Horizontal Pressure Research Articles

Design, simulation and application of multichannel microfluidic chip for cell migration

Cell migration is defined as the directional movement of cells toward a specific chemical concentration gradient, which plays a crucial role in embryo development, wound healing and tumor metastasis. However, current research methods showed low flux and are only suitable for single-factor assessment, and it was difficult to comprehensively consider the effects of other parameters such as different concentration gradients on cell migration behavior. In this paper, a four-channel microfluidic chip was designed. Its characteristics were as follows: it relied on laminar flow and diffusion mechanisms to establish and maintain a concentration gradient; it was suitable for observation of cell migration in different concentration gradient environment under a single microscope field; four cell isolation zones (20 μm width) were integrated into the microfluidic device to calibrate the initial cell position, which ensured the accuracy of the experimental results. In particular, we used COMSOL Multiphysics software to simulate the structure of the chip, which demonstrated the necessity of designing S-shaped microchannel and horizontal pressure balance channel to maintain concentration gradient. Finally, neutrophils were incubated with advanced glycation end products (AGEs, 0, 0.2, 0.5, 1.0 μmol·L -1), which were closely related to diabetes mellitus and its complications. The migration behavior of incubated neutrophils was studied in the 100 nmol·L -1 of chemokine (N-formylmethionyl-leucyl-phenyl-alanine) concentration gradient. The results prove the reliability and practicability of the microfluidic chip.

Analysis of Horizontal Earth Pressure Acting on Box Culverts through Centrifuge Model Test

Underground space is being utilized due to the saturation of surface ground. The box culvert, as a representative infrastructure that has moved underground, is installed to protect such fixtures as electricity and gas. Because buried box culverts are necessarily affected by soil, it is important to study the earth pressure according to soil type. Herein, the horizontal earth pressure of the buried box culvert was analyzed. Accordingly, a precisely simulated centrifuge model test was performed. Additionally, the coefficient of earth pressure was analyzed. The results had significant variability because, in the existing theory, the horizontal earth pressure acting on the side of the box culvert was only calculated using the coefficient of earth pressure and the friction angle of the soil. Therefore, a correction factor was deemed necessary for calculating the horizontal earth pressure acting on the side of the box culvert.

Thermosolutal LTNE Porous Mixed Convection Under the Influence of the Soret Effect

Abstract The onset of thermosolutal convection in a fluid-saturated porous medium in the presence of a horizontal pressure gradient and the Soret effect under the two-temperature model of local thermal nonequilibrium (LTNE) is investigated. The Darcy model with the time-dependent velocity term in the momentum equation is employed together with the Oberbeck–Boussinesq approximation. The eighth-order eigenvalue differential equation obtained by employing linear stability analysis is solved using Galerkin's method of weighted residuals (GMWR) and also analytically. The onset of convection instills through oscillatory rather than stationary mode, and the critical stability parameters for the same are determined. The horizontal pressure gradient reinforces together with the solute concentration gradient and the scaled interphase heat transfer coefficient in evidencing mixed behavior on the criterion for the onset of oscillatory convection. Besides, the similarities and differences between the results of thermal and thermosolutal LTNE porous mixed convection are discerned.

Prediction of particle saltation velocity for horizontal dilute phase negative pressure pneumatic conveying

The evaluation of particle saltation velocity is vital for the design of dilute negative phase pneumatic conveying systems. Nonetheless, the particle saltation velocity in dilute negative phase pneumatic conveying is largely understudied, it also lacks a consistent correlation over operating conditions and particle properties. As such, this paper investigates the effects of solid-gas ratio, particle size, and drill pipe rotational speed on particle saltation velocity in the drill pipe via CFD-DEM (computational fluid dynamics-discrete element method) simulation. Consequently, the particle saltation velocity increased gradually seemingly leaning toward a constant value with the increase of solid-gas ratio. The particle saltation velocity with larger particle size under similar solid-gas ratio was higher, while the speed of the drill pipe and the particle saltation velocity showed a negative correlation. The correlation for particle saltation velocity was established by dimension analysis method geared toward accurately predicting the particle saltation velocity in dilute negative phase pneumatic conveying. A comparison of the new correlation and the experimental data found that the error between the predicted value of the correlation and the measured particle saltation velocity is within 20% and the correlation derived by the dimensional analysis method give the well agreement.

