WO2002001008A1

WO2002001008A1 - Method and system for examination and optimal compaction of soil embankments

Info

Publication number: WO2002001008A1
Application number: PCT/IL2000/000371
Authority: WO
Inventors: Semion Novak
Original assignee: Dynasens Ltd.
Priority date: 2000-06-26
Filing date: 2000-06-26
Publication date: 2002-01-03
Also published as: AU5423900A

Abstract

A method and a system are proposed for optimal compaction of any (existing or constructed) soil base of a road, railway or the like with optimal examination of the soil base in real time, the system including one or more adjustable machines capable of effecting soil compaction, each being provided with an adjustable vibratory working member, and a computerized control unit capable of operating at least in one of two modes: one mode being a mode of soil examination enabling data on the soil base properties to be derived by processing a) a vibratory control signal fed to the soil base from one of the machines and b) the soil base's reaction; and the other mode being a mode of soil compaction enabling an optimal combination of parameters to be generated by the control unit for performing the optimal compaction of the soil basis by one of the machines.

Description

Method And System For Examination And Optimal Compaction Of Soil Embankments

FIELD OF THE INVENTION

This invention relates to a process and a system for examination and optimal compaction of single- or multi-layered soil embankments before constructing roads, railways and the like.

BACKGROUND OF THE INVENTION

A number of systems are known in the prior art which are capable of compacting soil during construction of automobile roads, railroads, airfields, etc. The proper compaction of the soil base is intended to ensure that the mentioned constructions will reliably withstand loads of various kinds, including non uniform, non-periodic and extremely high surface pressures. Methods and systems for evaluating soil compaction are also known, but generally, they are only capable of evaluating the compaction of an uppermost layer in a soil base. Further, even for the uppermost layer in a soil base, these methods are not capable of deriving both the compaction and the thickness of the single layer. Where these methods and systems work with compaction machines, they also cannot control the depth at which the compaction will take place.

US Patent 5426972 describes a method and an apparatus for determining whether soil is satisfactorily compacted. An operator delivers impact energy to the soil, and the amount of impact energy transmitted through the soil is repeatedly sensed and stored. A modeling formula, which approximates the variation of the stored amounts of impact energy, is used to generate current and target values for the level of compaction; if the current value equals or exceeds the target value, the soil is considered to be satisfactorily compacted. The target value is considered to be one common parameter of the soil regardless whether it comprises many different layers.

SU 717623 teaches a method of controlling the degree of compaction of soil embankments by transmitting into the embankment a vibratory signal with an adjustable frequency close to its calculated resonant frequency and estimating the compaction degree based on the real resonant frequency of the soil. Commercially available modern systems for soil compaction are manufactured by a widely known German company BOMAG and a Swedish company GEODYNAMIK and are adapted for continuously measuring in situ the degree of compaction of a layer currently undergoing treatment, namely detecting the condition of the upper layer of the construction. Such systems are suitable for successively (i.e. layer by layer) forming the multi-layered base for a road or the like.

However, if any multi-layered base already exists, no means for examining the compaction degree thereof are available in these systems. It should be emphasized that constructing a road or the like on a non-explored and/or improperly compacted base is likely to result in serious problems during further use of the road.

An approach to the compaction of existing multi-layered soils is suggested in SU 763506, which is incorporated herein by reference. According to the approach described therein, different layers of any existing soil base which are exposed to vibrations created by any particular compaction instrument, can be represented as a number of differential equations reflecting free oscillation of a mechanical system disposed between the compaction instrument and the immovable bottom of the base, wherein each of the equations has its own static and dynamic parameters reflecting the layer's characteristics. The method suggests generating and solving a system of equations for a particular multi-layer base, for determining resonant frequencies of different layers of the base, and further performing the compaction of the base using the minimal resonant frequency which has been determined for the system, thus obtaining the maximal deformation and compaction of the soil.

However, it has been found and proven by the inventor that compacting each and every layer of the base maximally may not always produce optimal compaction results.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a method and an appropriate system for effective soil compaction having improved performance over hitherto-proposed systems. Other aspects of the invention concern a method of computerized examination of the existing soil base and a system for accomplishing the mentioned methods. A further object of the present invention is to provide a method for evaluating the compaction of a soil base using a vibrator compaction device.

In the description, the term "layer" is used in the meaning of any kind of geological or artificially created massive body of soil, rock, pebble, limestone, sand, clay, waste (compacted or non-compacted), etc. which is generally horizontally disposed on top of an adjacent layer in an existing or artificially created base or embankment. The term "hard bottom layer" should be understood as an immovable ground layer, such as a rock bed.

According to one aspect of the present invention, the above object can be achieved by a method for compaction of an existing single- or multi-layer soil base of a road or the like by a vibratory compaction equipment, the method including the following steps:

a) obtaining initial data / on properties of a segment of the existing base disposed between a predetermined area section to be compacted and a hard bottom layer; b) introducing the obtained initial data / into a mathematical model capable of processing the initial data and generating an optimal combination C of conditions if the compaction degree of the base section is lower than a pre-selected optimal compaction degree K; the optimal combination C including static S and dynamic D parameters of an equipment for compacting the base section in a state close to the resonance, and characteristics T of a technological regime of compaction; the optimal combination C of conditions being appropriate for compacting the segment of the existing base in an optimal manner as long as the initial data I remains actual; c) selecting a piece of compaction equipment and adjusting the equipment according to the static S and dynamic D parameters appearing in the optimal combination C, and initiating the vibratory compaction according to the characteristics TOf the technological regime derived from the same optimal combination C; d) obtaining current data /'on properties of the soil base segment; e) introducing the current data /' into the mathematical model and repeating steps (b) to (d) until the compaction degree of the base segment is considered to be optimal.

