KR102701524B1 - METHOD FOR MARINE LAND RECLAMATION by SMARTSOIL USING SOFT SOIL LIKE CLAY AND SILT IN SEA FOR PREVENTING LAND SETTLEMENT - Google Patents

Abstract

The present invention aims to solve the problem of excessive subsidence and uneven settlement of the entire landfill site after completion, which has been pointed out as the biggest problem of conventionally disclosed marine reclamation grounds using sand, dredged soil or general soil, and thereby improves the lightweight mixed soil using dredged soil having low specific gravity and excellent compressive strength and uses it as a landfill and filling ground material, thereby reducing the load applied to the original ground of the seabed and creating a sturdy landfill site, thereby simultaneously solving the problem of ground subsidence and environmental problems occurring in existing marine reclamation sites.

Description

{METHOD FOR MARINE LAND RECLAMATION BY SMARTSOIL USING SOFT SOIL LIKE CLAY AND SILT IN SEA FOR PREVENTING LAND SETTLEMENT}

The present invention aims to simultaneously solve the problem of excessive subsidence and uneven settlement of the entire reclaimed ground over time after completion of site preparation, which has been pointed out as the biggest problem in the conventional marine reclamation site preparation using sand, dredged soil or general soil, and the problem of environmental destruction due to the large-scale use of sand, crushed stone and general soil for reclamation. The present invention relates to a method for marine reclamation site preparation using dredged soil, which enables solving the technical and environmental problems of the existing method by forming a solid reclamation site while significantly reducing the load applied to the marine original ground by using aerated mixed soil (smartsoil; lightweight mixed soil) having low specific gravity and excellent compressive strength.

Even now, many structures in industrial complexes, airports, and marine new cities built on reclaimed land in coastal areas are experiencing problems such as leaning to one side or cracks in the walls due to large-scale subsidence and uneven settlement (see Figure 1; provided by Busan Port Authority AD), and are highly vulnerable to sea level rise, ground shrinkage and expansion due to climate change, and disasters caused by earthquakes. In addition, there are serious concerns about the cost of maintenance and stability, but technological advancements to solve these problems are at a standstill. (see Table 1)

Comparison of predicted and measured settlement amounts for Busan clay (Jeong, Seong-Gyo, 1999; Beak et al., 2005) Unpredictable
Oversinking amount
(+cm) division The vulnerable layer
Thickness (m) At design time
Estimated sinkage
(cm) After measurement
Estimated sinkage
(cm) Growth rate (%) Signal Local Government Corporation 38.8 79.7 228.5 287 148.8 Noksan National Industrial Complex 43.9 131 217.3 166 86.3 Yangsanmul Geumtaekji 30 290.5 389.5 134 99 Noksan Industrial Complex entrance road 38.5 128.6 260.0 or higher 202 131.4 Signal entrance 33.7 184.1 250.9 136 66.8 Myongji residential complex 29.8 106 171 161 65 Kansai International Airport, Japan 180.0 or higher 800 1,150.00 144 350 Busan New Port
North side hinterland
(Including dredged soil) - - - - - A-1 zone 41.80 528 667.2 126 139.2 M-1 zone 39 543.8 692.5 127 148.7 M-2 zone 39 575.7 662.2 115 86.5 M-3 zone 41.8 437.5 589.4 135 151.9 M-4 zone 40.6 440.9 502.5 114 61.6 M-5 zone 47.2 504.3 696.9 138 192.6

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This is because the problem continues repeatedly due to technical limitations when considering the amount of subsidence in the development of existing landfill sites, and especially in cases where the depth of the seabed is deep, countermeasures for subsidence are established with allowances for residual subsidence and maintenance plans due to technical limitations in construction, but this also results in large errors beyond the expected range, resulting in enormous additional maintenance costs. In the case of Kansai International Airport in Japan, it is said that the residual subsidence after construction, which was predicted to occur over 50 years, occurred suddenly and significantly in just 6 years, causing the airport to submerge into the sea, resulting in astronomical maintenance costs.

Our country has also adopted Japan's vertical drainage method and is applying it to most of the ground improvement of offshore reclamation sites, but many experts in Japan and the United States are raising the issue of harmfulness, and in particular, if the ground height being filled above sea level increases, the ground strength will be reduced to about 1/3 when the original seabed ground is destroyed due to excessive load, and there is a very high concern that the expected pore water drainage during construction will be delayed, resulting in significant subsidence after completion, but there is currently no way to solve this.

It is realistically impossible to fully support a perfect ground investigation and the design and construction based on it, and in the case of landfilling dredged soil, it is realistically very difficult to wait for several years or even decades to meet the required consolidation time for the process of repeating self-weight consolidation and landfilling and the pre-consolidation ground improvement by filling.

In particular, when the depth of the seabed original ground is large and the target ground elevation is high, and the thickness of the landfill/fill is large, the error in predicting the size of the consolidation corresponding to the estimated settlement is bound to be large due to the physical limitations of the construction itself for subsidence reduction and the excessive load of the landfill/fill material. In addition, even when trying to solve the problem of residual settlement due to maintenance due to time and economic issues, if the settlement speed and size are large in a short period of time, excessive maintenance costs are expected and serious safety issues may arise.

Large-scale soils that are filled and filled on super-soft ground are putting excessive loads on the original ground, making the ground unstable. The problems of each soil material used as fill and fill materials in the existing construction method are briefly examined as follows.

In the case of sand reclamation, there are problems such as environmental destruction of marine fishing grounds during the sand extraction process, high costs for sand extraction, transportation, and installation, and increased construction costs for ground strength improvement such as vertical drains and horizontal drains for the original soft ground. In addition, these materials pose a very high risk of destruction of upper structures due to ground liquefaction in the event of an earthquake. The unit weight of the sand is approximately 20 KN/㎥.

In the case of landfilling and filling with high-quality general soil, there are problems such as environmental destruction of forests, etc. during the process of securing the soil, noise and dust, etc. during the process of transporting the soil, and the construction cost and construction period for improving the ground strength, such as vertical drainage (VD) and horizontal drainage of the saturated landfill soil itself when reclaiming underwater as well as the soft ground of the original ground, increase, and there is a high risk of destruction of upper structures due to ground liquefaction in the event of an earthquake. The unit weight of the above general soil is approximately 19 KN/㎥.

