CN113788665A - Method for configuring low-shear-strength grouting material for shield excavation gap - Google Patents
Method for configuring low-shear-strength grouting material for shield excavation gap Download PDFInfo
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- CN113788665A CN113788665A CN202111324390.4A CN202111324390A CN113788665A CN 113788665 A CN113788665 A CN 113788665A CN 202111324390 A CN202111324390 A CN 202111324390A CN 113788665 A CN113788665 A CN 113788665A
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
- C04B28/24—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing alkyl, ammonium or metal silicates; containing silica sols
- C04B28/26—Silicates of the alkali metals
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- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21D—SHAFTS; TUNNELS; GALLERIES; LARGE UNDERGROUND CHAMBERS
- E21D11/00—Lining tunnels, galleries or other underground cavities, e.g. large underground chambers; Linings therefor; Making such linings in situ, e.g. by assembling
- E21D11/04—Lining with building materials
- E21D11/10—Lining with building materials with concrete cast in situ; Shuttering also lost shutterings, e.g. made of blocks, of metal plates or other equipment adapted therefor
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
- C04B2111/70—Grouts, e.g. injection mixtures for cables for prestressed concrete
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Abstract
The invention discloses a method for preparing a low-shear strength grouting material for a shield excavation gap, which comprises the following steps of: selecting a grouting material; preliminarily designing a plurality of groups of grouting materials with different water-cement ratios and different expansion water ratios; manufacturing a plurality of groups of test pieces of grouting materials; testing the shear strength of each group of test pieces to obtain the optimal water-cement ratio and the optimal expansion water ratio of the grouting material; adding bentonite and water into a stirrer according to the optimal swelling water ratio, stirring to fully and uniformly mix the bentonite and the water, and standing to fully swell the bentonite and the water; measuring water glass with required Baume degree, adding the water glass into the swelled bentonite slurry, and stirring uniformly; adding cement powder, and continuously stirring uniformly to complete the preparation. The invention researches the filling problem of the shield construction excavation gap, and can solve the problem that the shield body is locked by the conventional shield body grouting material; the novel filling material preparation method is adopted, the pumping requirement in grouting equipment is met, and meanwhile, the high shear strength is achieved.
Description
Technical Field
The invention belongs to the technical field of shield construction, particularly relates to a shield grouting technology, and particularly relates to a configuration method of a low-shear-strength grouting material for a shield excavation gap.
Background
In the shield construction process, the grouting effect is influenced, besides grouting materials, the grouting effect is also related to grouting parameters such as pressure and grouting time adopted in grouting, and in the existing research, expert scholars study factors such as grouting diffusion radius and stone strength after grouting, so that the relationship between the grouting parameters and the filling effect is obtained.
The poplar terrace and the like adopt an indoor test method to carry out grouting test research on a sandy gravel stratum, thereby obtaining that the grouting pressure has the most obvious influence on the diffusion radius of the grout, and the secondary influence is the permeability coefficient and the grouting time, and the diffusion radius of the grouting mainly has a relation with stratum parameters and the grouting process. The relation between the diffusion radius of the grout and the medium structure characteristics of the filling material and grouting factors such as grouting pressure is obtained by indoor tests of Pujialian and the like. And (3) converting a shield tail gap formed after the shield tail is separated into the porosity of the soil body by means of theoretical derivation, such as leaf fly and the like, so that the influence caused by the shield tail gap is considered, and the dissipation rule of the slurry diffusion range and the grouting pressure is obtained. Zhu He Hua and the like adopt a finite element simulation method, research on the interaction between the lining and the stratum caused by the solidification of grouting materials along with time and the solidification of soil bodies through simulating the solidification process of converting liquid slurry into solid slurry, and obtain the applicability of a grouting pressure form through simulating the soil pressure and the lining internal force value under uniform and non-uniform grouting pressures. Tengli and the like adopt a numerical simulation method to research and analyze the instability mechanism and the settlement rule of the earth pressure balance shield crossing the sandy cobble stratum, and obtain the value range of the earth bin pressure of the excavation face of the tunneling shield in the sandy cobble stratum and the synchronous grouting pressure parameter. In the shield construction process, road leveling and the like perform numerical simulation analysis on parameters such as frictional resistance, cutter torque, tunnel face pressure, grouting pressure and the like of a shield shell, so that risk values of various risk factors are calculated, and corresponding fine control research is provided. The Luohai swallow uses Taiyuan subway as engineering support and combines theoretical analysis and numerical simulation to research the influence of grouting parameters such as grouting amount, grouting pressure and the like on surface deformation and duct piece displacement, and obtains reasonable grouting parameters as a guide for practical engineering. Raynaud and the like respectively compare four different grouting pressure distribution forms of non-uniform gravity distribution, triangular distribution, uniform distribution and non-uniform distribution by using a numerical simulation method and compare and analyze with a field monitoring result so as to obtain a reasonable grouting pressure distribution form in numerical calculation. And (4) the dangerous peaks and the like pass through a centrifugal model test, research on the construction period of the tunnel penetrating through the existing tunnel by different grouting rates and long-term displacement deformation after the construction is finished, and research on the influence of the grouting rate on the swelling caused by the unloading effect.
