Cohesive Soils Research Articles

Enzyme induced carbonate precipitation with fibers for the improvement of clay soil slopes against rainfall and surface runoff erosions

In order to improve the erosion resistance of the highway embankment slopes against rainfall and surface runoff erosions, the enzyme induced calcium carbonate precipitation (EICP) technology combined with different types of fibers, including steel, glass, and Polypropylene (PP) fibers, was studied for the treatment of the cohesive soil slope surface. The treatments were applied by a two-step method. In the first step, the treatment solutions were sprayed to the soil surface. In the second step, after the cracks were fully developed, quartz sand was filled into the cracks and another round of EICP spray treatment was applied in order to repair the cracks. Soil crack image analysis, crack repair test, rainfall and surface runoff erosion test, surface penetration resistance test, moisture content measurement, and soil microstructure analysis were carried out. The results show that the EICP technology can effectively cement the soil and improve the mechanical strength and erosion resistance of the cohesive soil slope. The average penetration resistance is about 10 times that of the untreated samples. The strength and erosion resistance of the fiber-added samples were further improved after EICP treatment with the addition of fibers. Both the glass fiber- and steel fiber-added samples exhibited excellent erosion resistance under rainfall and surface runoff erosion, with the amounts of eroded particles 35.78% and 1.89%, respectively, as compared with the sample treated with EICP only. The additions of fibers did not have any negative impact on the conversion efficiency of calcium. Meanwhile, the fibers could function together with calcium carbonate to form a net structure inside the soil so as to increase the strength and the durability, and reduce the water infiltration into soil. Therefore, the EICP treated samples with steel fibers and glass fibers have better treatment effects and are recommended for further applications.

Settlement of combined piled raft foundation of a nuclear power plant in non-liquefiable and liquefiable soils

The settlement analysis of a nuclear power plant (NPP) resting on the combined pile raft foundation (CPRF) under static and seismic loads is very important. However, it has not yet been reported in the literature as most NPPs are founded on raft foundation rather than on CPRF. In this paper, the settlement has been examined in detail. The geometrical nonlinearity at the interface of raft-soil and pile-soil is considered using the coulomb friction. The piles are rigidly connected to the raft. The nonlinear behaviour of the soil in the non-liquefiable soil is modelled using elasto-plastic Drucker Prager cap model and CycLiq model for the liquefiable soil. For this, user defined material (UDM) is implemented in the FLAC3D material library. Thus, a complete 3D finite difference model of an NPP considering raft-pile-soil-structure interaction (RPSSI) for nonlinear settlement analysis is developed. After successful validation of the present CPRF, numerical model with the literature, it has been used for further study under real earthquake acceleration–time history. Next, CPRF with NPP structure is studied under static loading, which is further extended for the nonlinear time domain settlement analysis. The effects of variation in various parameters i.e., spacing between piles, cohesion, friction angle, and Poisson's ratio of soil on the settlement, are examined and found to be significant. The dominant frequency of the earthquake significantly affects the response of the CPRF. It was inferred that the interface nonlinearity has greater significance in the liquefiable soil as compared to the non-liquefiable soil. Higher differential settlement in the liquefiable soil is attributed to the reduction in the stiffness of the soil. The findings of this study could be useful to frame the general guidelines for the economical design of NPP-CPRF systems.

Mechanical properties of a high plasticity clay mixed with sand and low-plastic silt

It is of fundamental importance in geotechnical engineering practice to have a comprehensive understanding of how the mechanical properties of widespread alluvial soils are affected with varying concentration of sand, silt, and clay particles. Moreover, among the available methods of chemical and mechanical stabilization of high plasticity cohesive soils, mixing this soil with sand and/or non-plastic silt still brings a cost-effective and environment friendly solution. In this study, clay-sand and clay-silt mixtures were prepared by adding sand and silt to the clay samples in different proportions to explore geotechnical properties of sand-clay and silt–clay mixtures and develop empirical correlations for Atterberg’s limits, compaction properties, unconfined compression strength, and consolidation characteristics for these soil mixtures. It was observed that for additive contents of up to 50%, the liquid limit and plasticity index of high plasticity clay sample decreased by 36% and 55% (with silt) and 47% and 58% (with sand), respectively. The reduction in undrained shear strength determined from unconfined compressive strength tests was about 37% with silt and 59% with sand contents. The compression index decreased by almost 13% with silt and 39% with sand. Likewise, it was also observed that the coefficient of consolidation increased with addition of silt and sand by 57% and 87%, respectively. As the increase in silt and sand content transformed the soil into a compact mass which ultimately should lead to a decreased total settlement as well as the rate of settlement of such soils. The statistical models proposed in this study have high coefficient of determination which depicts the reliability of these models in predicting the mechanical properties of sand-silt–clay mixtures.

