MINISTRY OF EDUCATION AND SCIENCE OF UKRAINE NATIONAL TECHNICAL UNIVERSITY OF UKRAINE
"IGOR SIKORSKY KYIV POLYTECHNIC INSTITUTE"
APPLIED GEOPHYSICS
lecture course
Recommended by the Methodological Council of the Igor Sikorsky Kyiv Polytechnic Institute
Kyiv
Igor Sikorsky Kyiv Polytechnic Institute 2019
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Reviewer N.S.Remiz, Dr.Tech. Sciences, prof.
Responsible
editor V.G.Kravets, Dr.Tech. Sciences, prof.
The Grief is provided by the Methodological Council of the Igor Sikorsky Kyiv Polytechnic Institute (protocol № 10 from 20.06.2019 )
on the submission of the Academic Council of the Institute of Energy Saving and Energy Management (protocol № 15 from 12.06.2019)
Electronic edition By editorship of contributors
Kravets V.G, Boyko V.V., Kovtun A.I., Han O.V.
APPLIED GEOPHYSICS
lecture course
"Applied geophysics" lecture course this is the educational edition for students of specialty 184 "Mining" / V.G.Kravets, V.V.Boyko, Kovtun A.I., Han O.V. Igor Sikorsky Kyiv Polytechnic Institute – Electronic text data (1 file: 2,10 МB). – Kyiv : Igor Sikorsky Kyiv Polytechnic Institute, 2019. – 64 р.
"Applied geophysics" lecture course – considers a complex of issues related to seismic safety of industrial explosives in the mountain spas, in geotechnical, industrial and civil construction. The lecture course is designed for use by foreign students and may be useful for full-time and part-time students of specialty 184 "Mining" in the course of completion of graduate and postgraduate projects, as well as for mining engineers in designing and organizing subcontracting works.
The lecture course contains information that corresponds to the current achievements of science and technology in the field of seismic security during blasting operations of mining and construction, highlights the features of shaping the forms and sizes of seismic boundaries.
"Applied geophysics" lecture course – recommended for students of specialty 184 "Mining" specializations "Geotechnical and urban underground construction",
"Development of deposits and extraction of minerals".
V.G.Kravets, V.V.Boyko, Kovtun A.I., Han O.V., 2019 Igor Sikorsky Kyiv Polytechnic Institute, 2019
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CONTENT
Definition of terms and concepts………..………..………....5
Theme 1 Normative and methodological issues of seismic safety by explosive works ………....7
Lecture 1 Preface. Classification of the territory of Ukraine by tectonic structure ……….7
Lecture 2Method of seismic wavesparameters measurement… ……….11
Lecture3Determination of the actual parameters of the seismable wave……..…….15
Lecture 4Narms of seismic safety and types of seismic waves………..…18
Theme2Features of theseismic action of explosion in rock massive……..……22
Lecture5Effect of cilinder charge expression in anisotropic rocks……….22
Lecture 6 Relationship of the seismic effect with the spectral composition of elastic oscillations………..………...…..27
Lecture7Transformation of the amplitude-frequency spectrum of mass explosionsin conditions of geological and tectonic structures……….…….31
Lecture8Seismic stability of the career side by acceleration criterion...35
Lecture9Seismicity of the career side by criterion of massive oscillation velocity………....40
Lecture10Estimation of the type of elastic waves per permissible deformation of the sides of the quarries………...………..44
Theme3Seismicity of building objects………. ………..…...48
Lecture11Seismic safety of undamaged buildings……….48
Lecture 12The theoretical basis of seismic safety of exploited buildings...52
Lecture 13Seismic stability of buildings weakened by cracks…………...…………..56
Lecture14 Forecast of seismic properties of objects with different configuration of foundations…………..………60
Literature..……….64
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Definition of terms and concepts
The following terms are used in this sense.
acceptable speed of seismic fluctuations of the ground is the speed at which the conservation of buildings and structures is fully guaranteed, and probable local deformations will not exceed the projected ones;
protected objects - buildings, buildings, engineering, natural and others. Objects, which should be fully guaranteed preservation, and the probability of local deformation does not exceed the permissible standards;
mass explosion (in open work) - an explosion of two or more well bore holes, boiler or chamber charges mounted in the general explosive network, as well as single charges in charging workings exceeding 10 m in length;
explosive substance (ES) is a chemical compound or mixture capable under certain conditions to a very fast self-propagating chemical transformation with the release of heat and a large number of gaseous products;
seismic wave (seismic explosive wave (SEW)) - transverse, elongated, volumetric, superficial (Rayleigh) waves formed in the environment from explosion charges of explosive substances;
explosive materials (EM) - materials, means of initiating an explosion, articles and devices containing explosives;
- blasting works - a complex of organizational and technical measures related to the preparation and conduct of explosions;
- ball - a standard unit of measurement that characterizes the intensity of the seismic effect of a charge explosion with certain quantitative and qualitative indicators on the building, engineering structures, natural objects, living creatures, etc.;
seismic stability - the ability of buildings and structures to withstand seismic effects without loss of operational qualities;
seismic equipment complexes - a set of basic devices for recording and reproduction of seismic information and auxiliary devices, which is intended to determine the parameters of soil seismic fluctuations or structures construction;
security zone (seismic security zone) - a zone planned by results of calculation during the design of blasting operations, in which there is no excess of the limit values of elastic waves intensity;
seismic zone - zone around the source of an explosion in which the boundary norms of the intensity of elastic waves are exceeded;
seismic boundary - the boundary, determined by the results of calculations during the design of explosive works, beyond which there is no exceeding the limit values of the intensity of elastic waves, or the isolation of permissible limit values of the intensity of elastic waves;
soil displacement - the distance to which a part of the soil has moved under the influence of elastic oscillations;
mass velocity or rate of soil displacement - the rate of displacement of the soil particle in a seismic wave;
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acceleration of soil displacement - change in time of mass velosity in a seismic wave;
period of oscillation - the time for which the part of the soil undergoes a complete cycle of oscillation;
frequency of oscillations - the number of total oscillations of the soil particles (periods) in one second;
isoseysm - a line around the source of the explosion with the same values of mass velocity or acceleration of oscillation, built on the results of calculations or equipment measurements.
