RU2162610C2 - Method of seismic microzoning - Google Patents

Abstract

FIELD: structural seismology. SUBSTANCE: proposed method deals with evaluation of seismic intensity with allowance for properties of soils composing construction site. Seismic vibrations are excited in soil with the aid of artificial source of vibration, they are recorded by geophones positioned on sections with different engineering and geological conditions, then spectra of vibrations of soils are constructed. Frequency of vibrations is determined by way of division of spectrum of horizontal vibrations by spectrum of vertical vibrations of examined and standard soils located at distance less or greater than length of wave of seismic vibrations. Increment of magnitude is found from relation

, where (f $\genfrac{}{}{0ex}{}{\text{2}}{\text{(}}$ _H/V)i)₁ is frequency of vibrations of standard soil located at distance less than length of wave of seismic vibrations, Hz; (f_(H/V)i)₂ is frequency of vibrations of standard soil located at distance greater than length of wave of seismic vibrations, Hz; (f_(H/V)o)₁ is frequency of vibrations of examined soil located at distance less than length of wave of seismic vibrations, Hz; (f_(H/V)o)₂ is frequency of vibrations of examined soil located at distance greater than length of wave of seismic vibrations, Hz. Increments of magnitude are used to evaluate degree of seismic effect. EFFECT: enhanced reliability and accuracy of method thanks to control over contribution of inelastic phenomena to resulting soil motion. 2 tbl

Description

 The invention relates to the field of engineering seismology, and in particular to methods for assessing the intensity of tremors taking into account the properties of the soils composing the construction site.

 A known method of seismic micro-zoning, including the excitation of seismic vibrations in the soil by a vibration source and recording them by geophones located in areas with different engineering and geological conditions, the construction of spectra of seismic vibrations of the corresponding soils and the assessment based on these characteristics of the increment of points (RF patent application No. 5018124 / 25 (065239) priority 1991, CL G 01 V 1/00, 1995).

 The disadvantage of this method is the low reliability.

 The closest in technical essence and the achieved result to the proposed one is the method of seismic microzoning, including the excitation of seismic vibrations in the soil by an artificial source, recording them by seismic receivers located in areas with different engineering and geological conditions, the construction of vibration spectra of the studied and reference soils, determining the frequency of the studied and reference soils and increments of scores and judgment on the values of increments of scores about the degree and seismic effect (RF patent, 1787276 class. G 01 V 1/00, 1993).

 The disadvantage of this method is the low reliability and accuracy due to the lack of control over the degree of non-linear behavior of soils composing the soil stratum, which is very important for assessing their physical condition or seismic properties due to the features of non-linear phenomena in soils under intense seismic effects.

 The technical task of the invention is to increase reliability and accuracy by controlling the contribution to the resulting ground movement of non-linear phenomena.

где (f_(H/V)i)₁ - частота колебаний эталонного грунта, находящегося на расстоянии, меньшем длины волны сейсмических колебаний, Гц;
(f_(H/V)i)₂ - частота колебаний эталонного грунта, находящегося на расстоянии, большем длины волны сейсмических колебаний, Гц;
(f_(H/V)o)₁ - частота колебаний исследуемого грунта, находящегося на расстоянии, меньшем длины волны сейсмических колебаний, Гц;
(f _(H/V)o)₂ - частота колебаний исследуемого грунта, находящегося на расстоянии, большем длины волны сейсмических колебаний, Гц.To achieve the technical task in the method of seismic microzoning, including the excitation of seismic vibrations in the soil by an artificial source, recording them by geophones located in areas with different engineering and geological conditions, the construction of vibration spectra of the studied and reference soils, the determination of the vibration frequency of the studied and reference soils and the increment points, and judgment on the values of the increment of points on the degree of seismic effect, the frequency of oscillation is determined by dividing the horizontal oscillation spectrum on the spectrum of the vertical oscillations of the test and reference ground, at a distance of less than and greater than the wavelength of seismic vibrations, and-intensity increment is determined from the relationship:

where (f _{(H / V) i} ) ₁ is the oscillation frequency of a standard soil located at a distance less than the wavelength of seismic oscillations, Hz;
(f _{(H / V) i} ) ₂ - oscillation frequency of a standard soil located at a distance greater than the wavelength of seismic vibrations, Hz;
(f _{(H / V) o} ) ₁ - oscillation frequency of the test soil located at a distance less than the wavelength of seismic vibrations, Hz;
(f _{(H / V) o} ) ₂ is the oscillation frequency of the investigated soil located at a distance greater than the wavelength of seismic oscillations, Hz.