Near-surface wind speed changes in eastern China during 1970–2019 winter and its possible causes

The changes in near-surface wind speed (NWS) have a crucial influence on the wind power industry, and previous studies have indicated that NWS on global and China has declined continuously for decades under global warming. However, recently, the decreasing trend of global NWS has slowed down and even showed a recovery trend. Using the observation data of 831 weather stations of the China Meteorological Administration and the Japanese 55-year reanalysis data from 1970 to 2019, NWS changes in eastern China were analyzed and the possible influencing factors were discussed. Results show that winter NWS presented a decreasing trend from −0.29 m s−1 per decade (p < 0.001) in 1970–1989 to −0.05 m s−1 per decade (p < 0.01) in 1990–2019. Moreover, NWS exhibited a significant upward trend of 0.18 m s−1 per decade (p < 0.1) in 2011–2019, resulting in a 19.6% per decade recovery of the wind power generation. A possible cause is asymmetric changes of the sea level pressure and near-surface air temperature differences between the mid-high latitudes (40°–60°N, 80°–120°E) and low latitudes (20°–40°N, 110°–140°E) altered the horizontal air pressure gradient. Furthermore, NWS changes were closely associated with the large-scale ocean-atmosphere circulations (LOACs). NWS at 77.4% of the stations in eastern China shows significant correlation (p < 0.05) with the East Asian winter monsoon index, besides, the inter/multidecadal variability of NWS was considerably correlated to four LOACs, including Arctic oscillation (AO), North Atlantic oscillation (NAO), Pacific decadal oscillation (PDO), and El Niño–Southern Oscillation (ENSO). The time-series reconstructed by a multiple linear regression model based on above five LOACs matches well with the NWS. Interannual variability of NWS were significantly correlated to AO (−0.45, p < 0.01) and NAO (−0.28, p < 0.05), while the correlation between NWS and ENSO was weak.

Mechanistic simulation of fracture effects on miscible CO2 injection

Miscible injection of carbon dioxide (CO2) into oil reservoirs as an Enhanced Oil Recovery (EOR) method has proved to be highly advantageous. According to the volume of the world's recoverable oil resides inside the fractured reservoirs, investigation of the controlling parameters in the efficient injection of miscible CO2 is of paramount importance, mainly owing to the intricacies and complexities associated with this process. This complexity in fractured reservoirs arises due to the presence of two distinct media for fluid transfer (i.e., matrix and fracture network) and the corresponding differences in fluid velocities. Accordingly, performance of miscible carbon dioxide injection in these reservoirs was investigated through mechanistic simulation model in the form of dual-porosity (DP), and dual porosity-dual permeability (DPP). Moreover, due to limited supply and high injection costs of this gas in its pure form, performance of the miscible CO2 injection combined with C1, N2, and H2S was also surveyed and compared to pure gas injection case. A sensitivity analysis was also performed based on fracture porosity, fracture horizontal and vertical permeability, matrix horizontal permeability, block height shape factor, matrix capillary pressure, and impure injected components in DP and DPP models, showing that matrix horizontal permeability and capillary pressure have the greatest, and porosity has the lowest impact on miscibility performance and oil recovery in these models. In the end, after investigating the effect of different injection cases on miscibility performance and oil recovery, it was concluded that the highest oil recovery in miscible gas injection obtained through optimization of a gas composition having the lowest minimum miscibility pressure (MMP) and the lowest density.

Experimental Study of Horizontal Flow Boiling Heat Transfer Coefficient and Pressure Drop of R134a from Subcooled Liquid Region to Superheated Vapor Region

For the past few years, research in the field of flow boiling heat transfer has gained immense popularity for unravelling the dominant mechanism responsible for controlling heat transfer and identifying a parametric trend for understanding the characteristics of flow boiling heat transfer. This has led to several assumptions and models for predicting heat transfer during flow boiling without any known generalized mechanism. This study therefore seeks to experimentally study the characteristics of heat transfer during flow boiling over a wide range but small increase in vapor quality from a single-phase subcooled region through to a two-phase superheated vapor region. The study was performed with an R134a refrigerant in a single horizontal circular stainless-steel smooth tube that had an internal diameter of 5 mm. In this experimental study, local heat transfer coefficients and frictional pressure drop were measured for low heat fluxes of 4.6–8.5 kW/m2, mass fluxes of 200–300 kg/(m2s), vapor quality from −0.1 to 1.2 and a low constant saturation pressure of 460 kPa. Flow patterns observed during the study were recorded with a high-speed camera at 2000 fps. In covering a wide range of vapor quality, a peak of heat transfer coefficient near a vapor quality of zero and a local minimum observed in the low vapor quality region were observed, and both were sensitive to heat flux and mildly sensitive to mass flux. Generally, at low vapor quality, the heat transfer coefficient deteriorated with vapor quality and this was sensitive to heat flux but insensitive to mass flux and vapor quality, indicating nucleate boiling dominance in low vapor quality regions. In high vapor quality regions, the heat transfer coefficient was sensitive to mass flux and insensitive to heat flux. This indicates the dominance of convective boiling. In the low vapor quality regions, the flow patterns observed were slug and intermittent, while in the high vapor quality region, annular and mist flow patterns were observed. Generally, frictional pressure drop increased with increasing mass flux and vapor quality in the two-phase region.

