جستجوی مقالات مرتبط با کلیدواژه « مسلح سازی خاک » در نشریات گروه « آب و خاک »

Soil improvement using plant roots has been considered by many researchers in order to strengthen soil mass in terms of environmental protection and natural resources.The effect of plant root system on soil resilience is a function of the biotechnical properties of roots But due to the complex interactions between soil and plant, the impact of root reclamation on soils remains a challenge.This study investigates the effect of alfalfa root density on soil consolidation in Pazannan region in Khuzestan province

In this study, for the first time, the effect of alfalfa root system was investigated on soil resilience in greenhouse conditions. Soil samples taken from the study area after a period of 5 months under greenhouse cultivation, 3 rootless soil samples and 12 soil samples with different root densities were tested for direct cutting to measure the shear strength of soil composition and roots And the parameters of internal friction angle and adhesion of root-reinforced soil were obtained and compared with rootless soil samples.

In general, the density and number of roots has been reduced with increasing depth, and also the root density index decreases with the depth increases.Using these results and direct cutting tests   was calculated the amount of armament.The presence of roots has created a significant resistance to soil shear strength, which has been affected by increasing the amount of soil adhesion.In contrast, the internal friction angle of reinforced soil decreases with respect to the rootless soil and has the opposite behavior of the adhesion factor.And its changes are much less than the changes of the adhesion factor.Therefore, it can be known that increasing the shear strength of soil reinforced with alfalfa root is equivalent to increasing adhesion.

The results of this study show that there is a direct relationship between root density index and soil shear strength. The highest and lowest reinforcement rates for 28 and 5% density index were 87.5% and 7.5% increase in soil adhesion, respectively and there has been a maximum reduction in internal friction angle relative to rootless soil of 5.5%. This study showed that there is a decrease in the relationship between depth and root density index, depth and strength of reinforcement as biotechnological characteristics of alfalfa species.

Changing the morphology of rivers, associated with erosion and sedimentation, has resulted in damaging riverside structures and loss of valuable agricultural lands. This process occurs in long length of rivers, which structural protection is virtually impossible due to high costs. Today, the use of bioengineering techniques (non-structural) is increasingly growing, due to economic and environmental sustainability. Lack of technical knowledge in biological characteristic of plant species is one of the important limitations of the bioengineering techniques in the protection of riversides. The matrix root and soil increase the soil shear resistance. The Wu (1976) model was employed to calculate the increase shear resistance. To apply this model, determination of the root tensile strength is required. The pilot of research was located 12 Km from Darashahr city, inside of Vahdatabad village, on the Seimareh riverbank, Ilam Province, Iran. Six trees (from Tamarix species) were randomly selected on the river bank by a distance about one km. The annual precipitation, temperature, evapotranspiration, relative humidity and wind speed in this region are 442 mm, 20.2 Cₒ, 1874.2 mm, 61.7% , 3.4 m/se and 122 m3/se, respectively. This zone is located in the semi-arid climate. The area of watershed is about 28.5 km2. Circle profile trenching method was employed to obtain characteristics of root system in direction of river flow and the riverbank slope. The trees were selected on the left riverbank. Circular trenches were dug at a distance of half a meter from the tree stem. The maximum depth of each tranches was 1.5 meters. Surface of the trenches were divided into four equal quadrants. To define the quadrants, X-axis was selected in the direction of flow and Y-axis in perpendicular to the river flow. Then, the quadrants were named in trigonometric direction. In this way, the first and second quarters were located on the upslope and the third and fourth quarters on the downslope. As well as, the second and third quarters were located in upstream and the first and fourth quarters in downstream. For testing tensile force, the sample roots were selected from each quadrant. The roots were cut in 20 cm length, and were kept in a solution of 15% alcohol. Before testing, root diameter in three points of the beginning, end and middle were measured. Using the arithmetic average diameter, cross-sectional areas of roots were calculated. Tensile force was applied on roots sample with 10 mm/m velocity. Root tensile strength was calculated through dividing the amount of tensile force at the moment of rupture (on the cross-section of root,) by the area (according to the mean root diameter). Hundred and forty eight root tensile tests were performed. Seventy three percent of them were successful. The main problem in these tests was the root slip and rupture in between the clamps. For the larger dimeter of roots likelihood of slipping is increasing. The minimum and maximum root diameters were tested, which were 1 and 8.2 mm. The minimum and maximum tensile forces were 16.1 and 1063 N. The relationship between the diameter and rupture force was a positive power function. Its coefficient of determination (R2) was equal to 0.92. In other words, by increasing the diameter of the root, the amount of force needed to rupture is increasing. In this way, the minimum and maximum root tensile strength was 6.1 and 44.7 MPa, respectively. The relationship between the diameter and tensile strength can be described as a negative power function. Its coefficient of determination (R2) was equal to 0.39. SPSS software was used for data analysis. Comparing the tensile strength of roots in the upstream and downstream slope and flow, Mann-Whitney and Kruskal-Wallis test were used. The result showed that average root tensile strength was not significantly different on the up and downslope and also by direction of the flow. Although the effect of flow and slope on root's tensile strength was slight, the effect of slope was more than flow. However, the average roots tensile for each tree was significantly different. The root tensile strength values decreased with diameter according to a negative power equation. In conclusion, the results suggest that it is likely the condition of environment and genetic characteristics of trees affects tensile strength. These findings may help to improve the application of soil bioengineering techniques in the protection of riverbanks.

