جستجوی مقالات مرتبط با کلیدواژه « مقاومت فشاری تک محوری » در نشریات گروه « جغرافیا »

Adding lime to increase the geotechnical characteristics of fine-grained soils, to achieve different goals always been done from ancient time. There are many techniques for stabilizing unstable slopes, among them lime treatment is a quick, simple and costeffective operation that can be incorporated into any unstable slopes. Some scientific techniques of soil treatment have been introduced by Bell (1996). The effect of lime on maximum compressive strength were studied by Indraratna (1996). He concluded that the addition of only 2% of lime results in a 50% increase in compressive strength and if this amount increases to the 5% of lime, the increase is doubled. Although lime stabilizes the soil rapidly after the treatment, the mechanical properties and strength of soil change over a long period of time (Bell, 1996; Sivapullaiah, Sridharan, & Ramesh, 2000). Recently a new method has been developed by which lime is injected into soil in the form of saturated solution. As it penetrates into the soil due to the gravity, it improves soil strength through pozzolanic reaction (Davoodi, 2007). Limited studies have been conducted to investigate the suitability of using saturated lime solution in slope stability. Optimum concentrations of lime solution and lime dosage were investigated by Pui Ling (2005) and Pedarla, Chittoori, Puppala, Hoyos, & Saride, (2010). Moreover, it is known by the studies of Khelifa (2010) that the curing time influences the physical properties of soil stabilized by lime, and considerably increases the shear strength of cohesive soils stabilized by lime. This study intends to assess the effect of calcium dosage on uniaxial strength of clayey soils stabilized by saturated lime solution in order to be applied in unstable slope stability and sediment control.
Material and Methods Soil: The clay soil chosen in this study was a fine grain soil, classified as ML–CL in the Unified Soil Classification System, underwent laboratory tests. The soil properties are as follow. Maximum dry mass density of approximately 1.88 g/cm3 at optimum moisture content of approximately 10.9%.The specific gravities of soil, Liquid limit and Plastic Limit were 2.63, 21.64, and 18.92 respectively.
Saturated Lime Solution :The lime used for preparing the saturated lime solution was a commercially available lime typically used for construction purposes. The simple method for preparing the saturated lime solution is to thoroughly stir 5 grams of hydrated lime into one liter of water, allowing the excess to settle; the excess in the bottom will ensure that the solution remains saturated.
Methods Laboratory : tests consisting of compaction and uniaxial strength were conducted on the specimens with a controlled humidity and temperature. Each specimen was compacted at optimum moisture content and maximum dry density and after preparation of specimens, 15 soil samples in five set were placed in saturated lime solution for 48 hours, then they were kept in the controlled chambers for a period of, 3, 7, 28, and 60 days and then mechanical properties were tested. One set for 48 hours only influenced by the water as a representative sample and comparison. By measuring the amount of calcium ions in the sample before and after the treatment, the calcium ion consumption was computed.
It is generally accepted that the penetration of lime solution in clayey based soils readily lead to the pozzolanic reaction that may cause increasing geotechnical characteristics. Different values of calcium consumption in the specimen after the mixture of lime solution with soil specimen showed the evolution of lime consumption with curing time. The Initial consumption of lime can be used as an indication of the minimum quantity of lime that must be added to the soil in order to achieve a significant change in soil properties in short time. In this study, determination of this minimum percentage of lime is based on measurement of calcium ion concentration in soils before and after solution affect. Average calcium consumption for short term treatment (3 day) was found 27 milligram per liter, for 7 day 34 milligram per liter, 28 days curing period 45 milligrams per liter and for 60 days curing period also 45 were found. This demonstrates that there is no important effect of lime addition after 28 days and it also demonstrates the minimum lime consumption for short term soil improvement. Uniaxial strength of specimens with 3 days curing time increased by 180% compared to the control sample. With increased calcium consumption and pozzolanic reactions, the permeability of the samples also showed a downward trend. This is due to the decrease in porosity and is due to pozzolanic reactions.
By comparing the results of the absorption of calcium in the treated samples and the relationships between them as well as the relationship between the curing time and strength of the samples, it was concluded that the minimum and maximum lime needed to increase the mechanical properties of soil resistance can be calculated. Also it was concluded that the most effective curing time for injection and increasing the mechanical properties of the soils with saturated lime solution is 28 days. This study has led to the valuable insights regarding the treatment of the soil by saturated lime solution in order to sediment and landslide control.

