CN110656943B - A kind of shield sandy slag improvement ability improvement and parameter determination method - Google Patents

Abstract

The invention discloses a method for improving ability of shield sandy slag and determining parameters. The consistent sandy soil of the stratum that the shield passes through is used as slag soil test material, and foaming agent and water are used as basic improvement materials. Slump value and apparent state, determine the suitable improvement area, and determine whether water injection is required, and whether bentonite or polymer polymerization is required according to whether the initial water content of the sandy soil in the stratum where the shield is located is within the water content range of the suitable area for improvement In order to improve the ability of sandy slag to be improved by foaming agent and water, the foam injection ratio is determined according to the appropriate improvement area; the slag in a suitable improved state is subjected to a penetration test to test its resistance to high water pressure on the shield tunnel site. Whether the seepage performance meets the construction requirements. The patent of the present invention proposes a clear muck improvement idea, with clear direction and reliable technology, which can be directly used for on-site construction of shield tunnels.

Description

A kind of shield sandy slag improvement ability improvement and parameter determination method

technical field

The invention belongs to the technical field of shield tunnel construction with earth pressure balance in sandy strata, and in particular relates to a method for improving the ability of shield sandy slag and determining parameters.

Background technique

Shield method construction has the advantages of high safety, fast excavation speed, and little effect on the surrounding environment, and is widely used in urban tunnels. The earth pressure balance shield is mainly suitable for the stratum where the mass of particles with a particle size of less than 0.06mm accounts for more than 30% of the total amount of slag, otherwise the mud-water balance shield is used. However, the mud-water balance shield construction requires a large mud-water treatment plant, covers a large area, and the mud-water treatment efficiency is often low, which often becomes a key factor restricting the progress of the tunnel construction. Therefore, unless crossing rivers and seas, most of them rely on muck improvement technology to expand the scope of use of earth pressure balance shields. The earth pressure balance shield slag in water-sand-rich strata requires good workability (including fluidity, cohesion and water retention) and impermeability. The workability of the muck is often judged by the slump test at the engineering site, and the slump value and the apparent state of the muck are used to determine whether the improved state of the muck is appropriate.

In recent years, a series of research results have emerged at home and abroad regarding the improvement of shield slag soil in sandy strata, and many scholars and engineers have continuously proposed new improvement techniques. For example, Chinese invention patent 201410317338.X proposes adding polyacrylamide to the "foam + gas + water" modifier to reduce formation disturbance and avoid gushing; Chinese invention patent 201510567925.9 points out that foam is injected separately in the early stage of excavation, if the slag state Not good, there are still phenomena such as "gushing", and bentonite can be injected; Chinese patent 201510983075.0 proposes a water-rich sand layer shield slag improvement construction system, and the modifier includes bentonite and foaming agent; Chinese invention patent 201610446189.6 proposes a simulated soil The device for pressure-balanced shield construction can study the influence of the type and amount of modifiers on the improvement of slag under different pressure conditions; Chinese invention patent 201710595112.X for high water pressure and high permeability sandy strata, it is proposed to use 0.8-1.5 Parts by weight of sodium bentonite, 0.04-0.06 parts by weight of carboxymethyl cellulose and 10 parts of water are mixed to form an improved slurry, and then different amounts of improved slurry are added depending on whether the original formation is supersaturated. Chinese invention patent 201410561509.3 proposes a method for selecting the improvement parameters of earth pressure balance shield slag soil in cohesive strata with foam as additive. The scope of application of this patent is limited to cohesive strata. Combined with slump test and liquid-plastic limit test, considering the effect of additives on The influence of the liquid and plastic limit of the slag, however, the cohesive slag does not have the problem of improving the sandy slag with water separation, foaming, and high permeability, and it is not necessary to adjust the slag improvement ability by bentonite or high molecular polymer.

Existing shield slag improvement technologies for sandy strata tend to propose new improver materials and test equipment for sandy pebbles and other strata. The slag improvement ideas are mostly at the stage of relatively primitive engineering experience. Soil improvement parameters are often at the expense of engineering and human resource losses. Even if the slump test is carried out to determine the improvement parameters, there is still a big blindness in the parameter adjustment, or the improvement ability of bentonite or high molecular polymer is excessively expanded, and the basic improvement performance of foaming agent and water is ignored, resulting in muck improvement. cost increase. In order to guide the improvement of shield slag soil in sandy strata and form a clear idea of slag improvement, it is necessary to propose a more scientific new method of shield slag improvement with earth pressure balance in sandy strata.

