آزمایش برش مستقیم

The use of FRP composites as an effective method for strengthening reinforced concrete structures has been a subject of research due to its numerous benefits. A common failure mode in the application of these composites is the debonding of the FRP sheet from the concrete surface, which can sometimes reduce the capacity of these composites to as low as 10% of their total capacity. As a result, researchers have begun to prestress the FRP sheets and strengthen them with prestressed FRP to optimize the efficiency of these materials. A crucial aspect in the strengthening of a reinforced concrete member with an FRP sheet is the examination of the connection behavior between the FRP sheet and concrete. The significance of this issue has led to dedicated research and experimentation in this field. In this study, a prestress-lab shear test was employed for the first time to investigate the bond behavior of prestressed FRP composites-to-concrete joints. Additionally, the particle image velocimetry (PIV) method was used for result analysis. To verify the effectiveness of this method, eight tests were conducted on prism specimens measuring 150×150×350 mm. The strengthening methods of the specimens involved the use of external bonded reinforcement (EBR) and external bonded reinforcement on grooves (EBROG) methods. Furthermore, the specimens were prestressed at different levels, including 0%, 20%, and 30% of the ultimate strain of FRP composites. This study examined the specimens in terms of bond strength capacity, failure mode, and stress and strain distribution on the joint surface. The results showed that prestressing increased the bond strength by 70% in the EBR method. Moreover, the bond strength of the EBROG specimen with 20% prestressing increased by 123% compared to the control specimen. These findings indicate that prestressing using the EBROG method is a viable technique for enhancing the performance of FRP-to-concrete joints.

Mobilized shear strength in the interaction between various materials such as sand and steel plays a crucial role in geotechnical applications, particularly in the design and performance of friction piles. This study presents an innovative approach through polymer injection to enhance the mobilized shear strength between the pile and soil. To investigate this idea, a series of direct shear tests were conducted under three values of vertical stresses on both smooth and rough surfaces. Parameters such as the amount of inject-ed polymer, curing time, and the roughness of the steel surface were examined. The test results indicate that polymer injection significantly increases the mobilized shear strength at the sand- steel interface, even after a short period of about one-hour post-injection. An increase in the amount of injected polymer from 0% to 20% resulted in a nonlinear increase in shear strength. The test results show a remarkable increase in shear strength on smooth surfaces after injection compared to rough surfaces. Additionally, with more time, the mobilized shear strength also increased. Microscopic images of the injected area in the sand demonstrate the bonds formed between the grains by the polymer, which ultimately improves the injected soil.

Shear banding is one of the most significant behavioral characteristics of granular soils, which is actually the result of localization of deformations under loads applied to the soil sample. Many studies have been conducted on the phenomenon of shear band formation. However, the comparison of the behavior of soil inside and outside the shear band has received less attention. The purpose of this study is to compare the behavior of soil inside and outside the shear band in the direct shear test at macro and micro scales using the two-dimensional discrete element method. To achieve this, the micro-material parameters were first calibrated through the comparison of simulation and experimental results. Then a parametric study was conducted by performing 9 direct shear tests with different vertical stresses on three soil samples with different relative densities. During the tests, quantities such as shear stress, porosity, particle rotation, coordination number, and interparticle plastic energy were measured both inside and outside the shear band. The results of the present study showed that the particle rotations at the end of the test inside the shear band were 5 to 17 times higher than those outside the shear band. Furthermore, the results showed that the dissipated energies at the end of the test inside the shear band were 12 to 96 times larger than those outside the shear band. Moreover, it was found that the coordination numbers at the end of the test inside the shear band were on average 3-19% lesser than those outside it.

In recent years, the use of embankment dams with asphalt concrete cores has become more popular in comparing with clay core dams owing to its implementation restrictions. Because in this type of dams, asphalt materials form the core of the dam and granular materials are used as a filter around the asphalt core. Therefore, investigation of behavior at the contact surface between these materials is of great importance. In this research, using large-scale direct shear experiment and applying vertical stresses of 1, 3 and 5 kg /〖cm〗^2 in both dry and saturated states, the mechanical behavior at the contact surface of asphalt materials and gravel filters has been investigated. The effect of parameters such as material density, gravel grain shape and bitumen type has been investigated. The results showed that the shear strength at the contact surface of the materials decreases with increasing the moisture content. Changing the shape of the filter material grains to the angular increased the shear strength of the contact surface and the ratio of maximum stress to residual stress at the contact surface for dry and saturated states with different relative densities showed that this ratio increased very little at low densities