The defects of the existing research are as follows:
since the excavation gap filling material is put into use only in recent years and is still in the trial use stage, some problems may be faced:
(1) the filling material has low early strength and cannot interact with the soil outside the shield shell in time, or the initial setting time is unreasonable, and other factors cannot realize filling in a real sense;
(2) the unreasonable proportion of the filling material can cause the filling material to have too good fluidity, the filling material is solidified at the position of the cutter head to cause the cutter head to be twisted and enlarged, or the workability is poor, the filling material is separated, so that the loss of the filling material is generated, and the strength and the impermeability of the filling material are improved at the positions of the fast-approaching tunnel door and the communication channel;
(3) the effectiveness of the use of the packing material may vary from formation to formation. If the filling effect is controlled by the filling amount, the soil around the shield shell cannot be effectively supported probably due to the reasons that the strength of the filling material is too low or the self-contractibility is large and the like. And for the section with high sedimentation control requirements, the grouting pressure and the filling amount should be strictly controlled, and the proportion of the filling material should be reasonably adjusted.
Disclosure of Invention
Based on the problems, the influence factors of the excavation gap filling material are analyzed by adopting an indoor test according to the physical and mechanical characteristics of the excavation gap filling material. By adjusting the proportion of the filling material, the influence rule of different factors on the filling effect of the filling material is researched. By adopting a direct shear test and a friction test, the adhesion characteristic of the filling material is researched, so that the shield tunneling parameters are optimized, and theoretical reference and technical support are provided for actual field construction.
The invention is realized by the following steps:
a method for configuring a low-shear strength grouting material for a shield excavation gap comprises the following steps:
and 8, measuring water glass with the needed Baume degree, adding the water glass into the bentonite slurry containing the cement, continuously stirring uniformly, and completing preparation.
In some embodiments, in step 1, the water used is purified water.
In some embodiments, in step 2, the plurality of different water-to-cement ratios are four groups, 16:1, 8:1, 4:1 and 2.6:1, and the plurality of different water-to-swelling ratios are also four groups, 1:4, 1:2.67, 1:2 and 1: 1.6.
In some embodiments, in step 2, the slurry configuration method is:
adding bentonite and water into a stirrer according to a plurality of preliminarily designed different swelling water ratios, stirring for 5-10 minutes to fully mix the bentonite and the water uniformly, and standing for 10-30 minutes to fully swell the bentonite and the water;
adding cement powder into the bentonite slurry according to a plurality of groups of different water-cement ratios designed preliminarily, and continuing to stir for at least 10 minutes until the mixture is uniform;
measuring water glass with required Baume degree, adding the water glass into the swelled bentonite slurry, stirring for at least 5 minutes until the mixture is uniform, and finishing the preparation.
In some examples, in step 3, test pieces were made as follows:
(1) selecting a sample preparation mold capable of preparing samples in batches, wherein the sample preparation mold is a needle cylinder injection type mold and comprises a cylinder body, the upper end of the cylinder body is open, and the lower end of the cylinder body is provided with a propeller;
(2) pouring the prepared groups of slurry into a sample preparation mold, standing the slurry for a certain time, and curing to form a sample;
(3) and pushing the sample out of the cylinder of the die by a certain length, cutting the first sample by a cutting ring, sequentially pushing the sample out by the same length, and cutting by the cutting ring to obtain a plurality of samples.
In some embodiments, the barrel has an inner diameter of 12cm and a wall thickness of 0.1 cm.
In some embodiments, the top of the propeller is provided with a rubber anti-leakage pad.
In some embodiments, in step (2), the slurry standing time is related to the shield advancing speed, and the slurry is ensured to be always kept in a low-shear strength and high-pumpability state in the standing time.
In some embodiments, in step (2), the slurry is cured until the sample preparation mold is inverted without displacement or deformation.
In some embodiments, step 6, preparing the slurry is performed under a normal atmospheric pressure and normal temperature condition, the bentonite and the water are stirred for 5-10 minutes, and the mixture is left standing for 10-30 minutes;
in step 7, stirring for at least 5 minutes;
in step 8, stirring is carried out for at least 10 minutes.
