CN105735374A - Method for testing bearing force of pile by high strain method - Google Patents

Abstract

The invention discloses a method for testing bearing force of a pile by a high strain method. The method comprises three steps of: (1) installation of instrument equipment; (2) data acquisition; and (3) calculation of the bearing force of the pile. Strain meters and acceleration sensors are serially arranged on a pile body at equal intervals; a heavy hammer is adopted to beat the top of the pile; the strain and the speed in different positions of the pile body are tested; the total frictional resistance of each section of the pile body and the total end resistance of pile ends can be calculated according to the measured strain in different positions of the pile body; the dynamic frictional resistance of each section of the pile body and the dynamic end resistance of the pile ends can be calculated according to the measured speed in different positions of the pile body; the difference between the total frictional resistance and the dynamic frictional resistance of each section of the pile body is static frictional resistance; the difference between the total resistance and the dynamic resistance of the pile ends is pile end static end resistance; and the obtained static frictional resistance and the pile end static end resistance are accumulated to obtain the limit bearing capacity of the pile. The method, proposed by the invention, can prevent influence of the uncertainty of a traditional fitting method on the testing result, and obtains actual bearing capacity of the pile.

Description

A kind of method of the bearing capacity of Large strain method test pile

Technical field

The invention belongs to engineering detecting field, be specifically related to a kind of method that civil engineering detection field is tested for bearing capacity of pile foundation.

Technical background

As the bearing capacity test method of a kind of, high strain testing is because it is convenient and swift, be used widely without advantages such as preloadings.During test, adopt weight to knock stake top and make stake produce enough pile penetrations, surveyed speed and the power time-history curves on stake top by the acceleration transducer and strain transducer being arranged on a side, and then obtained the bearing capacity of stake by the mode of indoor matching.But, speed and the power time-history curves on stake top is only included due to measured curve, very big uncertainty is there is during indoor matching, even if identical test curve, different people be fitted the bearing capacity of stake that obtains also can difference very big, thus hardly resulting in the actual carrying capacity situation of stake, the reliability of acquired results is also had a greatly reduced quality.

Summary of the invention

It is an object of the invention to Problems existing during the bearing capacity overcoming existing Large strain method test pile the method that the bearing capacity of a kind of Large strain method test pile is provided.

The technical solution adopted for the present invention to solve the technical problems is:

The method of the bearing capacity of a kind of Large strain method test pile, comprises the steps:

Step 1. instrument and equipment is installed: is equally spaced strain gauge and the acceleration transducer of tandem at pile body, and is connected to strain testing instrument and acceleration test instrument；

Step 2. data acquisition: adopt weight to knock stake top, utilizes the strain signal of strain testing instrument test pile body various location, utilizes the acceleration signal of acceleration test instrument test pile body various location simultaneously and converts rate signal to；

The bearing capacity calculation of step 3.: the strain according to the pile body various location recorded, calculates the total frictional resistance and the total end resistance of stake end that obtain each section of pile body；Speed according to the pile body various location recorded, calculate the dynamic frictional resistance and the stake end moved end resistance that obtain each section of pile body, total frictional resistance of each section of pile body and the difference of dynamic frictional resistance are quiet frictional resistance, the difference of stake end drag overall and dynamic resistance is the quiet end resistance of an end, finally the quiet frictional resistance tried to achieve and the quiet end resistance of stake end are added up, namely obtain the ultimate bearing capacity of stake.

The method by being equally spaced strain gauge and the acceleration transducer of tandem at pile body, test weight knocks strain and the speed of process pile various location respectively, and then the bearing capacity of stake can be obtained by the method directly calculated, the uncertainty impact on test result of tradition fitting process can be avoided well, it is thus achieved that the actual bearer ability of stake.

