KR101904229B1 - Replacement method of ground for raising seismic classification - Google Patents

Abstract

The present invention improves the earthquake ground grades which can be expected to be economically designed by increasing the shear wave velocity (V _S ) and standard penetration depth (N) of the entire ground by replacing part of the ground floor with reinforcing part This paper is about the ground replacement method for
(A) The shear wave velocity (V _S ) or the standard penetration depth (N) of the target ground is measured and the measured shear wave velocity (V _S ) or standard penetration depth (N) is measured Classifying the corresponding earthquake ground class; (b) setting a target ground class higher than the ground class of the target ground; (c) calculating a target standard penetration (N _T ) to reach the target ground grade; (d) calculating a target bearing force q _{T that} is a bearing force corresponding to the target standard penetration value N _T ; (e) further comprising: a portion of the target from the target wonjiban force _(T q) is calculated in terms of the physical data (P _S) of the substituted Soil substituted by a thickened portion; (f) the step of calculating the degree of substitution reinforcement portion (S) from the converted physical data (P _S); And (g) replacing a part of the target paper with a reinforcing portion by the substitution ratio (S) to form a substituted ground; And a control unit.

Description

{Replacement method of ground raising seismic classification for upgrading earthquake ground class}

The present invention improves the earthquake ground grades which can be expected to be economically designed by increasing the shear wave velocity (V _S ) and standard penetration depth (N) of the entire ground by replacing part of the ground floor with reinforcing part This paper is about the ground replacement method for

The seismic design means that the design is carried out considering the seismic load so that the structure can maintain its safety and exhibit its original function at the time of earthquake or after earthquake.

Structures selected as objects of seismic design for seismic design of various structures should have designed seismic strength considering seismic performance targets for each class so as to have seismic performance suitable for each class.

In the Basic Explanation of Structural Basic Design (2009), the ground is classified into 6 types as shown in Fig. 1, considering the local soil condition, geological condition, and the influence of the surface and underground terrain on the ground motion.

Since the earthquake ground class is classified according to the shear wave velocity (V _S ) or the interval of the standard penetration test value, the file format and the number of reinforcement vary greatly depending on the earthquake ground class.

In particular, even if the shear wave velocity (V _S ) or the standard penetration test value has a value close to the upper grade, it is classified as a low grade earthquake ground grade if it is lower than the corresponding grade.

However, due to the heterogeneity of the ground, the ground survey varies considerably depending on the survey location. Therefore, if it is not possible to approach the upper geological class by using these properties, it is frequent that the ground survey is repeated and the existing geological data is revised upward by discarding inappropriate data and replacing it with new data.

In this case, even if some grounds satisfy the earthquake ground classification, the ground part which is not suitable in the past will have a low ground grade, so the reliability of the ground survey can not be raised.

KR 10-1222565 B1

In order to solve the above-mentioned problems, the present invention provides a method of replacing and strengthening the ground itself, thereby increasing the earthquake resistance of the ground and the structure, increasing the earthquake ground grade itself, We want to provide the construction method.

또는

에 대입하여 목표 지반 등급에 도달하기 위한 목표표준관입치(N_T)를 산정하는 단계; (d) 상기 목표표준관입치(N_T)에 대응되는 지지력인 목표지지력(q_T)을 산정하는 단계; (e) 상기 목표지지력(q_T)으로부터 대상 원지반(1)의 일부가 보강부(2)에 의해 치환된 치환지반(3)의 환산물성치(P_S)를 Terzaghi의 지지력 공식에 의해 산정하는 단계; (f) 상기 환산물성치(P_S)는 단위 중량, 점착력 및 내부마찰각 중 어느 하나 이상으로, 상기 환산물성치(P_S)로부터 아래의 수학식에 의해 각각의 보강부(2)의 치환율(S)을 산정하는 단계;

