CN113174937A

CN113174937A - Method for processing soft clay layer and liquefied soil layer interactive foundation by using pneumatic vibrating rod compaction method

Info

Publication number: CN113174937A
Application number: CN202110390064.7A
Authority: CN
Inventors: 庄仲旬; 杜广印; 刘松玉; 杨泳; 高常辉
Original assignee: Southeast University
Current assignee: Southeast University
Priority date: 2021-04-12
Filing date: 2021-04-12
Publication date: 2021-07-27

Abstract

The invention relates to a method for processing a soft clay layer and a liquefied soil layer interactive foundation by a pneumatic vibrating rod compacting method, which comprises the steps of determining the depths of a field liquefied soil layer and a soft clay layer according to survey data; leveling a field, positioning a vibration point, and striking a plastic drainage plate; positioning a pile machine; resonance sinking; high-pressure air injection; the vibration hammer-vibration rod-foundation soil system is in a resonance state by adjusting the frequency of the vibration hammer, so that the vibration energy is effectively transmitted to the soil body around the vibration rod, and the soil layer capable of being liquefied is vibrated to be compact, so that the liquefaction performance of the soil layer is eliminated; meanwhile, when the vibrating rod sinks to the soft clay layer, high-pressure air injection can promote dissipation of ultra-static pore pressure in soil caused by vibration load, and the drainage consolidation process of the liquefied soil layer and the soft clay layer can be accelerated by matching with the plastic drainage plate, so that the method is an economic, environment-friendly and efficient soft clay layer and liquefied soil layer interactive foundation treatment method.

Description

Method for processing soft clay layer and liquefied soil layer interactive foundation by using pneumatic vibrating rod compaction method

Technical Field

The invention relates to a method for treating a soft clay layer and liquefied soil layer interactive foundation by a pneumatic vibrating rod compacting method, belonging to the technical field of foundation treatment methods.

Background

The east coastal region of Jiangsu province in China is influenced by geological operation, sinks from the beginning of late renewal, receives sea invasion, rises and falls for a few degrees later, so that settled layers are mutually overlapped with sea and land, lithology is reflected as mutual layers of silt and silty clay, mucky soil exists, and a special foundation of interaction of liquefied soil and soft clay is formed. The saturated silt is in a loose state, the standard penetration number is low, the engineering geological property is poor, the liquefaction phenomenon is easily generated under the action of dynamic load (earthquake) so as to endanger the normal use and safety of a building, the natural pore size of the soft clay layer is large, the mechanical index strength is low, the thixotropy is high, the compressibility is high, and continuous sedimentation is easily generated under the action of an overlying load. The soft clay and the liquefied soil can generate different stress states and deformation under the action of different loads and external force, and the disease treatment problem of the soft clay and the liquefied soil must be considered simultaneously when a special foundation formed by embedding and interacting the soft clay and the liquefied soil is treated.

The patent No. ZL200910185349.6, entitled "method for treating foundation with alternate layer of liquefied soil layer and soft soil layer", mainly adopts the combined construction of bidirectional stirring variable cross-section pile and compacted sand pile, and the treatment technology needs to construct bidirectional stirring variable cross-section pile in soft soil layer first and then compacted sand pile in liquefied soil layer, and has the disadvantages of complicated steps, high comprehensive construction cost, long construction period and the like.

At present, a vibration rod compacting method which is relatively wide is used, a special vibration rod is sunk into soil by a vibration hammer, and the vibration energy is effectively transmitted to the surrounding soil body by utilizing the vibration amplification effect when a vibration hammer-vibration rod-soil system is in a resonance state, so that the soil body compactness can be improved and the liquefaction resistance performance of the soil body can be improved after the super-pore pressure is dissipated. The vibration rod compaction method does not need additional filler during construction, so that the economic benefit is remarkable, the construction is convenient and fast, the reinforcement effect is good, and the vibration rod compaction method is widely applied to the coastal liquefaction foundation treatment in the east of China. However, for the soft clay layer and the liquefied soil layer interactive foundation, the low permeability of the soft clay can hinder the discharge of pore water in the vibration compaction process, thereby affecting the reinforcement effect of the vibration rod compaction method. This also becomes an important obstacle to the application of the conventional vibration rod compaction method in the field of liquefied foundation treatment.