In the case of unimproved viscous dredged soil reclamation, the construction period increases due to the series of processes of dredging-reclamation->self-weight consolidation->dredging->self-weight consolidation, and the self-weight consolidation period that takes several years makes it very difficult to proceed with the process for surface treatment and subsequent processes, and the problem of requiring a large amount of sand, crushed stone, and other drainage aggregates during the surface treatment process for equipment operation, and the phenomenon of mutual reversal between the high-moisture content soil and the drainage aggregate layer under the surface treatment layer during the vertical and horizontal drainage material installation process due to excessive load of sand, crushed stone aggregates, which causes uneven settlement after the construction of structures such as upper buildings, and the problem of public complaints due to noise and dust during the process of transporting a large amount of aggregate for drainage and filling. The unit weight of the above dredged soil is approximately 17 KN/㎥.

The present invention is intended to improve the construction method problems of the conventional offshore reclamation site construction, and is a technology for a method for improving dredged soil existing in large quantities on the seabed into a lightweight and high compressive strength reclamation material, thereby enabling offshore reclamation and site construction with excellent economic efficiency, safety, and environmental friendliness.

Utility Model Registration No. 20-0316779 (Registration Date: June 5, 2003)

In the present invention, the ground design concept and construction method are presented so that the size of the settlement can be absolutely reduced according to the use of the land and the location of the land development during the sea reclamation and land development, while minimizing the error in predicting the amount of residual settlement that occurs after the construction is completed, so that it is possible to respond to various land development purposes and plan and execute sea reclamation and land development in an environmentally friendly and economical way while ensuring safety according to the situation. (See Table 2)

The present invention makes it possible to solve various problems arising from a large-scale subsidence beyond the predicted range when developing a site on an ultra-soft ground in the sea using a conventional method, so that the estimated settlement amount (sinking amount during construction + residual settlement amount) after design of a new method can be made within the size of the excessive settlement amount of the existing method as shown in Table 1 above, and the method of sea reclamation and site development is proposed in which the ground level after the final long-term settlement after completion (middle sea level, MSL) is maintained within the target height range.

[A brief comparison between the conventional method and the method of the present invention]


division Offshore site development
load
increase


(ton)

calculation
Subsidence
(cm) Settlement reduction
Establishing countermeasures and
After design
calculation
Subsidence
(cm)
Additional
Error occurred
possible
Subsidence
(+cm)


note sub-sea surface soft layer Land layer Seabed
Ground layer
(m) Landfill layer
(m) Fill layer
(m) existing
Construction method 40 20 20 55 760 120 or more 60 and above Maintenance cost large The present invention
Construction method 40 20 20 20 190 60 or under 20 or less Maintenance cost small

Conventional technology sets the expected amount of settlement that may occur after construction is completed at the time of design, but in reality, as can be seen in Table 1 above, there is a problem that the size of the additional excessive settlement that occurs outside the predicted settlement range is significant.

The present invention enables the management of the total settlement amount within the range of the total design settlement amount (settlement amount during construction + residual settlement amount) set by the existing construction method or the range of the excessive settlement occurring in the existing construction method, while also enabling the creation of a safe and environmentally friendly offshore reclamation site from disasters such as subsidence and earthquakes.

This study proposes a design and construction method for marine reclamation and site development using dredged soil that is eco-friendly and highly economical, reducing the absolute load of landfill and fill materials, preventing the ground materials from losing ground bearing capacity due to groundwater such as seawater, maintaining a strong ground condition without a separate consolidation process or other ground improvement process, and distributing the load of the upper ground structure to maximize ground stability, thereby fundamentally solving various problems that arise during site development.

The method function of the present invention is to solve the problem of excessive subsidence and uneven settlement of the entire construction site over time, which has been pointed out as the biggest problem of marine reclamation ground using sand, dredged soil or general soil disclosed in the past, and the purpose of the invention is to prevent excessive subsidence of the seabed original ground due to the load of the reclamation and filling material applied to the marine original ground and the consolidation settlement caused by the consolidation of the reclamation soil itself buried in the sea surface by using a lightweight mixed soil (smartsoil) having low specific gravity and excellent compressive strength, thereby creating a sturdy reclamation site, and also to provide marine reclamation and site construction that prevents ground subsidence by utilizing dredged soil commonly existing on the seabed around the reclamation site.

The technical contents presented through the present invention in more detail are summarized and examined as follows.

First, as the first embodiment shown in Fig. 2, it is suitable for planning offshore reclamation and site development in a location relatively inland and thus expected to be relatively safe from high waves such as tsunamis, and also for presenting a design cross-section and construction method suitable for offshore reclamation and site development in a location where the middle sea level (MSL) after final ground subsidence corresponding to the land above sea level is relatively low.

Second, as for the second embodiment shown in Fig. 3, it is suitable for cases where the location of the offshore reclamation and site development is located in the open sea and the final post-sinking ground level (MSL), corresponding to the land above sea level, is relatively high to develop the site safely from high waves such as tsunamis, and also for cases where it is necessary to install underground facilities during construction to increase the usability of the site while reducing the settlement load caused by the high fill height, and a design cross-section and construction method for offshore reclamation and site development are presented.

Third, as the third embodiment shown in Fig. 4, this case is applied in a situation similar to the first embodiment above, and unlike the first embodiment of Fig. 2, it can be applied in a case where parallel laying of partially unimproved landfill soil is not appropriate.

Fourth, the fourth embodiment shown in Fig. 5 is suitable when there is sufficient time or when self-weight consolidation is completed after dredging and reclamation. This case is suitable for port hinterland and industrial complex development.

To achieve the above purpose,

The present invention relates to a method for creating an artificial marine area by reclaiming the sea, and can be presented in four embodiments.

As a first embodiment,

This relates to the design and method for creating an artificial marine area by reclaiming the sea.

Step (S10-A) of determining the height (h2) of the revetment (10) by considering the sea level, the location of the reclamation site to be created, and the reclamation height (h1) according to the purpose of use, and then constructing the revetment (10) accordingly.

Step (S20-A) of filling up unimproved mud or clay (20) onto the marine ground (100) without draining the seawater filled inside the above-mentioned constructed embankment (10), and sloping downwards toward the center of the inside of the embankment (10),

Step (S30-A) of filling the above-mentioned filled mud or clay (20) with a lightweight mixed soil improved by dredging, and filling all inclined portions to create the first ground (30) of the flat land,

A method for reclamation and site development using dredged soil is proposed, characterized by including a step (S40-A) of filling the first ground (30) formed above with improved lightweight mixed soil, up to the landfill height (h1), to form a second ground (40) and complete an artificial sea site.