Due to the growth of energy consumption, air pollution and global warming in the world, the use of renewable energy has become popular in the world due to its variety of resources, lower economic cost and environmental compatibility. One of the unlimited sources of renewable energy, is geothermal energy. Since geothermal energy resources are unlimited and can be exploit in many parts of the world, its application as a reliable source of energy is growing. The use of energy piles as a heat exchanger is one way to exploit this energy. These piles are being used to serve dual purposes transfer the structural load to the ground and act as heat exchanger elements to extract and inject heat from and to the ground. Energy piles are subjected to daily and seasonal cyclic temperature changes during their life span. These temperature changes (heat cycle) induce cyclic expansion-contraction along the pile-soil interface that may affect interface properties such as shear strength. The pile-soil interface is defined as a thin zone of soil that can be subjected to different boundary conditions with respect to the surrounding soil. Therefore, in order to investigate the influences of temperature on soil-pile interface, a series of direct shear tests is modeled in ABAQUS software. In this modeling the shear strength changes of Illite clay and concrete interface, are investigated under mechanical and thermo-mechanical loading. A series of analysis are conducted with sample temperature of 50 and the normal stresses of the direct shear analysis are 50, 100 and 150 kPa. This analysis is done at a shearing rate of 0.006 mm/min. In this investigation, it is assumed that the properties of concrete materials are not temperature dependent and their behavior is thermoelastic. In this paper, the main results of modeling show that the shear strength of Illite clay-concrete interface, increases by an average of 20 kPa with increasing in temperature by 50 .

In the present study, effect of natural cementation on the shearing behavior of carbonate sand of Khark Island, south of Iran, has been investigated. To do so, a pseudo-natural cementation method was employed. The importance of this technique lies in its suitability as a substitute for undisturbed samples of cemented carbonate soil that are hard and costly to prepare. Uncemented and cemented samples provided by this method were tested using direct shear apparatus and the results were analyzed and compared to one another. Furthermore, effects of factors such as curing time and relative compaction on the shearing behavior of the Khark sand were studied. It was observed that cementation results in the rise of the shearing resistance, in particular at high vertical stresses, and leads to a decline in the tendency of soil to dilation. While cementation led to growth in the internal friction angle of soil, it may cause increase, decrease or no change in the cohesion of the Khark sand. Increase in curing time led to considerable rise in the cohesion and minor change in the internal friction angle of the cemented soil. Furthermore, results showed that as the relative compaction of the investigated cemented carbonate soil goes up, the cohesion of the soil might increase, decline or stay unchanged while the internal friction angle always increases. Factors that are likely to contribute to the development of the behavior stated earlier were introduced and their effects were discussed thoroughly.

In the last few decades, due to the increasing use of geosynthetic reinforcements in reinforcing the soil, researchers have considered the significance of the behavior of the soil-geosynthetic interface. On the other hand, the use of geofoams in the form of block and/or bead due to a decrease in the weight of the soil mass behind the retaining structures has attracted the designers’ attention. In this regard, the current research was carried out to determine the interaction parameters of soil containing geofoam beads and geosynthetic reinforcements. For this purpose, a large-scale direct shear apparatus with box dimensions of 304.8*304.8*152 mm was used. The used soil was a mixture of Firoozkooh sand (#. 161) and geofoam beads with a diameter of 2 mm and the geofoam mix percentages were selected as 0.2, 0.4, and 0.6 percent by weight of the soil. Also, the reinforcements used in this research included geogrid, geotextile, and geocomposite; accordingly, further analysis and comparison of the obtained results could be possible. According to the results, in the sand-geofoam mixtures reinforced by geosynthetics, upon an increase in the mix percentage of geofoam, shear strength amounts decreased. Also, in these mixtures, the greatest increase in bearing capacity compared to the corresponding unreinforced mixtures was obtained for the samples reinforced with geogrid and also, for samples reinforced with geocomposite and geotextile, respectively. In general, based on the reinforcement type and geofoam mix percentage, an increase in the bearing capacity of the reinforced mixtures with respect to unreinforced mixtures was about 12% to 135%. By increasing the mix percentage of geofoam from 0.2 to 0.6, the amount of this increase was reduced. In the sand-geofoam mixtures reinforced by geosynthetics, the highest value of the interaction coefficient was obtained in the samples reinforced by geogrid, geocomposite, and geotextile, respectively. In the sand-geofoam mixtures reinforced by geogrid, the highest value of the interaction coefficient was observed in the geofoam of 0.4% and then, in the geofoam of 0.2%‌.

