JP2003129462A - Method for evaluating coefficient of earth pressure at rest of ground into which pile or sand compaction pile is driven, and method for evaluating coefficient of earth pressure at rest of sand compaction pile itself in ground into which sand compaction pile is driven - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for evaluating a coefficient of earth pressure at rest of ground into which a pile or a sand compaction pile is driven, which allows the proper evaluation of an increase in the coefficient of the earth pressure at rest of the ground due to the driving of the pile or the sand compaction pile, and enables the coefficient of the earth pressure at rest to be properly and simply applied to a design. SOLUTION: In this method, an electric static cone penetration test is carried out at a representative point in an execution area; after the obtainment of cone end resistance before the driving of the pile or the sand compaction pile, a test for obtaining the cone end resistance after the driving is carried out by driving a plurality of test piles or test sand compaction piles; and the coefficient of the earth pressure at rest of sandy ground is calculated for evaluation from test results.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pile or a sand compaction pile for reflecting a rise in the strength of the ground obtained by driving a pile or a sand compaction pile on the ground at the time of designing and contributing to cost reduction. The present invention relates to a method for evaluating the static earth pressure coefficient of the placing ground.

[0002]

2. Description of the Related Art Conventionally, it is generally well known that when piles or sand compaction piles (SCP) are driven into the ground, the static earth pressure coefficient (K _o ) of the ground is increased and the strength of the ground is increased. However, the present situation is that such advantages have not been incorporated at the time of design.

That is, when the static earth pressure coefficient (K _o ) of the ground increases, the shear strength of the ground increases, and the increase in shear strength of sand and clay due to the increase of K _o is expressed by SCP. Replacement rate (a _S ) of the cast composite ground,
That is, the area a _S occupied by SCP in the composite ground is shown as an example in the two diagrams of FIG. 7.

In FIG. 7, in a sand compaction pile SCP made of sand, a static earth pressure coefficient K _o = 1.
A shear strength of 0 and a _s = 0.4 is approximately equal to a shear strength of K _o = 0.4 and a _s = 0.7, and in the normally consolidated clay a static earth pressure coefficient of K _o = 1.0. The shear strength reaches about 1.5 times that of K _o = 0.5.

That is, although the replacement rate a _S may be reduced from 0.7 to 0.4 by appropriately evaluating the increase in the static earth pressure coefficient K _o , at present,
An appropriate method for evaluating K _o increase and a simple method for applying it to design have not yet been established.

[0006] The static earth pressure coefficient evaluation method of the present invention is focused on the fact that if such an increase in the static earth pressure coefficient is properly evaluated and appropriately applied to the design, it can naturally contribute to cost reduction of the related construction work. Arrived

[0007]

DISCLOSURE OF THE INVENTION The present invention appropriately evaluates the increase in the static earth pressure coefficient of the ground due to the driving of a pile or a sand compaction pile, and the static earth pressure coefficient can be appropriately and simply calculated. Static earth pressure of piles or sand compaction piles that can be evaluated by combining static static cone penetration test (CPT) and one-way shear test (DST) for design application. A coefficient evaluation method is provided.

[0008]

SUMMARY OF THE INVENTION The present invention is directed to
Select a representative point and use the electric static cone penetration test CPT
Perform and before placing piles or sand compaction piles
Cone tip resistance (q _T−σ_VO)₍₀₎And CPT implementation
Later, test piles or test sands surrounding the representative points
Place multiple compaction piles, then pile or
Sand compaction Central between piles or piles or sand
Conduct CPT at multiple points near the compaction pile
The piles or sand compaction piles
Tip resistance (q_T−σ_VO)₍₁₎After getting the pile or sun
Cone tip resistance before and after placing compaction pile (q
_T−σ_VO)₍₀₎And (q_T−σ_VO)₍₁₎And pile or
And compaction piles before and after placing
Static earth pressure coefficient K_{o (1)}Relational expression with:

[0009]

[Equation 3]

From the above, there is provided a method for evaluating a static earth pressure coefficient of a pile or a sand compaction pile driving ground for calculating a static earth pressure coefficient of a sandy ground after driving a pile or a sand compaction pile.

