JP7198406B2 - Vacuum Consolidation Method and Vacuum Consolidation Dredging Method and Vertical Drain - Google Patents

Description

The present invention relates to a vacuum consolidation dredging method for seabed soil, etc., in which ground improvement, high-vacuum vacuum consolidation and dredging are performed in a series of steps, aiming to reduce the consolidation time of the vacuum consolidation method by high vacuum and increase the consolidation settlement.

When constructing a heavy structure on soft cohesive ground, it is common to improve ground settlement, deformation, and strength in advance. As a countermeasure method for this, there is a preload method. In this construction method, an embankment load equal to or greater than that of the structure is applied on the ground in advance to cause consolidation settlement and increase the strength of the ground, and then the embankment load is removed to construct the structure. is. Normally, the preloading method uses a vertical drain method to shorten the consolidation drainage distance and promote consolidation.
Around 1949, Kjellman of Sweden invented the atmospheric pressure loading method using atmospheric pressure instead of embankment load. The basic system is to install a vertical drain in the improved area, connect the head with a drainage layer and cover the ground surface. Next, the entire surface of the drainage layer is covered with an airtight sheet, and the end of the sheet is buried in the ground to ensure airtightness in the improved area. Then, the vacuum pump continues to reduce the pressure in the drainage layer, and the pore water and air in the ground that are sucked out are discharged to the outside.
The "vacuum consolidation method", which was introduced to Japan under the name of "atmospheric pressure loading method" in the 1960s, had a long period of stagnation due to the low level of pressure reduction technology in the ground. However, in recent years, there has been progress in the development of vacuum pumps, highly airtight sheets, and drain materials that maintain good water permeability even under vacuum pressure. As a result, the vacuum consolidation method draws attention again for its advantage of placing a drain in soft ground where it is not possible to create a loaded embankment that promotes consolidation, and the effect of a loaded embankment height of approximately 3.5m or more can be expected. now have
As a construction method that contributed to the development of the vacuum consolidation method in our country (Japan), there is the N&H (reNew & High quality) forced consolidation and dehydration method, which was put into practical use for the first time in 1992. This is achieved by improving parts such as a drain (plastic drain) with low water head loss under vacuum pressure, an airtight sheet (made of vinyl chloride) that does not leak, and developing and introducing a vacuum driving device and a vacuum consolidation system. It is said to be a construction method that achieves quality, short construction period, low cost, and reduction of impact on the surrounding environment. (For example, see Non-Patent Document 1)
In 2002, we also developed the high vacuum N&H (reNew & High quality) construction method. In the previous construction method, a steam-water separation vacuum tank was installed outside the improvement area, and water and air were separated here. Therefore, as the ground subsides, the lift of water increases, and the depth of the vacuum-consolidated ground becomes shallower. On the other hand, the above construction method is a method in which the steam separation tank is installed in the improved area to suppress the increase in lift. By adopting this method, it is said that the most important thing in vacuum consolidation, "a stable high vacuum pressure can be continuously applied to the ground."
However, the method of separating air and water was carried out from 1972 to 1973 in a seabed experiment of the vacuum consolidation method. Ground improvement on the seabed has a lifting head corresponding to the water depth from the beginning. If the water depth exceeds 10m, the vacuum consolidation method will not work unless the air-water separation method is used. Inevitably, the air-water separation method is used on the seabed. (For example, see Non-Patent Document 2)
Another method that contributed to the development of the vacuum consolidation method is the capped drain method. A normal vacuum consolidation method uses an airtight sheet to maintain airtightness. In this construction method, a capped drain with a drainage hose attached in advance is driven vertically to a depth of about 1 m (cohesive soil layer) to ensure the airtightness. Therefore, an airtight effect can be obtained in a single process of placing a vertical drain, so labor can be saved in construction, and costs can be reduced and the construction period can be shortened. In addition, since an airtight sheet is not required, it is now possible to apply it to ground improvement under water, which was difficult with conventional construction methods. (For example, see Patent Document 1)
There is a vacuum consolidation dredging method as a construction method that utilizes the vacuum pressure of the seabed ground. This is a construction method that combines vacuum consolidation and dredging. This construction method uses a steel box type device called an airtight loading box that acts as a bucket for consolidation loading and dredging of the ground. The structure of the airtight loading box is a box-shaped structure with an opening at the bottom, and a thin vacuum tank is installed on the inner ceiling surface. is provided with a water-permeable lid, and an air-water separation airtight tank and a box tower are attached to the central portion of the outer upper surface of the box. (For example, see Patent Document 2)
The work process of the vacuum consolidation dredging method is divided into the installation process of setting the airtight loading box on the seabed, etc., the consolidation process, the dredging process, and the transport process of the dredged soil. The dredging process is the process of lifting the filling soil held by the box from the seabed and pushing it out from the box. This lifting corresponds to loading of the dredged soil, and pushing out the filling soil corresponds to loading and unloading of the dredged soil.
When the box is set on the seabed, airtightness is ensured. Then, the seabed soil is packed in the airtight loading box. In the consolidation process, the consolidation is carried out so that the strength of the seabed soil is greater than the strength that can be dredged by the box with the bottom opening, that is, the water content ratio of the seabed cohesive soil to be dredged is less than the liquid limit. Utilizes the vacuum pressure difference (vacuum suction) between the top and bottom surfaces of the clog. At this time, it is meaningless if only the upper surface of the filling soil is lifted and the rest falls down. Therefore, the filling soil must be strong enough not to separate and fall under its own weight. As a result of verification by model experiments, the integral condition of this filling soil is the strength obtained by consolidating the water content ratio of the filling soil below the liquid limit.
This realizes a construction method in which consolidation and dredging are performed as a series of processes using an airtight loading box with an opening at the bottom. This method is also used for maintenance dredging of the channel. Therefore, further shortening of the consolidation time is a subject.
The basic method for shortening the consolidation time of clay ground is the vertical drain method, which shortens the consolidation drainage distance based on the Terzaghi theory. On the other hand, the method of increasing the consolidation settlement of the clay ground is the method of increasing the outflow driving force of the clay pore water by the consolidation increasing load. The method of shortening the consolidation time of the clay ground and increasing the consolidation settlement at the same time is the method of temporarily lowering the water retention capacity of the clay. The former method is a preloading method by embankment loading or vacuum consolidation. A known method of the latter is the method of electrically disturbing the clay. The feature of this method is that by electrically disturbing the clay, the consolidation progresses rapidly by the overburden pressure without applying a consolidation increasing load. However, this method has not been put to practical use because it consumes a large amount of electrical energy. (For example, see Non-Patent Document 3)