Failure Mechanism and Bearing Capacity of Rigid Footings Placed on Top of Cohesive Soil Slopes in Spatially Random Soil

Failure Mechanism and Bearing Capacity of Rigid Footings Placed on Top of Cohesive Soil Slopes in Spatially Random Soil

Discrete Element Method Simulation and Field Evaluation of a Vibrating Root-Tuber Shovel in Cohesive and Frictional Soils

Soil-cutting forces are key indicators of root-tuber harvesters and other soil-engaging tools’ performance. To improve operational efficiency, minimise soil disturbance, and reduce fuel consumption, the draught and vertical forces involved in root and tuber crop harvesting must be minimised. Two field experiments assessed the harvester’s performance at a depth of 200 mm, varying frequencies, and travel speeds on clay and sandy loam soils. Discrete element models (DEM) were developed and subsequently used to replicate the field experiments and evaluate S-shaped and fork-shaped shovels. Linear regression and ANOVA (p < 0.05) were used to analyse the data. Draught force concurrently increased with speed in both soil textures but decreased with vibration frequency. The draught force decreased by approximately 41% in clay soil and 21% in sandy loam soil when the harvester was operated between 5 Hz and 14.5 Hz and between 10 Hz and 12.5 Hz, respectively. DEM simulations had relative errors of 4% (clay) and 4.7% (sandy loam) for draught force and drawbar power compared to experimental data. The S-shaped shovel was more efficient at crushing and translocating soil–crop mass to the rear of the harvester than the fork-shaped shovel. These DEM soil–crop models are reliable for evaluating other root-tuber harvesting tools.

Metamodel-assisted meta-heuristic design optimization of reinforced concrete frame structures considering soil-structure interaction

It is well known that conventional heuristic optimization is the most common approach to deal with structural optimization problems. However, metamodel-assisted optimization has become a valuable strategy for decreasing computational consumption. This paper applies conventional heuristic and Kriging-based meta-heuristic optimization to minimize the CO2 emissions of spatial reinforced concrete frame structures, considering an aspect usually ignored during modeling, such as the soil-structure interaction (SSI). Due to the particularities of the formulated problem, there are better strategies than simple Kriging-based optimization to solve it. Thus, a meta-heuristic strategy is proposed using a Kriging-based two-phase methodology and a local search algorithm. Three different models of structures are used in the study. Results show that including the SSI leads to different design results than those obtained using classical supports. The foundations, usually ignored in this type of research, also prove significant within the structural assembly. Additionally, using an appropriate coefficient of penalization, the meta-heuristic approach can find (on average) results up to 98.24% accuracy for cohesive soils and 98.10% for frictional ones compared with the results of the heuristic optimization, achieving computational savings of about 90%. Therefore, considering aspects such as the SSI, the proposed metamodeling strategy allows for dealing with high-complexity structural optimization problems.

Influence of different infill materials on the performance of geocell-reinforced cohesive soil beds

This paper presents a comprehensive study on the numerical and parametric study of geocell-reinforced cohesive soil beds, focusing on different infill materials. The numerical calculations were validated against model test results using FLAC3D software. Subsequently, the verified model was expanded to the geocell-reinforced cohesive soil beds. Six cases were simulated to investigate the reinforced performance, including pressure-settlement responses, bearing capacity improvement factor, settlement reduction percentage, and surface deformation. The numerical findings emphasize that the significance of superior geocell reinforcement should not overshadow the consideration of soil infill’s mechanical properties. In the case of cohesive soil as the infill material, the poor improvement in geocell-reinforced performance may be attributed to its low modulus and cohesion. Parametric studies suggest that geocells significantly impact reinforced performance when the infill material consists of foundation soil with a higher modulus and lower cohesion. Further, according to this numerical study, cohesionless soil with a modulus of 20 MPa and friction of 40° is the optimum infill soil in pockets to reinforce cohesive soil beds.