As a second embodiment,

This relates to the design and method for creating an artificial marine area by reclaiming the sea.

Step (S10-B) of determining the height (h2) of the revetment (10) by considering the sea level, the location of the reclamation site to be created, and the reclamation height (h1) according to the purpose of use, and then constructing the revetment (10) accordingly.

Step (S20-B) of filling the lightweight mixed soil from the center onto the marine ground (100) without draining the seawater filled inside the above-mentioned constructed embankment (10) to a predetermined height to create the first ground (30'),

Step (S30-B) of constructing a hollow structure (200) of tunnel structure on top of the above first ground (30'),

The present invention proposes a method for reclamation and site development using dredged soil, characterized by including a step (S40-B) of filling in the first soil (30') and the structure (200) sideways and upwards with improved lightweight mixed soil, up to the landfill (h1) to create a second soil (40') to complete an artificial sea site.

As a third embodiment,

This relates to the design and method for creating an artificial marine area by reclaiming the sea.

Step (S10-C) of determining the height (h2) of the revetment (10) by considering the sea level and the reclamation height (h1) according to the location and purpose of use of the reclamation site to be created, and then constructing the revetment (10) accordingly.

The present invention proposes a method for reclamation and site development using dredged soil, characterized by including a step (S20-C) of filling up a lightweight mixed soil improved from dredged soil onto a marine ground (100) from the center without draining the seawater filled inside the above-mentioned installed revetment (10), and completing the creation of an artificial marine site by filling up to the above-mentioned landfill (h1).

As the fourth embodiment,

This relates to the design and method for creating an artificial marine area by reclaiming the sea.

A step (S10-D) of determining the height (h2) of the revetment (10) by considering the sea level and the reclamation height (h1) according to the construction location and utilization purpose of the marine reclamation site to be constructed, constructing the revetment (10) accordingly, and then filling up the unimproved mud or clay (20) onto the marine original ground (100) without draining the seawater filled inside the constructed revetment (10), and creating a reserve ground (30") by filling up to the reclamation height (h1).

A step (S20-D) in which the landfill height of the above reserve ground is gradually lowered by self-weight consolidation (a) over time and the reserve ground composition state is maintained until the self-weight consolidation no longer occurs,

Step (S30-D) of cutting the preliminary ground (30") that has undergone the above steps, and cutting (b) the soil on the surface of the ground to a depth of 1/2 of the ground improvement thickness required for the bearing capacity that is suitable for the purpose of site utilization after the completion of the self-weight consolidation (a)

The present invention proposes a method for reclamation and site development using dredged soil, characterized by including a step (S40-D) of completing the creation of an artificial sea site by filling in the ground after cutting the preliminary ground, which has been lowered through the above-mentioned natural subsidence and cutting processes, up to the above-mentioned landfill (h1) with improved lightweight mixed soil from the dredged soil to create a main ground (40").

The method for reclamation and site development using dredged soil according to the present invention improves the reclamation and site development by using a lightweight mixed soil with excellent lightness and compressive strength, thereby resolving the problems of excessive subsidence and rapid uneven subsidence of the development site that occurred when creating an artificial sea site using sand, dredged soil or general soil in the past, thereby creating a safe sea reclamation site. In addition, when creating one artificial sea site and constructing an underground space, the usability of the site is doubled, so that the effect is achieved by constructing two sea reclamation sites.

In addition, by using the lightweight mixed soil, high-moisture content viscous dredged soil pumped from the bottom of the ocean, river, lake, port, etc. and improving it into a lightweight mixed soil, the supply of landfill materials used in creating artificial sea land is made smooth, making it possible to create an economical and environmentally friendly sea landfill site.

Figure 1 is a photograph showing an example of a structure built on a coastal landfill leaning to one side and developing cracks due to uneven settlement.
Figure 2 is a schematic diagram illustrating a process for creating a marine landfill site using lightweight mixed soil to prevent ground subsidence according to a first embodiment of the present invention.
Figure 3 is a schematic diagram illustrating a process for creating a marine landfill site using lightweight mixed soil to prevent ground subsidence according to a second embodiment of the present invention.
Figure 4 is a schematic diagram illustrating a process for creating a marine landfill site using lightweight mixed soil to prevent ground subsidence according to a third embodiment of the present invention.
Figure 5 is a schematic diagram illustrating a process for creating a marine landfill site using lightweight mixed soil to prevent ground subsidence according to a fourth embodiment of the present invention.
Figure 6 is a plan view showing various types of revetments or pond construction examples on the sea.
Figure 7 is an example of ground data for the Busan New Port area presented for explaining ground investigation according to the present invention.
Figure 8 is a cross-sectional view showing a method for managing the minimum ground subsidence of ground filled and filled with lightweight mixed soil.
Figure 9 is a conceptual diagram of a lightweight mixed soil (smartsoil) used in the present invention.
Figure 10 is a drawing illustrating the configuration of a lightweight mixed soil plant for manufacturing lightweight mixed soil used in the construction of a marine landfill of the present invention.

Hereinafter, we will examine specific technical details of a method for creating a marine landfill site to prevent ground subsidence using a lightweight mixed soil (smartsoil) improved from dredged soil according to the present invention, along with drawings.

The above method of creating a marine reclamation site is different from the existing method of using sand, etc. in that it improves dredged soil with a high moisture content, which is an ultra-soft soil such as viscous dredged soil, into a lightweight mixed soil (smartsoil), which is a ground reclamation/filling material with excellent lightness and compressive strength, in creating a marine reclamation site. As shown in FIGS. 2 to 5, the concept, design, and construction method of the reclamation ground structure are changed, and four representative concepts can be proposed.

In order to create an artificial offshore site by reclaiming the sea, it is necessary to determine the purpose and scope of the site utilization and review economic feasibility, safety, construction period, maintenance measures, etc. accordingly. In order to perform safe, economical, and environmentally friendly offshore reclamation and site development based on the technical contents presented in the present invention, it is necessary to review matters in advance. After reviewing these matters, the most appropriate model for the situation among the various embodiments presented in the present invention is applied to perform offshore reclamation and site development.

Before examining the four methods of creating a marine landfill according to the present invention, let us first examine the contents thereof.

