Precompression Stress Research Articles

Determination method and strain-attribute interact in the calculation of precompression stress from soil compression curves

Determination of soil precompression stress (σp) from compression curves has markedly changed in recent decades, with several available methods of varying complexity. The graphical procedure proposed more than eight decades ago remains a standard, though it is now emulated by statistical and numerical procedures. We tested nine determination methods based on linear, polynomial, nonlinear and spline regressions. Four attributes were used to represent soil deformation during compression (strain-attributes): bulk density (ρb), void ratio (e), total porosity (ϕ) and strain (ε). Undisturbed soil samples equilibrated either at 10 or 100 kPa water tension were subjected to confined, drained uniaxial compression tests. The experimental factors (determination method, strain-attribute, and water tension) and their interaction affected the determination of σp. Sigmoid equations converged for 84%–95% of the compression curves, failing for samples at 100 kPa with with steep virgin compression lines. Methods based on fourth-degree polynomials resulted in 10-94% of the values outside the range 10–1550 kPa, depending on the strain-attribute. Although ε and e are linearly related, the former suits better the application of methods based on polynomial and spline regression, also fitting well for methods based on sigmoid equations with samples at 10 kPa. The bi-linear intersection methods presented relaistic σp values for bi-linear curves and should be solely applied to ρb. The spline method resulted in σp values clustered along the loads applied during the compression tests.

Seismic performance of stabilised/unstabilised rammed earth walls

This experimental study investigates the in-plane seismic performance of unstabilised/stabilised rammed earth (RE) walls. The experimental program consists of five specimens including three unstabilised and two stabilised walls. All walls are 1000mm long, 900mm tall and 200mm thick. To simulate earthquake forces at the presence of gravity loads, the walls are subjected to an in-plane cyclic loading reversal combined with a constant vertical pre-compression stress. The experimental parameters comprise pre-compression stress (0.1, 0.3 and 0.5 MPa) and stabiliser type (lime and cement). The outcomes are compared in terms of failure mode, hysteretic response, ductility, energy dissipation, stiffness degradation, residual deformation and damage index. Further discussion is also provided by evaluating the envelope curves of the hysteretic load–displacement responses implementing a capacity spectrum approach. It is indicated that the level of vertical stress affects the hysteretic response of the walls with higher levels producing more favourable responses. However, increased vertical stress is caused by the greater gravity loads which in turn intensify the seismic induced forces that may dominate the seismic response of the walls. In addition, the effect of stabilisation process is highly dependent on the stabiliser type.

In-plane lateral cyclic behaviour of lime-mortar and clay-brick masonry walls in dry and wet conditions

This paper presents an experimental investigation into the structural and material response of ambient-dry and wet clay-brick/lime-mortar masonry elements. In addition to cyclic tests on four large-scale masonry walls subjected to lateral in-plane displacement and co-existing compressive gravity load, the study also includes complementary tests on square masonry panels under diagonal compression and cylindrical masonry cores in compression. After describing the specimen details, wetting method and testing arrangements, the main results and observations are provided and discussed. The results obtained from full-field digital image correlation measurements enable a detailed assessment of the material shear-compression strength envelope, and permit a direct comparison with the strength characteristics of structural walls. The full load-deformation behaviour of the large-scale walls is also evaluated, including their ductility and failure modes, and compared with the predictions of available assessment models. It is shown that moisture has a notable effect on the main material properties, including the shear and compression strengths, brick–mortar interaction parameters, and the elastic and shear moduli. The extent of the moisture effects is a function of the governing behaviour and material characteristics as well as the interaction between shear and precompression stresses, and can lead to a loss of more than a third of the stiffness and strength. For the large scale wall specimens subjected to lateral loading and co-existing compression, the wet-to-dry reduction was found to be up to 20% and 11% in terms of stiffness and lateral strength, respectively, whilst the ductility ratio diminished by up to 12%. Overall, provided that the key moisture-dependent material properties are appropriately evaluated, it is shown that analytical assessment methods can be reliably adapted for predicting the response, in terms of the lateral stiffness, strength and overall load-deformation, for both dry and wet masonry walls.

