KR101552644B1 - Soft soil improvement analysis method of Light-weighted Foam Soils - Google Patents

Abstract

A method for analyzing soft ground improvement of a bubble mixed lightweight soil is disclosed. The soft ground improvement analysis method of the bubble-mixed lightweight soil may include: a soft ground layer setting step (S110) of setting a virtual soft ground layer in which a wind load layer, a clay layer, a sand layer, and a clayey are sequentially stacked; A soft ground improvement step (S120) of applying a certain portion of the clay layer receiving the embankment load among the soft ground layers by applying the SCP method, the lightweight mixed soil method, and the DCM method; A three-dimensional numerical analysis step (S130) of applying the three-dimensional numerical analysis to the deformation behavior of the soft ground layer modified according to each of the above-mentioned methods due to the embankment load; And a comparing step (S140) of comparing a subsidence occurrence due to the embankment load of the improved soft ground layer by applying the SCP method, the lightweight mixed soil method, and the DCM method to a certain portion of the clay layer, Is characterized by using the finite element analysis model to apply excessive pore water pressure generated in the lightweight mixed soil layer due to the embankment load, dissipation and consolidation.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a soft soil improvement analysis method for light-

The present invention relates to a method for analyzing soft ground improvement, and more particularly to a method for analyzing soft ground improvement in a bubble mixed lightweight soil.

Currently, the dredging of marine dredged soil is continuously increasing due to the construction of a large-scale new port construction project and the maintenance of the marine route. In addition to the expansion of industrial facilities and the establishment and expansion of infrastructure facilities such as harbor and residential land development, And it is actively demanded to utilize it as landfill and embankment material.

The demand for recycling of dredged soils has increased due to the exhaustion of available onshore tobacco and marine products, the difficulty of securing large-scale sites for the treatment of dredged dredged soil, and the strengthening of environmental regulations to minimize damage to the marine environment.

Although the method of recycling marine dredged soil can be considered in various aspects, it can be considered to utilize the marine dredged material as lightweight ground material, which has been attracting attention as a treatment for soft ground in the port and airport construction business.

As the landfill progresses, the layer of soft clay layer is often increased. Therefore, the consolidation settlement of the ground increases and additional embankment and landfill are required to maintain the planned height. In addition, as is known from the case of the Haneda Airport Outer Sea Expansion Project in Japan, the consolidation settlement problem of the unconsolidated soft clay layer, which had not been considered in the past, should be considered.

In order to solve this problem, it is an effective means to reduce the load itself which causes settlement and deformation.

In case of backfilling of embankment or retaining wall and alternation using general soil on soft ground, problems such as settlement, activity fracture, lateral flow due to increase of stress in ground can occur. However, when replacing with lightweight ground material, Lateral flow reduction, and earth pressure reduction.

  In this context, a study on lightweight mixed soil (LWFS), which is a mixture of dredged soil with high fire and light fire, has been carried out as a way to recycle dredged soil from marine or terrestrial land as lightweight ground material (Tsuda, 1996; Kim and Lee, 2002; Yoon & Kim, 2004; Yoon & Yoo, 2004; Yoon & Yoo, 2005; Song, 2008; Hwang et al., 2010).

In this study, the physical and mechanical properties of lightweight mixed soil were investigated by conducting laboratory tests on various test conditions in order to investigate the engineering properties of lightweight mixed soil required for use as a ground material. In order to solve the problems such as material segregation, density increase and strength reduction for underwater casting condition of lightweight mixed soil in terms of workability, proper casting flow rate and flow rate of mixed soil were suggested through experiment of water tank casting.

In the present invention, a lightweight mixed soil (LWFS) method, a sand compaction pile (SCP) method, a lightweight mixed soil (LWFS) method, and a deep cement mixing (DCM) (LWFS) method is compared with the DCM (Deep cement mixing) method which is more than the level of application of the SCP (Sand compaction pile) method and the bubble which can minimize the residual settlement due to the excessive pore water pressure generation And to provide an analysis method of soft ground improvement of mixed lightweight soil.