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Theme 1 NORMATIVE AND METHODOLOGICAL ISSUES OF SEISMICSAFETY BY EXPLOSIVE WORKS
Lecture 1. Preface. Classification of the territory of ukraine by tectonic structure
The territory of our country undergoes significant technological мan-made loads, especially in industrialized regions. A large number of industrial sites, in particular mining enterprises, pose a threat to the environment and human health.
In mining, one of the main processes that have a negative influence on the environment is blasting. The explosion spends considerable energy on the destruction of rocks to a certain extent. At the same time, it pollutes the air with toxic gases, creates a dust cloud and generates a system of seismic waves threatening surrounding structures and violates the stability of mining, natural and man-made elements of relief.
The proposed course "Applied Geophysics" covers a number of problematic issues related to the study of the state of seismic security in the quarry of Ukraine, advanced achievements in the industrial seismic, seismic protection of various types of security objects. It includes the following areas of research in industrial seismic:
- studying the geological-tectonic structure of the granite terrains of the Ukrainian Crystalline Shield (UKSh) and limestones of the Precarpathian Trench and conducting their classification for forecasting the seismic intensity of the explosion;
- studying the nature of the distribution around the explosion of seismic waves in arrays, where anisotropy manifests itself in the form of a logical system of parallel cracks;
- studying the fluctuations of the "soil-structure" system and determining the influence of the frequency characteristics of buildings on their seismic stability with the estimation of the change in the intensity of seismic oscillations when they move from the ground to the foundation of the building and further to the building itself;
- determination of the features of the spread of the seismic explosive wave in a multi layer array of rocks;
- determination of seismic resistance of soft rock ramps and elaboration of methods for recalculation of slope steepness depending on physical and mechanical properties of overburden;
- estimation of the seismic effect of multiblock mass explosions with a non-electric system of initiating charges of ES for the determination of seismically safe scales of blasting operations.
The main volume of building materials in Ukraine is mined in quarries located within the boundaries of the Ukrainian Crystalline Shield (UCSh) and the Limestone of the Carpathian Trench. As a result of seismic events caused by industrial explosions, a number of problems arise in densely populated areas. To solve them, it is necessary to identify seismic zones on the basis of geological and tectonic analysis of the territory of Ukraine by determining the parameters of tectonic disturbances in places designated for the development of rocks.
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To assess the heterogeneity of granite UCSh, where the quarries of building materials are located, the geological-tectonic characteristic of the territory of Ukraine has been studied(Fig.1.1)
.
Fig.1.1. Geological and tectonic map of the territory of Ukraine
The study of the geological-tectonic map during long-term research in quarries, determination of the structure of the arrays of the UCSh allowed to determine the nature of the anisotropy of the arrays, to identify interblock and intra-block disorders.
Data of measurements and results of their processing are given in Table 1.1.
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Table 1.1.
Parameters of granite breakdown of UCHCH Область
Granite Area S, ths.
кm2
Total length of interblock
violations Lbl, ths km
Total length of intra-block
disorders, L, thousand km
S/L,
thousand km
Zhytomyr 29,9 0,45 0,583 51,29
Khmelnitsky 4,55 0,21 0,225 20,22
Vinnitsa 26,5 0,469 0,918 28,87
Kievskaya 26,3 0,3 0,325 80,92
Cherkassy 18,65 0,2 0,27 69,07
Kirovograd 24,6 0,112 0,14 175,71
Nikolaev 11,3 0,135 – -
Odesa 4,5 0,12 – -
On the basis of the complex of scientific researches, the classification of UСSh and limestones of the Precarpathian bend is developed on the basis of the presence of anisotropic properties in the area where the quarry and the adjoining territory of the living population are located. Classification contains three classes and two subclasses (Fig. 1.2).
Fig. 1.2. Scheme of classification of territory of Ukraine into classes and subclasses:
1 - career field; 2 - protected object 1 class- granites of the Ukrainian Crystal Shield:
subclass Ais territory with a regularly oriented system of parallel cracks in the zone of the mining enterprise and adjacent guarded objects;
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subclass B is a subclass A with block and interlock faults.
II class is the territory of the limestone of the Precarpathian trough with a system of vertical and stratum cracks, which has a quarry and an adjoining area with protected objects.
Class III - the territory located in the region at the boundary of the 1st and 2nd classes.
From the given classification, the direction of investigation of the nature of the spread of seismic waves around the source of an explosion in arrays, where the anisotropy manifests itself in the form of a regular system of parallel cracks, is established.The obtained research results can be used in the development of seismic engineering equipment for industrial and special blasting operations in areas with engineering and natural objects requiring seismic protection.
Control questions
1. Dangerous factors of explosion in mining 2. Explain the term "seismic security"
3. Justify the need to study the tectonics of the mountain regions of Ukraine 4. What does the term "anisotropy" mean?
5. Define the concept of a "seismic-safe zone"
6. Class of rocks for anisotropy 7. Subclasses of granite by tectonics.
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Lecture 2. METHOD OF SEISMIC WAVES PARAMETERS MEASUREMENT Instrumental recordings of seismic waves in an industrial seismic system are conducted in the explosion of individual and system of charges. The equipment used to study the seismic properties of the rock mass must provide not only the measurement of the velocity of oscillations, but also the program of spectral analysis of the oscillatory process of the system "source of explosion - a rock mass - an object" in connection with its seismic stability, technical condition, etc.
The main purpose of seismic measurements is to establish the patterns of interaction of seismic waves in the system, taking into account the frequency characteristics of soil oscillations. The results of these measurements are determined in different ranges of the frequency of massive oscillation velocities.
Measurement tasks:
a) operational control of the impact of seismic waves on security objects;
b) statistical accumulation of data on the parameters of oscillation (speed and frequency) and their use when adjusting the existing scale of the explosion;
c) the choice of safe levels of oscillation for objects;
d) the use of seismic parameters of the short-wave explosion of the BP system of boreholes for the development of recommendations for the determination of seismic- hazardous parameters of blasting operations at different parts of the quarry field and the transfer of these data to areas with similar mining-geological and technical conditions.
Seismic observations provide an opportunity to quantify the level of oscillations, and then develop recommendations for the safe operation of objects that are protected in the course of blasting operations. The value of the seismic safety criterion should not exceed the permissible values according to the standards.
