Undisturbed Samples Research Articles

Soil hydraulic properties and pore dynamics under different tillage and irrigated crop sequences

Soil hydraulic properties and pore continuity are important parameters of soil quality and may differ among tillage systems, crop rotations, and change over time. However, there are some contrasting results, depending on soil type, climate and cultivation history on the spatial and temporal variations. The objective of this study was to determine spatio-temporal dynamics of soil hydraulic properties and pore characteristics (i.e., pore volume, effective porosity, and continuity) on a silt loam long-term tillage field experiment, in Agramunt, NE Spain, during two cropping years. Undisturbed soil samples were used to determine soil water retention, θ(Ψ), and soil hydraulic conductivity, K(Ψ), curves in two different tillage systems (intensive tillage, IT vs no-tillage, NT), two crop sequences (short fallow-maize, FM vs legume-maize, LM) and two positions (within the row of crops, W-row vs between the rows of crops, B-row). The results revealed that LM had greater specific hydraulic conductivity, Kpc in its macroporosity (>1000 µm) than FM due to greater number of effective pores, Npc and effective porosity, εpc. Soil water content, θ was greater under IT than under NT at higher soil water matric potential, Ψ (≥-3 cm H2O), whilst the opposite was observed at lower Ψ (≤ − 50 cm H2O). Long-term NT showed greater hydraulic conductivity, K at higher Ψ (≥ − 10 cm H2O) than IT, and no difference at lower Ψ. Although IT had greater pore volume, ϕpc than NT in the macroporosity and coarse mesoporosity (1000–60 µm) pore size classes, NT had two times greater Kpc than IT due to increased Npc, εpc, and pore continuity, Cwpc. K(Ψ) and pore characteristics showed spatial variations (W-row vs B-row). W-row had significantly greater K at higher Ψ (≥ − 3 cm H2O) than B-row. Temporal dynamics of soil hydraulic properties and pore characteristics were not evident under IT during crop succession. This study shows that LM increases specific hydraulic conductivity of soil macroporosity by increasing the number of effective macropores and the effective porosity. In a Mediterranean climate, this may improve the hydrological functions of agricultural soil and associated crop yield. Further, long-term NT formed a stable number of effective macropores and coarse mesopores, and showed a greater pore continuity in coarse and fine mesopores, resulting in improved soil water flux.

Calibration of the capacitance probe for soil moisture monitoring

To obtain efficient use of water applied in irrigation, it is necessary to understand the dynamics of water in the soil, which is an important factor in agriculture. The aim of this study was to determine models for calibration and to evaluate thelysimetry methodwith undisturbed samples,using a capacitance probe for monitoring the moisture content of a TypicHapluderts soil under laboratory conditions. The predominant soil in the study area is from the TypicHapluderts soil unit. The soil samples were collected with undisturbed samples, in layers of 0 - 10 cm and 10 - 20 cm depth from the surface, using PVC pipes with a diameter of 315 mm and 600 mm height. The determination of the variation in soil moisture was carried out by weight difference (weighing lysimetry method). The measurements with a Frequency Domain Reflectometry (FDR) were made on a daily frequency and 6 repetitions per measurement. Analyzed calibration models (linear, potential and quadratic), was performed the Shapiro-Wilk normality test. The methodology used provided satisfactory results, with multiple repetitions being performed on the same sample. The model that showed greater precision and better fit for the two profiles under study was the quadratic model.

Engineering Properties Investigation of Soft Clay as Potential Subgrade Material

Highway pavement design using soft clay soil as a subgrade is always a great challenge and can cause problems such as roadbed instability and soil settlement. To overcome this problem, the knowledge of the subgrade soil characteristic should be studied first because it needs to be considered during the design phase of pavement. This study was conducted to investigate the engineering properties of soft clay that can be used as potential subgrade material. Some soil laboratory tests were performed to establish the engineering properties of the soft clay. From the standard proctor compaction test, the results revealed that the maximum dry density and optimum moisture content are 1.58 Mg/m³ and 20.15 %, respectively. The finding from the soil-water characteristic curve (SWCC) test indicates that the SWCC did not present a residual suction. The compression modulus and pre-consolidation pressure obtained from the compacted soil sample for the consolidation test are higher than the undisturbed soil sample. Based on triaxial test results, the effective cohesion acquired from the compacted soil sample is greater than the undisturbed sample. This research provides a reference for the study of soft clay engineering characteristics.

