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EXPERIMENTAL RESEARCHES DYNAMICS OF DISPLACEMENTS IN FAULTS ZONES
A.D. Sashourin & A.A. Panzhin
Mining Institute of Urals Division RAS, Ekaterinburg, Russia
N.K. Kostrukova & O.M. Kostrukov
Scientific-practical center "Geoecology", Surgut, Russia
Abstract: The paper includes results of experimental researches of dynamics displacements and deformations in zones of tectonics faults. The experiments were carried out on three faults zones located in Western Siberia in area of Surgut city. The displacements of a surface measured with applying systems of a satellite geodesy GPS. The measurements were executed in a mode of continuum monitoring with code-reading of results in 5 seconds, 10, 15 and 30 minutes. The experiments have revealed presence short-period of surface oscillatings in faults zones and on bordering territories. The discovery of dynamics displacements and deformations cardinally changes conception about parameters and laws of forming of the stress-deformed state of a rock mass in a natural conditions. The magnitudes of displacements and deformations are capable to arouse breaking downs in objects getting in a zone of their influencing. The researches are executed at financial support of the Russian Foundation for Basic Research (RFBR).
1. INTRODUCTION
The humanity in the own daily activity has got used to be guided by submissions about the Earth as "unrequited earth stronghold". Today all know about movements of lithospheric plates, about movements on such active faults as San-Andreas in California, North-Anatolisky in Turkey etc. In other parts the Earth - as environment of mining, underground structures, the basis for all kinds of building etc. - is represented as something static, stable.
In reality it is far from being so. The tectonics faults even of a low rank in general hierarchy of a block structure of a rock mass have the some mobility. She not always carries directional trend pattern, but can be introduced also dynamics oscillatings, aroused while by unknown endogenics processes. The look-alike contradictions of existing submissions are conjugate to real processes in an earth-crust with severe hazard to the objects, which have appeared in affected area of movable tectonics patterns. Most contrast this contradiction was reveal on extended objects, such as main oil pipelines and gas lines, underground manifolds etc. But specially it is important for ecologically dangerous objects, the emergencies on which one can become the cause of ecological disasters. To them it is possible to relate nuclear power stations, underground and ground-level storage of nuclear wastes.
In the paper the results of researches dynamics of faults zones, introducing interest in fundamental and problem fields of knowledge are given.
2. ORGANIZATION OF EXPERIMENT
From the end of the nineteenth century and until recently the stress-deformed state of a rock mass in geomechanics, geodynamics and other sciences about the Earth was represented as something static. The representation about its parameters, about parents their reasons, about dependences between values of stresses both deformations and bases of their measurements varied. But same remained invariable - static state of parameters of stresses and deformations in historical intervals of time. The dynamic or slow variations on the established concepts occur or for durable geological periods, or on a sites of progressing and display of geodynamic processes on short interims.
At 70-80 years of past century in scientific researches even more often meet of papers on researches dynamics of parameters of the stress-deformed state in interrelated the tidal phenomens from influencing the Moon and Sun. Today in many papers the question about fluctuations of parameters of the stress-deformed state is bring up, and anybody from geomechanicist will not become to deny dynamics of the stress-deformed state. But in practical sphere dynamics of stresses and deformations does not find the reflex. It takes place for the simple reason - nobody knows parameters of dynamic processes: amplitudes and frequencies of occurring variations.
At the same time, by practice exploitation of main oil and gaseous pipe lines and other extended objects is established, that the emergency breakings on them are clustered, more often, in zones of tectonics patterns. The mechanism of their breaking down in these zones allows suspect about presence of dynamics variations in the stress-deformed state of a rock mass and pipe line, laid on him. These conditions have induced to carry out experimental researches of dynamics of the stress-deformed state of faults zones.
3. CONDITION OF EXPERIMENT
3.1. Geographic disposition of objects
The research of dynamics of faults zones was carried out in Western Siberia
in area of Surgut city of the Tyumen region. The first experimental object is
in 17 kilometers from Surgut city on intersection of a main oil pipeline with
a local tectonic disturbance having a meridional direction of strike
(Fig. 1.).
On this area of an oil pipeline the emergency breakings of pipes took place.
The second object is located in the Surgut city on an joint of latitudinal and
meridional tectonics disturbances. On area of their articulation the system of
underground sewage headers of city, on which one there were some emergencies
(Fig. 2.).
The emergencies on sewage headers were tracked by formation of failures above
ground.