Disclosure of Invention

The invention provides a method for processing soft clay layer and liquefied soil layer interactive foundations by a pneumatic vibrating rod compacting method, which realizes the processing of the interactive foundations by utilizing a method combining resonance compacting effect and high-pressure air injection, and obviously improves the engineering efficiency.

The technical scheme adopted by the invention for solving the technical problems is as follows:

a method for processing soft clay layer and liquefied soil layer interactive foundation by a pneumatic vibrating rod compacting method comprises the following steps:

firstly, determining the depths of a liquefied soil layer and a soft clay layer of a field to be treated according to survey data;

secondly, leveling a field to be treated, positioning a plurality of vibration points, and arranging plastic drainage plates according to the distribution condition of the vibration points, wherein the arranging depth of the plastic drainage plates should exceed the depth of the soft clay layer bottom;

thirdly, positioning the pile machine, conveying the pile machine to a site to be treated, erecting a guide frame and fixing the guide frame through a triangular support rod, hoisting a vibration rod by using a crane and connecting the vibration rod with a vibration hammer fixed on the guide frame through a flange plate at the top end of the vibration rod to realize the fixation of the vibration rod, moving the guide frame through adjusting a hydraulic device, and moving the vibration rod to a position above an appointed vibration point;

fourthly, resonance sinking, starting the vibration hammer, and adjusting the vibration frequency of the vibration hammer to enable the vibration hammer-vibration rod-foundation soil system to be in a resonance state, wherein the vibration amplification effect generated in the resonance state can realize effective transmission of vibration energy to the soil layer around the vibration point, so that the rod is conveniently sunk while local liquefaction of the soil layer around the vibration rod is caused;

fifthly, high-pressure air injection is carried out, when the rod to be vibrated sinks to the depth of the top of the soft clay layer, an air valve is opened, and high-pressure air injection is carried out on the site to be treated through an air injection port at the bottom end of the vibrating rod;

sixthly, the vibration hole keeps vibrating, the vibration rod continues to sink, and when the vibration rod sinks to the preset treatment depth, the air valve is closed to keep vibrating;

seventhly, vibrating the lifting rod, starting the pile machine, lifting the vibrating rod in a vibrating state upwards, when the vibrating rod gradually separates from a hard soil layer and a liquefied soil layer to the bottom of a clay layer, reopening the air valve to jet air, controlling the vibrating rod to continuously lift until the vibrating rod reaches the ground surface of a field to be treated, closing the vibrating hammer and the air valve at the moment, finishing the construction of the position of the vibrating point, repeating the steps, and treating the next vibrating point;

as a further preference of the invention, a plurality of vibration points are arranged in a regular triangle, and a plastic drainage plate is arranged at the geometric center of three points of the triangle;

as a further preferred aspect of the present invention, a plurality of vibration points are arranged in a square, and a plastic drainage plate is arranged at the geometric center of four points of the square;

as a further preferred aspect of the present invention, the plurality of plastic drain plates are communicated through a drainage ditch, both ends of which are connected to a gutter located around the site to be treated;

as a further preferable mode of the present invention, in the fourth step and the sixth step, the vibration frequency range of the vibration hammer is 12Hz to 20 Hz;

in the seventh step, the vibration frequency range of the vibration hammer is 22Hz-28 Hz;

as a further preferable mode of the present invention, in the fifth step, the gas injection pressure of the gas injection port at the bottom end of the vibrating rod is in the range of 0.1MPa to 0.8 MPa;

as a further preferred mode of the present invention, in the sixth step, the sinking speed of the oscillating bar is in the range of 1.0m/min to 1.5 m/min.