및 (g) 상기 치환율(S)에 의해 대상 원지반(1)의 일부를 보강부(2)로 치환하여 치환지반(3)을 형성하는 단계; 를 포함하고, 상기 보강부(2)는 원지반(1)에 천공홀을 형성한 후, 천공홀 내부에 천공시 발생하는 부상토와 토양 고화제를 혼합하여 주입하여 형성되되, 상기 토양 고화제는 염화칼슘 22.4~35.7 중량부, 염화암모늄 12~26 중량부, 염화마그네슘 21.42~34.68 중량부, 황산 마그네슘 1.2~7 중량부, 알민산 소다 8~13 중량부, 리그린 설폰산염 4~10 중량부, 스테아린산 마그네슘 2.5~3.5 중량부, 2가 철화합물 1~2 중량부를 포함하는 것을 특징으로 하는 내진 지반 등급 상향을 위한 지반 치환 공법을 제공한다.
여기서, V_s는 목표 지반 등급의 최소전단파속도(m/s)이고, N은 표준관입치(타격횟수/300㎜)이며, P는 원지반의 물성치, P_PF는 보강부(2)의 물성치, P_S는 치환 후 환산물성치임.The present invention corresponding to (a) a target wonjiban (1), shear wave velocity (V _S) or standard penetration value (N) measured and the measured shear wave velocity (V _S) or standard penetration value (N) of the according to the preferred embodiment Classifying the earthquake ground class to be the earthquake ground class; (b) setting a target ground class higher than the ground class of the target ground board (1); (c) The minimum shear wave velocity of the target soil class is calculated using Equation

or

Calculating a target standard penetration value (N _T ) for reaching a target ground grade; (d) calculating a target bearing force q _{T that} is a bearing force corresponding to the target standard penetration value N _T ; (e) the step of estimating by the force formula for the converted physical data (P _S) of the substituted Soil (3) substituted by a part of the reinforcement part (2) of the target wonjiban (1) from the objective force (q _T) Terzaghi ; (f) the replacement ratio of the equivalent physical property values (P _S) per unit weight, the adhesive strength and to any one or more of the internal friction angle, the conversion properties, each of the reinforcement part (2) by the equation below from (P _S) (S) ;

And (g) replacing a part of the target ground board (1) with the reinforcing portion (2) by the replacement ratio (S) to form a replacement ground (3); Wherein the reinforcing part (2) is formed by forming a perforation hole in the ground sheet (1), mixing the floating soil generated during the perforation in the perforation hole with the soil strengthening agent, and injecting the soil strengthening agent From 22.4 to 35.7 parts by weight of calcium chloride, from 12 to 26 parts by weight of ammonium chloride, from 21.42 to 34.68 parts by weight of magnesium chloride, from 1.2 to 7 parts by weight of magnesium sulfate, from 8 to 13 parts by weight of sodium aluminate, from 4 to 10 parts by weight of leucine sulfonate, 2.5 to 3.5 parts by weight of magnesium stearate, and 1 to 2 parts by weight of a divalent iron compound.
Here, V _s is the minimum shear wave velocity of the ground target rates (m / s) and, N is the standard penetration value (count hit / 300㎜), P is the physical properties of wonjiban, P _PF is the physical properties of the reinforcing part (2), P _S is the converted property value after substitution.

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According to another preferred embodiment of the present invention, in the step (d), the target supporting force q _T is calculated by one of the bearing forces formulas of Meyerhof, Bowles, Parry. And provides a replacement method.

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According to another preferred embodiment of the present invention, the ground pattern is replaced with a reinforcing portion up to an upper depth of 30m.

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According to another preferred embodiment of the present invention, the reinforcing portion is formed up to a predetermined depth in the upper portion of the ground, and the enlarged portion is protruded from a portion of the reinforcing portion, thereby providing a ground replacement method for upgrading the earthquake ground grade.

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According to the present invention, in order to upgrade the earthquake ground class to an upper grade, the replacement ratio of the reinforcing portion may be calculated, and a portion of the ground surface may be replaced with the reinforcing portion according to the replacement ratio.

Therefore, it is possible to increase the seismic resistance of the ground and structure and to increase the shear wave velocity (V _S ) and standard penetration value (N) of the total displacement ground.

FIG. 1 is a table showing the types of ground according to the ground motion.
FIG. 2 is a flowchart showing a ground replacement method for upgrading the earthquake ground class according to the present invention. FIG.
3 is a view showing the ground displacement concept by the ground displacement method for upgrading the earthquake ground class according to the present invention.
4 is a view showing a position of an enlarged portion of a reinforcing portion according to a distribution of standard penetration values;
5 is a view showing an embodiment of a reinforcing portion formed with an enlarged portion;
6 shows various embodiments of the reinforcement arrangement according to the ground condition;

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings and preferred embodiments.