The applied problem of researches in both cases consist in finding - out of the reason of emergency breakings of an oil pipeline and breaking down of sewage headers.
3.2 Geological feature of an experimental area
On the geologic data the area of experiment is referred to Obsky kaylogenic field of the Western-Siberian lowland. In it is allocated heterogeneous folded foundation and the weakly dislocated overburden. The forming of the structural forms of overburden began in the end of trias and proceeds till now. By overburden term understood as a thick series of the sediments, formed for the specified period, folded, predominantly, sandclay and, on occassion, siliceous rock mass. The deep of overburden reach to 2700 meters.
From the geologic information follows, that in Neogene and Quaternary the rather intensive tectonic movements and took place that all large orographic elements of the Western-Siberian lowland grow out of the newest tectonic moves. Different neotectonic movements, cause growth of the local structural forms, have the amplitudes of movements up to 250-300 meters. The gradient them frequently reaches 20 meters/kilometers.
The experimental area is located is immediate on the Surgut arch, representing he extended rising of a north-northeast direction of strike of length 300 kilometers, width 150 kilometers of wide. The amplitude of rising on seam roof foundation reaches 1200 meters and is quick fades to a surface up to 70 meters.
The boundaries of tectonic zones are well traced in near-surface strata by electrometric methods on fall-off of specific electric resistance. In city conditions the position of boundaries of tectonic zones was updated during experiment.
4. TECHNIQUE OF EXPERIMENT
Dynamics of displacements in faults zones was researched with applying of technique of satellite geodesy. Is immediate were measured mutual vertical and horizontal displacements of two marks of special observant stations equipped on investigated areas (see a fig. 1 and fig. 2). For these purposes the kit of instruments of firm Trimble (USA) series 4600LS, including four GPS receivers was used.
The observant stations represented system of marks locked on ground surface with the use of pilling metallical datum marks. The applying of datum marks provides an opportunity of review of experiments. On the first object in area of an oil pipeline 15 marks of observations, and on second 13 were equipped.
The measurements were executed on technique of differential GPS in a uninterrupted mode with periodicity of code-reading 5 seconds, 10, 15 and 30 minutes. Simultaneously in operation there were 4 receivers located on 4 datum marks. It provided monitoring behind variations of lengths and leveling at 6 vectors. In total was executed of measurements on 29 vectors on the first object and 35 vectors on second. The endurance of continuous observations on each vector was various and amount from 1.5 hours till 30 hours.
The implementation of all requirements make to planning and execution of measurements, and also to post-processing of experimental data, provides accuracy of definition of a mutual position of two receivers within the limits of 1-3 mm. During executing of measurements the special check confirming the specified accuracy was carried out.
5. RESULTS OF MEASUREMENTS
The experimental data on deformation measurements on both objects are given in
tables 1 and
2.
The deformations of vectors observant stations in the tables are given in
absolute and relative values. For horizontal deformations this variation of
vector length (millimeters) and relative elongation (in relative units
10-3). For vertical deformations this variation of elevations
confining datum marks (millimeters) and variation of inclination
(10-3).
The plot representation of length vector variations in time for some
characteristic kinds of observations is showed in a
fig. 3, and in a
fig. 4
the variations elevations on the same vectors and in the same interims are
showed.
From the tables follows, that the amplitudes of horizontal and vertical deformations on both objects have rather close values. The max absolute value of horizontal deformations compounds 35-57 mm, and relative reach (1.03-1.17).10-3. For vertical deformations the max magnitudes compound, accordingly, 86-108 mm and (1.46-2.69).10-3.
The frequency response curves oscillatings of displacements and deformations have rather wide spectrum nature, but most precisely harmonics with endurance of the periods from 30 about 60 minutes are allocated. There are also other less expressed harmonics.
From figures follows, that the increase of the code-readings periods of the indications entails smoothing out of dynamics of oscillatings. From a wave pattern disappear short-periodical oscillating. The influencing of endurance of the code-reading periods of the indications is demonstrated by figures 3d and 4d, on which one the wave patterns are mated at 15 and 30 minute spacings.
The max values of deformations influences as well time and endurance of cycles of measuring. In table 2 the results of measurements on several vectors produced for different time and with different time cycle of measuring are given. In some cases the results differed in some times, and in others they were almost identical.
As whole is not revealed yet existence of the determined intercouplings of deformations with a direction of vectors concerning tectonic disturbances. Probably they will exhibit themselves at the subsequent researches and accumulation of the experimental information.