Role of compaction and drying-wetting cycles on the capability of precompression stress to indicate load history of heavily disturbed soils

Wetting and drying are common processes in agricultural soils, which change particle rearrangement, cementation and related properties. Some recent studies have noted that soil precompression stress (σp) – the soil capacity to support stress – can be affected by wetting and drying cycles and should be seen as state variable instead of a soil mechanical characteristic. In this study, we investigated how wetting and drying cycles change the σp of remolded samples, i.e. soil without distinct loading history. Soil material from three highly weathered soils with different textures (62, 35 and 15% of clay) of the most common soil classes of Brazil were used. The soils were milled and then used to create two set of samples with different compactness. In one set, named not compacted (NC), the milled material was just poured (loose material) into the cylinders, while in the other set the milled material inside the cylinders was compacted (COMP). In the NC samples, zero and three drying (under 33 kPa matric suction) and wetting (saturation) cycles (0D-S and 3D-S) were applied. The COMP samples were subjected to 0, 2, 4, and 6 D-S cycles. In the NC samples, the σp (35–49 kPa) in 0D-S was similar to the matric stress soil samples had experienced prior to the compression test (33 kPa), but σp increased to 60–92 kPa after 3D-S. In the COMP samples, σp increases ranged between 65 and 53 kPa from 0 D-S to 2 D-S and then decreased to a value similar to that of 0 D-S again after 6 D-S. Changes of σp tended to be more remarkable in the soils with 62 and 35% of clay, but only a weak association between σp and texture was noticed. These results indicate that internal forces a soil experiences during shrinkage and swelling are key drivers of the σp parameter of the topsoil of agricultural areas. Thus, one σp value cannot characterize a site over time as it might be altered thoroughly during the year and thus fail in reflecting documented load history by means of traffic.

Analyzing the impact of grazing and short-term irrigation management on soil mechanical strength of a volcanic ash soil under different types of pastures

In southern Chile, there are over 1.3 million ha of pastures on volcanic ash soils. The climate change scenario and the need to increase yields are forcing farmers to increase irrigated surface areas. This implies an intensified soil use that must be analyzed to prevent soil degradation. Therefore, this study analyzed the impact of initial pasture defoliation (mowing and grazing) and short-term irrigation managements on soil structure dependent properties of a volcanic ash soil under different types of pastures. Field penetration resistance (PR) profiles (0–80 cm), soil water content measurements (0–10 cm) and undisturbed soil samples (0–3 cm) displayed the impact of animal trampling due to repeated loading events. Though this experiment did not determine significant interactions such as pasture x defoliation method x applied load, the early developmental stage of this experiment provided a basis for better understanding deformation processes due to animal trampling when different types of pastures are irrigated in the short-term. The plastic deformation caused by loads higher than precompression stress induced an increase in soil mechanical strength (e.g. Pc increased after the first grazing, but not after mowing), affecting the macropore volume and air permeability. The short-term effects (<2 years) showed the incipient consequences of grazing and irrigation: PR increased due to animal trampling (data dispersion: grazed> mowed plots, showing footprint formation after 8 grazing events) and the higher sum of PR in non-irrigated pastures evidenced the increase of the cohesion between particles/aggregates after drying events. Therefore, it can be expected that in the medium-term (3-4 years), animal trampling could lead to significant soil deformation and a progressive increase in soil mechanical strength near the soil surface.

Detailed micro-modeling of partially grouted reinforced masonry shear walls: extended validation and parametric study

Partially grouted reinforced masonry (PG-RM) shear walls have been widely used as structural elements in low- and medium-rise earthquake-resistant buildings. Nonetheless, assessing its shear strength represents a complex task mainly because the partial grouting provides a non-constant cross section, which results in heterogeneous stress–strain patterns. Consequently, refined modeling techniques are needed to reproduce local failure mechanisms taking place in these walls, which significantly influence the global response. In response to this issue, a detailed micro-modeling approach based on the finite element method was proposed in previous studies by the authors. Although the numerical strategy provided accurate results, further validation is required. Therefore, in this study, the experimental results of seven PG-RM shear walls of multi-perforated clay bricks with bed-joint reinforcement are employed as validation cases. These seven walls presented variations in five design parameters. The validated numerical model was then employed to perform a parametric study to assess the influence of the wall aspect ratio, axial pre-compression stress, and horizontal reinforcement ratio on the in-plane lateral behavior of PG-RM shear walls. The obtained results show that the three studied design parameters modified the crack patterns of the walls. Besides, increasing the axial pre-compression stress or reducing the aspect ratio resulted in higher walls’ shear strength. Additionally, decreasing the horizontal reinforcement ratio or increasing the aspect ratio generated a higher story-drift ratio at maximum lateral force. Finally, it was corroborated that the positive effect of the axial pre-compression stress on the walls’ shear strength decreases inversely proportional to the aspect ratio.

