CN112227345A

CN112227345A - Construction method for improving cement mixing of expansive soil

Info

Publication number: CN112227345A
Application number: CN202011054229.5A
Authority: CN
Inventors: 谭文明; 何艳龙; 钟凯; 赵永旭; 韩继春
Original assignee: Road and Bridge International Co Ltd; China Communications Road and Bridge North China Engineering Co Ltd
Current assignee: Road and Bridge International Co Ltd; China Communications Road and Bridge North China Engineering Co Ltd
Priority date: 2020-09-29
Filing date: 2020-09-29
Publication date: 2021-01-15

Abstract

The application discloses a construction method for improving the mixing of ash in expansive soil, which relates to the technical field of civil engineering and aims to solve the problems that in the related technology, the construction needs to be repeatedly and uniformly mixed, the period is long, the working hours are consumed, the handling is not easy, and the potential quality hazard is easy to occur, and the technical key points are that S1, the expansive soil and the lime are taken; s2, mixing 3-6% lime with the mixture evenly to obtain mixed soil; S3-S6, preparing improved expansive soil by mixing soil; s7, dividing operation sections, wherein the length of each section is between 100 and 200m, and flattening and rolling the substrate; s8, performing layered filling according to a transverse full-width longitudinal horizontal layered filling compaction method, wherein the filling loose thickness is 30-60cm, then performing primary leveling by using a bulldozer, performing static pressure or weak vibration once by using a road roller, and performing fine leveling by using a land leveler to ensure that a working surface has no local concave-convex parts; and S9, sprinkling water and airing, checking the layering thickness and the flatness of the filling layer, and rolling and tamping after confirming that the layer thickness and the flatness meet the requirements.

Description

Construction method for improving cement mixing of expansive soil

Technical Field

The application relates to the technical field of civil engineering, in particular to a construction method for improving the mixing of ash in expansive soil.

Background

The expansive soil contains hydrophilic mineral montmorillonite and illite, which have the characteristics of remarkable water absorption expansion, water loss shrinkage and repeated expansion and shrinkage deformation in an external dry-wet alternating environment, and often cause serious damage to engineering structures and roadbed, so the expansive soil needs to be improved to reduce the expansion and shrinkage.

The existing method of adding lime and cement into the expansive soil filler is adopted, and the improved working mechanism is generally considered as follows: one is ion exchange, i.e. the calcium and magnesium ions in lime replace sodium and potassium ions in soil, or absorption, resulting in increased ion unit weight. After the expansive soil is contacted with lime, the ion exchange action is immediately carried out, so that the colloid adsorption layer is thinned, the clay colloidal particles are coagulated, the hydrophilicity of the adhesive force is weakened, and the fine particles are flocculated and coagulated to form larger concentrated force or aggregates. Second, carbonation, i.e. Ca (OH) in lime₂Absorption of CO₂Forming CaCO with firm texture and good water stability₃And (4) crystals. The crystallization enhances the cementation of the soil, thereby improving the later strength of the lime soil. Tests have shown that the carbonation reaction only proceeds in the presence of water, and that the carbonation reaction stops almost completely when dry carbonic acid gas acts on the completely dry lime powder, indicating that water is required for this effect. Thirdly, crystallization, in which a part of Ca (OH) is removed from the lime soil₂In addition to the carbonation, the other part crystallizes spontaneously in lime earth, Ca (OH)₂The colloid gradually becomes crystal, and the crystal can interact with soil to combine with the soil to form crystal, so that the soil particles are cemented into a whole, and the water stability of the lime soil is improved. Fourthly, the lime caking effect, namely after the expansive soil is added with the lime, the soil is alkaline, and the lime is gradually hardened with the alumina in the soil in an alkaline environment, namely: pozzolanic action-active silicon product minerals dissociate under alkaline excitation of lime and Ca (OH) in the presence of water₂The reaction produces aqueous calcium carbonate and calcium aluminate. The pozzolanic reaction is developed under the condition of continuously absorbing water, and thus it has hydraulic properties. In addition, lime itself generates a digestion reaction, CaO generates Ca (OH)₂The volume of the soil is increased by nearly one time, so that the soil is solidified.

