CN106841033B - Real-time testing device and method for PH value and porosity of nano-gel solidified sandy soil - Google Patents

Abstract

The invention discloses a device and a method for testing the PH value and the porosity of nano-gel solidified sandy soil along a seepage path in real time, wherein the device comprises a sample forming long cylinder, a monitoring device, a liquid collecting container, a water pressure controller and a pressure isolating device; placing a sand sample in the sample molding long cylinder; the monitoring device comprises n pore water pressure meters and a PH meter which are arranged in the sample forming long cylinder in a segmented manner; the pressure isolation device is isolated into two chambers by a rubber membrane, wherein one chamber is connected with a hydraulic pressure controller, and the other chamber is filled with silica sol and connected with a sample forming long cylinder; the water pressure controller, the pressure isolating device, the sample forming long cylinder and the liquid collecting container are sequentially connected. The invention overcomes the problems that the existing device is difficult to analyze the curing nonuniformity along the seepage path and cannot measure the pH value of the silica sol along the seepage path in real time and the porosity change of the sand during the curing process.

Description

Real-time testing device and method for pH value and porosity of nanogel-solidified sand

technical field

The invention belongs to the field of geotechnical engineering research, in particular to a device and method for real-time testing of pH value and porosity of nanogel-solidified sand along a seepage path.

Background technique

Nano-silica sol is a suspension of nano-silica particles in water. In an alkaline environment, these particles repel each other, and the suspension is a stable system. When the pH value is reduced to a certain range, these nanoparticles gradually condense into a chain structure and then form a gel with a three-dimensional network structure. This nanogel system can strengthen the loose sandy soil foundation. The strengthening method is to infiltrate the silica sol into saturated in sandy soil. During the seepage process, the advancing interface of the silica sol moves continuously in the sand foundation, and the pH value and the porosity reduced by solidification are different at different positions on the seepage path. Obtain the real-time pH value and porosity at different positions on the seepage path. The rate helps to establish a theoretical model of the curing of nano-silica sols. However, the existing technology cannot provide real-time measurement results of the pH value of silica sol along the seepage path and the porosity of sand during the solidification process, and it is difficult to analyze the inhomogeneity of solidification along the seepage direction. The device and method of pH and porosity are particularly important.

SUMMARY OF THE INVENTION

In order to overcome the problems that the existing device cannot measure the pH value of silica sol along the seepage path in real time and the change of sand porosity during the solidification process, and it is difficult to analyze the inhomogeneity of solidification along the seepage path, the present invention provides a Real-time testing device and method for pH value and porosity of nanogel-solidified sand in seepage path.

The technical scheme of the present invention: a real-time testing device for pH value and porosity of nanogel solidified sand, including a sample forming long cylinder, a monitoring device, a liquid collection container, a water pressure controller and a pressure isolation device; the sample forming A sand sample is placed in the long cylinder; the monitoring device includes n pore water pressure gauges and PH meters arranged in sections in the sample forming long cylinder; the pressure isolation device is separated into two chambers by a rubber membrane, wherein One chamber is connected with the water pressure controller, and the other chamber is filled with silica sol and connected with the sample forming long cylinder; the water pressure controller, the pressure isolation device, the sample forming long barrel and the liquid collecting container are connected in sequence.

Preferably, the sample forming long tube is a PVC cylindrical tube with open ends at both ends, the ratio of height to diameter is ≥10, and the diameter is 100 mm, the wall thickness is 6 mm, and the height is 1 m.

Preferably, the pH meter is an optical fiber pH meter.

Preferably, the pH meter and the pore water pressure gauge are equally spaced along the central axis of the sand sample on the inner wall of the sample forming long cylinder. The upper pH meter and pore water pressure meter are alternately arranged.

Preferably, a first rubber plug is plugged at the bottom of the sample forming long cylinder, a second rubber plug is plugged on the top of the sample forming long cylinder, and a metal filter screen is placed on the first rubber plug to prevent the silica sol from entering the channel. blocked.

Preferably, a permeable stone with a thickness of 5mm is placed on the metal filter screen, so that the silica sol can be uniformly injected into the cross section of the sand sample.