Theoretical investigation of the displacement ductility capacity of scoured fixed-head piles in cohesive soil

Scouring causes the exposure of structure foundations, which may influence their seismic performance. In this study, we develop a theoretical model to investigate the influence of foundation exposure caused by scouring on the displacement ductility capacity of fixed-head piles. The proposed theoretical model is based on consideration of a long pile in cohesive soil. The analytical solutions of the displacement ductility capacity and system overstrength ratio of scoured piles in linear soil are derived. The ultimate state of the pile is set as the state in which the pile-head moment reaches its ultimate capacity or when in-ground plastic hinging begins to occur. The proposed solutions are validated through numerical pushover analyses. A pile with a large scour depth is prone to in-ground plastic hinging. If no in-ground plastic hinging occurs, the displacement ductility capacity increases until an upper limit as the scour depth increases; however, the displacement ductility capacity decreases with increasing scour depth when in-ground plastic hinging occurs. The proposed model for linear soil provides a lower-bound estimate of the displacement ductility capacity. Soil nonlinearity can increase a pile’s ductility; however, this effect becomes negligible for large scour depths. The solutions for linear soil are modified for nonlinear soil by using an equivalent linear soil model.

Synergistic Improvement Earthen Mortars with Tung Oil, Sticky Rice Pulp, and Aerial Lime: Application for the Conservation of Rammed Earth Structures Damaged by Exfoliation

ABSTRACT Earthen sites are mainly made of earth and are widely located in the moist regions of south-eastern China; however, they suffer from serious damage. Sticky rice-lime mortar, one of the most important technological inventions in the ancient Chinese architectural history, are insufficient for earthen site conservation under adverse humid conditions. In this study, tung oil was used in conjunction with sticky rice pulp and aerial lime composites to evaluate the feasibility of protecting earthen sites damaged by exfoliation in moist environments. Several important experiments were conducted on a test soil as a substitute for the scarce site earth. The cohesion of the test soil with addition of tung oil (T), sticky rice pulp (R), and aerial lime (L) after 180 d was 16 times that of the untreated soil. The addition of these three materials to lean clay formed a double structure of aggregates, as determined by mercury intrusion porosimetry (MIP). The unique relationship depicting the hydraulic conductivity between TRL-treated soil and clay was uniform. Using SEM/EDS, and XRD analysis, the synergistic mechanism was primarily achieved through a TRL triangular interrelation, in which tung oil is indispensable for lean clay improvement. This study provided an effective technique for restoring deteriorated rammed earth remains made of lean clay. Two in situ pilot applications of rammed earth technology were performed on anomalous parts by multi-layer compaction to restore earth remains with potential exfoliation risk. This earth-based mortar was proved to be temporarily effective within one year of conservation.

Study on Shear Behavior and Mechanism Based on Shear Functional Unit of Loess Microstructure