Post-cyclic Loading Relationship Effects to the Shear Stress and Cyclic Shear Strain of Peat Soil

Peats originate from plants and denote the various stages in the humification process. This condition renders the peat extremely soft and can be considered problematic soil. Thus, this study is conducted to examine and comprehend the particularities of peat engineering behaviour in respect to the relationship effects to the shear stress and cyclic shear strain of peat soil various characteristics to establish suitable correlation. This study carried out by using triaxial testing described by geotechnical test standards BS-1377: Part 8: 1990. Methods of Testing Soils for Civil Engineering Purposes: Shear Strength Tests (Effective Stress) that required for consolidated undrained and consist of five main stages: saturation, consolidation, static, dynamic, and post-cyclic loading using the GDS Enterprise Level Dynamic Triaxial Testing System (ELDYN). The parameters of shear strength were obtained in the peak deviator stress at a maximum of 20% of axial strain by using an undisturbed sample with an effective pressure imposed of 25, 50, and 100 kPa. In this study, all specimens are subjected to cyclic loading up to 100 cycles based on a one-way loading system with strain-controlled conditions. Based on the analysis conveyed, the post-cyclic shear stress decreased compared to its initial value of about 65.56 kPa (PNpt-100 kPa) in static and decreased to 14.9616 kPa in post-cyclic (PNpt-25 kPa-1 Hz). The principal stress ratio (σ'1/σ'3) shows the maximum values of this ratio that are located in the narrow zone of 1.61 to 1.12. Doi: 10.28991/CEJ-2022-08-12-08 Full Text: PDF

Soil Physical Characteristics in Landslide-Affected Areas in Battang and Battang West Sub-District, Palopo City, Indonesia

Battang and West Battang sub-districts are buffer areas for Palopo City with protected forest areas, biodiversity, and drinking water sources for the people of Palopo City. They are also a link between Palopo City and Toraja Land. This potential requires special attention because landslides often occur and are affected by flooding in urban areas. The occurrence of landslides is influenced by several factors, one of which is the conversion of forest land and the physical condition of the soil. This study aimed to determine the soil's physical characteristics at several landslide points in Battang and West Battang Villages, Palopo City. The method used is a field survey to take disturbed and undisturbed soil samples and then analyze soil characteristics such as soil texture, permeability, porosity and organic matter in the laboratory. The results of this study obtained soil textures, namely dusty clay loam, dusty clay, clay and clayey loam, soil permeability of slow to moderate (0.65-2.90 cm/hour), soil plasticity properties ranging (from slightly plastic to very plastic) with low C-organic content to moderate (0.50-1.66%).

Soil Characteristics of Padma Multipurpose Bridge

Padma Multipurpose Bridge is situated on a section of the Padma river where the soil condition is highly heterogeneous and intermixed with different soil layers, for which pile design was the critical part. This paper describes the soil properties and ground profiling of the Padma Multipurpose Bridge. Different types of field and laboratory tests were carried out to obtain accurate soil parameters and ground profiles along the whole alignment of the bridge. Standard Penetration Tests, Cone Penetration Tests, and grain size analyses were conducted for the soil classifications and ground profiling. Flat Plate Dilatometer Tests, High Pressure Dilatometer Tests, and Self-Boring Internal Friction Tests were performed to obtain the stiffness of the different soil layers and shear strength parameters in field conditions. Cross-hole and Seismic Tomography Geophysical tests were executed to obtain seismic waves and dynamic shear modulus of each soil layer. Gel Push Soil Sampling technique was used to collect undisturbed samples of sandy soils to get accurate stress–strength-dilatancy characteristics of sandy soils through different laboratory tests. The soil was classified into three Units and some sub-units based on grain size and SPT-N value. Soil parameters were finalized based on both laboratory and field test results. The pile design was possible for accurate measurement of soil parameters and ground profiling along the alignment of the bridge.