The data of instrumental measurements are unified in the uniform form and are divided into the following groups.I. General Information.
Characteristics of rocks at the site of installation of seismic detectors, parameters BP.
A. Characteristics of covering rocks.
B. The parameters of the explosion of each block and the characteristics of the breeds that are undermined.
B. Parameters of seismic waves.
Fig. 2.1 depicts the elements of the measuring system.
Measuring element
Analog-to- digital converter
Personal Computer Fig. 2.1. Elements of the information channel
As a measuring element of an information channel, electromechanical sensors of the pendulum type are taken СМ-3 and СМ-3В.
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The principle of operation of the device is as follows: the body of the device with a magnet rigidly attached to the object under study and repeats its movements. A pendulum with a coil fixed on it tends to stay calm. Because of the relative motion of a magnet and a coil in the latter, an electromotive force (EMF) is induced, or a voltage whose magnitude is proportional to the velocity of motion. Changing this EMF and fixing it at the registration node.
The next element of the information channel is an analog-to-digital converter ADA1406, which works with frequencies 400 KHz and 100 KHz.
The last element of the measuring channel is a PC.
To measure the parameters of the seismic waves, at least 7 seismic sensors are located on the profile. The satellite system is used to set the coordinates of the sensors.
The maximum influence from the oscillation process can be estimated by the module of the complete vector of oscillation velocity
2,
2
2 y Z
x u u
u
u (2.1)
if the oscillation rate of the particles of the soil in the component oscillations reaches This is confirmed by the fragment of the oscillogram (Fig. 2.2), where the records of the velocity of soil displacement by the three components (X, Y, Z) in the joint observation point of the two apparatus complexes are presented.
From Fig. 2.2 it is evident that the difference in the time of entry of the maximum amplitudes by component of the oscillations is almost equal to the period of oscillations (T =
the module of the complete vector of velocity can not be determined by the formula (2.1). In this case, the module of the full speed vector is determined by the line 1-1 (Fig. 2.2), which corresponds to the time of the arrival of components of oscillations of 0.153 s, or along the line 2-2 (the arrival time of oscillations is 0.178 s). In this case, the maximum impact from the oscillation process according to the formula (2.1) is 1.9 cm / c and 1.66 cm / c, respectively.
Fig. 2.2. Characteristic oscillogram of a mass explosion for seismic sensors in the direction of X, Y, Z
Кан.1, СМ-3,Z, Vmax=1,6 см/с Кан.2, СМ-3,Y, Vmax=1,042 см/с Кан.3, СМ-3,X, Vmax=1,1 см/с
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As an example of the capabilities of the hardware complex, we will conduct a study of the impact of mass explosions # 1 and # 2 on the supports of transmission lines, located at distances of 380 m and 440 m from the blast blocks, respectively, which are undermined. Seismic sensors SM-3 were installed on a soil basis of the power transmission line and its construction at an altitude of 1.5 m. In Table. 2.1 the maximum values of the displacement rate of soil particles are given.
Table 2.1
Maximum values of the displacement rate of soil particles (cm / c)
Seismic detector installation location Explosion №1 Explosion №2
Support structure 0,64 сm/s 0,45 сm/s
Ground base support 0,85 сm/s 0,37 сm/s
Analyzing the data in the table. 2.1, it can be seen that during the explosion №1, the rate of oscillation of the soil is greater than the rate of fluctuation of the structure of the support. At explosion №2 - on the contrary.
0 50 100
0.00 0.06 0.12
Frequency (Hz)
Amplitude
а
0 50 100
0.00 0.06 0.12
Frequency (Hz)
Amplitude
1
Б
Fig. 2.3. The frequency response of seismic oscillations recorded by seismic detectors installed on the ground (a) and on the support structure (b) during the explosion № 1
0 50 100
0.00 0.01 0.02 0.03
Frequency (Hz)
Amplitude
10 100
0 50 100
0.00 0.05 0.10
Frequency (Hz)
Amplitude
-8000 -6000 -4000
-200002000400060000 100
а Б
Fig. 2.4. The frequency response of seismic oscillations recorded by seismic detectors installed on the ground (a) and on the support structure (b) in the explosion №2
Analyzing the frequency response, are presented in Fig. 2.3, b and 2.4, b it should be noted that they have a pronounced peak of the amplitude of oscillations at a frequency of 26.5 Hz for the support structure in the explosions No.1 and No.2, which is the frequency of the eigenvalues of the structure of the transmission line. There was
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no pronounced amplitude peak at frequencies close to 26.5 Hz among seismic oscillations fixed on a ground support base during the explosion # 1 (Fig. 2.4, a).
Therefore, the resonance phenomena did not occur at the interaction of the SOF with the ground base of the bearing with its construction, and the massive velocity of the elements of the construction of the support was less than the ground base, as a result of dissipative energy losses in the transmission of wave phenomena to the elements of the construction of the support.
In response №2 explosion seismic waves recorded in the dirt on a support (Fig.
2.4, a) contains a maximum amplitude at a frequency close to the natural oscillation frequency design support (22.5 Hz), so the effect of fire between the resonant elements and SVH design support, leading to increased rate fluctuations compared to the speed of the shift soil particles 1.22 times.
As a result of the studies received confirmation that the study SVH action on security facility is necessary to vibrational spectral analysis process, which all registered seymodatchyky. It was shown that the module full velocity displacement of soil particles from the values of the components of oscillation (X, Y, Z) is determined only at a time when there is an oscillatory process.
Control questions
1. Requirements for measuring equipment 2.The object of seismic measurements 3.The main task of measurements
4. Imagine the circuit of the measuring equipment 5. Principle of seismic sensor operation
6. The principle of determining the coordinates of the sensors
7.Formula of the module of the complete vector of oscillation velocity
8. Explain the reason for changing the vibration parameters when moving from the ground to the object
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Lecture 3
DETERMINATION OF THE ACTUAL PARAMETERS OF THE SEISMABLE WAVE
With the help of seismometric equipment, measure the velocity and the period of the fluctuations of the soil near the foundation of the building and compare them with the permissible speed of soil fluctuations for the building. Actual seismic stability of buildings that are to be preserved is determined by the ratio of periods of soil and building fluctuations.
