant root effects on soil shear strength and slope stability. Two species of Mediterranean plants, such as Asparagus acutifolius and Spartium junceum, were tested in the laboratory. More than 170 tensile tests have been performed on dry and saturated samples. In order to evaluate the effect of soil moisture, most several roots were also tested at different saturation ratios. Laboratory tests also included direct shear tests on root-reinforced and unreinforced samples. Comparison between reinforced and non-reinforced samples confirms the contribution of roots to improve the soil strength.

Effect of distribution pattern of DSM columns on the efficiency of liquefaction mitigation

Liquefaction during earthquakes can result in severe damage to structures, primarily from excess pore water pressure generation and subsoil softening. Deep Soil Mixing (DSM) is a common method of soil improvement and is also used to decrease shear stress in liquefiable soils to control liquefaction. The current study evaluated the effect of Deep Soil Mixing (DSM) columns and implementation of different column patterns on controlling liquefaction and decreasing settlement of shallow foundations. A series of shaking table physical modelling tests were conducted for three different distribution patterns of Deep Soil Mixing (DSM) columns (i.e.: square, triangular and single) with a treatment area ratio of 30%. The treatment was applied to a liquefiable soil under a shallow model foundation. The results showed that the excess pore water pressure decreased 20% to 50% in comparison with the unimproved soil, depending on the Deep Soil Mixing (DSM) column pattern used. For improved soil, the shallow foundation settlement was about 10% that of the unimproved soil in the best case. The increase in soil shear stiffness after use of the Deep Soil Mixing (DSM) columns was compared with the results of existing practical relations to increase soil shear strength.

Calculation of increased soil shear strength from desert plant roots

Tarim River is one of the most important water sources in western China, which experiences serious soil erosion. Desert plant roots of various species in the Tarim River Basin can effectively stabilize the slopes. In this study, a total of 28 soil samples were obtained including 17 samples of root-soil composites. The results of soil tests indicate that the cohesion of root-soil composites with values from 9.43 to 28.30 kPa is generally higher than that of no-root soils with values from 3.14 to 16.51 kPa. However, the roots have a minimal impact on the internal friction angle of soils. The results of single root tensile experiment indicate that the tensile strengths of root decrease with the increase of root diameter, while the tensile forces increase with it. Two models of the root and soil interaction were proposed based on the assumptions of roots rigid state and flexible state, which represent the increased maximum and minimum shear strengths, respectively. The calculated value of increased maximum and minimum shear strengths compared with the experimental results proved that the measured increased shear strengths were within the theoretical calculation range, which could provide a theoretical calculation method for evaluating the effects of desert plant roots on riverbank soil shear strength.

Shear strength of an unsaturated loam soil as affected by vetiver and polyacrylamide

Shear strength is an important soil mechanical property that its improvement is one of the rehabilitation program for the reduction of soil erosion and degradation. The objective of this study was to investigate the effect of polyacrylamide (PAM) and the vetiver system as a cheap and long-term bioengineering method and their combination on unsaturated shear strength parameters (effective cohesion, c' (kPa), angle of effective internal friction, φ' (°) and angle of internal friction related to matric suction, φb (°)) of a loam soil. The experimental treatments included vetiver plant (VP0), two concentrations of PAM dissolved in water [0.2% (V0P2) and 0.4% (V0P4)], and simultaneous presence of vetiver and two concentrations of PAM (VP2 and VP4). Direct shear tests were performed at combinations of three normal stresses of 25, 50 and 100 kPa and four matric suctions of 0, 10, 30 and 50 kPa (12 tests per each treatment) to determine the shear strength parameters. It was found that vetiver and PAM decreased apparent angle of internal friction (φ) and φ', and increased c', total cohesion (c), φb, and as a result increased unsaturated shear strength. However, the positive effect of vetiver on shear strength was greater than that of PAM. It seems that PAM and vetiver enhanced the contact area, inter-particles bonds, aggregation, and inter-aggregate porosity, and as a consequence, increased the soil effective saturation, effective stress, cohesion and shear strength. Also, when matric suction increased the c and shear strength increased although the φ increased slightly. Simultaneous application of vetiver and 0.4% of PAM resulted in maximum shear strength, indicated although vetiver can increase the cohesive strength, it would be more pronounced when PAM was simultaneously applied. Simultaneous application of vetiver and PAM through increasing soil shear strength can be suggested as the rehabilitation program to reduce soil erosion and degradation.