Numerical Modeling for Prediction of Compression Index from Soil Index Properties in Jimma town, Ethiopia

In this study, correlations are developed to predict compression index (Cc) from index parameters so that one can be able to model Jimma soils with compression index using simple laboratory tests. Undisturbed and disturbed soil samples from twelve different locations in Jimma town were collected. Laboratory tests like specific gravity, grain size analysis, Atterberg limit, and one-dimensional consolidation test for a total of twenty-four test samples were conducted. From one-dimensional consolidation tests, compressibility soil parameters (Cc and Cs) are determined. From the results of limited tests, an indicative good correlation is observed between Cc and LL, PL, and PI. However, a Poor correlation is developed between Cc and PL when related to the other parameters. The developed correlations will be important inputs in modeling Jimma clay soils with regression model and Artificial neural networks (ANN) analysis using simple index tests. In addition, the results of this study can serve as a basis for further study of such correlations on different clay soils in the country. In this study, regression analysis was used to explore the significance of individual independent (index) soil properties. Regression model and correlation of compression index for liquid limit, plastic limit, and plasticity index were obtained from the linear regression analysis and ANN. This correlation will be helpful for geotechnical engineers in developing the coefficient of compression (Cc) value of expansive/clay soil from index properties. Finally, based on the general findings of the study, suitable recommendations have been forwarded.

Investigation of the Impact of Tropical Red Clay Soils' Mineralogical Composition on their Physical and Mechanical Properties– a Case Study Ruaka – Kenya

Introduction: Residual soils covering large areas of the earth have been chiefly discovered in the last 30 years in most volcanic tropical and subtropical countries. Understanding their behaviour is essential for various infrastructure developments. Methods: The physical and mechanical properties of the soils are affected by their mineralogical composition. There is a need to determine the mineralogical composition of the soils and investigate the impact on properties. This paper presents the results of a laboratory study conducted on red clay soil from Ruaka, a suburb in Kenya, to investigate the effect of mineral and chemical composition on the soil’s physical and mechanical properties. Disturbed and undisturbed samples were subjected to different tests such as Atterberg limits, soil classification, consolidation test, X-ray fluorescence, X-ray diffraction and petrology test based on the British Standard soil classification system (1377-1994). The soils were classified as clay with high plasticity, and high clay content varied between 59-79% resulting in mechanical instability of the soil in this site. Results: The mineral and chemical analysis indicated the formation of unique minerals like Halloysite, Quartz, Kaolinite, and Mica, which influenced the geotechnical properties of clay. The index properties of clay recorded high values; the moisture content and plastic limit varied between 37- 46% with a slight increase as depth increased; the liquid limit varied between 63-68% with increased depth. Conclusion: The average value of maximum dry density was reported as around 1247 kg/m3 with high optimum moisture content, reaching 35.5%. Besides that, the soil had a high void ratio of 1.145 to 1.63, which increased the permeability of the clay to 1.223E-5 cm/s. The properties of red clay soils in more than ten tropical regions in Kenya compared with the soil under study are also presented in this paper.

Cyclic simple shear behavior of a tropical alluvial soil

Tropical alluvial soil has distinctive physical characteristics when compared to common sedimentary soils. Ignoring such distinctive characteristics might lead to geotechnical problems that require a thorough re-investigation. Foundation failures have been identified along some river banks of tropical alluvial soil deposits in Sarawak, Malaysia, which were speculated to be due to cyclic loading effects. This paper presents preliminary results on tropical alluvial soil engineering behaviors from simple shear cyclic loading tests. Specimens measuring 50 mm in diameter and 16 mm in height were obtained from three undisturbed samples. They were sheared using an Electro-Mechanical Dynamic Cyclic Simple Shear (EMDCSS) for thirty cycles at three different target displacements. The results showed hysteresis loops, where the shear stress decreases as the cycle increases. Excess pore water pressures develop during shearing, which correspond to the target displacement levels. The damping ratio increases as the shear strain increases but decreases as the cycle increases. The normalized shear modulus decreases as both the shear strain and loading cycle increase. A comparison with previous literature on cohesive soils shows that the tropical alluvial soil has a lower damping ratio and normalized shear modulus, which range from 3.3% to 9% and 0.0004 to 0.01, respectively. The findings indicate that the tropical alluvial soil has a potential reduction in strength when subjected to continuous cyclic loading. The paper provides a better understanding for academics and engineering professionals before conducting design or remedial work in the tropical alluvial soil environment.