The above-mentioned step of obtaining initial information on properties of the existing base segment usually includes obtaining data on a number, type and, optionally, compaction degree of the soil layers in the segment. The step of obtaining current data on properties of the segment undergoing compaction may include obtaining the same information as above, and can be performed either during a session of the compaction or thereafter.

According to one particular version of the invention, the step of obtaining the initial data / on the properties of the existing base can be performed by preliminary geological exploration of the base, thus directly obtaining the data on the number, the types of layers in the multi-layer base, and on their compaction degree.

Alternatively, (and especially for urgent works), the step of obtaining the initial data / can be performed using a compaction equipment as a diagnostic tool for indirectly obtaining data on the properties of a base section, as follows:

feeding into the base segment a control signal constituting mechanical vibrations of a predetermined amplitude, frequency and duration from an available piece of equipment having a vibratory working member of a pre-selected mass, after the control signal has ceased, registering a fading response signal received by the working member from the base segment, and estimating the number of layers in the soil base and their properties based on the number and frequencies of resonance peaks in the fading response signal.

The real compaction degree of a particular soil layer can be determined, for example, by feeding into the layer vibrations with a frequency adjustable in the range of the resonant frequency of the layer if optimally compacted, and estimating the real compaction degree of the layer based on the revealed real resonant frequency of the layer.

In accordance with another particular version of the method, the initial and current data are processed in the mathematical model by interaction between a dynamic model and a technological optimization model, wherein

the dynamic model describes a mechanical system, including the segment of the existing soil base and a vibrating compaction equipment, using a system of differential equations simulating vibrating motions of the mechanical system in the resonance condition and taking into account dynamic parameters of the compaction equipment and properties of the soil base segment; the technological optimization model is capable of generating a number of optimal combinations C_h C∑, ...-C_M each considering the properties of the soil base segment, the pre-selected optimal degree of compaction K, the static S and dynamic D parameters of the compaction equipment and characteristics T of the technological regime, and is adapted to select an optimal combination C, suitable for compacting the soil base segment in a condition close to the resonance using available compaction equipment.

According to one version of the method suitable for compacting either a single-layer soil base or a multi-layered soil base with layers having similar properties, the pre-selected optimal compaction degree K of the base segment is one averaged optimal compaction value determined for the base segment by the mathematical model.

In an alternative version of the method, for compacting a multi-layered soil base, the pre-selected optimal compaction degree K constitutes a set of optimal compaction degrees K], K2, —K_N corresponding to N different layers of the soil base and being supplied by the mathematical model. In this version, the mathematical model generates (Cj, C₂, ■■■ ■C_M) optimal combinations for each of the N different layers of the soil base, and selects one optimal combination C_in for each respective soil layer. Accordingly, the operation of selecting compacting equipment, adjusting thereof and initiating the vibratory compaction is provided successively for each particular soil layer of the base.

As has been found by the inventor, it is preferable to start the compaction process from a layer having the minimal resonant frequency (i.e. from the less compacted, "weak" layer). Moreover, there can be found a suitable phase regime of vibrations of the layers adjoining the layer to provide its effective compaction. Such a regime can be achieved, for example, by selecting such, a phase regime by the mathematical model (more particularly, the dynamic model), that two layers adjoining a layer undergoing the compaction perform vibrations having phases differing by 180°C from that of the layer to be compacted.

The novel method of soil compaction is advantageous over hitherto proposed methods, since it:

a) enables effective and deep compaction of an existing base using conventional compaction equipment owing to the fact that the equipment is caused to operate in conditions close to the resonance; quite often, the method ensures compaction of such multi-layered sites, which would be unsolvable problems for other compaction techniques. The method provides for a compaction depth of about 3m, while the hitherto-proposed methods afford a depth of lm- 1.2m only. b) allows achievement of optimal degrees of compaction in each and every layer of the existing base, and c) does not require any calibration both when one piece of the compacting equipment is replaced by another one, and when the soil base to be compacted changes its properties. The latter usually takes place either during the compaction process, or when the equipment is moved to another section of the base or to another site. Such an advantage stems from the fact that the method enables the optimal combinations of conditions for compacting any layer of the existing soil base to be produced, and more particularly - from the use of a mathematical model adapted to analyze and process in real time the information on properties of a plurality of soil layers, parameters of available compaction equipment, and the required optimal degrees of the soil layers' compaction.

In order to clarify the structure of the mathematical model, it should be acknowledged that the model also comprises two reference data tables RDl and RD2, wherein:

RDl is a soils data table representative of values of dynamic parameters L of a plurality of any known soils, each value being given at a particular compaction degree of the soil in tabulated form; preferably, the information on each specific type of soil is additionally classified according to a possible degree of its compaction: say, three groups of data for the minimal, the optimal and the maximal compaction degree, respectively;

RD2 is an equipment data table representative of technical characteristics of a plurality of known and available soil compaction machines, including both static S and dynamic D parameters thereof; the initial information / on the properties of the soil base serves as input data to be entered into data table RDl for obtaining therefrom tabulated sets of dynamic parameters L inherent in each of the detected soil layers and associated with its particular compaction degree; and the tabulated sets obtained from data table RDl, as well as the information comprised in data table RD2 are used as input data to both the dynamic model and the technological optimization model of the mathematical model.

For the sake of clarity of the further description, the following acknowledgement should be given:

The tabulated set of dynamic parameters L of any known soil layer comprises at least the following parameters: specific mass (M), elasticity modulus (E), and modulus-όf dissipation (γ).

The tabulated static parameters S of a known piece of compaction equipment include at least the following parameters: specific static pressure of the equipment upon the soil (fs_f), range of masses (m) of the equipment and the working member, and the total weight.