Compared with the prior art, the invention has the beneficial effects that:
(1) the invention researches the filling problem of the shield construction excavation gap, and can solve the problem that the shield body is locked by the conventional shield body grouting material;
(2) a novel filling material configuration method is adopted, and the influence factors of the performance of the filling material are studied in advance to obtain the optimal water-cement ratio and the optimal expansion water ratio, so that the performance requirements of the shield excavation gap on the filling material are met;
(3) the filling material has long setting time, namely, the filling material can be subjected to slow initial setting so as to meet the pumping requirement in grouting equipment;
(4) the filling material has lower early shear strength, namely, the slurry keeps lower shear strength when the shield is propelled, so that the shield can be smoothly propelled without locking the shield shell, and meanwhile, higher shear strength can be obtained at the later stage, and the excavation gap can be effectively filled, so that the effect of controlling the stratum deformation is achieved;
(5) the filling material has the characteristics of good lubricating property, high stability, small friction with the shield shell and the like;
(6) by adopting a more reasonable proportioning scheme, the flowability of the filling material is controlled, and the situation that the filling material flows to the cutter head and is fixedly connected to cause the torsion of the cutter head to be increased is prevented; the workability is good, the novel filling material is not easy to have segregation, the material loss is reduced, and the novel filling material is more economic and environment-friendly.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below. It should be apparent that the drawings in the following description are merely exemplary, and that other embodiments can be derived from the drawings provided by those of ordinary skill in the art without inventive effort.
The structures, ratios, sizes, and the like shown in the present specification are only used for matching with the contents disclosed in the specification, so that those skilled in the art can understand and read the present invention, and do not limit the conditions for implementing the present invention, so that the present invention has no technical significance, and any structural modifications, changes in the ratio relationship, or adjustments of the sizes, without affecting the functions and purposes of the present invention, shall fall within the scope covered by the technical contents disclosed in the present invention.
FIG. 1 is a schematic view of a sample preparation mold according to one embodiment of the present invention;
FIGS. 2-5 are graphs of shear stress versus displacement for four sets of water-to-cement ratios of 16:1, 8:1, 4:1, and 2.6:1 in accordance with the present invention;
6-9 are graphs of shear stress versus displacement for four sets of expansion ratios of 1:4, 1:2.67, 1:2, and 1:1.6 in accordance with the present invention;
FIGS. 10-12 are graphs of shear stress versus displacement (shear strength index) for comparative tests at normal pressures of 100kpa, 200kpa, and 400 kpa;
FIG. 13 is a shear strength fit plot for a comparative experiment;
FIGS. 14-17 are graphs of shear stress versus displacement (early strength indicator) for comparative tests at normal pressures of 50kpa, 100kpa, 200kpa, and 400 kpa;
FIG. 18 is a schematic view of a friction test apparatus according to an embodiment of the present invention;
FIG. 19 is a graph of cement usage versus frictional stress;
FIG. 20 is a graph showing the relationship between the amount of bentonite used and the frictional stress;
FIG. 21 is a graph showing the effect of the slurry fluidity test.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the present invention is described in further detail below with reference to the embodiments and the accompanying drawings. The exemplary embodiments and descriptions of the present invention are provided to explain the present invention, but not to limit the present invention.
In the description of the present invention, it is to be understood that the terms "comprises/comprising," "consists of … …," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a product, apparatus, process, or method that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such product, apparatus, process, or method if desired. Without further limitation, an element defined by the phrases "comprising/including … …," "consisting of … …," or "comprising" does not exclude the presence of other like elements in a product, device, process, or method that comprises the element.
In the present invention, unless otherwise expressly stated or limited, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can, for example, be fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.
It will be further understood that the terms "upper," "lower," "front," "rear," "left," "right," "top," "bottom," "inner," "outer," and the like, refer to an orientation or positional relationship illustrated in the drawings for convenience in describing the present invention and to simplify description, and do not indicate or imply that the referenced device, component, or structure must have a particular orientation, be constructed in a particular orientation, or be operated in a particular manner, and should not be construed as limiting the present invention.
Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.
The following describes the implementation of the present invention in detail with reference to preferred embodiments.
The invention relates to a method for preparing a low-shear strength grouting material for a shield excavation gap, which comprises the following steps of:
and 8, measuring water glass with the needed Baume degree, adding the water glass into the bentonite slurry containing the cement, continuously stirring uniformly, and completing preparation.
In the invention, the components of the grouting material can be selected according to the following concrete steps:
(1) the cement material used in the invention is P.O 42.5.5R ordinary portland cement of Jun brand company, and meets the requirements of ordinary cement in Portland cement and ordinary portland cement GB 175-2007.
(2) The bentonite is an unmodified bentonite which is prepared by Fushan Teddis materials Co, contains a large amount of active groups and is of a monoclinic structure, the content of the montmorillonite is generally more than 65%, the relative density is 2.4-2.8, the melting point is 1330-1430 ℃, the bentonite can play a role in enhancing the stability of the filling material, the material plasticity of the filling material is improved, and the bentonite has good water-washing resistance and dispersibility.
(3) The water glass is a water glass product of Wuxi Adita union company, commonly known as sodium silicate, is an alkaline solution generated by dissolving sodium silicate in water, and is a non-toxic non-free strong alkaline material. The sodium silicate is a transparent viscous solid with a chemical formula of Na2·mSiO2. The parameters of the sodium silicate liquid are shown in table 1. The water glass solution has better bonding capability and can play a role in blocking capillaries and preventing permeation. In engineering, water glass is often mixed into cement mortar, and the cement mortar is used for grouting reinforcement, emergency repair and the like of water-rich formations by utilizing the quick setting property and the adhesion property of the water glass.