Geomechanical parameters in the active zone of an unsaturated tropical soil site via laboratory tests

The seasonal variability of geotechnical parameters in the unsaturated zone is typically neglected in the design of geotechnical works. In most of the geotechnical projects the parameters are determined only for the saturated condition. Although it is known that this condition is the most critical to soil strength and deformability, this conservative approach may neglect a possible important contribution of the unsaturated condition, resulting in an increase in the cost of the geotechnical solution. This paper presents and discusses the site characterization of the active zone of an unsaturated sandy soil profile under different suction conditions. Laboratory tests with controlled suction (retention curves, triaxial compression with bender elements and oedometer tests) were carried out on undisturbed samples collected from 1.0 to 5.0 m depth. The results show that strength and deformability parameters are strongly affected by soil suction and are less influenced by confinement stress up to 5.0 m depth. All the investigated subsoil profile shows a collapsible behavior, more pronounced closer to the ground surface and under the effect of higher suction values. The findings highlight the importance of incorporating the suction influence in the site investigation, parameter determination, and geotechnical design for more economical, reliable, and environmentally sustainable solutions.

Prevention of additional compaction in eucalyptus and pasture land uses, considering soil moisture and bulk density

Soil compaction is harmful to agricultural and forestry areas, and strategies to avoid soil deformation are of great interest. The objective of this study was to evaluate the compressibility of a soil submitted to different land uses in an area located in southern Brazil. The land uses assessed were a) Anthropized Forest: constituted by tree and shrub species; b) Pasture: five years old; c) Eucalyptus 20: twenty years old; and d) Eucalyptus 4.5: conducted in 2nd rotation, and 4.5 years old, with Eucalyptus harvesting in the first cut made manually with a chainsaw and wood extraction with a Forwarder. Undisturbed soil samples were taken in 2006, and they were submitted to the uniaxial compression test. Bulk density and volumetric moisture were calculated before the test, as well as soil deformation, compression index and precompression stress at the end of the test. Anthropized Forest and Pasture soils presented the highest volumetric soil moisture, a mean of, respectively, 0.301 and 0.304 m3 m−3. Eucalyptus 20 had the lowest bulk density (mean of 1.15 Mg m−3), and Eucalyptus 4.5 the highest bulk density (mean of 1.47 Mg m−3). Precompression stress is low for all soil land uses, ranging from 31.24 to 50.92 kPa, and care should be taken to avoid further compaction. Load-bearing capacity of the soil presented positive and negative relationship with, respectively, bulk density and volumetric moisture, but the low coefficient of correlation (r) and determination (r2) shows the need of further studies for a better adjustment of the data. From the knowledge of volumetric soil moisture, it is possible to monitor and define the most suitable soil condition for traffic of machinery and animals trampling into the areas to avoid additional compaction, while the load-bearing capacity of the soil can be estimated by bulk density, being useful to monitor the occurrence or not of additional compaction.