Registration of oscillations is primarily carried out at places of maximum approximation of blasting works to buildings and structures that are subject to protection. Measurements are carried out at the foundation of the building to determine the pattern of propagation of the seismic burst wave from the cell of the explosion to the object. Measurements are performed simultaneously with the use of two groups of seismic receivers (three per group) at each point, which fix the fluctuations in 3 directions: for two horizontal components (x, y) and one vertical (z).
By the results of the processing of the received seismogram, the parameters of the seismic wave of the boom - the displacement or the rate of soil displacement, or the acceleration of the soil particles, the period of oscillation and the frequency of oscillations are determined.
Data processing includes:
- determination of parameters of seismic oscillations by seismograms;
- the velocity of oscillation (V) is calculated by the formula:
Т V 2 А
, (3.1)
where A is the displacement amplitude, cm, T is the oscillation period, p.
The period of oscillation was determined with seismograms at the time marks between the peaks of maximum amplitudes of oscillations;
The velocity of oscillation for each component (Vx, Vy, Vz), in centimeters per second, was calculated according to the formulas:
x x
x T
V A 10
2 ;
y y
y T
V A 10 2 ;
z z
Z T
V A 10
2 , (3.2)
whereТх, Ту, Тz– periods of oscillation for each component, s.
The resulting amplitude of the displacement of soil particles (A), oscillation velocity (V), acceleration (a), is calculated by the formulas:
2 2 2
у z
х А А
А
А ; (3.3)
2 2 2
z y
x V V
V
V ; (3.4)
а= а2х а2у а2z. (3.5)
The seismic load (G), in kilograms, on the building is calculated by the formula:
G = Р
g
а Ксηк, (3.6)
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where Р - weight of the building, kg
а - acceleration of fluctuations of the soil at the foundation of the structure, cm / s2;
g - acceleration of free fall, cm / s2;
Кс - coefficient of dynamism (coefficient of perception of fluctuations in the building).
The coefficient of dynamism is determined from the seismogram of the fluctuations of the soil and the building or by the formula
2 2 2 0 2 2 с =1 1 0
Т Т Т
К Т , (3.7) where Т0 - period of own fluctuations of the structure;
T - period of prevailing oscillations of the ground, which determine by seismogram, λ - decrement of attenuation of own fluctuations of buildings and structures. The value of the decay of attenuation is shown in Table. 3.1;
ηk is the coefficient of deformation form, ηk = 0,96.
Table 3.1 The value of the decay rate for different types
of buildings and structures Type of building Т0,
с λ Н/b
One-story brick house 0,20 0,25 0,28 Residential two-storey brick
building 0,26 0,17 0,88
Residential four-story brick
house 0,29 0,12 1,30
Three-story brick building with
reinforced concrete frame 0,24 0,20 0,86 Residential five-story panel
house 0,30 – 1,20
Garage for dump trucks (two- story, multi-pass, brick, reinforced)
0,50 – 0,985
Actual seismic stability of buildings and structures is determined by comparing the velocity of oscillation, which is calculated according to formula (2.3) with the permissible speed of soil fluctuations near the foundations of buildings and structures in accordance with existing norms.
The works are carried out in accordance with the measurement protocol, which contains the following information:
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1) a reference to the methodology;
2) the name and address of the measuring laboratory;
3) date and place of measurement;
4) place of blasting operations;
5) date and number of the protocol of measurements;
6) results of measurements;
7) signature of the responsible for the results of measurements;
8) other indicators that may affect the measurement result;
9) any transaction or any conditions that occurred during the determination and not set out in this standard that could affect the measurement results.
It is necessary to regularly check the equipment for reliable results. The frequency of verification is determined by each organization that performs the measurements and is certified in accordance with the established procedure.
The inspection should be as follows:
a) seismographers;
b) multichannel digital recording oscilloscope;
c) equipment for processing seismograms (computer software).
Control questions
1. Measured oscillation parameters
2. Priority places of measurements of oscillation parameters
3. Explain the connection between the period and frequency of oscillations 4. Formula for determining the velocity of oscillations
5. How is the period of oscillation determined?
6. Give a form of formulas to determine the resulting oscillation parameters 7. Formula for determining seismic load
8. Formula for dynamic coefficient 9. What is a "decay of attenuation"?
10. How to determine the seismic stability of buildings?
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Lecture 4NORMS OF SEISMIC SAFETY AND TYPES OF SEISMIC WAVES
The growth of the scale of construction necessitates an increase in the number of mining companies or the expansion of already existing territories. At the same time, the boundaries of quarries are gradually approaching civil and industrial buildings. The destructive impact of seismic waves from industrial explosions is increasing.
In these conditions it is necessary to constantly monitor the detrimental effect of explosions in order to preserve the integrity of buildings. Estimation of explosions and regulation of intensity of seismic action is carried out guided by the magnitude of the maximum speed of wave oscillations. The speed should be less than the permissible value taken from the existing standards. Experts try to construct such schemes of blasting, at which at the same mass of charge will be the minimum indicators of the intensity of seismic waves on buildings located nearby. But for the construction of seismic boundaries around the site of explosion it is necessary, along with a comparative analysis of the influence of various schemes of blasting, to carry out the analysis of seismograms by types of waves (surface, volumetric longitudinal and transverse, waves of Lyav). Dangers for a particular object are waves, which, in spectral composition, are close to the frequency characteristics of the structure.
Such work requires knowledge of the permissible level of seismic influences (the rate of fluctuations of the ground at the base of the object) on the surrounding industrial, civilian or natural objects. Determination of fluctuations in the state of buildings and structures during explosions is carried out according to the intensity scale of seismic oscillations, which is given in Table. 4.1 2.7.
Table 4.1.
