جستجوی مقالات مرتبط با کلیدواژه « تزریق » در نشریات گروه « عمران »

Injection soil improvement is one of the methods of modifying the properties of the site of construction projects or existing structures. Several stabilization techniques are available to improve such conditions, including compaction, consolidation, mechanical stabilization, and cement injection into the soil. The injection is often done by filling cavities and fractures with grout or cement mortar. Despite almost the same principles, injection methods have different equipment and procedures. These methods have their characteristics and advantages due to insufficient bearing capacity, shrinkage swelling, settling, and durability. This study intended to review the studies and methods of improving alluvial soils using the cement injection method. After reviewing the results of this study, we can get three main factors: percentage of cement, setting time (sample age), and percentage of coarse soils have a very effective and controlling role in the strength of soil-cement samples, but the effect of these three factors is not the same in increasing strength. The results of such experiments can be used as a basis for quality control of cement injections in porous media, especially in coarse-grained alluvial sediments and jointed and crushed rocks. The resistance of coarse-grained alluvial sediments with the potential for spillage can be increased, during or after tunnel excavation, by adding a minimum percentage of injected cement to the desired strength or design strength, which is essential from the technical and economic justification of injection projects.

Chemical injection is a useful geotechnical procedure for stabilizing soils and also making them impermeable. For characterizing the soil stabilized by colloidal silica, the clean and silty sand samples with silt values of 20 and 40 percent, in both unstabilized and stabilized conditions, were prepared with different concentrations of the stabilizer from 5 to 30 percent, and the effects of colloidal silica on its behavior were evaluated under cyclic loading. 30 cyclic triaxial tests were performed on various samples. A 100 kPa confining pressure was used in these tests. All 15 experimental samples were loaded at cyclic stress ratios of 0.2 and 0.4 with a frequency of 1 Hz and up to 200 sinusoidal cycles. In this research, for the stabilized and unstabilized samples, the double amplitude of axial strain of five percent or the pore water pressure ratio of one, whichever occurs earlier, was considered as the liquefaction criterion. By performing cyclic triaxial tests, it was observed that by stabilizing clean and silty sand with colloidal silica, liquefaction phenomenon is postponed. Thus, adding even low concentration of colloidal silica such as 5 percent can prevent liquefaction of soil at the low level of dynamic loads (such as cyclic stress of 0.2). By adding colloidal silica, the double amplitude of axial strain and the pore water pressure ratio were reduced in cyclic loading. For example, in silty sand with a silt content of 40%, by increasing the stabilizing concentration from 10% to 30%, the pore water pressure ratio reduced from 1 (the state of full liquefaction) in 10 cycles to about 0.1 in 100 cycles, and also the double amplitude of axial strain decreased from 5% in 10 cycles to about 0.7% in 100 loading cycles. Gelatinization of colloidal silica between soil grains causes elastic behavior for the soil sample and prevents permanent deformation between soil grains. Reducing permanent deformation in undrained conditions reduces the development of excess pore water pressure in the soil during cyclic loading. The choice of colloidal silica concentration to prevent the liquefaction of sand and silty sand in a specific area depends on the cyclic stress ratio in that area; thus, at a cyclic stress ratio of 0.2, colloidal silica concentration of five percent is sufficient. However, at a cyclic stress ratio of 0.4 (higher level of dynamic loads), colloidal silica with a concentration of 20% or more should be used.

Cement grouting is a common method for sealing and consolidating dam foundations. Since grouting is a cost and time- consuming process, understanding the amount of cement consumption is essential to estimate the cost of any dam construction. The geological setting is one of the main factors affecting the amount of cement take. In this paper, an attempt has been made to investigate the relation between the amount of cement take and the values of Rock Quality Designation (RQD), permeability, joint spacing, and joint aperture, measured in pilot holes drilled at the Khersan II Dam site (west Iran). The amount of cement take shows a direct relation with the values of permeability and joint aperture but presents a reverse relation with the values of RQD and joint spacing. Among the mentioned parameters, the Lugeon value has the highest correlation with cement consumption, however, poor correlation indicates the influence of other factors. To reduce the influence of other factors, the values of cement take were normalized to the injection pressure and then its correlation with the mentioned parameters was investigated again. Results show a significant improvement, especially between the normalized cement take and Lugeon values, resulted in at least the coefficient of determination of 0.7. After validation, the presented equation could be used to estimate the value of cement consumption at similar dam sites.