However, the reaction speed of lime, cement and soil is slow, the strength of the generated hydrate is low, the durability is poor, certain effect can be achieved only by the requirement on the mixing amount of the lime or the cement, the construction amount is high, the lime or the cement needs to be mixed uniformly repeatedly during construction, the period is long, the working hours are consumed, the control is difficult, and potential quality hazards are easy to occur. Meanwhile, the method also has the problems of environmental pollution, inconvenience for greening and the like. In order to find a new way for improving the expansive soil filler, which is economic, effective and environment-friendly, domestic and foreign scholars propose a large number of additive methods from different ways, wherein a high polymer material serving as an additive has become a hot spot. However, the test effect of the current domestic addition scheme is not ideal and the popularization is poor.

Disclosure of Invention

The application mainly aims to provide a construction method for improving the ash content of expansive soil, which aims to solve the problems that the construction needs to be repeatedly and uniformly mixed, the period is long, the working hours are consumed, the handling is difficult, and the quality hidden danger is easy to occur in the related technology.

In order to achieve the above object, the present application provides a construction method for improving the mixing of ash in expansive soil, comprising the following steps:

s1, mechanically crushing the expansive soil which is large in viscosity and is in a block shape in the soil taking pit, and repeatedly turning and stirring the expansive soil for multiple times to obtain a soil block without more than 5cm, wherein the lime requires quicklime above grade III, and the effective CaO and MgO contents of the calcareous quicklime are not less than 70%;

s2, taking 3-6% lime and mixing evenly to obtain mixed soil, wherein the total weight of the dry expansive soil to be improved by the expansive soil improver is 100%;

s3, culturing a bacillus megaterium liquid and preparing a cementing liquid;

s4, adding diluted 60-80% bacillus megaterium liquid into the mixed soil, stirring uniformly, and standing for 2 hours;

s5, sucking out the bacillus megaterium liquid after 2 hours, adding 60-80% cementing liquid for continuous solidification, stirring uniformly, and standing for 22 hours;

s6, sucking out the bacillus megaterium liquid and the cementing liquid, and repeating the steps S4 and S5 for seven times to obtain improved expansive soil;

s7, dividing operation sections, wherein the length of each section is between 100 and 200m, removing vegetation impurities on the surface layer of the substrate, making a temporary drainage system, and flattening and rolling the substrate;

s8, performing layered filling according to a transverse full-width longitudinal horizontal layered filling compaction method, wherein the filling loose thickness is 20-30cm, then performing primary leveling by using a bulldozer, performing static pressure or weak vibration once by using a road roller, and performing fine leveling by using a land leveler to ensure that a working surface has no local concave-convex parts;

and S9, sprinkling water and airing, checking the layering thickness and the flatness of the filling layer, and rolling and tamping after confirming that the layer thickness and the flatness meet the requirements.

Optionally, the culturing process of the bacillus megaterium liquid comprises: the strain is stored in a freeze-drying tube in a freeze-drying powder state in a vacuum drying way, wherein the culture medium of the basic liquid (g/L): beef extract 3, peptone 10, NaCl5, pH7.0, and distilled water as solvent; a basic solid culture medium, wherein agar of 15g/L is added on the basis of a basic liquid culture medium; basic culture strip: the inoculation amount is 1% (V/V), the bottle loading amount is 30mL/250mL, the mixture is shaken at the constant temperature of 30 ℃, and the mixture is cultured in an incubator for 48 hours at the rotating speed of 200 r/min.

Optionally, the bacterial activity of the bacillus megaterium liquid is in a decay trend along with time, and the activity is kept good in one day.

Optionally, in step S8, in order to ensure the compaction quality of the side slope, both sides of the roadbed are widened by 50cm during filling.

Optionally, in step S8, the bulldozer performs rough leveling and the grader performs final leveling, the control plane has no significant local unevenness, a 4% road crown is made, and the longitudinal direction is smooth.

Optionally, in step S9, when the water content of the filler is low, a watering measure should be taken in time; when the water content of the filler is too large, a method of airing on the embankment can be adopted to ensure that the water content of the improved expansive soil filler is controlled within the construction allowable water content range determined by the test section compaction process before rolling.

