JPS5845527B2 - Expansion piling method - Google Patents

Description

[Detailed Description of the Invention] The present invention is designed to form foundation piles in the ground without noise, vibration, or impact in urban areas with soft ground where there are concerns about uneven settlement or liquefaction during earthquakes. This is a construction method for improving the ground around piles, and relates to improvements to vibration-free built-in pile construction methods.

In the conventional vibration-free built-in pile construction method, the grout or mortar injected after drilling is non-expanding and generally has a high water-cement ratio and a high degree of hardening, so the ground around the pile disturbed by drilling As the pile hardens, the surface of the pile separates, causing loosening of the ground around the pile.

For this reason, the circumferential resistance of the pile is significantly reduced, and its ultimate bearing capacity is usually far inferior to that of a driven pile constructed by vibration or impact.

In addition, in concrete, mortar, grout, etc., by using an expansion additive such as expanded cement or aluminum powder in a part of the cement used, the volume expands when it hardens, and it acts as a void filler. By fully exerting it or by applying appropriate expansion restraint measures,
Methods such as creating a self-press stressing effect are generally known.

However, these expanding mortar, expanding grout, etc. are not utilized in the conventional built-in pile construction method.

In addition, in order to prevent liquefaction caused by seismic motion in medium-grained sand layers with high groundwater levels and loose soil, it is widely used to compact and improve the strata using dynamic pressure such as sand compaction and vibroflotation. This is commonly done.

However, these construction methods involve vibration and shock, and therefore cannot be used in urban areas where buildings are densely packed.

As a conventional pile driving method using expandable grout or mortar, JP-A-53-58105 and JP-A-52-5
Inventions described in No. 6706 and Japanese Unexamined Patent Publication No. 54-407 are known, but in both cases, expandable grout or mortar is applied to the tip of the pile and used as foot protection to increase the pile supporting capacity. However, this method had the problem that it could not be used in ground where the supporting ground was deep, such as an alluvial sand layer.

The present invention solves the conventional drawbacks and problems by filling the entire length of the pile with expandable grout or mortar and consolidating the entire length to increase the circumferential friction force and thereby increase the pile supporting force. Furthermore, we aim to provide an excellent expansion bailing method that effectively develops circumferential surface friction force.

The gist of this invention is that after drilling a hole in the ground, grout or mortar is injected into the hole, and a precast antibody or reinforcing steel material is inserted into the hole and hardened to form a pile in the ground. A hardened and expandable material is used to fill the entire length of the antibody or reinforcing steel in the hole, and the precast antibody or reinforcing steel inserted into the hole restrains the vertical expansion of the grout or mortar and converts it to the horizontal direction. Using a pile with several stages of protrusions or flanges on the outer periphery, the hardening expansion force of the grout or mortar applies horizontal pressure to the ground around the pile, statically improving the consolidation of the surrounding ground and improving the ground. It is an expansion building construction method that is characterized by forming piles inside.

This will be explained in detail below using examples.

First, as shown in Figure 1, (1) Drill a hole to the required depth from a predetermined position on the ground where the pile will be formed using an appropriate noise-free and vibration-free drilling machine 1. While raising the hole, expandable grout or mortar 2 is sequentially injected from the lower part of the hole to fill the hole, and (3) before the grout or mortar 2 starts hardening, a second
Insert the precast pile body 3 or reinforcing steel material shown in the figure into the hole, and (4) harden and expand the grout or mortar at a rate of 1/2 to horizontally spread the ground around the pile over the entire area from the bottom of the pile tip to the ground surface. This is a construction method in which the pile body 3 is compressed, consolidated, and fixed at a predetermined position.

In this construction process 1, if a non-evacuation soil boring machine is used for drilling, the initial horizontal pressure and expansion pressure associated with drilling will combine to further improve the compaction effect of the ground around the pile. In step 2, by appropriately adjusting the viscosity of the uncured grout or mortar/1/2, it is easy to penetrate into the surrounding ground, making it possible to improve the surrounding ground with the infiltrating liquid, and in step 3. By inserting antibodies or reinforcing steel materials with shapes such as A, B, and C in Figure 2, the vertical expansion of grout or mortar is restrained and converted to the horizontal direction. The compaction force is doubled, and in step 4, the expansion rate can be reduced to 0 by selecting the expansion additive and formulation.
．． It is possible to freely adjust the expansion or pressing force from about 01/1000 to about 50/1000 as necessary.

Hereinafter, the effects of the embodiments of the construction method of the present invention will be specifically explained.