FIG. 2 is a flowchart showing a ground replacement method for upgrading the earthquake-resistance ground level according to the present invention, and FIG. 3 is a diagram showing a ground displacement concept for ground earthquake ground level upgrading according to the present invention.

또는

에 대입하여 목표 지반 등급에 도달하기 위한 목표표준관입치(N_T)를 산정하는 단계; (d) 상기 목표표준관입치(N_T)에 대응되는 지지력인 목표지지력(q_T)을 산정하는 단계; (e) 상기 목표지지력(q_T)으로부터 대상 원지반(1)의 일부가 보강부(2)에 의해 치환된 치환지반(3)의 환산물성치(P_S)를 Terzaghi의 지지력 공식에 의해 산정하는 단계; (f) 상기 환산물성치(P_S)는 단위 중량, 점착력 및 내부마찰각 중 어느 하나 이상으로, 상기 환산물성치(P_S)로부터 아래의 수학식에 의해 각각의 보강부(2)의 치환율(S)을 산정하는 단계;

및 (g) 상기 치환율(S)에 의해 대상 원지반(1)의 일부를 보강부(2)로 치환하여 치환지반(3)을 형성하는 단계; 를 포함하는 것을 특징으로 한다. (A) The shear wave velocity (V _S ) or the standard penetration depth (N) of the target ground (1) is measured and the measured shear wave velocity (V _S ) or standard penetration depth N) of the earthquake ground class; (b) setting a target ground class higher than the ground class of the target ground board (1); (c) The minimum shear wave velocity of the target soil class is calculated using Equation

or

Calculating a target standard penetration value (N _T ) for reaching a target ground grade; (d) calculating a target bearing force q _{T that} is a bearing force corresponding to the target standard penetration value N _T ; (e) the step of estimating by the force formula for the converted physical data (P _S) of the substituted Soil (3) substituted by a part of the reinforcement part (2) of the target wonjiban (1) from the objective force (q _T) Terzaghi ; (f) the replacement ratio of the equivalent physical property values (P _S) per unit weight, the adhesive strength and to any one or more of the internal friction angle, the conversion properties, each of the reinforcement part (2) by the equation below from (P _S) (S) ;

And (g) replacing a part of the target ground board (1) with the reinforcing portion (2) by the replacement ratio (S) to form a replacement ground (3); And a control unit.

FIG. 2 (a) shows the process of replacing the paperboard 1 according to the present invention.

In the step (a), the shear wave velocity V _S or the standard penetration value N of the target ground 1 is measured through the ground survey, and the earthquake ground class 1 ) (Step S11).

If for example the 340m / s the shear wave velocity (V _S) seismic ground level is S _D rating.

Next, in step (b), a target ground class higher than the ground class of the target ground 1 is set (step S12).

If the earthquake ground class of the target ground 1 in the step (a) is S _D grade, the target ground grade is S _C grade.

And (c) a target standard penetration value (N _T ) for reaching the target ground grade is calculated (step S13).

In step (c), a minimum standard penetration value (N) is selected as the target standard penetration depth (N _T ) to upgrade the target ground grade.

At this time, in the step (c), the target standard penetration value (N _T ) may be constituted by the minimum standard penetration value of the target ground grade.

That is, the target standard penetration value (N _T ) can be directly calculated from the minimum standard penetration value of the target ground grade. For example, if the target ground grade is S _{C, the} target standard penetration value (N _T ) can be calculated to be greater than 50.

또는 중 어느 하나에 대입하여 계산할 수 있다.Alternatively, in the step (c), the target standard penetration value (N _T ) is obtained by multiplying the minimum shear wave velocity (V _S )

or Or the like.

Where V _s is the minimum shear wave velocity (m / s) of the target soil class and N is the standard penetration depth (number of impacts / 300 mm).

That is, unlike the case where the target standard penetration value (N _T ) is set to the minimum standard penetration value of the target soil class, the standard penetration value (N) corresponding to the minimum ground shear wave velocity V _S The target standard penetration value (N _T ) can also be calculated.

The shear wave velocity (V _S ) has a constant correlation with the standard penetration value (N). The range of the general shear wave velocity (V _S ) (1970) and the Ohba & Trauma equation (1990) can be used to estimate the target standard penetration value (N _T ).