Sugarcane straw effects on soil compaction susceptibility

Crop residues may buffer part of compressive stress applied over the soil surface. Thus, indiscriminate crop residue removal would magnify soil compaction in highly mechanized cultivation systems, such as sugarcane in Brazil. Nevertheless, the effect of different amounts of sugarcane crop residue (straw) on soil compaction mitigation still needs to be tested. We conducted a laboratory study to quantify the effects of sugarcane straw rates on soil compaction indicators in response to external applied stress. The experiment involved remolded soil cores with four initial bulk densities: 1.25, 1.35, 1.45 and 1.55 Mg m−3, and five amounts of straw were left on soil surface, equivalent to 0, 5, 10, 15 and 20 Mg ha−1. The soil cores were subjected to uniaxial compression test and seven successive vertical static loads (25, 50, 100, 200, 400, 800 and 1600 kPa) were applied over the soil surface using a pneumatic consolidometer. Soil displacement was measured after each applied load. Based on these values, apparent precompression stress (σp), apparent compression index (CI) and final bulk density were calculated as indications of soil deformation. Because, soil inherent properties should not change, we call the changes due to straw layer addition "apparent" in this study. Our results revealed that large amounts (>10 Mg ha−1) of straw increased subtly apparent soil load bearing capacity (i.e., increased up to 15 kPa in apparent σp; 7%). The bulk density change rate (soil deformation) decreased due to presence of straw under low stress (<100 kPa), and increased under high stress (>400 kPa) levels in loose soil. On the other hand, compaction was slightly reduced in compacted soil, with corresponding reduction on apparent CI values. Nevertheless, despite this buffer effect provided straw, we noticed that increases in surface straw amount are likely insufficient to reduce the risk of compaction (little gain in apparent load-bearing capacity), but a reduction of about 5% on the soil deformation (as apparent σp is overcome) could occurs in compacted soils. We advocate that benefits of leaving sugarcane straw covering the soil go beyond the direct “damper” effect, because straw is source of carbon, which is fundamental for enhancing soil structure stability and biological activity, and thus, reducing soil compaction risks or even alleviating soil compaction restrictions to plant growth. Finally, we encourage future studies to test the straw effects under machinery traffic in field conditions, which could involve the additional effect of shear stress over the tyre-straw-soil interface.

Pre-compression and capillarity effect of treated expansive subgrade subjected to compressive and tensile loadings

Pavement structures often are under tension and compression mobilised by the coupled effects of traffic loads and swelling stress. Seasonal moisture variations cause capillarity rise and volumetric movement within the subgrade. The objective of this investigation is to evaluate the pre-compression and capillarity effect of expansive subgrades stabilised with activated fly ash (α-FA), and sisal fibre, analysed for tensile (qt) and compressive qu strengths. Moulding moisture content corresponding to the optimum water content was used to prepare the subgrade soils by random inclusion of 0.25 %, 0.5 %, 0.75 %, and 1.0 % of sisal fibre by dry mass of the subgrade soils treated with 20 % and 30 % of α-FA. Confined pre-compression stresses equivalent to 10 kPa and 20 kPa after 12 h of preparation were applied followed by 14 days of air-curing condition. Subsequently, the prepared subgrades samples were subjected to capillary rise through soaking. The test results revealed that both tensile and compressive strengths of 10 kPa and 20 kPa precompressed specimens decreased from 1.48MPa to 0.98MPa on average due to the capillarity effect, compared to non-capillary specimens. Without capillarity effects, an equivalent strength increases of 12.21 % and 63 %.11 were recorded for 10 kPa and 20 kPa of pre-compressed specimens compared to un-precompressed specimens tested under tension. The results further revealed that the subgrade soils treated with the combination of fibre and α-FA exhibited significant strength resistance under tension. The strength indices (qt/qu) of 0.13 to 0.31 as the proportionality of tensile and compressive strengths is closely correlated for all the pre-compressed composites due to fibre deformability.