Petroleum contamination in soils induced by oil products such as crude oil, gasoline, and motor oil is an issue raised widely in oil-rich countries like Iran. Contaminated soil with oil products is considered as a common environmental problem, but under the physical-chemical processes that occurred between these contaminants and soil, new geotechnical behavior is expected, which can reduce the soil bearing capacity, change the soil strength parameters and vary engineering and geotechnical properties of soil. Once the leakage occurs, resulted by self-gravity, the oil flows towards the groundwater level, which will cause soil-saturation with this hydrocarbon liquid. In spite of this, lateral propagation of the liquid may result in a wider scale of contamination. Oil pollution near the shore, contaminates the soil across the entire coastline. In this case, to account for the pollution of soil, regarding the environmental conditions, soil type, and type of contaminants the geotechnical properties are revised. The largest oil contamination in soil occurred in recent decades due to the Persian Gulf war in Kuwait, where a volume of 9 million cubic meters of soil in 19.05 million square meters was contaminated to oil; about 69 lakes were created to gather the diffused crude oil. Another case is the destruction of tanks of the refinery of Tehran and Abadan in the war between Iran and Iraq, which caused intense oil-pollution.

With increasing urban population, the need for underground spaces increases and deep excavation is an inevitable affair in civil projects. deep tunnels and large buildings require deep excavations, which is a must use some techniques for stabilize it. grouted soil nail is a popular reinforcement to stabilize slopes, excavations and retaining walls. This method has been introduced to Hong Kong in the mid-1980s and has become an alternative solution to the conventional slope stabilizing methods such as compaction, earth retaining structure, or reduced inclination of the slope, etc. this method is based on sewing the potential failure wedge of soil on the stable soil using some inactive (un-prestressed) elements. the shear strength-displacement behavior at the interface between the grouted nail and surrounding soil is an important parameter in design of various geotechnical engineering projects, for example, soil nails, retaining walls, shallow foundations, pile foundations, etc. in soil nail system, the most common method to measure the interface shear strength is pullout test. It is also possible to determine the interface strength based on the development of resistance between soil and grout in direct shear tests. However, accurate perception of the shear behavior in the connection area of the soil and grout is essential to reach an optimum design. In other words, the interaction between soil and grouted nail is necessary to design an optimum soil nail system. the most common method for determination grouted soil interface resistance is pullout test but there is another experiment that can yield acceptable results. The current study investigates the interface shear behavior between cement-grout and granular soil in direct shear test with different grout pressures ( up to bar) and different overburden pressures ( up to 300 kPa). For this purpose, a number of direct shear tests are performed by modifying of the standard shear box for injection of grout. “Firozkooh” sand is used in this study. The soil is compacted to the relative density of % and the slurry is sprayed with pressure on its surface. Furthermore, results of two pullout tests were used for verification. These pullout test have already been presented in another study with different normal stress and grout pressure. it is shown that the results of direct shear test and pullout test at interface are similar. this may indicate the proper function of direct shear test as a suitable choice alongside pullout test. It was observed that shear stress–displacement curves of the soil-grout interface in direct shear tests are similar to the soil-soil tests; which are classified under different grouting pressures. In addition, increasing grout pressure increases shear strength by increasing the angle of friction and bonding of soil and slurry. The effect of adhesion is dominant. it is shown that The interface shear stress under different grouting pressures is greater than the shear stress of soil under the same normal stresses. it is shown that grouting pressure and normal stress have influence on the behavior of soil-cement interface. Therefore, interface shear strength increases with increase in overburden and injection pressure. The variation of the interface shear strength is approximately linear versus grouting pressure. Finally, a formula is proposed for interface shear strength considering grouting pressure.

