JPH0464618A - Pit excavation work method - Google Patents

Abstract

PURPOSE:To realize pit excavation of a great depth with a comparatively small quantity of raised water, by conducting the connection of a non-water pervasion layer which lies deeper than a pit bottom, and a hard layer which lies deeper than this layer, by means of anchor piles prior to pit excavation. CONSTITUTION:A continuous wall 4 which reaches a non-water pervasion layer consisting of a clay layer that lies deeper than a pit bottom 2 at a hard sand layer, is placed into the perimeter of the ground 1 to be excavated. Pits whose largest diameter is at the vicinity of the pit bottom 2, are bored by means of a concrete placement pile driver. Pressure support plates 6 are fitted to the tip portions by using perpendicularly PC steel wires, and ferro-reinforced cages 7 are suspended down within these pits. Concrete is poured into these pits, and anchor piles 9 which reach a hard layer 5 that lies at a deep layer, are formed, and connection between the non-water pervasion layer 3 and the layer 5 that lies deeper, is made. Meanwhile, pits that do not reach the pit bottom 2, are buried back by means of soil cement or the like.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention relates to a root cutting method for constructing the foundation of a building, and more specifically, to a root cutting method suitable for deep root cutting exceeding 20 m. .

[Prior art]

Generally, when cutting roots, an earth retaining wall such as a continuous wall that reaches the impermeable layer is installed around the area to prevent ground subsidence and an increase in the amount of water pumped up.

However, in the case of deep cutting exceeding 20 m, a retaining wall that is deeper than the depth of the excavation is required, but there is a risk of destruction of the ground at the bottom of the cutting, which is generally called heaving or boiling. , it was necessary to prevent this.

In many cases, Quaternary layers have clay layers in shallow areas, and sand and gravel layers in deeper areas, which are subject to large water pressure. In addition, this sand layer is generally a diluvial layer and has high strength, but it has the property of being easily permeable to water, and water treatment has been a major problem when cutting roots.

[Purpose of the invention]

This invention has been made in view of the above-mentioned problems. The purpose is to propose a root cutting method that does not require significantly deeper retaining walls, requires a relatively small amount of pumped water, and allows deep root cutting.

[Structure of the invention]

In the root cutting method invented in (1), the root cutting method involves surrounding the surrounding area with a mountain retaining wall that reaches an impermeable layer deeper than the bottom of the root cutting, and pumping water inside to perform the root cutting.
It is characterized by connecting the impermeable layer deeper than the bottom of the cut and the hard layer deeper than that with anchor piles. (2
)'s root cutting method is that, if there is no impermeable stratum at an appropriate depth below the root cutting base, a hardening material is injected below the root cutting base to form an impermeable outer layer prior to root cutting. It is characterized by connecting the impermeable layer and the deeper hard layer with anchor piles.

〔Example〕

This will be explained below with reference to the illustrated embodiments. In Figure 1-2, a continuous wall 4 is built around the ground 1 to be cut, reaching from the cutting bottom 2 in the hard sand layer to the impermeable layer 3 made of clay layer deeper than the cutting bottom 2. Using a cast-in-place concrete pile driver, drill holes in the ground at intervals of 5 to 10 m at intervals of 5 to 10 m so that the tip extends into the hard layer 5 deeper than the impermeable layer 3 and reaches its maximum diameter near the bottom of the root cut. Drill a hole. Inside this prepared hole, a PC steel wire is used for the vertical reinforcement, a bearing plate 6 is attached to the tip, and a reinforcing bar cage 7 whose length reaches from the hard layer 5 to the root cut bottom 2 is suspended.

Concrete is injected into this drilled hole to form an anchor pile 9 that penetrates the impermeable layer 3 from the hard sand layer 8 where the root cut bottom 2 is located and reaches the hard layer 5 located deep therein.

This anchor pile 9 has an enlarged diameter at its upper end, reaches its maximum diameter near the root cutting bottom 2, and connects the impermeable layer 3 and the hard layer 5 located deeper therein.

The holes shallower than root cutting bottom 2 should be backfilled with soil cement or the like so that they do not become an obstacle during root cutting. In this state, water is pumped up in the ground, excavated, and root cutting is performed to the root cutting bottom 2.