The tabulated dynamic parameters D of a known piece of compaction equipment include at least the following: specific dynamic pressure of the equipment (f_dy_r), vibration amplitude A of the working member (or operating element), its vibration frequency being a so-called forced vibrations frequency (ω), and a disturbing force (P) of the forced vibrations.

The tabulated data Ton technological regimes of compaction comprises at least the following characteristics: the depth of compaction (H), the time of compaction (t), and the number of compaction sessions.

Generally, the technological optimization model is capable of evaluating the sought for dynamic and technological parameters of the compaction process based on the following empiric form:

K =f(A, ω , fst, fdyπ, fs/fdyn, t, w, σ_cont, L,V, H) (1)

Where

K is the soil compaction degree

A is the vibration amplitude of the working member ω is the vibration frequency of the working member fst is the static pressure upon the soil fdyn is the dynamic pressure upon the soil st fd n is a ratio of static and dynamic pressures t is the time of compaction w is the dampness of the soil σ_cont is the value of contact pressure allowed for the soil

H is the depth of compaction

V is the velocity of the working member's motion

L is a coefficient of the working member's shape.

More particularly, the above empiric form can be presented as a polynomial model:

K^ ^Ko+ cXj + βX₂ + χ∑s + δX₄ ... + sX_n... φX_N , (2)

Where:

K_opt - the optimal compaction degree for a particular soil layer, given in percents or relative units;

Kn - degree of compaction of the layer at average values of eleven factors (parameters) forming the polynomial (2) and indicated in the equation (1); a, β, χ, δ, ε, φ - semi-empiric numerical coefficients;

Xi , X₂ , Xs , X4 , ••• XΠ -.XN - changes in at least the 11 factors of the compaction process indicated in equation (1); φXx reflects a possibility of introducing at least one additional new factor into the optimization model.

The invention involves an additional aspect, according to which there is provided a method for express-examination of an existing soil base, enabling the use of the above-described mathematical model for obtaining data on a number of layers in the base and their compaction degree.

The method for examination of an existing single- or multi-layer soil base of a road or the like by a vibratory compaction equipment, which includes the following steps: feeding into the base a control signal constituting mechanical vibrations from one piece of available equipment having known static S and dynamic D parameters, according to characteristics Jof a technological regime of vibrations; after the control signal has ceased, registering a fading response signal received by the working member from the base, and estimating a number of layers in the soil base and their properties based on the number and frequencies of resonance peaks in the fading response signal, the estimation being provided by a mathematical model capable of processing the obtained resonant frequencies, the static S and dynamic D parameters of the equipment, and characteristics T of the technological regime of vibrations.

As has been mentioned, the structure of the mathematical model suitable for the above-described method of soil examination can be essentially similar to that of the mathematical model used in the method of soil compaction.

According to the most preferred version of the compaction method, steps (a) and (d) thereof are performed using the above-described method of soil examination.

In accordance with a further aspect of the present invention, there is provided a system for optimal compaction or express-examination of an existing soil base of a road, railway or the like, the system including:

a stock of machines capable of effecting soil compaction, each being provided with a vibratory working member; a computerized control unit capable of being switched manually or automatically between a mode of soil compaction and a mode of soil examination in accordance with the above-described methods, respectively.

In the mode of soil compaction, the computerized control unit is capable of obtaining data on the soil properties, processing the data, generating recommendations for a compaction session including selection of one of the machines from the stock with its parameters and technological regimes of the compaction, controlling the compaction process, and checking results thereof in real time in accordance with the method of soil compaction. In the mode of soil examination, the computerized control unit is capable of:

-recording characteristics of a control vibratory signal being fed into the soil base, static S and dynamic D parameters of the equipment, and characteristics T of a technological regime of the control signal;

-registering a fading response signal received by the working member from the base, -estimating a number of layers in the soil base and their properties based on the number and frequencies of resonance peaks in the fading response signal, the estimation being provided by a mathematical model capable of processing the obtained resonant frequencies, the static S and dynamic D parameters of the equipment, and characteristics T of the technological regime of vibrations.

In one specific embodiment of the system the computerized control unit comprises an interface, a memory, and a processing module; wherein

the interface is capable of obtaining data on the soil properties, transmitting thereof to the memory and the processing module, receiving output data from the processing module, and displaying the data; the memory is intended for storing the mathematical model formed from the dynamic model, the technological optimization model, and the reference data tables RDl and RD2; the processing module is capable of processing data on the soil properties and data obtained from reference data tables RDl and RD2 according to the mathematical model, and of generating output data according to either the mode of soil compaction or the mode of soil examination.

According to one embodiment of the system, the processing module is a microprocessor; the memory being located in a computer. In the most preferred embodiment, the microprocessor is provided with a storage device serving as the memory, so there is no need to use an external computer in the system.

The obtained output data may or may not be displayed by the interface, and can either be used by an operator for manually adjusting the selected compacting machine, or be ^' automatically transferred to it via a commander module designed for the purpose. There is further provided, in accordance with an additional preferred embodiment of the present invention, a method for evaluating the compaction, by means of a vibrator compaction device having mass M_vj₀ and a bearing area F, of a preselected soil layer, for which a predetermined degree of compaction is desired, at a preselected depth £ in a soil base having at least one layer disposed between an exterior upper surface and a hard bottom layer, thereby defining a vibrator-soil-base system, which includes the steps of: evaluating a desired volumetric mass γ_S{ of the preselected soil layer corresponding to the desired degree of compaction, which may be performed by measurement or by calculation using standard soil data; calculating a mass per unit area m_soji of the preselected soil layer as a function of the desired volumetric mass, using the formula:

^msoil ⁼ y_st * -^ calculating the effective vibrating mass M of the vibrator-soil-base system as a function of the mass per unit area of the preselected soil layer and the mass of the vibrator, using the formula:

M = M_vib + l/3 ( m_soil * F ) ; determining the natural oscillation frequency ω₀ of the vibrator-soil-base system when the preselected soil layer is at the desired degree of compaction as a function of its effective mass, using the formula: ω₀ = (C / M)

wherein C is the stiffness coefficient of the soil of the preselected soil layer; measuring the forced oscillation frequency ω_res of the vibrator-soil-base system for frequencies close to the natural oscillation frequency ω₀;

deriving the volumetric mass γ of the preselected soil layer as a function of the desired volumetric mass of the preselected soil layer and of the natural oscillation frequency and the forced oscillation frequency of the vibrator-soil-base system, using the formula: y⁼ yst * ( es ^{/ co}o)² ; ^and determining compaction degree K of the compacted preselected soil layer. The step of determining the compaction degree K of the compacted preselected soil layer may be performed using the formula: κ = γ/γ_st ; or alternatively, if suitable measurements have been taken and the required parameters are known, using the formula: - (ω_res / ω₀)² .

Operation of the dynamic and the technological optimization models will be further explained in the specific description of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carried out in practice, a preferred embodiment will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

Fig. la is a schematic cross-sectional view of an existing multi-layer soil base to be compacted by compaction equipment before starting construction of a road or the like.

Fig. lb schematically illustrates a mechanical system with elastic, dissipative and mass properties being a dynamic simulation of the multi-layer soil base shown in Fig. la.

Fig. 2 is a schematic algorithm of the inventive method for compaction of a soil base.

Fig. 3 is a block-diagram schematically illustrating structure of the mathematical model indicated in Fig. 2.

Fig. 4 schematically shows an embodiment of a compacting machine adapted to be controlled according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Fig. la illustrates a soil core (base) to be compacted, while Fig. lb shows its dynamic model. The soil base consists of an embankment 2 (e.g., an additional soil layer of a railroad bed), (a fill) placed directly on sedimentary layers 3, below which there are a highly weathered soil layers 4, scarcely weathered soil layers 5, and a rock bed 6. Compaction is performed with a vibrator 1.

Data on dynamic (i.e. elastic, mass, and dissipative) properties of the soil base can be obtained for each of the soil layers down the rock bed from a preliminary geological exploration, as well as field and laboratory tests done before the beginning of the work. For example, the elastic properties of the soil are equivalent to elastic compression factors; mass properties are defined by volumetric masses of the soil layer, and dissipative properties can be inferred by any known technique, such as from a vibrogram of damped vibrations.

Based on static and dynamic parameters of the vibrator (its weight, frequency variation limits, disturbing force, power), natural frequency spectrum (i.e. resonance frequencies) of the dynamic system "vibrator - elastic base" can be obtained. Vibration amplitudes of the vibrator and mass displacements in different layers of the soil base can be determined by solving a set of differential equations for forced vibrations at a specific disturbing force of the vibrator and specific vibration frequencies, provided that the forced vibration frequency approaches to one or another natural vibration frequency of the system. Fig. lb shows a dynamic system having mass and elastic properties, which simulates the "vibrator - soil base" system illustrated in Fig. la. Dissipative properties are neglected in this specific model. In the figure, Mi to j designate mass properties of the vibrator 1 and three generalized layers between the vibrator 1 and the rock bed 6. Since soil layers 2 and 3 shown in Fig. la have substantially similar dynamic parameters and behavior, they are combined in one block M₂in this simulation. "Springs" Ci to C₄ designate elastic properties of each pair of the adjacent members of the system. Arrows Xj; to Xt indicate center displacements of masses Mi to M₄. Free vibrations of the system can be represented by the following differential equations:

d²X^' _x , 1 d i + C_l t². (X_l - X₂) = 0

(3)

M₂^ ~ C_X(X_X - X₂) + C₂(X₂ -X₃) = 0 at

M₃ ~ -C₂(X₂ -X₃) + C₃(X₃ -X₄) = 0

M₄^-C₃(X₃ -X₄) + C₄X₄ =0 at Upon solving the system of the equations by a known technique (as described, for example, in SU 763506), a number of resonance frequencies of the system can be obtained.

Entering particular physical-mathematical characteristics into the mathematical model enables motion parameters of the working member and of different soil layers to be computed and allows appropriate corrections to the working member motion to be entered.

On the other hand, monitoring the amplitude and frequency of the vibration of the soil layer in contact with the vibro-compactor surface enables estimation of dynamic stress in any region of the soil under compaction and prediction of its compaction rate by comparing obtained values with tabulated values thus allowing proper corrections to be made.

It will be shown now, how dynamic parameters of the system of Fig. la can be evaluated with account for specific values of a disturbing force Psinωt and modulus of dissipation γ. The dissipation modulus (or the so-called internal friction factor) is given by γ = δ/π, where δ is a logarithmic decrement of vibration.

For the case under study, differential equations of vibrating mass motion with account for plastic resistance can be represented in the following form (4):

d²x M_x ^- ^{x_x -x₂){\+iγ)+P^ ¹ dt²

d²x₂ , I = C_λ (x_λ - x₂ )(1 + iγ) - C₂ (x₂ ^■ x₃)(l + iγ)

d²X , iy)-C₃χ₃(l + iγ) ^~a ΛΨ2 C₂(x₂ ~ x₃)(l +

We seek the partial solutions of the set of equations (4) in the form:

x _j = a _λ e "" (5)

iwt In equations (4) and (5) :

xι ; x₂ ; x₃ are the complex values of displacements and af, a_{2 ;} a₃ are the complex values of amplitudes of vibration e is the base of natural logarithms; i is the imaginary number = - 1 (forming the base of complex numbers) .

