Pile foundation bearing parameter calculation method based on cone penetration technology

Abstract

Disclosed in the present invention is a pile foundation bearing parameter calculation method based on cone penetration technology, the method comprising: S1, performing a cone penetration test at a pile position, so as to acquire raw cone penetration data; S2, on the basis of a cone tip resistance, calculating a soil unit weight, an internal frictional angle and an overburden stress; S3, on the basis of a pile foundation size, calculating a pile foundation side frictional resistance; S4, calculating a pile end resistance at the pile bottom of a pile foundation; and S5, calculating pile foundation bearing parameters. In the method, the correlation between a penetration resistance of cone penetration and a unit side frictional resistance and a unit end resistance in pile foundation bearing parameters is established, and the correlation between cone penetration data and an ultimate bearing capacity of a pile foundation is reflected in a relatively direct manner. An ultimate side frictional resistance and an ultimate end resistance that can be exerted by the pile foundation can be directly calculated by using the cone penetration data, thereby making up for the deficiency of conventional methods excessively relying on empirical formulas. The method is simple, feasible, time-saving and efficient.

Description

Pile bearing parameter calculation method based on sounding technology TECHNICAL FIELD

[0001] The present application relates to the field of pile bearing parameter calculation research in engineering investigation, in particular to a pile bearing parameter calculation method based on sounding technology. BACKGROUND

[0002] Deep sounding has been widely used in engineering investigation due to its advantages of continuous data acquisition, fast investigation speed and consideration of real stress level of soil. The continuous test data obtained by deep sounding can obtain continuous pile bearing parameters along the depth. Compared with the only one pile bearing parameter of the single layer soil obtained by conventional drilling, the continuous pile bearing parameters obtained by deep sounding are more accurate and reasonable. Therefore, the pile bearing parameter calculation method based on sounding technology is of great significance to pile engineering.

[0003] At present, the pile bearing parameter calculation method based on sounding technology mainly includes empirical formula method and semi-empirical formula method considering pile bearing development. The empirical formula method is mainly used in China. The empirical formula method establishes an empirical formula between the sounding tip resistance and side resistance and the pile bearing parameter. This method is more experienced, the characteristic parameters in the formula do not have physical meaning, and is not suitable for new sites and new soil, and has certain limitations. The semi-empirical formula method considering pile bearing development is currently insufficiently studied, and is only suitable for soft clay in the Gulf of Mexico, northern Europe and other regions. However, the continental and marine soil bodies in China are generally distributed in silty clay and silt. Therefore, the applicability is low. The pile bearing parameter calculation method based on sounding technology has significant deficiencies in applicability and scientificity. SUMMARY

[0004] In view of the problems in the background art, the present application provides a pile bearing parameter calculation method based on sounding technology which has strong universality and high accuracy.

[0005] To this end, the present application adopts the following technical solutions:

[0006] A pile bearing parameter calculation method based on sounding technology comprises the following steps:

[0007] S1, performing sounding test at the pile position to obtain sounding original data;

[0008] arranging sounding holes in the engineering site, setting the sounding hole depth as D and the collection interval as Dh, and obtaining the sounding tip resistance q c and the sounding side friction f s in the range of the sounding hole depth D.

[0009] S2, obtaining the tip resistance q cThe soil bulk density γ varying with the buried depth, the internal friction angle varying with the buried depth and the self-weight stress σ varying with the collection depth are calculated.

[0010] S3, the pile side friction of the pile foundation is calculated according to the size of the pile foundation:

[0011] The pile foundation soil penetration depth L and the pile foundation radius R are obtained; the pile foundation soil penetration part is divided into I pile nodes using the collection interval Δh, then: L=(I-1)×Δh; i is used as the number of the pile node, i∈[1,I], L≤D-8R;

[0012] The pile foundation side friction F of the pile node i is calculated by the following formula: si : F si =α Fi σ Fi tanδ i ;

[0013] Wherein, α Fi is the pile foundation correction coefficient of the pile node i, is the distance from the pile bottom end of the pile node i;

[0014] σ Fi is the pile circumferential normal stress of the pile node i based on the cone tip resistance, q ci is the cone tip resistance at the same buried depth as the pile node i;