The structural specificity and hydrological sensitivity of loess have a strong impact on its long-term stability and safety. This topic is being actively researched and focuses on the macromechanical behavior of the shear strength of loess disturbed and its micromechanisms from the perspective of the dry–wet cycle (especially involving soluble salt erosion). In this paper, the correlation between micro-structural shear functional units and macroscopic degradation behavior was established by combining the changes in physicochemical properties of mass loss, surface cracking, strength deterioration, and structural disturbance of the loess with scanning electron microscopy (SEM) microscopic images in different dry–wet cycles and different salt contents. Results revealed that with the increase in dry–wet cycles and salt content, the mass loss of soil deteriorated and the surface crack rate increased. The cohesion of soil showed an overall decreasing trend, which decreased more obviously in the early stage of the dry–wet cycle, followed by a slow decrease, and tended to be constant after nine dry–wet cycles. However, the internal friction angle increased and then decreased during the whole cycle, and its value generally changed little. According to the deterioration and decay of shear strength, it can be concluded that the structural disturbance of loess increased with the increase in dry–wet cycles and salt content. At the same time, further linear quantization fitting of the structural disturbance parameters showed that the structural parameters had a positive correlation with salt content and a power function with dry–wet cycles, where dry–wet cycles seemed to play a dominant role in the loess structural deterioration rather than salt content. The microscopic study demonstrates that the dry–wet cycles and salt content do not directly affect the cohesion and internal friction angle of soil but change the basic shear structural unit of aggregate and then cause an essential impact on c and φ, which in turn have an essential impact on soil strength attenuation. This paper not only helps to elucidate the essence of water–soil–salt structural interactions but also provides theoretical references for sustainable development research in environmental engineering, geological engineering, and other related fields.

A study on soil conditioning for cohesive soils with high content of clay minerals: Microscopic simulation and laboratory experiment

An earth pressure balance shield machine (EPB) is prone to blockage when tunneling in strata with high clay mineral content. Engineers often improve soil fluidity and reduce soil adhesion through soil conditioning to ensure the safe and efficient tunneling of shields. This paper selected montmorillonite, kaolinite, and illite as research objects and used molecular dynamics simulation and laboratory experiments. The interfacial mechanical behavior between anionic surfactant (sodium dodecyl benzene sulfonate, SDBS) solution and clay minerals was simulated at the microscopic scale and the improvement mechanism of SDBS solution on clay minerals was revealed. Then, the zeta potential of clay minerals and the stirring torque of the soil under different foam injection ratios (FIR) were tested. Accordingly, the conditioning effect of the SDBS solution at the macroscopic scale can be evaluated. The results show that the electrostatic adsorption and repulsion of ions occur on the surface of clay minerals, which makes it difficult for clay particles to aggregate into clusters. The SO3H- groups of the SDBS surfactant are the key factor to change the hydrophilicity of clay minerals. When different soil samples are improved to the same state, montmorillonite requires the largest FIR due to its microstructure.

Stabilizing cohesive soils with Micro- and Nano- fly ash as Eco-friendly Materials: An experimental study

Soil stabilization is a popular technique for improving soil properties and creating sustainable and green buildings using rammed earth walls. Nano materials are a new type of additive that can enhance soil performance. Laboratory tests were performed to examine the geotechnical properties of clay mixed with nano fly ash. Scanning electron microscopy (SEM), X-ray fluorescence (XRF), and X-ray powder diffraction (XRD) were used to analyze the nature and changes of the particles before and after the grinding process. The effect of time and different dosages of nano fly ash (3%, 5%, and 7%) on the curing behavior was also investigated. The test results showed that the optimal amount of nano fly ash and fly ash added to soil was 7% by weight of soil after 28 days. This increased the unconfined compression strength of clay from 50 kPa to 410 kPa (8.2 times) and the triaxial strength of clay from 65, 80, and 90 kPa to 520, 640, and 720 kPa (8 times) respectively. The results showed that nano-fly ash as a nano soil-improvement suspension significantly improved the strength and stiffness of the soil-fly ash mixture by forming gel that filled the pores and bonded the soil particles. Nano-fly ash also acted as a nucleation site, enhancing the durability and strength of the mixture.

Stability analysis of riverbanks with a dual structure under water-root-soil coupling.

The collapse mechanism of dual-structure vegetation riverbanks at different water levels is unclear. A method for calculating the critical collapse width of a dual-structure vegetation bank under different failure modes that consider the variations in river and groundwater levels and the influence of vegetation roots is proposed. Combined with the influence of flow lateral erosion and slope toe accumulation, a calculation model of riverbank stability was established. The results show that shear failure is the main failure mode when the cohesive soil layer on a dual-structure bank is thick, and the critical collapse width of the bank with root soil is higher than that of the soil bank. The critical collapse width of the bank varied with the water level during different water level periods. Compared with a soil riverbank, a rooted soil riverbank can significantly prolong the bank collapse time. The collapse width of a soil bank without vegetation roots is smaller than that of a rooted soil bank, and the cumulative collapse width is related to calculation time. The greater the thickness of rooted soil, the slower the decay rate of bank stability under water flow erosion.