Described step 1 can specifically be adopted with the following method:

When 1-1. transfers steel reinforcement cage, it is arranged symmetrically with two steel pipes along pile body is elongated, and ensures to be in vertical state；

1-2. makes tandem strain gauge and tandem acceleration transducer according to the total length of stake, treat pile concrete build complete after, being respectively placed in two steel pipes by N number of tandem strain gauge and N number of tandem acceleration transducer, the distance between adjacent strain gauge and between acceleration transducer is 1～2 meter；Wherein tandem strain gauge numbers respectively 0,1,2 from top to bottom, ..., i-1, i, ..., N-1, N, tandem acceleration transducer numbers respectively 1,2 from top to bottom ..., i ..., N, the strain gauge of bottom and acceleration transducer are respectively positioned on an end place, build the cement grout prepared subsequently and tandem strain gauge and acceleration transducer are sealed in steel pipe in steel pipe；

Described step 2 can specifically be adopted with the following method:

2-1. is when concrete strength of pile reaches strong strain requirement, a narrow slit with certain depth is cut out between stake end face steel pipe opening and pile body extension, being drawn by wire by narrow slit, strain gauge and acceleration transducer are connected on strain testing instrument and acceleration test instrument；

2-2. lays certain thickness dry sand and is used as bed course on stake top, put down after weight is winched to certain altitude and knock stake top, tested the strain signal of pile body various location by strain testing instrument, test the acceleration signal of pile body various location by acceleration test instrument and convert rate signal to.

Described step 3 can specifically be adopted with the following method:

3-1. i-th (i=1,2 ..., N-1) the quiet frictional resistance of section stake pile body calculates

According to the pile strain ε that the strain gauge (pile cutoff between the two that is i-th section stake) being numbered i-1 and i is measured respectively_i-1And ε_i, total frictional resistance f of i-th section of stake can be obtained_iFor:

f_i=EA ε_i-1-EAε_i

Wherein: the elastic modelling quantity of E and A respectively stake and cross-sectional area, it is known quantity；

Total frictional resistance f of i-th section of stake_iIncluding dynamic frictional resistance f_diWith quiet frictional resistance f_siTwo parts, according to the acceleration transducer i speed v recorded_i, frictional resistance f can be moved_diFor:

f_di=v_iδ_iS_i

Wherein: S_iAnd δ_iRespectively i-th section of stake stake side surface area and pile side damping constant, the former is known quantity, and the latter can obtain according to engineering prospecting data；

The quiet frictional resistance that can try to achieve i-th section of stake accordingly is:

f_si=f_i-f_di=EA ε_i-1-EAε_i-v_iδ_iS_i

The 3-2. N section quiet frictional resistance of stake pile body and the quiet end resistance of stake end calculate

According to the pile strain ε that the strain gauge (pile cutoff between the two i.e. N section stake) being numbered N-1 and N is measured respectively_N-1And ε_N, total frictional resistance f of N section stake can be obtained_NEnd resistance f total with stake end_bSum is:

f_N+f_b=EA ε_N-1-EAε_N

Total frictional resistance f of N section stake (namely near at the bottom of stake one section of position)_NIncluding dynamic frictional resistance f_dNWith quiet frictional resistance f_sNTwo parts, the total end resistance f of stake end_bIncluding moved end resistance f_bdWith quiet end resistance f_bsTwo parts, according to the speed v that the acceleration transducer being numbered N records_N, the dynamic frictional resistance f of N section stake can be obtained_dNWith stake end moved end resistance f_bdIt is respectively as follows:

f_dN=v_Nδ_NS_N；

f_bd=v_Nδ_bS_b

Wherein: S_bAnd δ_bRespectively stake end cross-sectional area and pile-end soil damped coefficient, the former is known quantity, and the latter can obtain according to engineering prospecting data；

The quiet frictional resistance f of N section stake can be tried to achieve accordingly_sNEnd resistance f quiet with stake end_bsSum is:

f_sN+f_bs=EA ε_N-1-EAε_N-v_Nδ_NS_N-v_Nδ_bS_b

3-3. is after the quiet frictional resistance trying to achieve every section of stake and the quiet end resistance of stake end, and the ultimate bearing capacity that can obtain stake is:

$F=\underset{i=1}{\overset{N}{\Σ}}{f}_{si}+f_{bs}.$

The invention has the beneficial effects as follows: by burying tandem strain gauge underground and acceleration transducer measures strain and the rate signal of pile body various location respectively, and then quiet frictional resistance and the quiet end resistance of stake end of each section of pile body is obtained by the method directly calculated, thus obtaining the bearing capacity of stake, avoid the deviation of the test result that the occasionality of factor data matching and randomness cause in tradition strong strain method well so that test result is relatively reliable.

