CN108930294B - Method for determining uplift amount of low-embankment-base saline soil pile foundation after reinforcement - Google Patents

Abstract

A method for determining the uplift amount of low-embankment base saline soil pile foundation after reinforcement is used for scientifically and reasonably determining the uplift amount of low-embankment base saline soil after pile foundation reinforcement, and the method can adapt to the actual engineering needs and comprises the following steps: determining depth of neutral point of pile foundation in saline soill₀Calculating and determining the low embankment pile foundation uplift deformation calculation thickness h by using the atmospheric cooling influence depth l below the top surface of the low embankment₀(ii) a Determining the temperature T of the ith layer of soil before cooling in winter_i1The like; carrying out salt expansion test, water content test, soil particle specific gravity test and severe test on the saline soil sample to determine the salt expansion index C of the i-th layer soil_siThe like; determining the uplift amount s of the low embankment base after the saline soil pile base is reinforced through the following formula_e：

Description

Method for determining uplift amount of low-embankment-base saline soil pile foundation after reinforcement

Technical Field

The invention relates to the technical field of geotechnical engineering, in particular to a method for determining the uplift amount of a low-embankment base saline soil pile base after reinforcement.

Technical Field

At present, the salt expansion (i.e. uplift) of saline soil foundation is mostly determined by 'construction code of saline soil region' (SY/T0317-2012), i.e. the salt expansion is determined according to the following formula:

S_η0＝η·H

in the formula, S_η0The total salt expansion amount of the saline soil foundation is unit mm, η is the salt expansion coefficient, and H is the effective salt expansion area thickness is unit mm.

The saline soil foundation is raised and deformed under the condition of cooling in winter, so that the ballastless track plate of the high-speed railway is easy to crack, a great ballastless track disease is caused, and even the driving safety of a high-speed train is endangered. The pile foundation reinforcement can effectively control the uplift deformation of the saline soil foundation, but no feasible method exists for determining the uplift amount of the foundation after the pile foundation reinforcement at present, and if the determination is carried out by adopting the calculation formula, the technical defects exist in that the pile foundation replacement, pile foundation anchoring, the self gravity of the saline soil and the additional load influence of a low embankment cannot be considered, and the salt expansion difference of soil layers with different depths cannot be considered.

Disclosure of Invention

The invention aims to provide a method for determining the uplift amount of a low-embankment base saline soil pile foundation after reinforcement, so as to scientifically and reasonably determine the uplift amount of the low-embankment base saline soil after pile foundation reinforcement, and adapt to the actual engineering requirements.

The technical scheme adopted by the invention for solving the technical problems is as follows:

the invention provides a method for determining the uplift amount of a low-embankment base saline soil pile foundation after reinforcement, which comprises the following steps:

(1) determining the depth l of the neutral point of the pile foundation in the saline soil through field investigation or data query₀The unit m; determining the influence depth l of atmospheric cooling below the top surface of the low embankment in unit m; determining the bulging deformation of the low-embankment pile foundation by the following formula to calculate the thickness h₀：

In the formula, h₀Calculating the thickness in m for the bulging deformation of the low embankment pile foundation; l is the influence depth of atmospheric cooling below the top surface of the low embankment, unit m; h is_dFilling the height of the low embankment by m;

(2) determining the temperature T of the i-th layer soil before being cooled in winter through field investigation or data query or field in-situ test_i1Determining the lowest temperature T of the i-th layer soil during the winter cooling period in unit DEG C_i2In units of; determining the temperature T above the neutral point position_i1Down to T_i2Upward tangential force f generated by the i-th layer soil on the side surface of the pile foundation_iIn kPa; determining the temperature T below the neutral point_i1Down to T_i2Downward tangential force f generated by the i-th layer soil on the side surface of the pile foundation_i', units kPa;

(3) determining the salt expansion index C of the i-th layer soil by collecting saline soil samples on site and carrying out a salt expansion test, a water content test, a soil particle specific gravity test and a severe test indoors_si(ii) a Determination of the temperature T_i1Down to T_i2Salt expansion force sigma of i-th layer of saline soil_TiIn kPa; determination of the temperature T_i1Initial porosity e of lower i-th layer soil_0i(ii) a Determining effective dead weight stress sigma of ith layer soil_y0iIn kPa;