Patent No. 3777566 PCT/JP2017/010246

Vacuum Consolidation Technology Association "High Vacuum N&H Construction Method-Improved Vacuum Consolidation Method-Technical Data" pp. 1-12, 2013.4 Port and Harbor Giken Sample: Field Experiment of Vacuum Consolidation Method in Kinkai Bay No. 476 pp. 5-6, Mar. 1984 "Experimental study on consolidation of marine clays in alternating electric current field" Soils and Foundations Vol. 28. No. 4, pp. 38-46, Dec. 1988

The limit of the ground improvement depth by the vacuum consolidation method is about 10m with the position of the airtight sheet as the reference point. The pressure reduction under the airtight sheet by the air-water separation system at the actual site is about -70 to -80 kPa (gauge pressure). In other words, the effective utilization of the vacuum pressure to increase the outflow driving force of the interstitial water of the cohesive soil is about 70 to 80%. Problem 1 is to improve the pressure reduction under the airtight sheet to bring the utilization of the vacuum pressure closer to 100%.
A method of temporarily lowering the water retention capacity of clay, for example, a method of electrically disturbing clay, has a very large effect of promoting consolidation settlement. Problem 2 is to incorporate a method for temporarily lowering the water retention capacity of clay in the present invention as well. The ground improvement depth limit of 10m is when the inside of the vertical drain is filled with water. If the stagnant water inside the vertical drain can be replaced with air in some way, the 10m limit wall will disappear. For example, the improved depth is 20m and 30m. Problem 3 is a method of replacing stagnant water inside the vertical drain with air.