Piping is an erosive process that occurs in hydraulic structures under the influence of upward seepage. Lack of sufficient notice of this phenomenon may seriously affect the stability of hydraulic structures. In this research work the effect of reinforcement soil on the variations of critical hydraulic gradient and seepage force were investigated through experimental tests. Reinforcement of samples was performed by two geo grids with mesh diameters of 6mm (No.1) and 2mm (No.2). One dimensional piping test were carried out on non-reinforced vs. reinforced sandy soil samples, compacted and fabricated through static methods, and in a specially designed apparatus. The results indicated that the critical hydraulic gradient and resistance against seepage force increased by reinforcement of the samples and that the resistance is a function of the number of the geogrid sheets as well as their location. In addition, the results indicated that the effect of the two geo grids is nearly the same for treatment of the soil against piping.

In this research the effect of randomly reinforced soil and soil cement with different percent of cement and fiber and different length of fiber was investigated. Samples were prepared according to the maximum dry unit weight and optimum water content due to the corresponding compaction curves. Compressive and tensile strength were conducted on samples for different curing times. Regression equations were proposed based on the experimental data for prediction of the compressive and tensile strength of reinforced soil and soil cement. Comparison between the model predictions and the experimental results showed that the proposed model can predict the mechanical behavior of reinforced soil and soil cement satisfactory.

Assessing the root system and its tensile strength is necessary for determine the impact of roots in increasing the soil shear strength. The present study aims to investigate effects of slope and flow of riverbank on root system of riparian POPULOYS trees. In a relatively direct interval, 6 riparian POPULOYS trees were chosen on the slope of Simereh riverbank. To assess the root system, the circular profiles trenching method was utilized. The surface around each tree was divided into four quadrants: upper quadrant, lower quadrant, in slope direction and in flow direction. In every quadrant, number and diameter of roots were measured. The obtained results showed that the highest number of roots were in 90-100 cm depth. 59% of Roots, in the slop direction and 53% of roots in flow direction, were located in the top quadrant. Approximately, 97% of roots had up to 20 mm diameter. The greatest difference in the number of roots in upper, lower, in slop direction and in flow direction quadrants, were seen in diameters up to 5 mm. In slope direction, this difference was almost 2.7 times more than the difference seen in flow direction. The average ratio of root cross-section was 0.26%. The obtained results indicate that the root system of riparian POPULOYS trees on the riverbank is asymmetrical.

Root system is effective on increase soil shear strength. This study investigates the root system of Tamarix trees on slope of riverbanks. Five trees (from TAMARIX species) which grow on the river beech were selected in a distance about one km on SAIMEREHRiver in IlamProvince. Circle profile trenching method was employed to obtain characteristics. Results show that the number of roots on upslope is about 22 percent more than downslope. For all diameters, the number of roots in upslope is more than downslope. The average of root diameters on downslope is bigger than upslope. Total root area on upslope is about 27.6 percent more than downslope. It is concluded that root system on riverbank is unsymmetrical and slope has effect on the root system. The number of roots and root area on upslope was more than downslope.

Piping sometimes is occurred due to seepage of water in hydraulic structures. The continuty of this phenomenon decreases the safety or caused the failure of a structure. In this work، experimental tests were carried out on statically compacted natural and randomly reinforced silt sandy soil samples. The randomly reinforced samples were prepared with different lengths and percentages of an artificial fiber. The tests were done in special designed and made apparatus. During the tests، seepage velocity، hydraulic gradient، permeability and seepage force were measured and calculated in different samples and compared with natural soil. The results showed that in the case of randomly reinforced soil، the resistance of soil against piping was increased. in addition، the increasing of the length and percentage of fiber also have important role in improvement of soil.