RU2099751C1 - Process of seismic microzoning - Google Patents

Abstract

FIELD: structural seismology, evaluation of intensity of vibrations with allowance for properties of grounds of which construction site is made up. SUBSTANCE: seismic vibrations are excited in ground by vibration source, they are recorded by geophones positioned on sections with various geological conditions. Spectra of vibrations of examined and standard grounds are constructed, velocities of propagation of lateral waves and densities of examined and standard grounds are measured. Nonlinear increments of evaluation are calculated by obtained data. Values of nonlinear increments are used to judge degree of seismic effect. EFFECT: improved reliability of process. 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 by an non-explosive low-power pulse source, recording them by geophones located in areas with different engineering and geological conditions, determining the values of shear wave velocities, densities of the corresponding soils and evaluating based on these characteristics, increment in scoring [1]
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 a vibration 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 [2]
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 the soils composing the studied soil stratum, which is very important for assessing its physical state and seismic properties associated with features of the degree of manifestation of non-linearity in soils under intense impacts.

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

где:
ρ₁ плотность исследуемого грунта, кг/м,
V₁ скорость продольной волны в исследуемого грунте, м/с,
Δv₁ изменение скорости продольной волны в исследуемом грунте, м/с,
ρ₂ плотность эталонного грунта, кг/м,
V₂ скорость продольной волны в эталонного грунте, м/с,
Δv₂ изменение скорости продольной волны в эталонном грунте, м/с.To achieve the technical task in the method of seismic microzoning, including the excitation of seismic vibrations in the soil by a vibration source, recording them by geophones located in areas with different engineering and geological conditions, measure the propagation velocity of longitudinal waves in the region of shorter seismic waves and the density of the studied and reference soils and determine the nonlinear increment of the score from the ratio:

Where:
ρ _{1 the} density of the investigated soil, kg / m,
V _{1 the} velocity of the longitudinal wave in the studied soil, m / s,
Δv ₁ change in the velocity of the longitudinal wave in the studied soil, m / s,
ρ _{2 the} density of the reference soil, kg / m,
V _{2 the} speed of the longitudinal wave in the reference soil, m / s,
Δv _{2 the} change in the velocity of the longitudinal wave in the reference soil, m / s

 and the values of the nonlinear increments of the score are used to judge the degree of seismic effect.

 The method is based on the phenomenon of strain sensitivity, which characterizes the change in the physical properties of the hearth rocks of the speed of seismic waves, due to a change in the stress state.

 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 identified. After that, within the selected areas are sensors of an ultrasonic flaw detector.

 Within each section, a seismic vibration source is located and it produces a standard effect in the form of monochromatic oscillations or a “sweep” signal within the maximum action of the source, creating a voltage of at least 5 kg / cm in the ground, which allows you to get closer to real seismic effects.

 The velocity of longitudinal waves is measured in the absence of exposure and when exposed to a vibration source in the studied and reference soils. Determine the density of soils.

где:
ρ₁ плотность исследуемого, кг/м,
V₁ скорость продольной волны в исследуемом грунте, м/с,
Δv₁ изменение скорости продольной волны в исследуемом грунте, м/с.Determine the nonlinear increment of the point from the ratio:

Where:
ρ _{1 the} density of the investigated, kg / m,
V _{1 the} velocity of the longitudinal wave in the investigated soil, m / s,
Δv ₁ change in the velocity of the longitudinal wave in the studied soil, m / s

ρ _{2 the} density of the reference soil, kg / m,
V _{2 the} speed of the longitudinal wave in the reference soil, m / s,
Δv _{2 the} change in the velocity of the longitudinal wave in the reference soil, m / s

 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.

 A vibration source with a standard effect in the form of monochromatic oscillations or a “sweep” signal was used as a source of generated voltage within the maximum action of a source creating a voltage of at least 5 kg / cm in the ground, which would approach real seismic effects and the propagation velocity of longitudinal waves was determined in the ground ("tracking") using an ultrasonic flaw detector (for example, UK-14p, etc.). A comparison of the velocities of longitudinal waves in the soil, measured in a stressed and unstressed state, determines the change in the velocity of a longitudinal wave. The density of the investigated and reference soils was determined.

 The exposure time of the seismic vibrator was t = 20 s. the maximum impact was 100 kN.

 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 ballast of the territory of the city of Gori by known and proposed methods.

 The advantages of the seismic microzoning method are that the intensities of the excited oscillations approach the corresponding characteristics of earthquakes, and a comparison of the introduced nonlinearity indicators allows you to directly evaluate and control the degree of nonlinear phenomena in soils and their relationship with seismic properties in the form of increment in seismic stiffness and selected seismic stiffness strain sensitivity in the form of a change in the velocity of longitudinal waves in connection with a change in yazhennogo state of soil.

Claims (1)

A method of seismic microzoning, including the excitation of seismic vibrations in the soil by a vibration 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, characterized in that they measure the propagation velocity of longitudinal waves in the region of shorter seismic wavelengths and densities of the studied and reference soils and determine nonlinear increments of the point from the ratio

where ρ ₁ is the density of the investigated soil, kg / m;
V _{1 the} velocity of the longitudinal wave in the studied soil, m / s;
ΔV ₁ - change in the velocity of the longitudinal wave in the test soil, m / s;
ρ ₂ is the density of the reference soil, kg / m;
V _{2 the} velocity of the longitudinal wave in the reference soil, m / s;
ΔV ₂ - the change in the velocity of the longitudinal wave in the reference soil, m / s,
and the values of the nonlinear increments of the score are used to judge the degree of seismic effect.

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