A real-time testing method for pH value and porosity of nanogel solidified sand along the seepage path, comprising the following steps:

Step 1: Seal the bottom of the sample forming cylinder with the first rubber plug, place a metal filter screen on the first rubber plug, place a permeable stone on the metal filter screen, and then place sand into the sample forming cylinder. For soil samples, in the process of placing the sand samples, arrange the pore water pressure gauge and the fiber optic PH meter along the seepage direction of the sand samples, and finally seal the top of the sample forming long cylinder with a second rubber stopper;

Step 2: Connect the water pressure controller and the first chamber of the pressure isolation device, and the second chamber in the pressure isolation device is filled with silica sol, then connect the second chamber to the sample forming long barrel, and connect the sample forming long barrel. Cartridges and liquid collection containers;

Step 3: Start the water pressure controller to apply pressure to the rubber membrane in the pressure isolation device, record the reduction of the water volume in the water pressure controller in real time, and combine the cross-sectional area of the sample forming long barrel to obtain the sample forming long barrel in real time. PH value and water pressure at each monitoring point are recorded in real time. It is assumed that there are n PH meters along the length of the sample forming long cylinder. The number of the PH meter at the bottom is 1, and the numbers of the PH meters are sequentially from bottom to top. Increase, the top PH meter number is n, the corresponding real-time PH value is A ₁ (t), A ₂ ( _t ), Λ, An (t), the i-th PH meter and the i+1-th PH meter are calculated The PH value between is obtained by linear interpolation of A _i (t) and A _i+1 (t);

为：Step 4: Calculate the permeability coefficient of the sample in real-time segments: it is assumed that there are n pore water pressure gauges along the length of the sample forming long cylinder, the number of the pore water pressure gauge at the bottom is 1, and the pore water pressure gauges increase from bottom to top. The number of the top pore water pressure gauge is n, the corresponding real-time pore water pressure is P ₁ (t), P ₂ (t), Λ, P _n (t), and the sample forming long cylinder 1 is scored by the pore water pressure is n-1 sections, the permeability coefficient of each section

for:

In the above formula, _ρw is the water density, g is the gravitational acceleration, and L is the height of the sample forming long cylinder.

Find the corresponding real-time permeability coefficient at each pore water pressure node i (1≤i≤n):

Define the piecewise interpolation function f(x,t) of the permeability coefficient along the central axis of the sample:

In the above formula, l=L/(n-1), x _l =xl·(i-1), and l·(i-1)≤x≤l·i. The permeability coefficient of each point along the length of the sample can be obtained from the permeability coefficient piecewise interpolation function f(x,t);

为砂颗粒平均粒径，θ为孔隙率，c为常系数，应用渗透系数k和孔隙率的函数关系：Step 5: Calculate the change curve θ(x, t) of porosity along the length of the sample in real time: set

is the average particle size of sand particles, θ is the porosity, c is the constant coefficient, and the functional relationship between the permeability coefficient k and the porosity is applied:

The above formula is a single-valued function when the porosity is in the range of 0≤θ<1, and k in the above formula is replaced by the permeability coefficient piecewise interpolation function f(x, t), and the above formula is solved, that is, along the seepage direction and time-varying porosity function θ(x, t), so that the variation of porosity along the seepage direction and the inhomogeneity of nanogel-solidified sand can be analyzed.

The beneficial effects of the present invention: overcome the problems that the existing device cannot measure the pH value of the silica sol along the seepage path in real time and the change of the sand porosity during the solidification process, and the existing device is difficult to analyze the unevenness of the solidification along the seepage path. The invention provides a real-time testing device and method for the pH value and porosity of nanogel-solidified sand along the seepage path.

Description of drawings

Fig. 1 is the overall arrangement diagram of the present invention;

Fig. 2 is the top view of the sample forming long cylinder of the present invention;

Fig. 3 is a side view of the sample forming long cylinder of the present invention.

In the figure 1. Sample forming long cylinder, 2. Pore water pressure gauge, 3. PH gauge, 4. Water pressure controller, 5. Pressure isolation device, 6. Liquid collection container, 7. First rubber stopper, 8. Metal filter screen, 9. Permeable stone, 10. Sand sample, 11. Rubber membrane, 12. First chamber, 13. Second chamber, 14. Second rubber stopper.

Detailed ways

In order to make the technical means, innovative features, achievement goals and effects realized by the present invention easy to understand, the present invention will be further described below with reference to the specific figures.

A real-time test device for pH and porosity of nanogel-solidified sand along the seepage path as shown in Figure 1, including a sample forming long cylinder 1, a monitoring device, a liquid collection container 6, a water pressure controller 4 and a pressure isolation device 5; the sand sample 10 is placed in the sample forming long cylinder 1; the monitoring device includes n pore water pressure gauges 2 and PH meters 3 arranged in sections in the sample forming long cylinder 1; the pressure isolation device 5 The rubber membrane 11 is used to separate into two chambers, wherein the first chamber 12 is connected to the water pressure controller 4, and the second chamber 13 is filled with silica sol and is connected to the sample forming long cylinder 1; the water pressure controller 4. The pressure isolation device 5, the sample forming long cylinder 1 and the liquid collection container 6 are connected in sequence.

