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Jiashi Garden Test Pile Strain Test and Analysis Report
Release time: 2018-06-23

I. Overview

Entrusted by the Guangzhou Academy of Building Research, our company undertook the strain testing and analysis of the four bored cast-in-situ piles of Jiashi Garden in order to determine the distribution of frictional resistance along the pile body under vertical static load conditions and under various loads. The ratio of total friction resistance and end resistance, and evaluate the pile body quality. Solexperts 公司生产的滑动测微计。 The tester is a sliding micrometer produced by Solexperts , Switzerland .     

1-2m 有粉土及粉质粘土外,主要由强风化和中微风化泥岩组成。 The main design parameters of the four piles are shown in Table 1. The geological conditions of the bedrock are relatively simple. Except for the silt and silty clay in the upper 1-2m , they are mainly composed of strongly weathered and moderately weathered mudstone. 15cm 的混凝土护壁,因此实际桩径应为 1.5m 1.7m During the digging process, the hole wall is made of concrete with a wall thickness of about 15cm , so the actual pile diameter should be 1.5m and 1.7m .

Table 1. Main design parameters of test piles

Numbering

(m) Pile diameter (m)

(m) Pile length (m)

(m 2 ) Pile cap (m 2 )

Concrete design strength grade

(kN) Test load (kN)

17

1.2

20.5

× 1.8 1.8 × 1.8

C30

(加荷至 19000 18000 (loading to 19000 )

28

1.2

× 1.8 1.8 × 1.8

C30

(加荷至 19000 18000 (loading to 19000 )

43

1.2

21.0

× 1.8 1.8 × 1.8

C30

(加荷至 19000 19000 (loading to 19000 )

54

1.4

C30

(加荷至 21000 20000 (loaded to 21000 )

  14-20 日,制桩时在四根试桩的钢筋笼内安装了总计 168 个滑动测微计测环和 168m 套管,安装质量极佳,除 43 桩测管由于吊装时钢筋笼弯曲受损外,其余均正常,受损处经修补对测量无影响。 From May 14th to 20th , a total of 168 sliding micrometer measuring rings and 168m bushings were installed in the reinforced cages of the four test piles during pile making. Except for bending damage, the rest are normal. Repairing the damaged area has no effect on the measurement. 8 日开始试桩,采用堆载法加载, 1 × 1 × 2m 3 混凝土作为堆载体。 The pile test started on August 8 , and the pile was loaded using 1 × 1 × 2m 3 concrete as the pile carrier. 28 号桩二条测管连线方向与堆载体系不协调,因而放弃了滑动测微计测试;此外 54 号桩原计划加载 18000kN ,采用二根主梁,后增至 20000kN ,必须采用三根主梁,其中一根必定将测孔盖住,无法进行测试。 Due to the inconsistency between the connection direction of the two test tubes of the 28 pile and the pile carrier system, the sliding micrometer test was abandoned. In addition, the 54 pile was originally planned to be loaded with 18000 kN , using two main beams, and then increased to 20000 kN . Three mains must be used. Beams, one of which must cover the measuring hole and cannot be tested.

Test method

This test uses the principle of line measurement and the corresponding portable strain gauge-sliding micrometer. This method is suitable for strain testing of various pile types. It has been used in China for steel pipe piles, prefabricated piles, bored or dug bored piles. Both drilling and grouting piles have achieved very satisfactory results. 2000.7 For details, please refer to the relevant information of Europe and the United States Dadi Instrument Equipment Co., Ltd. and the "Geotechnical Engineering World" Volume 7 Issue 7 "Linear Principles and Portable Series Instruments in Geotechnical Engineering Strain Monitoring (1)" 2000.7 .

Third, test data analysis

1 及图 7 为二根试桩实测应变曲线,从二组曲线可看出如下规律: Figure 1 and Figure 7 are the measured strain curves of two test piles. From the two sets of curves, the following rules can be seen:

1,   43 6m 处应变偏小及 17m 应变偏大外,二根桩的实测应变曲线没有突变点,表明桩身质量较均匀,完整性较好, 6m 处应变偏小可能由于该点处于强、中风化岩层交界处,强风化层可能有局部超挖,桩身实际截面较大,而 17m 处应变偏大则可能是局部混凝土质量较差。 Except that the strain at the 6m of pile 43 is too small and the strain at 17m is too large, the measured strain curves of the two piles have no sudden points, indicating that the pile body is more uniform and the integrity is good. The small strain at 6m may be due to the strong point 2. At the junction of moderately weathered rock layers, the strong weathered layer may have local over-excavation, the actual cross-section of the pile body is large, and the large strain at 17m may be the poor local concrete quality.

2,   7 第一点( 1m 处)应变偏小,因处于桩头扩大部分,图 1 17 也有同一现象,因对摩阻力分析无意义,因而未标出。 The first point (at 1m ) in Fig. 7 has a small strain. Because it is in the enlarged part of the pile head, the same phenomenon occurs in pile 17 in Fig. 1. Because the analysis of friction resistance is meaningless, it is not shown. 1 桩端应变偏小,因作桩端地基承载力试验扩孔所致。 Figure 1 The strain at the end of the pile is too small, which is caused by the expansion of the bearing capacity test of the pile end.

3.   1 17 8 级荷载维持时间较长,应变增大,表明混凝土的弹模随加载时间延长而降低,桩身计算弹模应该低于标号所对应的弹模。 Figure 1 The 8th stage of pile 17 has a longer load retention time and increased strain, which indicates that the elastic modulus of concrete decreases with increasing loading time. The elastic modulus of the pile body should be lower than the corresponding elastic modulus of the number.