Problem 1 is to bring the utilization of vacuum pressure as close to 100% as possible. In the conventional vacuum consolidation method, a steam-water separation vacuum tank is installed in the airtight improved zone ground, air and water are collected in the steam-water separation vacuum tank via a vertical drain, and the water is discharged outside with a drainage device. It is vacuumed with a vacuum device. In this way, as the ground subsides, the steam-water separation vacuum tank also subsides, preventing an increase in the pump head of the vacuum pump. This is an important countermeasure. However, the air-water separation system alone cannot reduce the pressure to the high vacuum required by the construction method of the present invention. The main cause of this is water vapor pressure.
As we all know, water evaporates without boiling. In particular, water vapor is actively generated in a vacuum. When water turns into gas (steam), its volume increases dramatically. The generation of water vapor therefore acts as a large pressurization against the vacuum pressure. This effect is extremely large, and the steam separation system alone is completely insufficient, and it is necessary to solve the problem of water vapor pressure. The solution of the present invention is to incorporate a cold trap in the vacuum path of the vacuum consolidation system.
The vacuum path of the vacuum consolidation system of the present invention proceeds from a series connection of vacuum related devices to a network connection. The series-connected vacuum path starts from the vertical drain that sucks the pore water in the airtight improvement zone ground, passes through the air-water separation vacuum tank, and then connects the vacuum-related equipment in series in the order of the enhanced vacuum tank, the cold trap, and the vacuum pump. Connecting. After passing through the air-water separation vacuum tank, the network-connected vacuum path branches into multiple vacuum paths to connect vacuum devices in series. Get in touch and network.
The role of the air-water separation vacuum tank is to separate air and water, and the water is discharged to the outside through a drainage device installed here. The function of the cold trap is to cool the water vapor generated in the vertical drain and the vapor separation vacuum tank and collect it in the form of ice (frost). This allows the vacuum pump to perform at its maximum by not overloading the vacuum pump with water vapor. The enhanced vacuum tank has several times the volume of the steam separation vacuum tank. As for the role of this tank, a certain amount of vacuuming time is required to bring the vapor-water separation vacuum tank to a predetermined vacuum pressure. Therefore, the enhanced vacuum tank is evacuated prior to the vapor separation vacuum tank to ensure a predetermined vacuum pressure, and is used to quickly evacuate the vapor separation vacuum tank.
The intent of the network of boosted vacuum tanks is that the cold trap will trap water vapor as ice, requiring a step to melt the ice in preparation for the next run. In other words, it is necessary to have a vacuum path that is open to the steam-water separation vacuum tank for operation and a vacuum path that is closed to prepare for the next operation. Further, in securing the high vacuum pressure required by the construction method of the present invention, a plurality of vacuum paths of the vacuum apparatus can be operated simultaneously as required.
The vacuum consolidation method of the present invention proceeds to first, second and third stages. The first step of the vacuum consolidation method of the present invention is to bring the effective use of the reduced pressure under the airtight sheet to as close to 100% as possible. The vacuum consolidation system of the present invention in large scale soil improvement uses a networked vacuum path. The water vapor generated in the vacuum path is recovered by a cold trap to maximize the function of the vacuum pump, and the enhanced vacuum tank quickly secures a high vacuum pressure that does not exceed the limit vacuum pressure at which the current temperature of the interstitial water becomes the boiling point. This will shorten the consolidation time and increase the consolidation settlement.
The boiling point of water is 100° C. at 1 atmosphere (gauge pressure: 0.0 kPa). For example, if the temperature of the interstitial water is 13° C., 0.015 atm (gauge pressure: −99.8 kPa) at which the boiling point is 13° C. is the limit vacuum pressure at which the current temperature of the interstitial water becomes the boiling point. The vacuum pressure mentioned here is the pressure applied to the surface of the interstitial water of the clay, and is used synonymously with the external pressure.
A means for solving the problem 2, which greatly enhances the acceleration effect of consolidation settlement, uses a method of temporarily lowering the water retention capacity of the clay in addition to a method of increasing the outflow driving force of the interstitial water of the clay. The former is the first step of the vacuum consolidation method of the present invention. The latter boils the interstitial water by rapidly depressurizing it in an intensifying vacuum tank to a vacuum pressure at which the current temperature of the interstitial water of clay in the improved zone ground becomes the boiling point. (Precisely, it is part of the pore water and adsorbed water of the clay) In the actual process, the water retention capacity of the clay is temporarily lowered, and then the vacuum pressure is reduced to the limit at which the current temperature of the pore water becomes the boiling point. Implement a vacuum consolidation method with a high vacuum pressure that does not exceed
Boiling generates numerous air bubbles throughout the interstitial water and drastically reduces the water retention capacity of the clay. The generated bubbles turn into water vapor in a vacuum, and the volume of the air bubbles increases rapidly. If the pressurization of water vapor exceeds the decompression of the vacuum device, the vacuum pressure cannot maintain the boiling point and boiling stops. However, the boiling time required for the vacuum consolidation method may be several tens of seconds to several minutes. It takes at least several hours to restore the temporarily reduced water holding capacity of the clay. Consolidation progresses rapidly during this time. In other words, the vacuum device does not always need to maintain the vacuum pressure at which the temperature of the pore water pressure becomes the boiling point. Boiling more than necessary should be avoided because the water vapor pressure will reverse the vacuum pressure.
The vacuum consolidation method of the second stage of the present invention is in a state in which the problems 1 and 2 are solved. In other words, the vacuum pressure is rapidly reduced until the current temperature of the pore water reaches the boiling point, causing the pore water to boil. If so, the vacuum pressure should be set to a high vacuum pressure that does not exceed the limit vacuum pressure at which interstitial water boils, suppressing the evaporation of interstitial water. to significantly shorten the consolidation time and increase the consolidation settlement. Here, the ground improvement method using both vacuum boiling and vacuum consolidation is hereinafter referred to as "vacuum boiling consolidation method". In the second stage of the vacuum boiling consolidation method, if water remains in the vertical drain, the high vacuum pressure is not directly transmitted to the interstitial water of the clay, making it extremely difficult to boil the interstitial water.
