Ancient suffosian channels in coarse chip quaternary sediments in territory of Bishkek city.
Mandychev A.N.
During engineering -geological researches in territory of. Bishkek located on a foothill loop Kyrgyz edge, in coarse chip boulder - pebble and pebble sediments of quaternary age are found out texture, designate as ancient suffosian channels. This kind texture represents in denudation as a site of rocks, usual 0,3 - 0,5 m. by a diameter, where interchips the space does not contain small chips aggregate (fig. 1).
Such texture are observed in opposite walls pits, approximately at same level, that has allowed to identify them not as local cavity with absence aggregate between boulders and pebble, but as extended like of pipe channels in a ground.
The sediments, in which are observed specified texture, are submitted pebble fine with inclusion of boulders up to 5 -10 %. Aggregate - sand average (15 - 25 %), with the contents of clay particles from 2 up to 5 %. Chip a material good and average smooth. The ground is weak cement, by places meet discontinuous beds and lens of sand with slanting layer river-bed of a type. All this specifies on alluvial genesis of sediments.
Suffosian channels meet on various depth from a surface of ground within the limits of 15 meter investigated interval. The frequency of their distribution on a vertical makes 1 channel on 1 - 2,5 m., less often 1 channel on 4 - 6 m., on occassion they in pits are not observed. The greatest quantity suffosian of channels is concentrated on depths 2,5; 3,5; 5
ì.. The orientation of channels in a horizontal plane does not find out the certain law, in a vertical plane it is near to horizontal. The formation these texture is connected, probably, to activity of flows of underground waters, basically, in limits above - bottomland of terraces, where there was an opportunity carry out small chips of a material from accumulative of terraces in a river-bed.Apparently, process of formation ancient suffosian of channels was characteristic for stages of development of river valleys of a foothill loop, when the erosion prevailed above accumulation and occured erosion of the river in sediment bedding, in the following period of prevalence of accumulation, the system suffosian of channels interment and was dip on some depth in connection with general dip sediment of a cover. Thus, the new system suffosian of channels develops already on new higher hypsometric a level in the following stage of erosive development of a river valley.
Proceeding from such representation about genesis suffosian of channels, it is possible to assume, that extent suffosian of channels about first tens meters, and as a whole they form system of the connected and isolated channels, located in a certain interval of depths. In the plan they are associate for a bed of the ancient river and are focused under various corners to a river-bed. It is possible, that ancient suffosian channels are distributed in all coarse chip sediments of alluvial genesis, irrespective of age.
Fig. 1
At the expense of presence suffosian of channels, young weak cement quaternary of sediments can additional compression, give to a shrinkage on local sites, at significant, especially, dynamic loadings. This phenomenon can amplify in case of presence local infiltration of water owing to what can occur modern suffosian process to redistribution small chips of a material in a vertical direction from above downwards in ancient suffosian of a cavity, and last will move upwards on a section.
In light above-stated, it is necessary to mean, that the process infiltration of superficial waters and filtration of underground waters in alluvial coarse chip sediments can occur mainly on systems suffosian of channels, to speeds much exceeding speed of a filtration in sediment bedding of rocks.
Thus, mapping and the study ancient suffosian of channels has the weighty importance for an estimation of engineering -geological conditions at construction of large structures, and as for definition of a degree of vulnerability of underground waters by pollution.