Soil stabilization is an effective mechanical method for soil rehabilitation against applied loads. In recent years, synthetic fibers have been introduced as a novel technique for soil stabilization. Therefore, it is essential to assess the behavior of fiber-reinforced soils. In this study, the behavior of synthetic fiber-stabilized soil was investigated using laboratory tests. Direct shear experiments were performed on the specimens reinforced with glass and polypropylene fibers, 12 mm in length. The tested specimens were reinforced with random distribution of 0.05, 0.1, 0.2 and 0.5% of synthetic fibers. The direct shear experiments were performed under different vertical stresses. The tests results indicate that the addition of synthetic fibers improves the maximum shear strength of the tested soil samples. Reinforced samples with 0.1% fibers have the highest shear strength of tested soil. Also, the results indicate that under identical conditions, specimens reinforced with polypropylene fibers have higher shear strength than glass fiber-reinforced specimens.

Coastal sandy soils cover a large part of the soil of northern part of the country. These soils will have problems due to loose characteristic and lack of proper strength properties for roads building. Beach sand is encountered with the wash-out phenomenon due to uniform gradation and lack of cohesion at the time of the water flow in an unconfined state. To solve the problem of these soils, various methods such as reinforcement with different materials are used. In this research, the effect of adding various percentages of polypropylene fibers to non-cemented and cemented sand on the mechanical characteristics of sandy soils of Babolsar beach was investigated by performing direct shear tests and triaxial tests. According to the results, adding these fibers improves the internal friction angle, cohesion, maximum strength, Failure strain and residual strength of sand. Comparison of the results of direct shear tests and triaxial tests showed that, due to the proper orientation of the fibers relative to the direction of main tensile strains in triaxial tests, the efficiency and their effect on the soil resistance behavior in triaxial samples were more significant than direct shear tests.    

It has been of great interest among the researchers to investigate the behavior of soil_geogrid interface. Due to the wide use of geogrids between different layers of soil; these investigations are very important. This paper shows the results of experimental tests on soil_geogrid interface. This study conducts a series of large scale direct shear tests to investigate the interface shear strength of granular soil with various degrees of compaction and various sizes of geogrid apertures. The shear stress versus shear displacement curves and peak shear strength are important for evaluating the results. The interactions between soil and geogrid may include the following mechanisms: 1) shear resistance between soil and the surface of the geogrids; 2) internal shear resistance of the soil in the opening area; and 3) passive resistance of the transverse ribs. The value of α was defined to evaluate the effect of geogrid on the shear strength of the soil which is the ratio of geogrid_soil shear strength to internal shear strength of soil. The results showed that a larger degree of compaction reduces the resistance in soil_geogrid interface and shear strength of soil_geogrid interface will be reduced further by reducing the distances of transverse ribs of geogrid.

Since its simplicity and availability, direct shear test is a current one. This test, compared to the triaxial test, provides different values for the parameters of the gravel due to the specific shape of the test device and the test approach. Triaxial testing, due to the feasibility of providing conditions similar to the natural behavior of gravel in a natural state, can provide more realistic values of material strength parameters. Due to being time consuming, costliness, problems in performing a triaxial test and the difficulty of sample preparation, direct shear test is still used more than triaxial test. In this paper, by studying the results of direct shear test and triangular experiments on gravel material, the stress paths in p - q space and the internal friction angle of these two tests are compared and the relation between them is obtained. To ensure the obtained results, large-scale triaxial and direct shear tests are used. The values of φ, τf and бn are calculated in every direct shear test, and using different lateral pressure coefficients (k), the failure points in the space p and q are obtained. Using the points, failure envelope is depicted in these graphs and then, using the relationships, the gradient of the failure envelope is converted to the friction angle of the sample; and, it is compared with the triaxial test results. Subsequently, the stress path is studied via the results, and it is compared with the stress path of the triaxial test. Finally, it can be concluded that, when the internal friction angle of the gravel in direct shear test is analyzed via lateral pressure coefficient (kp), it is approximately the same with the internal friction angle obtained by the triaxial test in p- q space.

In this study, the fine weak materials replaced with different percentages of coarse aggregate to provide the best resistance and load capacity for heavy construction in the area. For this purpose, by using the Taguchi method and taking four classes of materials, different mixing of the materials were determined, and large scale samples with dimensions 30×30cm with the new material compounds was obtained and they were tested. By cooperating neural networks and artificial intelligence the most suitable mix designs and best resistance value determined.