[0015] K0 is the horizontal resistance coefficient,

[0016] is the internal friction angle at the same buried depth as the pile node i;

[0017] σ i is the self-weight stress at the same collection depth as the pile node i;

[0018] δ i is the external friction angle of the soil at the same buried depth as the pile node i,

[0019] S4, the pile end resistance q of the pile foundation at the pile bottom is calculated tI :

[0020] The pile end resistance of the pile foundation at the pile bottom is the pile end resistance of the pile node I, which is calculated by the following formula:

[0021] Wherein, is the weighted average value of all the cone tip resistances within the range of 8R above the pile bottom end and 8R below the pile bottom end; is the internal friction angle of the pile foundation at the pile bottom;​

[0022] S5, calculating the pile foundation bearing parameter:

[0023] The side friction of the whole pile is calculated by the method of S3, and the pile end resistance obtained by S4 is combined, so as to obtain the pile foundation bearing parameter and output.

[0024] In step S2:

[0025] When q c (z)<400kpa, γ(z)=8.23(q c (z)) 0.12 ;

[0026] When 400kpa≤q c (z)<4500kpa, γ(z)=9.56(q c (z)) 0.095 ;

[0027] When q c (z)≥4500kpa, γ(z)=21.3;

[0028] Wherein, q c (z) is the cone tip resistance at the depth z, is the internal friction angle of the soil at the depth z, and γ(z) is the bulk density of the soil at the depth z;

[0029] The self-weight stress σ(z * ) at different collection depths is calculated by the following formula:

[0030] Wherein, z * is the collection depth, which is an integer multiple of the collection interval Δh, and z * ≤D.

[0031] Preferably, Δh=0.1m.

[0032] The pile foundation bearing parameter calculation method of the present application is based on the pile-soil Coulomb friction principle, and the limit side friction and the limit end resistance that can be exerted by the pile foundation are calculated by using the sounding data.

[0033] Compared with the prior art, the present application has the following beneficial effects:

[0034] 1. The method of the present application establishes the correlation between the sounding penetration resistance, the unit side friction of the pile foundation bearing parameter and the unit end resistance based on the pile-soil Coulomb friction principle, which directly reflects the correlation between the sounding data and the limit bearing capacity of the pile foundation, and the limit side friction and the limit end resistance that can be exerted by the pile foundation can be directly calculated by using the sounding data, which makes up for the deficiency of the traditional method which excessively relies on empirical formula;

[0035] 2. The method is simple, time-saving and efficient, the calculated unit side friction and unit end resistance of the pile foundation are close to the actual bearing capacity of the pile foundation, the calculation is relatively accurate, and the method can be widely applied to the field of pile foundation design in China. BRIEF DESCRIPTION OF DRAWINGS

[0036] Fig. 1 is a flow chart of the method of the present application.

[0037] Fig. 2 is a curve diagram of the penetration cone tip resistance in the embodiment of the present application;

[0038] Fig. 3 is a curve diagram of the penetration side friction resistance in the embodiment of the present application;

[0039] Fig. 4 is a comparison diagram of the pile foundation bearing parameter curve obtained in the embodiment of the present application and the actual measurement result. DETAILED DESCRIPTION

[0040] The technical solution of the present application will be described in detail below in combination with the drawings and embodiments.

[0041] EMBODIMENT

[0042] The method of the present application is used to calculate the pile foundation bearing capacity parameters of a certain pile foundation engineering site. The certain pile foundation engineering site is a thick quaternary stratum, the main landform type is a tidal flat landform, and it has the characteristics of alternating marine and terrestrial deposition. The lithology mainly consists of silty clay and silt, and the distribution is relatively stable.

[0043] As shown in Fig. 1, the specific steps are as follows:

[0044] S1, performing a penetration test at the pile position to obtain penetration original data;

[0045] According to the geotechnical engineering investigation technical outline, penetration holes are arranged at the engineering site, the penetration hole depth is set as D, the collection interval is Δh; the site penetration original data is obtained, including the penetration cone tip resistance q c and the penetration side friction resistance f s .

