Investigation of Ground Subsidenc reasons and fractures in Rostagh Area, South of Meybod

 


Extended abstract
1- Introduction
According to the theory of structural geologists and scientists groundwater for the meeting and subsequent rupture and failure and deprive them of the tectonics and geotechnical.
Rostagh with more than 13 villages is located in 35 km NW of Yazd in Yazd-Ardakan plain, along the length of main road.
Yazd-Ardakan plain with 60 km length and an average width of 15 km is located between Yazd and Ardakan. The Rostagh aquifer is part of big Yazd-Ardakan field aquifer. The shortage and decline of Rostagh aquifer has been 15.4 m. during last 20 years ago.
The amount of subsidence which has occurred in this area is 50-120 cm.
In all cases, the thickness and type and size of the subsidence in the Holocene alluvium and was one of the most important group of minerals that are expanding on the Plain present forms.
 
An important group of minerals that are expanding on plain surfaces of clay minerals and is particularly special attention was montmorilonite, because of the abundance of clay minerals largest reserves are in plain Yazd-Ardekan.
 
2- Methodology
Monitoring and Measurement Methods has been considered for recognition of subsidence causes, in Rostagh area, South of Meybod.
After gathering information, during field survey and with getting use of satellite images surface subsidence and alluvium has been studied. The most cracks and fractures on the earth with the greatest length and extension measured with Branton compass and assigned their coordinates with GPS.
The axis point of cracks has drawn with Eshmith diagram and we used Wintek software for determining and analyzing of cracks and fractures. In this way the point diagram poles changed to contours. With Rose diagram software joint distribution and direction is sketched. With stratigraphy of well’s sediment nature from top to wet layered and the water table information in piezometric wells has distinguished also some sample analysed for main elements.
 
3- Discussion
Tensile and shear fractures in the region are divided into two categories:
Extension fractures are constituted from extension forces and its planes is judge.
This is a dense clay layer separation caused. Two kinds of fractures may be constitutes from subsidence and shear zones by tectonics activity.
In agriculture zone not only there are little fracture and cracks but also fractures is not deep,
Because watered, plants and vegetations are reducing fractures and cracks in land.
In Yazd province there are 3000 wells that 1300 ring tapping deep and semi-deep so on.
The deepest wells in the well Charkhab Rstagh that more than 270 m deep drilling in 1985 and has been declined level during drilling at a depth of 60 meters and 80 meters deep, but in 2004 years time that in 19 years the water level has dropped about 20 meters.
This subject shows declining water table in Yazd province and Rostagh area very important and there are direct relation to earth subsidence.
 
4- Conclusion
As a result we found pumping of water through the Rostagh and Ardakan aquifer has be
en decreased piesometric pressure about 3 m per year. The Decline of pressure is response to disturbing balance and increasing pressure of upper sediments. So, porosity of reasserted sediments has decreased and increasing of compaction brings about land subsidence. Land subsidence is recognized in Rostagh and Roknabad specially near the wells with growing pipesDirection of the cracks is correspond with main direction of Yazd- Ardakan field in NW-SE.
The most cracks on this area have specific direction so the land subsidence is not responsible to creation all of them. Generally, the subsidence and tectonic even tees occurred by active faults are the two factors that caused the cracks on Rostagh area.
There are two reasons for fracturing and subsidence like Geotechnical and Tectonics, based on Hydrogeologists, Geologist and building scientist's theory.
In this research, effective of two subjects has been investigated in Rostagh area that is located in 35 km NW of Yazd, with more than 13 villages.
Nain –Baft and Khranagh faults that forming parallel strike slip faults and sheer zone and causes fracturing in clay deposit. Then fell down water table (static and dynamic), develops subsidence and fracturing in this area.
We suggest Improvement of water resource method, transform of irrigation procedure and artificial recharging as control methods for subsidence in this area