TABLE 1 Water glass Material Properties
(4) The water used in the invention is pure water to eliminate impurities possibly existing and the influence of pH value, considering that other water contains impurities with different components and the pH value is different to influence the performance of the grouting material.
In the invention, when a plurality of groups of grouting materials with different water-cement ratios and a plurality of groups of grouting materials with different water-expansion ratios are preliminarily designed, four groups of water-cement ratios of 16:1, 8:1, 4:1 and 2.6:1 and four groups of water-expansion ratios of 1:4, 1:2.67, 1:2 and 1:1.6 are preliminarily designed according to engineering experience, and a configuration scheme shown in the following table 2 is specifically adopted:
TABLE 2 materials proportions used in the test
After a plurality of groups of grouting materials with different water-cement ratios and different expansion water ratios are preliminarily designed, slurry preparation of a test material is carried out, and the preparation method specifically comprises the following steps:
adding bentonite and water into a stirrer according to a plurality of groups of preliminarily designed different swelling water ratios, stirring for 5-10 minutes preferably to fully mix the bentonite and the water uniformly, and standing for 10-30 minutes to fully swell the bentonite and the water;
adding cement powder into the bentonite slurry according to a plurality of groups of different water-cement ratios designed preliminarily, and continuing to stir for at least 10 minutes until the mixture is uniform;
measuring water glass with required Baume degree, adding the water glass into the swelled bentonite slurry, stirring for at least 5 minutes until the mixture is uniform, and finishing the preparation.
After test slurry is obtained, a plurality of groups of test pieces of grouting materials are manufactured, and the method comprises the following steps:
(1) selecting a sample preparation mold capable of preparing samples in batches, wherein the sample preparation mold is a needle cylinder injection type mold and comprises a cylinder body 1, as shown in figure 1, the upper end of the cylinder body 1 is open, and the lower end of the cylinder body 1 is provided with a propeller 2;
the inner diameter of the cylinder body 1 is 12cm, the wall thickness is 0.1cm, and the upper end of the cylinder body is open to form a shear port;
the invention further arranges a rubber leakage-proof pad 3 on the top of the propeller 2 to prevent slurry leakage.
(2) Pouring the prepared groups of slurry into a sample preparation mold, standing the slurry for a certain time, and curing to form a sample 4;
the slurry standing time is related to the shield advancing speed, because the shield advances forward at a certain speed, and the time required for a certain shield machine to advance for one loop is 20 minutes, the slurry is required to be configured in advance when the slurry is configured, and the slurry is required to be configured in advance, the time is controlled, and the slurry still keeps a state of low shear strength and high pumpability in the 20 minutes so as to meet the shield requirement.
After standing for a certain time, the basic requirement of slurry solidification is that the slurry does not generate displacement and deformation under the state of mold back-off, so that the test requirement can be met.
(3) The method comprises the steps of pushing a sample 4 out of a cylinder 1 of a die by a certain length, pushing the sample by stages, pushing the sample by 1cm each time, pushing the sample by 3cm in total, cutting the sample by a cutting ring at a shearing opening to obtain a first sample, sequentially pushing the sample by the same length, and cutting the sample by the cutting ring to obtain a plurality of samples.
The invention cuts 4 samples in steps to prepare for the next direct shear test under vertical pressures of 50kPa, 100kPa, 200kPa and 400 kPa.
After the test pieces are manufactured, the shear strength of each group of test pieces is tested, and the direct shear test is carried out on each group of test pieces under the vertical pressure of 50kPa, 100kPa, 200kPa and 400kPa respectively.
Firstly, carrying out shear strength tests of the filling material under different water-cement ratios, wherein the test results are shown in fig. 2-5, when the vertical load is 50kPa, the water-cement ratio has small influence on the shear stress, and the shear stress is about 10-20 kPa; when the vertical load is 100kPa, the shear stress of the A2 filling material is greatly increased, the shear stress of the A3 filling material is closer to that of the A4 filling material, the shear stress of the A3 and the A4 is about 40-45 kPa, the shear stress of the A1 filling material is 11.67kPa, and the shear stress of the A2 filling material is 12.54kPa and is increased by 7.4%; at 400kPa, the effect of water-cement ratio on shear stress increased dramatically, with a peak shear stress of 193kPa for the A4 packing material. The increase of the cement consumption causes the aggregation phenomenon, the cement enables smaller soil particles to form larger aggregates under the action of the cement, so that the shear strength of the filling material is increased, the cement hydrates to generate a large amount of water-insoluble stable combination substances such as calcium silicate, calcium aluminate hydrate and the like, the water-insoluble stable combination substances are gradually hardened when being contacted with air, and the dense-structure substance is formed, so that the shear strength of the filling material is increased.
The conclusion can be drawn from the above tests: when the water-cement ratio is too high, the strength of the material is reduced, the filling requirement cannot be met, and meanwhile, the performance of the material is excessive due to the too low water-cement ratio, so that the use cost is high, so that the water-cement ratio of 8:1 or 4:1 is the most effective and economical configuration scheme.