Strength, swelling and compressibility of unsaturated sugarcane soils

Large-scale sugarcane plantation is characterized by successive and disordered traffic of heavy machinery and equipment over the cycle, which can cause damage to the soil structure. As the stress induced by traffic exceeds the soil load-bearing capacity, it results in soil compaction. However, the mechanisms and key variables that govern the compressive characteristics in agricultural unsaturated soils to support those applied loads without plastic deformations (compaction) is not fully understood. To investigate this process, we measured the strength, swelling and compressibility characteristics of unsaturated soils with contrasting texture from sugarcane fields. Undisturbed soil cores were sampled in nine cultivated sugarcane fields, equilibrated at a matric potential of –100 hPa and subjected to confined uniaxial compression tests. Precompression stress (σp), compression (λ) and swelling (κ) indexes were extracted from the soil compression curves. Soil organic C (SOC), degree of compactness, total porosity and particle size fractions were also measured and correlated to the compressive parameters σp, λ and κ. Principal components, correlation and multiple regression models were used to the data analyses. Overall, reductions in soil strength and increases in the soil compressibility and elasticity occurred with the increase in SOC, whereas increases in the degree of compactness resulted in higher soil strength and lower soil compressibility and elasticity. Furthermore, our results revealed that silt + clay content considerably increased soil compressibility. In combined scenarios for a range of soil texture, SOC and degree of compactness at matric potential at around field capacity (i.e. –100 hPa), the maximum σp observed was approximately 200 kPa, which is a much lower load-bearing capacity than the estimated stress for some trucks and trailers used in sugarcane harvest (∼600−800 kPa). Our study suggests that soil compaction is eminent in sugarcane fields at matric potential close to field capacity, and can be aggravated in clayey soils with high SOC content and low degree of compactness. Therefore, urgent strategies of traffic control are necessary to prevent or mitigate soil compaction induced by mechanized sugarcane operations.

Consequences of gas pipeline hauling on changes in soil properties over 3 years

The manifold requirements of arable soils e.g. as construction sites for gas pipes or electricity cable hauling can result in extensive stress and deformation processes. It is therefore hypothesized, that external impacts as the load applications by the used construction machinery, the excavation and following refilling activities cause a loss of important soil functions and changes in soil strength. The recovery of soil functions requires efficient amelioration methods in order to re-achieve the site-specific crop yield potential.In course of the gas pipe installation in Eutric Cambisols in the Weichselian glacial till region of Mecklenburg West Pommerania (North Eastern Germany), undisturbed soil samples were taken below the plowed A-horizon in 50 and 80 cm depth in the traffic lanes and refilled pipeline trenches in the construction area as well as in the adjacent arable soils (which were used as references) directly and 3 years after the construction process.Analyses of soil porosity characteristics, air and saturated hydraulic conductivity as well as of soil strength (precompression stress value) indicate a severe loss of soil functions (especially air capacity and hydraulic conductivity) directly after the construction process (refilling of the material) compared to the reference soil. A harmful soil degradation could be verified down to 80 cm depth in the traffic lanes as a consequence of much too heavy machines used for the transportation and hauling of the pipes. After the refilling and leveling process together with the amelioration measures like the application of in total 5 Mg CaO ha−1 and the following cultivation of alfalfa seeded at the surface after the refilling and leveling, the air capacity and air conductivity was improved, but the precompression stress and the saturated hydraulic conductivity only slightly increased during the following 3 years. We conclude that such intense impacts require a longer time period to regain more rigid soil functions in spite of all the supportive amelioration approaches.

Effective stress and pore water dynamics in unsaturated soils: Influence of soil compaction history and soil properties

Effective stress is an important strength indicator for understanding and fundamentally predicting soil behaviour due to mechanical disturbance. This study investigated the influence of `soil properties on effective stress in relation to matric potential, and soil sampling direction (vertical/horizontal). Undisturbed soil samples representing 3 different locations were collected at 4 depths and in 2 sampling directions, to determine which soil properties mostly affect the effective stress in response to the magnitude of the stress applied. The soil properties included texture, organic carbon content, dry bulk density, void ratio, pre-compression stress and prevailing matric potential. The results showed that both the effective stress and the concomitant changes in pore water pressure largely depend on the prevailing matric potential in the soil. In addition, changes in soil structure caused by subsurface soil compaction as a result of tillage, organic carbon and clay content influenced the magnitude of the effective stress and pore water pressure in soils during loading. The porewater pressure measured under static loading is sampling direction dependent due to differences in hydraulic conductivity and pore continuity. Porewater pressure increases (become less negative) with increases in the fraction of fine pores in the soil while it may either remain constant or decrease, when the medium and coarse pore fractions in the soil increases. This implies that the smaller the pore connectivity and continuity, the less negative the changes in pore water pressure become. Also, the higher the pre-compression stress (sometimes due to higher organic carbon content), the more consistent the applied stress induced an increase in the calculated effective stress.