(4) determining the uplift amount s of the low-embankment base after the saline soil pile foundation is reinforced by the following formula_e：

In the formula, s_eThe uplift amount of the reinforced low-embankment base saline soil pile foundation is unit mm; n is the number of divided soil layers in the thickness calculation range of the uplift deformation of the pile foundation at the bottom of the low embankment; Δ s_eiThe uplift amount of the i-th layer soil is unit mm; c_siThe salt swelling index of the ith layer soil; Δ z_iThe thickness of the i-th layer of soil is the layering thickness in mm; e.g. of the type_0iIs a temperature T_i1Initial porosity ratio of lower i-th layer soil；σ_y0iThe effective self-weight stress of the i-th layer soil is expressed in unit of kPa; delta sigma_yiThe effective stress change of the i-th layer soil under the load action of the low embankment is expressed in unit of kPa; sigma_uiEndowing the pile foundation with the anchoring force of the ith layer of soil in unit of kPa; sigma_biIs a temperature T_i1Down to T_i2Salt expansion force of the ith layer of soil of the rear pile foundation in unit of kPa.

The method has the advantages that on the basis of considering pile foundation replacement, pile foundation anchoring, self gravity of saline soil and additional load influence of the low embankment, the method for determining the uplift amount of the reinforced low-embankment base saline soil pile foundation is established by combining the characteristics of cooling difference and salt expansion difference of different soil layers of the foundation, not only makes up for the technical defects of the saline soil region building specification (SY/T0317-2012), but also provides reference for the reinforcement design of the low-embankment base saline soil pile foundation based on uplift deformation control, is convenient to implement, needs few in calculation parameters, is clear in process, and meets the actual engineering requirements.

Drawings

Fig. 1 is a schematic cross-sectional view of reinforcement of a low-embankment-base saline soil pile base.

The figures show the components and corresponding references: low embankment M, pile foundation 1, salinized soil D, pile foundation pile diameter D, pile foundation pile spacing s, air cooling influence depth l below low embankment top surface, low embankment filling height h_d。

Detailed Description

The invention is further illustrated by the following specific examples in conjunction with the accompanying drawings.

Referring to fig. 1, the method for determining the uplift amount of the low-embankment-base saline soil pile foundation after reinforcement comprises the following steps:

(1) determining the depth l of the neutral point of the pile foundation 1 in the saline soil D through field investigation or data query₀The unit m; determining the influence depth l of atmospheric cooling below the top surface of the low embankment in unit m; determining the bulging deformation of the low-embankment pile foundation by the following formula to calculate the thickness h₀：

In the formula, h₀Calculating the thickness in m for the bulging deformation of the low embankment pile foundation; l is the influence depth of atmospheric cooling below the top surface of the low embankment, unit m; h is_dFilling the height of the low embankment by m;

(2) determining the temperature T of the i-th layer soil before being cooled in winter through field investigation or data query or field in-situ test_i1Determining the lowest temperature T of the i-th layer soil during the winter cooling period in unit DEG C_i2In units of; determining the temperature T above the neutral point position_i1Down to T_i2The upward tangential force f generated by the i-th layer soil on the side surface of the pile foundation 1_iIn kPa; determining the temperature T below the neutral point_i1Down to T_i2Downward tangential force f generated by the i-th layer soil on the side surface of the pile foundation 1_i', units kPa;

(3) determining the salt expansion index C of the i-th layer soil by collecting a saline soil D sample on site and carrying out a salt expansion test, a water content test, a soil particle specific gravity test and a severe test indoors_si(ii) a Determination of the temperature T_i1Down to T_i2Salt expansive force sigma of i-th layer of saline soil D_TiIn kPa; determination of the temperature T_i1Initial porosity e of lower i-th layer soil_0i(ii) a Determining effective dead weight stress sigma of ith layer soil_y0iIn kPa;

(4) determining the uplift amount s of the low-embankment base after the saline soil pile foundation is reinforced by the following formula_e：

In the formula, s_eThe uplift amount of the reinforced low-embankment base saline soil pile foundation is unit mm; n is the number of divided soil layers in the thickness calculation range of the uplift deformation of the pile foundation at the bottom of the low embankment; Δ s_eiThe uplift amount of the i-th layer soil is unit mm; c_siThe salt swelling index of the ith layer soil; Δ z_iThe thickness of the i-th layer of soil is the layering thickness in mm; e.g. of the type_0iIs a temperature T_i1Initial porosity of the lower i-th layer of soil; sigma_y0iThe effective self-weight stress of the i-th layer soil is expressed in unit of kPa; delta sigma_yiThe effective stress change of the i-th layer soil under the M load action of the low embankment is expressed in unit of kPa; sigma_uiEndowing the pile foundation 1 with the anchoring force of the ith layer of soil in unit of kPa; sigma_biIs a temperature T_i1Down to T_i2Salt expansion force of the ith layer of soil of the rear pile foundation 1 in unit of kPa.