Then, the shear strength test of the filling material under different expansion water ratios is carried out. The bentonite expands when meeting water and is filled into the space between the skeletons of the concreting bodies, thereby reducing the pores of the concreting bodies and reducing the permeability coefficient of the concreting bodies. And meanwhile, after meeting water, the bentonite particles can play a role in lubricating in the framework, but when the dosage of the bentonite is too high, the friction stress between the fluidity of the filling material and the pipeline is increased, the pipeline is blocked when the pumping pressure cannot overcome the flow resistance, and the filling material is generally considered not to meet the pumping requirement. If the consumption of the bentonite is too small, the water content in the filling material is higher, at the moment, the filling material is thinner, the initial setting time of the filling material is prolonged, the filling material is easy to run off in soil, and the filling material may run off to a cutter head to be condensed to cause the increase of the torque of the cutter head, thereby influencing the shield tunneling. Therefore, the dosage of the bentonite in the filling material not only influences the pumpability of the filling material, but also influences the fillability of the filling material, and therefore, the shear strength tests under different vertical loads are respectively carried out on each group of filling materials, so that the influence of the bentonite on the shear strength of the filling material is verified.
The test results are shown in fig. 6-9, and the analysis in the figure shows that the influence of the expansion water ratio on the shear strength of the filling material is small, when the expansion water ratio is 1:4 and 1:2.67, the shear stress difference is small when the vertical load is 400kPa, and the shear stress difference is gradually obvious along with the reduction of the load. It can be seen from the comparative analysis in fig. 9 that the increase of the usage amount of the bentonite material can reduce the shear strength of the filling material, mainly because the montmorillonite material in the bentonite can have a hard setting reaction with products such as calcium hydroxide and the like generated by cement hydration, but the hard setting reaction of the bentonite is slow, so that a large amount of bentonite particles are filled in the pores of the cement framework after absorbing water and expanding, compared with the traditional cement slurry, the particles between the cement slurries fully contact to show a strong shear resistance under the vertical load effect, and the bentonite particles filled in the cement framework play a role in lubrication to reduce the direct contact between the cement frameworks, so that the internal friction angle of the filling material is reduced. The influence of the increase of the consumption of the bentonite material on the cohesive force of the filling material is small, after the internal friction angle between the particles is reduced, a large amount of free water causes stones in the filling material, and the distance between the particles is increased, so that the cohesive force is reduced.
The conclusion can be drawn from the above tests: the bentonite has low influence on the strength of the material, and the bentonite is the most ideal choice for saving the cost as much as possible while ensuring the strength of the material, so the adoption of the expansion-water ratio of 1:2 is the most effective and most economical configuration scheme.
After the optimal water-cement ratio and the optimal expansion water ratio of the required slurry are obtained, according to the optimal water-cement ratio and the optimal expansion water ratio, weighing cement, bentonite and a water raw material; the solid is prepared by weighing the required raw materials with an electronic scale, and the liquid is measured with a measuring cylinder.
Adding bentonite and water into a stirrer according to the optimal swelling water ratio, stirring to fully and uniformly mix the bentonite and the water, and standing to fully swell the bentonite and the water; in the invention, the preparation of the slurry is carried out under the conditions of standard atmospheric pressure and normal temperature, the bentonite is stirred with water for 5-10 minutes to ensure that the bentonite is uniformly stirred, and the bentonite is kept stand for 30 minutes to ensure that the bentonite is fully expanded.
Then adding cement powder into the bentonite slurry, and continuously stirring uniformly; the cement powder is added into the swelled bentonite slurry to slow down the hydration reaction of the cement, delay the initial setting and hardening time of the cement, achieve the aim of lower shearing strength of the filling material when the shield passes through, and prevent the slurry from locking the shield shell. In the invention, the cement powder is added and stirred for at least 10 minutes, so that the cement powder is uniformly stirred and has sufficient hydration reaction with water.
After the cement is fully stirred, water glass with required baume degree is measured and added into the swelled bentonite slurry, the stirring is uniform, the water glass is similar to a catalyst and has opposite charge property with a cementing body of the cement, and the water glass can play a role in neutralization after being mixed, so that the coagulation of the cementing body is promoted. In the invention, stirring is carried out for at least 5 minutes, so as to ensure that the water glass and the bentonite slurry are uniformly mixed.
The following comparative tests were used to verify the effectiveness of the grouting material of the present invention.
Test one, shear strength test:
the new proportion filling material used in the invention is compared with the common powdery clay, the new proportion filling material is uniformly mixed, then the mixture is stood and reacted for 30 minutes at normal temperature and under a standard atmospheric pressure, then the normal pressure of 100kap, 200kpa and 400kpa is adopted to carry out direct shear test (the normal pressure of 50kpa is too low to be distinguished), and the comparison test result is shown in fig. 10-12.
As can be seen from fig. 10, under a normal pressure of 100kpa, the shear strength of the filling material with the new formulation is similar to that of the mealy clay, and the difference is not large.