1. Hwang, J. H., An, Y. K. and Kim, T. H. (2010), Effect of water on a lightweight air-mixed soil containing silt used for road embankment, Journal of Korean Geotechnical Society, Vol. 26, No. 2, pp. 23 ~ 32 (in Korean). 2. Kim, Z. C. and Lee, C. K. (2002), Mechanical characteristics of light-weighted foamed soil composed of dredged soils, Journal of Korean Geotechnical Society, Vol. 18, No. 4, pp. 309 ~ 317 (in Korean). 3. Lee, M. (2013), Assessment of applicability of lightweight air-trapped soil for abutment backfill, Master's thesis, Korea Maritime University, pp. 27 ~ 28 (in Korean). 4. Song, J. H. (2008), Analysis of compressive strength of lightweight air-mixed soil according to the properties of soil, Journal of Korean Geotechnical Society, Vol. 24, No. 11, pp. 157 ~ 166 (in Korean). 5. Yoon, G. L. and Kim, B. T. (2004), Compressibility and strength of the lightweight air formed soils, Journal of Korean Geotechnical Society, Vol. 20, No. 4, pp. 5 ~ 13 (in Korean). 6. Yoon, G. L and You, S. K. (2004), Deformation and strength characteristics of lightweight soil using in situ soils, Journal of Korean Geotechnical Society, Vol. 20, No. 9, pp. 125 ~ 132 (in Korean). 7. Yoon, G. L and You, S. K. (2004), Behaviors of lightweight foamed soils considering underwater curing and water pressure conditions, Journal of the Korean Geotechnical Society, Vol. 21, No. 4, pp. 21 ~ 29 (in Korean). 8. Tsuda (1996), Development and Application of Lightweight Mixed-Handling Method in Port-Airport Business. Ministry of Transport and Technology Bay Industrial Research Institute, pp. 1 to 252 (in Japanese).  9. Tsuda (1999), Application of lightweight mixed treatment soil using construction soil to airport operations, Ministry of Transport and Communications, pp. 1 to 186 (in Japanese).

(LWFS) method, a sand compaction pile (SCP) method, a lightweight mixed soil (LWFS) method and a DCM (deep cement mixing) method, which are applied to soft grounds under arbitrary site conditions, In comparison with the settlement management and the DCM (Deep cement mixing) method, the lightweight mixed soil (LWFS) method is applied to the sand compaction pile (SCP) method and the bubble mixing which minimizes the residual settlement due to the excess pore water pressure And to provide a method for analyzing the improvement of the soft ground of a lightweight soil.

According to an aspect of the present invention, there is provided a method for analyzing soft ground improvement in a bubble-mixed lightweight soil, comprising the steps of: setting a soft ground layer in which a wind pile layer, a clay layer, a sand layer, S110); A soft ground improvement step (S120) of applying a certain portion of the clay layer receiving the embankment load among the soft ground layers by applying the SCP method, the lightweight mixed soil method, and the DCM method; A three-dimensional numerical analysis step (S130) of applying the three-dimensional numerical analysis to the deformation behavior of the soft ground layer modified according to each of the above-mentioned methods due to the embankment load; And a comparing step (S140) of comparing a subsidence occurrence due to the embankment load of the improved soft ground layer by applying the SCP method, the lightweight mixed soil method, and the DCM method to a certain portion of the clay layer, Characterized in that the generation and dissipation and consolidation of excess pore water pressure generated in the lightweight mixed soil layer due to the embankment load are applied by using a finite element analysis model.

In the soft ground layer setting step (S110), a displacement boundary condition of the same condition and a hydraulic boundary condition for a stress-pore hydraulic pressure connection analysis are applied to the soft ground layer improved according to each of the above methods.

In the soft ground layer setting step (S110), excess pore water pressure due to the embankment load is dispersed so that the pore water pressure at the upper part of the clay layer becomes zero.

The soft ground layer setting step (S110) is a step of setting a settling characteristic of the soft clay ground during consolidation by applying a Modified Cam-Clay (MCC) model.

As a result of using the soft ground improvement analysis method of the bubble mixed lightweight soil according to the embodiment of the present invention, when the lightweight mixed soil method is applied to the soft ground improvement, it is possible to manage the settlement more than the application level of the SCP method, The flow can be significantly reduced. It can also be seen that this is due to the light weight and the desired strength and deformation characteristics of the lightweight mixture.

  Further, when the soft ground improvement analysis method of the bubble mixed lightweight soil according to the embodiment of the present invention is used, when the soft ground is improved by using a material having a large self-load and a small water permeability like the DCM (Deep cement mixing) It is possible to analyze that the consolidation settlement can be minimized, but the long-term residual settlement due to progressive excess pore pressure dissipation can be analyzed.

Also, it has been investigated that it is possible to control the sinking occurrence level according to the target performance of the lightweight mixed soil by using the method of analyzing the soft ground improvement of the bubble mixed lightweight soil according to the embodiment of the present invention. As the unconfined compressive strength of lightweight mixed soil increased, the settlement amount decreased and linear relationship within the yield load was shown.