SUMMARY OF THE INVENTION

The present application aims to solve at least one of the technical problems existing in the prior art. Therefore, one of the objectives of the present invention is to provide a method for improving the ability of shield sandy slag and determining parameters.

In order to solve the above-mentioned technical problems, the present invention adopts the following technical solutions:

A method for improving ability of shield sandy slag and determining parameters, comprising the following steps:

Step 1. Determination of suitable area for improvement

The sandy soil that is consistent with the stratum that the shield passes through is selected as the slag soil test material, and the foam agent and water are used as the basic improvement materials to carry out a series of slump tests, and the test data is drawn with the foam injection ratio-water content as the coordinates According to the slump value and apparent state of the slag soil, the area where the slump value is 15-20cm and there is no water or foam precipitation is the suitable area for improvement;

Step 2. Realization of target moisture content and foam injection ratio

According to whether the initial water content ω _n of the sandy soil in the stratum where the shield is located is within the water content range of the suitable area for improvement, it is necessary to determine whether water injection is required, and whether it is necessary to inject bentonite or high molecular polymer to improve the sandy slag. The ability of water improvement, there is no foam in the initial stratum, according to the appropriate improvement area, determine the target foam injection ratio FIR, and the target water content after muck improvement is ω;

Step 3: Detection of the impermeability of the slag

Carry out the impermeability test on the improved slag to ensure that the permeability coefficient of the slag meets the engineering requirements. If it does not meet the engineering requirements, adjust the water injection amount and foam injection ratio in step 2 within the appropriate improvement area in step 1. After the slag permeability coefficient does not meet the impermeability requirements, it is necessary to adjust the injection amount of bentonite or high molecular polymer to change the suitable improvement area of the slag in step 1. The final permeability coefficient of the slag meets the engineering requirements.

Generally graded slag, under the condition of constant head permeability test, the permeability coefficient of suitable improved slag can meet the engineering requirements (less than ^10-5 m/sec, and the duration can exceed 90min). For strata with high water head and strong permeability, the requirements for the impermeability of the slag are strict, so it is necessary to carry out the constant head permeability test of the slag under the condition of shield water pressure on site to ensure that the permeability coefficient of the slag meets the requirements.

Further, the specific process of step 2 is:

For the target water content ω: determine whether the initial water content ω _n of the sandy soil in the stratum where the shield is located is within the water content range [ω _min , ω _max ] of the suitable improvement area, which can be divided into three cases

When ω _n is less than ω _min , it means that water needs to be injected, so that the target water content ω after the improvement of the muck falls into the water content range of the suitable improvement area [ω _min ,ω _max ];

When ω _n is greater than ω _max , it means that the original formation is rich in water, and the water content exceeds the water content range of the suitable improvement area. It is necessary to inject bentonite or polymer solution to correct the suitable improvement area and increase the upper limit of water content. ω _max , so that the initial water content ω _n falls into the water content range of the suitable improvement area [ω _min , ω _max ]; the content of the injected bentonite or polymer solution is recorded as ω _o , and the target water content ω after the improvement of the slag soil is the initial water content ω _n ;

When ω _n is within the moisture content range [ω _min ,ω _max ] of the suitable improvement area, the initial moisture content ω _n can meet the requirements, and no water injection is required; the target moisture content ω after the improvement of the slag soil is the initial moisture content ω _n ;

For the target foam injection ratio: Since there is no foam in the initial formation, the target foam injection ratio FIR can be determined according to the suitable improvement area or the corrected suitable improvement area.

Further, it also includes the steps of field application:

Considering the influence of soil bin pressure on the foam volume, using P×V=constant, where: P is the pressure, V is the foam volume, the foam volume under the soil bin pressure can be obtained; Forming loose slag, considering the slag loosening coefficient, the volume of slag formed by each ring segment is V _s = πD ² Lξ/4; after deduction, the foam volume under the atmospheric pressure required for each ring segment can be obtained as:

V _f =(P'·V _s ·FIR+P _a V _g /KP'V _g /K)/P _a (1)

In the formula, P′-soil pressure, _Pa -atmospheric pressure, _Vf -foam volume under atmospheric pressure, _Vg -foaming agent volume, K-foaming agent solution concentration, D-shield excavation diameter, L-segment length, ξ-loose factor;

According to the concentration K of the foaming agent solution and the foaming rate FER of the foaming agent, the required volume of the foaming agent for each ring segment of the earth pressure balance shield for muck improvement is:

According to the target water content ω after the improvement of the slag soil and the water content ω _n of the undisturbed soil itself, the water injection amount V _w required for the footage of each ring segment is determined as:

V _w =πD ² Lγ(ω-ω _n )/(4γ _w ) (3)

In the formula: γ - dry density of the stratum where the shield is located before excavation, γ _w - water weight.

