JPH04174134A - Method of swell preventive construction of earth anchor - Google Patents

Abstract

PURPOSE:To prevent the floating (swell) of an excavated base by excavating a through-hole reaching the support layer of a poor subsoil, fixing a tension member to the support layer while injecting a solidifying material into an excavated pit and pit-excavating the ground in specified depth. CONSTITUTION:Through-holes reaching a support layer (e) are excavated to a poor subsoil M composed of an upper sand layer (a), a clay layer (b), a silt layer (c), a gravel (d), etc., and tension members 3 such as PC steel bars having anchor bodies 3a at noses are anchored to the support layer (e). solidifying materials 4 are injected into excavated pits, thus forming earth anchors (m). The ground M is dug down up to an excavated base N and pit-excavated while conducting a landslide protection wall. Support plates 5 are installed, and the excavated base N is pushed, and made to resist the uplift of groundwater. Accordingly, the earth anchor can be executed easily.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention uses an earth anchor to prevent the entire bottom of the excavation from lifting when excavating the upper ground of a sandy soil layer where uplift pressure is applied by pressurized groundwater. This relates to a construction method for preventing board bulges.

(Conventional technology) When constructing the foundation or basement of a building, the ground is dug down while retaining the mountain, which is called root cutting. In the case of soft ground that is composed of a 3-layer structure, if the upper part of the pressurized permeable layer is excavated, the bottom surface of the excavation may rise due to the pressurized groundwater, which is a so-called bulging phenomenon.

As measures to prevent this blistering, groundwater level lowering methods and ground improvement methods are generally taken.

The above-mentioned groundwater level lowering method lowers the groundwater level by using well points, deep wells, etc. in order to reduce the uplift pressure applied to the bottom of the excavation, and the ground improvement method lowers the groundwater level by using well points or deep wells to reduce the uplift pressure applied to the bottom of the excavation. The purpose is to solidify and improve the embedded part of the earth retaining wall on the entire bottom surface to form an impermeable layer and increase its strength.

(Problem to be solved by the invention) However, in the above-mentioned groundwater level lowering method, the lowering of the groundwater level affects a wide area and causes construction pollution in which the surrounding ground is consolidated and subsides. It was necessary to construct a horizontal impermeable wall around the site that reached quite deep into the lower permeable layer.

In addition, in order to pump up groundwater, a pumping well had to be dug and built horizontally to reach the lower permeable layer, and furthermore, a large amount of expense was required to discharge the pumped groundwater into the sewer over a long period of time.

On the other hand, the ground improvement method solidifies and improves the permeable layer to make it impermeable, which has the problem of increasing the cost of improvement.

The present invention was made in view of the above-mentioned problems, and its purpose is to improve economic efficiency without pumping up groundwater to lower the groundwater level or solidifying and improving the ground at the bottom of excavation. To provide a construction method for preventing board bulges that can effectively and easily prevent board bulges.

(Means for Achieving the Problems) The first invention of the method for preventing slab bulges using earth anchors in order to achieve the above-mentioned problems involves drilling an excavation hole in the ground that penetrates to the support layer, and A tensile material is inserted from the tip of the hole to the bottom of the excavation, and after the tip of the tensile material is fixed to the support layer, a solidifying material is injected into the excavation hole. The second invention is to drill an excavation hole in the ground that penetrates to the support layer, insert separable tensile materials at predetermined intervals from the tip of the excavation hole to an appropriate depth above the bottom of the excavation, and The present invention is characterized in that a solidifying material is injected into the excavated hole after the tip of the tensile material is fixed to the support layer.

(Function) According to the method for preventing slab bulging using the earth anchor of the first invention as described above, the soil layer from the lower end of the impermeable layer to the bottom of the excavation, where uplift force acts, is fixed to the supporting layer. Because it is held down by the frictional force of the tensile material, it is economical and easy to prevent slab bulges, and since it can be installed in advance, it has almost no negative impact on excavation work.

Further, according to the method for preventing slab bulges using earth anchors of the second invention, since the tension member can be separated, it is possible to stabilize the excavated bottom ground at any arbitrary excavation depth, and
It is also possible to prevent rebound during deep excavation.

(Example) Hereinafter, an example of the present invention will be described in detail based on the drawings.

1 to 2 are cross-sectional views showing an embodiment of the method for preventing board bulging using the earth anchor of the first invention.

[Drilling of an excavation hole] First, an excavation hole 1 penetrating the ground M up to the support layer e is drilled.