The present invention also provides for the representative points within the construction area.
Select and conduct an electric static cone penetration test CPT,
Cone tip resistance before placing sand compaction pile
(Q_T−σ_VO)₍₀₎At the same time, get undisturbed at the same point
A sample is taken and recompressed for all undisturbed samples.
A surface shear test DST was performed and the sand compaction
Undrained shear strength S before casting_{u (B)}, S_{u (B)}When
(Q_T−σ_VO)₍₀₎After determining the correlation of
Perform DST in a normal consolidation state with a random sample
Increase in shear strength in dense state (S_{un (DST)}/ Σ^' _V)
Next, test sand compaction around the representative point.
Place multiple piles of piles, and after consolidation, add multiple CPTs.
At the point and after the sand compaction pile has been cast.
Tip resistance (q_T−σ_VO)₍₁₎Get S_{u (B)}And (q_T−
σ_VO)₍₀₎The correlation of the sand compaction pile
Undrained shear strength S after casting_{u (D)}And (q_T−σ_VO)₍₁₎
Apply to the relationship of S_{u (D)}After asking for the sand compaction
Soil pressure coefficient before and after placing piles
K_{o (0)}And K_{o (1)}And S_{u (D)}And S_{un (DST)}/ Σ^' _V
Relational expression with:

[0012]

[Equation 4]

From the above, there is provided a method for evaluating the static earth pressure coefficient of the sand compaction pile placing ground for calculating the static earth pressure coefficient of the clay ground after the sand compaction pile placing. Further, the present invention provides the above-mentioned sand compaction pile placing The static earth pressure coefficient calculated after installation, consisting of an evaluation method of the static earth pressure coefficient of the sand compaction pile itself of the sand compaction pile placing ground to evaluate as the static earth pressure coefficient of the sand compaction pile itself, and the present invention is a plurality. Conducted an electric static cone penetration test CPT near the boundary between the sand compaction pile and clay,
An average value of the obtained plurality of cone tip resistances (q _T −σ _VO ) ₍₁₎ is obtained, and the static earth pressure coefficient obtained according to the method of the present invention is evaluated as the static earth pressure coefficient of the sand compaction pile itself. Sand compaction pile It consists of the evaluation method of the static earth pressure coefficient of the sand compaction pile itself of the ground.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment to which a method for evaluating a static earth pressure coefficient of a pile or a sand compaction pile driving ground of the present invention is applied will be described below with reference to the drawings. Terms used in the following description And their symbols and a brief description are summarized in the table below.

[0015]

[Table 1]

[0016] Therefore, the target sand Ground pile or SCP per evaluation method of stationary earth pressure coefficient K _o increase in Sand by piles or SCP hitting set in one embodiment is pouring of the present invention, the K _o increase The procedure of the survey and the evaluation method for obtaining will be described according to the flows of the following items 1 to 5.

1. Perform CPT in the whole construction area,
_T − σ _VO ) ₍₀₎ , grasp the ground composition. However, it is not necessary if a sufficient soil survey is conducted in advance and a representative point in the entire construction area can be selected.

2. Select representative points from the above survey (multiple points if necessary) and implement CPT. On this occasion,
It is preferable to perform CPT twice or more per point, and the state of implementation of this CPT is as shown in FIG. From this test, (q _T −σ _VO ) before placing pile 1 or SCP ₍₁₎
Is obtained.

3. After the CPT, multiple test piles or test SCPs will be placed around the representative points. In addition,
In this embodiment shown in FIG. 1, four piles 1 are arranged in a square arrangement, but three piles may be arranged in a triangular arrangement or five or more piles may be arranged in a polygonal arrangement.

4. Next, CPT is performed at a plurality of points such as the pile 1 or the central portion between the SCPs and the pile 1 or the vicinity of the SCP.
From this test, (q _T −σ _VO ) ₍₁₎ is obtained. Note that (q
Fig. 2 shows an example of measurement of _T- σ _VO ) ₍₀₎ and (q _T- σ _VO ) ₍₁₎ .

5. (Q _T −σ _VO ) ₍₀₎ and (q _T −σ _VO )
_{From the (1)} , the K _{o (1)} is calculated by the equation (1). However, in general, K _{o (0)} = 0.4 is often set.

[0022]

[Equation 5]

In practice, the φ increase may be included in the K _o increase to simplify it as in equation (2).

[0024]

[Equation 6]

For soils with slow drainage speed, such as silty sand and clay sand, the standard penetration speed (1-2 cm / s) shown in JGS1435-1995 "Electric static cone penetration test method" is used. Regardless of s), CPT is carried out at such a rate that the excess pore water pressure during penetration becomes zero.