And the neutral point is a boundary point of circumferential tangential force and downward tangential force of the pile foundation 1 after the foundation is uplifted.

In the step (4), the pile foundation imparts an anchoring force σ to the i-th layer soil_uiDetermined by the following equation:

in the formula sigma_uiEndowing the pile foundation with the anchoring force of the ith layer of soil in unit of kPa; d is the pile diameter of the pile foundation and is unit m; f. of_iIs the temperature T below the neutral point_i1Down to T_i2The downward tangential force of the i-th layer soil on the side surface of the pile foundation is expressed in unit of kPa; Δ z_iThe thickness of the i-th layer of soil is the layering thickness in mm; s is the pile spacing of the pile foundation, unit m; l₀The depth of a neutral point of a pile foundation at the bottom of the low embankment is unit m; f. of_iIs the temperature T above the neutral point_i1Down to T_i2And the upward tangential force of the i-th layer soil on the side surface of the pile foundation is expressed in unit of kPa.

In the step (4), the temperature T_i1Down to T_i2Salt expansive force sigma of i-th layer soil of rear pile foundation_biDetermined by the following equation:

in the formula sigma_biIs a temperature T_i1Down to T_i2Salt expansion force of the ith layer of soil of the rear pile foundation in unit of kPa; sigma_TiIs a temperature T_i1Down to T_i2The salt swelling capacity of the saline soil of the ith layer is expressed in unit of kPa; m is the replacement rate of pile soil area, m is pi d²/4s²(ii) a d is the pile diameter of the pile foundation and is unit m; s is the pile spacing of the pile foundation, unit m; l is the pile length of the pile foundation and is unit m; h is₀For low embankmentThe bottom pile foundation uplift deformation is used for calculating the thickness in m; z is the foundation depth at the bottom of the low embankment in m.

In the steps (1) - (4), the pile foundation 1 is arranged with square equal-interval piles.

In the steps (1) - (4), the ith layer of soil is located within the calculated thickness range of the uplift deformation of the pile foundation at the bottom of the low embankment.

In the step (3), the temperature T_i1Down to T_i2Salt expansion force sigma of i-th layer of saline soil_TiIs a temperature T_i1Down to T_i2The pressure corresponding to the initial pore ratio in the soil body salt expansion curve; the abscissa of the salt swelling curve is pressure, and the ordinate is porosity ratio.

In the step (3), the salt swelling index C of the i-th layer soil_siIs a temperature T_i1Down to T_i2The average slope of the soil body salt expansion e-logp curve in a certain pressure range is determined according to the following formula:

in the formula e_jFor the post-compression stabilization temperature T of the soil body under the j-th stage pressure_i1Down to T_i2The resulting void ratio; p is a radical of_jIs the j stage pressure; e.g. of the type_j+1The temperature T after the soil body is compressed and stabilized under the j +1 th level pressure_i1Down to T_i2The resulting void ratio; p is a radical of_j+1Is the j +1 th stage pressure.

In the above steps (3) to (4), the effective dead weight stress σ of the i-th layer soil_y0iCan be determined by a hierarchical summation method.

In the steps (3) - (4), the effective stress change delta sigma generated by the i-th layer soil under the action of the low embankment load_yiCan be determined by using Boussinesq theory.

Example (b):

referring to fig. 1, a high-speed ballastless track low embankment M is built on a certain saline soil D foundation, the filling height is 1.9M, the top surface width is 13.4M, and the side slope ratio is 1: 1.5. The saline soil D of low embankment M bottom is cooling process easily takes place the uplift and is out of shape in winter, in order to weaken or eliminate saline soil D foundation uplift and warp, plans to adopt pile foundation 1 to carry out the foundation reinforcement, and 1 pile length of pile foundation 6M, pile footpath 0.5M, pile foundation 1 are according to the equidistant stake of laying of square, and the stake interval is 1.4M.