The volume of bentonite or high molecular polymer solution required for each loop segment footage for soil improvement is:

V _o =πD ² Lγω _o /(4γ _o ) (4)

In the formula: γ _o -bentonite or high molecular polymer solution density.

Further, the foaming agent is evaluated, and the foaming rate FER of the foaming agent under atmospheric pressure and the dissipation time curve of the foam produced by the _foaming agent are determined. 5min, only foaming agents that meet FER and t ₅₀ requirements can be used.

Further, if there is no reasonable improvement area in step 1, it is necessary to carry out a test to improve the ability of sandy slag to be improved by foaming agent and water by adding bentonite or high molecular polymer, so that the slag can be improved in the ratio of foam injection to water content. There is a reasonably sized area area in the coordinates.

Further, according to the on-site excavation rate, the injection rate of the slag-improving foaming agent, the water injection rate and the rate of the bentonite or high molecular polymer solution are determined.

Compared with the prior art, the beneficial effects of the present invention are:

The invention takes foaming agent and water as the basic improvement materials, and improves the ability of the slag to be improved by the foaming agent and water through the modifying agent such as bentonite or macromolecular polymer. It is used for on-site earth pressure balance shield construction to avoid the increase of engineering cost and extension of construction period based on construction experience and repeated attempts on site.

Description of drawings

FIG. 1 is a zoning diagram of the muck improvement category in the foam injection ratio-water content space of the present invention.

Detailed ways

The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

A method for determining improvement parameters of shield sandy slag based on foam injection ratio and water content, comprising the following steps:

Step 1: Select soil samples from the stratum in the interval traversed by the on-site earth pressure balance shield. For the convenience of soil sampling, the same soil sample can be taken from the foundation pit near the shield interval to determine the initial water content of the stratum.

Step 2: Evaluate the foaming agent, measure the foaming rate FER of the foaming agent under atmospheric pressure and the dissipation time curve of the foam produced by the _foaming agent. More than 5min, only the foaming agent that meets the requirements of FER and t ₅₀ can be used.

The third step: stir a certain amount of foam, pure water and muck evenly, carry out a slump test, and measure the muck slump under a certain foam injection ratio-water content. According to the slump T of the muck and the apparent state (whether it is water or foam), as shown in Figure 1, the muck is divided into five categories in the foam injection ratio-water content coordinate: suitable improvement "①": The slump value is 15-20cm, the fluidity of the slag is good, and there is no water or foam; under-improvement "②": the slag has poor cohesion, is in a loose state, or has insufficient fluidity; suitable improvement but Water separation "③": The slump value is between 15 and 20 cm, and the fluidity of the muck is good, but due to the high water content, the muck will separate water; if it is over-improved and foam may be formed, "④": The muck slump value More than 20cm, the fluidity is too large, and because the foam injection ratio is too large, foam may be precipitated; the muck is over-improved and water is separated "⑤": The muck slump value is greater than 20cm, the fluidity is too large, and due to the water content If it is too large, it will shed water. That is to say, the area "①" where the slump value is 15-20 cm, and there is no water or foam precipitation, is a suitable improvement area.

Due to the influence of slag gradation, for coarse-grained soils such as pebble soil and gravel soil with too large particle size, it may not be possible to achieve the ideal slag soil improvement effect only by relying on foaming agents and water. The improvement area, in other words, the area of the reasonable improvement area is zero, then it is necessary to inject bentonite or high molecular polymer solution to improve the improvement ability of the sandy slag, so that the slag has a certain value in the foam injection ratio-water content coordinate. Reasonably sized area means that the original sandy slag can be reasonably improved by foaming agent and water by adding bentonite or polymer solution.

Step 4: Check whether there is a reasonable improvement area in Figure 1. If there is no reasonable improvement area, a test needs to be carried out to improve the improveability of sandy slag by adding bentonite or high molecular polymer, so that the slag is in the foam. There is a reasonably sized area in the injection ratio-water content coordinate.