Through the technical scheme, compared with the prior art, the invention has the following beneficial effects:

1. aiming at the engineering difficulty that the reinforcing effect is poor when the soft clay layer and the liquefied soil layer interactive foundation is processed by the traditional vibration rod compacting method, the vibration hammer-vibration rod-to-site soil system to be processed is in a resonance state by adjusting the frequency of the vibration hammer, so that the vibration energy is effectively transmitted to the soil body around the vibration rod, and the liquefaction performance of the liquefied soil layer is eliminated;

2. according to the invention, high-pressure air injection is assisted when the vibrating rod sinks to the soft clay layer, so that soil layer cracks can be enlarged, thus hyperstatic pore pressure dissipation in soil caused by vibration load is promoted, the drainage consolidation process of the liquefied soil layer and the soft clay layer can be accelerated by matching with the plastic drainage plate, the bearing capacity of the soft clay layer is improved, and the post-construction settlement is reduced;

3. when the soft clay layer and the liquefied soil layer interactive foundation is treated, no extra filling materials such as broken stones and sand filling materials need to be added, the economic benefit is remarkable, the construction method is simple, and the engineering efficiency is high.

Drawings

The invention is further illustrated with reference to the following figures and examples.

FIG. 1 is a flow chart of an operation method for processing soft clay layer and liquefied soil layer interactive foundation by a pneumatic vibrating rod compacting method provided by the invention;

fig. 2 is a schematic view of the arrangement of the plastic drain board provided by the invention.

In the figure: 1 is the liquefaction soil layer, 2 is soft clay layer, 3 is the hard soil layer, 4 are stake machines, 5 are the vibratory hammer, 6 are the pole that shakes, 7 are the air jet, 8 are the plastics drain bar.

Detailed Description

The present invention will now be described in further detail with reference to the accompanying drawings. In the description of the present application, it is to be understood that the terms "left side", "right side", "upper part", "lower part", etc., indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of describing the present invention and simplifying the description, but do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and that "first", "second", etc., do not represent an important degree of the component parts, and thus are not to be construed as limiting the present invention. The specific dimensions used in the present example are only for illustrating the technical solution and do not limit the scope of protection of the present invention.

As stated in the background art, the technical support on which the method is based is a vibration rod compaction method, then high-pressure air injection is superposed on the basic principle of treating the liquefied foundation based on the vibration rod compaction method, so that the purpose of the method can be achieved, and the compaction effect is further deepened while the soil layer compaction of the treatment site is obtained;

that is, the processing method of the application is roughly divided into two parts, one is a vibration rod compaction method for processing a liquefied foundation, the method sinks a rod into the soil in a vibration mode, in the rod sinking process, vibration energy is mainly transmitted to the surrounding soil layer along a rod body in a vertical polarized wave mode, the strong vibration of saturated loose sandy soil is caused to cause the pore pressure in the soil around the rod to suddenly rise, the soil body is in a circulating flow state and liquefied, then consolidation settlement is carried out under the action of self-weight stress to achieve a compact state, in the rod sinking process, a vibration hammer-vibration rod-foundation soil system is enabled to achieve a resonance state by adjusting a vibration hammer 5, the vibration amplification effect generated at the moment can enable the vibration energy to be transmitted to the surrounding soil body in an optimal mode, and therefore effective compaction of the soil body is achieved; but only rely on the closely knit method of pole that shakes can only be in the closely knit of preliminary realization pending place liquefaction ground, consequently this application continues to adopt the jet-propelled mode of second high pressure for further strengthening closely knit effect, combines together with the closely knit method of pole that shakes, guarantees treatment effect.

Specifically, the application provides a method for processing a soft clay layer and a liquefied soil layer interactive foundation by a pneumatic vibrating rod compacting method shown in fig. 1, which comprises the following steps:

first, according to the reconnaissance data, confirm the place liquefaction soil layer 1 of pending place and the degree of depth that soft clay layer 2 is located, figure 1 can know, the embodiment that this application is aimed at, the distribution of soil layer is liquefaction soil layer, soft clay layer, liquefaction soil layer and hard soil layer 3 from last to down.