Scale of intensity of seismic fluctuations during explosions
Characteristics of vibrations Ball Velocityof oscillation, сm/s
Fluctuations register only devices 1 less than 0.2
Fluctuations are felt in some cases in quiet weather 2 0,2–0,4
Fluctuations are felt by some people or who are aware of an explosion 3 0,4–0,8
Fluctuations are felt by many people, glass tempering 4 0,8–1,5
Loss of whitewashing, damage to old buildings 5 1,5–3,0
Thin cracks in plaster; damage to buildings that had deformations 6 3,0–6,0 Damage to buildings that were in satisfactory condition: cracks in plaster, falling
pieces of plaster, thin cracks in walls, cracks in furnaces and pipes
7 6,0–12,0
Significant damage to buildings: cracks in the supporting structures and walls, large cracks in the partitions, fall of stove pipes, plaster coatings
8 12,0–24,0
Building destruction: large cracks in the walls, masonry bundle, falling of individual parts of walls
9 24,0–48,0
Large destruction and collapse of buildings and structures 10–12 48,0
The most acceptable criterion for seismicity of buildings in explosive operations is the rate of displacement of soil particles in their basis [4,8,18]. Damage to structures occurs when the rate of displacement of soil particles (U, cm / s) exceeds its permissible value [U]. Particularly dangerous situation becomes,
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when the frequency of oscillations of the ground base of the building approaches its own. The use of this criterion in practice leads to an overestimation of the maximum permissible norms, when the determination of the permissible volatility of the soil in the basis of the construction is carried out without taking into account the technical condition of the buildings (weakening of the cracks) and the frequency spectrum of the
"soil-building" system. Due to the overestimation of boundary norms, an error is assumed with regard to the definition of seismic parameters of mass explosions in quarries. This leads to the further development of existing and the formation of new cracks in the surrounding buildings.
Seismic stability of mountain ranges is determined by the absence of residual deformations during the passage of seismic explosive waves. The criterion for seismic resistance of a rock is the relative elastic deformation (E0), which is calculated by the formula:
Е0 =U/Vр, (4.1)
where U - velocity of oscillation of particles of soil of a seismic wave, m / s;Vp - velocity of seismic wave propagation, m / s.
The permissible relative elastic deformation of rocks for the engineering structures contained therein establishes the class of structures, their characteristics and the period of operation, respectively (Table 4.2).
Table 4.2
Permissible relative elastic deformation of rocks for the engineering structures contained in them
Class of buildings
Characteristics of the structure and its period of operation Permitted relative elastic deformation 1
Particularly responsible buildings of a long service life of 10 to 15 years:
hydrotechnical tunnels, trenches of mines, capital tunnels, chambers of crushing, mines
0,0001
2
Responsible buildings with a lifetime of 5 to 10 years: bypass and transport tunnels of hydrotechnical structures, over-chamber helicopters, overheads, quays and dumps
0,0002
3 Buildings that are used for a short time (from 1 to 5 times): chambers,
drifts, ledges 0,0003
4 Nonresponsive structures, which are used once: cleaning blocks, work
benches, workbenches of quarries, etc. 0,0005
Згідно "Єдиних правил безпеки при вибухових роботах" [14] визначення безпечних відстаней при короткосповільненому вибухуN зарядів загальною масою Q з часом сповільнення між вибухами кожного заряду не менше 20 мс проводиться за формулою:
3 / 1 4 /
1 Q
K N K
rc r c , (4.2 )
where Кr - coefficient, which depends on the soil properties in the basis of the protective structure;
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Kc - coefficient, which depends on the type of security building;
α - coefficient, which depends on the performance of the explosion;
N - number of charge groups, units;
Q - total mass of charges, kg.
This calculation of the safe distance applies only to buildings that are in a satisfactory technical condition. In the presence of violations in buildings (cracks in walls, etc.), the safe distance, calculated by the formula (4.2), should be increased by at least twice.
Here are the results of calculations for the following conditions of use of the system of short-term initiation: explosions with a total mass of 12000-16000 kg of explosive, in the zone 300-700 m there is a factory for processing raw materials for crushed stone and settlement. Soils in the basis of houses - not watered sand and clay, depth of more than 10 m. Accordingly:
Kr = 12; Kc = 2; α = 1.
The safe distances for different numbers of charge groups N and total mass Q charges are calculated according to the formula (4.2), which is doubled as the houses are in unsatisfactory technical condition (Table 4.3).
Table4.3 Seismically safe distances
Q, кг 4000 6000 10000 12000 16000
Rс 2,м(N=6 шт.) 480 658 660 700 770
Rс 2,м(N=15 шт.) 398 440 526 550 614
Rс 2,м(N=20 шт.) 360 400 480 560 570
Data analysis of Table 4.2.2.11 indicates that for a 16,000 kg mass explosion with 6 degrees of deceleration, the minimum size of the dangerous distance will be 770 m, and with 20 degrees of deceleration - 570 m. Although the latter significantly reduces the size of the danger zone, but to mount the short-wave explosion scheme With 20 groups, when the total mass of BP is small, it is practically impossible. Such requirements can be fulfilled by a non-electric system of initiation such as "Nonel", which in recent years has been widely implemented in Ukrainian quarries. However, the influence of the method of initiating the prediction of the seismic effect of short- term blasting has not yet been reviewed by scientists in this area.
Therefore, it should be noted that the received dimensions of seismic distances are approximate.
From the analysis of existing literature data and normative documents, it is determined that the type of waves which is most closely related to the spectrum of the eigenvalues of the protected object is based on the frequency spectrum at the maximum values of the amplitude of the oscillations. It is erroneous to assess the seismic security of a security object only for one of the wave-surface types. Taking into account that during
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explosions of stress and relative deformations of objects directly proportional to the velocity of oscillations, the seismic hazard will create those types of waves in which these parameters will be maximal.
Control questions
1. What parameter describes the intensity of the seismic wave?
2. What is the permissible level of seismic impact?
3. List the main types of seismic waves
4. Explain the concept of oscillation stability
5. Name a particularly dangerous situation for buildings
6. Explain why the indicators of seismic security are overestimated.
7. Demonstrate how the seismic stability of the rock mass is determined.
8. What parameters characterize the technical condition of the building?
9. How does the number of slowdown groups affect the seismic effect?
10. For which houses need to double the calculated radius of a safe area?
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Theme 2 FEATURES OF THE SEISMIC ACTION OF EXPLOSION IN ROCK MASSIVE
Lecture 5Effect of cilinder charge expression in anisotropic rocks
Theoretical investigations of the character of the distribution of the wave field from the explosion of charge BP are based on the model of the medium close to the real anisotropic array. The output model is a homogeneous infinite environment with a system of parallel cracks. The physical and mechanical properties of the filler are different from the properties of the medium itself. Detonation of the charge along its length is taken instantaneously, and the seismic wave is considered at a considerable distance from the place of the explosion.