On the other hand, if the shear stress on the overburden load exceeds the uniaxial compressive strength of the lightweight mixed soil, the occurrence subsidence significantly increases and the actual settlement amount may be larger than the result obtained by the general analysis due to the rapid strain hardening behavior Can be confirmed.

Fig. 1 (a) is an illustration showing the stress-strain behavior of the dredged soil with the initial water content ratio of 150% and the cement content ratio of 18% Strain behavior behavior of cement content ratios of 6, 9, 12 and 18%.
FIG. 2 is a flowchart for explaining a method of analyzing soft ground improvement in a bubble mixed lightweight soil according to an embodiment of the present invention.
FIG. 3 is a view illustrating the state of the soft ground layer to which the LWFS method, the SCP method, and the DCM method are respectively applied.
FIG. 4 is an exemplary diagram applied to a three-dimensional numerical model of the soft ground layer shown in FIG.
FIG. 5 is an illustration showing the subsidence of the embankment corresponding to the point of 2 years after the final embankment (6 m) and the hives at the end of the embankment, respectively.
6 is an exemplary view showing the horizontal displacement in the ground.
7 (a) is a graph showing settlement (consolidation) curves at the center of the embankment and the point at the upper part of the clay layer according to the elapsed embankment and the passage of time, FIG. 7 (b) The history is an excess pore water pressure graph.
FIG. 8 is a graph showing the result of showing the residual settlement () over time after completion of the embankment with respect to the settling amount () at the completion of embankment in each method.
FIG. 9 is an exemplary view showing the settlement profile at the top of the embankment at the end of two years after completion of the embankment by the soft ground improvement method.
10 is an exemplary view showing the lateral flow profile at the lower end section of the article.
11 is an exemplary view showing a time-history settlement curve for each uniaxial compressive strength of a lightweight mixed soil.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a detailed description of preferred embodiments of the present invention will be given with reference to the accompanying drawings. In the following description of the present invention, detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

Embodiments in accordance with the concepts of the present invention can make various changes and have various forms, so that specific embodiments are illustrated in the drawings and described in detail in this specification or application. It is to be understood, however, that it is not intended to limit the embodiments according to the concepts of the present invention to the particular forms of disclosure, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

It is to be understood that when an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, . On the other hand, when an element is referred to as being "directly connected" or "directly connected" to another element, it should be understood that there are no other elements in between. Other expressions that describe the relationship between components, such as "between" and "between" or "neighboring to" and "directly adjacent to" should be interpreted as well.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, the terms "comprises ",or" having ", or the like, specify that there is a stated feature, number, step, operation, , Steps, operations, components, parts, or combinations thereof, as a matter of principle.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: FIG.

First, before explaining the soft ground improvement analysis method of the bubble mixed lightweight soil of the present invention, the engineering characteristics of the lightweight mixed soil using the dredged clay will be briefly described.

Generally, a lightweight mixed soil is a mixture of water (seawater) and cement such as marine dredged soil as a raw soil material, which is a construction soil, and is mixed with a lightweight agent, and a unit weight of about 6 to 12 kN / m ³ .

The former is a mixture of bubble-mixed soil and a mixed foamed beads. The former is a mixture of bubbles and solidified fire in slurry-state soil, and the latter is a mixture of foamed styrofoam particles of 1 to 3 mm in diameter in a slurry- It is to blend. The features of the lightweight foamed composite soil are as follows.

a) Because it is homogeneous ground material which can be adjusted with proper density and strength, unlike natural ground material, it is possible to reduce settlement settlement of ground.

b) Preventing segregation in the surrounding area by mixing design because it prevents separation in water.

c) It has moderate fluidity and it is not necessary to compaction by pump feeding, so that it can be tacked to desired shape.

d) Use dredged material with high water content as a raw material.

1) Stress-strain behavior of lightweight mixed soil

The strain - strain behaviors of lightweight mixed soil generally increase as the initial water content increases, and the maximum compressive strength decreases. On the other hand, as the content of cement increases, the strain decreases and the maximum compressive strength increases.

Also, the maximum strength is expressed in the range of 1 to 2% of axial strain, and strain softening phenomenon occurs after the fracture. Especially, it is known that after the fracture, it shows a brittle fracture pattern showing a rapid decrease in stress, and it is known that the tendency is more apparent when the cement content is larger. It is considered that the strength characteristics of the lightweight mixed soil is dominated by the cementation by the cement solidifying agent.

FIG. 1 shows a part of the unconfined compression test results of the lightweight mixed soil performed by Yoon & Yoo (2004), which shows the stress-strain behavior characteristics of the lightweight mixed soil.

