ali komak panah

Rockfill materials are used in construction projects such as dam construction, road construction and so on. Due to the increasing use of these materials, experiments and studies have also been carried out on this material and usually, these studies have been carried out on strong rockfill materials. Today, the use of soft and weak rockfill materials has expanded because the economic and environmental issues. These marginal materials traditionally would not be used owing to their unfavorable engineering properties that is, low strength, high compressibility, and proneness to material degradation with time. Therefore, the use of soft rocks excavated on site as rockfill materials for high rockfill dams is still a controversial issue, as weathering takes place when the rock is exposed to an environment in which variations in air, temperature, and water content are involved. and still no comprehensive studies have been conducted on soft rockfill materials and need more information on the behavior of these materials in different conditions. One of the most important subject discussed in the rockfill materials is the particle breakage phenomena. Particle breakage index that quantifies the degree of particle breakage, can reflect the degree of particle crushing of material. To select weak rockfill materials, we visited the Nohob dam that is under construction and rockfill material in spillway excavation section is thrown away and it is not used in the construction of the dam. With considering that the dimensions of the usable rockfill material may be much larger than the dimensions of the laboratory equipment. Therefore, it is always a matter of scaling and matching the results of the laboratory and the field from the important items of rockfill materials. In this research, the behavior of weak rockfill materials has been studied in medium scale oedometer apparatus, in dry, wet and saturate conditions and also Los Angeles experiment is done. Based on the present study, the particle breakage increases with the addition of water and in saturate conditions, particle breakage also has a slight increase compared to wet conditions and for settlements and deformations of wet and dry specimens of materials show that wet specimens settlements are more than dry specimens.

In the history, Earthquakes have been a major source of many damages and human losses and there has always been a lot of concern about the destruction of large structures such as dams due to significant financial losses and casualties caused by it as well as the uncontrolled release of water in the towns and villages located downstream. Seismic risk analysis, one of the most important methods to deal with earthquake hazards. In this study a type of seismic risk analysis in dams is discussed and used and seismic hazard analysis is conducted for the Chah Nimeh Zabol dam. Semi-quantitative risk analysis for Chah Nimeh Zabol dam by seismic hazard analysis for the location of the dam was conducted which placed it in the medium risk category and there is no requirement to redesign or reinforce the dam body. The results can be used as a guide for seismic risk of the dams.

Determination of ultimate pile capacity is important for proper design and construction of pile foundations. Most of the time, the pile load test is carried out shortly after the installation of pile. The pile capacity obtained from the load test is often assumed to be the ultimate pile capacity in most of design methods. However, during pile installation, the soil around the pile experiences large deformations and changes in excess pore water pressure, which in turn reduces the shear strength and pile bearing capacity. After the completion of pile driving, the pile capacity increases as the strength of the surrounding soil increases mainly by reconsolidation, manifested by the dissipation of excess pore pressure at the soil-pile interface zone. the ultimate pile capacity could be underestimated if pile load test was carried out while excess pore water pressure still remains, which may lead to a conservative pile design. It should be noted that a pile static load test (SLT) and a dynamic load test (DLT) only measure the pile load–displacement relation and ultimate load at the time of testing; they do not provide any information on pile capacity variations over time. Pile load tests must be repeated at different times to evaluate any set-up effects, which can be time-consuming and costly during pile construction. Therefore, it is essential to develop empirical and numerical solutions to enable analyzing and estimating long-term pile set-up effects on the basis of limited numbers of SLT and DLT tests. Accurate estimation of pile setup, rather than measuring directly in the field, may reduce the cost of piling and still provide the required performance for the pile. Prediction of pile capacity gain with time after driving would certainly be advantageous from an economic standpoint. Incorporating the effects of setup into pile design is expected to reduce the general cost of piling project by reducing pile diameter, pile length, size of driving equipment, and subsequently piling duration. The major reasons for set-up can be categorised into the following two groups: (1) the generation of excessive pore water pressure during pile driving and subsequent dissipationover time, leading to soil consolidation, and (2) the aging process. The purpose of this research is to conduct experimental research aimed at developing an understanding of pile capacity in soft clays and to develop relationship between the pile capacity and elapsed time after the end of initial driving for cohesive soils. An experimental program was developed to study the evolution of pile capacity increase with time for piles driven into a type of soft clay in northern Iran. results of a series of pile load tests conducted on small-scale Aluminum pile foundations driven into soft clay. The piles were tested instantly after driving to measure their initial bearing capacities, and were tested repeatedly over different elapsed times to study the evolution of pile capacity over time. Results show pile capacity increases approximately 80% of initial value, 14 days after initial pile driving. A large proportion of this pile capacity increase over time, also known as setup, was generated within the three days due to fast excess pore water pressure dissipation, and afterward, the pile capacity increased at a lower rate.