Biomechanical properties of plant root systems and their ability to stabilize slopes in geohazard-prone regions

Vegetation is widely used for reinforcing slopes, and thus controlling shallow landslides, because plant root systems can increase soil shear strength by anchoring soil layers and modifying hydrological characteristics. However, limited information is available regarding the vertical variation of soil reinforcement by roots at the slope scale, and how slope stability is influenced, especially in plantation areas. In this paper we examine the biomechanical effects on slope stability of the roots of Populus tomentosa, Robinia pseudoacacia and Olea europaea in a geohazard-prone region in China. Root density, variation in root area ratio (RAR) with depth, root tensile strength and root peak tensile force are measured, along with calculating the contribution of root cohesion to the factor of safety. The Wu-Waldron model and fiber bundle model are used to estimate static stress and dynamic stress adherence of plant roots to soil during debris flows and landslides, and a two-dimensional finite element model is used to calculate the increase in the factor of safety caused by additional root cohesion. The results show that RAR is higher for P. tomentosa than for R. pseudoacacia and O. europaea. The vertical soil profile of R. pseudoacacia roots has the highest soil water content (7.06%). The additional cohesion provided by R. pseudoacacia roots (10.35–15.12 kPa) is greater than that provided by P. tomentosa roots (6.19–10.26 kPa) and O. europaea roots (2.31–5.06 kPa). The stable area is also larger on a slope planted with R. pseudoacacia compared with the other two species. Young growth roots (8 years) are shown to affect the distribution of soil water and are limited by soil water in the semi-humid region. R. pseudoacacia roots provide significant additional cohesion by both static and dynamic stress for slope stability. This study aims to increase current understanding of the biomechanical properties of plantation species roots and their efficacy in soil reinforcement.

Modeling and measurements of triaxial tests for a sandy loam soil

The knowledge and understanding of soil mechanical properties is essential for designing agricultural machines. However, little information is available regarding shear properties of agricultural soil. In this study, triaxial compression tests were performed to measure shear properties of a sandy loam soil at three moisture levels: low (10.5±0.5%), medium (19±1.0%), and high (28±1.0%), and three confining pressures of 50, 100, and 150 kPa. A discrete element model was developed to simulate the triaxial compression tests. The test results showed a linear increase in soil shear strength at a decreased soil moisture level and an increased confining pressure. The effect of moisture level on the modulus of elasticity changed with the confining pressure. The highest modulus of elasticity was observed for the low moisture level with 150 kPa confining pressure. The model results showed that the particle friction coefficient was the most influential model micro-parameter to the simulated soil shear strength. This model micro-parameter was calibrated with the triaxial test data. The calibrated particle friction coefficients varied from 0.2 to 1.0, depending on the soil moisture content and confining pressure. As compared to the test data, the simulated soil shear strengths had relative errors ranging from 0 to 6%.

Effects of Root Architecture Characteristics on Soil Reinforcement in Undisturbed Soil

The effects of plant roots on the increase in soil shear strength involve a complex interaction of mechanical and hydrological processes operating over a scale of very diverse root architecture. Understanding the effects of mechanical mechanisms on soil shear strength is challenged by this inherent complexity. A high level of inaccuracy in field measurements of soil reinforcement makes field measurements much more challenging than that of indoor observations. This paper presents a simple experimental study where the shear strength of undisturbed soil is measured at different soil depths and at different distances from the main stems of 7 tree species, a bamboo, a herbaceous perennial, perennial grass and a fern by measuring their root area ratio, diameter class, and tensile strength. The result confirms that root distribution varies widely within root diameter classes and root area ratio between species and soil layers. Root architecture characteristics were the dominant factors influencing shear strength in the 0.2–0.4 m soil layer. In the process of vegetation restoration, O. compositus and H. fulva were used as colonizing vegetation. Later, S. lucida and L. kwangtungensis were recommended to stabilize the shallow soil in the Three Gorges reservoir region.