The fifth step is to determine whether the initial water content ω _n of the sandy soil in the stratum where the shield is located is within the water content range [ω _min , ω _max ] of the suitable improvement area, which can be divided into three situations:

(1) When ω _n is less than ω _min , it means that water needs to be injected, so that the improved water content ω falls into the water content range of the appropriate improvement area [ω _min , ω _max ];

(2) When ω _n is greater than ω _max , it means that the original stratum is rich in water, and the water content exceeds the water content range of the suitable improvement area. It is necessary to modify the suitable improvement area by adding bentonite or high molecular polymer to obtain the correct improvement Improve the area to increase the upper limit value ω _max of its water content (the lower limit value ω _min can be variable and unchanged);

(3) When ω _n is located at [ω _min , ω _max ], the initial water content can meet the requirements, no water injection is required, and only foam injection can meet the requirements. Note that the content of injected bentonite or high molecular polymer is ω _o (if it is equal to zero, it is the sum of bentonite or high molecular polymer added in the whole determination process). The water content ω is the initial water content ω _n (without the water in the bentonite or high molecular polymer solution, ≥ω _n ).

Step 6: Determine the target foam injection ratio FIR after muck improvement according to the appropriate improvement area (after correction).

Step 7: Check the impermeability of the improved slag to ensure that the permeability coefficient of the slag meets the engineering requirements. If it does not meet the engineering requirements, adjust the water injection amount and foam injection in step 2 within the appropriate improvement area in step 1. If the permeability coefficient of the slag after adjustment does not meet the impermeability requirements, it is necessary to adjust the injection amount of bentonite or macromolecular polymer to change the suitable area for improvement of the slag in step 1, and select the amount of water injection and foam injection in the changed area. ratio, so that the improved slag permeability coefficient can meet the engineering requirements.

Generally graded slag, under the condition of constant head permeability test, the permeability coefficient of suitable improved slag can meet the engineering requirements (less than ^10-5 m/sec, and the duration can exceed 90min). For strata with high water head and strong permeability, the requirements for the impermeability of the slag are strict, so it is necessary to carry out the constant head permeability test of the slag under the condition of shield water pressure on site to ensure that the permeability coefficient of the slag meets the requirements.

The eighth step: Calculate the volume V _g of foaming agent required for the improvement of the muck soil of each ring segment of the earth pressure balance shield footage by formula (2).

The ninth step: Calculate the water injection volume V _w required for the improvement of the muck soil of each ring segment of the earth pressure balance shield footage by formula (3).

Step 10: Calculate the volume V _o of bentonite or high molecular polymer solution required for the improvement of each ring segment of the earth pressure balance shield footage by formula (4).

Step 11: Finally, according to the on-site excavation rate, the injection rate of the slag-improving foam agent, the water injection rate and the rate of the bentonite or polymer solution are determined.

The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity, all possible combinations of the technical features in the above-described embodiments are not described. However, as long as there is no contradiction between the combinations of these technical features, All should be regarded as the scope described in this specification.

The above-mentioned embodiments only represent several embodiments of the present invention, and the descriptions thereof are specific and detailed, but should not be construed as a limitation on the scope of the invention patent. It should be pointed out that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can also be made, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the appended claims.

Claims (6)

1. A shield sandy muck improvement capability improvement and parameter determination method is characterized by comprising the following steps:

step one, determining a suitable improvement area

Selecting sandy soil consistent with a stratum penetrated by a shield as a muck test material, taking a foaming agent and water as basic improvement materials, carrying out a series of slump tests, drawing test data points by taking a foam injection ratio-water content as coordinates, and taking the slump value of 15-20cm according to the slump value and the apparent state of muck, wherein the area of the test data points without water separation and foam separation conditions is a proper improvement area;

step two, realizing the target water content and the foam injection ratio

According to the initial water content omega of sandy soil of the stratum where the shield is positioned_nWhether water injection is needed or not is determined within the range of the water content of the proper improvement area, whether bentonite or high molecular polymer is needed to be injected to improve the sand muck improvement capability or not is determined so as to adjust the proper improvement area in the step one, and because foam does not exist in the initial stratum, a target foam injection ratio FIR is determined according to the proper improvement area, and the target water content is omega after muck improvement;

step three, detecting the impermeability of the residue soil

And (3) carrying out impermeability detection on the improved slag soil to ensure that the permeability coefficient of the slag soil meets the engineering requirements, if the permeability coefficient of the slag soil does not meet the engineering requirements, firstly adjusting the water injection amount and the foam injection ratio in the step two in the range of a proper improved area in the step one, if the permeability coefficient of the slag soil does not meet the impermeability requirements yet, adjusting the injection amount of bentonite or high molecular polymer to change the proper improved area of the slag soil in the step one, and selecting the water injection amount and the foam injection ratio in the changed area to ensure that the permeability coefficient of the slag soil after improvement meets the engineering requirements.