A means for solving the problem 3 is a method of replacing interstitial water (hereinafter, stagnant water) stagnant inside the vertical drain with air. The vertical drain used in the vacuum consolidation method of the present invention consists of hollow hard perforated pipes of two types, large and small, which are covered with a filtering material and whose inner and outer diameters are exactly the same, a pull-out prevention device, a flexible pipe, and sinks in water under its own weight. Consists of buffer particles. By inserting two types of large and small hollow rigid perforated pipes (drain) alternately, attaching devices to prevent the drain from coming out, and connecting them in sequence, a drain body that shrinks following land subsidence is formed, and the tip of the drain body is formed. is attached with a flexible tube that connects to a pneumatic tube that connects to the compressor, and the drain body contains cushioning particles that are limited to movement inside it. Here, the pull-out prevention device is a device that connects two kinds of large and small hollow rigid perforated pipes with a wire rod of a certain length so that they do not slip out. Also, the reason why the pipe for sending compressed air attached to the tip along the drain body is a flexible pipe is that this pipe also needs to follow the ground subsidence.
The method of removing stagnant water inside the vertical drain is to send the stagnant water to the air-water separation airtight tank by blowing stagnant water together with buffer particles from the tip of the vertical drain to the top with compressed air, and replacing the stagnant water with air. . As a result, the vacuum consolidation method of the present invention greatly expands the ground improvement depth. Further, in the method for placing a vertical drain in the vacuum consolidation method of the present invention, the tip of the drain is gripped by a drain placing machine and placed. Therefore, the vertical drain at the end of casting is in a fully extended state.
Here, the role of the buffer particles is to act as a buffer layer in which the compressed air pushes up the stagnant water together. When the stagnant water is jetted to the top of the vertical drain, the compressed air penetrates the stagnant water without the buffer particles, leaving more than half of the stagnant water. Therefore, the buffer particles must be deposited on the tip of the drain by their own weight when the stagnant water is blown up. It is not convenient for the buffer particles to be too heavy, and a suitable specific gravity is about 1.3 to 1.5. Also, the thickness of the buffer layer is suitably about 5 to 10 times the inner diameter of the vertical drain pipe. Moreover, the need for the buffer particles to be particles is due to the fact that the vertical drain of the present invention has hollow rigid perforated tubes with different inner diameters that are alternately connected. In addition, vertical drains may bend slightly due to land subsidence. If the buffer layer were replaced by a single draining piston, submersion failure would occur.
In the third step, the vacuum consolidation method of the present invention, the stagnant water inside the vertical drain is replaced with air to expand the ground improvement depth, and the synergistic effect of vacuum boiling and vacuum consolidation greatly shortens the consolidation time and consolidates. This is a vacuum consolidation method to increase subsidence. Stagnant water in the vertical drain makes it extremely difficult to deliver the high vacuum pressure that boils the pore water. Therefore, the vacuum consolidation method of the third stage is used in combination with the vacuum consolidation method of the second stage and the method of replacing the stagnant water inside the vertical drain with air.
The third step, the vacuum consolidation method of the present invention, uses the vertical drain and network vacuum path vacuum consolidation system described above. In the vacuum consolidation method, when the consolidation speed decreases, the vacuum path on the downstream side (vacuum pump side) of the steam separation vacuum tank is closed, the compressed air discharge pipe and flexible pipe are opened, and the compressed air is sent to the vertical drain. By blowing up the remaining pore water together with the buffer particles from the tip of the vertical drain to the top, the pore water is sent to the air-water separation vacuum tank. After replacing the stagnant pore water with air, close the compressed air discharge pipe and flexible pipe, open the vacuum path downstream of the air-water separation vacuum tank, and increase the vacuum pressure until the current temperature of the pore water reaches the boiling point. The interstitial water is boiled by reducing the pressure at once in the enhanced vacuum tank. If the water retention capacity of the cohesive soil is temporarily reduced by the action of countless air bubbles generated in the pore water, the vacuum pressure is increased to a high vacuum pressure that does not exceed the limit vacuum pressure at which the pore water boils. The process of suppressing evaporation and maintaining it stably is repeated intermittently.
The boiling time required for the vacuum consolidation method may be several tens of seconds to several minutes. It takes at least several hours to restore the temporarily reduced water holding capacity of the clay. At the time when the residual water inside the vertical drain is replaced with air, the steam-water separation vacuum tank is in a state of normal pressure. For this reason, the enhanced vacuum tank in the network vacuum path secures a high vacuum pressure at which the current temperature of the interstitial water becomes the boiling point in advance, and quickly decompresses the vertical drain and the steam-water separation vacuum tank to a predetermined high vacuum pressure. do.
The vacuum consolidation system of the vacuum consolidation method of the present invention does not limit the improved zone ground and the method of making this ground airtight. For example, in the vacuum consolidation dredging method for seabed ground using an airtight loading box with a bottom opening, a vacuum consolidation system with a network vacuum path is applied to the consolidation process of this method. However, seafloor vacuum consolidation is loaded with water pressure in addition to atmospheric pressure. Therefore, when the water depth is large in the vacuum consolidation dredging method, it is difficult to quickly boil the pore water because a large excess pore water pressure is generated in the cohesive soil. In this case, it is preferable to use a vacuum consolidation method using a high vacuum pressure that does not exceed the critical vacuum pressure at which the current temperature of the interstitial water becomes the boiling point.
The vacuum consolidation dredging method for submarine ground, etc. is consolidation by rapidly and stably sustaining a maximum vacuum pressure that does not exceed a predetermined vacuum pressure (vacuum pressure that boils pore water) by mutual backup of each vacuum device. Aim to shorten the time and increase the consolidation settlement. The vacuum consolidation dredging method uses the vacuum consolidation system of the present invention to consolidate the seabed ground, etc. to a strength that enables dredging in an extremely short period of time, and to suppress the generation of dredged soil by increasing consolidation settlement. can be made larger.

