CN102809642B - Method for determining hydrogeological parameters of aquitard - Google Patents

Abstract

The invention discloses a method for determining hydrogeological parameters of an aquitard. The method includes deducing an analytical solution of a flow formula of the unit horizontal area of the aquitard under the condition that a water head of one side of a cylinder of the aquitard is decreased by a certain constant; and then providing experimental data on the basis that flow varies along with time, and determining a conductivity coefficient, a permeability coefficient and a water storage rate of the aquitard by a curve fitting method. The analytical solution deduced in the method is rigorous in theory, an experiment device and an experiment process are simple and are easy to operate, the parameters are determined by the curve fitting method, the method is easy to control; the large quantity of parameters including the conductivity coefficient, the permeability coefficient and the water storage rate of the aquitard can be obtained by one experiment; and the flow is measured easily, errors are low, and accordingly precision of the obtained parameters is high. Accordingly, the method has high popularization and application values.

Description

A kind of method determining aquitard hydrogeological parameter

Technical field

The present invention relates to a kind of method determining aquitard hydrogeological parameter, especially a kind of method determining the hydrogeological parameter such as aquitard transmissibility factor, infiltration coefficient, water storage rate.

Background technology

Along with the quickening of urbanization, the resources and environment problem relevant with underground water is on the rise.Only Yangtze River in China delta, the area that the land subsidence caused due to groundwater mining is greater than 200mm has accounted for 1/10th of region area, and wherein cumulative maximum settling amount reaches 2.80m, and the economic loss caused reaches 50,000,000,000 dollars; The pollution of underground water is also expanded to deep by water-bearing zone, top.The hydrogeological characteristic of the ingredient aquitard that all these and aquifer System are important is closely related.The hydrogeological parameter (as transmissibility factor, infiltration coefficient, water storage rate) of aquitard is not only significant to prediction, evaluation and control land subsidence, and has great significance to the research of groundwater resources development, evaluation and calculating and aquifer System Contaminants Transport rule and thermal energy conduction rule.

Have more research for water-bearing zone hydrogeological parameter defining method, great majority are for drawing water the method that (or water filling) test at scene.But, the aquitard of adjacent aquifers hydrogeological parameter defining method research little, this is because we think that aquitard is water-resisting layer or relative water resisting layer all the time on the one hand, very little as its contribution rate of water resources quantity, therefore seldom attach the importance specially and obtain necessary research, often aquitard to be ignored or as a kind of boundary treatment; Also lack on the other hand a kind of effective principle and method can be used for scene or indoor and directly determine these parameters.

Summary of the invention

Goal of the invention: the present invention is based on the flow formula analytic solution that aquitard cylinder side head reduces aquitard unit level area under a certain constant condition, propose a kind of method determining aquitard hydrogeological parameter, and Binding experiment is verified.This method is not only theoretical tight, and there is experimental provision and experimentation simple, easy to operate, the parameter of acquisition is complete, precision advantages of higher.Therefore good application value is had.

Technical scheme: a kind of method determining aquitard hydrogeological parameter, first, based on soil-column test model, the flow formula analytic solution of under aquitard cylinder side head the reduces a certain constant condition aquitard unit level area of deriving; Then, provide based on the time dependent experimental data of flow, adopt the method for herbal combination determination aquitard transmissibility factor, infiltration coefficient and water storage rate.

Described soil-column test model comprises lower filtering layer, sample section, upper filtering layer, water from top to bottom successively; The aquitard cylinder bottom sidewall of described lower filtering layer upper end is provided with rising pipe, and rising pipe extends upwardly to more than sample section, the corresponding water receiving container of water delivering orifice of rising pipe, and water outlet is provided with valve; Described soil-column test model top is provided with overflow vent, and the height of overflow vent is greater than the height of water delivering orifice; Described soil-column test model is provided with water inlet topmost; Described water inlet is provided with valve.

Described based on the time dependent experimental data of flow, adopt the method for herbal combination determination aquitard transmissibility factor, infiltration coefficient and water storage rate, be about to the flow Q of the aquitard of record divided by aquitard cylinder cross-sectional area S, turn to unit area flow q (cm/min), with the log-log coordinate system of typical curve identical molds in make q ~ t measured curve, with typical curve distribution, makes two curves overlapped best, an optional match point, writes down corresponding coordinate figure [q], [t], substitutes into respective formula and calculates transmissibility factor a, coefficient of permeability K, water storage rate μ.