Fig. 1 (a) shows the stress-strain behavior of the dredged soil with the initial water content of 150% and the cement content of 18%. (B) shows the cement content of the dredged soil at an initial water content ratio of 150% , 9, 12, and 18%, respectively.

2) Compressive strength characteristics of lightweight mixed soil

Secondly, it is known that lightweight mixed soils show higher compressive strength with increasing density, cement content and curing pressure, and decrease with increasing initial water content of dredged soil. Especially, in case of recycling of marine dredged soil, it is necessary to pay attention to the change of strength characteristics by water pressure when lightweight mixed soil is poured into water for the improvement of seabed ground.

According to Yoon and Yoo (2005), the uniaxial compressive strength increased by 3 ~ 14% and the triaxial compressive strength increased by 18 ~ 32% as the curing pressure increased from 50kPa to 100kPa have.

This is due to the increase in the density of the specimen due to the compression of bubbles, one of the components of the specimen, due to the hydrostatic pressure acting on the surface of the specimen until the curing period is completed in the initial stage of curing of the specimen.

의 1/2 정도로 나타난다고 보고한 바 있다. On the other hand, the compressive strength characteristics according to the confining pressure effect of lightweight mixed soil have different results for each researcher. For example, UU-test results of the tests conducted by Japan's port technical research institute show that shear strength (c ) Is the uniaxial compressive strength

Of the total population.

인 재료로 취급해야 함을 의미한다. This is because the shear strength of the lightweight mixture is not affected by the confining pressure,

It should be handled as a material.

인 재료임을 보여주는 것으로서 일본의 항만기술연구소의 연구결과와는 상이한 결과라 할 수 있다.
On the contrary, Kim & Lee (2002) and Yoon & Kim (2004) reported that the compressive strength of lightweight mixed soil increases proportionally with increasing confining pressure. This is because the shear strength of the lightweight mixture

And it is a result different from the results of the port research institute in Japan.

3) Deformation characteristics of lightweight mixed soil

Next, as an important analysis parameter showing the stress-deformation behavior of the material, the shear strength and deformation coefficient are important factors.

)로 나타내며, 일축 및 삼축압축강도 결과를 이용하여 다음과 같이 추정된다.The deformation modulus of the lightweight mixed soil was determined by the shear modulus

), And is estimated as follows using the uniaxial and triaxial compressive strength results.

는 일축압축강도의 100200배 정도라고 제시하였으며, 김주철과 이종규(2002)는

를 일축압축강도의 82.85배, 삼축압축강도의 22~167배 정도로 제시하였다. Yoon & Kim(2004)의 연구에서는 일축압축강도의 18~120배로, Yoon & Yoo(2004)의 연구에서는 일축압축강도의 130배, 삼축압축강도의 52배로 제시하였다. Tsuda (1999) reported that a lightweight mixture made from clay in Japan

Of the uniaxial compressive strength were 100200 times, and Kim, Joo-cheol and Lee (2002)

Was 82.85 times the uniaxial compressive strength and 22 to 167 times the triaxial compressive strength. Yoon and Kim (2004) proposed a uniaxial compressive strength of 18 to 120 times, and Yoon & Yoo (2004) suggested 130 times of unconfined compressive strength and 52 times of triaxial compressive strength.

가 서로 다르게 평가된 것은 각각의 실험조건별로 고화제 함유율과 기포 함유율이 다르고, 사용한 준설토의 성분이 상이한 데서 원인을 찾을 수 있다. 또한 전반적으로 구속압력이 커지면

의 값이 작아지는 경향을 나타내고도 있다.In this way,

Were different from each other. The cause of the difference in the content of solidifying agent and the content of air bubbles in each experimental condition and the difference in the components of the dredged soil used can be found. Also, when the overall restraint pressure increases

The smaller the value is.

On the other hand, according to the results of the Japan Institute of Port Technology (Tsuida, 1996), the pearl ratio of lightweight mixed soil in compressive shear is 0.1 ~ 0.2 at 1 ~ 2% axial strain, The comparison is remarkably small.

4) Long-term deformation and permeability of lightweight mixed soil

Lee (2013) investigated the creep characteristics of lightweight mixed soil by performing shear creep test and long-term compression test. The shear creep test proposed by Lee (2013) showed that the target unit weight was 10 kN / m ³ , The shear stress at 70% and 80% of the maximum shear strength was loaded for one week under the condition of normal stress at 50% of the unconfined compressive strength for the mixed soil. The long term compression test using the one - , 11 kN / m ³ , uniaxial compressive strength of 200 and 500 kPa, respectively, at 0.5 and 1.5 times the yield load.