In the ground improvement method using vacuum pressure, the decompression to high vacuum is greatly affected by the pressurization action of water vapor generated in the vertical drain and the steam-water separation vacuum tank. Therefore, in the vacuum consolidation system of the present invention, an enhanced vacuum tank and a cold trap are added in this order in the middle of the vacuum path from the steam separation vacuum tank to the vacuum pump. Furthermore, by providing a plurality of such vacuum paths as a network path, it is easy to secure a high vacuum pressure, and compared to the conventional vacuum consolidation method, the effect of increasing the effective utilization of the vacuum pressure by about 20 to 30%. brought
In addition, by replacing the pore water (accumulated water) in the viscous ground that has accumulated in the vertical drain with air, it has the effect of greatly expanding the limit depth of 10 m for ground improvement by the vacuum consolidation method. (e.g. 30m) Furthermore, by removing stagnant water in the vertical drain, the high vacuum pressure that boils the interstitial water can be transmitted directly to the cohesive soil. It brought about the effect of realization of vacuum consolidation method for shortening and increasing consolidation settlement.

FIG. 1 is a vertical sectional view showing an example of implementation of the vacuum consolidation method of the present invention.
FIG. 2 is a vertical sectional view of the steam-water separation vacuum tank.
FIG. 3 is a vertical sectional view of a vertical drain.
FIG. 4 is an explanatory diagram showing an example of the vacuum consolidation system of the present invention.
FIG. 5 is a front view of an exemplary vacuum consolidation dredger.
FIG. 6 is a front view of the dredger with the airtight loading box installed on the seabed.