The invention has the beneficial effects that:

1. in the scheme, the free expansion rate and the expansion potential of the expansive soil improved by the modifying agent are far lower than those of the plain soil, and the improvement effect is obvious; the shrinkage characteristic of the improved soil is obviously improved compared with that of plain soil, and the linear shrinkage of the improved soil under indoor conditions is obviously lower than that of the unmodified soil; the strength of the improved expansive soil is improved to a certain degree, and the fly ash component in the modifying agent and soil body minerals are subjected to a series of physical and chemical actions to generate gelled products for connection, particle wrapping and gap filling, so that a stable soil body structure is formed.

2. The modifier is simple and economic to apply and has strong operability, the application steps of the expansive soil modifier are simple and clear, and the needed modified material can be obtained after simple physical drying and chemical reaction are carried out on the components by microorganisms without complex technical equipment and professional operators; the novel modifier is applied to the improvement of the expansive soil of the roadbed, basically the same as the construction method of the traditional roadbed soil mixing method, does not need additional mechanical equipment, and has simple method and strong operability.

3. According to the scheme, the bacillus megatherium induced calcite deposition (MICP) technology is utilized, different cementing liquids are matched to solidify the expansive soil, the improvement effect can be further improved, and the soil body strength, the rigidity, the free expansion rate, the shearing strength, the expansive force and the like of the expansive soil are reflected.

4. The construction method has low implementation cost and simple and feasible construction process, and can be widely applied to the fields of geotechnical and hydraulic engineering such as side slopes, retaining walls, road beds, foundations, embankments and the like.

Detailed Description

In order to make the technical solutions of the present application better understood by those skilled in the art, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application, and it is obvious that the described embodiments are only some embodiments of the present application, but not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

It is noted that the terms first, second and the like in the description and in the claims of the present application are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It should be understood that the data so used may be interchanged under appropriate circumstances such that embodiments of the application described herein may be used. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.

Moreover, some of the above terms may be used to indicate other meanings besides the orientation or positional relationship, for example, the term "on" may also be used to indicate some kind of attachment or connection relationship in some cases. The specific meaning of these terms in this application will be understood by those of ordinary skill in the art as appropriate.

In addition, the term "plurality" shall mean two as well as more than two.

It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict. The present application will be described in detail with reference to examples.

Example 1:

a construction method for improving the mixing of ash in expansive soil comprises the following steps:

s2, taking 3% lime and mixing evenly to obtain mixed soil, wherein the total weight of the dry expansive soil to be improved by the expansive soil improving agent is 100%;

s3, culturing a bacillus megaterium liquid and preparing a cementing liquid;

wherein, the culture process of the bacillus megaterium liquid comprises the following steps: the strain is stored in a freeze-drying tube in a freeze-drying powder state in a vacuum drying way, wherein the culture medium of the basic liquid (g/L): beef extract 3, peptone 10, NaCl5, pH7.0, and distilled water as solvent; a basic solid culture medium, wherein agar of 15g/L is added on the basis of a basic liquid culture medium; basic culture strip: inoculating 1% (V/V), bottling 30mL/250mL, shaking at constant temperature of 30 deg.C, and culturing in incubator at rotation speed of 200r/min for 48 hr;

the bacterial activity of the bacillus megaterium liquid shows a decay trend along with time, and the activity is kept good in one day;

s4, adding diluted 60% bacillus megaterium liquid into the mixed soil, uniformly stirring, and standing for 2 hours;

s5, sucking out the bacillus megaterium liquid after 2 hours, adding 60% cementing liquid for continuous solidification, stirring uniformly, and standing for 22 hours;

s8, performing layered filling according to a transverse full-width longitudinal horizontal layered filling compaction method, wherein the filling loose thickness is 20cm, then performing primary leveling by using a bulldozer, performing static pressure or weak vibration once by using a road roller, and performing fine leveling by using a land leveler to ensure that a working surface has no local concave-convex parts;

in order to ensure the compaction quality of the side slope, the two sides of the roadbed are widened by 50cm respectively during filling;

