JP5261839B2 - Method for preventing decay of wooden piles by capillary head - Google Patents

Description

  The present invention relates to a method for preventing decay of a wooden pile by a capillary head, and more specifically, the upper end of the wooden pile is prevented from coming out above the capillary water that has risen from the groundwater surface of the ground through the soil gap. The present invention relates to a method for preventing decay of wooden piles.

  Ground measures will be taken to strengthen the soft ground by placing wooden piles in the ground. In that case, the decay and insect damage of the wooden piles will be a problem. Based on the investigation of excavation of wooden piles of existing structures, the wooden piles in the ground will not decay or damage if they are in the groundwater. Therefore, for example, the Building Standards Act construction order states, “When using a wooden pile as the foundation of a building, the wooden pile should be under normal water unless it is used for a one-story wooden building. Must be made. " In the case where a wooden pile driven into the ground comes out from the groundwater surface, generally, an anti-corruption measure by a chemical is performed on the upper part of the wooden pile. In general, the chemical treatment is not limited to the upper part of the wooden pile, and is often performed over the entire length of the wooden pile, resulting in high costs. In addition, since the insect damage does not occur if the wooden pile is under the groundwater surface, the method for preventing decay includes a method for preventing insect damage here.

  The prevention of the decay of the wooden pile of Patent Document 1 is to form a covering portion of the air barrier layer in a portion from the lower position to the upper end of the bottom water surface fluctuation region of the wooden pile. The wooden pile is placed so that, for example, a portion that goes above the groundwater surface becomes an air barrier layer. However, it may take time to cover the corresponding part of the wooden pile so as to be an air barrier layer, including checking whether the covered wooden pile is not scratched or broken.

JP 2008-223379 A

  An object of the present invention is to provide a method for preventing decay of a wooden pile by means of a capillary head, which can prevent the decay of the portion protruding from the groundwater surface without chemical treatment of the wooden pile. Here, the “groundwater surface” is defined as a surface where the groundwater comes into contact with the air that appears in the hole or in the pipe when a hole is formed in the ground by boring or when a pipe is inserted into the hole.

  The method for preventing decay of a wooden pile by capillary head according to the present invention is a method for preventing decay of a wooden pile placed on soft ground, where the height (Δh) from the groundwater surface to the top of the wooden pile is The wooden pile is provided on the soft ground so that the volumetric water content of the soil occupying up to the upper end of the pile is smaller than the height (ψcr) of the capillary head in the saturated state (Δh <ψcr).

  The soil is of natural ground, measuring the depth (Δp) to the groundwater surface of the soft ground and the height of the capillary head (ψcr) when the volumetric water content of the soil is saturated; A step of placing the wooden pile until the height (Δh) from the groundwater surface to the upper end of the wooden pile is smaller than the height (ψcr) (Δh <ψcr), and a step of stacking the embankment thereafter. It is characterized by that.

  The soil is a backfill soil having a capillary head height (ψcr) with a saturated volumetric water content, digging the soft ground until the groundwater surface appears on the ground surface dug down, and a wooden pile from the groundwater surface. Placing a wooden pile until the height (Δh) to the upper end is smaller than the height (ψcr) (Δh <ψcr), and refilling the backfilled soil surface. Are provided.

  The soil is an embankment having a capillary head height (ψcr) with a saturated volumetric water content, and projects from the ground surface to a soft ground having a groundwater surface at a depth (Δp) from the ground surface. The stage where the wooden pile is placed, the stage where the capillary head with the volumetric moisture content is saturated is piled up on the ground surface where the wooden pile is placed, and the piled pile. Due to its own weight, the lower surface of the embankment sinks until the depth (Δp) exceeds the depth (Δp), and the upper end of the wooden pile is pushed down so that the height (Δh) of the upper end of the wooden pile from the groundwater surface is smaller than the height (ψcr). Are provided.

  According to the present invention, the method for preventing decay of a wooden pile by a capillary head is a capillary head in which the height (Δh) from the ground water surface to the top of the wooden pile is saturated with the volumetric water content of the soil occupying from the ground water surface to the top of the wooden pile. Since the wooden pile is provided on the soft ground so that it is smaller than the height of (φcr) (Δcr <φcr), the wooden pile will not be exposed to the air and will not decay in the same way as below the surface of the water. it can.