As a result, shear creep test results show that the shear deformation mostly appears at the initial stage of loading and the additional displacement over time is very small. The long - term compression test results show that the creep coefficient is 0.19 ~ 0.31%, and the creep coefficient was 0.74 ~ 0.80% when the compressive load was 1.5 times the yield stress. In other words, it can be seen that the long-term deformation at the stress below the yield stress is very small.

As another example, Hwang et al. (2009) reported the results of a study on the permeability of lightweight mixed soils and reported that the target unit weight and unconfined compressive strength of the target lightweight mixture are 10 kN / m ³ and 500 kPa, respectively , And the permeability test for saturated condition was 4.857 × 10 ^-6 cm / sec similar to that of clay (3.0 × 10 ^-6 cm / sec).

Therefore, the present invention is based on the technical properties (for example, the stress-strain behavior characteristics of lightweight mixed soil, the compressive strength characteristics of lightweight mixed soil, the deformation characteristics of lightweight mixed soil, the long- This paper presents a method for the analysis of soft ground improvement in bubble - mixed lightweight soils, which can compare numerically the state of soft ground applied to soft ground by SCP method and DCM method respectively.

)를 각 공법의 성토완료 시점의 침하량(

)을 기준으로 도시한 결과를 나타낸 예시도이다. 도 9는 연약지반개량 공법별 성토 완료 후 2년 경과시점의 성토부 최상단의 침하 프로파일을 나타낸 예시도이며, 도 10은 제체 하단부 단면에서의 측방유동 프로파일을 나타낸 예시도이다. 도 11은 경량혼합토의 일축압축강도별 시간이력 침하곡선을 나타낸 예시도이다.FIG. 2 is a flow chart for explaining a soft ground improvement analysis method of a bubble mixed lightweight soil according to an embodiment of the present invention, and FIG. 3 is an example of a soft ground layer to which an LWFS method, a SCP method, and a DCM method are respectively applied . FIG. 4 is an exemplary diagram applied to a three-dimensional numerical model of the soft ground layer shown in FIG. FIG. 5 is an illustration showing the settling of the embankment zone corresponding to the point of 2 years after the final embankment (6 m) and the hives at the end of the embankment, and FIG. 6 is an illustration showing the horizontal displacement in the ground. 7 (a) is a graph showing settlement (consolidation) curves at the center of the embankment and the point at the upper part of the clay layer according to the elapsed embankment and the passage of time, FIG. 7 (b) The history is an excess pore water pressure graph. Fig. 8 is a graph showing the relationship between the residual settling time

) At the settlement completion time of each construction method (

) As a reference. FIG. 9 is an exemplary view showing the settlement profile at the top of the embankment at the end of two years after completion of embankment completion by the soft ground improvement method, and FIG. 10 is an exemplary view showing a lateral flow profile at the bottom end of the embankment. 11 is an exemplary view showing a time-history settlement curve for each uniaxial compressive strength of a lightweight mixed soil.

As shown in FIG. 2, the numerical analysis method S100 of the soft ground improvement method of the lightweight mixed soil using the dredged clay according to the embodiment of the present invention includes a soft ground layer setting step S110, an soft ground improvement step S120, Dimensional numerical analysis step S130 and a comparison step S140.

The soft ground layer setting step (S110) may be a step of setting a virtual soft ground layer in which the wind pile layer, the clay layer, the sand layer, and the embankment layer are sequentially stacked.

In the soft ground improvement step (S120), a certain portion of the clay layer receiving the embankment load among the soft ground layers may be improved by applying the SCP method, the lightweight mixed soil method, and the DCM method.

The three-dimensional numerical analysis step (S130) may be a step of analyzing the deformation behavior of the soft ground layer, which has been improved according to the above-mentioned respective methods due to the embankment load, by applying a three-dimensional numerical analysis.

Here, the three-dimensional numerical analysis may be a three-dimensional numerical analysis using an excessive pore water pressure generated in the soft ground layer due to the embankment load and dissipation and consolidation using a finite element analysis model.

In the comparing step S140, a certain portion of the clay layer may be subjected to a SCP method, a lightweight mixed soil method, and a DCM method, respectively, so as to compare the subsidence occurrence due to the embankment load of the improved soft ground layer.

The soft ground layer setting step (S110) may be a step of applying the same boundary boundary condition and the hydraulic boundary condition for the stress-pore hydraulic pressure coupling analysis to the soft ground layer modified according to each of the above-mentioned methods.

In the soft ground layer setting step (S110), excess pore water pressure due to the embankment load may be dissipated so that the pore water pressure at the top of the clay layer becomes zero.

The soft ground layer setting step (S110) may be a step of setting a settlement characteristic of the soft clay ground during consolidation by applying a Modified Cam-Clay (MCC) model.