the method comprises the following steps of (1) carrying out primary leveling by using a bulldozer, carrying out final leveling by using a land leveler, and making a 4% road arch longitudinally smoothly without obvious local concave-convex on a control layer;

s9, sprinkling water and airing, checking the layering thickness and the flatness of the filling layer, and rolling and tamping after confirming that the layer thickness and the flatness meet the requirements;

when the water content of the filler is low, a watering measure is adopted in time; when the water content of the filler is too large, a method of airing on the embankment can be adopted to ensure that the water content of the improved expansive soil filler is controlled within the construction allowable water content range determined by the test section compaction process before rolling.

Example 2:

s2, taking 5 percent of lime to be uniformly mixed with the dry expansive soil to be improved by the expansive soil improving agent by taking the total weight of the dry expansive soil to be improved as 100 percent to obtain mixed soil;

s3, culturing a bacillus megaterium liquid and preparing a cementing liquid;

s4, adding diluted 70% bacillus megaterium liquid into the mixed soil, uniformly stirring, and standing for 2 hours;

s5, sucking out the bacillus megaterium liquid after 2 hours, adding 70% cementing liquid for continuous solidification, stirring uniformly, and standing for 22 hours;

s8, performing layered filling according to a transverse full-width longitudinal horizontal layered filling compaction method, wherein the filling loose thickness is 25cm, then performing primary leveling by using a bulldozer, performing static pressure or weak vibration once by using a road roller, and performing fine leveling by using a land leveler to ensure that a working surface has no local concave-convex parts;

Example 3:

s2, taking 6 percent of lime to be uniformly mixed with the dry expansive soil to be improved by the expansive soil improving agent by taking the total weight of the dry expansive soil to be improved as 100 percent to obtain mixed soil;

s3, culturing a bacillus megaterium liquid and preparing a cementing liquid;

s4, adding diluted 80% bacillus megaterium liquid into the mixed soil, uniformly stirring, and standing for 2 hours;

s5, sucking out the bacillus megaterium liquid after 2 hours, adding 80% cementing liquid for continuous solidification, stirring uniformly, and standing for 22 hours;

s8, performing layered filling according to a transverse full-width longitudinal horizontal layered filling compaction method, wherein the filling loose thickness is 30cm, then performing primary leveling by using a bulldozer, performing static pressure or weak vibration once by using a road roller, and performing fine leveling by using a land leveler to ensure that a working surface has no local concave-convex parts;

The above description is only a preferred embodiment of the present application and is not intended to limit the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. The construction method for improving the mixing of the ash in the expansive soil is characterized by comprising the following steps of:

s3, culturing a bacillus megaterium liquid and preparing a cementing liquid;

2. The method as claimed in claim 1, wherein the culturing of the bacillus megaterium solution comprises: the strain is stored in a freeze-drying tube in a freeze-drying powder state in a vacuum drying way, wherein the culture medium of the basic liquid (g/L): beef extract 3, peptone 10, NaCl5, pH7.0, and distilled water as solvent; a basic solid culture medium, wherein agar of 15g/L is added on the basis of a basic liquid culture medium; basic culture strip: the inoculation amount is 1% (V/V), the bottle loading amount is 30mL/250mL, the mixture is shaken at the constant temperature of 30 ℃, and the mixture is cultured in an incubator for 48 hours at the rotating speed of 200 r/min.

3. The method as claimed in claim 2, wherein the bacterial activity of the bacillus megaterium solution is attenuated with time and remains good in one day.

4. The method of claim 1, wherein in step S8, the width of the roadbed is increased by 50cm to ensure the compaction quality of the side slope.

5. The method of claim 1, wherein in step S8, the construction is initially leveled by a bulldozer and the final leveling is performed by a grader, the control layer has no significant local unevenness, and the construction has 4% of road camber and is longitudinally smooth.

6. The method of claim 1, wherein in step S9, when the water content of the filler is low, the sprinkling is timely performed; when the water content of the filler is too large, a method of airing on the embankment can be adopted to ensure that the water content of the improved expansive soil filler is controlled within the construction allowable water content range determined by the test section compaction process before rolling.