A flow chart of the evaluation method in the above embodiment is shown in FIG. 3, and as a concrete example of use of K _{o (1)} after pile driving obtained in this evaluation, the circumference of the pile according to the following equation is given. Calculation of surface friction force can be mentioned.

Τ = σ ′ _VO tan φ ₍₁₎ K _{o (1)} Next, with respect to the evaluation method of the static earth pressure coefficient K _o increase of the clay ground by SCP casting in another embodiment of the present invention, S
The procedure of the investigation and evaluation method for obtaining the increase in K _o will be explained for the clay in which CP is placed, following the flow of items 1 to 6 below.

1. Perform CPT in the whole construction area,
_T − σ _VO ) ₍₀₎ , grasp the ground composition. However, it is not necessary if sufficient soil surveys have been conducted in advance and representative points in the entire construction area can be set.

2. Select representative points from the above survey (multiple points if necessary) and implement CPT. From this test, (q _T −σ _VO ) ₍₀₎ before placing SCP2 is obtained.

3. Undisturbed test at the same point at the same time as the above 2 items
Of all the undisturbed samples by the recompression method
Perform T, S_{u (B)}Ask for. Then, shown in equation (3)
(Q _T−σ_VO)₍₀₎And S_{u (B)}Find the correlation of.

[0031]

[Equation 7]

The recompression method is a method in which the test is conducted after the sample is compacted by the in-situ effective overburden pressure. FIG. 4 shows the relationship between (q _T −σ _VO ) ₍₀₎ obtained from two clays and Su _(B) . There is usually a good correlation between them, as shown in the figure.

4. DST in a normal consolidation state is performed using a typical undisturbed sample, and (S _{u (B) (D ST} / σ ′ _v ) is obtained.

5. Test SCP2 around the representative points
To place. In this embodiment, as shown in FIG.
Shows the case of placing four, but three in a triangular arrangement.
When placing, or when placing 5 or more in a polygonal arrangement
possible. After finishing the consolidation by casting, CP at multiple points
Perform T as in FIG. From this test, (q_T−
σ _VO)₍₁₎Is obtained. Average (q_T−σ_VO)₍₁₎And expression
Using k obtained in (3), S is obtained by the equation (4)._{u (D)}Seeking
Meru.

[0035]

[Equation 8]

6. Using S _{u (D)} , K _{o (1)} is calculated from equation (4). However, it is often the case that K _{o (0)} = 0.5.

[0037]

[Equation 9]

A flow chart of the evaluation method in the above-mentioned embodiment is shown in FIG. 6, and as a concrete use example of K _{o (1)} obtained by this evaluation method, embankment on the ground after SCP placement by the following formula The calculation of the shear force of the clay ground when performing

[0039]

[Equation 10]

Furthermore, sand compaction pile SC
Explaining the method of evaluating the static earth pressure coefficient K _o of P itself, the K _o evaluation of SCP itself is also important for the composite ground composed of sand compaction pile SCP and clay. The horizontal stress exerted by the SCP casting is high at the center of the SCP and decreases toward the clay ground as shown in FIG. Here, the following two methods are used for K of SCP itself.
_{o As an} evaluation method. It is up to the designer to decide which one to use.

A) The K _{o (1)} of the clay obtained from equation (5) is considered as the K _o of the SCP itself.

B) Near the boundary between SCP and clay (No. in FIG. 5)
Perform CPT from 1'to No.4 '). Average (q _T −
sigma _VO) seek _(1), equation (4) and (5) K _{o (1)} obtained from the K _o of SCP itself.

As described above, in the method for evaluating the static earth pressure coefficient of the pile or sand compaction pile placing ground of the present invention, the pile 1 or the sand compaction pile SCP2 is experimentally placed on the actual ground. After testing the condition before the test by a certain test method, the condition after driving the pile 1 or the sand compaction pile SCP2 is also tested by the same test method, and the results before and after the driving Therefore, the static earth pressure coefficient K _{o (0)} and K _{o (1)} are to be evaluated, and when the increase in K _o of the sand ground is evaluated as in the embodiment shown in FIG. Electrical static cone penetration test CPT only test and evaluate, while Fig. 6
In the case of evaluating the increase in K _o of the clay ground as in the embodiment shown in FIG. 2, it is characterized by performing two tests, an electric static cone penetration test CPT and a one-sided shear test DST. Is.