Beneficial effect: compared with prior art, provided by the present inventionly determine that the method for aquitard hydrogeological parameter has the following advantages:

1. the analytic solution pushed away, theoretical tight, because the method has strict theoretical foundation;

2. experimental provision and experimentation simple, easy to operate, also can directly enchashment field former state soil experiment;

3. adopt herbal combination determination parameter, method is simple and easy to grasp;

4. once experiment can try to achieve aquitard transmissibility factor, infiltration coefficient and water storage rate simultaneously, and the parameter of acquisition is many;

5. because flow measurement easily realizes and error is little, the parameters precision of trying to achieve thus is high.Therefore, the method has good application value.

Accompanying drawing explanation

Fig. 1 is the process flow diagram of the embodiment of the present invention;

Fig. 2 is the soil-column test model of the embodiment of the present invention;

Fig. 3 is cross section flow typical curve;

Fig. 4 is cross section flow typical curve;

Fig. 5 is that the herbal combination of the embodiment of the present invention asks ginseng principle schematic;

Fig. 6 is flow rate calculation value and the observed reading matched curve of the embodiment of the present invention.

Embodiment

Below in conjunction with specific embodiment, illustrate the present invention further, these embodiments should be understood only be not used in for illustration of the present invention and limit the scope of the invention, after having read the present invention, the amendment of those skilled in the art to the various equivalent form of value of the present invention has all fallen within the application's claims limited range.

Determine the method for aquitard hydrogeological parameter, first, based on soil-column test model, the flow formula analytic solution of under aquitard cylinder side head the reduces a certain constant condition aquitard unit level area of deriving; Then, provide based on the time dependent experimental data of flow, adopt the method for herbal combination determination aquitard transmissibility factor, infiltration coefficient and water storage rate.

Soil-column test model comprises lower filtering layer, sample section, upper filtering layer, water from top to bottom successively; The aquitard cylinder bottom sidewall of described lower filtering layer upper end is provided with rising pipe, and rising pipe extends upwardly to more than sample section, the corresponding water receiving container of water delivering orifice of rising pipe, and water outlet is provided with valve; Described soil-column test model top is provided with overflow vent, and the height of overflow vent is greater than the height of water delivering orifice; Described soil-column test model is provided with water inlet topmost; Described water inlet is provided with valve.

The principle that aquitard parameter is determined:

(1) analytic solution of aquitard pattern of water flow

Suppose the saturated pressure-bearing of aquitard cylinder and pressure head is equal everywhere, on the downside of aquitard cylinder, head reduces certain certain value and water level is constant on the upside of aquitard, the upper and lower effluent amount of Simultaneously test over time.At this moment aquitard is vertical flow, gets as Fig. 2 coordinate system, and such aquitard pattern of water flow is

In formula, u (z, t) is the SEA LEVEL VARIATION value of aquitard z point t; for drawdown on the downside of cylinder; L is aquitard thickness; A=K/ μ is aquitard transmissibility factor; K is aquitard infiltration coefficient; μ is aquitard water storage rate.

For aquitard pattern of water flow I, through variables separation and Fourier transform, obtaining solution is

(2) analytic solution of aquitard flow

T is by the flow of position z unit level area

Nondimensionalization:

Wherein, for dimensionless flow, and with for dimensionless position and time;

for with aquitard character and thickness relevant parameters, be called lagging index.

Order in formula (3) with aquitard bottom surface and end face unit level area flow (get on the occasion of, do not consider direction of the traffic) change as Fig. 3 and Fig. 4.

From aquitard bottom surface unit level area flow variation diagram 3 is found out, originally moment flow is maximum and increase rapidly decay along with the time, when i.e. t>=τ ₀after, flow is tending towards definite value end face the change of unit level area flow is contrary (as Fig. 4) then, and originally moment flow is 0, and increases rapidly along with the time increases, when later speedup eases up; When i.e. t>=τ ₀after, flow is also tending towards definite value

Aquitard parameter determination method:

For moment passes through position the flow of unit level area

$\stackrel{\‾}{t}=\frac{a}{l^2}t---\left(5\right)$

Taken the logarithm in above-mentioned two formula both sides simultaneously, have

$\lg \stackrel{\‾}{t}=\mathrm{lgt}+\lg \frac{a}{l^2}---\left(7\right)$

(6) Section 2, on the right of (7) two formulas is all constant, therefore in log-log coordinate system, q that experiment obtains (0, t) ~ t and cross section typical curve (as Fig. 3) is identical in shape, just coordinate translation in length and breadth with adopt herbal combination, by two curves overlapped, an optional match point, writes down corresponding coordinate figure [q], [t], substitutes into above-mentioned (4), (5) two formulas:

Infiltration coefficient:

Transmissibility factor: $a=\frac{\left[\stackrel{\‾}{t}\right]}{\left[t\right]}{l}^2---\left(9\right)$