Active earth pressure against flexible retaining wall for finite soils under the drum deformation mode

A reasonable method is proposed to calculate the active earth pressure of finite soils based on the drum deformation mode of the flexible retaining wall close to the basement’s outer wall. The flexible retaining wall with cohesionless sand is studied, and the ultimate failure angle of finite soils close to the basement’s outer wall is obtained using the Coulomb theory. Soil arch theory is led to get the earth pressure coefficient in the subarea using the trace line of minor principal stress of circular arc after stress deflection. The soil layers at the top and bottom part of the retaining wall are restrained when the drum deformation occurs, and the soil layers are in a non-limit state. The linear relationship between the wall movement’s magnitude and the mobilization of the internal friction angle and the wall friction anger is presented. The level layer analysis method is modified to propose the resultant force of active earth pressure, the action point’s height, and the pressure distribution. Model tests are carried out to emulate the process of drum deformation and soil rupture with limited width. Through image analysis, it is found that the failure angle of soil within the limited width is larger than that of infinite soil. With the increase of the aspect ratio, the failure angle gradually reduces and tends to be constant. Compared with the test results, it is shown that the horizontal earth pressure reduces with the reduction of the aspect ratio within critical width, and the resultant force decreases with the increase of the limit state region under the same ratio. The middle part of the distribution curve is concave. The active earth pressure strength decreases less than Coulomb’s value, the upper and lower soil layers are in the non-limit state, and the active earth pressure strength is more than Coulomb’s value.

Experimental Investigation on the Pressure Distribution Law and Calculation Method of Muddy Water with High Silt Content

The pressure distribution law of muddy water with high silt content has great influence on the stress and strain calculation of the dam body. Currently, there is a few research studies referring to the calculation method of high silt content muddy water pressure, which leads to no reliable theoretical basis for muddy water pressure calculation in dam design. In this paper, muddy water with high silt content was prepared and the imitation tests and model tests were carried out to investigate the pressure distribution law. Based on the test result analysis, it is indicated that the muddy water with high silt content is also in a flowable and viscous state, which is consistent with the law of fluid behavior; the horizontal pressure is equal to the vertical pressure at the same position, and this relationship is generally time independent; through the test result analysis, a pressure formula for muddy water with high silt content is proposed; through comparison between the pressure formula-calculated results and monitoring data, it is indicated that the proposed pressure formula is applicable in the calculation of muddy water pressure. The formula can be a useful tool in the dam safety and design calculation.

Shaking table test for seismic optimization of soil slope reinforced by new EPS pile under earthquake

To explore the optimal seismic performance of new EPS pile, we carried out a series of shaking table test by comparing different pile types. We measured and obtained the seismic data with various attributes, such as the characteristic image of different probability horizontal seismic action, acceleration and dynamic soil pressure. By analyzing the time-domain characteristics of multi-attribute data such as deformation characteristics and acceleration, we revealed the instability mode of the slope model and the regional response characteristics of particle spatial position. Based on the Fast Fourier Transform (FFT) and Statistical Probability Sperm Matrix (SPSM), we proposed the damage level correlation between the spectral characteristics of acceleration and dynamic soil pressure. We obtained the relationship between the variation of the frequency and specific period between acceleration and dynamic soil pressure at different seismic stages through in-depth study, and then calculated the regional differences of spectrum displacement (Sd) by using Seism Signal. In the frequency domain of acceleration and dynamic soil pressure signals, the predominant frequencies were mostly concentrated in 0.5–8 Hz. Under high seismic acceleration, the amplitude frequency of acceleration spectrum of conventional pile and EPS pile was both 1.51 Hz, and the dominant frequency of dynamic soil pressure was significantly different. There was a positive correlation between seismic acceleration and dynamic soil pressure. The shift of frequency profile and main frequency band of EPS pile was mainly caused by the propagation stage after the acceleration main shock. Under high seismic acceleration, the deformation of EPS pile and conventional pile occurred to some extent. EPS plate was used as the damping layer to buffer and dissipated the deformation of the slope under earthquake, and its effect was linked to the seismic data attributes. The spectral displacement of EPS pile was reduced as a whole was higher than that of conventional pile. The slip surface of pile body was sensitive to earthquake, and it was easy to become the weak seismic link of the EPS pile. These results are helpful for us to provide a theoretical basis for improving the reliability optimization design of dynamic parameters of the pile structure.