[Key considerations when planning offshore reclamation and land development]

1. Review of the location, scale, purpose, form and height of sea reclamation and land development

In the case of existing construction methods, there is much controversy over stability and excessive maintenance costs due to short- and long-term excessive subsidence after completion of offshore reclamation and site development, but the construction method of the present invention solves these problems, and by utilizing this method when building airports, marine cities, and industrial complexes through offshore reclamation, it is possible to prepare for disasters such as sea level rise, ground compression and expansion, and earthquakes due to climate change.

It is necessary to appropriately set and review the middle sea level (MSL), which is the ground level corresponding to the land area above sea level, after the final ground subsidence, and this review step is very important when planning sea reclamation and site development.

2. Data collection and analysis for securing dredged soil for landfill and investigation of the seabed original ground

Since the data on the structure and ground strength of the seabed original ground have a great influence on the total construction cost, such as the height, shape, and amount of settlement of the embankment, various ground investigations should be conducted, and if necessary, indoor tests should be conducted in parallel to identify soil characteristics. In addition, measures should be established at the same time to secure dredged soil to be used in the production of lightweight mixed soil.

3. Step for setting the final middle sea level (MSL) after ground subsidence

In this step, the ground investigation data from item 2 above is reviewed to set the final MSL considering air, etc.

4. Estimation of the amount of subsidence of the seabed (using Terzaghi's primary consolidation theory, etc.)

In this step, the estimated total settlement amount is reviewed. Unlike the existing method, the settlement due to the compaction of the lightweight mixed soil filling layer itself is not reviewed.

5. Estimation stage for filling and filling volume and construction cost of lightweight mixed soil (Smartsoil modified soil) based on the estimated total settlement amount (settlement during construction + residual settlement amount)

During design, the estimated work volume and material volume are calculated based on the settlement amount and embankment height during construction, and the estimated construction cost and construction period are estimated. Therefore, the estimate must include the settlement amount that occurs during construction.

6. A stage to review the reclamation of unimproved dredged soil and installation of underground space to reduce reclamation and filling costs according to the purpose of utilizing the offshore reclamation site.

In the past, it was virtually impossible to build underground spaces in landfill ground during reclamation and site development. However, if reclamation and site development are done using improved soil, such as lightweight mixed soil (Smartsoil), large-scale underground space construction is possible, and this method secures constructability, stability, and economy, so it is necessary to actively review this.

7. Step 7: Setting up a tentative landfill plan

8. Review safety assurance and maintenance plans, etc.

9. Confirmation of landfill plan and design after revision and supplementation

[Major review items related to design and construction]

1. Review of various types of revetments or ponds on the sea (Fig. 6)

This is the stage where the construction of lightweight mixed soil (smartsoil) landfill and filling materials is reviewed according to the determined revetment type, etc., with reference to the ground level (middle sea level, MSL) after the final ground subsidence in item 2 of the review of major matters among the sea reclamation/filling and site development methods in [Other Review] below. This stage is very important for reducing construction costs through efficient construction.

2. Dredging and transportation stage to secure raw soil for manufacturing lightweight mixed soil (Smartsoil)

High moisture content seabed soil such as viscous and silty is dredged by methods such as dragging. The amount of dredged soil required at this time is approximately 55% (±10%) of the amount of lightweight mixed soil (smartsoil) manufactured based on a moisture content of 200%.

3. Step of improving the transported dredged soil into lightweight mixed soil (smartsoil)

The unit weight of lightweight mixed soil (smartsoil) for sea level reclamation is 11KN/㎥ (±10%), and the unit weight of lightweight mixed soil (smartsoil) for ground filling above sea level is 9KN/㎥ (±10%). Target ground strength The target ground strength is determined together with the design according to the purpose of site utilization. The strength of lightweight mixed soil is usually determined between 50kpa and 2Mpa.

4. The stage of laying soil improved with lightweight mixed soil (smartsoil) for filling and embankment of a revetment or pond.

At this stage, partial underwater reclamation of unimproved dredged soil can be carried out in parallel to ensure economic feasibility and stability, if necessary.

5. After the landfill and filling are completed, the stage is to spread sand and other drainage aggregates and landscaping soil on the top of the landfill layer.

Lay at least 30 cm of well-drained, high-aggregate soil such as sand or crushed stone.

6. Completion of offshore reclamation and land development

The lightweight mixed soil generated during excavation and installation of infrastructure on the upper part of the site will be used for park creation, etc.

[Other considerations]

This additional review presents additional items required for project review in order to minimize errors between design content and actual construction when calculating rough subsidence, estimating construction costs, and setting construction periods.

1. Collection and analysis of ground investigation data on the seabed (required for establishing and designing measures to reduce ground subsidence) - Review of seabed ground data for planned reclamation and land development sites. Ex) Ground data for Busan New Port area (see Figure 7)

The process of collecting and analyzing ground investigation data in the horizontal direction (A-A') and vertical direction (B-B') of the seabed original ground of the landfill site as shown in the above figure 7 is a very important process.

The process of identifying the ground structure of the seabed through data collection and analysis and identifying the characteristics of the soil on site through additional indoor tests is intended to find the optimal design and construction method for offshore reclamation and site development that ensures economic feasibility and stability.

2. Construction review according to the setting of the ground level (middle sea level, MSL) after final settlement after completion of site development

ex) Create cross-section of landfill and fill layer and set unit weight, strength, etc. for h1 and h2 (Table 3)

The load of the lightweight mixed soil (smartsoil) layer to be filled and filled on top of the seabed (H) ) is used as the basis for estimating the residual settlement after completion of construction by considering the settlement during construction from the first consolidation settlement of the seabed (H). If necessary, it is necessary to actively review the adjustment of the unit weight of lightweight mixed soil and the construction of underground space to minimize the ground settlement occurring after completion. In addition, settlement management measures through maintenance after completion should also be reviewed at the same time.

a. The settlement amount is estimated using the Terzaghi primary consolidation calculation formula (Formula 1) in normally consolidating ground, and when there is a preceding overconsolidation load, the settlement amount is roughly estimated by reflecting it. It is also acceptable to estimate the settlement amount using the average ground compression coefficient.