  Claim 2 is applied when the soil around the wooden pile is natural ground. In advance, the depth to the groundwater surface (Δp) of the soft ground and the height of the capillary head (ψcr) when the volumetric water content of the soil is saturated are measured. When placing a wooden pile on soft ground, the height (Δh) from the groundwater surface to the upper end of the wooden pile is placed so as to be smaller than the capillary head height (ψcr) from the groundwater surface. Filling fills the hole up to the ground surface and prevents the top of the wooden pile from coming into contact with air. According to this, since the upper part of the wooden pile is above the ground water surface but below the capillary head height, it is not exposed to air and can be prevented from decaying as it is under the water surface. The wooden stakes are not placed until they are below the groundwater surface, which saves energy. In addition, it is not necessary to apply chemicals to the wooden pile or an air barrier layer, and it is possible to reduce the cost and the risk of environmental pollution.

  Claim 3 is applied when the soil around the wooden pile is backfilled soil. The soft ground is dug in advance until the groundwater surface comes out. The wooden pile is driven so that the upper end of the wooden pile protrudes by a height (Δh) from the ground surface dug down. Since the projected height (Δh) is made smaller than the height of the capillary head (ψcr), after backfilling, water rises between the backfilled soil in contact with the groundwater surface due to capillary action, Over the top. For this reason, the wooden pile is not exposed to the air and can be prevented from decaying as it is under the water. As the backfilling soil, a soil whose capillary head height (ψcr) is known is used. For example, fine sand has a capillary water head height (ψcr) of 35 to 70 cm when the volumetric water content is saturated, so that it is not necessary to apply a chemical to this portion and an air blocking layer, so that the cost can be reduced. There is no risk of environmental pollution.

  Claim 4 is applied when the soil around the wooden pile is embankment. The ground is intended for soft ground where the bottom of the embankment sinks and reaches the groundwater surface. The wooden pile is placed so as to protrude from the ground surface, and then pushed down by the settlement of the embankment. In this case, the height (Δh) from the groundwater surface at the upper end of the pushed down wooden pile is made smaller than the height of the capillary head of the embankment (ψcr), so that the wooden pile is not exposed to the air. You can prevent it from decaying. That is, for the embankment, soil having a known capillary head height (ψcr) is used. According to this, it is not necessary to dig down the soft ground until the groundwater surface comes out. If the height (Δh) from the groundwater surface at the top of the wooden pile is smaller than the height of the capillary head of the embankment (ψcr), the water rises through the gap of the embankment in contact with the groundwater surface by capillary action, and the top of the wooden pile is As it crosses, the wooden stakes are not exposed to the air and can be prevented from decaying as underwater.

  Since the capillary head is used, the following effects are also expected. In coarse sand, the height of the capillary head (ψcr) in the saturated state is small, and in fine sand, the height of the capillary head (ψcr) in the saturated state is large. Therefore, the capillary head height (ψcr) in the saturated state can be increased if the gap is narrowed by tamping even rough sand. In the saturated state, the higher the capillary head height (ψcr), the lower the water permeability. Although the groundwater surface changes every day, if the water permeability is low, it takes time to change the groundwater. Therefore, the followability of the groundwater variation becomes extremely slow, and the fluctuation range of the groundwater surface becomes small. For this reason, the lower limit of the groundwater surface fluctuation region will be raised. That is, it is possible to increase the lower limit value of the groundwater surface fluctuation region by increasing the height of the capillary head (ψcr) in the saturated state.

It is the example which applied the decay prevention method of the wooden pile by the capillary head by this invention when the soil around a wooden pile is natural ground. It is the example which applied the decay prevention method of the wooden pile by the capillary head by this invention when the soil around a wooden pile is a backfill soil. It is the example which applied the decay prevention method of the wooden pile by the capillary head by this invention when the soil around a wooden pile is embankment. It is a graph which shows the moisture characteristic curve of a general soil. It is a table | surface which shows the height ((psi) cr) of a typical soil capillary head.

  Hereinafter, a method for preventing decay of a wooden pile by a capillary head will be described with reference to the drawings.