Secondly, the field to be treated is leveled, a plurality of vibration points are positioned, plastic drainage plates 8 are arranged according to the distribution condition of the vibration points, and the arrangement depth of the plastic drainage plates is more than the depth of the soft clay layer

The arrangement of the plastic drainage plates follows a certain rule, two embodiments are provided, and the plastic drainage plates are arranged in a triangular shape as shown in fig. 2, namely, the plastic drainage plates are arranged at three geometric centers of the triangular shape, namely, the vibration points are arranged at three corners of the triangular shape, the plastic drainage plates are arranged at the three geometric centers of the triangular shape, in the preferred embodiment, the distance between each vibration point in fig. 2 is d, the distance d needs to be determined according to the characteristics of a field to be treated and treatment requirements, and the arrangement depth of the plastic drainage plates needs to penetrate through a topmost liquefied soil layer, a soft clay layer below the top liquefied soil layer and a liquefied soil layer below the soft clay layer to a hard soil layer; secondly, arranging a plurality of vibration points in a square shape, and arranging plastic drainage plates at the four-point geometric centers of the square, namely, the four corners of the square are vibration points, and the plastic drainage plates are arranged at the four-point geometric centers of the square;

it should be noted here that, in the conventional vibration rod compacting method, the site to be treated has obvious phenomena of liquefied sand blasting and drainage, so a plastic drainage plate needs to be arranged in the site in advance, and the geometric center of the vibration point is selected as the position where the plastic drainage plate is arranged, because the geometric center of the vibration point has the best reinforcing effect, the plastic drainage plate is communicated through the drainage ditch which is dug in advance as shown in fig. 2, so that drainage is facilitated, the drainage ditch has a side ditch which surrounds the periphery of the site to be treated, the depth of the drainage ditch is controlled to be 50cm-80cm, the drainage ditch which penetrates through the site to be treated and is positioned between the vibration points is controlled to be 10cm-20cm, and both ends of each drainage ditch are connected with the side ditch.

And thirdly, positioning the pile machine 4, as shown in figure 1, which is a mechanical arrangement schematic diagram provided by the application, conveying the pile machine to a site to be treated, erecting a guide frame and fixing the pile machine through a triangular support rod, hoisting a vibration rod 6 by using a crane and connecting the vibration hammer fixed on the guide frame through a flange plate at the top end of the vibration rod to realize the fixation of the vibration rod, and moving the guide frame through adjusting a hydraulic device to move the vibration rod to the position above an appointed vibration point.

in the process of resonance sinking, three aspects are involved, namely dynamic liquefaction, wave and energy transfer and stress condition change;

the dynamic liquefaction is that the repeated powerful vibration of the vibration rod is relied on to cause the temporary liquefaction or structural damage of the saturated sand layer around the vibration rod, and the soil particles are rearranged after liquefaction and transferred to the low potential energy position to reduce the pores and increase the compactness; on the other hand, the sandy soil is vibrated and extruded to be compact by the transverse extrusion force generated by the vibrating rod, so that the bearing capacity and the liquefaction resistance of the soil layer are improved, and the purpose of reinforcement is achieved; moreover, the vibration holes formed by the vibration rods are good drainage channels, so that the dissipation of excess pore water pressure generated by the extrusion and vibration actions can be accelerated, and the increase amplitude of the pore water pressure is reduced;