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Imai & Yoshimura expression

Ohba & Trauma formula

The above equations are reliable because they are based on actual measurement results although there is some variance. Any of the N values calculated from the above three equations may be selected.

For example, if the target ground grade is S _C grade, then the minimum shear wave velocity (V _S ) is 360 m / s, and the target standard penetration value (N _T ) can be calculated using the above equation.

Next, (d) a target supporting force q _T , which is a supporting force corresponding to the target standard penetration value N _T , is calculated (step S14).

In the step (d), the target bearing force q _T may be calculated by any one of the bearing forces formulas of Meyerhof, Bowles, and Parry.

The bearing capacity and the standard penetration value (N) have a constant correlation, and the target bearing capacity (q _T ) is calculated by inserting the target standard penetration value (N _T ) calculated in step c) into the Meyerhof, Bowles, can do.

The Meyerhof equation is a formula that suggests the relationship between the standard penetration value (N) and net allowable bearing capacity in sandy soil.

Where N _T is the target standard penetration depth (number of strikes / 300 mm), and B is the width of the foundation (m).

The Bowles equation can be expressed as a modified bearing capacity formula as follows.

, S_e는 탄성 침하량(㎜), B는 기초의 폭(m), D_f는 기초의 깊이(m)를 의미한다.Where N _T is the target standard penetration depth (number of strikes / 300 mm), F _d is the depth coefficient

, S _e is the elastic settlement (mm), B is the width of the foundation (m), and D _f is the depth of foundation (m).

The Parry equation suggested a correlation between the standard penetration value (N) and the ultimate bearing capacity at a shallow foundation of sand soil.

Where N _Tf is the target site standard penetration (number of strikes / 300 mm) located at a depth of 0.75B from the expected foundation ground, B is the width of the foundation (m) and D _f is the depth of foundation (m) .

Later, (e) calculates the equivalent physical property values (P _S) of the substituted Soil (3) substituted by a part of the reinforcement part (2) of the target wonjiban (1) from the objective force (q _T) (step S15).

The (e) step, by assuming an arbitrary initial rates in terms of physical property values (P _S) the home, and by trial and error approach (trial and error) in terms of the calculated the target bearing capacity (q _T) estimating physical data (P _S) .

In addition, the physical properties in terms of (P _S) in the step (e), can be estimated by the formula of Terzaghi force.

That is, it is possible to calculate the converted physical properties (P _S ) of the ground after inversion from the value of q _T given from the bearing capacity formula of Terzaghi as follows.

Here, γ ₁ is the unit weight of the base unit weight of the lower surface the upper ground, γ ₂ is based on a bottom below the ground, c is the cohesive, α, β is a shape factor, B is the base width, D _f is embedment depth, N _c, N _q and N _γ are the bearing capacity factors for the overall shear failure, respectively, as follows:

Here, φ denotes an internal friction angle.

And (f) calculates a replacement ratio (S) of the reinforcement part (2) from the physical properties in terms of (P _S) (step S16).

That is, the (f) step, to calculate the degree of substitution (S) to obtain an equivalent physical property values (P _S) calculated by the input value the properties of the target wonjiban (1) Physical properties and the reinforcing portion (2).

The replacement ratio S is a ratio of the reinforcing portion 2 to be replaced with the reinforcing portion 2 of the target base fabric 1 and can be expressed as the following formula.

Here, S is the replacement ratio, A is the volume of the target area (m 3), and A _PF is the volume (m 3) of the reinforced portion to be replaced.

And in step (f) above, in terms of physical property values (P _S) is any one or more of a unit weight, the adhesion and internal friction angle, each of which can be calculated by the equation below.

Where P is the physical property of the paper, P _PF is the physical property of the reinforcement, and P _S is the converted physical property.

In the above-mentioned Terzaghi bearing capacity formula, the bearing capacity is determined by unit weight, cohesion, and internal friction angle.

In this case, the converted physical properties (P _S ) of the ground after substitution, unit weight, adhesive force and internal friction angle can be calculated by the following equations.

Therefore, it is possible to calculate the replacement ratio (S) by inputting the converted physical property value P _S , the physical property value P of the paperboard, and the property value P _PF of the reinforcement portion calculated from the step (e)

For example, given the physical properties (P) of the paper and the physical properties (P _PF ) of the reinforcement, and the replacement ratio (S) is calculated as 50%, the converted physical properties (P _S ) are as shown in Table 1 below.