First order reliability-based design optimization of 3D pile-reinforced slopes with Pareto optimality

As verified structures for landslide mitigation, stabilizing piles are often adopted to treat local failure zones of width-limited soil slopes. To achieve a balance between slope safety and construction cost, an optimized piling scheme for treating width-limited soil slopes should be obtained through three-dimension (3D) stability analysis. In this regard, this paper presents a novel calculation framework for the multi-objective optimization (MOO) design of stabilizing piles. It is based on the first-order reliability method (FORM) and considers a 3D width-limited slope failure with geological uncertainties. The study first develops a deterministic 3D stability model of pile-reinforced slopes using limit analysis. Accounting for soil shear strength uncertainties, reliability analyses of 3D reinforced slopes are conducted based on the prescribed pile-reinforcement patterns. Then, a multi-objective probabilistic design procedure combining the Pareto front and reliability analysis results is proposed. The effectiveness and significance of the proposed MOO design framework are demonstrated through two illustrative examples: one involves designing stabilizing piles in a homogenous slope, and the other involves designing for an inhomogeneous earth slope with depth-dependent soil cohesion. To gain better understanding of the probabilistic impact of uncertain pile design parameters on reinforced slope stability, comprehensive parametric studies are conducted.

Impact of Rock Fragment Shapes and Soil Cohesion on Runoff Generation and Sediment Yield of Steep Cut Slopes under Heavy Rainfall Conditions

The erodibility and erosion resistance of Quaternary sediments play a pivotal role in both the hydrologic and erosion processes of soil cut slopes. To investigate the runoff and sediment yield of soil cut slopes along the Pai-Mo road, we performed indoor simulated rainfall experiments under a 50° steep slope and high rainfall intensity (120 mm/h), based on the area’s climatic characteristics and Quaternary sediment properties. The experiments included various rock fragment contents (30%, 40%, and 50%), different levels of rock fragment roundness (i.e., rounded gravel, angular gravel), and varying soil cohesion. The results indicated that the average infiltration rate of the uncemented rounded gravel soil slope (URGSS) was higher than that of the uncemented angular gravel soil slope (UAGSS), resulting in less runoff and a delayed initial runoff time. The runoff shear stress, runoff power, drag coefficient, and Reynolds number of the URGSS were smaller than those of the UAGSS. In contrast, the Froude number and flow velocity of the URGSS were larger, resulting in a stronger runoff erosion capacity. The sediment yield of the URGSS was approximately two times that of the UAGSS, and the cumulative sediment yield was about 20% higher. The cemented angular gravel soil slope (CAGSS) had a larger runoff rate, runoff shear stress, runoff power, and flow velocity than those of the UAGSS, leading to less sediment yield. Overall, a more rounded shape and a larger radius of curvature of the spherical particles resulted in stronger erosion, due to local turbulence. Therefore, the rill density and cumulative sediment yield of the steep alluvial cut slope were greater than that of the steep colluvial cut slope under heavy rainfall. Moreover, due to its strong cohesion, only raindrop splash erosion and inter-rill erosion occurred on the steep moraine cut slopes under heavy rainfall.