[0044]

According to the method for evaluating the static earth pressure coefficient of the pile or the sand compaction pile driving ground of the present invention described above, the static earth pressure coefficient of the ground by driving the pile or the sand compaction pile can be calculated. Appropriate evaluation can be applied to the design appropriately and easily, cost reduction of related construction can be achieved, and the economic efficiency of construction can be improved.

[Brief description of drawings]

FIG. 1 is a graph of 4 in one embodiment for evaluating the increase in K _o of sand ground by pile or SCP driving according to the method of the present invention.
It is a CPT test implementation position explanatory drawing before and after driving of the pile of a book.

2 is a CP before and after driving a pile in the embodiment of FIG.
It is a diagram showing the tip resistance force by T.

3 is a flowchart of an evaluation method in the embodiment of FIG.

FIG. 4 Clay ground by SCP casting by the method of the present invention
K_oTwo places in another embodiment for evaluating the increase
Tip resistance (q_T−σ
_VO)₍₀₎And undrained shear strength S_{un (DST)}Is a relationship diagram of
It

FIG. 5: 4 SCs in one embodiment for evaluating K _o increase of clay ground by SCP casting by the method of the present invention
It is explanatory drawing of the CPT test implementation position before and after the placement of P.

6 is a flowchart of an evaluation method in the embodiment of FIG.

FIG. 7 is a diagram showing a shear strength increase ratio of sand and clay due to an increase in K _o of the ground, as a replacement rate of the composite ground on which SCP is placed.

[Explanation of symbols]

1 pile 2 SCP

Claims (4)

[Claims] 1. A representative point in a construction area is selected, an electric static cone penetration test CPT is performed, and a cone tip resistance (q _T − before placing a pile or sand compaction pile).
σ _VO ) ₍₀₎ is obtained, and after CPT is performed, multiple test piles or sand compaction piles for test are placed so as to surround a typical point, and then the central portion between piles or sand compaction piles or piles or sand compaction piles are placed. performed CPT at a plurality of points, such as near, corn tip resistance of piles or sand compaction pile droplet after casting (q _T -σ _VO)
After obtaining ₍₁₎ , the cone tip resistance (q _T −σ _VO ) before and after placing the pile or sand compaction pile (q _T −σ _VO ) ₍₀₎ and (q
_T −σ _VO ) ₍₁₎ and static earth pressure coefficient K _{o ( 0)} and K before and after driving the pile or sand compaction pile
Relational expression with _{o (1)} : To calculate the static soil pressure coefficient of sandy ground after pile or sand compaction pile driving. 2. A representative point in the construction area is selected and electricity is selected.
Type Cone Penetration Test CPT
Cone tip resistance (q _T−σ_VO)
₍₀₎At the same time, obtain undisturbed sample at the same point,
Single shear test by recompression method for all undisturbed samples D
Perform ST and make sure that the sand compaction pile is not
Drainage shear strength S_{u (B)}Ask for, S_{u (B)}And (q_T−
σ_VO)₍₀₎After obtaining the correlation of
Performing DST in a more regular consolidated state,
Shear strength increase rate (S_{un (DST)}/ Σ^' _V), Then
Test sand compaction pie surrounding a representative site
Multiple Cements are placed, CPT is performed at multiple points after consolidation is completed
The cone tip resistance after sand compaction pile placement.
Anti (q_T−σ_VO)₍₁₎Get S_{u (B)}And (q_T−σ_VO)
₍₀₎After placing the sand compaction pile,
Undrained shear strength S of_{u (D)}And (q_T−σ_VO)₍₁₎connection of
Apply to S_{u (D)}After asking for
Static earth pressure coefficient K before and after placing the pile_{o (0)}
And K_{o (1)}And S_{u (D)}And S_{un (DST)}/ Σ^' _VSeki
Engagement: [Equation 2] From the clay ground after placing the sand compaction pile
Sand compaction pile driving to calculate static earth pressure coefficient
Evaluation method of static earth pressure coefficient of ground. 3. The static soil pressure coefficient of claim 2 calculated after placing the sand compaction pile is evaluated as the static soil pressure coefficient of the sand compaction pile itself. Evaluation method of pressure coefficient. 4. A plurality of cone tip resistances (q _T −σ _VO ) obtained by conducting an electric static cone penetration test CPT near the boundary between a plurality of sand compaction piles and clay.
The average value of ₍₁₎ is obtained, and the static earth pressure coefficient obtained according to the method of claim 2 or 3 is evaluated as the static earth pressure coefficient of the sand compaction pile itself. Evaluation method of static earth pressure coefficient.