[0046] In this embodiment, the penetration hole depth D = 50 m, the collection interval Δh = 0.1 m, the curve diagram of the penetration cone tip resistance is shown in Fig. 2, and the curve diagram of the penetration side friction resistance is shown in Fig. 3; the calculation process of the present application is described taking the first 3 m as an example, and the data of the first 3 m is shown in Table 1.

[0047] Table 1 Cone tip resistance and side friction resistance data table of 0-3 m burial depth

[0048] In the table, the unit of the cone tip resistance is MPa, and the unit of the side friction resistance is kPa.

[0049] S2, calculate the soil unit weight, internal friction angle, and self-weight stress based on the cone tip resistance:

[0050] Based on the cone tip resistance q at each location c Calculate the soil unit weight γ and the soil internal friction angle. have:

[0051] q c When (z)<400kpa, γ(z)=8.23(q c (z)) 0.12 ;

[0052] 400kPa≤q c When (z)<4500kpa, γ(z)=9.56(q c (z)) 0.095 ;

[0053] q c When (z)≥4500kpa, γ(z)=21.3.

[0054] Where, q c (z) represents the cone tip resistance q at a burial depth z. c , The internal friction angle of the soil at depth z. γ(z) is the soil unit weight γ at a burial depth z.

[0055] In the above embodiment, taking a burial depth of 0.5m as an example, at z = 0.5m, the soil unit weight γ(0.5) = 9.56 × (2.48) 0.095 ; soil internal friction angle

[0056] The soil unit weight and internal friction angle of 0-3m were calculated using the above calculation method, and the results are shown in Table 2.

[0057] Table 2. Unit weight and internal friction angle at burial depths of 0–3 m

[0058] In the table, the unit of soil unit weight is kN; the unit of internal friction angle is °.

[0059] Based on the calculated soil unit weight, the self-weight stress σ(z) at different sampling depths is calculated using the following formula. * ):

[0060] Among them, z * The acquisition depth is an integer multiple of the acquisition spacing Δh, where z is the acquisition depth. * ≤D;

[0061] In the above embodiments, z *Taking a depth of 0.5m as an example, the soil self-weight stress at the sampling depth of 0.5m is calculated as follows: σ(0.5)=(20.41+20.24+20.16+20.09)×0.1=10.11kPa;

[0062] The self-weight stress of soil at a burial depth of 0-3m was calculated using the above calculation method, as shown in Table 3.

[0063] Table 3. Soil self-weight stress at burial depths of 0–3 m

[0064] In the table, the unit for soil self-weight stress is kN.

[0065] S3, Calculate the side skin resistance of the pile foundation based on the pile foundation dimensions:

[0066] Obtain the pile penetration depth L in meters; the pile radius R in meters; divide the pile penetration portion into I pile nodes using the acquisition interval Δh, then: L = (I-1) × Δh; use i as the pile node number, i∈[1,I], L≤D-8R.

[0067] The pile foundation side friction F at pile node i is calculated using the following formula. si F si =α Fi σ Fi tanδ i ;

[0068] Among them, F si The unit is kPa;

[0069] α Fi Let be the pile foundation correction factor at pile node i. This represents the distance from pile node i to the bottom of the pile, in meters.

[0070] σ Fi The normal stress around the pile at pile node i, obtained based on the resistance of the cone tip, is expressed in kPa:

[0071] in:

[0072] q ci The cone tip resistance is located at the same depth as pile node i.

[0073] K0 is the horizontal resistance coefficient.

[0074] The internal friction angle at the same depth as pile node i

[0075] σ iis the self-weight stress at the same depth as the pile node i;

[0076] δ i is the external friction angle of the soil at the same depth as the pile node i,

[0077] In the above embodiment, the pile foundation enters the soil to a depth L = 45 m, the pile foundation radius R = 0.5 m, and I = 450.

[0078] Taking a depth of 0.5 m as an example, here i = 5. The pile foundation side friction force F si is:

[0079] The pile foundation side friction force at a depth of 0-3 m is calculated according to the above method, as shown in Table 4.

[0080] Table 4 Pile foundation side friction force table at a depth of 0-3 m

[0081] In the table, the unit of the pile foundation side friction force is kPa.