Since all types of waves that are excited by the explosions of industrial BP are characterized by low amplitude, and the task is to establish only a qualitative picture of the distribution of seismic waves around the explosion, then the solution uses the theory of the sound wave [21].
Using the equations describing the propagation of seismic waves in a cracked rock, we obtain the character of the distribution of isoeism around the explosion(Fig.5.1).
Fig.5.1. Results of calculation of isoeism in a cracked array around an explosion: 1-3 - isoeism; "O" - place of explosion; 4 - system of parallel cracks
Investigation of the destructive and seismic effects of the explosion of single cylindrical charges of BP was carried out within the array of granites of the 1st (subclass A) and limestone of the 2nd class, respectively, of the quarries classification. Theoretical and experimental investigations of the explosion were concentrated on granite and limestone massifs, where anisotropy was manifested as a system of naturally oriented cracks.
The laws characterizing the mechanical motion of anisotropic rock around the explosion were investigated in two areas: in the zone of irreversible deformations (parameters of the funnel of destruction) and in the following elastic region (parameters of seismic waves). With the first zone we associate the concept of a seismic emitter (a destroyed zone that is a source of seismic energy). In this case, seismic waves from the explosion arise as a result of the release of energy in the irreversible deformation of the rock.
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The main source of information about the necessary destructive parameters, wave motion and their change from the distance around the explosion are the shape and size of the visible crater of destruction, as well as seismograms that record the fluctuations in various azimuthal points of seismic receivers installation. The processing of seismograms gives an opportunity to obtain a number of characteristic kinematic force, amplitude-frequency indices of oscillation of various types of anisotropic rocks for the establishment of forms of isoeism.
The first zone is interesting for the intensity and uniformity of destruction and the parameters of the isoeism on its outer boundary, which determine the uneven formation of oscillations in remote parts of the array. With this information, it is possible to establish the relationship of destructive and seismic action with the strength and elastic characteristics of rock massifs.
The diagram of installation of seismic sensors around the charge is shown in Fig.
5.2.
The radius of the destruction zone was determined at the location of the sensors, further in the plan the shape of the zone of destruction was built. The next stage is the registration of oscillations in different directions, which allows determining the maximum mass velocity in each type of seismic wave (longitudinal Pp, transverse Ps and surface R) depending on the directional angle.
The difference in the time of receiving the input signals at the points N1-N7 in waves, excited by the explosion of a single charge, determined the velocity of the spread of seismic waves in different azimuthal directions.
Fig.5.2 Scheme of installation of seismic detectors for determination of zones of destruction and isoeism: S - charge; N1 .... N7 - location of sensors; 8 - theoretical contour of the destruction zone; r1 ... r7 - value of the radii of the destruction zone;
According to the results of the measurements, the radii of the zone of destruction and isolation of the velocities of oscillations, frequencies and oscillation energies were constructed (Fig. 5.3-5.6).
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Fig.5.3 Interconnection of the crater of destruction (8) and the zone of isoeism (9). Q - Q - direction of the main system of cracks
Fig.5.4 Parameters of the zone of destructionfrom an explosion of an extended charge of BP weighing 0.63 kg:
8- in granite of the first class of subclass A, 9 - in limestone of the II class; 10 - system of cracks; 0,57 ... 1,1 - numerical values of the radius of the destruction zone in meter
For each explosion of the borehole charge, the anisotropy coefficient of the rock strength ka equal to the ratio of the maximum length of the fracture funnel radius (rmax) to the minimum (rmin) was determined.
The processing of the results of the hardware measurements allowed to obtain data for each type of waves at the massive oscillation velocities in different profile
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directions. According to these data, the deviation of the form of the isoeism from the circle was determined. It is characterized by a seismic anisotropy coefficient ksa equal to the ratio of the maximum values of massive oscillation velocities to the minimum obtained at identical distances from the cell of the explosion.
Analyzing Fig. 5.4, we see that the parameters of the destruction zone in the explosion of charge BP depend on the type of rock, acoustic rigidity and width of the cracks. In limestone, the size of the destruction zone is 1.3 times larger than in granite. The absorbing action of the crack in relation to the explosive wave leads to the fact that in the direction of greater frequency of cracks the radius of the destruction zone is smaller. Therefore, the geometry of the destruction zone has minimum dimensions along the main axis of anisotropy of fracture.
Analysis of the calculated values of the coefficient of anisotropy of rock solid properties shows that the value of ka, with increasing fracture, is increasing. For granites the value of ka is 1,2-1,4, for limestones - 1,05-1,16.
Fig. 5.5 Isotope zones 8, 9, 10 are obtained around the explosion of an extended charge VR, respectively, the indicated mass of charge is 0.089; 0.041 and 0.027 kg / m
Fig. 5.6 Interconnection of isolated energy zones at different frequency ranges with a funicular funnel:
8-10 - energy isolation in the surface, longitudinal and transverse waves;
11 - Destruction funnel zone
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The difference in the shape of the zone of destruction from the circle, obtained from the explosions of single charges of the BP, indicates the anisotropy of the rock mass with respect to its elastic properties. Therefore, we can assume that in such an array massive velocity of oscillations will be directional values, and each direction of anisotropic medium will need to be characterized by the indicative velocity - a spatial figure that outlines the shape of the isoeism.
Control questions
1. Give a description of the theoretical model of the array 2. Explain what you mean by "isoseism"
3. Explain what is meant by the anisotropy of the real array 4. Give an explanation of the term "seismic emitter"
5. What parameters characterize the shape and size of the funnel of the explosion?
6. Give the definition of the anisotropy coefficient 7. Explain the concept of seismic anisotropy
8. Name the approximate values of seismic anisotropy coefficient for granite and limestone
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Lecture 6
Relationship of the seismic effect with the spectral composition of elastic oscillations
Subsequently, the analysis of the oscillation process was carried out in terms of its amplitude-frequency spectrum, which allows to determine the band of frequencies that bear the main energy of seismic oscillations.
