Lateral capacity of pile with grouted upper soil: field test and numerical simulation

  • Guangming Yu
  • Weiming Gong
  • Yuchen Liu
  • Guoliang Dai
  • Meihe Chen
Technical Paper
  • 262 Downloads
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  1. Topical Collection from GeoMEast 2017 – Sustainable Civil Infrastructures: Innovative Infrastructure Geotechnology

Abstract

Laterally loaded piles may entail large deformation under some circumstances such as ship impact, earthquake and long-term horizontal thrust of arch bridges, etc. The arch bridges are especially sensitive to horizontal displacement of foundation. Lateral load test was performed on a full-scale pile in virgin soil and pile with post-grouted soil around pile. Further numerical simulation analysis was carried out by PLAXIS3D based on field test result. The analytical and measured results are found to be in fairly satisfactory agreement. According to test results of single pile, lateral response of piles largely depends on profile of limiting force in shallow soil. Horizontal bearing capacity of bored piles is improved via grouting technique. For pile with post-grouted soil around, horizontal displacement of pile top is significantly reduced. The maximum bending moments of pile with grouting decrease dramatically. The grouted upper soil expands range of effective soil around pile, and more horizontal thrust was shared.

Keywords

Thrustful foundation Lateral displacement Upper soil grouted Load sharing 

Introduction

At present, drilled grouting pile remains the preferred foundation scheme for super high-rise buildings and large-scale bridges, which have many advantages of strong bearing capacity of single pile, little settlement and deformation easily controlled, and so on. At the same time, post-grouting technique has been widely applied to drilled grouting pile foundation engineering construction, etc. This technique has been used in engineering practice for many years to develop more perfect construction technology and method than before. A more profound understanding of its functional mechanism is acquired by engineering personnel. The cement slurry is pressed into the mud around pile by upper soil post-grouted technique. That contributes to developing coarser interface between pile and soil and increase friction between them.

In reinforced concrete facility such as Highway Bridge, port and pier, and offshore oil platform, etc, horizontal load is applied in these infrastructures more frequently. Even combined load applied which include lateral load, vertical load, and bending moment. According to a large number of literatures [1, 2, 3, 4, 5], response of pile under lateral load is mainly in the range of upper soils around piles. Therefore, this measurement that it is post-grouted only in the upper soil around piles can satisfy the requirement of practical engineering. There are significantly applied values to study horizontal load-bearing properties of piles with soil post-grouted around.

Project profile

New street across the Luo River bridge connects north with south of Luo River in Luoyang city. It consists of south, north, and river channel section of the bridge. Main bridge is designed for arch bridge in river channel section and its topside structure for nine spans arch with a single arch span of 45–95 m. Substructure is designed for low-cap grouting pile foundation which adopts rotary digging bored piles construction technology: bridge floor width of 35.5 m, total length of 618 m, the north approach span length of 289 m, the south approach length of 206 m, and the flood control standard for 100 a.

Arch bridge is a kind of statically indeterminate structure bearing long-termly horizontal thrust. It is very sensitive to foundation’s displacement, especially lateral displacement. In some circumstance, pile group foundation is adopted, and subgrade just provides part constraints to horizontal displacement. However, lateral displacement of piers is likely to exceed the allowed limit and change arch axis of the main arch ring in adjacent cross when arch bridge produces long-term lateral force to piers. As a result, a large additional bending moment is produced in the main arch ring, so that the adjacent cross collapsed. Even bridge collapsed in a row.

Geological conditions and soil parameters

There are nine layers of soil around piles. Soil parameters which show in Table 1 are used to calculate the response of piles in PLXIS3D. Figure 1 shows particle size distribution of sand contained in gravel. By analyzing the sieve analysis test data, it was found that the gradation of sand was bad, with even coarse grains with diameters mostly exceeded 0.5 mm.
Table 1

Soil parameters

Item

Natural unit weight (KN/m3)

Friction resistance (kPa)

Compression modulus (MPa)

Internal friction angle (°)