An embodiment of the present invention will be described below with reference to FIGS. 1 to 6. FIG.
FIG. 1 is a schematic vertical sectional view showing an example of implementation of a vacuum consolidation method for land soft ground according to the method of the present invention. In the figure, 1 is an airtight sheet, 7 is soft ground, and the ground surface of the improved area of the soft ground 7 is covered with the airtight sheet 1 to make it airtight. 2 is a vertical drain, 3a is a vacuum line, 3b is a pneumatic line, and 4a is a steam-water separation vacuum tank. The steam-water separation vacuum tank 4a is installed outside the improvement area. For this reason, although not shown, flexible joints are attached to the vacuum line 3a and air pressure line 3b to prevent uneven subsidence.
FIG. 2 is a vertical sectional view of the steam-water separation vacuum tank 4a. In the figure, 3c is a compressed air discharge pipe, and 3d is a drain pipe. Interstitial water and air in the soft ground 7 pass through the vertical drain 2 and the vacuum pipe line 3a, are collected in the air-water separation vacuum tank 4a, and are separated into air and water. Water is discharged outside by a drainage device 4e (drainage pump).
FIG. 3 is a vertical sectional view of the vertical drain 2. FIG. (a) of the figure is an upper portion of the vertical drain 2, and (b) is a vertical sectional view of the lower portion. In the figure, the structure of the vertical drain 2 used in the construction method of the present invention consists of a drain body 2a, a drain pull-out preventing device 2b, a compressed air flexible tube 2c, and cushioning particles 2d. 2a1 is a large-diameter drain of the drain body 2a, and 2a2 is a small-diameter drain. Two types of drains are alternately inserted into the drain body 2a, attached with a pull-out preventing device 2b, and sequentially connected to form a vertical drain 2 having a function of contracting following land subsidence. A soft flexible tube 2c is connected to the tip of the drain body 2a. The pore water remaining inside the vertical drain 2 is removed by blowing compressed air from the tip of the drain to remove the pore water together with the buffer particles 2d into the air-water separation vacuum tank 4a, and the remaining pore water is released into the air. replace. Here, the device 2b for preventing the drain from falling out shown in the figure is of a type in which a wire rope prevents the drain from being pulled out more than a certain amount.
FIG. 4 is a schematic illustration of an example of a vacuum consolidation system in the construction method of the present invention. The system is divided into a vacuum system (vacuum line 3a) and a pressure system (air pressure line 3b). The vacuum line 3a shown in FIG. 4 is an example branched into two after passing through the steam-water separation vacuum tank 4a from the vertical drain 2. As shown in FIG. The two branched vacuum lines 3a connect an enhanced vacuum tank 4b, a cold trap 4c, and a vacuum pump 4d in series. Form a network of tanks 4b. A compressor 4f in FIG.
FIG. 5 is a front view of an example of a vacuum consolidation dredger, and FIG. 6 is a front view of the same vacuum consolidation dredger with an airtight loading box installed on the seabed. In the figure, 5 is a vacuum consolidation dredger, 5a is a barge, 5b is a barge connecting gate beam, and 5c is a tower guide. 6 is a tower-type airtight loading box, 6a is an airtight loading box, 6b is a box tower, and 6c is an air-water separation airtight tank. 8 is the sea surface, and 9 is the seabed ground (marine soil). Incidentally, the air-water separation airtight tank 6c of the vacuum consolidation dredger 5 is called an airtight tank rather than a vacuum tank because it may be in a pressurized state as well as in a vacuum state. In addition, in the consolidation process of the vacuum consolidation dredging method for seabed ground (seabed soil), etc., a vacuum consolidation method with high vacuum pressure that does not exceed the limit vacuum pressure at which the current temperature of pore water becomes the boiling point is used.