Horizontal Pressure Reduction on the Underground Contour of the Structure by Means of a Cut-Off Wall

The article deals with the issue of reducing the horizontal pressure of the ground on the underground walls. The relevance of this issue is stipulated by the need to ensure the strength and operational reliability of the underground part of buildings and structures having a large burial in the foundation. It is important to solve this problem and to ensure the strength of the shallow subway vertical walls. One of the ways to reduce the horizontal ground pressure on the retaining structures is the construction of the cut-off walls. These walls should be located in the zone of expected soil collapse. The simplest way of theoretical solution of this problem is the finite element method (FEM), which cannot be regarded as absolutely reliable because in this situation, we deal with limit equilibrium of soil mass, i.e. with the class of problems for which FEM does not always give guaranteed reliable results even in qualitative terms. Therefore, an additional control in the form of some approved schemes based on obvious, easily verifiable provisions is required. The paper presents a technique for determining the size and position of cut-off walls on the basis of known solutions of the theory of limiting equilibrium of soils. The calculation algorithm is exemplified by an illustrative calculation model.

A sensitivity analysis of factors affecting in geologic CO2 storage in the Ordos Basin and its contribution to carbon neutrality

To accelerate the achievement of China’s carbon neutrality goal and to study the factors affecting the geologic CO2 storage in the Ordos Basin, China’s National Key R&D Programs propose to select the Chang 6 oil reservoir of the Yanchang Formation in the Ordos Basin as the target reservoir to conduct the geologic carbon capture and storage (CCS) of 100000 t per year. By applying the basic theories of disciplines such as seepage mechanics, multiphase fluid mechanics, and computational fluid mechanics and quantifying the amounts of CO2 captured in gas and dissolved forms, this study investigated the effects of seven factors that influence the CO2 storage capacity of reservoirs, namely reservoir porosity, horizontal permeability, temperature, formation stress, the ratio of vertical to horizontal permeability, capillary pressure, and residual gas saturation. The results show that the sensitivity of the factors affecting the gas capture capacity of CO2 decreases in the order of formation stress, temperature, residual gas saturation, horizontal permeability, and porosity. Meanwhile, the sensitivity of the factors affecting the dissolution capture capacity of CO2 decreases in the order of formation stress, residual gas saturation, temperature, horizontal permeability, and porosity. The sensitivity of the influencing factors can serve as the basis for carrying out a reasonable assessment of sites for future CO2 storage areas and for optimizing the design of existing CO2 storage areas. The sensitivity analysis of the influencing factors will provide basic data and technical support for implementing geologic CO2 storage and will assist in improving geologic CO2 storage technologies to achieve China’s carbon neutralization goal.©2022 China Geology Editorial Office.

A Comparison of Shale Gas Fracturing Based on Deep and Shallow Shale Reservoirs in the United States and China