ANTHROPOGENIC TRANSFORMATION OF THE LYUTITSA RIVER BASIN

The Liutytsia is a typical small river of the Polissya part of the Volyn region. It flows through the territory of Rozhyshche and Kopachivka united territorial communities. The river is 37 km long, with a catchment area of 208 km2, 3.6% forest cover, 1.4% marshland, and 60.5% ploughed. About 10,000 people live within the basin. The territory has long been developed. Agricultural use predominates. Specialisation: growing potatoes, cereals, industrial crops, dairy and meat farming and processing of agricultural products. In the structure of land use in the basin, 87.6% of the land is used for agricultural purposes. All land available for agricultural use has been ploughed and is actively used. Within the basin, the permissible land use limits are exceeded. This contributes to the aggravation of the environmental situation and requires the implementation of measures for the rational use of natural resources and nature protection. 8.8% of the basin's territory is occupied by settlements, industrial, transport, communications, etc. The basin's water resources are also actively used. Most of the water is used for water supply to the population, industry and agriculture. In a year of 95% runoff availability, total water withdrawals exceed 20% of the annual runoff, and irreversible water consumption in the basin is 15%. In the future, runoff shortages may become a problem in low-water years. The frequency of dry years has been increasing recently. The concentration of most chemicals in the river water does not exceed the maximum permissible concentration. The content of ammonium nitrogen exceeds the per capita values by 15.6 times in the first and 2.92 times in the river channel 2, nitrite nitrogen by 1.7 times and 1.91 times, respectively, and total iron by 16 times and 2.4 times. The excessive content of nitrogen compounds is caused by surface runoff from urban areas, fields, farms, and spontaneous solid waste dumps. The area of drained land within the basin is 8,606 thousand hectares, with a land reclamation rate of 41.4%. There are 5 drainage systems within the basin. Soil overdrainage is widespread within the basin's drainage systems, leading to loss of soil cohesion, loss of vegetation cover and deflation. With distance from the drainage network, water drainage is worse, there are waterlogged areas, rewetting occurs due to inefficient drainage channels that are silted and overgrown with vegetation. Some reclaimed areas have not been ploughed for many years and are overgrown with selfseeding. Hazardous exogenous processes are occurring within the basin: karst, secondary waterlogging, and siltation of the riverbed. Soils are also undergoing negative changes. Erosion processes are occurring, the depth of the humus horizon is decreasing, and the content of humus and plant nutrients is decreasing. Environmental problems in the basin include: violation of water protection zones, ploughing and rewetting of the floodplain; lack of hydroecological monitoring in the river basin; poor condition of drainage systems; lack of soilprotective technologies for growing crops, violation of recommendations for the use of drained land; illegal landfills in the basin; low forest cover, lack of protected areas within the basin, lack of an effective local ecological network.
 Keywords: river basin, geoecological state of the basin, sources of anthropogenic impact within the basin, anthropogenic transformation of the basin.

Effects of straw incorporation on soil erosion resistance along a land degradation gradient in the black soil region of China

Soil erosion resistance (reflected by rill erodibility and critical shear stress) is a useful parameter for evaluating soil erosion subjected to concentrated flow. The changes in soil properties and root trait induced by straw incorporation and land degradation likely affect soil erosion resistance considerably. Nevertheless, few studies have been conducted to quantify the effects of straw incorporation on soil erosion resistance of degraded croplands in the black soil region. In this study, a large hydraulic flume (5.0 m in length and 0.4 m in width) was utilized to quantify the impacts of straw incorporation on soil erosion resistance of four croplands with different degradation degrees (non-degradation, light degradation, moderate degradation and strong degradation) and further to determine the related influencing mechanisms in Northeast China. The results showed that straw incorporation reduced rill erodibility by 44.9%, 41.2%, 27.1% and −11.4% for non-degradation, light degradation, moderate degradation and strong degradation croplands, respectively. Land degradation degree had much stronger influence on soil erosion resistance than that of straw incorporation and regulated the roles of straw incorporation in mitigating erosion. Rill erodibility was significantly and negatively correlated with clay content, organic matter content, aggregate stability, soil cohesion, physical crust thickness and root mass density, whereas positively correlated with silt content. The increase in soil organic matter and clay content was the key to improve soil erosion resistance and prevent land degradation. Straw incorporation was suggested in non-degradation, light degradation and moderate degradation croplands, but vegetation restoration was recommended in strong degraded cropland. The results are helpful to understand the mechanism of straw incorporation to improve soil erosion resistance and make reasonable agricultural management strategies in semi humid region.