Chiselling and wheeling on sandy loam long-term no-tillage soil: compressibility and load bearing capacity

Traffic on arable land is one of the main causes of soil compaction, threatening soil function and quality. The objective of this study was to evaluate tillage and wheeling effects on mechanical properties on Hapludalf soil. We evaluated four combinations of management system and wheeling traffic: 13 years of no-tillage (NT), NT compacted with additional wheeling (NTc), minimum tillage (chiselling) soil (MT), and MT compacted with additional wheeling (MTc). Soil bulk density (Bd), macroporosity (Mp), precompression stress (σp), compressibility coefficient (Cc), and relative deformation were determined in four soil layers. Soil with greater Bd had higher σp and lower Mp and Cc, where statistical significance varied depending on soil depth, tillage, and additional compaction. Soil tillage did not affect Bd, but Mp was lowest in the no-till pan layer (0.05–0.15 m), and additional compaction decreased Mp in deeper layers. Long-term NT had greater σp and Cc than MT soil, while wheeling increased σp and decreased Cc in MT, only in the upper layer. Four wheelings with 1.1 Mg wheel load on no-tillage soil and two wheelings with 3.2 Mg wheel load on chiselled-soil decreased Mp in deeper (down to 0.25–0.35 m) layers, but only high load increased σp and decreased Cc in upper layers of chiselled-soil. Surface compaction in conservation agriculture is a major issue, since soil mobilisation by soil tillage should be avoided.

Investigating the effect of inoculation of chickpea with rhizobium and mycorrhizal fungi (Funneliformis mosseae) on soil mechanical and physical behavior

Symbiosis with plants by mycorrhiza and rhizobium (bio-fertilizers) is effective in improving soil structure and increasing the stability of aggregates against compression. In addition to soil deformation, soil structural properties should be included for the assessment of compaction. The purpose of this study was to investigate the effect of application of rhizobium and mycorrhizae on plant yield, some soil physical properties, and the confined compression curve and its characteristics, which have not been reported in any research so far. Experiments were conducted in a completely randomized design with three replications in the field and glasshouse. Mycorrhizal fungi (Funneliformis mosseae), rhizobium (Mesorhizobium), mycorrhiza - rhizobium and control (no inoculation) were the treatments of the field experiment. Sterilized mycorrhiza background material and non-plant-non-inoculation were the two additional treatments of the glasshouse experiment. The plant cultivated in this experiment was chickpea. Mycorrhizal and rhizobium treatments increased the stability of aggregates compared to non-plant-non-inoculation treatment. Mycorrhiza and rhizobium increased the macroporosity and near-saturation water content. The smallest total yield was found in the sterilized mycorrhiza background material and control treatments. Mycorrhiza and rhizobium increased the void ratio at different compression stresses by 9–16% and 19–25%, respectively, compared to non-inoculation treatments under the glasshouse experiment. Pre-compression stress was increased by 84.3% in the control treatment with plant compared to the mycorrhiza treatment in the glasshouse experiment, but did not change significantly in the field experiment. Symbiosis of mycorrhiza and rhizobium as a sustainable biological method improved the physical and mechanical properties of the soil by affecting plant yield and root exudates.

Numerical Verification of the Elastic-Plastic Menétrey-William Model (M-W-3) for Masonry Shear Walls Made of Calcium Silicate Masonry Units

This paper is a continuation of the author’s papers on numerical verification of masonry structures. It describes the proposed method of validating the elastic and plastic Menétrey-Willam model (M-W-3) implemented in the ATENA software. Material parameters of the model were determined from triaxial tests on masonry units. This paper presents a practical use of the calibrated numerical model for stiffening walls. Flat, four-node finite elements (2D model) were used with two degrees of freedom for each node. Simulation covered stiffening walls of various length (l = 4.5 m and 2.25 m), height of 2.45 m, and thickness of 0.18 m. Sequential loading in two stages was performed on walls. Precompression stresses σc of 0.1; 0.75 and 1.5 N/mm2 were applied in the first stage, and walls were exposed to monotonic horizontal shearing in the second stage. Calculations were performed at the plane stress (σ1≠0, σ1≠0, σ3=0). The obtained calculations were compared with results for unreinforced walls made of calcium silicate masonry units tested under the identical initial-boundary conditions. The relationship between shear stress and non-dilatational strain angle and values of cracking and failure stresses were compared. Calculations showed that shear stresses at the time of cracking demonstrated the closest similarity. The biggest differences occurred for deformation at the moment of destruction.