Determining the mechanism of the root effect on soil detachment under mixed modes of different plant species using flume simulation

Soil detachment is the separation and dislodgment of soil particles from a soil mass by the force of raindrops and flow, which is also the initial process of soil erosion. Plant roots have significant effects on the soil detachment rate (SDR). Current studies have mainly focused on root effects on the SDR under single species. Because it is difficult to identify the roots of different species in mixed-plant areas, few studies have evaluated the root effects on the SDR under mixed-plants. Natural, undisturbed soil samples containing roots were collected from four natural sampling plots with single plant types, and six natural sampling plots with mixed plant types. Bare soil was used as the control. The samples were subjected to flow scouring through indoor hydraulic flume experiments under six shear stresses (3.65, 7.28, 7.67, 8.59, 10.15, and 12.19 Pa). The results showed that the root reduction effect on the SDR under the mode of tap roots mixed with fibrous roots was 55.54 % weaker than that the mode of fibrous roots mixed with other fibrous roots. When fibrous roots were mixed with tap roots, the fibrous roots indirectly affected the SDR through soil mechanical properties, while the indirect path of the tap roots on the SDR was not unique. However, the indirect effect of roots on the SDR was weaker than the direct effect. The mixed roots affected the SDR mainly by rill erodibility, not critical shear stress. The variation in rill erodibility at the mixed root sites was similar to the SDR variation at those sites. The mode of grasses with fibrous roots mixed with other grasses with fibrous roots was considered as better for soil and water vegetation conservation.

Land degradation rating under different land use types

Soil degradation is a major challenge to agricultural production and often leads to low crop yield in most parts of the world. Hence, a field study was carried out in the University of Ibadan to assess soil physical and chemical properties, and their level of degradation under different land use types. Six land use types consisting of fallow land (FL), arable land (AL), Oil palm plantation (OP), Residential land (RL), paddock (P) and valley bottom (VB) were identified and examined in this study. Disturbed and undisturbed soil samples were obtained from 0-3cm depth and analyzed for their chemical and physical properties using standard procedures. Soil colloidal fractions (organic matter, clay and silt) were integrated to estimate the soil structural stability index (S), while soil degradation rating (SDR) was determined from selected soil physical (Particle size distribution, bulk density and saturated hydraulic conductivity) and chemical (pH, organic carbon, total nitrogen and available phosphorus) properties. Data were analyzed using descriptive statistics and analysis of variance at α0.05. The land use types were slightly acidic with pH range of 5.7 (FL) to 6.9 (RL). Soil organic carbon differed significantly and was in the order: RL (29.8 g kg-1) > VB (20.0 g kg-1) > P(19.1 g kg-1) > FL (12.3 g kg-1) > OP (11.9 g kg-1) > AL (10.7 g kg-1). Significant differences were recorded for soil bulk density among the land use types. The VB had the lowest value (1.43 Mg m-3), followed by FL (1.52 Mg m-3), OP (1.64 Mg m-3), P (1.66 Mg m-3), RL (1.71 Mg m-3), and highest in AL (1.83 Mg m-3). The S also differed significantly among the land use types and was highest under VB (32.4), while AL had the lowest (3.1). On the average, AL, FL, OP, P and RL appeared to be moderately degraded, while VB was slightly degraded. The soil degradation rating mirrored the adverse effect of agricultural land use types, especially arable land, paddock and oil palm plantation on soil quality. Thus, soil conservation measures such as the use of organic fertilizers and organic mulch should be put in place in order to rehabilitate these land use types.

Comparative Investigation on Small-Strain Stiffness Characteristics of Undisturbed and Compacted Highly Weathered Granites at Various Densities