(1)

b. Estimate the amount of settlement that occurs during construction or compare it with the Terzaghi primary consolidation settlement estimate after installing a settlement meter on site, etc. to estimate the amount of residual consolidation settlement during and after construction. When installing a settlement meter on site, install it in the center of the area where the settlement is estimated to be the greatest among the entire ground, and install it firmly so that it is not damaged by waves, etc.

c. To induce an increase in the strength of the original seabed ground through stable pore water drainage following landfill and filling with lightweight mixed soil (smartsoil), care must be taken not to disturb the original seabed ground.

d. When estimating the residual settlement, the settlement of the clay layer on the side of the revetment that has been pushed out by heaving, etc. during the construction of the revetment structure or the dredged soil layer that has been partially filled in while remaining unimproved on the side of the revetment is ignored. However, the negative upward pressure generated from the unimproved dredged revetment layer on the side and the positive pressure generated from the bottom of the smartsoil layer are examined to confirm that they are less than the downward force generated by the smartsoil revetment layer, and the unit weight of the improved soil is appropriately managed to prevent the smartsoil revetment layer from rising.

3. Step of filling and embedding the soil improved with lightweight mixed soil (smartsoil) into the embankment or pond.

As shown in S30-A of Fig. 2 and S20-B of Fig. 3, when filling and embanking with improved lightweight mixed soil (smartsoil), it is intensively laid and embanked from the longitudinal axis center of the embankment to a certain height to promote compaction and improve ground strength early during construction in the center of the seabed original ground, thereby stabilizing the ground after site development is completed.

When installing an underground space, as in the first ground (30') of S30-B in Fig. 3, the underground space structure (200) is installed after filling in the lightweight mixed soil (smartsoil) underwater, and after installing the underground space structure, as in the second ground (40') of S40-B, the lightweight mixed soil (smartsoil) filling is finally completed on the above-ground part, and then the drainage layer and landscaping soil are constructed.

4. Review of the bearing capacity of the upper structure of the landfill/fill ground

The top layer of the fill layer is designed to increase the uniaxial compressive strength of the improved soil so that the structural load is distributed as much as possible within the upper ground.

The bearing capacity formula for the upper structure of the site development is applied by applying the bearing capacity formula for the case of strong upper clay and soft lower clay (Φ1=0, Φ2=0) from the rectangular foundation bearing capacity formula of Meyerhof & Hanna (1978). (Top strong clay => 1/2 of the uniaxial compressive strength of lightweight mixed soil, undrained shear strength (c1) applied)

[Review of maintenance and subsidence measures]

Since the unit weight of the ground improved with lightweight mixed soil (smartsoil) and filled in and filled in is lighter than that of the embankment or pond, there is a possibility that the embankment and pond sections will settle earlier. In the case where a space is formed between the ground improved with lightweight mixed soil (smartsoil) and the ground filled in and ...

[ Review of final establishment of design and construction measures, including modification of cross-section of landfill and fill]

After reviewing the plan for offshore reclamation and site development discussed above, the appropriate method presented in Figures 2 to 5 is selected to carry out offshore reclamation and site development.

At this time, the actual final settlement expected can be estimated as 75% of the total settlement estimated in calculations, but it should be applied only when the soil and ground information such as the gap ratio, compression index, preload applied to the seabed original ground, and presence of an immediate settlement layer under the seabed original ground used for settlement estimation are relatively reliable.

The lightweight mixed soil (smartsoil) layer prevents uneven settlement by distributing the load of the upper structure within the lightweight mixed soil (smartsoil) ground layer (Φ=50° or more). In addition, in the case of Fig. 2, the upward force generated from the unimproved dredged reclaimed soil layer (treated as a Non-Newton material) of drawing symbol 20, which is in a saturated soil state when the sea level rises and an earthquake occurs, contributes to the stability of the smartsoil ground layer, such as ground balance and prevention of settlement. However, the portion where groundwater contained in the unimproved layer infiltrates into the smartsoil layer due to capillary phenomenon and increases the load is within the tolerance unit weight managed in the design, and the unit weight of the improved soil for laying is set by taking this into consideration during design and construction. In addition, since the lightweight mixed soil has no concerns about volume change due to compression and expansion due to climate change, etc., there is no need to worry about this during the design.

However, when planning to manufacture lightweight mixed soil, check the on-site soil and confirm the optimal mixing ratio in advance before construction to manufacture and manage the quality of lightweight mixed soil.

Hereinafter, the artificial seabed creation method of four embodiments according to the present invention based on the contents presented above will be specifically examined with drawings.

The first embodiment is to first fill the marine ground with mud or clay, and then second fill it with lightweight mixed soil, as shown in Fig. 2.

In more detail,

This relates to the design and method for creating an artificial marine area by reclaiming the sea.

Step (S10-A) of determining the height (h2) of the revetment (10) by considering the sea level, the location of the reclamation site to be created, and the reclamation height (h1) according to the purpose of use, and then constructing the revetment (10) accordingly.

Step (S20-A) of filling up unimproved mud or clay (20) onto the marine ground (100) without draining the seawater filled inside the above-mentioned constructed embankment (10), and sloping downwards toward the center of the inside of the embankment (10),

Step (S30-A) of filling the above-mentioned filled mud or clay (20) with a lightweight mixed soil improved by dredging, and filling all inclined portions to create the first ground (30) of the flat land,

It includes a step (S40-A) of completing an artificial seabed by filling up the first ground (30) formed above with a lightweight mixed soil improved from dredged soil up to the landfill (h1) to form a second ground (40).

As previously presented, the above-mentioned seawall (10) is constructed by determining the height according to the purpose of land use after reviewing the main matters for creating an artificial seabed, taking into account the landfill height (h1) of the landfill ground and the rise in sea level or occurrence of tsunamis.

After the above-mentioned embankment (10) is constructed, dredged soil in an unimproved state of mud or clay is filled in and embanked on the original seabed ground. At this time, the embankment is filled in without draining the seawater inside the embankment (10).

In the past, a water drainage method was applied to completely fill the inside of a revetment (10) with dredged soil or other landfill materials and then remove seawater within the landfill soil. However, this method had the disadvantages of incurring additional costs and requiring a considerable amount of additional time, and stability may be significantly reduced in the event of a disaster such as an earthquake. Therefore, in the present invention, a marine site is created by landfill and filling, where the water drainage method can be omitted.

The height of the embankment where the dredged soil of the above-mentioned unimproved mud or clay comes into contact with the embankment (10) is up to the sea level, and as you go towards the center in the inward direction from the embankment (10), the height of the embankment below the original ground decreases, forming a slope.

The purpose of filling the area with a downward slope starting from the embankment (10) and going toward the inner center is to prevent deformation of the ground improved with lightweight mixed soil (smartsoil) that may occur due to the use of the mud or clay, while reducing the amount of lightweight mixed soil (smartsoil) used through the use of the mud or clay, thereby ensuring economic efficiency.