After proper manipulations, the solution of the set (5) takes the following general form:

X, = Aj cosfω t + (a-β)] (6)

X₂ = A₂ cosfω t + (a_rβ)] (7)

X₃ = A₃ cosfω t + (_a2-β)] (8)

The full solution is not given because of its awkwardness.

Solutions of equations (6), (7) and (8) define the values of vibration amplitudes Ai, A₂, A₃, the phase shift angles (α-β); (αi-β); (α -β) at specific values of the system parameters, of the disturbing force and dissipation modulus. Signs (+ or -) of the obtained amplitude values and the angles enable the choice of a suitable phase regime for compacting each specific layer of the soil base. In other words, the above equations comprise information for selecting the regime when two layers adjoining a layer undergoing the compaction to vibrate with having phases differing by 180° from that of the layer to be compacted.

The obtained results are used as follows: the known values of P and ω and, say, the obtained value of amplitude A₂ of the second layer are introduced in the technological optimization model for obtaining an optimal combination C of parameters suitable for effective compaction of the second layer. Optimal combinations for compaction of other layers are found in the similar way. If the optimization model is unable to suggest a suitable combination based on the mentioned input, the disturbing force P or the frequency ω can be adjusted.

Fig. 2 shows a schematic block-diagram of the method for optimal soil compaction according to the invention. Initial data on the soil properties is obtained (block 10 of the algorithm) according to any of the above-described techniques. From block 10 the information is entered into a mathematical model generally marked 12 where it is processed. If the compaction degree of a particular layer of a multi-layered base (or the compaction degree of a single-layer base) is not lower than the optimal degree Ko_Pt, pre-set for this layer (block 14), compaction is not required. If it is lower, the mathematical model will generate at least one optimal combination C of parameters of equipment and technological process suitable for compacting this layer up to the optimal compaction degree in the resonance condition or close to it (block 16). According to the obtained optimal combination, a specific piece of compaction equipment is selected and adjusted, and the compaction process is carried out in a recommended regime (block 18). Simultaneously or after a session of compaction, current data on the soil properties is obtained (block 19) and fed back to the mathematical model for evaluation whether the optimal compaction degree has been achieved. If not, a new optimal combination C will be generated until the particular layer is compacted optimally. Then, if the multi-layered base is considered, the process can be repeated for another layer thereof.

Fig. 3 explains in more detail how the mathematical model 12 can be organized. For example, after initial or current data on the soil properties is obtained, a particular layer thereof is selected for being compacted first. Usually, it is a layer having the minimal resonant frequency. The initial data on the selected layer is entered in a reference data table RDl (block 22) representative of dynamic properties of any known soil materials, wherein the dynamic properties of each soil material are presented in groups being associated with maximal, optimal and minimal compaction degrees for this material. That enables the real compaction degree of the layer to be compared with the tabulated compaction degree (block 14) so that, if they are sufficiently close, another layer may be chosen to be compacted. If the compaction degree is lower than the optimal, the data is further processed by the interacting dynamic model (block 24) and technological optimization model (block 26) with the aid of a reference data table RD2 (block 28) comprising information on static S and dynamic D parameters of different compaction machines. The dynamic model, based on the initial or current input obtained from RDl and provisional data from RD2, is capable of determining an amplitude A and frequency ω of the working member of a provisional compaction equipment, the frequency being close to one of the resonance frequencies of the system, corresponding to the selected soil layer. In turn, the technological optimization model generates a number of optimal combinations C where the optimal compaction degree K is supposed to be associated with the amplitude A and frequency ω, as well as with specific static S and dynamic D parameters of a specific compaction machine and with specific characteristics T of the technological process. The process of discovering such combinations may be iterative, which is shown by two-directional arrows in the drawing.

Fig. 4 illustrates a vibratory compaction machine 30 being part of a semi-automatic system for optimal soil compaction. The machine 30 is positioned on a soil base 32 and comprises a working vibrating member 34 placed on a working plate 36 which is provided with optional interchangeable weights 38 for regulation of amplitude, static pressure, and dynamic pressure of the machine. Frequency of vibrations ω of the working member 34 is controlled by a regulator 40 resting on a plate 42. The plate 42 is protected from vibrations by springs 44; the springs 44 support the plate 42 above a plate 46 which is itself carried by springs 48 secured to the working plate 36. The machine is provided with accelerometers 50 (i.e. detectors of frequency, amplitude, acceleration or the related values) which are connected to a computer 52 via interface 54. The computer is capable of obtaining and processing initial and current information on the soil properties according to the inventive method, and is adapted to produce recommended sets of parameters A, ω, S, D, etc. and regimes T on a display 56. According to the recommended parameters, an operator (with or without the aid of the interface 54 and a commander module 58) adjusts the weight, frequency and amplitude of the compaction machine and performs the compaction in agreement with the optimal regime.

The present invention further includes a method for evaluating the compaction of a preselected soil layer, for which a predetermined degree of compaction is desired, at a preselected depth £ in a soil base having at least one layer disposed between an exterior upper surface and a hard bottom layer. The compaction is achieved by means of a vibrator compaction device having mass M_vjD and a bearing area F, thereby defining, with the soil base, a vibrator-soil-base system for modeling and calculation as discussed hereinabove. The method includes the following steps: evaluating the desired volumetric mass γ_S{ of the preselected soil layer corresponding to the desired degree of compaction; calculating the mass per unit area m_sojι of the preselected soil layer as a function of the desired volumetric mass, using the formula:

^msoii ⁼Yst * ^ ; calculating the effective vibrating mass M of the vibrator-soil-base system as a function of the mass per unit area of the preselected soil layer and the mass of the vibrator, using the formula:

M = M_vib + l/3 (m_soil * F ) _; determining the natural oscillation frequency ω₀ of the vibrator-soil-base system when the preselected soil layer is at the desired degree of compaction as a function of its effective mass, using the formula: ω₀ = V(C / M)

deriving the volumetric mass γ in field conditions of the preselected soil layer as a function of the desired volumetric mass of the preselected soil layer and of the natural oscillation frequency and the forced oscillation frequency of the vibrator-soil-base system, using the formula:

Y ⁼ Yst * es ^{/ ω}o)² ; ^and determining compaction degree K of the compacted preselected soil layer.