4.   17 8 9 10 级荷载及桩 43 10 级荷载下桩顶应变明显增大,表明混凝土弹模随荷载量级增大而降低。 The strain at the top of piles under the loads of grades 8 , 9 , and 10 of pile 17 and the load of grade 10 of pile 43 increased significantly, indicating that the concrete elastic form decreases with the magnitude of the load.

Fourth, friction resistance calculation

  1 、图 7 )是一切计算分析的依据,但由于测量中不可避免的误差,不应该直接用它进行摩阻力和端阻力计算,否则其误差将被恶性放大,因此首先必须对其进行平滑处理。 The measured strain curve (Figures 1 and 7 ) is the basis for all calculations and analysis. However, due to the inevitable errors in the measurement, it should not be directly used to calculate friction and end resistance calculations, otherwise the errors will be amplified viciously, so you must first Smooth it. 43 桩, 1 6 17 点将不被考虑。 Some special points, such as 43 piles, 1 , 6 , 17 will not be considered. 17 桩第 18 点按桩端和桩身截面积比值增大。 The measured values of some points must be corrected for the cross section. For example, the 18th point of the 17 piles increases according to the ratio of the cross-sectional area of the pile ends to the pile body.

、图 2 、图 8 为平滑处理后的曲线,利用各级荷载下顶部应变可计算各级荷载下桩身平均弹性模量,如图 5 、图 11 所示。 1. Figures 2 and 8 are the smoothed curves. Using the top strain under each load, the average elastic modulus of the pile body under each load can be calculated, as shown in Figures 5 and 11 . The relationship between the elastic modulus and the strain level (load) can be obtained by linear regression calculation:

i =27.00 0.007 ε i (MPa) (桩 17 E i = 27.00 0.007 ε i (MPa) (Pile 17 )

i =26.40 0.0077 ε i (Mpa) (桩 43 E i = 26.40 0.0077 ε i (Mpa) (pile 43 )

、利用上述二式并根据图 2 、图 8 两组曲线可得到桩身轴力曲线组,如图 3 ,图 9 所示;以及摩阻力曲线组,如图 4 、图 10 2. Using the above two formulas and according to the two sets of curves in Figs. 2 and 8 , the shaft force curve group of the pile can be obtained, as shown in Figs .

    = E i ε i A Axial force = E i ε i A

    = ( ε i - ε i+1 ) E i A/ π D Unit friction resistance = ( ε i - ε i + 1 ) E i A / π D

ε i - ε i+1 ) E i D /4 = ( ε i - ε i + 1 ) E i D / 4

、根据图 3 、图 9 可计算各级荷载下总摩阻力及端阻力增长曲线,如图 6 、图 12 所示。 3. According to Fig. 3 and Fig. 9 , the growth curve of total friction resistance and end resistance under various loads can be calculated, as shown in Fig. 6 and Fig. 12 .

V. Results analysis

、桩身混凝土质量较均匀、完整、平均弹模约 25Mpa 1. The concrete quality of the pile body is relatively uniform and complete, and the average elastic modulus is about 25Mpa .

、孔壁直径较一致,桩 43 6m 处可能有超挖。 2. The diameter of the hole wall is relatively consistent, and there may be over-digging at the 6m of pile 43 .

、承载力主要由摩阻力承担,桩 43 端阻力极小,最高荷载下只占约 5% ,桩 17 3. The bearing capacity is mainly borne by friction resistance. The resistance at the 43 end of the pile is very small, only about 5% under the highest load , and the 17 end of the pile .

   18000kN 时端阻力约 2500kN ,占 14% The resistance is not high, and the end resistance is about 2500kN at 18000kN , accounting for 14% .

5.   17 最大单位摩阻力处于 14~18m ,而桩 43 则处于 10~12m 段,而 14m 8m The maximum unit friction of pile 17 is between 14 and 18m , while pile 43 is between 10 and 12m , and 14m and 8m.

   In the deep, just at the junction of the strong weathering and middle weathering layers where the two piles are located, the average friction resistance of the strong weathering layers is small.

   200kPa ,而中风层摩阻力则高达 400kPa 以上。 At 200kPa , the abrasion resistance of the stroke layer is over 400kPa .

6.   17 最大摩阻力点处于约 2/3 桩深处,符合一般规律,而桩 43 最大摩阻力点 The maximum friction point of pile 17 is about 2/3 of the pile depth, which is in line with the general rule, while the maximum friction point of pile 43 is

   10~12m ,可能由于下述原因,中风化岩层埋藏深度浅,承担了大部分 It is high, about 10 ~ 12m . It may be because of the following reasons, the buried depth of the weathered rock layer is shallow, and it takes most of the   

   The friction resistance and the settlement are very small. The friction resistance under the pile body has not been exerted. In addition, the lower part of the pile body is highly weathered mud.

   Sandstone cannot have high friction.

7.   43 桩, 15m Neither pile has reached the ultimate bearing capacity, and the frictional resistance and end resistance have not been fully exerted, especially 43 piles, 15m

   30kPa ,端阻力只有约 800kN ,按桩端面积(约 3.5m 2 )计算, The following frictional resistance is less than 30kPa , and the end resistance is only about 800kN . Based on the pile end area (about 3.5m 2 ),

   228kPa The average unit end resistance is only 228kPa .

8,   From the test of two piles, it is known that the frictional resistance of the embedded rock in the weathered rock is far more than the survey data and specifications provided.

   For the strength value of friction resistance, friction resistance cannot be ignored for rock-socketed piles.

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