فهرست مطالب seyed hamid lajevardi

In the present study, the effectiveness of a new combination of industrial wastes including calcium carbide residue (CCR) and silica-fume (SF) along with polypropylene fiber was investigated in comparison with cement for improving soft clays and increasing their durability. The results showed that in normal curing conditions, the use of CCR alone has little effect on the soil geo-mechanical performance. On the other hand, despite the initial favorable performance of cement, the W-D cycle with the failure of cement nanostructures can lead to the disturbance and even complete loss of the soil-bearing capacity. In contrast, the combination of CCR with SF had a prominent role in the stabilization process and a much lower deterioration potential was observed in the presence of the optimal ratio of CCR-SF. According to SEM-EDX and XRD analysis, expansion of solidification and reduction of voids were evaluated as the main factors of the more appropriate response of the recent system. Adding fiber to this series of samples had a significant effect on the growth of tensile strength, better absorption of energy, reduction of cracking ability, and as a result, improving the stability of the soil matrix. Following such a condition, the strength of the reinforced sample containing a 15% additive was found to be about 1.8 times the threshold allowed for successful stabilization. This can be attributed to the synergism of CCR-SF and fibers in improving the particle conjunction and reducing the access of voids for soil-water interaction. Based on the obtained results, the use of an optimal combination of CCR-SF with fiber can be recommended as a low-cost, environmentally friendly, and efficient option in improving the behavior of problematic soils and reducing their post-failure potential.

One of the methods to improve soft soil is to use embankments along with geo-synthetic reinforcement on piles. This embankment system is called piled embankment. The objective of designing this system was to transfer higher load to piles through embankment and reinforcement. Due to the phenomenon of soil arching in the embankment, part of the surgerch load (A) was directly transferred to the piles, reducing the remaining surgerch load (B) applied to the reinforcement between the piles. One of the objectives of piled embankment design regulations is that the reinforcement with less settlement can transfer higher load to the piles. In this article, 2D tests were first performed using rigid steel rods as embankments with 2D behavior. Then, analytical calculations were performed for the deflection of the reinforcement after the tests. The test device was designed and made in such a way that can measure the values of A and B separately. Studies on the variables of the embankment height and the number of reinforcing strands showed that by increasing the height of the embankment by 4 times due to the formation of a more stable arch and the distributed load accumulation near the piles, the reinforcement can transfer higher load up to 3.7 times to the piles with a fixed settlement. While by tripling the number of reinforcing strands, for a fixed settlement of the reinforcement, it can increase the maximum load transferred to the piles by 1.78 times.

In the present paper, results of a study on the use of Bacillus pasteurii to reduce wind and water erosion in alkaline silty soils are presented (Kim et al., 2014). The treated soil specimens were prepared in different periods and different concentrations and amounts of bacteria on different surfaces and were exposed to a wind tunnel constructed and calibrated for the present study and their surface erosion was measured. For further analysis of the samples, melting and freezing tests, cone penetration, electrical conductivity, pH and SEM, XRD, and EDS analyzes were also performed on the treated and untreated specimens. The results of this study showed that the use of MICP as a surface crust is an effective and environmentally friendly process to control dust caused by wind erosion in the Meighan Wetland. 

2.1. Experimental study The treated soil specimens were prepared in different periods and different concentrations and amounts of bacteria on different surfaces and were exposed to a wind tunnel constructed and calibrated for the present study and their surface erosion was measured. For further analysis of the samples, water erosion test (Gao et al., 2020), freeze and thawing test (Qi et al., 2006), cone penetration, electrical conductivity, pH and SEM, XRD, and EDS analyzes were also performed on the treated and untreated specimens. To compare the stabilization method with bacteria and conventional stabilizers, surface stabilized samples were prepared by spray method (Ivanov & Stabnikov, 2016) of cement and lime and exposed to wind tunnels and surface erosion was measured. 

3.1. Effect of bacteria on reducing wind erosion The results of this study showed that the use of MICP as a surface crust is an effective and environmentally friendly process to control dust caused by wind erosion in the Meighan Wetland. With this method, the surface resistance of 28-day-old samples can be increased up to 95% and the rate of wind erosion can be reduced to 89.8%. 3.2. Effect of bacteria on water erosion The formation of biological crust in a scouring cycle by 98.59% has reduced the surface scouring, which can indicate the stability of this crust against water erosion in the study area. 3.3. Effect of bacteria on freeze and thawing cycles Freeze and thawing cycles do not cause surface crust loss and increase wind erosion in bacterial-modified soil samples. 