wave and energy transfer, namely, the vibration rod transfers energy to surrounding soil to cause vibration under the action of vertical exciting force of the vibration hammer, so that body waves (longitudinal waves and transverse waves) and surface waves (Rayleigh waves and Leff waves) are generated, the longitudinal waves are compression waves generated by vertical reciprocating impact motion of the rod end, the vibration direction of mass points is consistent with the advancing direction of the waves, and volume change is generated along with the vibration direction, so that the vibration direction is generally represented as short period and small amplitude, and the longitudinal waves are mainly generated by the bottom end of the vibration rod in a resonance compaction stage; the transverse wave is the shear wave generated by the vertical reciprocating shear motion of the vibration rod, is transmitted to the surrounding soil body on the whole vibration rod main body in a columnar mode, generally has the characteristics of long period and large amplitude, and the vibration direction of mass points is vertical to the advancing direction of the wave, so that the volume change is avoided; from the action form, the longitudinal waves mainly have the compaction action on the soil body, so that the pore ratio of the soil body is reduced, and the compactness is improved; the transverse waves mainly enable the soil body to generate shear deformation, and the microscopic structure of the soil body is changed on the premise of not changing the volume;

the stress condition changes, namely the friction action of soil and a vibration rod can generate horizontal compression waves to increase the horizontal stress, and the existing research shows that the horizontal vibration speed of each depth of a soil layer is greater than the vertical vibration speed in the construction process of the vibration rod compaction method, and the compaction can cause the horizontal stress of the soil body to increase to cause the soil layer pre-consolidation effect, the pre-consolidation effect has important significance for predicting the actual settlement of the compacted granular soil, and if the condition is not considered, the settlement estimation is overlarge and the liquefaction judgment is not in accordance with the reality.

Fifthly, high-pressure air injection is carried out, the vibration rod is sunk to the top of the soft clay layer, the air valve is opened, high-pressure air injection is carried out on the site to be treated through an air injection port 7 positioned at the bottom end of the vibration rod, and the air injection pressure range of the air injection port is 0.1MPa-0.8 MPa;

the reason of adopting high-pressure air injection is mainly explained, namely in the vibration compaction process, the existence of a clay interlayer can cause that the pore water pressure of a soil layer is difficult to dissipate so as to influence the effect and the compaction degree of foundation consolidation, in order to solve the problem, the application is supplemented with the high-pressure air injection technology on the basis of the technology of treating the liquefied foundation by the original vibration rod compaction method, when the vibration rod sinks to a soft clay layer, the dissipation of the ultra-static pore pressure in the soil caused by vibration load can be promoted by utilizing the high-pressure air injection, the drainage consolidation process of the liquefied soil layer and the soft clay layer can be accelerated by matching with a plastic drainage plate, and the three are combined together to realize the interactive foundation treatment of the soft clay layer and the liquefied soil layer; in the implementation of the preferred embodiment of the present application, when the air injection pressure of the air injection port is set at 0.5 MPa, the consolidation effect of the whole process is the best.

Sixthly, the vibration hole is kept vibrating, the vibration rod continues to sink, the sinking speed range of the vibration rod is 1.0-1.5 m/min, when the vibration rod sinks to the preset treatment depth, the air valve is closed, the vibration is kept, and the vibration frequency of the vibration hammer keeps unchanged during the vibration keeping period;

and seventhly, vibrating the lifting rod, starting the pile machine, lifting the vibrating rod in a vibrating state upwards, gradually separating from a hard soil layer and a liquefied soil layer to the bottom of a clay layer, reopening the air valve, continuously lifting the vibrating rod until the vibrating rod reaches the ground surface of the field to be treated, closing the vibrating hammer and the air valve at the moment, finishing the construction of the position of the vibrating point, repeating the steps and carrying out next vibration point treatment.