⑥-2Fine sand

19.2

35

15

23

⑥-3Round Gravel

20

70

22

27

⑥Gravel

21.2

100

30

33

⑨-2Round Gravel

20.8

90

27

30

⑨Gravel

21.6

140

35

35

⑩-2Round Gravel

21

110

30

32

⑩Gravel

22

170

40

38

Fig. 1

Particle size distribution of sand

Grouting scheme

Pile under vertical load ability is stronger, but a lot of engineering pile top will bear horizontal load; Piles’ vertical bearing capacity is higher than horizontal bearing capacity. In a vast quantity of engineering, however, pile foundations have to bear lateral load. Soil post-grouted technique was used in drilled grouting pile foundation engineering construction to improve its bearing capacity, so that safety of arch bridge can be ensured. The piles have a diameter of D = 2.0 m and a length of L = 35.0 m (relative length L/D = 17.5). Figure 2 shows grouting scheme. The Chinese JGJ design code (JGJ94-2008) recommends mainly influenced depth under lateral load is 2 (D + 1), so the depth of grouted soil is 6 m. Grouting pipe’s diffusion radius is 0.5 m. The range of grouted soil around pile is half ring with 1.0 m in diameter away from lateral sides of piles.
Fig. 2

Grouting scheme. a Structure diagram of grouting hole. b Structure diagram of steel flower tube

Establishment of numerical model

We performed numerical simulation of lateral load test process employing the FE method, using the geotechnical finite-element analysis software PLAXIS3D. Two pile models were calculated, general drilled grouting pile and drilled grouting pile with upper soil grouted, respectively. The soil model range is 30 m × 30 m, and 60 m in depth, which is consisted of nine layers of soil. Volume pile from PLAXIS is chosen to simulate mechanical characteristic of pile. We modelled soil with tetrahedral continuum finite elements. We employed the elastoplastic constitutive relationship: Mohr–coulomb failure criterion. In this test, lateral surface load is applied at the top of pile according to slowly maintaining load method. It is divided into nine levels of load with increment of 150 KN. The maximum load value is 1500 KN. Figure 3 shows the distribution of soil layers.
Fig. 3

Soil model

Parameters back analysis

Figures 4, 5 illustrate arrangement for two piles under lateral loading and field test pile schematic. In this test process, lateral loads vary from 300 to 1500 KN at the increment of 150 KN, and load divided into nine levels, and unload divided into five levels. Figure 6 shows piles’ lateral displacements in loading and unloading processes for pile in virgin soil and pile with upper soil grouted. It can be concluded from figure that the finite-element analytical and measured results are found to be in fairly satisfactory agreement. Therefore, the further analysis of pile–soil interaction is conducted via PLAXIS on the basis of testing data, which makes up for the deficiency that the particular situation of piles–soil interaction cannot be observed under the existing test condition. Residual deformation of pile head is 4.2 mm for pile in virgin soil after unloading, while it is only 2.5 mm for pile with upper soil grouted. By parameters back analysis method, it is suitable that Mohr–coulomb model is used for grouted soil. Its Young’s modulus is 3.4 times than virgin soil, and can increase from 0.5 kpa to 19, and internal friction angle can be changed from 27° to 40°.
Fig. 4

Arrangement for two piles under lateral loading. a Field test, b high-pressure oil pump

Fig. 5

Field test pile schematic

Fig. 6

Lateral load vs. displacement curve

Analysis of results

Displacement of piles

Figure 7 shows deformation curve of pile shaft from PLAXIS result for two kinds of pile under different levels of horizontal load. In loading process, deformation of pile head varies from 1.23 to 10.2 mm for pile in virgin soil, while it varies from 0.97 to 7.27 mm for pile with upper soil grouted under the same levels of lateral load, and increases slowly. The depth of the lateral displacement response is −10.5 m when load reaches to 1500 KN. It is −10.2 m for pile with upper soil grouted. Therefore, there is no distinct difference in the depth of the lateral displacement response. Therefore, it is soil grouted around pile that enhances the ability of resistance to lateral displacement of pile. This method of soil post-grouted around pile can be considered to apply to pile foundation engineering, especially when it is sensitive to lateral displacement, improving the safety and reliability in engineering.
Fig. 7

Pile deformation vs. depth curve. a Pile in virgin soil, b pile with grouted soil

Moments of piles

Figure 8 shows pile-bending moment distribution of pile in virgin soil and pile with upper soil grouted under different levels of horizontal load. The bending moments of pile in virgin soil increase more quickly than pile with grouting. Maximum moments of pile in virgin soil vary from 460 to 3437 KN m as different levels of lateral load are applied. However, maximum moments of pile with grouting vary from 346 to 2580 KN m as different levels of lateral load are applied. The maximum moments were decreased by 25%.
Fig. 8

Bending moments vs. depth curve. a Pile in virgin soil, b pile with grouted soil

Therefore, this treatment method that soil around pile is post-grouted can make moments of piles to decrease dramatically and improve the safety of pile greatly. More horizontal thrusts are shared by soil around pile.