In the following, numerical experiments are carried out to demonstrate the effect of improving the soft ground according to the LWFS, SCP (sand compaction pile), and DCM (Deep cement mixing) method under the same environmental conditions.

- Numerical Simulation of Improvement Effects of Soft Soils by Soft Soil Method -

1) Field conditions

First, in this experiment, the case of a girder having a height of 6 m and a width of 68 m in the upper part of a soft ground of a thickness of 10 m with an undrained shear strength of about 50 kPa is applied with a slope of 2H: 1 V.

Here, the lower part of the clay layer is assumed to have a relatively hard weathering layer. In the upper part of the soft ground, a sand layer of 1 m height was installed to secure the equipment running ability and the drainage layer. The soft ground improvement method was considered to be a condition of reinforcing and excavating substitution by applying DCM method, SCP method and lightweight mixed soil (LWFS) Respectively.

DCM method was applied to the range of 5m horizontally from the bottom of the bank. In case of SCP method, sand pile with diameter of 700mm was laid up to the weathered soil and the replacement rate was set to 30% by square arrangement. For the lightweight mixed soil (LWFS) method, the condition of 2H: 1V gradient after soft ground excavation was considered.

2) Analysis condition

In order to compare the application effects of the soft ground improvement method and the behavior characteristics according to the unconfined compressive strength characteristics of the lightweight mixed soil method, the analytical conditions as shown in Table 1 were selected.

[Table 1]

3) Comparison of Applicability of Lightweight Mixed Soil

In the interpretation of the embankment embankment on the soft ground, excessive pore water pressure generation and dissipation in the soft ground due to the embankment and the consolidation phenomenon should be treated in the analytical model. For this, analytical modeling in which the stress- need.

In the present invention, a general purpose finite element analysis program, Abaqus ver.6.10, which can efficiently perform the modeling of the ground-groundwater interaction and the construction process, is used.

In the analytical modeling, only the right half section is included in the analytical model because the construction conditions are symmetrical with respect to the center of the embankment bank, and a kind of plane strain condition in which the same conditions are repeated in the longitudinal direction under the SCP construction conditions considered in the square arrangement Therefore, three-dimensional modeling of single row of SCP was performed.

In the displacement boundary conditions, the left and right sides of the analytical section constrained the horizontal displacement and the floor constrained the horizontal and vertical displacements. The vertical plane perpendicular to the plane constrained the longitudinal displacement so that the plane deformation condition was established.

The hydraulic boundary conditions for the linkage analysis were such that the groundwater level was located at the top of the clay layer during initial and construction and the hydrostatic pressure was kept constant on the right horizontal plane. The excess pore water pressure for embankment load was dissipated by giving the pore water pressure to 0 at the top of the clay layer.

On the other hand, in the discretization of the model, the soft ground, the lower ground layer, the lightweight mixed soil, the DCM, and the sand pile located at the bottom of the groundwater are modeled by the 8-point stress-pore pressure coupling factor (C3D8P) (C3D8R).

In the material modeling, the soft ground was modeled by Modified Cam-Clay (MCC) model to simulate the settlement characteristics of the soft clay soil during consolidation. Mohr-Coulomb model was applied to the sandwich pile and sandy pile Respectively.

Considering that DCM is a relatively strong material with a high strength and rigidity, it is considered to have an elastic behavior.

The finite element analysis model and analytical application properties applied in the present invention are shown in FIG. 3 and Table 1, respectively.

인 재료로 취급하였다. 표 2는 경량혼합토에 대한 추가 매개변수 해석조건을 정리한 것으로서 목표일축압축강도를 105 ~ 180kPa로 고려시 적용한 경량혼합토의 물성을 나타내며, 표 3은 LWFS의 파라미터들의 상태를 나타낸 표이다.First, referring to Table 1, the physical properties of the lightweight mixed soil are considered as the target uniaxial compressive strength of 120 kPa considering the embankment height of 6 m. From the conservative point of view,

Lt; / RTI > Table 2 summarizes the additional parameter analysis conditions for lightweight mixed soil. It shows the properties of lightweight mixed soil considering the target uniaxial compressive strength of 105 ~ 180kPa. Table 3 shows the state of parameters of LWFS.

[Table 2]

[Table 3]

 For realistic analysis modeling of the embankment formed on the soft ground, detailed modeling of the actual construction process on site should be considered in the analysis process.

In this numerical experiment, it was considered that excavation and replacement, and step - by - step embankment were performed sequentially after securing initial underground stress and pore water pressure in the analysis stage.