At this time, the depth of penetration into the support layer e is set appropriately depending on the size of the pressure head.

This ground M consists of a permeable upper sand layer a and an impermeable clay layer b.
, a silt layer C1, a permeable layer, and a gravel layer d, and the gravel layer d has a high pressure head.

This excavation hole 1 is excavated by penetrating the ground M with gauging 2 and removing the earth and sand in the casing 2, and by taking into consideration the frictional resistance of the silt layer C, an appropriate interval (2 to 2 Excavate with a depth of about 6m).

[Fixation of tensile material] Next, the tensile material 3 is inserted into the range from the bottom of the excavation hole 1 to the excavation bottom surface N, and while the casing 2 is pulled out, a solidifying material 4 such as mortar or cement milk is applied. The ground anchor m is formed by pressurized injection from the tip to at least the bottom surface N of the excavation, and the remaining excavated soil is filled into the remaining air space m1.
Alternatively, fill with acid-strength injection material and backfill.

At this time, in order to prevent the tensile material 3 from rising when the casing 2 is pulled out, a solidifying material 4 for foot protection is injected into the bottom of the excavation hole 1 in advance, or a solidifying material 4 is provided at the tip of the tensile material 3. The fixing body 3a may penetrate into the support layer e.

In addition, not only excavated soil but also solidified material 4 is added to the air space ml.
It may be filled with.

Incidentally, as the tensile material 3, a PC steel bar is preferable;
It is also optional to use a steel stranded wire, and it is also possible to insert and fix a plurality of stranded wires as shown in FIG. Also,
If the depth from the excavation bottom surface N to the support layer e is large,
The tension member 3 may be connected as appropriate using a coupler 3e or the like.

In addition, when constructing this earth anchor m, the ground M
The construction is not limited to the ground surface, but can be performed even during the excavation stage if the ground at the excavation bottom surface N is stable.

[Root Cutting of the Ground] Next, after fixing the tensile material 3 as described above, the upper part of the pressurized ground M is excavated and root cutting is performed while performing both straightening.

At this time, the ground below the excavation bottom surface N is in a state of being tightly connected to the support layer e due to the frictional resistance with the earth anchor m, so it is necessary to sufficiently maintain a stable state by sufficiently resisting the uplift pressure caused by the pressurized groundwater. I can do it.

Note that when the final excavation depth is reached, a bearing plate 5 is attached to the head of the tensile member 3 to support the excavation bottom surface N, thereby increasing the resistance against the uplift pressure of groundwater. Further, this tensile member 3 can be tensioned with a tension jack depending on the properties of the ground and the uplift force at the excavation bottom surface N to provide a high tension.

At this time, the bearing pressure plate 5 is attached by inserting a plurality of wedge-shaped fixtures 5a sandwiched between the head portions of the tension member 3 into the through holes of the bearing pressure plate 5.

Next, an embodiment of the second invention will be described based on FIG. 2.

2 to 2 are cross-sectional views showing a method for preventing board bulging using an earth anchor according to the second invention.

[Drilling of an excavation hole] First, an excavation hole 1 penetrating the ground M up to the support layer e is drilled.

This ground M consists of a permeable upper sand layer a and an impermeable clay layer b.
, a silt layer C2, a permeable layer, and a gravel layer d, and the gravel layer d has a high pressure head.

[Fixation of tensile material] Next, the tensile material 3, which can be separated at predetermined intervals, is inserted into the excavation hole 1 from the tip of the excavation hole 1 to an appropriate depth above the excavation bottom surface N. By pouring a solidifying material 4 such as mortar or cement milk into the bottom of the hole 1, the tip thereof is fixed to the support lie and hardened.

After this hardening, the casing 2 is pulled out and a solidifying material 4 such as mortar or cement milk is injected under pressure to the ground surface to form an earth anchor m.

The tensile member 3 is a PC steel rod 3b of a predetermined length, and the coupler 3
e'? ``Continuously connected and formed, with a fixing body 3 at the tip.
a, and can be set to any length by removing the coupler 3e.

Further, as the tensile member 3, a PC steel stranded wire may optionally be used instead of the PC steel rod 3b.

[Root Cutting of the Ground] After fixing the tensile material 3 as described above, the upper part of the pressurized ground M is excavated while performing both straightening.

After excavating to a predetermined depth, the hardened part of the earth anchor m exposed upward from the bottom surface N of the excavation is removed, the tensile member 3 is separated by removing the coupler 3e, and the bearing plate 5 is attached to its head. By supporting the bottom surface N of the excavation, it resists the uplift pressure of groundwater.