In the past, due to technical limitations in the design process for predicting the amount of subsidence for the creation of coastal artificial ground, it was difficult to collect accurate numerical information up to a certain sufficient depth for the coastal original ground, and thus the design and construction were performed with insufficient accurate information. In addition, when the depth of the soft ground was deep or the landfill/fill height was high, the possibility of calculation errors being greater was very high. In addition, since landfill was performed using sand, dredged soil, or general soil with a high specific gravity compared to the lightweight mixed soil to be used in the present invention, stability problems such as excessive settlement and uneven settlement of the entire ground inevitably occurred after a certain period of time after the completion of the artificial ground creation.

After filling in the above mud or clay, the area is filled in with a lightweight mixed soil (smartsoil) that is improved from dredged soil.

At this time, the above lightweight mixed soil (smartsoil) is filled up to the landfill (h1) on top of the first filled mud or clay layer, and by filling the second lightweight mixed soil in this way, the ground composition of the first embodiment is completed.

The present invention has a technical feature of creating a safe artificial ground by absolutely reducing the size of the subsidence by replacing sand, dredged soil or general soil previously used with a lightweight mixed soil (smartsoil) having excellent lightness and compressive strength to avoid such problems.

The above lightweight mixed soil is manufactured by first settling and second settling highly water-containing viscous dredged soil collected from the bottom of oceans, rivers, lakes, ports, etc., and supplying the dredged soil with the moisture content minimized through such settling treatment to a plant that improves it into lightweight mixed soil (smartsoil). At the same time, the lightweight mixed soil is transported to the landfill site as improved soil in a highly fluid and liquid state before it hardens, and then spread and fill it.

The above improved lightweight mixed soil is an improved soil that has improved the structural framework between soil particles to increase the volume and has improved strength, and is an improved soil that can be manufactured by adjusting the strength and unit weight in various ways depending on the purpose of use, such as ground improvement, by applying the foamed mixed soil manufacturing method and manufacturing device presented in the applicant's registered patent 10-1666074 (registration date October 7, 2016). The conceptual diagram of the lightweight mixed soil is illustrated in FIG. 9. As illustrated in FIG. 9, a foamed mixed soil, i.e., lightweight mixed soil (smartsoil), can be presented by improving dredged soil to have the effects of increasing the volume and improving the strength.

By creating an artificial seabed using lightweight mixed soil (smartsoil) improved from dredged soil in this way, the following various effects can be expected.

1) Compared to existing construction methods, landfill/fill load and subsidence can be reduced by more than 50%.

2) Since the impact of subsidence on the seabed original ground is minimized, unlike existing construction methods, there is no significant post-completion ground subsidence or stability issues due to accelerated subsidence that occur rapidly in a short period of time. Instead, it progresses at a very gradual pace, making maintenance response easy and significantly reducing costs.

3) Since underground space can be installed in the landfill, efficient use of land is possible, and the effect of creating one more landfill site can be expected.

4) Construction costs can be reduced by shortening the construction period.

5) The abundant seabed viscous dredged soil can be used as landfill and filling material.

6) There is no need for separate ground improvement, so there is no need for surface treatment for equipment entry.

7) It is possible to omit vertical drainage and horizontal drainage processes for improving the seabed original ground and landfill/fill ground.

8) It is possible to omit the prior loading process to promote consolidation of the seabed original ground and reclaimed ground.

9) Self-weight compaction time is unnecessary.

10) It is an eco-friendly method that reduces carbon emissions and protects marine fishing grounds during the process of extracting large amounts of sand, etc.

11) Prevents deformation of structures such as buildings due to compression and expansion of the ground caused by climate change.

12) Unlike existing methods, there is no concern about destruction of the original ground during the landfill and filling process.

The second embodiment is a case where an artificial offshore site is created as shown in Fig. 3, in which a lightweight mixed soil is used for the first filling on the marine original ground, a hollow structure in the form of a tunnel is constructed, and then the second filling is performed using lightweight mixed soil to create the site. This is proposed to increase the usability of the site and reduce subsidence of the seabed original ground.

In more detail,

This relates to the design and method for creating an artificial marine area by reclaiming the sea.

Step (S10-B) of determining the height (h2) of the revetment (10) by considering the sea level, the location of the reclamation site to be created, and the reclamation height (h1) according to the purpose of use, and then constructing the revetment (10) accordingly.

Step (S20-B) of filling the lightweight mixed soil from the center onto the marine ground (100) without draining the seawater filled inside the above-mentioned constructed embankment (10) to a predetermined height to create the first ground (30'),

Step (S30-B) of constructing a hollow structure (200) of tunnel structure on top of the above first ground (30'),

It includes a step (S40-B) of completing an artificial seabed by filling up the first ground (30') and the structure (200) with a lightweight mixed soil improved by dredging the soil to the side and top, and filling up to the landfill (h1) to create a second ground (40').

The above S20-B step, as illustrated in Fig. 3, is to intensively lay and fill the seabed core from the longitudinal axis center of the embankment to a certain height of the remaining fill layer above ground, thereby promoting compaction and improving ground strength early during construction, thereby minimizing ground subsidence after site development is completed.

The above structure (200) is intended to provide additional space underground of the finally constructed artificial seabed, and is proposed as a method to increase the usability of the site, for example, as an air-raid shelter, underground shopping mall, or parking lot.

The third embodiment is to completely fill the marine ground with lightweight mixed soil, as shown in Fig. 4.

Step (S10-C) of determining the height (h2) of the revetment (10) by considering the sea level and the reclamation height (h1) according to the location and purpose of use of the reclamation site to be created, and then constructing the revetment (10) accordingly.

It includes a step (S20-C) of completing the creation of an artificial seabed by filling up a lightweight mixed soil improved from dredged soil onto the marine original ground (100) from the center without draining the seawater filled inside the above-mentioned installed revetment (10) up to the landfill (h1).

The fourth embodiment is a case where, as shown in Fig. 5, after the self-weight consolidation period has ended after the dredged soil, etc. has been filled into the revetment area on the marine original ground, the upper soil is improved to a certain thickness with lightweight mixed soil to create a site.