Research of Influence of Bed Joints Reinforcement On Strength of Masonry Shear Walls with Openings Made of Calcium Silicate Masonry Units

This article describes results from testing reinforced and unreinforced walls made of calcium silicate units and having openings of different shapes. Conducted tests mainly focused on determining the effect of used reinforcement on the cracking morphology and values of cracking and failure forces. Every wall was made of calcium silicate units with vertical hollows (group I acc. to PN–EN 1996-1-1:2013). Tests covered 12 walls with the following external dimensions l = 4.45 m, h = 2.45 m, t = 180 mm, which varied in shape and dimensions of openings. Steel trusses of EFZ 140 / Z 140 type (Z1 type) and plastic meshes (Z2 type) were used as reinforcement. Models were divided into six series with a difference in the opening shape and the reinforcement type. Openings in walls were marked with letters A. B, and C. The opening of A type was a single window opening with a length of 1.50 m and a height of 1.12 m. That series included two models with truss type reinforcement (HA-Z1 (Z1 type of reinforcement) and two models with plastic mesh reinforcement (HA-Z2 (Z2 type of reinforcement). The opening of B type was also a window opening of 1.12 m in height, but longer - 2.50 m. That series included two models with truss type reinforcement (HB-Z1 (Z1 type of reinforcement) and two models with plastic mesh reinforcement (HB-Z2 (Z2 type of reinforcement). The opening of C type combined the window opening of 1.50 m in length and 1.12 in height and a door opening of 1.0 m in width and 1.90 in height. As in case of series of A and B type openings, tests were also performed on HC-Z1 series (Z1 type of reinforcement) and HC-Z2 series (Z2 type of reinforcement). The results were compared with test results for unreinforced walls with openings, tested under the same initial conditions. Reinforcement ratio in all reinforced models was ρ=0.07 (>ρmin=0.05). Walls were tested at different values of precompression stress σc = 0.1; 1.5 or 0.75 N/mm2. A mechanism of cracking and destruction, and values of cracking and failure stresses were analysed.

Numerical analysis applied to the study of soil stress and compaction due to mechanised sugarcane harvest

Crop harvesting has been pointed as the main source of soil compaction in sugarcane fields because of the high stresses induced by the machinery; however, little is known about the magnitude of the stress transmitted to the soil by these machines in the compaction process. The aim of this study was to use numerical simulations to analyse the impact of vehicles used in mechanised sugarcane harvesting on soil stress and soil compaction response. For that, numerical simulations were performed for a set of machines and tyre configurations used to harvest sugarcane: tractor, truck and trailer. The model was formulated as a 2D plane strain problem, meshed for a soil domain 9.0 m in width and 4.0 m in depth, while using the Modified Cam Clay model as the constitutive relationship. Up to 1 m depth, the domain was layered every 0.20 m using measured soil mechanical properties. Effective vertical stress, precompression stress and soil total porosity were analysed in response to the applied stress by the harvest machines. The truck and the trailer applied stresses to the soil surface that reached 800 kPa, while the stresses applied by the tractor did not exceed 300 kPa. Numerical simulations showed that the truck and the trailer can transmit stresses higher than precompression stress that exceeds 1.00 m depth, causing a reduction in the soil total porosity and hence subsoil compaction. These stresses can extend to the planting row by stress bulbs overlapping at around 0.60 m, and could cause soil damage in case of greater stress than precompresion stress. Finally, the simulations revealed variability in soil compaction as dependent on the magnitude of the transmitted stress, as well as due to heterogeneity of mechanical properties along the soil profile. The simulations indicate the relevance of detailing the compressive properties of arable soils rather than considering the soil profile as homogeneous.