  FIG. 1 shows a first embodiment of the present invention in which a method for preventing decay of a wooden pile by a capillary head is applied when the soil around the wooden pile is natural ground. The ground improvement work is performed by placing the wooden pile 2 on the soft ground 4. (A) shows the step of measuring the depth (Δp) from the groundwater surface W to the ground surface F of the soft ground 4 in advance. The depth (Δp) of groundwater can be measured, for example, by ground boring. Further, the soil from the groundwater surface W to the ground surface F is analyzed, and the height of the capillary head (ψcr) when the volumetric water content is saturated. This can be obtained by collecting undisturbed soil using a cylindrical container, etc., and measuring how far the water rises by bringing the bottom of the container into contact with the free water surface. (B) shows the stage where the wooden pile 2 is placed. The wooden pile 2 is placed until the height (Δh) from the groundwater surface W becomes smaller than the height of the capillary head (φcr) when the volumetric water content is saturated. (C) shows the stage where the embankment is piled up. When the subsidence amount ΔS due to embankment is known, the height (Δh) from the groundwater surface W may be obtained by subtracting ΔS from the height (Δh) from the groundwater surface W. The embankment is a structure most suitable for this method, and of course, other structures may be used.

  As shown in FIG. 1, the soil around the wooden pile 2 is natural ground. When the upper end of the wooden pile 2 is driven to the height (Δh) from the groundwater surface W, the height of the capillary head (ψcr) is larger than the height (Δh) from the groundwater surface W. Over the top of the wooden pile 2. Therefore, even if the wooden pile 2 protrudes above the groundwater surface W, it does not decay. Here, Δh is a distance L between the ground surface and the upper surface of the wooden pile. Since Δh = Δp−L, Δp−L obtained by substituting Δp−L for the left side in order to satisfy Δh <ψcr. From the relationship of L <ψcr, the wooden pile may be placed on the soft ground so that Δp−ψcr <L.

  FIG. 2 is an example in which the method for preventing decay of a wooden pile by a capillary head is applied in the second embodiment according to the present invention when the soil around the wooden pile is backfilled soil. The ground improvement work is performed by placing the wooden pile 2 on the soft ground 4. (A) shows the step of digging the ground surface F in advance. The ground surface F is dug down, and the groundwater surface W is shown on the ground surface F. (B) shows the stage where the wooden pile 2 is placed. The wooden pile 2 is placed so that the upper end protrudes from the ground surface F dug down, that is, the groundwater surface W by a height (Δh). (C) shows the stage where the ground surface dug down is backfilled with backfill. The periphery of the upper part of the wooden pile 2 becomes the backfill soil 5. In the backfill 5, the height of the capillary head (ψcr) when the volumetric water content is saturated has a larger value than the height (Δh) of the wooden pile 2 from the groundwater surface W, and therefore Δh <ψcr. be able to.

  It is desirable to know in advance the height of the capillary head (ψcr) when the volumetric water content of the backfill soil 5 is saturated. In the backfilled state, the groundwater on the lower surface of the backfill soil 5 rises by capillary action and exceeds the upper end of the wooden pile 2. Therefore, even if the wooden pile 2 protrudes above the groundwater surface W, it does not decay. The reason why the volumetric water content of the backfill soil 5 is used in a saturated state is that wood does not decay when the soil does not contain air. If the backfill soil 5 is not mixed with impurities such as oil, the backfill soil 5 is in contact with the groundwater surface W, so that the volumetric water content can be saturated.

  FIG. 3 is a third embodiment of the present invention, which is an example in which a method for preventing decay of a wooden pile by a capillary head is applied when the soil around the wooden pile is embankment. The ground improvement work is performed by placing the wooden pile 2 on the soft ground 4. The soft ground 4 is a ground where subsidence occurs due to the embankment 1. (A) shows the step of measuring the depth (Δp) from the groundwater surface W to the ground surface F of the soft ground 4 in advance. (B) shows a stage where the wooden pile 2 is placed on the soft ground 4. The wooden pile 2 is driven until it reaches a state protruding from the ground surface F by a height (Δt). (C) shows the stage where the embankment 1 is piled up on the ground surface F which laid the wooden pile. The embankment 1 is assumed to have a capillary head height (ψcr) when the volumetric water content is saturated. It is assumed that the embankment 1 and the wooden pile 2 sink due to the weight of the accumulated embankment 1. Here, the bank 1 sinks until the lower surface of the embankment 1 exceeds the depth (Δp), and the wooden pile 2 is also pushed down. Thereby, the wooden pile 2 protrudes from the groundwater surface by the height (Δh). Since the lower surface of the embankment 1 exceeds the depth (Δp) and sinks to the depth (ΔS) here, the groundwater rises through the gap of the embankment 1 by capillary action and reaches the height of the capillary head (ψcr). Filled with capillary water. The protruding height (Δh) of the wooden pile 2 is smaller than the height (ψcr), and thus exceeds the upper end of the wooden pile 2. Therefore, even if the wooden pile 2 protrudes above the groundwater surface W, it does not decay.