Tables A and B above show examples of the composition of grout and mortar for the construction method of the present invention that were actually constructed, and Figures 3 to 5 are construction drawings thereof.

As shown in the construction drawings, the ground condition is a uniformly loose, medium-broken layer saturated with water, with a standard penetration test average N value of 8 to 10 and a uniformity factor of around 5, up to a dozen meters below the ground surface. This is a geological formation with an extremely high risk of subsidence and liquefaction during earthquakes.

Therefore, even with a pile foundation structure in which the piles are significantly longer and reach the supporting layer several tens of meters below, the risk of liquefaction due to seismic motion in the upper ground is difficult to reduce, and the risk of liquefaction caused by horizontal seismic motion during a quicksand phenomenon is very high. It is not easy to create a structure that can avoid the same collapse.

The site is located in the center of the city, so it is of course impossible to carry out sand compaction, vibrations, etc. that involve vibrations and shocks.

For this reason, we decided to adopt the construction method of the present invention, and first, we constructed deformed steel piles with a total length of 1.5 meters (1'7"1) and 15 meters at the bottom of the cloth foundation that was laid along the outer wall of the building. The area of ground improvement using the method of the present invention overlaps with the ground improvement method of the present invention, and a completely sealed foundation structure is created up to 15 meters underground, and inside this, irregularly shaped precast concrete piles with a total length of 8 meters are installed at the intervals shown in Figure 3. By performing this construction, we created a structure in which the ground improvement effect associated with pile construction using the method of the present invention extends over the entire foundation.

The results of the standard penetration test at each location shown in Figure 3, which was conducted to confirm the ground improvement effect after the required period of hardening of the grout and mortar after completion of construction, are as shown in Tables A and B of Table 2.

As is clear from this table, the improvement effect extends to a cylindrical range with a radius of 2 to 4 meters around the antibody, from a deep layer of 4 to 6 meters below the tip of the antibody to near the ground surface. All of them reached an N value of 15 to 19, indicating that concerns about liquefaction during an earthquake had increased to an almost unthinkable level.

In addition, the results of vertical and horizontal loading tests on actual piles conducted at the same time also support this fact. It was revealed that the strength was more than twice that of the previously driven pile.

For example, N value 10, free expansion rate 25/1000, pile diameter 5
At 0 cm, it was possible to generate a pressing force of 22 tons per square area.

In general, it is known that at a depth of 10 to 15 meters or more below the ground surface, there is no concern about liquefaction due to earthquake motion as long as the upper layer is normal. Therefore, it is said that it is effective to construct a foundation structure that seals the area 10 to 15 meters below the ground surface.

In Japan, there are many alluvial sand layers where supporting foundations extend from tens of meters to hundreds of meters below the ground surface, and it would be a mischief to support piles directly on the foundation without preventing liquefaction of the upper layer near the ground surface. This not only causes the piles to become longer, which is an economic problem, but also poses problems in terms of horizontal strength during earthquakes.

In the case of a pile foundation constructed using the method of the present invention, the structure of the foundation can cope with uneven settlement and liquefaction during an earthquake as described above, and the supporting capacity of the upper ground is improved, making the entire foundation a floating foundation structure. Since it is possible, the economic effect is very large.

[Brief explanation of drawings]

FIG. 1 is a construction order explanatory diagram of an embodiment of the construction method of the present invention. FIG. 2 is an explanatory diagram showing various shapes of antibodies or reinforcing steel materials used in the construction method of the present invention. FIG. 3 is a plan view showing a construction site of an example of construction using the construction method of the present invention. Figure 4 is a vertical cross-sectional view showing the piles inserted into the surrounding wall of the same construction site. Figure 5 is a vertical cross-sectional view showing the pile inserted in the center of the construction site. Figure 6 is a soil column diagram showing the soil conditions at the construction site.

Claims (1)

[Claims] 1. After drilling a hole in the ground, grout or mortar is injected into the hole, and a precast antibody or reinforcing steel material is inserted into the hole and hardened to form a pile in the ground. Moreover, in addition to filling the entire length of the antibody or reinforcing steel in the hole, several steps of protrusions are used to restrain the vertical expansion of the grout or mortar and convert it to the horizontal direction as a precast antibody or reinforcing steel inserted into the hole. Alternatively, by using a flange on the outer periphery, the hardening expansion force of the grout or mortar applies horizontal pressure to the ground around the pile, statically improving the consolidation of the surrounding ground and forming the pile in the ground. The expansion pie link construction method is characterized by