[0082] S4, calculate the pile tip resistance q tI at the bottom of the pile foundation:

[0083] The pile tip resistance at the bottom of the pile foundation is the pile tip resistance at the pile node I, which is calculated by the following formula:

[0084] In the formula, is the weighted average value of all cone tip resistances in the range of 8R above the pile bottom and 8R below the pile bottom, with the unit of MPa.

[0085] Therefore, in the above embodiment, the cone tip resistances in the range of 8R above the pile bottom and 8R below the pile bottom are shown in Table 5.

[0086] Table 5

[0087] Pile tip resistance at the bottom of the pile

[0088] S5, calculate the pile foundation bearing parameters:

[0089] The side friction force of the whole pile body is calculated using the method of S3 as the unit side friction of the pile foundation, and the pile tip resistance obtained by S4 is taken as the unit end resistance. The unit end resistance and the unit side friction are combined to obtain the pile foundation bearing parameters and output.

[0090] In the above embodiment, the side friction force of the whole pile body of the pile length 45 m is calculated and combined with the result of S4. The obtained result is compared with the result obtained by the field test pile, as shown in FIG. 4.

[0091] As shown in FIG. 4, the result calculated by the method of the present application is similar to the actually measured result, which verifies the rationality and reliability of the method of the present application.

Claims

1. A method for calculating bearing parameters of a pile foundation based on a sounding technique, characterized in that, The method comprises the following steps: S1, a sounding test is performed at a pile site to obtain sounding original data; Sounding holes are arranged at the engineering site, the sounding hole depth is set as D, and the collection interval is set as Δh; Obtaining the penetration cone tip resistance q in the range of the penetration hole depth D c and the penetration side friction f s ; S2, the cone tip resistance q obtained from S1 c calculating the bulk density of the soil γ varying with the burial depth, the internal friction angle φ varying with the burial depth and the self-weight stress σ varying with the collection depth; S3, the pile foundation side friction is calculated according to the size of the pile foundation: The pile foundation soil penetration depth L and the pile foundation radius R are obtained; the pile foundation in the soil penetration part is divided into I pile nodes using the collection interval Δh, then L=(I-1)×Δh; i is used as the number of the pile node, i∈[1,I], and L≤D-8R; The pile side friction force F at the pile node i is calculated by the following formula si : F si = a Fi s Fi tan d i ; wherein a Fi is a pile foundation correction coefficient at pile node i, is the distance of the pile node i from the bottom end of the pile; σ Fi The normal stress around the pile at pile node i is obtained based on the resistance of the cone tip. wherein: q ci q is the tip resistance at the same depth as the pile node i; K0 is the horizontal force coefficient, is the internal friction angle of the soil at the same buried depth as the pile node i; σ i σi is the self-weight stress at the same depth as the pile node i; delta i the external friction angle of the soil at the same depth as the pile node i, S4, calculate the pile tip resistance q at the pile bottom of the pile foundation tI : The pile tip resistance at the pile base is the pile tip resistance at the pile node I and is calculated by the following equation: wherein a weighted average of all said point resistance in the range of 8R above the pile toe and 8R below the pile toe; is the internal friction angle of the pile foundation at the bottom of the pile; S5, the pile foundation bearing parameter is calculated: The side friction of the whole pile is calculated using the method of S3, and is combined with the pile end resistance obtained by S4, to obtain the pile foundation bearing parameter and output.

2. The pile bearing parameter calculation method based on the sounding technology according to claim 1, characterized in that, S2: when q c (z) < 400 kPa, γ(z) = 8.23(q c (z)) 0.12 ; when 400 kPa ≤ q c (z) < 4500 kPa, γ(z) = 9.56(q c (z)) 0.095 ; when q c (z) ≥ 4500 kPa, γ(z) = 21.3; wherein q c (z) is the cone tip resistance at depth z, is the internal friction angle of the soil at the buried depth z, and γ(z) is the soil bulk density at the buried depth z; The self-weight stress σ(z) at different collection depths is calculated by the following formula: * ​ where z * is the collection depth, is an integer multiple of the collection pitch Δh, z * ≤ D.

3. The pile bearing parameter calculation method based on the sounding technology according to claim 1, characterized in that: Δh=0.1m.

Images