The method is adopted to determine the uplift amount (the position is the center of the roadbed) of the reinforced low-embankment M-base saline soil D pile foundation 1, and the method comprises the following specific steps:

(1) determining the depth l of the neutral point of the salinized soil D pile foundation 1 through field investigation or data query₀Is 3.0 m; determining the influence depth l of atmospheric cooling below the top surface of the low embankment M to be 3.9M; determining the bulging deformation calculation thickness h of the pile foundation 1 at the bottom of the M low-embankment through the following formula₀：

When l is 3.9m>h_d1.9M, so the thickness h is calculated by the bulging deformation of the pile foundation 1 at the bottom of the low embankment M₀＝l-h_d＝3.9-1.9＝2.0(m)。

(2) Determining the temperature T of the i-th layer soil before being cooled in winter through field investigation or data query or field in-situ test_i1Determining the lowest temperature T of the i-th layer soil during the winter cooling period in unit DEG C_i2In units of; determining the temperature T above the neutral point position_i1Down to T_i2The upward tangential force f generated by the i-th layer soil on the side surface of the pile foundation 1_iIn kPa; determining the temperature T below the neutral point_i1Down to T_i2Downward tangential force f generated by the i-th layer soil on the side surface of the pile foundation 1_i', units kPa; f. of_iAnd f_i' determination results are shown in Table 1, T_i1And T_i2The results of the determination are shown in Table 2.

TABLE 1. sigma_uiAnd the result of the determination of

i	Δzi	d	fi	fi'	s	σ	ui
								1	200	0.5	51	/	1.4	40.9
2	200	0.5	51	/	1.4	40.9
							3	200	0.5	51	/	1.4	40.9
4	200	0.5	42	/	1.4	33.7
							5	200	0.5	42	/	1.4	33.7
6	200	0.5	42	/	1.4	33.7
							7	200	0.5	40	/	1.4	32.1
8	200	0.5	40	/	1.4	32.1
							9	200	0.5	40	/	1.4	32.1
10	200	0.5	40	/	1.4	32.1
							11	200	0.5	40	/	1.4	32.1
12	200	0.5	40	/	1.4	32.1
							13	200	0.5	40	/	1.4	32.1
14	400	0.5	40	/	1.4	32.1
							15	300	0.5	/	32	1.4	0
16	400	0.5	/	32	1.4	0
							17	400	0.5	/	48	1.4	0
18	400	0.5	/	48	1.4	0

(3) Determining the salt expansion index C of the i-th layer soil by collecting a saline soil D sample on site and carrying out a salt expansion test, a water content test, a soil particle specific gravity test and a severe test indoors_si(ii) a Determination of the temperature T_i1Down to T_i2Salt expansive force sigma of i-th layer of saline soil D_TiIn kPa; determination of the temperature T_i1Initial porosity e of lower i-th layer soil_0i(ii) a Determining effective dead weight stress sigma of ith layer soil_y0iIn kPa; c_si、σ_Ti、e_0i、σ_y0iThe results of the determination are shown in Table 2.

(4) Determining the uplift amount s of the reinforced low-embankment M-base saline soil D pile foundation 1 by the following formula_e：

The i-th layer soil uplift quantity delta s of the bottom of the low embankment M (roadbed center)_eiThe detailed calculation process of (1) is shown in Table 2, and in the calculation process of Table 2, if Δ s_ei< 0, then Δ s_eiTake 0.

Then, the uplift amount s of the salinized soil D pile foundation 1 of the M base (the center of the roadbed) of the low embankment after reinforcement_e：

Therefore, the uplift amount of the pile foundation 1 of the salinized soil D of the obtained low embankment M base (roadbed center) after reinforcement is 0.65 mm.