In the spectral analysis of seismic waves from the explosion of a single cylindrical charge for the three types of waves, in each of the directions of the installation of the sensors, the amplitude-frequency spectrum and the mean mass velocity of oscillations were determined (Fig. 6.1).
Analysis of the amplitude-frequency characteristics in Fig. 3.11 shows that when the directional angle changes with respect to the direction of propagation of cracks in the range of 0-90O harmonics in the direction along the cracks, the main peaks of the maximum amplitudes are shifted to the region of high values (longitudinal waves) perpendicular to the cracks (φ = 90O) low harmonics (surface waves), and in the direction located at an angle (φ = 45O) to the cracks, the maximum amplitudes in the spectrum occupy an intermediate value (transverse waves).
а А,мм в б
в
Fig. 6.1. Amplitude-frequency spectra of an explosion of an extended charge VR:
a, b, c - perpendicularly, along and at an angle of 45 ° to cracks, respectively
Such a distribution of the frequency spectrum in the characteristic directions around the explosion suggests that each type of seismic waves in different ways reacts to the environment, where the anisotropy of the rock mass is manifested in the form of a system of parallel cracks. As a result, there is anisotropy of seismic detection around the explosion. According to theoretical and experimental studies, isoeism around the explosion has a form close to the elliptic asymmetry. This is due to the fact that in anisotropic array in different directions, the conductivity of each type of seismic waves is not the same and depends on the number of cracks in the way of propagation of oscillations, and on the width of the cracking.
In the direction of greater frequency of the cracks, their absorbing action in
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relation to the longitudinal and transverse waves with high frequency component oscillations leads to the fact that at the same distance around the explosion surface waves propagating in this direction, which carry low harmonics, and seismic oscillations are characterized by the lowest degree of attenuation.
It should be noted that although along the cracks there is the highest degree of damping of longitudinal and transverse seismic waves, in this direction the values of mass velocity are maximal and vary in the range of 0.7-1.15 cm / sec. The latter situation is explained by the best conductivity of seismic oscillations in the direction along the cracks with the advantage in the high-frequency component of the spectrum of oscillations.
The leading properties of anisotropic rock massif in different directions differ not only by the decay of the massive velocity of oscillations but also by the velocity and length of the seismic wave.
Using the interconnection of the velocity of propagation of waves with the frequency of oscillations f, we determine the wavelength (m) along the cracks (φ = 0О) at an angle (φ = 45О) and perediducular to the cracks (φ = 90О) in the frequency bands that carry the maximum load.
Calculations for different quarries have shown that within the same type of rocks forming an array the values of the velocity of seismic waves propagation and the frequency of oscillations vary depending on the diffraction angle. In granites of the UkrSh, the values of the velocities of the spread of seismic waves along directions along the cracks and perpendicular to them vary 2-3.8 times, and for limestones of the Carpathian Trench - in 1.1-1.3 times.
The increase in the velocity of the spread of seismic waves in the direction along the cracks and a significant decrease of its perpendicular to the cracks once again convincingly confirms the difference in the conducting properties of the medium.
The screening effect of a crack in relation to the seismic wave leads to the fact that the wave propagation velocity is significantly reduced. This is the reason that the values of the velocity of oscillations in the indicated direction take the minimum values, and therefore the axis of the ellipse of the isoeism is the same as the main direction of anisotropy of fracture.
Since the parameters of the elastic wave vary with an increase in the distance from the explosion due to the non-uniform absorbing properties of the medium in different directions of the anisotropic array, the shape of the contour of the isoeism is due to the coefficient of seismic anisotropy (ksa> 1), which depends on the magnitude of the wave length ratio to the width of the single cracks d in the system of a cracked array (Fig. 6.1).
As can be seen from Fig. 6.2, the functional dependence ksa = f ( /d) has a curvilinear form and decreases with increasing ratio of ksa value.
ksa
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/ d х10–3
Fig. 6.2 Dependence of the coefficient of anisotropy on the ratio /d; - wavelength; d - average value of crack width in the system of cracks, 1, 2 - direction of measurement, respectively, in normal and at an angle of 45O to the direction of propagation of cracks
The average ksa varies for this case in the range 1.8-1.1. However, in the direction perpendicular to the cracks (φ = 90O), in comparison with the direction at an angle φ
= 45O, the value of ksa is more than 1.3 times (at /d = 250-1100). In the range of /d=1100-2200, the value of ksa decreases. For larger values, it approaches the unit, therefore, the elliptic form of the isoeism is converted to a circle.
Thus, the analysis of experimental data suggests that one of the main causes of the change in the shape of the isoeism is the uneven frequency oscillation in different directions, as well as a different rate of propagation of seismic waves. These results are well-compatible with theoretical studies, according to which the dimensionless parameter at d = λ is critical, in which the transition of the isoeism from elliptic to circular occurs only with a decrease in frequency.
The study of energy loads formed from the explosion of a wave packet was carried out using the equipment and techniques given in Section 2.
The curve, which combines the energy levels of oscillations in each of the directions of the sensor installation, allows us to describe the shape of the distribution of isomers of seismic waves in terms of anisotropic rock massif.
As we see from Fig. 5.6 (Lecture 5), the isolation of the energy of oscillations in all three types of waves is in the form of an oval. Comparing it with the form of isolines of equal mass velocity of oscillations allows to establish their coincidence in the surface wave in the range of low frequencies. Therefore, surface waves for security buildings and structures with low natural frequencies are the most dangerous, and the orientation of these forms with respect to fracture is a reliable basis for predicting seismic zones.
Therefore, surface waves for security buildings and structures with low natural frequencies are the most dangerous, and the orientation of these forms with respect to fracture is a reliable basis for predicting seismic zones.
Thus, established on the basis of the above studies in semi-industrial conditions, the relationship of seismic anisotropy with the anisotropy of the rock massif allows us to deepen knowledge in the study of the physico-technical foundations of the nature of the distribution of isoeism and subsequently use them in industrial conditions
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Control questions
1. Explain how you understand the concept of spectral analysis of seismic oscillations
2. How does the frequency spectrum of waves depend on the direction of measurement?
3. What is the relative conductivity of each type of seismic waves?
4. What is the absorbing environment?
5. In what direction is the highest conductivity relative to the system of the main cracks?
6. How are the wavelengths different depending on the direction of observation?
7. On what parameters depends seismic anisotropy coefficient?In what conditions the elliptic isoeism is circular?
8. Name the main cause of the danger of a surface wave
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Lecture 7
Transformation of the amplitude-frequency spectrum of mass explosions in conditions of geological and tectonic structures
When studying the interaction of an object with different types of seismic waves it is necessary to know the security criteria for objects with different constructive and functional features.