To investigate the small-strain stiffness characteristics of highly weathered granite (HWG), a resonance column test system was used to conduct resonance column tests on highly weathered granite taken from the Lincang City, Yunnan Province, China. The effects of effective consolidation stress and structural changes is caused by remodeling process and initial dry density on the small-strain stiffness of HWG. Furthermore, the difference between the test data and other geotechnical materials were compared and analyzed. The test results show that the maximum dynamic shear modulus <math xmlns="http://www.w3.org/1998/Math/MathML" id="M1"> <mfenced open="(" close=")"> <mrow> <msub> <mrow> <mi>G</mi> </mrow> <mrow> <mi mathvariant="normal">max</mi> </mrow> </msub> </mrow> </mfenced> </math> of remodeled highly weathered granite samples is greater than that of undisturbed samples once the effective consolidation stress is smaller than 300 kPa, but the opposite result is observed once the effective consolidation stress exceeds 300 kPa, and the phenomenon was also explained from a microscopic perspective based on the scanning electron microscopy (SEM). The <math xmlns="http://www.w3.org/1998/Math/MathML" id="M2"> <msub> <mrow> <mi>G</mi> </mrow> <mrow> <mi mathvariant="normal">max</mi> </mrow> </msub> </math> of remodeled highly weathered granite gradually increases with the increase in dry density and effective consolidation stress. At an identical effective consolidation stress, the dynamic shear modulus ratio <math xmlns="http://www.w3.org/1998/Math/MathML" id="M3"> <mfenced open="(" close=")"> <mrow> <mi>G</mi> <mo>/</mo> <msub> <mrow> <mi>G</mi> </mrow> <mrow> <mi mathvariant="normal">max</mi> </mrow> </msub> </mrow> </mfenced> <mo>−</mo> <mi>γ</mi> </math> curves of remodeled highly weathered granites at different initial dry densities are nearly consistent. Additionally, according to the test data, the mathematical model of <math xmlns="http://www.w3.org/1998/Math/MathML" id="M4"> <msub> <mrow> <mi>G</mi> </mrow> <mrow> <mi mathvariant="normal">max</mi> </mrow> </msub> </math> for remodeled highly weathered granite considering effective consolidation pressure and initial dry density was established and agrees well with the test results of practical engineering cases. The range of variation in <math xmlns="http://www.w3.org/1998/Math/MathML" id="M5"> <mfenced open="(" close=")"> <mrow> <mi>G</mi> <mo>/</mo> <msub> <mrow> <mi>G</mi> </mrow> <mrow> <mi mathvariant="normal">max</mi> </mrow> </msub> </mrow> </mfenced> </math> was given by the research results, which were compared with the <math xmlns="http://www.w3.org/1998/Math/MathML" id="M6"> <mfenced open="(" close=")"> <mrow> <mi>G</mi> <mo>/</mo> <msub> <mrow> <mi>G</mi> </mrow> <mrow> <mi mathvariant="normal">max</mi> </mrow> </msub> </mrow> </mfenced> </math> of weathered granite obtained from the existing research, and the results in this work can provide a valuable reference for analyzing dynamic stability of buildings in the engineering construction of weathered granite sites.

Predictors of plant endemism in two west African forest hotspots

Centres of endemism have been much studied by biogeographers, ecologists, and evolutionary theorists, and are considered conservation priorities. It is therefore important to understand the ecological traits of restricted range taxa, and the landscape-scale drivers of high endemism. Here, we investigate correlates of floristic endemism within two of west Africa’s forest biodiversity hotspots at local scale. We assembled distribution data for 1,042 vascular plant taxa from 114 sample locations within forest reserves of south west Ghana, and for 1,735 vascular plant taxa from 454 sample locations within the Nimba Mountains (Liberia and Guinea). A quantitative index of global endemism called the Genetic Heat Index was modelled linearly. We tested the significance of modern climate, altitude and disturbance as factors predicting endemism rates in these two forest reserves. Annual rainfall was significantly and positively related to endemism rates in both south west Ghana and the Nimba Mountains. Altitude was a significant predictor of endemism rates in the Nimba Mountains, with a quadratic relationship highlighting particularly high endemism over 1,000 m. Local topography rather than altitude was a significant predictor or endemism in SW Ghana, where altitude varies less. Areas of high rainfall and high altitude are geographically restricted across the western African forests, acting as edaphic islands driving spatial isolation. Disturbed vegetation samples had lower endemism rates than undisturbed samples in both Nimba and SW Ghana, and overall pioneer species had wider areas of occupancy than shade-bearing species. Endemism rates increased slightly with each year following clearance. Disturbance thus creates and maintains vegetation types which support a lower proportion of globally rare species in the two biodiversity hotspots surveyed. From the point of view of the conservation of globally rare plants, it is important to keep additional disturbance in the south west Ghana hotspot, particularly Ankasa, to a minimum, as is the current practice, and in the Nimba mountains to establish community forests which may be left relatively undisturbed amid farming and mining activities.