6. DISCUSSION OF RESULTS
The obtained experimental data about presence dynamic forms of movements in zones of tectonic disturbances and aroused by them alternating deformations and movements entails severe fundamental and problem consequences. In fundamental area they, first of all, are connected to aggravation of submissions about the natural stress-deformed state of a rock mass. To the established today gravitational and tectonics multipliers is added dynamic compounding. At the obtained horizontal compression strains-extensions 1.27.10-3 and modulus elasticity of a rock mass from 3000 MPa up to 5000 MPa of magnitude of dynamic stresses will make from 3.9 up to 6.4 MPa.
If to take into account results of generalizings (Brown and Hoek 1978; Sashourin 1999), according to which one the magnitude of first invariant of horizontal normal stresses σ1+σ2 in near-surface stress of a rock mass compounds from (16.3 ± 1.1) MPa up to (30.8 ± 2.3) MPa, the dynamic components will be rather essential. At the mentioned above arguments first invariant of dynamic horizontal stresses will make from 7.8 up to 12.8 MPa, that is compared to his values for static components. By these magnitudes already it is impossible neglect. Moreover, it is necessary to allow for their cyclic alternating nature.
Presence dynamic forces in zones of tectonics faults, which one, apparently, have an endogenic genesis, causes many features in progressing and existence of the stress-deformed state not only faults zones, but also in the whole rock mass. But it leaves for frameworks of the given report and, is interquartile, will serve as a theme of other researches.
It is difficult to overestimate a role of dynamic deformations and in problem sphere. All artificial objects which have got on tectonics faults with dynamic deformations, is undoubtedly will appear under their affecting, testing influencing fatigue effects from cyclic loading. According to the obtained frequencies, the construction will be subjected not less than 500000 cycles loading per one year. First of all extended underground objects, such as gas mains and oil pipelines, water lines, heating mains, sewage headers, undergrounds etc. are exposed to affecting of dynamic deformations
The special attention to dynamics of tectonics zones should be given on leases of building and exploitation ecologically dangerous objects, the emergencies on which one can be tracked by ecological debacles. Thus it is necessary to have in view of, that dynamics can be inherent also in tectonics faults of a low rank. Therefore examination industrial zones of nuclear power stations, underground and ground-level storage of nuclear wastes and other dangerous objects under the factor of presence of dynamics should become norm.
7. CONCLUSION
Thus, by instrumentals measurements in zones of tectonic faults obtained following results:
1. In zones of tectonics faults the dynamic deformations take place, the magnitudes which one in a horizontal plain (contraction-extension) reach 1.27.10-3, and in a vertical plain (slope) up to 2.69.10-3. Harmonics of oscillatings with endurance of the periods most precisely are exhibited within the limits of 30-60 seconds and 30-60 minutes.
2. The revealed dynamics deformations of tectonics faults entail radical reconsideration of submissions about forming the natural stress-deformed state of a rock mass, that has mean not only for geomechanics, but also for other sciences about the Earth.
3. Dynamic deformations of tectonic faults is undoubtedly render negative affecting on artificial objects. The severe attention on this fact is required by extended structures and ecologically dangerous objects, such as nuclear power stations and underground storages of nuclear wastes.
LIST OF FIGURES
Figure 1. Schema of observant station in area of intersection oil pipeline with a tectonic disturbance
Figure 2. Schema of observant station on articulation of tectonic disturbances in Surgut city
Table 1. Experimental data of deformations measurements in area of oil pipeline
Table 2. Experimental data of deformations measurements in area of sewage header
Figure 3. Nature of lengths variation at various spacings of code-reading: a - 5 sec; b - 10 min; c - 15 min; d - 15 min (-) and 30 min (-.-)
Figure 4. Nature of elevations variation at various spacings of code-reading: a - 5 sec; b - 10 min; c - 15 min; d - 15 min (-) and 30 min (-.-)
REFERENCES
Sashourin, A.D. 1999. Movements of rock mass on ore mines of black metallurgy. Ekaterinburg: MI UD RAS (Russia).
Brown E.T. & Hoek E. 1978. Trends in relationships between measured in-situ stresses and depth. Int. J. Rock Mech. Min. Sci. & Geomech. Abstr. Vol. 15, No 4.
© 2001 Anatoly D. Sashourin, Andrey A. Panzhin, Nataly K. Kostrukova & Oleg M. Kostrukov,