Accompanying drawing explanation

Below in conjunction with Figure of description, the invention will be further described.

Fig. 1 is the detection schematic diagram of the present invention.

Fig. 2 is that detection pile top narrow slit cutter sets schematic diagram.

In figure: weight 1, stake end face 2, acceleration test instrument 3, strain testing instrument 4, ground surface 5, wire the 6, second steel pipe the 7, first steel pipe 8, cement grout 9, strain gauge 10, acceleration transducer 11, narrow slit 12.

Detailed description of the invention

Below in conjunction with drawings and Examples the present invention it is further elaborated and illustrates.In the present invention, the technical characteristic of each embodiment is not under having conflicting premise, all can carry out respective combination.

The method of the bearing capacity of a kind of Large strain method test pile, comprises the steps:

Step 1. instrument and equipment is installed: is equally spaced strain gauge 10 and the acceleration transducer 11 of tandem at pile body, and is connected to strain testing instrument 4 and acceleration test instrument 3.

This step is specific as follows:

When 1-1. transfers steel reinforcement cage, being arranged symmetrically with two steel pipes along pile body is elongated, two steel pipes lay respectively at pile body both sides, and are in vertical state.

1-2. treat pile concrete build complete after, N number of tandem strain gauge (being composed in series by N number of strain gauge 10) is placed in one in the first steel pipe 8, N number of tandem acceleration transducer (being composed in series by N number of acceleration transducer 11) is positioned in the second steel pipe 7.In same steel pipe, the distance between adjacent strain gauge 10 and between acceleration transducer 11 is 1～2 meter.Wherein tandem strain gauge numbers respectively 0,1,2 from top to bottom, ..., i-1, i, ..., N-1, N, tandem acceleration transducer numbers also respectively 1,2 from top to bottom ..., i ..., N, the strain gauge 10 of bottom and acceleration transducer 11 are respectively positioned on an end place, build the cement grout 9 prepared subsequently and tandem strain gauge 10 and acceleration transducer 11 are sealed in steel pipe in steel pipe.The equipment installed is as shown in Figure 1.

Step 2. data acquisition: adopt weight to knock stake top, utilize strain testing instrument 4 to test the strain signal of pile body various location, utilize acceleration test instrument 3 test the acceleration signal of pile body various location and convert rate signal to simultaneously.

This step is specific as follows:

2-1. is as shown in Figure 2, when concrete strength of pile reaches strong strain requirement, all cutting out a narrow slit 12 with certain depth between 2 two steel pipe openings of stake end face and pile body extension, narrow slit 12 degree of depth is advisable to match with wire 6, makes wire 6 to draw smoothly.By narrow slit 12, wire 6 is drawn, and strain gauge 10 and acceleration transducer 11 are connected on strain testing instrument 4 and acceleration test instrument 3；

2-2. lays certain thickness dry sand and is used as bed course on stake top, and concrete thickness is depending on practical situation.Put down after weight 1 is winched to certain altitude and knock stake top, tested the strain signal of pile body various location by strain testing instrument 4, test the acceleration signal of pile body various location by acceleration test instrument 3 and convert rate signal to.Acceleration test instrument 3, strain testing instrument 4 are positioned on ground surface 5.

The bearing capacity calculation of step 3.: the strain according to the pile body various location recorded, calculates the total frictional resistance and the total end resistance of stake end that obtain each section of pile body；Speed according to the pile body various location recorded, calculate the dynamic frictional resistance and the stake end moved end resistance that obtain each section of pile body, total frictional resistance of each section of pile body and the difference of dynamic frictional resistance are quiet frictional resistance, the difference of stake end drag overall and dynamic resistance is the quiet end resistance of an end, finally the quiet frictional resistance tried to achieve and the quiet end resistance of stake end are added up, namely obtain the ultimate bearing capacity of stake.

