جستجوی مقالات مرتبط با کلیدواژه "نشست زمین" در نشریات گروه "مهندسی معدن"

Today, with the cities expansion and population growth, the need for high-rise buildings and deep excavations for their implementation is increasingly felt. Under constant loading conditions, soil undergoes deformations over time which is called time-dependent deformations. This is of particular importance in terms of safety in the long run. In this study, based on the physical modelling technique, the long term behaviour of stabilized deep excavation in silty sand, using the nailing method, has been investigated. The test results indicated that with increasing the depth of excavation the lateral displacements, the surface settlements behind the excavation wall and also the time-dependent deflections increase as well. In addition, if the excavation operation is brought to a temporary halt or is led to the abandonment, it results in a significant increase in the time-dependent deflections. Finally, the recorded data revealed that the rate of the experienced deformations over time decreases which is due to the gradual mobilization of forces in the nails.

Groundwater exploitation, when the aquifer discharge is greater than its recharge, changes the balance of the aquifer and results in temporal and spatial decline of hydraulic heads in the aquifer. Decline in hydraulic head or water level, decreases pore water pressure and increases effective stress on aquifer sediments. This phenomenon leads to consolidation of interbed layers which consequently results in land subsidence. In recent years, over-withdrawals from aquifer of Neyshabur plain in the North East Part of Iran have been reported. As a result, an average of 90 cm/year decline in water level and maximum displacement rate of 19 cm/year in ground level have been recorded. This study focuses on the estimation of effective parameters related to the land subsidence in Neyshabur Plain. These parameters include the thickness of the fine compressible sediments and inelastic skeletal specific storage (Sskv), which are directly involved in inelastic displacement computations. In the first step, using the geologic log of 231 boreholes and Kriging interpolation method, a map showing the distribution of fine sediments in Neyshabur plain was prepared. This map was used to investigate for reasonable relationships between annual subsidence rate and groundwater yield with the thickness of the fine sediment. Comparisons of maps indicate that the least amount of discharge is seen in regions where the fine layers have the most thickness. In the second step, subsidence rate, extracted from InSAR images, and water level decline at several observation wells located in the study area were analyzed. Investigation of the trend of land subsidence during the recharge and discharge seasons at observation wells showed that the compaction of the aquifer is majorly due to plastic deformation and that the share of elastic deformation is significant. Then, by using the fine sediments distribution map prepared in the first step, the Sskv values were calculated at different locations. The end result of the proposed procedure was a map showing the spatial distribution of inelastic skeletal specific storage (Sskv) in Neyshabur plain.

The investigation and estimation of surface subsidence and ground settlement is an important aspect in the design of shallow tunnels in urban areas. Proper exploration could lead to correct measures and avoiding any damage to structures over and underground.
In this study, four sections of the east-western part of Tehran’s Metro Line 7 with the most potential for surface subsidence were chosen and studied. This part of the metro project is positioned in the young alluvial deposits of Tehran and consists mainly of fine grained soil. Ground settlement requires three dimensional design. Hence, FLAC 3D was used to investigate the surface subsidence of the ground along the tunnel route in sections mentioned above. One of the most important advantages of three dimensional design is the possibility of stepwise excavation, and to explore the effect of each excavation step on the surrounding ground. Hence, the stepwise excavation was carried out and continued in 1.5 m advancing stages, until the advancement stopped affecting the ground settlement at the point over the tunnel portal considered in the model.
Even though, analytical and empirical methods are unable to evaluate the effect of ground water and the effect of overburden due to the presence of structures and traffic at the surface, because of not installing the monitoring system, analytical methods suggested by Sagaseta, Loganathan and Poulos, Verruijt and Booker, and Bobbet, and also Peck’s empirical method were used to investigate the ground settlement in this project.
After using the various methods to study the four chosen sections of the metro line, and analyzing the settlement curves in these sections, it was concluded that the ground settlements is permissible (except the second section).

Subsidence is one of the inevitable phenomena of most underground mining and excavations، especially in long-wall mining methods (i. e. in filling، with out filling and mechanized long-wall methods). It may also occur in room and pillar mining methods (i. e. in both with and without pillar recovery methods). Subsidence phenomenon occurs due to some vertical and horizontal displacements of the ground surface located just above the excavated area. This may also in turn causes surface destructions and eventually result in irretrievable loss of life and property. In this study، a higher order displacement discontinuity method (HODDM) which is a subdivision of the boundary element method (BEM) was used to model the subsidence. To be able to evaluate the horizontal strains on the surface of the excavation the finite difference method (FDM) is also added to the proposed numerical method. The vertical displacement and the horizontal strain (relative displacement) of the ground surface of the excavating area can be evaluated by this modeling technique. It should be noted that، subsidence due to the mining of both horizontal and inclined (oblique) layers were considered in this study. Some of the numerical results are compared with their corresponding empirical ones given in the literature. This comparison shows a good agreement between the numerical and empirical results.