Under the normal pressure of 200kpa, the curve of the new proportioning filling material is more gentle, as shown in fig. 11, mainly because the friction force between molecules is reduced by the bentonite and the water glass, the shearing process is smoother, which further shows that the new proportioning filling material is more beneficial to pumping compared with powdery clay, and the problem of locking a shield shell or blocking a pumping pipeline is not easy to cause. In addition, under the normal pressure of 200kpa, the shearing strength of the filling material with new formula ratio is obviously improved compared with that of the silty clay, which shows that the filling effect is better.
Under the normal pressure of 400kpa, the shear strength of the filling material with the new mixing ratio is greatly higher than that of the silty clay, as shown in fig. 12, and the method is more suitable for the working condition of shield high pressure.
In summary, the new formula filling material is obviously superior to the silty clay in mechanical property, the novel mixed material is favorable for controlling the sedimentation generated in the shield process, the excavation gap can be effectively filled to achieve the effect of controlling the formation deformation, and compared with the filling silty clay, the novel mixed material has better filling effect and higher benefit.
The invention further fits the shear strength, the fitting result is shown in fig. 13, and as can be seen from fig. 13, the cohesive force of the filling material newly matched is lower, which indicates that the material does not cause locking of the shield machine, the internal friction angle is larger, which indicates that the strength is high, the filling effect is obvious, and the requirement of the shield machine on the filling material is met.
Test two, early strength test:
the new proportioning filling materials used in the invention are compared according to the time sequence, the time intervals of 2h, 7h and 24h are respectively adopted to carry out direct shear tests of 50kpa, 100kpa, 200kpa and 400kpa, and the comparison test results are shown in figures 14-17.
As can be seen from FIG. 14, under the action of a normal pressure of 50kpa, the shear strength of the sample in 2 hours is the lowest, and the shear strength of the sample in 24 hours is the highest, which indicates that the shear strength of the sample in the early stage is lower, and the shear strength in the later stage is higher, and meets the shield requirements.
As can be seen from FIG. 15, the shear strength of the test specimen at 2 hours is the lowest at a normal pressure of 100kpa, and the shear strength of the test specimen at 7 hours and 24 hours is closer, indicating that the final shear strength of the test specimen at 7 hours and 24 hours is not significantly different at a normal pressure of 100 kpa. However, when the shear displacement is insufficient, the shear strength of the sample in 2 hours is obviously lower than that of the samples in other two time periods, which indicates that the sample meets the requirement of the shield on low early strength in the shear displacement interval of 0-8 mm.
As can be seen from FIG. 16, the final shear strengths of the samples at the three time periods are very close to each other under the normal pressure of 200kpa, except that the shear strength of the sample at 2 hours is significantly lower than that of the samples at the other two time periods when the shear displacement is 5mm, which means that the shear strength of the sample at 2 hours is lower than that of the samples at 7 hours and 24 hours when the shear displacement is insufficient, and the shield requirements are also met.
As can be seen from fig. 17, under the normal pressure of 400kpa, the final shear strength of the sample in three time periods is gradually decreased from 24h to 2h, the maximum shear strength is 160kpa, the minimum shear strength is 140kpa, and in the shear displacement interval of 0 to 6mm, the early strength of the sample is obviously lower than that of the sample in other two time periods, which also indicates that under the high-pressure environment and the small shear displacement, the early strength of the sample is very low, which meets the working condition when the shield starts grouting and meets the shield requirement.
Test three, frictional resistance test:
the present invention proceeds with the following test for frictional resistance detection to detect and verify the effect of the filler material on the frictional resistance of the shield shell.
The test respectively studies the influence of the water-cement ratio and the expansion ratio of the filling material on the frictional resistance. In the shield advancing process, the friction between the shield shell and the filling material is similar to the friction between the overlying material and the lower steel, so that the interaction relation between the shield and the filling material is simplified, and the friction resistance research is carried out by adopting the modified direct shear apparatus. A permeable stone 8 and a stainless steel block 7 with the thickness of 2cm are placed in the lower shearing box 5 and are flush with the surface of the lower shearing box, as shown in figure 18, the roughness of the surface of the steel block 7 is similar to that of the shield shell, a filling material sample 9 and a field soil sample are respectively placed in the upper shearing box 6, and filter paper, the permeable stone 8, a pressurizing cover plate, a steel ball, a pressurizing frame and a displacement meter are sequentially placed above the filling material sample 9 and the field soil sample.
The tunneling speed of the shield in the propelling process is related to a plurality of factors and is an unstable value, and researches show that the influence of the rotating speed of the hand wheel on the test result is small and the friction stress is increased along with the increase of the burial depth. Therefore, in the test, the main buried depth of the tunnel is about 15-25 m in a field line magnetic 1# interval of a Beijing subway Daxing machine, the penetrating stratum mainly comprises a fine sand stratum, a fine clay stratum and a pebble stratum, the soil covering pressure range of the upper part of the vault of the tunnel is 250-450 kPa through calculation, so that the test applies 400kPa vertical stress to the sample, and the influence of the filling material and the field soil sample on the friction resistance of the shield shell under the action of the upper soil covering pressure during shield tunneling is simulated by adopting the shearing speed of 0.8 mm/min.