Cement production is one of the most important sources of CO2 emission in the world and an energetically demanding process. Therefore, the replacement of a part of it with cheaper and environmentally friendly materials such as zeolite is of great importance. Small strain shear modulus (G0) of soil is an important parameter in many aspects of geotechnical engineering. In the present study, a series of bender element tests on loose sandy soils grouted with zeolite and cement was conducted to investigate the effects of cementation on the G0 of them. The results showed that the G0 of grouted samples increased with an increase in zeolite content up to 30%. After this (Z30), any increase in the zeolite content reduced the G0. Also, in all W/CM and Z, the G0, decreased with increase in the sand grain size. The G0 corresponding to Z30 for D11 sand (the smallest particles) samples grouted with suspension having W/CM of 3, 5 and 7 is, respectively, 21.7, 16.7 and 12.5 times that of pore sand. The minimum G0 is observed in samples grouted with Z90 and W/CM of 7, which is 2.16, 1.2 and 1.19 times the G0 of corresponding unstabilized sands for D11, D1 and D2 sands, respectively. By replacing 50-60% cement with zeolite in the grouting suspension, no reduction in the G0 of the grouted specimens compared to specimens grouted with cement is achieved. Therefore, from an economic and environmental point of view the replacing this amount of cement with zeolite is important.

Due to the growing population growth in cities, the use of injection technology in the ground improvements, construction industry, geotechnical and geological engineering is increasing day by day. In this regard, the grout and its additive play a very important role in terms of injection conditions. In this research, viscosity and rheological measurements of grout using the viscosimeter of the model (DV-II + Pro) as well as the physical criteria of the grout, including shrinkage, specific gravity (Gs), acidity (pH) on the cement base grout with the chemical additive like sodium silicate, kaolinite as mineral additive, cement and water were investigated. In this research, various grout compounds containing various percentages of sodium silicate, kaolinite and water were prepared. The results show that cement, kaolinite and sodium silicate have a reverse effect on the viscosity of the grout. If the amount of soil specific soil is acceptable and the soil acidity is more than 11, which is very suitable for injection operations. Also, the effect of various sodium silicate percentages on the binding properties, specific mass and gravity of acidity were investigated, and the results are recommended for geological and geotechnical engineers especially people who are working ans studying in this field.

Passive method is a new way in stabilizing loose soils. This method is as a type of interlocking of soil structure. In order to successfully improve in this method, it is necessary to achieve proper penetration length and increase the shear strength of parameters. Previous studies have shown an increased resistance to liquefaction and decreased permeability due to colloidal Nano silica injection. In this research, sandy soil was mixed with silt in 5, 10 and 15 percent. Then, specimens in dry and saturated conditions were placed under the influence of Nano silica colloid. For determining geotechnical properties of improved specimens direct shear test was performed in three situation (dry, saturated, and grouted). Also, for studying drainage condition after improving constant head permeability test was carried out. The results showed that by adjusting ionic strength and rheometry properties such as viscosity and gel modulus, it is possible to achieve proper penetration length and obtain the required strength for injection in silty sand with a high non plastic fines content. Besides, with the injection of Nano silica colloid, the amount of vertical settlement in the samples decreased significantly. Also, the amount of permeability of the stabilized materials showed a decreasing trend.