The step of evaluating the desired volumetric mass may be performed by measurement on samples compacted to the desired degree under laboratory conditions or by measurement taken in situ on actual soil layers suitably compacted. Alternatively, the desired volumetric mass may be evaluated by calculation from standard soil data.

In the step of calculating the effective vibrating mass of the vibrator-soil-base system, the factor "1/3 ( m_soji * F )" is the effective portion of the soil base participating in the oscillations of the vibrator-soil-base system. In the step of determining the natural oscillation frequency, the stiffness coefficient of the soil, C, may be experimentally determined; or it may be calculated as a function of the elastic modulus of the soil, E, using the formula:

C = E * F / . The step of determining the compaction degree K of the compacted preselected soil layer may be performed using the formula:

K = γ/γst ; or alternatively, if suitable measurements have been taken and the required parameters are known, using the formula:

K = (ω_res / ω₀)² .

The method and mathematical model described hereinabove may also be applied to evaluate the quality of building structures wherein the frequency response characteristics of a structure to mechanical or other excitations are measured and compared to those of measured, tested, or idealized reference structures.

It will further be appreciated by persons skilled in the art that the scope of the present invention is not limited by what has been specifically shown and described hereinabove, merely by way of example. Rather, the scope of the present invention is defined solely by the claims, which follow.

Claims

1. A method for examination of a soil base having at least one layer disposed between an exterior surface and a hard bottom layer, said method including the steps of:

- feeding into the soil base a control signal constituting mechanical vibrations from one available equipment having known static S and dynamic D parameters and according to characteristics f of a technological regime of vibrations;

- after the control signal has ceased, registering a fading response signal received by a working member from the soil base; and

- estimating the number of layers in the soil base and their properties based on the number and frequencies of resonance peaks in the fading response signal, the estimation being provided by a mathematical model capable of processing the obtained resonant frequencies, the static S and dynamic D parameters of the equipment and characteristics T of the technological regime of vibrations.

2. A method for compaction of a soil base having at least one layer disposed between an exterior surface and a hard bottom layer, said method including the steps of: a) obtaining initial data I representative of the properties of a segment of the existing base disposed between a predetermined area segment to be compacted and a hard bottom layer;

b) introducing the obtained initial data I into a mathematical model capable of processing the initial data and generating an optimal combination C of conditions if the compaction degree of the soil base segment is lower than a pre-selected optimal compaction degree K; the optimal combination C including static S, and dynamic D parameters of an equipment for compacting the soil base segment in a state close to the resonance of the segment, and characteristics T of a technological regime of compaction; the optimal combination C of conditions being appropriate for compacting the segment of the soil base an optimal manner as long as the initial data I remains representative of the properties of the segment of the soil base to be compacted; c) selecting one of the compaction equipment and adjusting operation thereof according to the static S and dynamic D parameters appearing in the optimal combination C, and initiating the vibratory compaction according to the characteristics T of the technological regime derived from the optimal combination C; d) obtaining current data T representative of the properties of the soil base segment; and e) introducing the current data I' into the mathematical model and repeating steps (b) to (d) until the compaction degree of the soil base segment is at least equal to the pre-selected optimal compaction degree K; and performing said steps (a) and (d) using the mathematical model in accordance with the method of Claim 1.

3. A system for compaction and examination of a soil base having at least two layers disposed between an exterior surface and a hard bottom layer , the system including: at least one adjustable machine capable of effecting soil compaction, each being provided with an adjustable vibratory working member; and a computerized control unit capable of operating in at least one of first and second modes, said first mode being a mode of soil examination enabling acquisition of data representative of the soil base properties, including the number of layers and their degrees of compaction, to be derived by processing a vibratory control signal fed to the soil base from one of said machines and the soil base's reaction thereto, and said second mode being a mode of soil compaction enabling an optimal combination of parameters to be generated by said control unit for performing optimal compaction of each of the layers of the soil base by one of said machines.

4. The system according to claim 3 wherein said computerized control unit is capable of working in both said modes intermittently, and of being switched manually or automatically from said second mode of soil compaction to said first mode of soil examination and vice versa.

5. A system for compaction and examination of a soil base having at least one layer disposed between an exterior surface and a hard bottom layer, the system including: at least one adjustable machine capable of effecting soil compaction, each being provided with an adjustable vibratory working member; and

a computerized control unit capable of operating in at least one of first and second modes, said first mode being a mode of soil examination enabling acquisition of data representative of the soil base properties to be derived by processing a vibratory control signal fed to the soil base from one of said machines and the soil base's reaction thereto, and said second mode being a mode of soil compaction enabling the method according to Claim 2 to be performed.

6. A system for compaction and examination of a soil base having at least one layer disposed between an exterior surface and a hard bottom layer , the system including:

at least one adjustable machine capable of effecting soil compaction, each being provided with an adjustable vibratory working member; and a computerized control unit capable of operating in at least one of first and second modes, said first mode being a mode of soil compaction enabling an optimal combination of parameters to be generated by said control unit for performing the optimal compaction of said soil base by one of said machines, and said second mode being a mode of soil examination according to the method of Claim 1.