 The method is based on the phenomenon of strain sensitivity, which characterizes the change in the physical properties of rocks caused by a change in the stress state and the established increase in the reliability and reliability of determining the frequency of soil vibrations by dividing the spectrum of horizontal vibrations by the spectrum of vertical vibrations.

 The method of seismic microzoning is as follows.

 In the territory subject to seismic micro-zoning, geotechnical studies are carried out, on the basis of which typical sites with different engineering and geological conditions are distinguished. After that, geophones are located within the selected sections.

Within each section, an artificial source is located (for example, SI-32, GSK-6, SV-10/100, etc.) and produce a standard effect within the maximum action of the source, creating a voltage of at least 5 kg / cm ² in the soil , which allows you to get closer to real seismic impacts.

 The frequencies of soil vibrations are determined by dividing the spectrum of horizontal vibrations by the spectrum of vertical vibrations of the studied and reference soils located at a distance shorter and longer than the wavelength of seismic vibrations.

где (f_(H/V)i)₁ частота колебаний эталонного грунта, находящегося на расстоянии, меньшем длины волны сейсмических колебаний, Гц;
(f_(H/V)i)₂ - частота колебаний эталонного грунта, находящегося на расстоянии, большем длины волны сейсмических колебаний, Гц;
(f_(H/V)o)₁ - частота колебаний исследуемого грунта, находящегося на расстоянии, меньшем длины волны сейсмических колебаний, Гц;
(f_(H/V)o)₂ - частота колебаний исследуемого грунта, находящегося на расстоянии, большем длины волны сейсмических колебаний, Гц;
и по значениям приращений балльности судят о степени сейсмического эффекта.The increment of the point is determined from the ratio:

where (f _{(H / V) i} ) ₁ is the oscillation frequency of a standard soil located at a distance less than the wavelength of seismic oscillations, Hz;
(f _{(H / V) i} ) ₂ - oscillation frequency of a standard soil located at a distance greater than the wavelength of seismic vibrations, Hz;
(f _{(H / V) o} ) ₁ - oscillation frequency of the test soil located at a distance less than the wavelength of seismic vibrations, Hz;
(f _{(H / V) o} ) ₂ - oscillation frequency of the test soil located at a distance greater than the wavelength of seismic vibrations, Hz;
and by the values of the increments of the points judge the degree of seismic effect.

 An example implementation of the method of seismic microzoning.

 On the territory of the city of Gori, geological and geophysical work was carried out to assess the seismic hazard of soils composing the main zones of the city with a manifested intensity of seismic impact.

An SI-32 pulsed non-explosive source (exposure energy of 50 kJ) with a standard impact in the form of a pulse within the maximum action of a source creating a voltage of at least 5 kg / cm ² in the ground, which allows approaching real seismic influences, was used as a source of generated voltage, and the prevailing oscillation frequencies of the studied and reference soils were determined.

 Table 1 shows the calculation of the increment in the grade of soils in the territory of Gori.

 Table 2 shows the calculations of the increment of the soil grade of the territory of the city of Gori by known and proposed methods.

 The advantages of the proposed method of seismic microzoning are that the intensities of the excited vibrations approach the corresponding characteristics during earthquakes, and a comparison of the nonlinearity in soils at distances shorter and longer than the wavelength of seismic vibrations allows us to directly evaluate and control the degree of nonlinearity in soils and their relationship with seismic properties in the form of an increment in the points in the selected areas according to the magnitude of the change in the frequency of oscillation s soils due to changes in the stress state of the soil.

Claims (1)

A method of seismic microzoning, including the excitation of seismic vibrations in the soil by an artificial source, recording them by geophones located in areas with different engineering and geological conditions, plotting the vibration spectra of the studied and reference soils, determining the frequency of the studied and reference soils and the increment of the ballast and judging by the values of the increment points on the degree of seismic effect, characterized in that the oscillation frequency is determined by dividing ktra of horizontal vibrations to the spectrum of vertical vibrations of the studied and reference soils located at a distance shorter and longer than the wavelength of seismic vibrations, and the increment of the point is determined from

where (f _{(H / V) i} ) ₁ is the oscillation frequency of a standard soil located at a distance less than the wavelength of seismic oscillations, Hz;
(f _{(H / V) i} ) ₂ - oscillation frequency of a standard soil located at a distance greater than the wavelength of seismic vibrations, Hz;
(f _{(H / V) 0} ) ₁ - oscillation frequency of the investigated soil located at a distance less than the wavelength of seismic vibrations, Hz;
(f _{(H / V) 0} ) ₂ - oscillation frequency of the investigated soil located at a distance greater than the wavelength of seismic vibrations, Hz.

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