For each step, we made 2 m of cover over 15 days, and we modeled the embankment with SCP and 10 days after embankment.

In the following, numerical experiments described above will be used to compare the effect of soft soil improvement with the application of SCP method and DCM method.

 In the present invention, the SCP method, the DCM method, and the analysis result of the soil improvement without soil treatment are compared for the analysis of the soft soil improvement effect when applying the lightweight mixed soil method.

At this time, as described above, the lightweight mixed soil method was studied under the condition that the target unit weight and the uniaxial compressive strength were 11 kN / m ³ 120 kPa, and the SCP method was set to have a condition of securing a substitution rate of 30%.

 FIG. 5 is a view showing subsidence of the embankment zone and heaving at the end of the embankment corresponding to two years after the final embankment (6 m), and FIG. 6 is an example showing the horizontal displacement in the ground.

5 and 6, it was analyzed that the maximum settlement within the embankment area was about 615 mm when the ground improvement was not carried out, and the horizontal displacement in the ground due to the maximum displacement could be up to 249 mm and the heaving in the end of the embankment to 29 mm.

When LWFS method is applied, the maximum settlement is about 92mm, 1/6 ~ 1/7 level at the untreated level, the heaving is about 1/10 level at about 3mm, and the maximum horizontal displacement in the ground is about 1/8 .

In SCP method, the maximum settlement is 148mm, about 1/4 of the untreated level, the heaving is about 1/3 level, and the maximum horizontal displacement in the ground is 42mm, which is about 1/6 .

When DCM method was applied, settlement, horizontal displacement, and hibbling were significantly decreased in comparison with other methods.

Therefore, it can be seen that the settlement control over the level of applying the SCP method is possible when the lightweight mixed soil method is applied, and it can be deduced that the horizontal displacement in the ground, that is, the lateral flow can be remarkably reduced.

It is believed that this is due to the fact that the pumice ratio of the lightweight mixture is 0.15, which is twice as small as that of the general ground.

Referring to FIG. 7, it can be predicted that consolidation is still in progress at the time of two years after completion of embankment in the case of no soil improvement.

On the other hand, it is predicted that consolidation is completed within 1 year and 6 months after completion of embankment, although there are qualitative and quantitative differences in each method when applying the ground improvement.

In addition, in the SCP method, the surplus pore water pressure did not occur in the ground due to the progress of drainage through the sand pile in the step of embankment step. In the DCM method, the unit weight of the remediation body was large and the coefficient of permeability was very small, The progress speed is similar to the level of the ground level, but the own stiffness is so large that the total settlement is relatively small. As a result, the pore water pressure was partially generated in the excavation and replacement stage due to the small unit weight of the pavement, and the excess pore water pressure was also small in the embankment. As a result, the excess pore water pressure was expected to dissipate about 70 days after completion of the embankment.

)를 각 공법의 성토완료 시점의 침하량(

)을 기준으로 도시한 결과이다. Fig. 8 is a graph showing the relationship between the residual settling time

) At the settlement completion time of each construction method (

) As a reference.

As shown in the graph of excess pore pressure dissipation in Fig. 7 (b), in the case of the SCP method, the excess pore water pressure was completely dissipated in the step-by-step embankment step and the residual settlement hardly occurred. It was analyzed that no additional residual settling occurred after 70 days of dissipation.

On the other hand, the results of the DCM method show that residual settlement can occur over 1 year and 6 months after completion of embankment due to progressive excess pore water dissipation.

In the case of the DCM method, since the self-stiffness is very high, the amount of settlement at the construction stage is not large, but the self weight of the reformer is relatively large, so that it is predictable that the residual settling in the under- have.

In the present invention, when the soft ground layer is considered as a relatively strong weathering layer, the quantitative residual settlement after the completion of the embankment is not relatively large. However, when the compressive ground is present under the soft ground, a relatively large settlement may occur when the DCM method is applied Can be expected.

Therefore, it is more advantageous to use lightweight ground materials such as lightweight mixed soil in the case of high degree of soft ground.

FIGS. 9 and 10 show the settlement profile at the uppermost embankment and the lateral flow profile at the lower end section of the embankment at the end of two years after completion of embankment, respectively, by the soft ground improvement method.

As mentioned above, it can be confirmed that the lightweight mixed soil method can control the settlement more than the SCP method, and the lateral flow of the slope can be significantly reduced.

In the following, the performance condition of the lightweight mixed soil, that is, the soil improvement effect according to uniaxial compressive strength, is compared.

11 is a graph showing a time-history settlement curve for each uniaxial compressive strength of a lightweight mixed soil.