During the shield propulsion process, according to different grouting modes, surrounding geological conditions and the disturbance degree of a cutter head to a soil body, the filling material may be subjected to compaction grouting or penetration grouting, a filling material consolidation body or a filling material-soil complex is formed at the periphery of the shield body, and if the filling material consolidation body or the filling material-soil complex is not subjected to shearing damage, the shield shell moves forwards along the surface of the filling material during the shield propulsion process. If compaction grouting occurs, the periphery of the shield body is wrapped by the solidification body of the filling material, and the water-cement ratio and the expansion-water ratio of the filling material have obvious influence on the frictional resistance. Therefore, the group A and the group B filling material samples are respectively applied with 400kPa vertical pressure and are stood for 24 hours to carry out friction tests, and the influence of the water-cement ratio and the expansion ratio of the filling materials on the friction resistance of the shield body is researched.
Research results show that the water cement ratio is too low, namely, the excessive cement dosage can cause the calculus rate in the filling material to be too high, the filling material is changed from a plastic state to a hardening state, and the cementing material is adhered to the steel block to increase the frictional resistance. From the analysis in fig. 19, after 24 hours of standing, the frictional resistance curve after the water-cement ratio of 16:1 increased linearly with the decrease in the water-cement ratio at a constant amount of other components. The cement hydrate reacts with the bentonite material to realize an ion exchange process, cement gel is wrapped around the soil particles, the cement gel has high viscosity, the effect of increasing the strength of the slurry is achieved, and meanwhile, the interaction force of the shield shell and the filling material is increased. The effect of different cement amounts on friction is given in table 3 below.
TABLE 3 influence of different water-cement ratios on Friction
As can be seen from table 3, the friction of the a2 group slurry (8: 1) and the A3 group slurry (4: 1) is moderate, the friction of the a4 group slurry (2.6: 1) is too high, and the water-cement ratio is too low, which results in slurry agglomeration, no pumping and shield thrust, while the water-cement ratio of the a1 group slurry (16: 1) is too high, which results in slurry strength too low to achieve good filling effect, although the friction is lower.
The effect of the expanded water ratio on the shield-filling material interaction was further investigated based on a water-cement ratio of 8: 1. As can be seen from fig. 20, the frictional resistance increases with the bentonite content, but the increase is relatively small. The bentonite material is mainly montmorillonite, has extremely strong water absorption capacity and hardly reacts with cement, is mainly expanded when meeting water and becomes dozens of times or even dozens of times of the volume of the bentonite material, can absorb a large amount of free water molecules, can influence the fluidity of the filling material when the consumption of the bentonite is too much, is one of important factors for leading the filling material to be changed into a plastic state from a flow plastic state, not only can influence the pumpability of the filling material, but also can increase the frictional resistance between the shield shell and the filling material, and is not beneficial to shield propulsion. The effect of different amounts of bentonite on the friction is given in table 4 below.
TABLE 4 influence of different expansion ratios on the Friction force
As can be seen from Table 4, the change of the Peng/W ratio has less influence on the slurry performance compared with the water-cement ratio, and the lower Peng/W ratio is adopted as much as possible on the premise of meeting the engineering requirements so as to achieve the purpose of saving the cost. In the table, the slurry (1: 1.6) in the B4 group has large friction force and the bentonite dosage is the largest, the slurry (1: 4) in the B1 group and the slurry (1: 2.67) in the B2 group have small friction force and the bentonite dosage is not large, but the strength is not enough, and the slurry (1: 2) in the B3 group obviously best meets the proportioning requirement while the strength is ensured according to the principle that the bentonite dosage is lower.
Test four, flowability test:
in order to verify the fluidity and the workability of the slurry prepared according to the above ratio, the fluidity test was also carried out according to the present invention. Because the fluidity and workability tests are relatively difficult to implement, the invention adopts an inverted cup method which is a common method in the industry, the fluidity of the slurry is judged by the inverted cup method, the test effect is shown in figure 21, and the results of a plurality of groups of tests show that the slurry with new mixing ratio is not easy to flow down from an inverted measuring cup under the condition of meeting the pumping condition, which shows that the fluidity of the slurry is better controlled, the fluidity is not high, and the slurry is not easy to flow to a cutter head to be solidified.
In summary, the invention researches the filling problem of the excavation gap in the prior art, in particular the problem that the shield body is locked by the filling material which is generally not concerned much in the prior art, adopts a novel filling material configuration method, and through theoretical analysis and tests, the newly-formulated filling material has the characteristics of good lubricating property, high stability, longer coagulation time, lower early strength, small friction with the shield shell and the like, the shield body is prevented from being locked by the early low shear strength, the excavation gap can be effectively filled by the later higher shear strength so as to achieve the effect of controlling the formation deformation, meanwhile, the flowability is better controlled, the flowability is not high, the workability is better, the pumping requirement in grouting equipment is met, the segregation effect is not easy to occur, and the material loss is reduced.