The use of bacteria to improve the soil and create a biological crust by spraying has shown a significant effect on the rate of erosion of samples exposed to wind and this method can be used in fine-grained soils of Meighan area and soils with similar conditions to prevent surface erosion. This method increases the surface resistance of the soil against melting and freezing, scouring, and penetration of the cone. Soil bacterial stabilization in the study area is more suitable than cement and lime stabilizers in terms of reducing erosion and reducing pollution.

In urban areas with high population density, lack of surface space has led to the development of the transport network, especially the construction of underground tunnels, which is usually inevitable in the construction of buildings near deep foundations. When a tunnel is excavated, the surface settlements will result in damage to the surface and deep structures. Therefore, control of surface settlements and other environmental impacts is key to the design of tunnelling projects. Thus, in the present study, using the three-dimensional analysis by Abaqus finite element software, the effect of New Austrian tunnelling method (NATM) including Top heading (TH) and Central diaphragm wall (CDW) on the surface settlements and the forces applied to the single pile and the 2 × 2 pile group was investigated when the tunnel is adjacent to the piles in weathered residual soil. The results showed that the amount of net forces applied to the pile due to tunnelling patterns when running as a pile group was significantly lower than those for the single pile. It was also proved that, in the pile group, the CDW method created a lower amount of net surface settlements and net axial forces compared to the TH method. Also, unlike surface settlements, the influence zone on the pile head settlement in the longitudinal direction can be identified as ±2D in TH, and in the CDW method from -2D to +1D from the pile center (behind and ahead of the pile axis), where D is the tunnel diameter.

In this paper, the performance of the strip of scrap tires (Geo Scrap Tire(GST)) with horizontal transverse members evaluates as reinforcement elements in mechanically stabilized earth walls (MSEWs) by large scale pullout test (i.e. 1.4 m × 0.8 m × 0.8 m). In this regards, the experimental pullout results of GST reinforcement compared with theoretical equations and conventional reinforcement of Geosynthetic Strip (GS), Steel Strip (ST) and Steel Strip with Rib (STR). The experimental pullout results showed that the innovative suggested reinforcement element performed better than the other strips so that the GST strip was capable of increasing pullout resistance by more than 3, 2.5 and 1.5 times compared to the steel strip, the geosynthetic strip and the ribbed steel strip. The results show maximum pullout resistance of GST affected by the S/B ratio and with adding three horizontal transverse members can be increasing pullout resistance by more than 5.9, 4.9 and 3.2 times compared to ST, GS and STR. Thus, using GST reinforcement with three horizontal transverse member needs a smaller length (less than 30%) comparing to conventional strip reinforcement (ST, GS, STR). Therefore, using Geo Scrap Tire reinforcement can open a new horizon in solving the problem of scrap tires and assure geotechnical engineers in achieving superior and more economical systems of reinforced soil walls.

Soil dynamic properties play fundamental roles in the analysis and design of various earth structures. Shear modulus and damping ratio are two important dynamic properties. In particular, shear modulus, especially at the level of very small strains typically denoted as Gmax, is a dynamic property of great significance, which is frequently implemented in the seismic design of geo-structures against the destructive earthquakes. The shear modulus reveals the resistance of geo-structure to the deformations imposed by the external loading. On the other hand, one of the commonly used methods to increase the strength and stiffness properties of soft soils is to stabilize them using either cement or lime. Addition of these stabilizing agents to the parent soil strengthens the bonding among particles, thus resulting in the overall increase in the shear stiffness of the mixture. Therefore, the stabilization technique is always considered as an efficient method of soil improvement. In the current study, the small strain shear modulus of soft clay stabilized with various lime contents is thoroughly evaluated using the results of a comprehensive series of bender elements tests under isotropic stress states. Bender element is a nondestructive experiment commonly used to estimate the velocity of shear waves propagating through the soil samples. Using the shear wave velocity obtained, the small strain shear modulus of the specimens could be easily evaluated with a simple equation in soil dynamics. The applicability of the bender element test to measure the shear wave velocity for the stiff stabilized samples in this study was extended using a new innovative method. The influence of input frequency on the shear wave velocity measurements was also rigorously examined and it was concluded that it barely affects the received signals. Based on the bender elements experimental results, the influence of lime inclusion (5%, 10%, 15% and 20%), water content (45%, 65% and 85%) and curing time (28 and 56 days) on the small strain shear modulus is thoroughly investigated. The amount of water in the soft clay-lime mixture was selected to be about 1, 1.5 and 2 times of the liquid limit moisture of the parent clay. According to the experimental results, it is observed that the small strain shear modulus decreases dramatically with the increase in the water content over the liquid limit. The addition of lime to the clay, up to a particular level, leads to a considerable increase in the small strain shear modulus. However, beyond this optimum value, the shear modulus shows a declining trend with the increase in the lime content, which is an indicative of the inefficiency of the stabilization process. Thus, it is a common practice to limit the lime content to a specific percentage so as to obtain the maximum possible value of shear stiffness. The general trends of shear modulus variation for the samples stabilized at different curing periods are also observed to be quite similar. In general, the small strain shear modulus increases with the increase in the curing time, as more chemical reactions could occur within the mixture. Finally, a microstructural analysis was also conducted using the scanning electron microscopy (SEM) images of the treated specimens so as to somehow justify the trends of variation in small strain shear modulus obtained from the bender element experiments. Utilizing the results obtained in the course of this study, useful information is provided for the prediction of the small strain shear modulus of the clays stabilized with lime using deep mixing or grouting methods. Indeed, the results of this study could be effectively used in different geotechnical construction projects to improve the parent soil strength and stiffness properties and ensure about the serviceability and efficient performance of the underlying soil deposit.