Soil improvement a method is used for increasing bearing capacity of materials applied in pavement layers. Stabilization generally performed based on two methods chemically and mechanically. Currently geosynthetic materials are used for soil improvement in retaining walls and earth fall. The application of geogrid layers is one of the effective method in many engineering projects and pavement design for soil improvement. Increase of clay or silt content in sand in various percent can basically change geotechnical behavior of mixture. Main aim of this research is experimental study of georid layers locating and number of them effects on bearing capacity and shear strength of sandy and clayey soils from Barandouz area. In this study sandy soil mixed with clay in 25, 50 and 75%. The effect of geogrids on geotechnical properties of specimens studied in two positions: first a geogrid embedded in the middle of materials and second two geogrids by equal depth from each other used in soils. For evaluating geotechnical behavior of sand-clay mixtures California bearing ratio (CBR) and Direct shear tests performed based on ASTM in both dry and saturate conditions. Also, percent of swelling in fines content saturated soils assessed. Results showed that in unreinforced specimens with increasing fines content in bearing capacity and geotechnical properties decreased. Then, with embed a geogrid layer in middle part of specimens compared to two geogrid layers value of sand skeleton void ratio decreased and maximum dry unit weight increased and at that time bearing capacity and shear strength of materials in both dry and saturate condition improved. Also, swelling percent of fines content soils with embed a geogrid layer significantly as compared to an unreinforced decreased. Therefore, it is recommended application of one geogrid layer in sand-clay mixtures is optimum for design subgrade and sub base layers in pavement.

Population and civil infrastructure continue to expand at unprecedented rates. On the one hand, the growing needs for the development and, on the other hand, the environmental crisis, stress the importance of finding methods not harming the environment while they are able to meet the requirements for development. Infrastructure demands are even more severe in other countries, particularly in developing ones. Infrastructure is insufficient in countries such as China, where 10 million people immigrate to major cities each year. Population growth is particularly acute for historic cities and regions where expansion is limited by geographical boundaries and inadequate soil conditions. The confluence of these factors necessitates the exploration and development of new alternative soil improvement methods and associated reliable monitoring techniques. Bio-mediated soil improvement is an innovative, and interdisciplinary technique with the approach of being environmentally friendly, which utilizes some bacteria utilizing some bacteria to precipitate calcite on soil particles. In addition, this system broadly refers to a chemical reaction network that is managed and controlled within soil through biological activity and whose byproducts alter the engineering properties of soil. Therefore, Microbial carbonate precipitation (MCP) has experienced an increased level of interest in recent years for applications such as restoration of calcareous stone materials , bioremediation, wastewater treatment, strengthening of concrete and selective plugging for enhanced oil recovery. In this research, to attain the highest number of experiments without repeating the unnecessary ones, Taguchi design method was utilized. The Taguchi method was developed to improve the implementation of total quality control. The effect of factors on characteristic properties (response) and the optimal conditions of factors can be determined using the Taguchi design. It is feasible to find out the optimal experimental conditions with the least variability. Taguchi analysis is based on choosing the best run by analyzing signal-to-noise ratio (S/N), whose form depends on the experiment objective. A standard L9 orthogonal array with four parameters consisting of bacterial cell concentration, molar concentration ratio of nutrient solution, curing time, and inoculum ratio, each was assigned three levels, was selected. In this regard, soil samples were stabilized in sandy soil columns. Two-phase stabilization were conducted by adding the bacterium Sporosarcina pasteurii PTCC 1642 in the first phase and nutrient in the second phase. Specimens were subjected to direct shear stress test with the normal stress of 12.5, 40, 68 kPa. ANOVA suggested that the effect of each parameter on the direct shear stress. The most effective parameter was curing time with 45.97% of the overall variance of the experimental data followed by bacterial cell concentration (22%), molar concentration ratio of nutrient solution (20%), and inoculum ratio (12%). The direct shear strength increased from 6, 18, 31 kPa for the normal stress of 12.5, 40, 68 kPa to 470, 491, 512 kPa in optimally treated specimens.

