JPS6250510A - Ground liquefaction prevention method - Google Patents

Abstract

PURPOSE:To prevent the liquefaction of sandy ground where the level of groundwater is high by a method in which the fine powder of an inorganic substance is moved together with groundwater flowing from a charge well to a pump-up well point and allowed to deposit on sandy ground of the water path. CONSTITUTION:A sheet pile 2 is driven into sandy ground 1 where the level of groundwater is high, a charge well 3 is provided in the central part, and a plurality of pump-up well points 4 are provided in the peripheral sides. Groundwater 9 is sucked up by the pumps 5 of the well points 4 and allowed to flow to the direction of the well points 4 to produce a difference in the groundwater level 6 along the direction from the well 3 to the well points 4. In this case, when particles 10 of an inorganic substance such as silica stone or kaolin are dispersed into the well 3 in a suspended state, the suspension diffuses into the groundwater 9 around the well 3 and moves with the groundwater 9 to the direction of the well points 4. The particles 10 are settled on the gaps of sand grains 8.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a construction method for preventing liquefaction of the ground by improving loose sandy ground with a high groundwater level that may cause liquefaction during an earthquake.

Conventional technology When sandy ground with a high groundwater level is subjected to vibrations caused by an earthquake, the sandy ground is destroyed and liquefied, causing severe damage to the buildings on it.

As a means to prevent this liquefaction, ground improvement methods such as vibration compaction, injection of solidifying materials, gravel drain construction methods, and dynamic consolidation methods have been used. However, these conventional construction methods cannot improve the ground on which existing structures are built.

OBJECT OF THE INVENTION This invention has been made in view of the above circumstances. The purpose of this study is to propose a ground liquefaction prevention method that can prevent liquefaction by improving the ground without affecting the structure in any way, even on the ground where structures have already been built.

Structure and Embodiments of the Invention This ground liquefaction prevention construction method includes providing a charge well in loose sandy ground with a high groundwater level and a pumping well point separated from the charge well by a predetermined distance, and moving from the charge well in the direction of the pumping well point. A water gradient is formed and inorganic particles are dispersed in a charge well without being suspended.
It is characterized by moving inorganic particles along with the groundwater flowing from the charge well toward the pumping well point and depositing them in the sandy ground along the water flow path, replacing the groundwater in the ground with the inorganic particles.

FIG. 1 shows an example of an embodiment of this construction method. In this construction method, sheet piles 2 are driven into sandy ground 1 with a high groundwater level that is at risk of liquefaction, enclosing the surface to be improved, and a charge well 3 is installed in the center and multiple pumping well points 4 are installed in the periphery. .

Groundwater is sucked up by the pump 5 of the pumping well point 4, and the groundwater flows in the direction of the pumping well point 4, thereby forming a hydraulic gradient, that is, a difference in groundwater level 6, along the direction of the pumping well point 4 from the charge well 3. In addition, 7 in the drawing
This is a silty clay stratum with no risk of liquefaction.

In this method, inorganic particles are dispersed in a suspended state in the charge well 3 configured as described above. This suspension is diffused into the surrounding groundwater of the charge well 6,
It moves along with groundwater in the 4-way direction of the well point. During this movement process, the suspended inorganic fine particles gradually settle and are deposited in the sandy ground along the movement route.

In other words, the area around the loose sand particles 8 in Fig. 2 is filled with moving groundwater 9, and the fine particles 1° of inorganic substances in a suspended state dispersed in this groundwater gradually settle down to form the particles 8 in Fig. 3. As shown, it is deposited in the gaps between the sand particles 8. The groundwater 9 around the sand particles 8 is replaced by the deposited inorganic fine particles 10.

As a result, the ground is formed with little water, densely packed with sand particles and fine inorganic particles, and free from the risk of liquefaction.

Inorganic substances include sandstone (main component 5iO2), kaolin,
Diatomaceous earth (main component AjzOs・SiO2・2H20
), barite (main components: BaSO, talc, and other minerals that are insoluble in water are used. This is crushed into ultrafine particles and used. It varies depending on the particle density, diameter, affinity with water, etc.) Usually, a surfactant or a protective colloid such as a water-soluble polymer is used to create a suspension.

The sedimentation property of fine particles of inorganic substances in a suspended state is influenced by the density of the fine particles, the particle size, the nature of the particle interface, etc. Actual sedimentation in the ground depends on the properties of the suspended solids themselves, as well as
It is controlled by conditions such as groundwater flow velocity, sand particle size, pore size, groundwater movement distance, and hydraulic gradient.

In other words, based on the properties of the ground to be improved and conditions such as the distance between both wells, pumping speed, hydraulic gradient, etc., the suspended state of fine particles is adjusted so that the fine particles gradually settle in the ground between both wells. must be adjusted. Alternatively, on the contrary, construction conditions such as the distance between both wells, pumping speed, hydraulic gradient, etc. may be set so that fine particles in a predetermined suspended state are deposited in a desired state.

For example, if a colloidal solution containing suspended ultrafine particles of sandstone is added and dispersed in a charge well, if the water permeability of the sandy ground is about I Set the distance between points to 20~30r
When the water level difference between the rL1 wells is set to 6 to 5 rIL, ultrafine particles of sandstone can be deposited in the sandy ground between the wells and can be mixed with groundwater.

In order to create this level of water level difference, the water level can be lowered by pumping at the pumping well point for about half a day once a week (if there is no rain). Furthermore, since the water does not move inside the charge well, suspended fine particles will settle, so it is necessary to stir them with an air blower or the like to prevent settling.

If construction is carried out under these conditions, the period required for ground improvement will be approximately several months to one year.

As shown in Fig. 4, if there is a building 11 in the center of the ground 1 to be improved, this construction method uses, for example, the required number of charge wells 3 on one edge of the ground, and the required number of charge wells 3 on the opposite side of the ground across the building 11. Construction can be carried out by installing several pumping well points 4 and forming a hydraulic gradient between both wells. The suspended inorganic particles dispersed in the charge well 6 move in the direction of the pumping well point 4 together with groundwater.
It is possible to improve the ground under the building 11 by depositing it in the ground between them.

Effect of the invention This invention is as described above, and brings about the following effects.

■ In order to slowly and gradually fill the voids filled with groundwater in loose sand with fine particles of inorganic substances, e.g.
Liquefaction countermeasures can be taken while using above-ground structures in buildings with pile foundations, factories with jumbled equipment and piping, etc.

■ There is no need for large machinery as there is no vibration or solidification.

[Brief explanation of drawings]

Figure 1 is a vertical cross-sectional view of a sandy ground showing an example of this construction method, Figures 2 and 3 are vertical cross-sectional views of loose sand particles constituting the ground and fine particles deposited between the loose sand particles, respectively. The figure is a plan view showing an example of construction when improving the ground on which a building is located. 1. Sand ground, 2. Sheet pile, 3. Cheeji well, 4. Pumping well point, 5. Pumping pump, 6
・・Groundwater level, 7.・Milled clay stratum, 8.・Sand particles,
9. Groundwater, 10. Inorganic particles, 11. Buildings.

Claims (1)

[Claims] (1) A charge well and a pumping well point are provided at a predetermined distance from the charge well on loose sandy ground with a high groundwater level, a hydraulic gradient is formed from the charge well to the pumping well point, and inorganic materials are placed in the charge well. The fine particles are dispersed in a suspended state, and the fine inorganic powder is moved along with the groundwater flowing from the charge well toward the well point, and is deposited in the sandy ground along the water flow path. A method for preventing ground liquefaction, which is characterized by replacing the soil with soil.