This step is specific as follows:

3-1. i-th (i=1,2 ..., N-1) the quiet frictional resistance of section stake pile body calculates

According to the pile strain ε that the strain gauge 10 (pile cutoff between the two that is i-th section stake) being numbered i-1 and i is measured respectively_i-1And ε_i, total frictional resistance f of i-th section of stake can be obtained_iFor:

f_i=EA ε_i-1-EAε_i

Wherein: the elastic modelling quantity of E and A respectively stake and cross-sectional area, it is known quantity；

Total frictional resistance f of i-th section of stake_iIncluding dynamic frictional resistance f_diWith quiet frictional resistance f_siTwo parts, according to the acceleration transducer i speed v recorded_i, frictional resistance f can be moved_diFor:

f_di=v_iδ_iS_i

Wherein: S_iAnd δ_iRespectively i-th section of stake stake side surface area and pile side damping constant, the former is known quantity, and the latter can obtain according to engineering prospecting data；

The quiet frictional resistance that can try to achieve i-th section of stake accordingly is:

f_si=f_i-f_di=EA ε_i-1-EAε_i-v_iδ_iS_i

The 3-2. N section quiet frictional resistance of stake pile body and the quiet end resistance of stake end calculate

According to the pile strain ε that the strain gauge 10 (pile cutoff between the two i.e. N section stake) being numbered N-1 and N is measured respectively_N-1And ε_N, total frictional resistance f of N section stake can be obtained_NEnd resistance f total with stake end_bSum is:

f_N+f_b=EA ε_N-1-EAε_N

Total frictional resistance f of N section stake_NIncluding dynamic frictional resistance f_dNWith quiet frictional resistance f_sNTwo parts, the total end resistance f of stake end_bIncluding moved end resistance f_bdWith quiet end resistance f_bsTwo parts, according to the speed v that the acceleration transducer 11 being numbered N records_N, the dynamic frictional resistance f of N section stake can be obtained_dNWith stake end moved end resistance f_bdIt is respectively as follows:

f_dN=v_Nδ_NS_N；

f_bd=v_Nδ_bS_b

Wherein: S_bAnd δ_bRespectively stake end cross-sectional area and pile-end soil damped coefficient, the former is known quantity, and the latter can obtain according to engineering prospecting data；

The quiet frictional resistance f of N section stake can be tried to achieve accordingly_sNEnd resistance f quiet with stake end_bsSum is:

f_sN+f_bs=EA ε_N-1-EAε_N-v_Nδ_NS_N-v_Nδ_bS_b

3-3. is after the quiet frictional resistance trying to achieve every section of stake and the quiet end resistance of stake end, and the ultimate bearing capacity that can obtain stake is:

$F=\underset{i=1}{\overset{N}{\Σ}}{f}_{si}+f_{bs}.$

Embodiment described above is the one preferably scheme of the present invention, and so it is not intended to limiting the invention, the technical scheme that all modes taking equivalent replacement or equivalent transformation obtain, and all falls within protection scope of the present invention.

Claims (4)

1. the method for the bearing capacity of a Large strain method test pile, it is characterised in that comprise the steps:

Step 1. instrument and equipment is installed: is equally spaced strain gauge and the acceleration transducer of tandem at pile body, and is connected to strain testing instrument and acceleration test instrument；

Step 2. data acquisition: adopt weight to knock stake top, utilizes the strain signal of strain testing instrument test pile body various location, utilizes the acceleration signal of acceleration test instrument test pile body various location simultaneously and converts rate signal to；

The bearing capacity calculation of step 3.: the strain according to the pile body various location recorded, calculates the total frictional resistance and the total end resistance of stake end that obtain each section of pile body；Speed according to the pile body various location recorded, calculate the dynamic frictional resistance and the stake end moved end resistance that obtain each section of pile body, total frictional resistance of each section of pile body and the difference of dynamic frictional resistance are quiet frictional resistance, the difference of stake end drag overall and dynamic resistance is the quiet end resistance of an end, finally the quiet frictional resistance tried to achieve and the quiet end resistance of stake end are added up, namely obtain the ultimate bearing capacity of stake.