In this example, the upper end of the anchor pile is fixed to the hard sand layer above the impermeable layer, and the impermeable layer and hard layer are connected to improve the connection strength with the relatively low strength impermeable layer. Although this is the case, various other embodiments may be adopted.

If a permeable layer does not exist at an appropriate depth, as shown in Figure 3, a hardening material is injected into the hard sand layer 8, which is deeper than the root cutting bottom 2, to create an artificial layer with impermeability and strength. A water permeable layer 3 is formed.

In this case as well, as in the case of Fig. 1, regular holes are drilled at predetermined intervals, the reinforcing bar cage 7 is suspended, and from the hard layer 5, the root cut bottom 2 is reached, and the maximum diameter is reached near the root cut bottom. Anchor pile 9
The water-impermeable layer 3' is connected to the hard layer 5 located deeper therein.

[For production]

This construction method consists of the above-mentioned structure. Prior to root cutting, an impermeable layer deeper than the bottom of the root cut or an artificial impermeable layer formed by injecting a hardening material is connected to the hard layer deeper than that and the anchor. Connect with stakes. Therefore, if water is pumped up within the ground 1 surrounded by the connecting wall 4 as shown in Fig. 4, and the roots are cut,
Groundwater pressure P acts on the lower surface of the impermeable layer 3'.

However, a tension T corresponding to this water pressure P is automatically generated in the anchor pile 9, balance is maintained, and destruction of the root cut bottom 2 is prevented.

Since the diameter of the anchor pile in the example is expanded at the upper end, the groundwater pressure acting on the lower surface of the impermeable layer acts as a compressive force on the reverse taper part of the anchor pile. The sand layer 5 or the impermeable layer 3, 3'' is required to have strength and water-blocking properties to withstand it.As a result, the connection strength between the anchor pile and the impermeable layer or the hard sand layer can be increased.

〔Effect of the invention〕

With the conventional root cutting method, even if there is an impermeable layer such as a clay layer, it is necessary to pump up an amount of water commensurate with the difference between the load acting on the top surface and the groundwater pressure acting on the bottom surface, and it is necessary to pump water at a volume that is commensurate with the difference between the load acting on the top surface and the groundwater pressure acting on the bottom surface. Cutting requires deep earth retaining walls and pumping up a large amount of water, but with this construction method, relatively shallow earth retaining walls are erected and roots can be cut at great depths with only a small amount of water pumped.

In addition, if there is no impermeable layer at a suitable depth, conventional retaining walls would have to be lowered very deeply, making the construction period and cost extremely expensive, and sometimes impossible. Even in such cases, it is possible to perform deep root cutting efficiently.

[Brief explanation of the drawing]

The drawings show the construction method of the example, and Figures 1 and 2 are longitudinal cross-sectional views and plan views showing examples of construction on the ground with an impermeable layer, and Figure 3 is a construction method in which a hardening material is injected to make the ground impermeable. A cross-sectional view showing an example of construction of the ground with layers formed, and FIG. 4 is a cross-sectional view after root cutting. DESCRIPTION OF SYMBOLS 1... Root cut ground, 2... Root cut bottom, 3... Impermeable layer, 4... Continuous wall, 5... Hard layer, 6... Bearing plate, 7... Reinforced cage, 8...Hard sand layer, 9...Anchor pile.

Claims (2)

[Claims] (1) In the root cutting method, in which the surrounding area is surrounded by a mountain retaining wall that reaches an impermeable layer deeper than the root cutting bottom, and the root cutting is performed by pumping water inside, the impermeable layer that is deeper than the root cutting bottom is removed before root cutting. A root cutting method that is characterized by connecting the hard layer and the deeper hard layer with anchor piles. (2) In the root cutting method, in which the surrounding area is surrounded by a retaining wall that reaches an impermeable layer deeper than the bottom of the root cut, and the root cutting is performed by pumping water inside, hardening material is injected into the depth below the bottom of the root cut prior to root cutting. A root cutting method characterized by providing an impermeable layer in the ground and connecting this impermeable layer to a deeper hard layer using anchor piles.