Reinforced soil structures are finding increasing applications in seismic active zones. This makes it important to study the dynamic behavior of these structures. Therefore, the present article is an attempt to study the seismic behavior of reinforced soil retaining walls with polymeric strips. The effects of the most important parameters including the length of reinforcement, reinforcement arrangements (zigzag vs. parallel), maximum base input acceleration, and wave frequency on the wall displacement were investigated for sensitivity analyses. The main drawback of dynamic analysis is that numerical methods are time consuming. Therefore, determination of equivalent coefficients is a suitable and simple approach to converge results of pseudo-static and dynamic methods. In this case, a relatively accurate design is achieved by using pseudo static method that requires far less time. To this end, the earthquake equivalent horizontal acceleration coefficient is proposed by considering horizontal displacement of the wall as the basis for comparison.

The behavior of pile foundations under earthquake loading is an important factor affecting the performance of structures. Observations from past earthquakes have shown that piles in soils generally perform not well, while those installed in sandy soils are more susceptible to problems excessive soil movements or bending moment in the pile.This paper describes a study on the behavior of piled raft foundations under dynamic loading. This research comprises three major components: the first step including the effect of granular layer on piled raft performance using shaking table test under seismic load, the second step verification of numerical program with shaking table tests on sand and then, to investigate about performing piled raft foundation with granular layer under seismic load.

Lateral ground displacement due to liquefaction causing damages to major infrastructures like buildings، bridges، pipe، shore line utilities etc. When the surface slope is mild، a common mode of failure is lateral spreading with surface displacements that can exceed several meters. Considering the widespread use of pile foundations، their safety in the occurrence of earthquake has a special importance. Studies after the earthquake have shown that both the force due to structure and the Kinematics interaction between the pile foundations and the soil play an important role in mechanical behavior of piles. Since the effect of the superstructure on the pile-soil interaction analysis is significant; the analysis should be done based on the interaction axis of pile-soil-structure. In this study، finite difference method (FDM) has been used to investigate the effect of the thickness of liquefied layer، slope of liquefied layers and the underground water level on behavior of pile foundations. Results indicate that with an increase in the slope of liquefied layers، the maximum bending moment raises but the slope of this graph for low underground water level (near the surface) is higher. This type of behavior also is observed in the shear force created in the pile foundation.

There are significant number of pile supported wharves around the world and this type of structures are commonly chosen for the construction of new waterfront port facilities. Batter piles have been used for a long time to resist large lateral loads from winds, water waves, impacts and earthquake. Their distinct advantage over vertical piles is that they transmit the applied lateral loads partly in axial compression and tension, rather than only through shear and bending. Thus, batter piles offer larger stiffness and bearing capacity compared to vertical piles with the same diameter and depth. However, batter piles have been extensively damaged at several ports worldwide during past earthquakes. This paper is focused on the application of seismic isolation devices for improving seismic performance of existing pile supported wharves with battered piles. To assess efficiency of this method, a structure with batter piles was selected to represent typical seismically vulnerable pile supported structures. The selected structure is analyzed using dynamic time history analysis taking into account the nonlinear behavior of structure components and soil–pile-structure interaction effects. 2D models of structure and soil are developed using OPENSEES platform. The soil is modeled using nonlinear elasto plastic elements and the soil pile structure interaction behavior is modeled using p-y, t-z and Q-z nonlinear spring elements. Models that include axial load effects in lead rubber bearing (LRB) isolator behavior are used. Time history analyses for 475 and 2475 years level have been carried out for existing and retrofitted structures. The structures retrofitted by seismic isolators had longer period of vibration and increased damping both of which reduced the seismic base shear, axial force of battered piles for tension and compression and also moment and shear action in deck.

Creep is a time-dependent deformation of soil under constant effective stresses. For investigation on the creep of rock fill materials, 3 samples from 3 dams of Iran that are already under construction were selected. Normal effective stresses were applied on the specimens with a large-scale odometer apparatus that is specially designed for the research. Comparison of creep rate, amount of particle breakage and results of Los Angeles test shows a relationship between these three parameters. Consequently Los Angeles test that is a simple and accessible test, can give a prediction and estimation of behavior and properties of rock fill materials. Based on the test results, an approximate relationship could be found between creep, particle breakage and Los Angeles test results.