It will be readily appreciated by those skilled in the art that the above-described preferred embodiments may be freely combined, superimposed, without conflict.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (10)
1. A method for configuring a low-shear strength grouting material for a shield excavation gap is characterized by comprising the following steps of:
step 1, selecting a grouting material, wherein the grouting material comprises the components of cement, bentonite, water glass and water;
step 2, preliminarily designing a plurality of groups of grouting materials with different water-cement ratios and a plurality of groups of grouting materials with different expansion water ratios, and configuring a plurality of groups of grout according to the preliminarily designed water-cement ratios and expansion water ratios;
step 3, correspondingly manufacturing a plurality of groups of test pieces of grouting materials by adopting the plurality of groups of prepared grout;
step 4, testing the shear strength of each group of test pieces, and determining that the optimal water-cement ratio of the grouting material is 8:1 or 4:1 and the optimal expansion water ratio is 1:2 according to the shear strength of the test pieces;
step 5, weighing cement, bentonite and a water raw material according to the obtained optimal water-cement ratio and optimal expansion water ratio;
step 6, adding bentonite and water into a stirrer according to the optimal swelling water ratio, stirring to fully and uniformly mix the bentonite and the water, and then standing to fully swell the bentonite and the water;
step 7, adding cement into the swelled bentonite slurry according to the optimal water cement ratio, and uniformly stirring;
and 8, measuring water glass with the needed Baume degree, adding the water glass into the bentonite slurry containing the cement, continuously stirring uniformly, and completing preparation.
2. The method for configuring the low-shear-strength grouting material for the shield excavation gap according to claim 1, wherein the method comprises the following steps:
in step 1, the water used is purified water.
3. The method for configuring the low-shear-strength grouting material for the shield excavation gap according to claim 1, wherein the method comprises the following steps:
in step 2, the water-cement ratios of the plurality of groups are respectively 16:1, 8:1, 4:1 and 2.6:1, and the water expansion ratios of the plurality of groups are also respectively 1:4, 1:2.67, 1:2 and 1: 1.6.
4. The method for configuring the low-shear-strength grouting material for the shield excavation gap according to claim 1, wherein the method comprises the following steps:
in the step 2, the slurry preparation method comprises the following steps:
adding bentonite and water into a stirrer according to a plurality of preliminarily designed different swelling water ratios, stirring for 5-10 minutes to fully mix the bentonite and the water uniformly, and standing for 10-30 minutes to fully swell the bentonite and the water;
adding cement powder into the bentonite slurry according to a plurality of groups of different water-cement ratios designed preliminarily, and continuing to stir for at least 10 minutes until the mixture is uniform;
measuring water glass with required Baume degree, adding the water glass into the swelled bentonite slurry, stirring for at least 5 minutes until the mixture is uniform, and finishing the preparation.
5. The method for configuring the low-shear-strength grouting material for the shield excavation gap according to claim 1, wherein the method comprises the following steps:
in step 3, the test piece is manufactured as follows:
(1) selecting a sample preparation mold capable of preparing samples in batches, wherein the sample preparation mold is a needle cylinder injection type mold and comprises a cylinder body, the upper end of the cylinder body is open, and the lower end of the cylinder body is provided with a propeller;
(2) pouring the prepared groups of slurry into a sample preparation mold, standing the slurry for a certain time, and curing to form a sample;
(3) and pushing the sample out of the cylinder of the die by a certain length, cutting the first sample by a cutting ring, sequentially pushing the sample out by the same length, and cutting by the cutting ring to obtain a plurality of samples.
6. The method for configuring the low-shear-strength grouting material for the shield excavation gap according to claim 5, wherein the method comprises the following steps:
the inner diameter of the cylinder body is 12cm, and the wall thickness is 0.1 cm.
7. The method for configuring the low-shear-strength grouting material for the shield excavation gap according to claim 5, wherein the method comprises the following steps:
the top of the propeller is provided with a rubber leakage-proof pad.
8. The method for configuring the low-shear-strength grouting material for the shield excavation gap according to claim 5, wherein the method comprises the following steps:
in the step (2), the standing time of the slurry is related to the shield advancing speed, so that the slurry is ensured to be always in a state of low shear strength and high pumpability in the standing time.
9. The method for configuring the low-shear-strength grouting material for the shield excavation gap according to claim 5, wherein the method comprises the following steps:
in the step (2), the slurry is not displaced and deformed when the slurry is solidified to the reverse buckle of the sample preparation mould.
10. The method for configuring the low-shear-strength grouting material for the shield excavation gap according to claim 1, wherein the method comprises the following steps:
step 6, preparing slurry under the conditions of standard atmospheric pressure and normal temperature, stirring bentonite and water for 5-10 minutes, and standing for 10-30 minutes;
in step 7, stirring for at least 5 minutes;
in step 8, stirring is carried out for at least 10 minutes.
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