Water storage rate: $\mathrm{\μ}=\frac{K}{a}---\left(10\right)$

As t=τ ₀or aquitard flow tends towards stability during t → ∞.At this moment top, bottom surface unit interval flow into equal with discharge, are designated as q _y, have formula (2) can infiltration coefficient be obtained equally:

In addition, have formula (3) for moment passes through position the flow of unit level area

$\stackrel{\‾}{t}=\frac{a}{l^2}t---\left(13\right)$

Taken the logarithm in above-mentioned two formula both sides simultaneously, have:

$\lg \stackrel{\‾}{t}=\mathrm{lgt}+\lg \frac{a}{l^2}---\left(15\right)$

When experiment records z=l cross section q ~ t data, equally with cross section typical curve as shown in Figure 4, adopts herbal combination determination above-mentioned parameter.

As shown in Figure 1, test procedure:

(1) check test device: whether device is airtight, whether pipeline is normally unimpeded.

(2) fill sample: with clean rag wiping aquitard cylinder consolidation container inwall, after on inwall uniform application one deck silicone grease (or vaseline).Filter screen is laid in bottom, places the on-the-spot former state soil (or inserting sample) obtained in test chamber.Top covers filter screen.

(3) saturated sample: after soil layer is populated, slowly adds water to A elevation (the water delivering orifice elevation of bottom rising pipe) place, closes bottom aqueduct valve; Continue to add water to B elevation (overflow vent elevation) place, allow unnecessary water freely overflow.After this more than 24 hours are left standstill, until sample stable level.If any bubble in sample, tainer air extracted out by vacuum available pump.

(4) test: open bottom valve, water is overflowed from A elevation place, flows into graduated cylinder.Continuing to supply water in top, keeps B elevation place water level constant.

(5) record: the time of graduated cylinder Flow Observation, should after opening bottom valve the 1st, 2,3,4,6,8,10,15,20,25,30,40,50,60,80,100,120min clock respectively observes once, be recorded in table, later can every the observation of 30min clock once.

(6) observation is continued, until substantially constant every 30min clock measurement cylinder reading rising value, can termination test.

(7) parameter calculate: by record flow Q divided by vessel cross-sectional area S, turn to unit area flow q (cm/min), with the log-log coordinate system of typical curve identical molds in do q (0, t) ~ t measured curve, with typical curve distribution, makes two curves overlapped best, an optional match point, writes down corresponding coordinate figure [q], [t], substitutes into formula (8), (9) and (10) calculation permeability coefficient K, transmissibility factor a and water storage rate μ.

A kind ofly in the present embodiment determine that the concrete steps of the method for aquitard hydrogeological parameter are as follows:

(1) empirical model

Test model main body is plexiglass cylinder, high 205cm, external diameter 40cm, internal diameter 38cm.Cylinder divides three sections, under-filled loaded filter, and the soil sample of middle part filling test, upper filter layer adds water.Arranging silty clay layer (aquitard) thickness in test is 20cm, starts to test front aquitard all equal with the head of upper and lower filtering layer.When starting to test, the head in lower filter layers is reduced suddenly and remain unchanged.The flow in observation overflow groove exit, bottom, observational data, as table 1, continues to have observed 1760min.

Table 1 Flow Observation data

(2) parameter is determined

In showing, flow Q is divided by vessel cross-sectional area S=1133.54cm ², turn to unit area flow q (cm/min), do in log-log coordinate system q (0, t) ~ t measured curve (punctuating in Fig. 5) with typical curve (in figure solid line) distribution, makes two curves overlapped (as Fig. 5), an optional match point, writes down corresponding coordinate figure [q]=0.0123, [t]=22, substitute into formula (8), (9) and (10) obtain:

Infiltration coefficient

Transmissibility factor $a=\frac{\left[\stackrel{\‾}{t}\right]}{\left[t\right]}{l}^2=\frac{0.1}{22}\×{20}^2=1.818({\mathrm{cm}}^2/\min )$

Water storage rate $\mathrm{\μ}=\frac{K}{a}=\frac{0.001025}{1.818}=5.637\×{10}^{-4}(1/\mathrm{cm})$

Lagging index ${\mathrm{\τ}}_0=\frac{l^2}{a}=\frac{{20}^2}{1.818}=220.02\left(\min \right)$

(3) verify

Equally, formula (11) is adopted to try to achieve infiltration coefficient.Got near t=τ by table 1 ₀the empirical flow Q=0.1183ml/s that neighbouring (t=225min) is corresponding.Therefore:

With the formula of employing (8) the infiltration coefficient relative error of trying to achieve only 1.8%.