7. The system according to Claim 3, wherein said computerized control unit includes an interface, a memory; and a processor module; and wherein said interface is operative to receive data representative of the soil properties and parameters of said at least one machine, to feed thereof to said memory and to said processing module, to obtain output data from said processor module, and to display said data;

said memory being intended for storing a mathematical model, a first set of reference data representative of the properties of various soils and a second set of reference data representative of the static S and dynamic D parameters of a plurality of compaction equipments; said processor module is operative to process data obtained from said interface, and said first and said second sets of reference data according to the mathematical model, and to generate output data according to one of said second mode of soil compaction and said first mode of soil examination to be fed to said interface.

8. The system according to Claim 7, wherein said processor module is a microprocessor.

9. The system according to Claim 8, wherein said microprocessor is provided with a storage device serving as said memory.

10. A method for compaction of a soil base disposed between an exterior surface and a hard bottom layer, said method including the steps of: a) obtaining initial data / representative of properties, including the compaction degree, of a segment of a soil base to be compacted, having at least one layer disposed between a predetermined surface section and a hard bottom layer; b) processing the obtained initial data / so as to determine therefrom resonant frequencies for each layer of the soil base, and

if the compaction degree of the base segment is lower than a preselected optimal compaction degree K, then also to generate an optimal combination of conditions C including: static parameters S and dynamic parameters D for at least one of a preselected set of compaction apparatuses for compacting the segment of the soil base at a frequency within a preselected frequency range of one of the generated resonance frequencies; and characteristic parameters 7 of a technological procedure of vibratory compaction;

wherein combination of conditions C is optimal for compacting the segment of the soil base, as long as the data continues to be representative of the properties of the segment of the soil base to be compacted;

c) selecting a compaction apparatus for performing compaction in accordance with combination of conditions C, capable of being configured in accordance with said parameters S and D, and operating the compaction apparatus in accordance with said parameters T; d) obtaining current data /' representative of properties of the soil base segment undergoing compaction; and e) repeating said step (b) of processing with the current data /' in place of the initial data / and also repeating said steps (c) of selecting and operating, and (d) of obtaining, until the compaction degree of the base segment is at least substantially equal to the oreselected ootimal comoaction degree K.

1. A method according to claim 10 wherern said step of processing includes introducing the obtained data into a mathematical model operative to generate two multiplicities of resonant frequencies associated with the layers of the soil base from the data, a first multiplicity based on initial data / representative of properties of the soil base segment and a second multiplicity based on a preselected optimal compaction degree K for the soil base segment, and, if the compaction degree of the base segment is lower than the preselected optimal compaction degree K, further to generate an optimal combination C of conditions for compacting said segment of the existing base, as long as the initial data / continues to be representative of the properties of the segment of the soil base to be compacted.

12. A method according to claim 10 wherein said step of obtaining initial data / representative of properties of the segment of the soil base includes obtaining data on the number, type, and degree of compaction of the soil layers in the segment.

13. A method according to claim 10 wherein said step of obtaining initial data / representative of the properties of the segment of the soil base includes performing a preliminary examination of the base, thereby directly obtaining the data on the number, the types of layers in the soil base, and their compaction degree.

14. A method according to claim 10 wherein said step of obtaining initial data / representative of the properties of the segment of the soil base is performed using compaction apparatus having a vibratory working member of a preselected mass and includes the following substeps: exciting the segment of the soil base with vibrations of a predetermined amplitude, frequency, and duration by means of the vibratory working member of the compaction apparatus; receiving, via the vibratory working member, a vibratory response from the segment of the soil base after excitation; providing an output signal corresponding to the received vibratory response; performing frequency analysis of the output signal to determine the resonance frequencies of the layers in the segment of the soil base and to estimate therefrom the number and selected properties thereof.

15. A method according to claim 10 wherein said step of obtaining current data I' representative of properties of the soil base segment undergoing compaction includes obtaining data on the degree of compaction of the layers of the soil base segment, and wherein said step of obtaining current data /' further is performed at one of: during and after the step of selecting and operating.

16. A method according to claim 15 wherein said step of obtaining current data /' representative of properties of the soil base segment undergoing compaction includes the following substeps: exciting the segment of the soil base with vibrations of a frequency within a preselected frequency range of the generated resonance frequency of a particular soil layer within the soil base segment when the layer is optimally compacted; receiving a vibratory response from the segment of the soil base after excitation; providing an output signal corresponding to the received vibratory response;

performing frequency analysis of the output signal to determine the resonance frequencies of the layer in the segment of the soil base and to estimate therefrom the current degree of compaction of the layer.

7. A method according to claim 11 wherein said step of processing includes the substeps of: representing, by means of a dynamic mathematical model, the segment of the existing soil base and a compaction apparatus as a system of differential equations simulating their vibratory motion as oscillatory motion substantially at the resonance frequencies thereof and taking into account the dynamic D parameters of the compaction apparatus and the properties of the soil base segment; generating, by means of a technological optimization model, a multiplicity of optimal combinations Cj, C₂, —.C_M, wherein each combination is derived from the properties of the soil base segment, the preselected optimal degree of compaction K, the static S and dynamic D parameters of a selected compaction apparatus, and the characteristic parameters T of the technological procedure, and selecting, by means of the technological optimization model, an optimal combination C, suitable for compacting the soil base segment at a frequency within a preselected frequency range of the resonance frequency of a selected soil layer within the soil base segment by a selected compaction apparatus.

18. A method according to claim 17 wherein:

the preselected optimal compaction degree K is a set of optimal compaction degrees Kj, K , ...K_M corresponding respectively to N different layers of the soil base segment;

said step of processing further includes the substeps of: generating the set of optimal compaction degrees and a set of N optimal combinations (Cι, C₂, .... C_M )_N f r each of the N layers of the soil base segment, and selecting one optimal combination C,„ for each respective soil layer; and wherein said step of selecting and operating is performed for each respective layer of the soil base segment.