In a career, a source of seismic radiation in mass explosions is located in a rock mass, over which in most cases the sediment layer occurs. A seismic wave in the transition from a rock massif to this layer, reflected and refracted within its limits, can run several times in it. In this case, the following reflected and refracted waves are superimposed on the previous ones. This can lead to resonant phenomena. This interference effect depends on the combination of the thickness of the layer of sediment (h) and the wavelength ( ). Obviously, this motion can not be described analytically.
In the transition from the rock mass to the deposits even in the absence of the effect of interference, the parameters of the seismic wave change due to the refraction on the boundary. After its release on the earth's surface, the surface Rayleigh wave seismic wave (R) begins with other attenuation laws and parameters of motion than in volumetric waves (P and S). The interaction of this wave with the foundations of buildings (objects with a period of their own oscillations to 5-7s) causes them in the tension and deformation that determine the degree of seismic security of mass explosions.
In spite of the fact that in real conditions of conducting explosive work in the environment emitted a large number of waves of different types, usually researchers are limited to the consideration of three major. These are bulk waves (P and S) in the array and surface (R) propagating along the free surface.
Proceeding from this, in order to reduce the seismic effect with unchanged total mass of charge, it is necessary to apply such a technology of landing, in which the maximum value of the amplitudes of the seismic process will be formed in transverse or in longitudinal waves. This can be achieved by changing the slowing intervals, the mass of charges and their number in groups.
On an example of an oscillogram (Fig. 7.1), we consider the distribution of the vibrational process on the phase by wave types. The superficial phase reflects the segment with the largest period of oscillation (Vr). The transverse phase has the so- called "core" (Vs), and the longitudinal phase corresponds to a segment with a high frequency (Vp). The safest phase for objects with a low frequency spectrum of proper oscillations will be those whose maximum amplitude will fall on areas with a maximum frequency.
On the contrary, in the case of obtaining maximum values of amplitudes of oscillations for a period with a maximum period, due to the fluctuations in the seismic wave, the process of its own fluctuation of buildings will cause the greatest danger.
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Bulk waves are characterized by relatively high frequencies (10-40 Hz), the surface wave is characterized by weak attenuation with distance, large amplitudes and low (2-8 Hz)
frequencies.
Fig. 7.1 Characteristic oscillograms with the distribution of the oscillatory process on segments that correspond to different types of waves
Surface types of waves are the greatest danger to buildings of mass development around active quarries. They are in the frequency spectrum and at the maximum value of the amplitudes of oscillations most closely related to the parameters of their own oscillations of these objects. Therefore, the object of research is taken by the surface waves of Relay.
When short-wave explosions of BP charges in various geological and tectonic models of anisotropic rock mass seismic oscillations are distorted and form a rather complicated wave picture. Differences in the periods of bulk and superficial waves occur both at the expense of heterogeneity of rocks, and because of the spillage of waves from adjacent charges, which are broken shortly slowly. To compare such very important characteristics of the explosion as the spectral composition, the energy of different frequencies, the form of the spectrum and other possible only by operating the spectral density of seismic flows.
The graphic representation of seismic oscillations in the form of spectra allows to analyze the seismic manifestations of a short-wave explosion, when the velocity of oscillations is described by a more complex form compared with the extinct sinusoid.
It is supposed that the finite or infinite number of components of oscillations propagates in an anisotropic medium independently of each other.
In fig. 7.2, 7.3 depicts the spectra of oscillations obtained for identical schemes of short-term landing of charges, but in different rocks. For arrays of rocks, where anisotropy manifests itself in the form of naturally oriented cracking, only one maximum is observed in the oscillation spectrum. In arrays of blocks with block structure, two maxima are observed: in the range of low and high frequencies.
This peculiarity in the formation of spectral characteristics is explained by the fact that:
a) the presence of rocks in the system of parallel cracks for surface waves is not a source of additional reflection of oscillations. Therefore, the wave freely extends over the medium, only with the distance loses the magnitude of its amplitude;
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b) in the massifs of the block structure (geological-tectonic structure of the 1st class of subclass B) in the spectrum of oscillations two maximum values of density are observed. From Fig. 7.3 it is evident that the maximum amplitudes of ground oscillations include both bulky high-frequency (40-100 Hz) and surface surface low- frequency (10-15 Hz) waves. The displacement rate of soil particles for bulk and surface waves is almost the same. Consequently, the amplitude-frequency characteristics of the wave process are unfavorable for objects with both low and high harmonics of proper oscillations.
Fig. 7.2 Spectrum of oscillations in rock masses with a system of parallel cracks.
Career in the I class - subclass A (mass of charge 7200 kg, distance 150 m)
Fig.7.3 Spectrum of oscillations in an array with a system of parallel cracks and interblock violations. Career of the I-th class - subclass B (mass of charge 7200 kg, distance of 250 m)
Consequently, the influence of technological factors on the seismic security of objects located in various geological and tectonic structures of Ukraine's territory can be predicted by studying the spectral density relative to each type of seismic waves.
Such a factor may be the slowness interval in the charge plan. If the interval of deceleration is carried out by regular means, for example, with the help of pyrotechnic means of the KSDP-69 relay at intervals of 10; 20; 35; 50; 75; 100 ms, it is possible to obtain resultant oscillations at different distances and in different azimuthal directions from the epicenter of the explosion, in the spectrum of which will be observed both the minimum and maximum values in different frequency ranges.
In fig. 7.4 shows spectrograms of short-wave explosion of charges with a delay of 20; 35; 50 ms in array rocks with cracking and block structure.
From the above spectra it can be seen that as the velocity interval increases, the spectrum changes. With an increase in the slower interval, the maximum value of the spectral density decreases. The reduction of seismic hazard is due to the absence of fluctuations after each subsequent burst charge in the CSR scheme and the creation of
f, Гц f, Гц
А, мм А, мм
