JPS6330450B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for constructing piles that reduce negative friction in piles used as foundations for buildings, structures, etc. in soft strata.

For the foundations of these buildings, negative friction reduction piles have been driven to protect, strengthen, or stabilize the ground for a long time.

As a means of constructing negative friction force reduction piles for the above-mentioned purpose, a method of driving the pile by hitting the head of the pile using an impact hammer, a diesel hammer, or a steam hammer has been adopted.

According to such a foundation pile driving method, the stability of the pile is extremely high because the stratum in the ground and the pile surface are in close contact.

However, when these prefabricated piles are constructed by driving near residences, the noise caused by impact, the accompanying vibrations, and the noise emitted from the driving equipment are added, which adversely affects the surrounding environment, resulting in a number of complaints from residents. In addition, with the enforcement of laws and regulations regarding pollution prevention, the search for low-noise and low-vibration construction methods continues, and the above-mentioned pile driving is currently becoming difficult.

As an alternative to this conventional construction method, for example, when using hollow pipe piles, a cutting blade that can excavate the stratum from the inside of the pipe at the end of the pipe is set and rotated down to excavate the stratum. At the same time, piles are erected in the stratum by embedding a pipe (excavation combined method) or by first drilling a hole in the stratum and inserting the pile there (embedding method), and then cement the area around the pile body and the void between the tip and the stratum. Methods of solidifying with solidifying agent materials such as these are beginning to be used.

After a certain period of time, piles constructed in soft strata are subject to downward shear stress (hereinafter referred to as negative frictional force) due to ground subsidence that occurs due to the consolidation effect of the strata.

Therefore, if a building, etc. is placed on top of a pile that has been constructed as a foundation, the negative frictional force acting on the pile will gradually accumulate, and at some point this may have a negative impact on the building, etc. This is not desirable.

This negative frictional force appears more strongly when the area around the pile is strengthened with cement or the like in order to increase the bearing capacity or horizontal resistance of the constructed pile, and this problem is more likely to occur.

For example, if the area around the pile body is consolidated with cement milk that has a compressive strength of 6 to 70 kgf/cm ² at the time of consolidation,
Observations have been made that when this pile body is not subjected to negative friction reduction treatment, it is subjected to a peripheral surface friction force of 30 tonf/m ² .

Generally, piles used to form a foundation are aligned to a certain length from the viewpoint of manufacturing and transportation (hereinafter referred to as pile bodies) and are used while being connected at the actual construction site. Therefore, even if the surface of the antibody is coated to reduce negative frictional force, the uncoated part is exposed at the connection part, so stress concentration occurs in this part, resulting in This means that the original significance or effect of using piles that have been treated to reduce negative friction will be diluted.

The present inventors have developed a construction method that minimizes the negative frictional force acting in the ground and allows the negative frictional force reduction effect to be fully exerted when constructing the pile using piles for reducing negative frictional force. As a result of various studies, the present invention was arrived at.

The present invention will be explained below using the drawings.

FIG. 1 shows a case where, for example, a steel pipe pile 1 is inserted into an excavated hole 2, which has a diameter larger than the outside diameter of the pile, drilled in a geological formation. In the figure, 3 is the coated part that reduces negative friction on the surface of the pile body, 4 is the uncoated part, and 5 is the uncoated part.
is the pile body connection part, 6 is the pile body cross section, 7, 8 and 9 are the strata, 7 is the soft stratum, 9 is the fixed support layer, 8
indicates the middle layer located in between.

In addition, both 8 and 9 are collectively called a hard stratum.

The tip of the antibody 1 inserted into the stratum reaches the support layer 9, and is fixed there with cement milk 10 for root hardening. The pile body 4 corresponds to the intermediate layer 8 where hardly any consolidation of the stratum occurs thereafter.
(The surface is not coated to reduce negative frictional force.) The surrounding void area has the unconfined compressive strength shown by the stratum ("Basic Engineering Handbook", edited by Sakuro Murayama and others, November 15, 1962). Unconfined compressive strength test method (JIS
A1216). ) approximately the same or greater compressive strength,
Specifically, a fixative (A) 11, such as cement milk, which has a compressive strength upon solidification of 5 Kgf/cm ² or more is injected and fixed. The significance of doing so is due to the following reason.

In other words, the intermediate layer 8 is a layer that is expected to produce frictional force acting on the circumferential surface of the pile body 4, and has the same role as that in the normal embedding method. By injecting cement milk that has been adjusted to have a compressive strength at consolidation comparable to the unconfined compressive strength of the surrounding soil, it is hoped that circumferential frictional force will be generated from the ground.

Specifically, if the compressive strength of the cement milk to be injected after solidification is lower than that of the surrounding soil, only a small peripheral frictional force will appear, which will be disadvantageous in supporting antibodies. On the other hand, if it is too large, the compressive strength of the surrounding soil will be relatively small and the compressive strength received here will only be the compressive strength of the surrounding soil. Even if it is used, it becomes uneconomical.