  As shown in FIG. 3, for example, it is assumed that the lower surfaces of the wooden pile 2 and the embankment 1 are sunk by a depth (Δp). In that case, the height (Δh) of the wooden pile 2 after subsidence from the groundwater surface W is equal to the height (Δt) from the ground surface F before subsidence of the wooden pile 2. Therefore, the height (Δt) is set to a value smaller than the capillary head height (ψcr). Of course, if the wooden pile 2 is submerged more than the height (Δt + Δp) from the groundwater surface W before subsidence, the upper end of the wooden pile 2 falls below the groundwater surface W and sinks into the groundwater surface. According to the method of FIG. 3, the decay of the wooden pile 2 can be prevented without causing the embankment 1 and the wooden pile 2 to sink to that extent.

  FIG. 4 is a graph showing a general soil moisture characteristic curve. The horizontal axis represents the volumetric water content (θ) of the soil, and the vertical axis (left side) represents the height of the capillary head. The height of the capillary head decreases downward as shown by the θ-ψ curve. That is, when the volumetric water content (θ) is low, water greatly increases due to capillary action, and in a saturated state where the volumetric water content (θ) is 1, it falls to the height indicated by the capillary head height (ψcr). When the volumetric water content (θ) is low, it indicates that air is contained in the soil gap.

  FIG. 5 is a table showing typical soil capillary head heights (ψcr). The height of the capillary head (ψcr) when the volumetric water content is saturated is 2 to 5 cm for coarse sand, 12 to 35 cm for medium sand, 35 to 70 cm for fine sand, 70 to 150 cm for silt, and 200 to 200 for viscous soil. 400 cm. The height (ψcr) is higher as the soil grain is finer and the density is higher. Here, the condition of Δh <ψcr is used in which the height (Δh) of the wooden pile 2 from the groundwater surface W is smaller than the height of the capillary head (ψcr) when the volumetric water content is saturated.

  The method for preventing decay of a wooden pile by a capillary head according to the present invention utilizes soil water retention, and is suitable for improvement work on soft ground where safety to the environment and durability of functions are required.

1 Filling 2 Wooden pile 4 Soft ground (natural ground)
5 Backfill soil T Capillary head height F Ground surface W Groundwater surface

Claims (4)

A method for preventing decay of wooden piles placed on soft ground,
The height (Δh) from the groundwater surface to the top of the wooden pile is smaller than the height (ψcr) of the capillary head when the volumetric water content of the soil occupying from the groundwater surface to the top of the wooden pile is saturated (Δh <ψcr) A method for preventing decay of a wooden pile by a capillary head, wherein the wooden pile is provided on soft ground.
The soil is of natural ground,
Measuring the depth to the groundwater surface of the soft ground (Δp) and the height of the capillary head (ψcr) when the volumetric water content of the soil is saturated;
Placing the wooden pile until the height (Δh) from the water table to the top of the wooden pile is smaller than the height (ψcr) (Δh <ψcr);
The method for preventing decay of a wooden pile by a capillary head according to claim 1, further comprising a step of stacking embankment thereafter.
The soil is a backfill soil having a capillary head height (ψcr) with a saturated volumetric water content;
Digging the soft ground until the groundwater surface appears on the ground surface dug down,
Placing the wooden pile until the height (Δh) from the groundwater surface to the top of the wooden pile is smaller than the height (ψcr) (Δh <ψcr);
The method according to claim 1, further comprising the step of backfilling the backfilled soil surface to the ground surface dug down.
The soil is an embankment having a capillary head height (ψcr) with a saturated volumetric water content,
A stage in which a wooden pile is placed so as to protrude from the ground surface to a soft ground having a groundwater surface at a depth (Δp) from the ground surface;
A step of stacking a bank with a height of the capillary head having a volumetric water content saturation state (ψcr) on the ground surface where the wooden pile is placed;
Due to the weight of the accumulated embankment, the bottom surface of the embankment sinks until the depth (Δp) exceeds the depth (Δp) and the upper end of the wooden pile is pushed down, and the height (Δh) of the upper end of the wooden pile from the groundwater surface is the height ( The method of preventing decay of a wooden pile by a capillary head according to claim 1, further comprising: a step of making it smaller than ψcr).

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