The working process of the pH value and porosity real-time testing method of nanogel solidified sand along the seepage path of the present invention is as follows:

Step 1: Seal the bottom of the sample forming long cylinder 1 with the first rubber stopper 7, place the metal filter screen 8 on the first rubber stopper 7, place the permeable stone 9 on the metal filter screen 8, and then proceed to the test. The sand sample 10 is placed in the sample forming long cylinder 1. During the placement of the sand sample 10, the pore water pressure gauge 2 and the pH gauge 3 are arranged along the seepage direction of the sand sample. Finally, the second rubber plug 14 is used to seal the sample. The top of the sample forming long cylinder 1 is sealed;

Step 2: Connect the water pressure controller 4 and the first chamber 12 of the pressure isolation device 5. The second chamber 13 in the pressure isolation device 5 is filled with silica sol, and then the second chamber 13 is connected to the sample forming long cylinder 1. Connect the sample forming long cylinder 1 and the liquid collection container 6;

Step 3: Activate the water pressure controller 4 to apply pressure to the rubber membrane 11 in the pressure isolation device, record the reduction of the water volume in the water pressure controller 4 in real time, and combine the cross-sectional area of the sample forming long cylinder 1 to obtain the test sample in real time. The flow velocity V in the sample forming long cylinder 1 is recorded, and the pH value and water pressure on each monitoring point are recorded in real time. It is assumed that there are n pH meters along the length direction of the sample forming long cylinder 1, and the pH meter number at the bottom is 1. The number of the PH meter 3 increases sequentially, the number of the top PH meter is n, and the corresponding real-time pH values are A ₁ (t), A ₂ (t), Λ, A _n (t), the i-th PH meter and the th The pH value between i+1 pH meters is obtained by linear interpolation of A _i (t) and A _i+1 (t);

为：Step 4: Calculate the permeability coefficient of the sample in real-time segments: it is assumed that there are n pore water pressure gauges along the length of the sample forming long cylinder 1, the pore water pressure gauge at the bottom is numbered 1, and the pore water pressure gauge is 2 from bottom to top increasing in turn, the number of the top pore water pressure gauge is n, the corresponding real-time pore water pressure is P ₁ (t), P ₂ (t), Λ, P _n (t), the sample forming long cylinder 1 is affected by the pore water pressure The score is divided into n-1 sections, the permeability coefficient of each section

for:

In the above formula, _ρw is the water density, g is the gravitational acceleration, and L is the height of the sample forming long cylinder.

Find the corresponding real-time permeability coefficient at each pore water pressure node i (1≤i≤n):

Define the piecewise interpolation function f(x,t) of the permeability coefficient along the length of the sample:

In the above formula, l=L/(n-1), x _l =xl·(i-1), and l·(i-1)≤x≤l·i. The permeability coefficient of each point along the length of the sample can be obtained from the permeability coefficient piecewise interpolation function f(x,t);

为砂颗粒平均粒径，θ为孔隙率，c为常系数，应用渗透系数k和孔隙率的函数关系：Step 5: Calculate the change curve θ(x, t) of porosity along the length of the sample in real time: set

is the average particle size of sand particles, θ is the porosity, c is the constant coefficient, and the functional relationship between the permeability coefficient k and the porosity is applied:

The above formula is a single-valued function when the porosity is in the range of 0≤θ<1, and k in the above formula is replaced by the permeability coefficient piecewise interpolation function f(x, t), and the above formula is solved, that is, along the seepage direction and time-varying porosity function θ(x, t), so that the variation of porosity along the seepage direction and the inhomogeneity of nanogel-solidified sand can be analyzed.

Claims (6)

1. A test method of a PH value and porosity real-time test device of nano-gel solidified sandy soil comprises the PH value and porosity real-time test device of the nano-gel solidified sandy soil, and the real-time test device is provided with:

the device comprises a sample forming long cylinder, a monitoring device, a liquid collecting container, a water pressure controller and a pressure isolating device; placing a sandy soil sample in the sample molding long cylinder; the monitoring device comprises n pore water pressure meters and an optical fiber PH meter which are arranged in the sample forming long cylinder in a segmented manner; the pressure isolation device is isolated into two chambers by a rubber membrane, wherein one chamber is connected with a hydraulic pressure controller, and the other chamber is filled with silica sol and connected with a sample forming long cylinder; the water pressure controller, the pressure isolating device, the sample forming long cylinder and the liquid collecting container are sequentially connected; a first rubber plug is plugged at the bottom of the sample forming long cylinder, a second rubber plug is plugged at the top of the sample forming long cylinder, and a metal filter screen is placed on the first rubber plug to prevent a silica sol inlet channel from being blocked;

the method is characterized in that: the test method comprises the following steps:

step 1: sealing the bottom of the sample molding long cylinder by using a first rubber plug, placing a metal filter screen on the first rubber plug, placing a permeable stone on the metal filter screen, then placing a sandy soil sample into the sample molding long cylinder, arranging a pore water pressure gauge and an optical fiber PH gauge along the seepage direction of the sandy soil sample in the process of placing the sandy soil sample, and finally sealing the top of the sample molding long cylinder by using a second rubber plug;

step 2: the first chamber is connected with the water pressure controller and the pressure isolating device, the second chamber in the pressure isolating device is filled with silica sol, and then the second chamber and the sample forming long cylinder are connected, and the sample forming long cylinder and the liquid collecting container are connected;

and step 3: start hydraulic controller and exert pressure to the rubber membrane among the pressure isolating device, the reduction of the water volume in the hydraulic controller of real-time recording, combine the cross-sectional area of a sample shaping long section of thick bamboo, obtain the velocity of flow V in the sample shaping long section of thick bamboo in real time, simultaneously PH value and water pressure on each monitoring point of real-time recording, it has n along the long section of thick bamboo length direction optic fibre PH meter of sample shaping, the optic fibre PH meter serial number of bottom is 1, from up optic fibre PH meter serial number increases in proper order down, top optic fibre PH meter serial number is n, the real-time PH value that corresponds is A₁(t),A₂(t),…,A_n(t) the pH between the ith fiber pH meter and the (i + 1) th fiber pH meter is represented by A_i(t) and A_i+1(t) linear interpolation;

and 4, step 4: calculating the permeability coefficient of the sample in real time in a segmented manner and obtaining a permeability coefficient segmented interpolation function f (x, t);

and 5: and calculating a change curve of the porosity along the length direction of the sample in real time, and calculating the porosity theta (x, t) according to a function relation between the permeability coefficient and the porosity and a permeability coefficient piecewise interpolation function f (x, t).

2. The method for testing the PH value and the porosity of the nanogel solidified sandy soil in real time as claimed in claim 1, wherein the method comprises the following steps:

in the step 4, n pore water pressure meters are arranged along the length direction of the sample forming long cylinder, the number of the pore water pressure meter at the bottom is 1, the pore water pressure meters sequentially increase from bottom to top, the number of the pore water pressure meter at the top is n, and the corresponding real-time pore water pressure is P₁(t),P₂(t),…,P_n(t) dividing the sample forming long cylinder into n-1 sections by a pore water pressure gauge, wherein the permeability coefficient of each section

Comprises the following steps:

in the above formula rho_wThe water density is adopted, g is the gravity acceleration, and L is the height of the sample molding long cylinder;

and (3) solving the corresponding real-time permeability coefficient on each pore water pressure node i (i is more than or equal to 1 and less than or equal to n):

defining a permeability coefficient piecewise interpolation function f (x, t) along the central axis direction of the sample:

wherein L ═ L/(n-1), x_lX is not less than x and not more than l.i (i-1); and (3) obtaining the permeability coefficient of each point along the length direction of the sample by the permeability coefficient piecewise interpolation function f (x, t).

3. The testing method of the device for testing the PH value and the porosity of the nanogel cured sandy soil in real time according to claim 1 is characterized in that:

in step 5, let

Taking the average grain diameter of sand particles, theta is porosity, c is constant coefficient, and applying the functional relation between permeability coefficient k and porosity:

the formula is a single-value function when the value range of the porosity is theta <1 and is more than or equal to 0, k in the formula is replaced by a permeability coefficient piecewise interpolation function f (x, t), and the formula is solved to obtain the porosity theta (x, t) which changes along the seepage direction and time, so that the change of the porosity along the seepage direction and the nonuniformity of the nano-gel solidified sandy soil are analyzed.

4. The testing method of the device for testing the PH value and the porosity of the nanogel cured sandy soil in real time according to claim 1 is characterized in that:

the sample forming long cylinder is a PVC cylindrical pipe with two open ends, and the ratio of the height to the diameter is more than or equal to 10.

5. The testing method of the device for testing the PH value and the porosity of the nanogel cured sandy soil in real time according to claim 1 is characterized in that: the optical fiber PH meter and the pore water pressure meter are arranged on the inner wall of the sample forming long cylinder at equal intervals along the central axis of the sandy soil sample, the optical fiber PH meter and the pore water pressure meter on the same horizontal plane use the central axis as a symmetry axis, and the optical fiber PH meter and the pore water pressure meter are alternately arranged on the same vertical line.

6. The testing method of the device for testing the PH value and the porosity of the nanogel cured sandy soil in real time according to claim 1 is characterized in that:

a piece of permeable stone with the thickness of 5mm is placed on the metal filter screen, so that the silica sol can be uniformly injected into the cross section of the sandy soil sample.

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