2. the method for the bearing capacity of Large strain method test pile as claimed in claim 1, it is characterised in that described step 1 is specific as follows:

When 1-1. transfers steel reinforcement cage, it is arranged symmetrically with two steel pipes along pile body is elongated, and ensures to be in vertical state；

1-2. treat pile concrete build complete after, N number of tandem strain gauge and N number of tandem acceleration transducer are respectively placed in two steel pipes, the distance between adjacent strain gauge and between acceleration transducer is 1～2 meter；Wherein tandem strain gauge numbers respectively 0,1,2 from top to bottom, ..., i-1, i, ..., N-1, N, tandem acceleration transducer numbers respectively 1,2 from top to bottom ..., i ..., N, the strain gauge of bottom and acceleration transducer are respectively positioned on an end place, build the cement grout prepared subsequently and tandem strain gauge and acceleration transducer are sealed in steel pipe in steel pipe.

3. the method for the bearing capacity of Large strain method test pile as claimed in claim 1, it is characterised in that described step 2 is specific as follows:

2-1. is when concrete strength of pile reaches strong strain requirement, a narrow slit with certain depth is cut out between stake end face steel pipe opening and pile body extension, being drawn by wire by narrow slit, strain gauge and acceleration transducer are connected on strain testing instrument and acceleration test instrument；

2-2. lays certain thickness dry sand and is used as bed course on stake top, put down after weight is winched to certain altitude and knock stake top, tested the strain signal of pile body various location by strain testing instrument, test the acceleration signal of pile body various location by acceleration test instrument and convert rate signal to.

4. the method for the bearing capacity of Large strain method test pile as claimed in claim 1, it is characterised in that described step 3 is specific as follows:

3-1. i-th (i=1,2 ..., N-1) the quiet frictional resistance of section stake pile body calculates

According to the pile strain ε that the strain gauge being numbered i-1 and i is measured respectively_i-1And ε_i, total frictional resistance f of i-th section of stake can be obtained_iFor:

f_i=EA ε_i-1-EAε_i

Wherein: the elastic modelling quantity of E and A respectively stake and cross-sectional area；

Total frictional resistance f of i-th section of stake_iIncluding dynamic frictional resistance f_diWith quiet frictional resistance f_siTwo parts, according to the acceleration transducer i speed v recorded_i, frictional resistance f can be moved_diFor:

f_di=v_iδ_iS_i

Wherein: S_iAnd δ_iRespectively i-th section of stake stake side surface area and pile side damping constant；

The quiet frictional resistance that can try to achieve i-th section of stake accordingly is:

f_si=f_i-f_di=EA ε_i-1-EAε_i-v_iδ_iS_i

The 3-2. N section quiet frictional resistance of stake pile body and the quiet end resistance of stake end calculate

According to the pile strain ε that the strain gauge being numbered N-1 and N is measured respectively_N-1And ε_N, total frictional resistance f of N section stake can be obtained_NEnd resistance f total with stake end_bSum is:

f_N+f_b=EA ε_N-1-EAε_N

Total frictional resistance f of N section stake_NIncluding dynamic frictional resistance f_dNWith quiet frictional resistance f_sNTwo parts, the total end resistance f of stake end_bIncluding moved end resistance f_bdWith quiet end resistance f_bsTwo parts, according to the speed v that the acceleration transducer being numbered N records_N, the dynamic frictional resistance f of N section stake can be obtained_dNWith stake end moved end resistance f_bdIt is respectively as follows:

f_dN=v_Nδ_NS_N；

f_bd=v_Nδ_bS_b

Wherein: S_bAnd δ_bRespectively stake end cross-sectional area and pile-end soil damped coefficient；

The quiet frictional resistance f of N section stake can be tried to achieve accordingly_sNEnd resistance f quiet with stake end_bsSum is:

f_sN+f_bs=EA ε_N-1-EAε_N-v_Nδ_NS_N-v_Nδ_bS_b

3-3. is after the quiet frictional resistance trying to achieve every section of stake and the quiet end resistance of stake end, and the ultimate bearing capacity that can obtain stake is:

$F=\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{f}_{si}+f_{bs}.$