The parameter of being tried to achieve by herbal combination substitutes into computing formula (2), calculate aquitard bottom boundaries flow Q (the t)=q (0 of corresponding observation time, t) S, with measured value to such as Fig. 6, through correlation calculations analysis, all measured values are 0.976 with the related coefficient of corresponding moment calculated value, show that the parameter determined has reacted aquitard water movement rule preferably.

Claims (1)

1. determine a method for aquitard hydrogeological parameter, it is characterized in that: first, based on soil-column test model, the flow formula analytic solution of under aquitard cylinder side head the reduces a certain constant condition aquitard unit level area of deriving; Then, provide based on the time dependent experimental data of flow, adopt herbal combination determination aquitard transmissibility factor, infiltration coefficient and water storage rate;

Described soil-column test model comprises lower filtering layer, sample section, upper filtering layer, water from top to bottom successively; The aquitard cylinder bottom sidewall of described lower filtering layer upper end is provided with rising pipe, and rising pipe extends upwardly to more than sample section, the corresponding water receiving container of water delivering orifice of rising pipe, and water outlet is provided with valve; Described soil-column test model top is provided with overflow vent, and the height of overflow vent is greater than the height of water delivering orifice; Described soil-column test model is provided with water inlet topmost; Described water inlet is provided with valve;

Described based on the time dependent experimental data of flow, adopt herbal combination determination aquitard transmissibility factor, infiltration coefficient and water storage rate, be about to the flow Q of the aquitard of record divided by aquitard cylinder cross-sectional area S, turn to unit area flow q, with the log-log coordinate system of typical curve identical molds in make q ~ t measured curve, with typical curve distribution, makes two curves overlapped best, an optional match point, writes down corresponding coordinate figure [q], [t], substitutes into respective formula and calculates transmissibility factor a, coefficient of permeability K, water storage rate μ;

(1) analytic solution of aquitard pattern of water flow

If the saturated pressure-bearing of aquitard cylinder and pressure head is equal everywhere, on the downside of aquitard cylinder, head reduces certain certain value and water level is constant on the upside of aquitard, the upper and lower effluent amount of Simultaneously test over time; At this moment aquitard is vertical flow, and aquitard pattern of water flow is

In formula, u (z, t) is the SEA LEVEL VARIATION value of aquitard z point t; for drawdown on the downside of cylinder;

L is aquitard thickness; A=K/ μ is aquitard transmissibility factor; K is aquitard infiltration coefficient; μ is aquitard water storage rate;

For aquitard pattern of water flow Ι, through variables separation and Fourier transform, obtaining solution is

(2) analytic solution of aquitard flow

T is by the flow of position z unit level area

Nondimensionalization:

Wherein, for dimensionless flow, and with for dimensionless position and time; for with aquitard character and thickness relevant parameters, be called lagging index; Order in formula (3) with obtain aquitard bottom surface and the change of end face unit level area flow;

Aquitard parameter determination method:

For moment passes through position the flow of unit level area

$\stackrel{\‾}{t}=\frac{a}{l^2}t---\left(5\right)$

Taken the logarithm in above-mentioned two formula both sides simultaneously, have

$\lg \stackrel{\‾}{t}=\mathrm{lgt}+\lg \frac{a}{l^2}---\left(7\right)$

(6) Section 2, on the right of (7) two formulas is all constant, and therefore in log-log coordinate system, experiment obtains with cross section typical curve is identical in shape, just coordinate translation in length and breadth with adopt herbal combination, by two curves overlapped, an optional match point, writes down corresponding coordinate figure [q], [t], substitutes into above-mentioned (4), (5) two formulas:

Infiltration coefficient:

Transmissibility factor: $a=\frac{\left[\stackrel{\‾}{t}\right]}{\left[t\right]}{l}^2---\left(9\right)$

Water storage rate: $\mathrm{\μ}=\frac{K}{a}---\left(10\right)$

As t=τ ₀or aquitard flow tends towards stability during t → ∞, at this moment top, bottom surface unit interval flow into equal with discharge, are designated as q _y, can infiltration coefficient be obtained equally by formula (2):

In addition, by formula (3) for moment passes through position the flow of unit level area

$\stackrel{\‾}{t}=\frac{a}{l^2}t---\left(13\right)$

Taken the logarithm in above-mentioned two formula both sides simultaneously, have:

$\lg \stackrel{\‾}{t}=\mathrm{lgt}+\lg \frac{a}{l^2}---\left(15\right)$

When experiment records z=l cross section q ~ t data, equally with cross section typical curve, adopts herbal combination determination above-mentioned parameter.