Unconfined compressive strength of rocks is one of the most important parameters in projects related to engineering geology, mining, geotechnics and rock engineering. For determination the unconfined compressive strength in laboratory tests, high-quality samples are necessary. However, such core samples cannot always be obtained from weak, thinly bedded and block-in-matrix rocks. For this reason, the development of predictive models for determination the mechanical properties of rocks such as unconfined compressive strength, seems to be an attractive study area in rock engineering. In this paper, fuzzy and statistical models were utilized to predict unconfined compressive strength of rocks based on data from the access tunnel in longwall mining. A total of 93 datasets of different rocks was used to develop the fuzzy and statistical models, from which, 75 datasets were considered for model construction and the rest was used for testing the models. Three parameters including Schmidth hardness, density and porosity were considered as input parameters. For evaluation of model performance, Root Mean Square Error (RMSE) and determination coefficient (R2) indices were used. For the fuzzy and statistical models, R2 equal to 94.3% and 87.9 and RMSE equal to 3.2 and 6.8, respectively. The results show that fuzzy model is significantly accurate comparing to the statistical model and its results are quite close to the actual values. Also, fuzzy model sensitivity analysis showed that Schmidth hardness is the most effective parameter on the unconfined compressive strength, whereas porosity is the least effective in this study.

Introduction Geomorphological Landforms and processes are of the most significant parameters that affect the volume, distribution and quality of construction materials especially aggregates. Some geomorphological landforms like river beds, river terraces, alluvial fans and taluses have large amounts of weathered rocks and sediments that are appropriate for aggregate exploitation. Geomorphological processes like physical and chemical weathering also affect the quality of aggregates. Aggregates, a type of construction materials, are produced from sand and gravel and weathered bedrock that can be used for concrete, road pavement and other construction purposes. These materials have been weathered, detached from the parent rocks, transported and finally deposited in geomorphological landforms. Study area, Khoramabad catchment in north of town of Khoramabad with a drainage area of 442.19 km2, is part of Zagros Folded Belt. The aim of this research is to evaluate the effect of geomorphological processes and landforms in the formation, distribution and quality of aggregates. Methodology The purpose of this research is to evaluate the effect of geomorphological landforms in the distribution of aggregate and to assess the effect of geomorphological processes in the quality of aggregates. To achieve the purpose of this study, at first, Geologic map of the study area at a scale of 1:250000 and the topographic maps at a scale of 1:50000 from Iranian National Geography Organization top sheets were used to derive lithology and DEM of study area. Geomorphological landforms and processes were recognized by Quick bird satellite images. Precise field works and observations also have been carried out for the identification of landforms and processes. To study the quality and strength of study area aggregates, resistance to abrasion (Los Angeles test), uniaxial compressive strength and Impact Value of aggregates have been done. To determine the aggregate resistance to abrasion, Los Angles test (based on National Standard number 448) of 2 samples (30 kilograms for each sample) of aggregates in old and new river beds was performed. Uniaxial Compressive Strength test has been done based on ASTM D2938 method. Three samples of rack fragments with a dimension of 20 × 20 × 15 centimeters were obtained in talus, old and new alluvial fans. Two cylindrical cores (two-inch) were prepared for each sample and then Compressive Strengths of samples were determined in wet and dry conditions. The aggregate Impact Value test has been done based on sieve No. 8 for 10 samples in taluses, alluvial fans and river beds. Results and Discussion Result of this study shows that landforms such as taluses, old and young alluvial fans and old and young river beds have a lot of weathered and crushed materials that can be used as aggregates. Processes of physical weathering such as thermoclastic and cryoclastic processes as well as tectonic joints play an important role in the production of building materials especially in taluses in the base of steep ridges. To study the quality and strength of study area aggregates, resistance to abrasion (Los Angeles test), uniaxial compressive strength, and aggregate Impact Value tests were carried out. Results of Los Angeles test represent that aggregate abrasion of two samples in old and new river beds are 24% and 18% respectively that show rather high quality of aggregates in mentioned landforms. Uniaxial compressive strength of aggregates for 3 samples in new alluvial fans, old alluvial fans and taluses are respectively 641, 343 and 778 kg/cm2 in dry condition and 495, 249 and 720 kg/cm2 in wet condition. Results of aggregate Impact Value tests show that mean of this test in taluses, new river beds, old river beds, new alluvial fans and old alluvial fans are 11.05, 11, 11.95, 13.2 and 13.8 percent respectively. Overall results of mentioned tests reveal that geomorphological landforms such as taluses, old and young alluvial fans and old and young river beds have construction materials with appropriate quality. Also, because of more weathering in old alluvial fans, the strength of construction materials of old alluvial fans is weaker than those of new alluvial fan. Conclusion Aggregates are produced from sand and gravel and weathered bedrock that can be used for concrete, road pavement and other construction purposes. Location, volume and quality of aggregates are often important for engineers. Results of this study reveal that location and volume of aggregates are efficiently affected by the geomorphological landforms. Aggregate quality and resistance to abrasion are strongly related to geomorphological processes like degree of weathering. For example, because of more weathering in old alluvial fans, the strength and therefore quality of aggregates of old alluvial fans are lower than those of new alluvial fan. Some processes like karstification have negative effect on the aggregate quality because it can result in the formation of voids and cavities in rock fragments. On the other hand, some processes like physical weathering can prepare fresh materials as appropriate aggregates. Thus, geomorphological mapping, identification of landforms and processes, determining the degree of weathering and paleogeomorphological appraisal of areas are of great important in better understanding and exploitation of aggregates.