19. A method according to claim 17 wherein: the soil base segment is one of: a single-layer soil base segment and a multi-layered soil base with layers having similar properties; and the preselected optimal compaction degree K is an average value of the set of optimal compaction degrees j, K₂, ...K_N corresponding respectively to N different layers of the soil base segment.

20. A method according to claim 18 further including, before said step of selecting and operating, the step of determining the layer of the soil base segment having a minimal resonant frequency, and wherein said step of selecting and operating is performed initially for the layer of the soil base segment having the minimal resonant frequency.

21. A method according to claim 17 wherein said substep of representing further includes the substep of selecting a phase regime of vibratory motion of two layers adjacent to a layer undergoing compaction having phases differing by 180° from that of the motion of the layer to be compacted.

22. A method according to claim 11 wherein the mathematical model includes two reference data tables RDl and RD2, wherein:

RDl is a soils data table representative of values of dynamic parameters L of a plurality of known soil types, each value associated with a particular compaction degree of the soil, the data table preferably providing parameter values for each soil type corresponding to at least three degrees of compaction, including minimal, optimal and maximal compaction;

RD2 is an equipment data table representative of technical characteristics of a plurality of known and available soil compaction apparatuses, which includes both static S and dynamic D parameters thereof; and wherein said step of processing further includes, prior to any other substeps, the substeps of: choosing, from RDl, based on the initial data / for the soil base segment, tabulated sets of dynamic parameters L representative of each of the soil layers and of its respective degree of compaction; and using the tabulated data obtained from RDl and from RD2 as input data for processing.

23. A method according to claim 22 wherein: the tabulated set of dynamic parameters L of known soil types includes at least: specific mass (M), elasticity modulus (E), and modulus of dissipation (γ); the tabulated set of static parameters S of a compaction apparatus includes at least: specific static pressure of the equipment upon the soil (f_st), range of masses (m) of the apparatus and its working member, and its total weight;

the tabulated set of dynamic parameters D of a compaction apparatus includes at least: specific dynamic pressure of the apparatus fd_yn), vibration amplitude A of the working member, its vibration frequency (ω), and the disturbing force (P) of the vibrations; and the tabulated set of characteristic parameters T of technological procedures of compaction includes at least: the depth of compaction (H), the time of compaction (t), and the number of compaction sessions.

4. A method according to claim 17 wherein said substep of generating, by means of a technological optimization model, includes generating the desired dynamic and technological parameters for the compaction process based on the following empiric form:

K =f(A, ω , f_st, fdyn, fs fdyn, t, w, σ_cont, L, V, H), wherein:

K is the soil compaction degree

A is the vibration amplitude of the working member ω is the vibration frequency of the working member

f_t is the static pressure upon the soil

fdyn is the dynamic pressure upon the soil

fst/f yn is a ratio of static and dynamic pressures t is the time of compaction w is the dampness of the soil

σ_cont is the value of contact pressure allowed for the soil

H is the depth of compaction

V is the velocity of the working member's motion

L is a shape coefficient for the working member.

25. A method according to claim 24 wherein said empiric form of the technological optimization model is a polynomial which has provision for including additional factors in the optimization model.

6. A method for evaluating the compaction, by means of a vibrator compaction device having mass M_vj_b and a bearing area F, of a preselected soil layer, for which a predetermined degree of compaction is desired, at a preselected depth I in a soil base having at least one layer disposed between an exterior upper surface and a hard bottom layer, thereby defining a vibrator-soil-base system, said method including the steps of: evaluating a desired volumetric mass y_st of the preselected soil layer corresponding to the desired degree of compaction; calculating a mass per unit area m_so}i of the preselected soil layer as a function of the desired volumetric mass; calculating the effective vibrating mass M of the vibrator-soil-base system as a function of the mass per unit area of the preselected soil layer and the mass of the vibrator; determining the natural oscillation frequency ω₀ of the vibrator-soil-base system when the preselected soil layer is at the desired degree of compaction as a function of its effective mass; measuring the forced oscillation frequency ω_res of the vibrator-soil-base system within a preselected frequency range of the natural oscillation frequency ω₀;

deriving the volumetric mass γ of the preselected soil layer as a function of the desired volumetric mass of the preselected soil layer and of the natural oscillation frequency and the forced oscillation frequency of the vibrator-soil-base system; and determining compaction degree K of the compacted preselected soil layer.

27. A method for evaluating the compaction according to claim 26 wherein said step of evaluating the volumetric mass is measuring the volumetric mass of a sample of the soil of the preselected soil layer compacted to the desired degree of compaction.

28. A method for evaluating the compaction according to claim 26 wherein said step of evaluating the volumetric mass is performed by calculation using standard soil data.

29. A method for evaluating the compaction according to claim 26 wherein in said step of calculating a mass per unit area: ^msoil ⁼ Yst ^:

30. A method for evaluating the compaction according to claim 26 wherein in said step of calculating the effective vibrating mass:

M = M_vib + l/3 ( m_soil * F )

31. A method for evaluating the compaction according to claim 26 wherein in said step of determining the natural oscillation frequency: ω₀ = V(C / M)

wherein C is the stiffness coefficient of the soil of the preselected soil layer.

32. A method for evaluating the compaction according to claim 26 wherein in said step of deriving the volumetric mass:

Y ⁼ Yst * (ω_res / ω₀)²

33. A method for evaluating the compaction according to claim 26 wherein in said step of determining compaction degree: κ = γ/γ_st

34. A method for evaluating the compaction according to claim 26 wherein in said step of determining compaction degree:

"- v^res ' ^(y