TABLE 2 calculation procedure for the amount of uplift of the i-th layer of soil

i	Δzi	Ti1	Ti2	Csi	σTi	e0i	γi	σy0i	σbi	σui	Δσyi	Δsei
													1	200	4.8	-17.3	0.035	123.5	0.71	19.8	2	111.1	40.9	48.8	0.37
2	200	4.4	-15.9	0.035	115.1	0.71	19.8	5.9	103.5	40.9	48.8	0.24
													3	200	4.1	-14.7	0.035	102.1	0.71	19.8	9.9	91.8	40.9	48.8	0.04
4	200	3.8	-13.6	0.035	87.8	0.71	19.8	13.9	79.0	33.7	48.7	0
													5	200	3.5	-12.5	0.035	74.8	0.71	19.8	17.8	67.3	33.7	48.5	0
6	200	3.2	-11.5	0.035	61.1	0.71	19.8	21.8	55.0	33.7	48.3	0
													7	200	3	-10.7	0.035	45.5	0.71	19.8	25.7	40.9	32.1	48.1	0
8	200	2.7	-9.8	0.035	32.5	0.71	19.8	29.7	29.2	32.1	47.8	0
													9	200	2.5	-9.1	0.034	26.0	0.706	19.8	33.7	23.4	32.1	47.5	0
10	200	2.3	-8.4	0.033	21.5	0.702	19.8	37.6	19.3	32.1	47.1	0

The method is established by combining the characteristics of cooling difference and salt expansion difference of different soil layers of the foundation on the basis of considering the influence of pile foundation replacement, pile foundation anchoring, self gravity of saline soil and additional load of the low embankment, not only overcomes the technical defects of the conventional construction specification (SY/T0317-2012) of the saline soil area, but also provides reference for the reinforcement design of the saline soil pile foundation of the low embankment base based on the bulge deformation control, and is convenient to implement, less in required calculation parameters, clear in flow and capable of meeting the actual engineering requirements.

The foregoing is illustrative of the principles of the present invention for determining the amount of post-consolidation heave for a low-embankment base saline soil pile foundation, and is not intended to limit the invention to the specific methods and applications shown and described, and it is intended that all modifications and equivalents thereof which may be utilized are within the scope of the claims.

Claims (7)

1. A method for determining the uplift amount of a low-embankment base saline soil pile base after reinforcement comprises the following steps:

(1) determining the depth l of the neutral point of the pile foundation (1) in the saline soil (D) through field investigation or data query₀The unit m; determining the influence depth l of atmospheric cooling below the top surface of the low embankment in unit m; determining the bulging deformation of the low-embankment pile foundation by the following formula to calculate the thickness h₀：

In the formula, h₀Calculating the thickness in m for the bulging deformation of the low embankment pile foundation; l is the influence depth of atmospheric cooling below the top surface of the low embankment, unit m; h is_dFilling the height of the low embankment by m; the neutral point is a boundary point of circumferential tangential force and downward tangential force of the pile foundation (1) after the foundation is uplifted;

(2) determining the temperature T of the i-th layer soil before being cooled in winter through field investigation or data query or field in-situ test_i1Determining the lowest temperature T of the i-th layer soil during the winter cooling period in unit DEG C_i2In units of; determining the temperature T above the neutral point position_i1Down to T_i2The upward tangential force f generated by the i-th layer soil on the side surface of the pile foundation (1)_iIn kPa; determining the temperature T below the neutral point_i1Down to T_i2Downward tangential force f generated by the i-th layer soil on the side surface of the pile foundation (1)_i', units kPa;

(3) the salt expansion index C of the soil at the i-th layer is determined by collecting a soil sample of the saline soil (D) on site and carrying out a salt expansion test, a water content test, a soil particle specific gravity test and a severe test indoors_si(ii) a Determination of the temperature T_i1Down to T_i2Salt expansive force sigma of the i-th layer of saline soil (D)_TiIn kPa; determination of the temperature T_i1Initial porosity e of lower i-th layer soil_0i(ii) a Determining effective dead weight stress sigma of ith layer soil_y0iIn kPa;

(4) determining the uplift amount s of the low-embankment base after the saline soil pile foundation is reinforced by the following formula_e：

In the formula, s_eThe uplift amount of the reinforced low-embankment base saline soil pile foundation is unit mm; n is the number of divided soil layers in the thickness calculation range of the uplift deformation of the pile foundation at the bottom of the low embankment; Δ s_eiThe uplift amount of the i-th layer soil is unit mm; c_siThe salt swelling index of the ith layer soil; Δ z_iThe thickness of the i-th layer of soil is the layering thickness in mm; e.g. of the type_0iIs a temperature T_i1Initial porosity of the lower i-th layer of soil; sigma_y0iThe effective self-weight stress of the i-th layer soil is expressed in unit of kPa; delta sigma_yiThe effective stress change of the i-th layer soil under the load action of the low embankment (M) is expressed in unit of kPa; sigma_uiEndowing the pile foundation (1) with the anchoring force of the ith layer of soil in unit of kPa; sigma_biIs a temperature T_i1Down to T_i2Salt expansion force of the ith layer of soil of the rear pile foundation (1) in unit of kPa.