A step (S10-D) of determining the height (h2) of the revetment (10) by considering the sea level, the location of the marine reclamation site to be created, and the reclamation height (h1) according to the purpose of use, and then constructing the revetment (10) accordingly, and then reclaiming unimproved mud or clay (20) on top of the marine original ground (100) without draining the seawater filled inside the constructed revetment (10), and creating a reserve ground (30") by filling up to the reclamation height (h1),

A step (S20-D) in which the landfill height of the above reserve ground is gradually lowered by self-weight consolidation (a) over time and the reserve ground composition state is maintained until the self-weight consolidation no longer occurs,

Step (S30-D) of cutting the preliminary ground (30") that has undergone the above steps, and cutting (b) the soil on the surface of the ground to a depth of 1/2 of the ground improvement thickness required for the bearing capacity that is suitable for the purpose of site utilization after the completion of the self-weight consolidation (a)

From the ground surface after cutting the reserve ground that has been lowered through the above natural subsidence and cutting process It includes a step (S40-D) of completing the creation of an artificial seabed by filling the dredged soil up to the above-mentioned landfill (h1) with improved lightweight mixed soil to create a main ground (40").

Below, the improvement of the lightweight mixed soil used in the creation of an artificial seabed in the present invention will be described.

The lightweight mixed soil used in the present invention is manufactured by taking highly water-containing viscous dredged soil collected from the bottom of oceans, rivers, lakes, ports, etc., and processing the moisture content appropriately through sedimentation treatment, supplying it to a lightweight mixed soil plant, and then transporting the lightweight mixed soil manufactured in this manner to a landfill site in a liquid state and then spreading it to form a fill. The dredged soil finally used uses a dredged soil having a moisture content in the range of 100 to 300%.

If dredged soil of this type is continuously supplied to the lightweight mixed soil plant (50), the lightweight mixed soil produced from the lightweight mixed soil plant (50) can be continuously transported to the landfill site and used for continuous filling, thereby significantly reducing the time required to create an artificial seabed.

Dredging is the process of digging out clay or sand accumulated on the bottom of a river or coast to deepen the bottom. The rocks, gravel, sand, clay, etc. produced by this dredging are collectively called dredged soil. Depending on where it occurs, dredged soil can be classified into port, reservoir, and river dredged soil.

Since dredged soil is an economical material that is easy to secure in quantity, it is efficient to use it in creating marine reclamation sites.

The viscous dredged soil according to the present invention is used after being suitably processed to be improved into a lightweight mixed soil (smartsoil) through a lightweight mixed soil plant (50) as shown in Fig. 10.

The above lightweight mixed soil plant (50) includes a solidification material storage silo (501) that supplies solidification material, a conveyor (502, 503, 504) that transports the solidification material supplied from the solidification material storage silo (501) to a mixing unit, a mixing unit (505) that mixes the solidification material supplied through the conveyor with mixed dredged soil supplied from a temporary dredged soil storage yard to create a mixture, and a bubble mixing unit (506) that dynamically supplies bubbles during the process of transporting the dredged soil mixed with the solidification material through the mixing unit (505) to a landfill.

The above-mentioned hardener is added to secure a certain strength, and is selected from one or more types of cementitious materials, hardeners utilizing industrial by-products, and environmentally friendly soil stabilizer NSS (natural stabilizer soil).

The strength of lightweight mixed soil manufactured from dredged soil is determined by the amount of the above-mentioned solidifying agent added, the moisture content of the raw soil, the type of soil, etc.

The cement-based materials used above are mainly 1st or 2nd type Portland cement. The mixing ratio of cement varies depending on the expected improvement effect and the type of soil, but it is generally desirable to use it within the range of 20% of the total weight of the lightweight mixed soil. At this time, as the clay content and water content in the soil increase, the amount of cement also increases.

The solidification mechanism of cement is not physical mixing but chemical interaction. Cement hardens and sets by creating hydrates through a hydration reaction in which cement compounds, called clinker constituent minerals, react with water.

It is recommended that the high-temperature refractory material utilizing the above industrial by-products have a component based on fine powder such as blast furnace slag and ferronickel.

It has the advantage of being economical as it reduces the use of general cement by up to 80%, reducing damage to nature and carbon dioxide emissions caused by indiscriminate mining of limestone during the cement manufacturing process, and being environmentally friendly as it makes maximum use of industrial by-products.

The above-mentioned environmentally friendly soil stabilizer, NSS (natural stabilizer soil), is made mainly of a mixture of natural fibers, extracted short fibers, and lime. It increases the shear strength of the soil, thereby improving the bearing capacity and durability of the ground, and has the characteristics of simultaneously preventing flooding and freezing damage.

The above foam is a lightweight material mixed to make the ground material lighter. The above foam is used after diluting the foaming agent in water, seawater, or fresh water and foaming it.

The foaming agent used to secure lightness and fluidity is greatly affected by air pressure, temperature, organic matter content, and time elapsed after foaming. The types of foaming agents include animal protein-type foaming agents and surfactants that form bubbles by surface tension. Regardless of the shape of the foaming agent, it must maintain stable bubbles until the cement sets and hardens.

More specifically, to create bubbles, a foaming agent and water are mixed in a weight ratio of 1:20 and foamed in advance for use. The foaming agent is a synthetic surfactant foaming agent and is a high-grade alcohol sulfur ester compound.

The above foaming agents include animal, vegetable, and synthetic oil-based ones, and physically introduce bubbles using surface-active action.

The method of generating bubbles is divided into a method of physically foaming in advance using a bubbler and a method of mixing a foaming agent into a sample to generate gas through a hydration reaction. In this case, it is important for the foaming agent to evenly disperse bubbles within the modified soil to secure lightness and fluidity, so the method of mixing a foaming agent, which is greatly affected by temperature, is rarely used.

In the case of the above animal-based foaming agent, the specific gravity is 1.2, pH (4℃) 7.0, saponification value is 210, sedimentation value is 10, and salt concentration is 4.2%, and in the case of the vegetable-based foaming agent, the specific gravity is 1.03, pH (4℃) 7.1, saponification value is 5.3, sedimentation value is 0, and salt concentration is 1.7%.

Aqueous solutions of synthetic surfactants are widely used as foaming agents because they are easy to foam. Surfactants used as foaming agents must maintain the bubbles stably until the cement hardens regardless of their shape. Amphoteric surfactants exhibit surface activity regardless of acidity or alkalinity, so they exhibit excellent performance as foaming agents. Nonionic surfactants are not affected by ionicity and can be used as foaming agents, but they are generally weak in foaming properties and the stability of bubbles in slurry is unstable, so they are not used alone.