It should be emphasized that the present application provides a vibration rod compacting method, which utilizes the vibration amplification effect generated by the vibration hammer-vibration rod-foundation soil system during resonance, in this state, the ground vibration is greatly enhanced, the compacting efficiency of the soil vibration is improved, the vibration hammer frequency is adjusted to the resonance frequency of the vibration hammer-vibration rod-soil system to be inserted into the ground, the soil resistance along the rod body and the tip of the vibration rod can be reduced, and when the vibration rod reaches a preset depth, the ground vibration can be amplified, so as to realize effective compaction. Specifically, the vibration frequency required in the resonance sinking and vibrating hole vibration-remaining stages is approximately equal to the natural vibration frequency of the foundation soil, namely in the fourth step and the sixth step, the vibration frequency range of the vibration hammer is 12Hz-20 Hz; the vibration frequency in the vibration lifting rod stage is slightly larger than the natural vibration frequency of the foundation soil, namely in the seventh step, the vibration frequency range of the vibration hammer is 22Hz-28Hz, and the lifting rod can be conveniently lifted.

In conclusion, it can be confirmed that the method for processing the soft clay layer and the liquefied soil layer interactive foundation by the pneumatic vibrating rod compacting method provided by the application solves the problems pointed out in the background technology, and has the advantages of remarkable economic benefit, simple construction method and high engineering efficiency.

It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

The meaning of "and/or" as used herein is intended to include both the individual components or both.

The term "connected" as used herein may mean either a direct connection between components or an indirect connection between components via other components.

In light of the foregoing description of the preferred embodiment of the present invention, many modifications and variations will be apparent to those skilled in the art without departing from the spirit and scope of the invention. The technical scope of the present invention is not limited to the content of the specification, and must be determined according to the scope of the claims.

Claims

1. A method for processing soft clay layer and liquefied soil layer interactive foundation by a pneumatic vibrating rod compacting method is characterized by comprising the following steps: the method comprises the following steps:

sixthly, the vibration hole keeps vibrating, the vibration rod is controlled to continue sinking, and when the vibration rod sinks to the preset treatment depth, the air valve is closed to keep vibrating;

and seventhly, vibrating the lifting rod, starting the pile machine, lifting the vibrating rod in a vibrating state upwards, gradually separating from a hard soil layer and a liquefied soil layer to the bottom of a clay layer, reopening the air valve to jet air, controlling the vibrating rod to continuously lift until the vibrating rod is lifted to the ground surface of the field to be treated, closing the vibrating hammer and the air valve at the moment, finishing the construction of the position of the vibrating point, repeating the steps, and treating the next vibrating point.

2. The method for processing the soft clay layer and liquefied soil layer interactive foundation by the pneumatic vibrating rod compacting method according to claim 1, which is characterized in that: and a plurality of vibration points are arranged in a regular triangle, and plastic drainage plates are arranged at the geometric centers of the three points of the triangle.

3. The method for processing the soft clay layer and liquefied soil layer interactive foundation by the pneumatic vibrating rod compacting method according to claim 1, which is characterized in that: and a plurality of vibration points are arranged in a square shape, and plastic drainage plates are arranged at the geometric centers of four points of the square shape.

4. The method for processing the soft clay layer and liquefied soil layer interactive foundation by the pneumatic vibrating rod compacting method according to claim 1, which is characterized in that: the plastic drainage plates are communicated through a drainage ditch, and two ends of the drainage ditch are connected with side ditches positioned around the field to be treated.

5. The method for processing the soft clay layer and liquefied soil layer interactive foundation by the pneumatic vibrating rod compacting method according to claim 1, which is characterized in that: in the fourth step and the sixth step, the vibration frequency range of the vibration hammer is 12Hz-20 Hz;

in the seventh step, the vibration frequency of the vibration hammer is in the range of 22Hz-28 Hz.

6. The method for processing the soft clay layer and liquefied soil layer interactive foundation by the pneumatic vibrating rod compacting method according to claim 1, which is characterized in that: in the fifth step, the air injection pressure of the air injection port at the bottom end of the vibrating rod ranges from 0.1MPa to 0.8 MPa.

7. The method for processing the soft clay layer and liquefied soil layer interactive foundation by the pneumatic vibrating rod compacting method according to claim 1, which is characterized in that: in the sixth step, the sinking speed range of the vibrating rod is 1.0 m/min-1.5 m/min.