Classification Unit weight
(t / m3) adhesiveness
(t / m 2) Internal friction angle
(°) Paperboard 1.8 0 15 Reinforced portion 1.9 5 30 Substituted ground 1.85 2.5 25

Finally, (g) Substituting the portion (s) of the target ground 1 into the reinforcing portion 2 by the replacement ratio (S), a replacement ground 3 is formed (Step S21).

That is, as shown in FIG. 3 (a), the pre-replacement ground 1 can be reinforced by forming the replacement ground 3 as shown in FIG. 3 (b). Fig. 3 (b) shows an embodiment in which the reinforcing portion 2 is constructed as a pile.

In the step (g), the target ground 1 may be replaced with the reinforcing portion 2 up to the depth of 30m.

Most of the grounds in Korea are located within 30m of bedrock, and amplification of response spectrum occurs in short period rather than long period.

In addition, the reinforcement portion 2 may be formed by forming a perforation hole in the ground plate 1, and then injecting the floating soil and the soil strengthening agent, which are generated when the perforation hole is formed, into the perforation hole.

When the soil strengthening agent is mixedly injected into the floating soil, the compressive strength can be increased to increase the supporting force.

Since the substitution ratio S is the ratio of the reinforcing portion 2 to be replaced in the entire ground surface 1, the ground improvement method of dividing the ground in the vertical direction and replacing only the upper part, that is, the shallow part with a shallow depth of 0.5-1.0 m Can be considered.

However, since it is difficult to control the lower ground settlement, it is difficult to control the lower ground settlement. Therefore, in the present invention, it is possible to efficiently cope with the ground settlement by perforating the perforation hole at the entire depth, preferably, Respectively.

The soil toughening agent comprises 22.4 to 35.7 parts by weight of calcium chloride, 12 to 26 parts by weight of ammonium chloride, 21.42 to 34.68 parts by weight of magnesium chloride, 1.2 to 7 parts by weight of magnesium sulfate, 8 to 13 parts by weight of sodium aluminate, To 10 parts by weight, magnesium stearate 2.5 to 3.5 parts by weight, and divalent iron compound 1 to 2 parts by weight.

The addition of the sodium aluminate and the recrystallized sulfonate salt enables uniform distribution among the weak soil particles, improves the bonding of the soft soil and induces a stable hydration reaction.

The soil stabilizer is preferably in the form of an aqueous solution for 30 to 35 liters of water per 1 m 3 of soil in order to improve workability and structural stability.

Preferably, the soil solidifying agent is mixed with 1 to 2 kg of a soil solidifying agent and 50 to 12 kg of a binder containing cement to 1 m 3 of soil to solidify the soft ground.

The binder may be applied only with cement. However, when mixed with 30 to 40 parts by weight of cement, 50 to 60 parts by weight of slag or fly ash, and 5 to 15 parts by weight of gypsum, excellent physical properties can be obtained, It can also be mixed with a topic and provided in the form of a premix.

FIG. 2B is a flowchart showing a process in which the earthquake ground grades are upgraded after replacing part of the ground 1 with the reinforcement 2. FIG.

That is, after the replacement of the paperboard 1 (S21), the physical properties of the corresponding ground are increased (S22), so that the ground supporting force also increases (S23), and the standard penetration value N or the shear wave velocity V _S increases (S24).

As a result, the earthquake ground class can be upgraded (S25).

As described above, according to the present invention, the replacement ratio S of the reinforcement portion 2 is calculated to raise the earthquake ground class to an upper grade, and a portion of the ground board 1 is reinforced by the reinforcement portion 2 in accordance with the replacement ratio S . Therefore, the earthquake ground class can be upgraded by increasing the shear wave velocity (V _S ) and the standard penetration depth (N) of the total displacement ground (3).

Especially, when the ground level (1) is S _D class, which is hard soil layer, it can be upgraded to S _C grade, which is very dense soil or soft rock so that economic basic design is possible.

Fig. 4 is a view showing the position of the enlarged portion of the reinforcing portion according to the distribution of the standard penetration value, and Fig. 5 is a view showing an embodiment of the reinforcing portion formed with the enlarged portion.

As shown in FIG. 4, the reinforcing portion 2 is formed to have a predetermined depth from the upper portion of the ground, and the enlarged portion 21 may be protruded from a portion of the ground.