Referring to FIG. 11, it can be seen that the uniaxial compressive strength secures the streak stress abnormality except for the uniaxial compressive strength 106 kPa of the lightweight mixed soil, because the continuous stress level acting on the embankment 6 m is about 114 kPa.

Comparing the quantitative settlement amount by unconfined compressive strength condition, the settlement amount decreases with increasing uniaxial compressive strength. In the uniaxial compressive strength range of 120 to 180 kPa, the final settlement amount is in the range of 48 to 92 mm, and the relationship between strength and settlement amount is inversely proportional Can be confirmed.

On the other hand, when the unconfined compressive strength of the lightweight mixed soil is 106 kPa, the final settlement amount is about 160 mm, and the settlement amount is remarkably increased. This is because the shear stress caused by the embankment exceeds the uniaxial compressive strength of the replacement material, As shown in Fig.

From the viewpoint of material, it can be expected that the lightweight mixed soil will have a larger strain softening behavior when the yield load is exceeded, so that a greater settlement will occur than the analysis result of FIG. 10.

Therefore, it is important to set the yield stress in the mixed soil not to exceed the yield stress in consideration of the overburden load level when the lightweight mixed soil method is applied.

Therefore, according to the present invention, it is possible to control the settlement more than the level to which the SCP method is applied when the lightweight mixed soil method is applied for the improvement of the soft ground, in particular, the advantage that the lateral flow in the improvement section can be remarkably reduced, It can be predicted that this is due to the light weight and the desired strength and deformation characteristics of the lightweight mixture.

In addition, when the soft ground is improved by using a material having a large self-load and a small permeability such as the DCM method, the short-time consolidation settlement can be minimized, but excessive pore water pressure dissipation is slow, It provides the advantage of being able to predict in advance.

In addition, it is possible to control the settlement level of the soft ground according to the target performance of the lightweight mixed soil, and it can be seen that the occurrence settlement decreases with increasing uniaxial compressive strength of the lightweight mixed soil and linear relationship within the yield load .

In addition, when the shear stress on the overburden exceeds the uniaxial compressive strength of the lightweight mixed soil, the occurrence subsidence increases markedly, and the actual settlement amount can be larger than the result obtained by the general analysis due to the rapid strain hardening behavior Can be predicted.

Therefore, it is important to plan the yield stress in the mixed soil so that the yield stress does not exceed the yield stress in lightweight mixed soil method for the improvement of soft soil.

The previous description of the disclosed exemplary embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these exemplary embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention.

S100: Soft ground layer setting step S110: Soft ground improvement step
S120: Three-dimensional numerical analysis step S140: Comparison step

Claims (4)

In a soft ground improvement analysis method of a bubble mixed lightweight soil, which is configured to perform a process for determining an optimal construction method by a computer or dedicated hardware by comparing and analyzing the improvement effect on a plurality of construction methods for improving the soft ground, ,
The above-
A soft ground layer setting step of setting a hypothetical soft ground layer in which a ground layer, a clay layer, a sand layer, and a clay layer are sequentially stacked;
Light-weighted foam sheets (LWFS), sand compaction pile (SCP), and deep cement mixing (DCM) are applied to a part of the clay layer receiving the embankment load among the soft ground layers, Ground improvement stage;
For each of the soft ground layers modified according to the lightweight mixed soil method, the SCP method, and the DCM method in the soft ground improvement step, an excessive amount of excess ground particles generated in the lightweight mixed soil layer due to the embankment load, A deformation behavior analysis step of comparing and analyzing the deformation behavior due to the embankment load by applying the generation of the pore water pressure and the dissipation and consolidation phenomenon through the three-dimensional numerical analysis based on the stress-pore hydraulic interaction analysis;
In the soft ground improvement step, each of the soft ground layers improved by applying the lightweight mixed soil method, the SCP method, and the DCM method to a part of the clay layer is compared with the subsidence occurrence due to the embankment load, A settlement occurrence analysis step; And
And a determining step of determining an optimal construction method for improving the soft ground based on the comparison analysis results of the deformation behavior analysis step and the settlement occurrence analysis step. Way.
The method according to claim 1,
In the soft ground layer setting step,
And a hydraulic boundary condition for the stress-pore hydraulic pressure connection analysis is applied to the soft ground layer according to each of the above-mentioned methods.
3. The method of claim 2,
In the soft ground layer setting step,
Wherein the excess pore water pressure due to the embankment load is dispersed so that the pore pressure at the top of the clay layer becomes zero.
The method of claim 3,
In the soft ground layer setting step,
And modifying Cam-Clay (MCC) model to set settlement characteristics of the soft clay soil during consolidation.

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