Shear force of pile

Figure 9 shows pile’s shear force distribution of pile in virgin soil and pile with upper soil grouted under different levels of horizontal load. Pile’s maximum shear force locates in the top of pile. From the perspective of shear overall distribution, shear force of pile with grouting along depth is less than pile in virgin soil. The maximum shear force of lower part of pile in virgin soil varies from 54 KN to 433 KN m as different levels of lateral load are applied; while the maximum shear force of pile with upper soil grouted in the same position varies from 39 to 323 KN with increasing lateral load, it reduces by 25% under maximum load value.
Fig. 9

Shear force vs. depth curve. a Pile in virgin soil, b pile with grouted soil

Nephogram analysis

Planar nephogram analysis

Figure 10 shows lateral displacement nephogram of soil around pile. The initial phase in Fig. 10a is K0 procedure that the initial effective stresses, pore pressures, and state parameters are generated directly. There is no displacement in this calculation.
Fig. 10

Planar nephogram of soil

Figure 10b–d shows different lateral displacement planar nephograms at mud surface when loads are applied at the top of pile from 300, 750, and 1500 KN. Compared with pile in virgin soil, influence scope of soil subjected lateral load is larger for pile with upper soil grouted and has smaller deformation. Along the direction of loading, displacement isoline of pile with grouting is sparser than pile in virgin soils. Along the direction perpendicular to the loading, effective soil resisting lateral load expands dramatically for pile with grouting. The range of treated soil increases significantly in terms of lateral displacement.

Profile nephogram analysis

Figure 11 shows lateral displacement profile nephogram of soil around pile under 1500 KN. In terms of working soil profile, influence scope of soil subjected lateral load is also larger for pile with upper soil grouted than for pile in virgin soil. Expanding soil shares more lateral loads, so that horizontal displacement of pile with grouting becomes smaller. It can be concluded that increasing strength of grouted soil results in decreasing displacement field from Fig. 12.
Fig. 11

Profile nephogram (1500 KN)

Fig. 12

Displacement field of pile and soil (1500 KN)

Ashour et al. [6] and Ardalan and Ashour [7] used an envisaged 3D strain wedge (SW) model to determine pile reaction under lateral loads. The SW model was able to link between the more complex 3D soil–pile interaction and a simpler one-dimensional characterization. Figure 13 shows that the shape of soil resistance on front of pile is like three-dimensional wedge.
Fig. 13

Iso-surfaces of lateral displacement (1500 KN)

Conclusion

From this test result and numerical calculation study, several interesting conclusions can be drawn. These can be used in practice as a design guideline for the case, where piles are sensitive to horizontal displacement.
  1. 1.

    The finite-element analytical results coincide well with the measured results for pile in virgin soil and pile with upper soil grouted. It meets the requirements of validation.

     
  2. 2.

    The key to the response of pile under horizontal load is profile of limiting force in shallow soil. Resistant ability of lateral displacement can be effectively enhanced by this method of upper soil grouted around pile.

     
  3. 3.

    Compared with un-grouted pile, the value of maximum bending moments for grouted pile and pile’s shear force reduces with superior safety of pile.

     
  4. 4.

    Soil around pile is treated with post-grouted technique, and the range of effective soil providing resistance expands to share more lateral load, reducing displacement of pile head.

     
  5. 5.

    In terms of reducing lateral displacement, this treatment method that soil around pile is post-grouted can be considered to adopt in pile foundation sensitive to lateral displacement.

     

Notes

Acknowledgements

The research work presented in this paper is supported by the National Basic Research Program of China (973 Program, Grant 2013CB036304) and the National Natural Science Foundation of China (NSFC) (Grant 51478109), for which the authors are grateful.

References

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Copyright information

© Springer International Publishing AG 2017

Authors and Affiliations

  • Guangming Yu
    • 1
    • 2
  • Weiming Gong
    • 1
    • 2
  • Yuchen Liu
    • 1
    • 2
  • Guoliang Dai
    • 1
    • 2
  • Meihe Chen
    • 1
    • 2
  1. 1.School of Civil EngineeringSoutheast UniversityNanjingChina
  2. 2.Key of Laboratory for RC and PRC Structure of Education MinistrySoutheast UniversityNanjingChina

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