Near-surface-mounted retrofitting of damaged/undamaged adobe walls using steel bars: Analytical evaluation of experimental results

This study examines the results of an extensive experimental program pertaining to seismic strengthening of adobe walls using near-surface-mounted (NSM) steel bars. The experiments were conducted on seven adobe wall panels (1020×800×200mm) subjected to the combined action of vertical pre-compression stresses (0.1 and 0.3 MPa) and incremental lateral loading reversals. The parameters investigated included NSM reinforcement ratio, level of vertical stress, and pre-existing damage. The load–displacement curves obtained from pushover tests were employed in the seismic evaluations using a capacity spectrum approach called the N2 method. Based on the experimental and analytical findings, the adopted retrofitting technique was found capable of effectively enhancing the in-plane seismic performance of both the undamaged and damaged adobe walls in terms of lateral strength, displacement capacity, energy dissipation, and the tolerated peak ground acceleration. It was found that the retrofitting intervention has a more beneficial contribution to the displacement capacity, rather than lateral resistance, of adobe walls under high axial pre-compression loads. Finally, analytical models originally developed for masonry walls were modified for estimating the in-plane lateral resistance of reinforced/unreinforced adobe walls.

Surface quality and residual stress variation of ceramics after abrasive grinding under pre-compressive stress

Grinding surface quality and residual stress of Al2O3 and ZrO2 ceramics were investigated after grinding under pre-compressive stress. The damage induced by abrasive grinding on the Al2O3 and ZrO2 ceramics surface was decreased using a pre-compressive stress grinding method. Pre-compressive stress on ceramics was applied by a custom-made compressive stress loader before abrasive grinding. The surface quality of both the Al2O3 and ZrO2 ceramics was improved after pre-compressive stress grinding. However, the surface roughness of ZrO2 was lower than that of Al2O3 under the same grinding parameters. Surface residual stress variation is found to be related to both grinding depth and pre-compressive stress. After abrasive grinding with pre-compressive stress, the surface residual stress tended to be compressive. Furthermore, in both Al2O3 and ZrO2 ceramics, the residual compressive stress was higher at a grinding depth of 30 μm under the same grinding parameters.

Experimental investigation into the effect of vertical loading on in-plane cyclic behavior of adobe walls

Adobe buildings are highly susceptible to lateral loads, which is responsible for their collapse during earthquakes in the past resulting in vast damages and immense human casualties. Nonetheless, a majority of such buildings in the seismic-prone regions worldwide, including those in the Iranian plateau, are in every-day use. Thus, close examination of their behavior under lateral loading is vital for developing appropriate retrofit techniques aimed at preventing their severe damage and the associated casualties during strong ground motions. Towards this, the present experimental investigation was designed and implemented to study the in-plane lateral behavior of adobe walls under different axial pre-compression loads. The experimental program consisted of 12 adobe wall panels, all 1000 mm long and 200 mm thick but of three different heights of 800, 900, and 1000 mm. Loading was applied in the form of an incremental lateral loading regime in the presence of four vertical pre-compression stresses of 0.1, 0.3, 0.5, and 0.7 MPa. The aim was to investigate the effects of vertical loading and wall height on the in-plane lateral responses of adobe walls. The results were compared in terms of hysteretic load-displacement response, lateral resistance, displacement capacity, ductility, stiffness degradation, and energy absorption. Another aspect of the study involves a detailed examination of the failure modes and general behavior of the specimens.

Compression and rebound characteristics of agricultural sandy pasture soils from South Greenland

The reduction of permafrost areas and a prolonged vegetation period, both due to the ongoing climate change, open up new possibilities for agricultural activities in the circumpolar region. Presently, not much is known about the physical and functional properties of subarctic agricultural soils, making it challenging to evaluate soil impacts from increased agricultural activity. This study aims at assessing the mechanical properties of sandy Greenlandic pasture soils regarding a potential future land-use change.The compression curves of 210 undisturbed soil core samples of three pasture fields in South Greenland and, as comparison, four intensively cultivated agricultural fields in Denmark were generated by uniaxial confined compression tests (UCCT). Four soil mechanical properties were determined: the precompression stress (σpc) as a measure of soil strength, the compression index (Cc) as a measure of compressibility, the swelling index (Cs) as a measure of resilience to compaction and the rebound (Δε) after a relaxation time of 60 s as a measure of short-time recovery from compaction.The Greenlandic pasture soils exhibited significantly higher σpc than the Danish cultivated soils despite their significantly lower initial bulk density, ρb. The Cc negatively correlated with ρb, and the Greenlandic soils showed higher Cc values than the Danish soils. The Cs showed a reciprocal correlation with ρb and, partly due to lower ρb of the Greenlandic soils, higher Cs than the Danish soils. The South Greenlandic sandy pasture soils showed compression and rebound characteristics on level with Danish loamy cultivated soils, likely due to a high content of particulate organic matter (non-degraded organic matter, including grass root-mat residues).