The bearing capacity of piles shaft and stability of retaining walls and reinforced soil structures depend on the behavior of soil-structure interfaces. Using direct shear apparatus، behavior of a sand with fine angular grains was studied. Steel plates with two surface roughness values were separately embedded at the lower half of the shear box and consequently، the upper half was filled with dense or loose sand. Then، the behavior of interfaces forming between dense/loose sand and rough/medium rough steel plates was studied. Tests show that the shear strength and dilation in sand-structure interfaces are significantly less than the corresponding values for sand. In this regard، the peak friction angle of rough steel plate in contact with dense and loose samples is، respectively، about 40 and 25 percent less than those of dense and loose sand. In a similar fashion، the peak friction angle of medium rough steel plate in contact with dense and loose samples is about 60 and 45 percent less than those in dense and loose sand، respectively.

There are some kinds of soils in nature which show a significant decrease in volume by increasing the humidity percentage under a fixed pressure.these solis are called collapsible soils. Collapsible soil shows a noticeable decrease in its volume with an increase in its moisture content under fixed stress. This decrease in
volume causes irreversible damages to any structures on collapsible soil and the ones which are under construction. The study of the behavioral characteristics of collapsible soil and its stabilization is crucial. The main purpose of this study is stabilizing collapsible soil and increasing shear strength by adding E.M. Super Repair with different combinations. A sample was collected from Hamidiyeh region near Ahvaz. The primary geotechnical tests were done on the sample. Then shear strength parameters were determined by adding E.M. Super Repair with different combinations. The results show this substance improve the shear strength parameters. The most shear strength has been observed in 1% combination.

One of the most important geotechnical issues is problematic soils (dispersive soils, expansive soils, collapsing soils, liquefying soils, soluble soils …) which may affect the constructing projects on these soils and may even cancel them [1]. In this research collapsing soils are studied. A sudden collapse of the land is called collapsing. It is because the strength of the bonding among soil particles no longer exists. Studies have shown the of these soils structure need to be improved before constructing any structures on them [2]. Improvement of these soils with various substances leads to different results. The effect of Polyurethane B with different combination percentages (0.5, 1, 1.5, 2, 3 and 5 weight percentage) on improving the structure of these soils were examined. Polyurethane B is one of the most common elastomerics in engineering which has numerous uses. It has unique characteristics such as high mechanical and wear resistance, flexibility in low temperature, high cutting potential and elasticity and resistance to absorbing water, oils and solvents. The most significant feature of these polymers is that a fixed structure is obtained after reaction. In this research, direct shear test was used with stress control. Vertical pressures of 54.5, 109 and 218 Kilopascals were applied out on specimens. In order to determine the collapsing rate, ASTM D 5333-03 standard criteria were used [3]. The sample was collected from Hamidiyeh Region near Ahvaz city. Atterberg limits, simple shear test and collapsible index experiments were carried out on the specimen to determine some of the physical and geotechnical features of the soil. The results are shown in Table 1. Collapsing tests revealed that by increasing the percentage of additive substance, collapsing index decreases. The value of collapsing index for 0.5, 1, 1.5, 2, 3 and 5 combination percentages were 45%, 58%, 75%, 86% and 92%. After conducting the direct shear test on the soil which was combined with Polyurethane B, it was concluded that the most shear strength can be obtained in 1% combination percentage. In this combination, the value of adhesion and angle of internal friction were increased 27% and 3%, respectively.

In modern times, the necessity of tunnel construction is inevitable with regards, to the development of the transportation industry, and as a result it is very important to analyse its stability while it is adjacent to some geologic features, such as discontinuities. The direct shear test is one of the most applicable geotechnical tests to investigate geological features such as joints and discontinuities. The dilation and shear behaviour of two sliding surface can be analysed with this test, and in this paper, a constant strain joint element has been presented and a combination of a slider and a shear spring have been applied to this joint element to model the plastic shear behaviour of the joint in contrast to previous joint models. Then, the direct shear test has been programmed based on the finite element method in MATLAB. Subsequently, the joint behaviour has been analysed with an increasing normal stress with various shear stiff¬ness values and JRC (Joint Roughness Coefficient). The results of this numerical study demonstrate that the shear displacements reduce with an increase in shear stiffness, and consequently the dilation decreases as well. Meanwhile, by increasing the normal stress, the joint experiences more dilation in spite of a reduction in the rate of increasing the dilation. Moreover, the peak shear stress and shear strength of the joint have been increased as the JRC increases, but the effect of the normal stress on the shear strength increases with greater significance than with the JRC. Also, the increase in JRC has a direct relationship with dilation increase in the joint.