China began to build its national shale gas demonstration area in 2012. The central exploration, drilling, and development technologies for medium and shallow marine shale reservoirs with less than 3,500 m of buried depth in Changning-Weiyuan, Zhaotong, and other regions had matured. In this study, we macroscopically investigated the development history of shale gas in the United States and China and compared the physical and mechanical conditions of deep and shallow reservoirs. The comparative results revealed that the main reasons for the order-ofmagnitude difference between China’s annual shale gas output and the United States could be attributed to three aspects: reservoir buried depth, reservoir physical and mechanical properties, and engineering technology level. The current engineering technology level of China could not meet the requirements of increasing production and reducing costs for deep shale gas reservoirs; they had reached the beneficial threshold development stage and lacked the capacity for large-scale commercial production. We identified several physical and mechanical reasons for this threshold development stage. Deep shale reservoirs were affected by the bedding fracture, low brittleness index, low clay mineral content, and significant areal differences, as well as by the transformation from elasticity to plasticity, difficulty in sanding, and high mechanical and strength parameters. Simultaneously, they were accompanied by six high values of formation temperature, horizontal principal stress difference, pore pressure, fracture pressure, extension pressure, and closure pressure. The key to deep shale gas horizontal well fracturing was to improve the complexity of the hydraulic fracture network, form adequate proppant support of fracture surface, and increase the practical stimulated reservoir volume (SRV), which accompanied visual hydraulic discrete network monitoring. On this basis, we proposed several ideas to improve China’s deep shale gas development involving advanced technology systems, developing tools, and supporting technologies in shale gas exploration and development in the United States. These ideas primarily involved stimulation technologies, such as vertically integrated dessert identification and optimization, horizontal well multistage/multicluster fracturing, staged tools development for horizontal wells, fractures network morphology monitoring by microseismic and distributed optical fiber, shale hydration expansion, soak well, and fracturing fluid flow back. China initially developed the critical technology of horizontal well large-scale and high-strength volume fracturing with a core of “staged fracturing with dense cutting + shorter cluster spacing + fracture reorientation by pitching + forced-sand addition + increasing diameter perforating + proppant combination by high strength and small particle size particles”. We concluded that China should continue to conduct critical research on theories and technical methods of horizontal well fracturing, suitable for domestic deep and ultra-deep marine and marine-continental sedimentary shale, to support and promote the efficient development of shale gas in China in the future. It is essential to balance the relationship between the overall utilization degree of the gas reservoir and associated economic benefits and to localize some essential tools and supporting technologies. These findings can contribute to the flourishing developments of China’s deep shale gas.

Effectiveness of road embankment reinforcement in the light of model tests on a laboratory scale

The subject of the article concerns road embankments made of reinforced soil. The results of the analysis of the effectiveness of the reinforcement of these structures as a function of selected variable factors concerning the soil medium and the parameters of reinforcement inserts are given. The efficiency analysis was carried out on the basis of measurements of the horizontal unit pressure made on a physical model of a soil massif with a vertical wall of reinforced soil. The large-scale model was constructed on a laboratory scale. The article ends with a summary containing conclusions of a cognitive and practical nature.

ГЕОДИНАМИЧЕСКИЕ ПРОЦЕССЫ В СКЛОНЕ ПОДНЯТИЯ

The flow for the uplift slope is considered in the viscous liquid model. The relevance of the study is justified by the need for experimental and theoretical analysis of the geodynamic processes occurring in the slopes of rises. The object of the study is the slopes of rises, formed by mantle thermochemical plumes which have not come to the surface. The objectives of the study are to present the velocity profile of the viscous flow of the uplift slope and to determine the friction coefficient for it; to find out the effect of the dynamic viscosity coefficient of the slope on the appearance of compressive and tensile stresses; on the basis of laboratory and theoretical simulations to find out the hydrodynamics of the flow when the liquid flows from a rectangular vessel and using the results of geodynamic simulations to determine the flow parameters in the area of the uplift slope fault formation. The flow occurring in a viscous liquid at a constant inclination angle of the free surface of the elevation slope is considered. In a highly viscous liquid at low flow velocities, the inertial terms in the equation of motion can be neglected. For this case, the solution of the equation of motion in a layer with an inclined free surface at a constant horizontal pressure gradient is obtained. The flow velocity profile in such a layer and the relation for the maximum flow velocity are obtained. The tangential stress on the sole of the layer is determined. The tangential stress does not depend on the viscosity, but depends on the layer thickness. With a constant viscosity of the layer, the elevation slope is under conditions of compressive stresses. Strain conditions for the uplift slope are possible when the viscosity of the layer decreases with distance from the main ridge. Discontinuities occur on the elevation slopes due to changes in viscosity along the slope and changes in the velocity. Under the influence of gravitational forces caused by the density difference at the rupture boundary, flow occurs and the resulting free volume is filled. The motion in a highly viscous liquid during the formation of a free vertical surface has been studied experimentally when liquid flows out of a transparent rectangular vessel. Photographs of the free surface were obtained. A linear dependence of the relative height of the free surface location on the relative horizontal coordinate is observed. Expressions are obtained for the average velocity and expiration time of a viscous liquid from a rectangular vessel. Estimates of the average velocity and outflow time for the specified slope parameters are presented

Horizontal Wave Pressures on the Crown Wall of Rubble Mound Breakwater under Non-Breaking Condition

The crown wall with parapet on top of the rubble mound breakwater represents a relatively economic and efficient solution to reduce the wave overtopping discharge. However, the inclusion of parapet leads to increased wave pressure on the crown wall. The wave pressure on the crown wall is investigated by physical model test. To design the crown wall the wave loads should be available, and the horizontal wave pressure is still unclear. Regarding to the horizontal wave pressure on the crown wall, a series of experiments were conducted by changing the rubble mound type structure and the wave conditions. Based on these results, pressure modification factors of Goda’s (1974, 2010) formula have been suggested, which can be applicable for the practical design of the crown wall of the rubble-mound breakwater covered by tetrapods.