2. The method for improving the shield sandy muck and determining the parameters according to claim 1, wherein the specific process of the second step is as follows:

for a target water cut ω: according to the initial water content omega of sandy soil of the stratum where the shield is positioned_nWhether the water content is in the range [ omega ] of suitable modification region_min,ω_max]In the interior, three situations can be divided:

when ω is_nLess than omega_minWhen the water content is required to be injected, the target water content omega is within the water content range [ omega ] of the proper improvement area after the dregs are improved_min,ω_max]；

When ω is_nGreater than omega_maxWhen the water content of the original stratum is rich, the water content exceeds the range of the water content of the proper improvement area, bentonite or high molecular polymer solution needs to be injected to improve the capability of the muck which can be improved by water and foam, the proper improvement area is corrected, and the upper limit value omega of the water content is increased_maxTo an initial water content omega_nFall within a suitably modified region water cut range [ omega ]_min,ω_max](ii) a The content of the injected bentonite or the high molecular polymer solution is marked as omega_oThe target water content omega after the improvement of the dregs is the initial water content omega_n；

When ω is_nWater content range [ omega ] in suitably modified zone_min,ω_max]At the inner time, the initial water content omega_nThe requirements are met without water injection; the target water content omega after the improvement of the dregs is the initial water content omega_n；

For the target foam injection ratio: and determining the target foam injection ratio FIR according to the proper improved area or the corrected proper improved area because no foam exists in the initial stratum.

3. The method for improving the shield sandy muck improving capacity and determining the parameters as claimed in claim 1 or 2, further comprising the step of field application:

considering the effect of the soil bin pressure on the foam volume, we use P × V ═ constant, where: p is pressure, V is foam volume, and the foam volume under the soil bin pressure condition can be obtained; in addition, loose muck is formed by cutting stratum by the earth pressure balance shield cutter head, and the volume of the muck formed by each ring of pipe segments is V by considering the coefficient of the loose muck_s＝πD²L ξ/4; by derivation, the required volume of foam for each ring of pipe pieces under atmospheric pressure conditions can be obtained as follows:

V_f＝(P′·V_s·FIR+P_aV_g/K-P′V_g/K)/P_a (1)

in the formula, P' -pressure of soil bin, P_a-atmospheric pressure, V_fFoam volume under atmospheric pressure, V_g-the volume of the foaming agent, the concentration of the K-foaming agent solution, the D-shield excavation diameter, the L-segment length, and the xi-loosening coefficient;

obtaining the volume of the foaming agent required by the advancing footage of each ring of pipe piece of the earth pressure balance shield for improving the muck according to the concentration K of the foaming agent solution and the foaming rate FER of the foaming agent:

according to the target water content omega and the initial water content omega after the improvement of the dregs_nTo determine the water injection quantity V required by each ring pipe slice footage_wComprises the following steps:

V_w＝πD²Lγ(ω-ω_n)/(4γ_w) (3)

in the formula: dry density of stratum where shield is located, gamma-excavation_w-the severity of the water;

the volume of bentonite or high molecular polymer solution required by each ring segment for advancing the segment for improving the muck is as follows:

V_o＝πD²Lγω_o/(4γ_o) (4)

in the formula: gamma ray_o-bentonite or high molecular polymer solution density.

4. The method for improving the shield sandy muck improving ability and determining the parameters according to claim 1 or 2, wherein the method comprises the following steps: evaluating the foaming agent, measuring the foaming rate FER of the foaming agent under the atmospheric pressure condition and the dissipation time curve of the foam generated by the foaming agent, wherein the FER is required to be more than 10, and obtaining the half-life period t of the foam according to the dissipation time curve of the foam₅₀More than 5min, only satisfying FER and t₅₀The desired foaming agent can be used.

5. The method for improving the shield sandy muck improving ability and determining the parameters according to claim 1 or 2, wherein the method comprises the following steps: if no reasonable improvement area exists in the first step, a test needs to be carried out, and the capability of improving the sandy muck by the foaming agent and water is improved by adding bentonite or high molecular polymer, so that the muck has a reasonable area in a foam injection ratio-water content coordinate.

6. The method for improving the shield sandy muck and determining the parameters according to claim 3, wherein the method comprises the following steps: and determining the injection rate and the water injection rate of the muck-improving foaming agent and the rate of the bentonite or the high molecular polymer solution according to the on-site tunneling rate.

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