Effects of innovative long-term soil and crop management on topsoil properties of a Mediterranean soil based on detailed water retention curves

Abstract. The effectiveness of conservation agriculture (CA) and other soil management strategies implying a reduction of tillage has been shown to be site-dependent (crop, clime and soil), and thus any new soil and crop management should be rigorously evaluated before its implementation. Moreover, farmers are normally reluctant to abandon conventional practices if this means putting their production at risk. This study evaluates an innovative soil and crop management (including no-tillage, cover crops and organic amendments) as an alternative to conventional management for rainfed cereal cropping in a calcareous soil in a semi-arid Mediterranean climatic zone of Navarra (Spain), based on the analysis of soil water retention curves (SWRCs) and soil structure. The study was carried out in a small agricultural area in the municipality of Garínoain (Navarre, Spain) devoted to rainfed cereal cropping. No other agricultural area in the whole region of Navarre exists where soil and crop management as proposed herein is practiced. Climate is temperate Mediterranean, and the dominant soil is Fluventic Haploxerept. Within the study area there is a subarea devoted to the proposed soil and crop management (OPM treatment), while there is another subarea where the soil and crop management is conventional in the zone (CM treatment). OPM includes no-tillage (18 years continuous) after conventional tillage, crop rotation, use of cover crops and occasional application of organic amendments. CM involves continuous conventional tillage (chisel plow), mineral fertilization, no cover crops and a lower diversity of crops in the rotation. Undisturbed soil samples from the topsoil and disturbed samples from the tilled layer were collected for both systems. The undisturbed samples were used to obtain the detailed SWRCs in the low suction range using a HYPROP©device. From the SWRCs, different approaches found in the literature to evaluate soil physical quality were calculated. The pore-size distribution was also estimated from the SWRCs. Disturbed samples were used in the laboratory to assess soil structure by means of an aggregate-size fractionation and to perform complementary analysis from which other indicators related to soil functioning and agricultural sustainability were obtained. The approaches evaluated did not show clear differences between treatments. However, the differences in soil quality between the two forms of management were better observed in the pore size distributions and by the analysis of the size distribution and stability of soil aggregates. There was an overabundance of macropores under CM, while the amount of mesopores (available water) and micropores were similar in both treatments. Likewise, more stable macroaggregates were observed in OPM than in CM, as well as more organic C storage, greater microbial activity, and biomass. The proposed management system is providing good results regarding soil physical quality and contributing also to the enhancement of biodiversity, as well as to the improvement in water-use efficiency. Finally, our findings suggest that the adoption of the proposed practice would not result in a loss in yields compared to conventional management.

Fault displacement analysis using a multidisciplinary approach on the Gerede Segment of the North Anatolian Fault Zone

The North Anatolian Fault Zone (NAFZ) is the world's most seismically significant strike-slip fault and Turkey's most active tectonic structure. A segment of NAFZ known as Gerede is located in northwest Turkey. It is debatable whether the Gerede segment of the NAFZ exhibits evidence of tectonic creep formation. The movement of the Gerede Segment of the NAFZ was investigated using various methods in this study. The Global Navigation Satellite System (GNSS) and soil mechanics-based methods were used in the Gerede Segment of the NAFZ for fault displacement analysis using a multidisciplinary approach. The GNSS technique is widely used in geodynamics-kinematics and cartography studies of earth crust movements, as well as in determining deformations during earthquake periods and as a source of data in defining geological and atmospheric phases. By establishing a GNSS network composed of regional or geodetic station points around the fault zone, it is possible to determine the deformations, velocities, and possible seismic slip rates of permanent GNSS stations on this network. The shear box test is used in soil mechanics to determine the shear strength parameters c and φ. A shear box test is performed to determine the pattern of fault movement (seismic or aseismic) and to determine the shear strength parameters (c, φ). An undisturbed block sample from a paleoseismology trench was used for a consolidated drained (CD) type shear box test. It was found that the fault movement near the Gerede Segment was not creeping. This study makes a new contribution to the debate on whether the Gerede Segment's movement pattern is creep or seismic.