Numerical simulation of influence parameters on induced stresses distribution during first weighting process of longwall mining

Investigation of first weighting process due to greater caving span and higher induced stresses when compared to the periodic ones is imperative in the planning stage of a longwall coal mining project. Hence, a reliable prediction of caving span and abutment pressure during this process has major role in stability analysis of operation. This paper presents the results of numerical simulation intended to examine stress distribution in terms of peak abutment pressures during first weighting process in longwall mining. Longwall mining was simulated by incorporating Universal Distinct Element Code (UDEC) to investigate the effects of five critical parameters included roof strata uniaxial compressive strength, immediate roof height, spacing of bedding planes and mining depth and in-situ stresses ratio on vertical and horizontal peak abutment pressures. The results showed that relationships between all critical parameters with the exception of in-situ stresses ratio and front and rear abutment pressures in vertical and horizontal directions are the same. In addition, it was concluded that all parameters have a direct relationship with the rear and front abutment pressures whereas this relationship is indirect for the immediate roof height and the extraction height.

On the assessment of non-metallic inclusions by part 13 of API 579 -1/ASME FFS-1 2016

Improvement of nondestructive inspection techniques has allowed more frequent detection of closely spaced zones of non-metallic inclusions in pressure vessels made of low carbon steel. In the present study, closely spaced inclusions in an in-service cylindrical horizontal pressure vessel were detected by Scan-C ultrasonic inspection and considered as laminations to be assessed by Part 13 of the API 579-1/ASME FFS-1 2016 standard. The outcoming results were considered as a rejection for Level 1 assessment, and a repair or replacement of the component was required, even though it retained a significant remaining strength. Thus, an alternative procedure to assess the mechanical integrity of pressure vessels containing zones of non-metallic inclusions is proposed by adopting some criteria of the API 579-1/ASME FFS-1 Part 13 standard procedure and taking into consideration the dimensions and grouping characteristics of the inclusion zones.

Why Do some Labour Alliances Succeed in Politicizing Europe across Borders? A Comparison of the Right2Water and Fair Transport European Citizens' Initiatives.

Under what conditions can organized labour successfully politicize the European integration process across borders? To answer this question, we compare the European Citizens' Initiatives (ECIs) of two European trade union federations: EPSU's successful Right2Water ECI and ETF's unsuccessful Fair Transport ECI. Our comparison reveals that actor‐centred factors matter – namely, unions' ability to create broad coalitions. Successful transnational labour campaigns, however, also depend on structural conditions, namely, the prevailing mode of EU integration pressures faced by unions at a given time. Whereas the Right2Water ECI pre‐emptively countered commodification attempts by the European Commission in water services, the Fair Transport ECI attempted to ensure fair working conditions after most of the transport sector had been liberalized. Vertical EU integration attempts that commodify public services are thus more likely to generate successful transnational counter‐movements than the horizontal integration pressures on wages and working conditions that followed earlier successful EU liberalization drives.

Development of swelling induced shear and slickensides in Vertisols

Vertisols shrink and crack as they dry, and swell as they wet. Shear surfaces, sometimes called slickensides, are often observed within the profile of such clay soils. A hypothesis for the appearance of these surfaces is in reaction to lateral swelling forces that induce shear within the soil mass. No direct proof supporting this hypothesis is found in the literature.Test data presented verify the development of lateral soil swelling pressure in response to wetting of a compacted clay soil. The data illustrate that the swell induced pressure can cause the soil to reach failure conditions and in essence, shear itself.During wetting, laboratory compacted specimens of clay were subjected to constant vertical pressure and allowed to swell in the vertical direction. Strain in the lateral direction was restrained and the horizontal soil pressures monitored as they approached a residual magnitude. From the series of tests it was found that the ratio between the residual horizontal swell pressure to the applied vertical pressure decreased monotonously with increase of applied vertical pressure.Mohr's circles representing the state of stress within the specimen at the residual state align along the Mohr-Coulomb failure envelope for tests performed at vertical pressures of 4 kPa through 27 kPa.These results provide credence to the hypothesis that slickensides are formed due to internal shear of the clay, and as such are expected to form at limited depths.