2. The method for determining the uplift amount of the low-embankment-base saline soil pile foundation after reinforcement according to claim 1, wherein the method comprises the following steps: in the step (4), the pile foundation (1) gives the anchoring force sigma to the i-th layer soil_uiDetermined by the following equation:

in the formula sigma_uiEndowing the pile foundation (1) with the anchoring force of the ith layer of soil in unit of kPa; d is the pile diameter of the pile foundation (1) and the unit m; f. of_iIs the temperature T below the neutral point_i1Down to T_i2Downward tangential force of the i-th layer soil on the side surface of the pile foundation (1) in unit of kPa; Δ z_iThe thickness of the i-th layer of soil is the layering thickness in mm; s is the pile spacing of the pile foundation (1) and the unit m; l₀The depth of a neutral point of a pile foundation (1) at the bottom of a low embankment (M) is unit M; f. of_iIs the temperature T above the neutral point_i1Down to T_i2The upward tangential force of the i-th layer soil on the side surface of the pile foundation (1) is expressed in unit of kPa.

3. The low-embankment-base saline soil pile foundation of claim 1The method for determining the amount of bulging after reinforcement is characterized in that: in the step (4), the temperature T_i1Down to T_i2Salt expansion force sigma of ith layer soil of rear pile foundation (1)_biDetermined by the following equation:

in the formula sigma_biIs a temperature T_i1Down to T_i2Salt expansion force of the ith layer of soil of the rear pile foundation (1) in unit of kPa; sigma_TiIs a temperature T_i1Down to T_i2The salt expansion force of the i-th layer of saline soil (D) is expressed in unit of kPa; m is the replacement rate of pile soil area, m is pi d²/4s²(ii) a d is the pile diameter of the pile foundation (1) and the unit m; s is the pile spacing of the pile foundation (1) and the unit m; l is the pile length of the pile foundation (1) and is a unit m; h is₀Calculating the thickness in m for the bulging deformation of the pile foundation at the bottom of the low embankment; z is the foundation depth at the bottom of the lower embankment (M) in M.

4. The method for determining the uplift amount of the low-embankment-base saline soil pile foundation after reinforcement according to claim 1, wherein the method comprises the following steps: in the steps (1) - (4), the pile foundation (1) is arranged at equal intervals according to a square shape.

5. The method for determining the uplift amount of the low-embankment-base saline soil pile foundation after reinforcement according to claim 1, wherein the method comprises the following steps: in the steps (1) - (4), the ith layer of soil is located within the calculated thickness range of the uplift deformation of the pile foundation at the bottom of the low embankment.

6. The method for determining the uplift amount of the low-embankment-base saline soil pile foundation after reinforcement according to claim 1, wherein the method comprises the following steps: in the step (3), the temperature T_i1Down to T_i2Salt expansive force sigma of the i-th layer of saline soil (D)_TiIs a temperature T_i1Down to T_i2The pressure corresponding to the initial pore ratio in the soil body salt expansion curve; the abscissa of the salt swelling curve is pressure, and the ordinate is porosity ratio.

7. The method for determining the uplift amount of the low-embankment-base saline soil pile foundation after reinforcement according to claim 1, wherein the method comprises the following steps: in the step (3), the salt swelling index C of the i-th layer soil_siIs a temperature T_i1Down to T_i2The average slope of the soil body salt expansion e-logp curve in a certain pressure range is determined according to the following formula:

in the formula e_jFor the post-compression stabilization temperature T of the soil body under the j-th stage pressure_i1Down to T_i2The resulting void ratio; p is a radical of_jIs the j stage pressure; e.g. of the type_j+1The temperature T after the soil body is compressed and stabilized under the j +1 th level pressure_i1Down to T_i2The resulting void ratio; p is a radical of_j+1Is the j +1 th stage pressure.

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