Journal of Shandong University(Engineering Science) ›› 2020, Vol. 50 ›› Issue (6): 82-91.doi: 10.6040/j.issn.1672-3961.0.2020.090

• Civil Engineering • Previous Articles     Next Articles

Optimal structure of pressure cast-situ-pile with spray-expanded frustum

Lianxiang LI1,2(),Hongxia XING1,2,Jinliang LI3,Hengli HUANG1,2,Lei WANG1,2   

  1. 1. Research Center of Foundation Pit and Deep Foundation Engineering, Shandong University, Jinan 250061, Shandong, China
    2. School of Civil and Hydraulic Engineering, Shandong University, Jinan 250061, Shandong, China
    3. Shandong Biteli Foundation Engineering Technology Corporation, Jining 272100, Shandong, China
  • Received:2020-04-07 Online:2020-12-20 Published:2020-12-15

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Abstract:

According to the field test results of pressure cast-situ-pile with spray-expanded frustum, with the help of Abaqus to establish the numerical model of the experiment, the influence rule of expanded body with frustum (hereinafter referred to as frustum) on surrounding soil under vertical load was obtained. It was clarified that the soil mass had squeezing effect within the 2D~3D range (D is frustum's diameter) and it reached the limit at 0.5 m under the frustum. Stress relaxation occured in the upper soil of frustum, which reached the limit value at the top of the frustum, and of which the vertical influence range was extended by 1.25D and the horizontal influence range was 1.5D~2.5D. Revealed that the optimal spray angle for frustum expanding was 50°~55°, the optimum expanding ratio was 2~2.75, the optimal position was in the D~2D range of upper part of pile, and it was optimal when the fixed spray wing was 7~8 m below the pile top. The optimal construction model could increase the bearing capacity by 19%, therefore it was suggested to adopt the optimal structural pile type to further improve efficiency and promote application of the pile.

Key words: pressure cast-situ-pile with spray-expanded frustum, numerical model, law of influence, optimal construction

CLC Number: 

  • TU473

Fig.1

Drill nozzle"

Fig.2

The forming process of expansion body"

Fig.3

Expanded body with double-frustum"

Fig.4

Process chart"

Table 1

Construction process parameters table of expanded body"

土名称 扩出尺寸/mm 升降速度/(cm·min-1) 旋喷喷射压/MPa 气压/MPa 钻机转速/(r·min-1) 喷嘴层数 喷嘴个数 喷嘴直径/mm
黏性土 200 15 20 0.7 10~25 3 3×1(3×2) 2.4~2.8(2.0~2.4)
150 20 20
100 20 15
粉土 250 20 15
200 20 12
150 25 12
砂土 300 20 20
200 20 15
100 25 12

Fig.5

Wing plate and its parameter"

Fig.6

Field geological conditions and schematic diagram of test piles"

Table 2

Parameters of test piles"

桩号 桩长/m 桩径/mm 锥台直径/mm 侧翼板高度/m
SZ1 17.5 600 1 200 10
SZ2 18.0 600 1 200 全喷翼
SZ3 24.5 600 1 200 10
SZ4 24.5 600 1 200 全喷翼

Fig.7

Load-settlement curves of testl piles"

Table 3

Comparison of each test pile's bearing capacity"

桩型 桩长/m 单桩极限承载力/kN
SZ1 17.5 4 360
SZ2 18.0 3 750
SZ3 24.5 6 223
SZ4 24.5 7 696

Fig.8

Schematic diagram of test pile and soil grid"

Fig.9

Comparison between load-settlement curves of field and simulation"

Table 4

Parameters of Soil and pile shaft material"

土层名称 层厚/m Es/MPa E/MPa Er/MPa c/kPa φ/(°)
粉砂 2.00 12.00 96.0 未加强 12.0 12.0
粉质黏土 3.50 4.40 35.2 未加强 26.0 8.1
黏土 2.20 7.62 61.0 116 42.0 11.1
粉砂 1.40 20.00 160.0 316 12.0 34.0
粉质黏土 7.10 8.50 68.0 130 45.0 11.1
粉砂 1.50 30.00 240.0 469 15.0 34.0
粉质黏土 9.28 75.00 145.0 46 11.8
桩身 36 000.0
水泥土 1 500.0 200.0 30.0

Fig.10

Horizontal displacement increment of soil around the pile body"

Fig.11

Horizontal stress increment of soil around the pile body"

Fig.12

Horizontal displacement increment of soil at the lower surface of frustum"

Fig.13

Horizontal stress increment of soil at the lower surface of frustum"

Fig.14

Horizontal displacement increment of soil at the upper surface of frustum"

Fig.15

Horizontal stress increment of soil at the upper plate of surface of frustum"

Table 5

Parameters of soil and pileshaft material"

名称 变形模量E/MPa 黏聚力c/kPa 内摩擦角φ/(°)
桩侧土 82.7 14.4 32.1
桩端土 75.0 46.0 11.8
桩身 36 000.0
水泥土 1 500.0 200.0 30.0

Fig.16

Expansion angle of expanded body"

Fig.17

Comparison of bearing capacity of piles with different frustum angles"

Fig.18

Comparison of frustum expansion ratio"

Fig.19

Improving efficiency of bearing capacity of test pile under different diameter expansion ratio"

Fig.20

Position of frustum"

Fig.21

Influence curves of position change of frustum on bearing capacity"

Fig.22

Wing height's effect on bearing capacity"

Fig.23

Comparison of different models"

Table 6

Model parameter"

模型 桩长L/m 桩径d/mm 扩径D/mm 扩径比D/d 扩径角/(°) 锥台位置 喷翼高度
最优构造 15 600 1 500 2.5 55 桩端上2D 喷至桩顶下8 m
原模型 15 600 1 200 2.0 45 桩端 未喷翼

Fig.24

Comparison of Q-S curves of different models"

Fig.25

Load bearing ratioof side resistance"

Fig.26

Load bearing ratioof frustum"

Fig.27

Load bearing ratioof end resistance"

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