Since the shear wave velocity (V _S ) or the standard penetration value (N) is an average value for the 30 m soil layer below the earth's surface, a certain deviation may occur depending on the vertical depth.

Therefore, when the ground survey results show that the bearing capacity is relatively low, the enlarged portion 21 is provided so as to secure a uniform supporting force over the entire depth of the ground.

Generally, as shown in FIG. 4 (a), when the soft layer is present on the upper portion, the enlarged portion 21 is positioned on the upper ground portion. In some cases, as shown in FIG. 4 (b), when reinforcement is required in the middle of the ground, the enlarged portion 21 may be located at the intermediate portion.

When the enlarged portion 21 is positioned as described above, there is no need to reinforce the ground over the entire depth of the ground, which is economical.

4 (a), the enlarged portion 21 is disposed in accordance with the calculated replacement ratio, and the reinforced portion 2 under the enlarged portion 21 is controlled to control the settlement For example.

A plurality of reinforcement portions 2 under the enlarged portion 21 may be provided as shown in FIG.

6 is a view showing various embodiments of reinforcement arrangement according to the ground condition.

As shown in FIG. 6 (a), the reinforcing portion 2 may have a different depth depending on the vertical distribution of the ground supporting force. In this case, the depth of the reinforcing portion 2 can be formed within 30 m depending on the ground condition.

It is also possible to adjust the distance between the adjacent reinforcing portions 2 according to the horizontal distribution of the ground supporting force as shown in Fig. 6 (b).

Of course, it is also possible to adjust the vertical depth and the horizontal spacing of the reinforcing portion 2 simultaneously according to the distribution of the supporting force.

1: Paperboard
2:
21:
3: Replacement ground

Claims (10)

(a) classifying the seismic soil rating corresponding to the target wonjiban (1), shear wave velocity (V _S) or standard penetration value (N) measured and the measured shear wave velocity (V _S) or standard penetration value (N) of ;
(b) setting a target ground class higher than the ground class of the target ground board (1);
(c) The minimum shear wave velocity of the target soil class is calculated using Equation

or

Calculating a target standard penetration value (N _T ) for reaching a target ground grade;
(d) calculating a target bearing force q _{T that} is a bearing force corresponding to the target standard penetration value N _T ;
(e) the step of estimating by the force formula for the converted physical data (P _S) of the substituted Soil (3) substituted by a part of the reinforcement part (2) of the target wonjiban (1) from the objective force (q _T) Terzaghi ;
(f) the replacement ratio of the equivalent physical property values (P _S) per unit weight, the adhesive strength and to any one or more of the internal friction angle, the conversion properties, each of the reinforcement part (2) by the equation below from (P _S) (S) ; And

(g) forming a replacement ground (3) by replacing part of the target ground board (1) with the reinforcing portion (2) by the replacement ratio (S); Lt; / RTI >
The reinforcement portion 2 is formed by forming a perforation hole in the ground sheet 1 and then injecting a mixture of a floating soil and a soil strengthening agent generated in the perforation hole into the perforation hole,
The soil toughening agent comprises 22.4 to 35.7 parts by weight of calcium chloride, 12 to 26 parts by weight of ammonium chloride, 21.42 to 34.68 parts by weight of magnesium chloride, 1.2 to 7 parts by weight of magnesium sulfate, 8 to 13 parts by weight of sodium aluminate, To 10 parts by weight of magnesium stearate, 2.5 to 3.5 parts by weight of magnesium stearate, and 1 to 2 parts by weight of a divalent iron compound.
Here, V _s is the minimum shear wave velocity of the ground target rates (m / s) and, N is the standard penetration value (count hit / 300㎜), P is the physical properties of wonjiban, P _PF is the physical properties of the reinforcing part (2), P _S is the converted property value after substitution.
delete delete The method of claim 1,
In the step (d), the target supporting force (q _T ) is calculated by one of the bearing forces formulas of Meyerhof, Bowles, Parry.
delete delete The method of claim 1,
Wherein the object ground (1) is replaced by a reinforcement (2) up to a depth of 30m above the ground.
delete The method of claim 1,
The reinforcing part (2) is formed up to a predetermined depth in the upper part of the ground, and an enlarged part (21) is protruded in a part of the section. delete

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