GEOTECHNICAL CHARACTERIZATION AND GEOREFERENCING OF SOME SOFT SOIL DEPOSITS OF THE METROPOLITAN REGION OF ARACAJU

Preliminary and complementary geotechnical investigations allow to obtain important information about the subsoil layers. However, in daily practice, this step is usually neglected. This problem becomes harder when there are layers of soft soils in the subsoil, due to the particularities of this kind of soil. Metropolitan Region of Aracaju (MRA) have few recorded data about their soft soil deposits, which difficult geotechnical design. Hence, this study aims to perform the geotechnical characterization of some soft soil deposits existent in the MRA and georeferencing these deposits, using a Geographic Information System (GIS). The results obtained show that the studied deposits have a medium plastic to very plastic behavior (PI ranging from 8.00 to 33.00). Values of natural moisture content were considerably lower than those obtained in other Brazilian states (between 29% and 84%), possibly due to the influence of the sand lenses. As for the activity, the MRA clays are predominantly inactive. Furthermore, the analysis of the quality of samples made it clear that is difficulty to collect undisturbed soil samples in these deposits. In the future, complementary research needs to be developed to increase the knowledge about these soft soil layers.

Modeling Undrained Shear Strength of Sensitive Alluvial Soft Clay Using Machine Learning Approach

Soft soils are commonly located in many regions near seas, oceans, and rivers all over the world. These regions are vital and attractive for population and governments development. Soft soil is classified as problematic soil owing to sustaining low shear strength and high settlement under structures. Constructing structures and/or infrastructures on soft soil is a considerable risk that needs great attention from structural engineers. The bearing capacity of structure foundations on soft soil depends mainly on their undrained shear strength. This soil feature strongly influences the selection of appropriate soil improvement methods. However, determining undrained shear strength is very difficult, costly, and time-consuming, especially for sensitive clay. Consequently, extracting undisturbed samples of sensitive clay faces several difficulties on construction sites. In this research, accurate field-tested data were fed to advanced machine learning models to predict the undrained shear strength of the sensitive clay to save hard effort, time, repeated laboratory testing, and costs. In this context, a dataset of 111 geotechnical testing points were collected based on laboratory and field examinations of the soil’s key features. These features included the water content, liquid limit, dry unit weight, plasticity index, consistency index, void ratio, specific gravity, and pocket penetration shear. Several machine learning algorithms were adopted to provide the soft clay modeling, including the linear, Gaussian process regression, ensemble and regression trees, and the support vector regression. The coefficient of determination was mainly used to assess the performance of each predictive model. The achieved results revealed that the support vector regression model attained the most accurate prediction for soil undrained shear strength. These outcomes lay the groundwork for evaluating soil shear strength characteristics in a practical, fast, and low-cost way.

Simple Shear Strength Analysis of Inherent Anisotropy for a Tropical Alluvial Soil

ABSTRACT Tropical alluvial soils have unusual engineering properties and their behavior is not typical of fine-grained soils. The literature regarding strength properties of alluvial soils is limited. This study presents an experimental evaluation of inherent anisotropy of undisturbed tropical alluvial soil samples by comparing the direct simple shear (DSS) test results of 52 specimens cut in horizontal and vertical orientations. The tests were carried out under consolidated undrained constant volume with excess pore water pressure measurements. The peak shear strength, effective stress paths, and secant shear modulus analyses showed that the difference in properties between horizontally and vertically cut specimens was negligible. Nonetheless, the results for vertically cut specimens presented a higher random error compared to the results for horizontal specimens in all aspects. A good relationship between the undrained shear strength and over-consolidation ratio was found but was not comparable to past DSS results for natural clays. Scanning electron microscopy images revealed flocculated edge-to-edge and edge-to-face particle associations. Directionality analysis of microfabric showed that the alluvial soils had low preferred orientation of particles. The general notion that all alluvial soils are highly anisotropic was not evident, based on the experiments reported in this study. The findings herein are useful for geotechnical engineers to better understand the strength behavior of tropical alluvial soils.