Scaling of the reinforcement of soil slopes by living plants in a geotechnical centrifuge

Understanding root-reinforcement of vegetated slopes is hindered by the cost and practicality of full scale tests to explore global behaviour at the slope scale, and the idealised nature of smaller-scale testing to date that has relied on model root analogues. In this study we investigated the potential to use living plant roots in small scale experiments of slope failure that would use a geotechnical centrifuge to achieve soil stress states comparable to those in the field at homologous points. Three species (Willow, Gorse and Festulolium grass), corresponding to distinct plant groups with different root architecture and ‘woodiness’ were selected and cultivated for short periods (2 months for Willow and Festulolium grass, 3 months for Gorse). The morphologies, tensile strength and Young’s modulus of these juvenile root samples and their effects on increasing soil shear strength were then measured (via tensile tests and direct shear tests) and compared with published results of more mature field grown specimens. Our test results show that when all juvenile root samples of the three species are considered, the commonly used negative power law does not fit the data for the relationship between root tensile strength and root diameter well, resulting in very low R2 values (R2<0.14). No significant differences in tensile strength were observed between roots with different diameter for Willow and Gorse, and the average root tensile strength for all juvenile root samples was 8.70±0.60MPa (Mean±SE), 9.50±0.40MPa, 21.67±1.29MPa for Willow, Festulolium grass and Gorse, respectively. However, a strong linear relationship was observed between tensile strength and Young’s modulus of the roots of the juvenile plants (R2=0.55, 0.69, 0.50 for Willow, Festulolium grass and Gorse, respectively). From a centrifuge modelling perspective, it was shown that using juvenile plants could potentially produce prototype root systems that are highly representative of corresponding mature root systems both in terms of root mechanical properties and root morphology when a suitable growing time (2 months) and scaling factor (N=15) are selected. However, it remains a challenge to simultaneously simulate the distribution of root biomass with depth of the corresponding mature plant. Therefore, a compromise has to made to resolve the conflicts between the scaling of rooting depth and root reinforcement, and it is suggested that 1:15 scale would represent a suitable compromise for studying slope failure in a geotechnical centrifuge.

Slope Stability Analysis Using the Unsaturated Stress Analysis. Case Study

Paper approaches the problem of considering the unsaturation of soils above water table in the slope stability analysis, condition for obtaining realistic results in both cases of rainfall infiltrating into the soil mass and drainage for improving soil stability. It presents in its first part a brief review methods related to unsaturated stress analysis applied for slope stability analysis, such as Unsaturated phi-b, Unsaturated Fredlund, Unsaturated Vanapalli, Unsaturated Khalili and Unsaturated Vilar model. These methods are estimating in different manners the shear strength depending on soil unsaturated conditions. These methods are applied in the second part of the paper in a case study, presenting a site affected by landslides located in Cluj-Napoca, Romania. For the slope stabilization a siphon drain system has been proposed and installed. An experimental program started and is ongoing on site, compromising site monitoring of suction using jet fill tensiometers and laboratory testing. Site measurement of suction in presence of drainage system was used for perform slope stability analysis using SVSlope software and the embedded methods for estimating the increase in soil shear strength when passing from saturated to unsaturated state.

Tree Water Uptake And Suction Distribution On Tropical Residual Soil Slope

This paper present an exploration of soil matric suction effected by water uptake via tree root at toe of slope on various condition between wet condition (high rainfall) and dry condition (prolonged no rainfall). Matric suction generated by active root tree has substantial influence soil moisture content on residual soil slope. A field monitoring was carried out to collect matric suction data at slope in two conditions; with a tree located at toe of slope and absent of a tree. The installations of instruments particularly at slope with tree at toe were placed within vicinity of the tree with certain depths and distances. The matric suction data from field monitoring was influence by the rainfall events that lead to the instability of soils slope. Analysis of soil matric suction distribution pattern indicates that the highest matric suction value was at shallower depth and proximity of tree. The matric suction profiles obtained from field monitoring are applied as an input data to develop soil matric suction contour. The effect of transpiration driven by active root zone generated matric suction on soil at vicinity of tree may create dry soil to increase soil shear strength.