1 Airtight sheet 2 Vertical drain 2a Drain main body 2b Drain extraction prevention device 2c Flexible tube for compressed air 2d Buffer particles 3a Vacuum conduit 3b Air pressure conduit 4a Air-water separation vacuum tank 4b Enhanced vacuum tank 4c Cold trap 4d Vacuum pump 5 Vacuum consolidation Dredger 6 Tower-type airtight loading box 7 Soft ground 9 Seabed ground (marine soil)

Claims (7)

In the vacuum consolidation method, the vacuum related equipment of the vacuum consolidation system of the method is installed in the order of the enhanced vacuum tank and the cold trap between the steam separation vacuum tank and the vacuum pump, and the water vapor generated in the vacuum path is the cold trap. By recovering the water, the vacuum pump functions to the maximum, and the enhanced vacuum tank quickly secures a high vacuum pressure that does not exceed the limit vacuum pressure at which the current temperature of the pore water becomes the boiling point, shortening the consolidation time and consolidation settlement. A vacuum consolidation method characterized by increasing the In the vacuum consolidation method, the vacuum related equipment of the vacuum consolidation system of the method is installed in the order of the enhanced vacuum tank and the cold trap between the steam separation vacuum tank and the vacuum pump, and the water vapor generated in the vacuum path is the cold trap. By recovering, the vacuum pump functions to the maximum, and the vacuum pressure is increased until the current temperature of the interstitial water reaches the boiling point. If the water retention capacity of the cohesive soil is temporarily reduced by the action of the A vacuum consolidation method characterized by a synergistic effect of reduced pressure boiling and vacuum consolidation to significantly shorten the consolidation time and increase the consolidation settlement. In the vertical drain used in the vacuum consolidation method, the vertical drain is covered with a filter material and consists of two types of large and small hollow rigid perforated pipes with matching inner and outer diameters, pull-out prevention devices, flexible pipes, and water under its own weight. It consists of sedimenting buffer particles, and two types of large and small hollow rigid perforated tubes are alternately inserted, attached with a pull-out prevention device, and connected in sequence to form a drain body that shrinks with the ground subsidence. A vertical drain with a flexible tube attached to the tip that connects to a pressure tube connected to a compressor, and a drain body containing cushioning particles that restrict movement inside the tube. In the vacuum consolidation method of claims 1 and 2, the vacuum path of the vacuum consolidation system of the method is branched into a plurality of vacuum paths after passing through a steam-water separation vacuum tank from a drain for sucking pore water from the improvement area ground. The enhanced vacuum tank, cold trap, and vacuum pump are connected in series, and the vacuum paths are connected so that the enhanced vacuum tanks of each branched vacuum path are parallel to form a network, and a predetermined vacuum pressure is achieved. A vacuum consolidation method characterized by rapid and stable maintenance through mutual backup of each reinforced vacuum tank. In the vacuum consolidation method using a vertical drain according to claim 3, the method for removing the interstitial water that has accumulated inside the vertical drain is to blow up the interstitial water together with the buffer particles from the tip of the drain to the top of the drain with compressed air. A vacuum consolidation method characterized by sending water to a steam-water separation vacuum tank and replacing stagnant pore water with air to greatly expand the ground improvement depth. In the vacuum consolidation method of claim 2 using the vertical drain of claim 3, if the consolidation speed decreases, the vacuum path downstream of the steam-water separation vacuum tank is closed and the compressed air discharge pipe and flexible pipe are opened. If compressed air is used to blow up the pore water remaining in the vertical drain together with the buffer particles from the tip of the vertical drain to the top, the pore water is sent to the air-water separation vacuum tank, and the retained pore water is replaced with air. For example, by closing the compressed air discharge pipe and flexible pipe, opening the vacuum path on the downstream side of the air-water separation vacuum tank, and quickly reducing the vacuum pressure with the boosting vacuum tank until the current temperature of the pore water reaches the boiling point. If the pore water is boiled and the water retention capacity of the cohesive soil is temporarily reduced by the action of countless bubbles generated in the pore water, the vacuum pressure does not exceed the limit vacuum pressure at which the pore water boils. By intermittently repeating the process of maintaining the pressure to suppress the evaporation of pore water and stably maintaining this, the depth of ground improvement can be expanded and the consolidation time can be shortened by the synergistic effect of boiling under reduced pressure and vacuum consolidation. The vacuum consolidation method is characterized by a significant shortening and an increase in consolidation settlement. In the vacuum consolidation dredging method for seabed soil etc. using the airtight loading box with the bottom opening by the vacuum consolidation system according to claim 4, a predetermined high vacuum pressure is quickly and stably provided by mutual backup of the network of each vacuum related device. In order to significantly shorten the consolidation time and increase the consolidation settlement, the airtight loading box with the bottom opening consolidates the seabed soil, etc. to a strength that can be dredged in an extremely short time, and further increases the consolidation settlement. A vacuum consolidation dredging method characterized by greatly suppressing the generation of dredged soil by

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