South Pars gas reservoir is considered one of the largest gas fields in the world. The present study in PSEEZ that surveyed the environmental groundwater aquifers and strategies to deal with, draw down of water and increasing impurities through mapping of isobaths, isosulfate, isochlorine, isosalt, hardness and electrical conductivity contours. Results indicate that the soil is contaminated with heavy elements, progressing serious growing problems that can strongly affect the aquifers of pars region in the near future. Furthermore, aquifer recharge in Assaluyeh Plain is approximately 4.5 million cube meters per a year in which currently more than 3 (million m3/year) is not essentially gathered. Specific storage of alluvial fan deposits of about 5%, one percent of the flood plain and in other regional is less than one percent, so the capability storage of aquifers is low and cannot save a considerable amount of water, or discharge from the aquifer. Future water resources requirements will be provided from outside of the region, but it will take a long time for implementation. In this period, water necessities must be supplied from such aquifers.

In discussion about digging tunnel and well in loose ground¡ there are methods and different machines to control special conditions for ground reinforcing. One way which has global utilization is cement grouting (cement and additive materials) for hollow places in construction. There are some elements which delay and prolong the dig such as decreasing the thickness into upper layers in tunnel project of surface parts relate to civic ground and presenting non resistant and loose mineral materials. This subject makes that digging method change abruptly. And other special methods will be used such as cement grouting by influence of cement grouting by means of cement compaction grouting to jet-grouting and etc. Selecting the correct method for rock and soil resisting depend on different conditions for example type and alternative layers of charged scale¡ mode and project type. The various kinds of cement grouting methods will be reviewed on their properties in this paper. We hope that geotechnical and mine engineering can select proper methods for improving problematic soil and solve their problems.

The most important problem in shallow tunnels excavated in soft ground of the urban areas is the surface settlement and its effect on the adjacent structures and facilities of the city, depending on the effects of the range of surface settlement profiles. This feature is clearly visible in Bimeh Station (A4-2) Line 4 of Tehran Metro. One method of supporting tunnel in this circumstance is using the umbrella arch method such as a pre-supporting. Due to the small radius and volume of grout injected into the umbrella arch method and manner of its implementation in field, a homogeneous area containing slurry and soil can be build up around the tunnel. To conduct laboratory studies, soil sampling and in-situ soil characteristics is used to achieve sample preparation. Shear and compressive strength tests were carried out according to the ASTM standards. The shear strength parameters of the soil samples (containing various percentages of silica in the slurry) were determined. The results are presented in tables and figures.

In this study, a non-plastic silt is grouted by sodium silicate in an electrokinetic cell. The silicate solutions are injected through the reservoir next to the anode electrode. The injection of Na- silicate solution increases the strength adjacent to the anode electrode between 5 to 8 times compared with the base soil. Increasing silicate concentration generates lower increase in strength across the specimen. This means that decreasing the silicate concentration increases the penetration length of the grout. Neglecting the results for anode side of the specimens, the maximum increase in strength has been observed for injection of 5% silicate solution through the anode with acid in the cathode chamber. The obtained strength is 3.3 to 4.0 times greater than the strength of the base soil with the highest penetration length. The application of this technology for increasing the strength of the soil underneath an existing foundation or generation of pile through the soil is proven.

In this paper, the improvement potential of calcareous sand produced in KishIsland by using a chemical grout is investigated. The main characteristics of this sand are its high voids ratio and tendency to be crushed under moderate stresses. The improvement process of sand is conducted using a sodium silicate grout injected with additives such as formamide and sodium aluminate. Samples were prepared in different initial relative densities and then grouted. It is observed that the maximum uniaxial strength, initial tangent modulus and failure strain are obtained in water/silicate ratio of 0.5.Uniaxial strength and initial tangent modulus are increased with time but failure strain variation with time is a function of water/sodium silicate ratio and additives content. Formamide increases and sodium aluminate decreases the uniaxial strength and initial tangent modulus. Furthermore, increasing of grain size decreases grouted sand uniaxial strength. Uniform grading results in brittle and non-uniform grading results in ductile stress-strain behavior. Presence of sulphates and chlorides solved in water reduces the uniaxial strength and increases the initial tangent modulus of grouted sand.