In addition to the types of fire retardants presented above, steel slag may also be used. However, the mixing ratio at this time is determined by the on-site mixing ratio as there are differences in the ingredients depending on the slag vendor. In addition, cement may be added if necessary.

The uniaxial compressive strength of dredged soil mixed with steel slag was greater than that of pure dredged soil, and showed an increasing trend as the curing period and mixing ratio increased. In addition, the strength increased by approximately 2.27 to 11.77 times compared to pure dredged soil when 20 to 40% of slag was mixed.

The bearing capacity of dredged soil mixed with steel slag was greater than that of pure dredged soil, and showed an increasing trend as the curing period and mixing ratio increased. In addition, the bearing capacity increased by approximately 7.6 to 33.6 times compared to pure dredged soil when 20 to 40% of slag was mixed.

Lightweight mixed soil can be adjusted in unit weight and shear strength to suit the intended use. To reduce the unit weight of the material used, air foam is mixed in, and cement, a solidifying agent, is used to achieve the desired shear strength.

The unit weight is designed to be 10 kN/㎥ to 14 kN/㎥ to prevent lightweight soil from floating on water when used on the coast, and when used as landfill soil, the uniaxial compressive strength is designed to be in the range of 50 kPa to 2,000 kPa, and the final decision is made on site considering on-site work conditions, etc.

The method for creating a landfill site by offshore reclamation using dredged soil according to the present invention improves the dredged soil to secure lightness and excellent compressive strength and thereby creates an offshore reclamation site, thereby solving the problem of large-scale subsidence occurring after construction due to excessive load that occurred when creating an artificial offshore reclamation site using sand, dredged soil or general soil in the past, thereby ensuring the stability of the offshore reclamation site called a sand castle.

In addition, there were difficulties in terms of construction methods and costs when installing large-scale underground facilities in conventional landfills, but if this method is used, underground space can be easily constructed during site development in an artificial seabed, so there is an advantage in that the usability of the site can be greatly increased.

By using the above lightweight mixed soil, dredged soil that exists in large quantities in oceans, rivers, lakes, ports, etc. can be economically utilized for the creation of artificial marine sites, thereby preventing environmental destruction at sea and on land to secure a large quantity of high-quality aggregate, minimizing concerns about stability caused by excessive ground subsidence due to the use of heavy aggregate, and significantly reducing maintenance costs caused by ground subsidence.

In the case of the present invention method, the problem of load increase, which is a fundamental problem of existing methods, is solved by a method of significant load reduction, so it becomes possible to dramatically improve the safety of the offshore reclamation site.

Due to these advantages, the present invention has great potential for industrial application.

10: Hoan
20: Mud or clay
30: 1st ground
30': 1st ground
30": Reserve ground
40: Secondary ground
40': 2nd ground
40": Main body
100: Marine ground
200: Structure

Claims (4)

This relates to the design and method for creating an artificial marine area by reclaiming the sea.
Step (S10-A) of determining the height (h2) of the revetment (10) by considering the sea level, the location of the reclamation site to be created, and the reclamation height (h1) according to the purpose of use, and then constructing the revetment (10) accordingly.
Step (S20-A) of filling up unimproved mud or clay (20) onto the marine ground (100) without draining the seawater filled inside the above-mentioned constructed embankment (10), and sloping downwards toward the center of the inside of the embankment (10),
Step (S30-A) of filling the above-mentioned filled mud or clay (20) with a lightweight mixed soil improved by dredging, and filling all inclined portions to create the first ground (30) of the flat land,
A method for reclamation and site development using dredged soil, characterized by including a step (S40-A) of completing an artificial sea site by filling up the first ground (30) formed above with a lightweight mixed soil improved from dredged soil up to the landfill height (h1) to form a second ground (40).
This relates to the design and method for creating an artificial marine area by reclaiming the sea.
Step (S10-B) of determining the height (h2) of the revetment (10) by considering the sea level, the location of the reclamation site to be created, and the reclamation height (h1) according to the purpose of use, and then constructing the revetment (10) accordingly.
Step (S20-B) of filling the lightweight mixed soil from the center onto the marine ground (100) without draining the seawater filled inside the above-mentioned constructed embankment (10) to a predetermined height to create the first ground (30'),
Step (S30-B) of constructing a hollow structure (200) of tunnel structure on top of the above first ground (30'),
A method for reclamation and site development using dredged soil, characterized by including a step (S40-B) of filling in the first soil (30') and the structure (200) sideways and upwards with improved lightweight mixed soil, and filling up to the landfill (h1) to create a second soil (40') to complete an artificial sea site.
This relates to the design and method for creating an artificial marine area by reclaiming the sea.
Step (S10-C) of determining the height (h2) of the revetment (10) by considering the sea level and the reclamation height (h1) according to the location and purpose of use of the reclamation site to be created, and then constructing the revetment (10) accordingly.
A method for reclamation and site development using dredged soil, characterized by including a step (S20-C) of completing the creation of an artificial marine site by filling up a lightweight mixed soil improved from dredged soil onto a marine ground (100) from the center without draining the seawater filled inside the installed revetment (10) up to the reclamation height (h1).
This relates to the design and method for creating an artificial marine area by reclaiming the sea.
A step (S10-D) of determining the height (h2) of the revetment (10) by considering the sea level and the reclamation height (h1) according to the construction location and utilization purpose of the marine reclamation site to be constructed, constructing the revetment (10) accordingly, and then filling up the unimproved mud or clay (20) onto the marine original ground (100) without draining the seawater filled inside the constructed revetment (10), and creating a reserve ground (30") by filling up to the reclamation height (h1).
A step (S20-D) in which the landfill height of the above reserve ground is gradually lowered by self-weight consolidation (a) over time and the reserve ground composition state is maintained until the self-weight consolidation no longer occurs,
Step (S30-D) of cutting the preliminary ground (30") that has undergone the above steps, and cutting (b) the soil on the surface of the ground to a depth of 1/2 of the ground improvement thickness required for the bearing capacity that is suitable for the purpose of site utilization after the completion of the self-weight consolidation (a)
A method for reclamation and site development using dredged soil, characterized by including a step (S40-D) of completing the creation of an artificial sea site by filling in the ground after cutting the preliminary ground that has been lowered through the above-mentioned cutting process up to the above-mentioned landfill (h1) with improved lightweight mixed soil from the dredged soil to create a main ground (40").