Next, around the negative friction force reduction coated pile corresponding to the layer 7 located above and causing consolidation settlement,
A fixative, such as cement milk, which exhibits a compressive strength at consolidation that is lower than the unconfined compressive strength of the surrounding soft stratum 7, for example, lower than 5 Kgf/cm ²
Fix by (B).

The negative friction force reducing pile according to the present invention is intended for use on soft ground, and if a fixative that becomes harder than the soft ground is injected between the side wall of the coated part of the pile and the ground, the pile When the pile and the fixed layer formed by injection work together, frictional force is transmitted at the interface between the soft ground and the fixed layer, making it impossible to expect the original effect of a covered pile.

For example, even if the ground sinks due to consolidation in the 7 parts of the soft stratum, the resistor constructed in the ground as described above has a compressive strength when consolidated that is smaller than the unconfined compressive strength exhibited by the surrounding strata. Since the area around the pile body is solidified with the fixative (B), shearing of the surrounding strata easily occurs against the antibody, and a coating 3 is formed on the pile body surface to reduce this negative friction force. This means that the original effect of the pile in reducing negative frictional force can be fully demonstrated, and the pile can continue to stably perform its original function over a long period of time without absorbing most of the negative frictional force. It can be done.

FIG. 2 is a diagram showing another embodiment, in which a cutting blade and a fixative liquid injection pipe are provided inside the tubular pile body, and a combined excavation method is used.As the excavation of the stratum progresses, After the pile has entered the stratum and reaches a predetermined depth, pour cement milk for root hardening from the injection pipe.
This figure shows the state in which .

After the injection of the cement milk 10 for root hardening is finished, although not shown in the figure, the gap between the surrounding area of the pile and the stratum is naturally filled with fixative (B) and fixative as needed, as shown in Figure 1. Needless to say, it is fixed by injecting liquid (A).

The required number of coated piles to reduce negative friction (required length), the length of uncoated piles, the performance and amount of fixing fluid, etc. are determined based on the soil strata through boring tests etc. prior to foundation pile construction. Since the configuration is known in advance, the decision can be made easily.

Figure 3 shows the change in strain at each measurement point when a load of 200 tonf is applied to the top of the pile after constructing a pile in the geological formation, which is a pile with a negative friction reduction coated pile and an uncoated pile. It is something that

The unconfined compressive strength of the strata in the figure from the ground surface (GL) to a depth of approximately 30 m is 2 Kgf/
cm ² , Behavior A uses a combination of excavation method and a fixative with a compressive strength of 20 Kgf/cm ² is applied to the gap, while Behavior B uses an embedding method and a compressive strength of 0.3 when solidified.
The behavior when filled with a fixative solution of Kgf/cm ² and solidified is shown.

As can be seen from this figure, when using a fixative with a compressive strength at consolidation that is lower than the unconfined compressive strength of the surrounding strata around the antibody where the negative friction force reduction coating was applied, a stress of 200 tonf was applied. It can be seen that almost no distortion is accumulated.

Note that the strain was measured using a pile body that was previously equipped with a strain measurement detection section at each position indicated by G in the figure.

As explained above, when a pile body is installed on soft ground, the present invention provides cement milk that has a compressive strength when consolidated that is smaller than the unconfined compressive strength shown by the surrounding strata in the part of the pile facing the soft ground. is injected to easily cause shearing of the surrounding strata, while
For piles that touch the support layer, a fixative for root hardening is applied near the tip of the pile, and the compressive strength at consolidation is applied to the intermediate layer, which is a hard stratum between the soft ground and the support layer. Cement milk that is equal to or greater than the unconfined compressive strength of the soil is injected into the pile, and the pile uses circumferential frictional force to perform its original function.

By adopting such a configuration, we have established a method for constructing a covered pile that has a reliable bearing capacity and also has the effect of reducing negative frictional force at the same time.

[Brief explanation of the drawing]

Figures 1 and 2 are explanatory cross-sectional views when a negative friction force reduction pile is constructed (or is) installed in a stratum, and Figure 3 is a scene in which a pile equipped with a strain measurement detection section is constructed in a stratum. It is a correlation diagram between a cross-sectional view of the pile and a graph showing the strain detected by each measurement detection unit when a load is applied to the pile. 1... Pile body, 3... Negative friction force reduction coating part, 4
...uncovered part.

Claims (1)

[Claims] 1 When constructing a foundation pile in a soft stratum, a negative friction reduction coating is provided on the surface of the pile body located in the soft stratum among the multiple pile bodies that make up the foundation pile, and The surface of the pile body located in the stratum is left uncovered, a foundation pile made by connecting these pile bodies is inserted into the stratum, and the area around the tip of the pile is injected with a fixing solution for root hardening and solidified. Cement milk A is injected into the gap between the surface of the covered pile body and the hard stratum and allowed to solidify, and the compressive strength of the solidified cement milk A upon solidification is equal to or greater than the unconfined compressive strength of the surrounding hard stratum, Cement milk B is solidified in the gap between the surface of the covered pile body and the soft stratum, and the foundation pile is placed in the stratum with the compressive strength of the solidified cement milk B being less than the uniaxial compressive strength of the surrounding soft stratum. A method for constructing a negative friction force reducing pile, which is characterized by being fixed inside.