The load-carrying capacity of the aggregate piers increases by circumferential confinement created by the surrounding soil. In soft clay soils, the amount of confinement is usually not sufficient to develop a load-carrying capacity. Because of that, it is practical to use geosynthetic reinforcement aggregate piers in this type of soils. This paper intends to evaluate the use of vertical steel bars as an alternative for geosynthetics. In this study, some small-body laboratory tests were performed on floating aggregate piers with diameters of 80 and 100 mm and a length of 400 and 500 mm, respectively reinforced with vertical steel bars. Moreover, two-dimensional numerical modelling using the Plexis software was conducted. The results show that using the bars with more stiffness leads to more increase in load-carrying capacity. Reinforcing the full length of the aggregate piers, compared to half-length, will further improve the load-carrying capacity of the aggregate piers. In the early stages, by applying the load, the stone aggregates tend to compress, so load-carrying capacity increases and by continuing this process, the tendency to the occurrence of lateral bulging is seen and due to the low resistance of kaolin clay to the bulging, the increase of load-carrying capacity is negligible. Also, numerical modelling results show that the floating aggregate pier penetrated into soft clay soil in the full-length case, and the failure state changed from bulging to slip.

One of the important applications of geosynthetics in the earth's slopes, such as landfills and waste disposal areas, is to use them as liner system. Proper assessment of the interaction of geosynthetics at slopes, such as landfill, is an important issue in preventing the slip and instability of the slopes. The inclined plane is a suitable method for assessing the interaction between the geosynthetics interacting in a sloping and tilted state under low normal stresses. The European Standard EN ISO 12957-2 provides a "standard displacement" for estimating the geocynthetic interface's friction angle. In this paper, inclined plane device, which for the first time in Iran was completely designed and constructed, describes the technical characteristics of the device and prepares the sample. This apparatus has the ability to perform experiments to investigate the interaction of soil-soil, soil-geosynthetics and geosynthetic-geosynthetic interfaces at low normal stress. Experiments are carried out on geomembrane and geotextile types to investigate the interaction of their surface. By changing the type of geosynthetics, it was observed that friction angle of geosynthetic interfaces is not constant and depends on the type of geomembrane and the woven or non-woven geotextile. The geomembrane-geotextile interface is the least amount of geomembrane with hard polyethylene, and the highest amount is used when polyvinyl chloride is used.

Soft clayey soil generally has high compressibility and low strength. Presence of this soil type in the site of ‎civil projects can always be a challenge for construction issues. Soil stabilization is one of the useful ways to ‎improve problematic soils. Cutter Soil Mixing (CSM) is almost a new method for deep stabilization. This ‎experimental study, investigate the effect of different depths on soft clay ‎properties which stabilized by CSM ‎method. To simulate various depths and related surcharge pressures, new devices were designed, modified ‎and used for laboratory tests. Moreover, mixture of blast furnace slag and hydrated lime slurry was used in this ‎method for the first time. The samples were cured for 28 and 56 days ‎under various surcharge pressures, which actually represent different depths. The results revealed that by increasing the depth, mositure content and saturated/dry densities of the samples were decreased and increased respectively. In addition, by ‎passing the critical depth, fewer changes were obsorved in the moisture contents and saturated/dry densities of the samples. Finally, the strength parameters of stabilized samples were icreased significantly.