A hybrid estimation procedure for modeling shallow foundation’s settlement: RBF-optimized neural network

The complexity of the cohesive soil structure necessitates settlement modeling beneath shallow foundations. The goal of this research is to use recently discovered machine learning techniques called the hybridized radial basis function neural network (RBFNN) with sine cosine algorithm (SCA) and firefly algorithm (FFA) to detect settlement (Sm) of shallow foundations. The purpose of using optimization methods was to find the optimal value for the primary attributes of the model under investigation. With R2 values of at least 0.9422 for the learning series and 0.9271 for the assessment series, both the produced SCA - RBFNN and FFA - RBFNN correctly replicated the Sm, which indicates a considerable degree of efficacy and even a reasonable match between reported and modeled Sm. In comparison to FFA - RBFNN and ANFIS - PSO, the SCA - RBFNN is believed to be the more correct method, with the values of R2, RMSE and MAE was 0.9422, 7.2255 mm and 5.1257 mm, which is superior than ANFIS - PSO and FFA - RBFNN. The SCA - RBFNN could surpass FFA one by 25% for the learning component and 14.2% for the test data, according to the values of PI index. Ultimately, it is apparent that the RBFNN combined with SCA could score higher than the FFA and even the ANFIS - PSO, which is the proposed system in the Sm forecasting model, after assessing the reliability and considering the assumptions.

Quantifying root-induced soil strength, measured as soil penetration resistance, from different crop plants and soil types

A common soil mechanical property for assessing soil strength is soil penetration resistance (PR) or soil cone index (CI), which is related to the undrained shear strength of saturated and cohesive soil. Plant roots can increase soil strength, but physical conditions may confound this. Pot experiments were conducted using 70 cm soil columns, three soil types (beach sand, erosion-prone soil, and two typical arable soils), and four crop plants (maize, sorghum, Napier, and vetiver grass). We tested the hypothesis that plant roots impact soil strength, measured as soil PR, and the induced soil strength differs based on plant species. The CI and root system architecture (RSA) traits were measured. Napier grass grown in arable soils recorded higher total biomass. Together with maize, Napier grass had a more significant root length density, particularly at 25–40 cm depth. The CI increased with increasing depth, with a 57–99% increase in CI in the bottom layer compared to the top layer of the soil column. The overall CI of soils grown to Napier grass (2.0 and 2.3 MPa) and maize (1.7 and 2.2 MPa) were similar, but both were higher than the soils cultivated with the other crop plants and unplanted control. The overall CI of the SEA sand of ∼2.0 MPa was 36%, higher than that for the arable soils. Soil moisture content did not significantly increase CI, but the interaction of soil bulk density and root system traits could be implicated in increased CI of root-permeated soils. It is concluded that (i) roots growing in arable soils can increase CI and hence soil strength, possibly due to the binding effect of root systems, even when the transpiration effect of plants on soil moisture is low; (ii) crop plants contribute differently to soil strength, and (iii) Napier grass could offer a rapid growth and establishment option when considering plants for soil reinforcement and stability.

Response of Sandy and Clayey Soils to Weak And Strong Seismic Loading

The response of sandy and clayey near-surface soils representing the classes of noncohesive and cohesive soils to seismic loading of various intensities is analyzed from the in situ data —from the records by vertical groups of the Japanese nationwide KiK-net strong motion seismograph network. For the analysis, out of a total of ~800 stations, we selected five stations with near-surface sandy soils and five stations with near-surface clayey soils, most purely represented in the upper layers. Using the method (Pavlenko and Irikura, 2003), we have constructed and analyzed the models of strong ground motion behavior for “sandy” and “clayey” stations, showing the distributions of earthquake-induced stresses and strains in the soil layers. Close estimates of the amplification of seismic waves in sands and clays at weak seismic ground motion and close stress-strain relationships characterizing the behavior of the near-surface soils at moderate seismic ground motion are obtained. The liquefaction of sandy soils under strong shaking (the 2011 Tohoku earthquake with Мw ~ 9.0) is analyzed. The effects of the extended seismic sources (directivity of their radiation pattern) on the behavior of sandy and clayey soils and the amplification of seismic waves in these soils is studied. Differences in the behavior of sandy and clayey soils are noted only at strong seismic motions: liquefaction in sandy soils is possible if the groundwater level is on the order of a few meters from the surface, while in clayey soils there is no liquefaction.