Then, struts are hung across both of the front walls to support the side wall on the side of the root cut.

In this way, by connecting the tensile material 3 using the coupler 3e, the tensile material 3 after being separated can be reused.

Next, after passing the strut, the bearing plate 5 is removed from the head of the tensile member 3, and the excavation bottom surface N is excavated again.

After excavating to a predetermined depth, the hardened part of the earth anchor m exposed upward from the bottom surface N of the excavation is peeled off as described above, and the coupler 3e is removed.
Separate.

Next, a bearing plate 5 is attached to the head of the excavation to support the bottom surface N1 of the excavation, and a strut is hung on the retaining wall to support the side wall on one side of the root cut.

In this way, each time the ground M is excavated to a predetermined depth, the tension member 3 is cut off and the bearing plate 5 is attached to the head of the tension member 3 to support the bottom surface N, N of the excavation until the final excavation depth is reached. Perform root cutting.

When reaching the excavation bottom surface N1 at the end of the shell, a bearing plate 5 is attached to the head of the tensile member 3 to resist the uplift force.

In addition, the tensile material 3 can be tensed with a tension jack at the final excavation bottom surface N, depending on the properties of the ground and the uplift force, to provide a high tension, thereby obtaining strength capable of resisting the uplift force.

Note that the bearing pressure plate 5 is attached by inserting a plurality of wedge-shaped fixtures 5a sandwiched between the head portions of the tension member 3 into the through holes of the bearing pressure plate 5, as in the first invention.

In addition, in deep excavation where the final excavation depth is 30 m or more, the amount of swelling of the ground at the bottom of the excavation (rebound phenomenon) increases due to the stress release associated with excavation and removal, but the present invention can also suppress the rebound phenomenon. be.

What is shown in Fig. 5 is the ground M with the second pressured water retention layer, and in order from the top, permeable upper sand Jla, impermeable clay layer b, silt layer C1, permeable gravel layer d, It is composed of a silt layer e and a gravel layer f in this order, and the gravel layers d and f have a high pressure head.

Even in the case of such a ground M, swell of the ground can be prevented by the methods of the first and second inventions described above.

(Effects of the Invention) The present invention has the following effects by having the above configuration.

■ Drill a hole in the ground that penetrates to the support layer, insert a tensile material to an appropriate depth from the tip of the hole to the bottom of the excavation, fix the tip to the support layer, and insert the tensile material into the support layer. By injecting grout into the ground, the earth anchor can be easily installed, making it possible to prevent board bulging economically and easily.

■ Since it can be installed in advance, it has little effect on the excavation work of the ground where the roots will be cut, increasing work efficiency.

■ Since the earth anchor has a high yield strength, it is highly reliable as a method of preventing board bulges.

■ Drilling a hole in the ground that penetrates to the support layer, inserting separable tensile materials into the hole at predetermined intervals, fixing the tip of the material to the support layer, and grouting the material into the hole. By injecting the material, excavation work can be carried out in parallel with the erection of the struts, making underground work easier.

■ In deep excavation, in addition to measures to prevent plate bulges, measures can also be taken to prevent rebound by unloading the excavated soil.

[Brief explanation of drawings]

■~■ in Figure 1 and ■~■ in Figure 2 are cross-sectional views showing the method for preventing slab bulges using earth anchors of the present invention, Figure 3 is an enlarged cross-sectional view of the main parts, and Figure 4 is Figure 3. I-I line sectional view of
5 - 5 are cross-sectional views of the state in which the present invention is implemented on the ground where there is a second pressurized water retention layer. In the figure, 1; excavation hole 3: tension member 5: bearing plate M: ground N: excavation bottom surface e: support layer m: earth anchor. Patent applicant: Toda Construction Co., Ltd.

Claims (2)

[Claims] (1) Drill a hole penetrating the ground to the support layer, insert a tensile material from the tip of the hole to the bottom of the excavation, fix the tip of the tensile material to the support layer, and then A method to prevent plate blistering using earth anchors, which is characterized by injecting a solidifying material into the interior. (2) Drill an excavation hole in the ground that penetrates to the support layer, insert separable tensile material at predetermined intervals from the tip of the excavation hole to an appropriate depth above the bottom of the excavation, and A method for preventing slab blistering using an earth anchor, characterized in that a solidification material is injected into the excavation hole after the tip part is fixed to the support layer.