- 295 -

Classification of Micropile Underpinning Methods Exemplified by

Projects in Turku

Jouko Lehtonen Turku University of Applied Sciences, Turku, Finland

Email: jouko.lehtonen@turkuamk.fi

Ville-Veikko Hyyppä

Turku University of Applied Sciences, Turku, Finland Email: ville.hyyppa@turkuamk.fi

ABSTRACT

The most common among the many reasons for foundation underpinning are seismic retrofit and prevention of harmful settlement. Micropiles are typically used for underpinning, whereby a separate load transfer structure is often provided between the micropiles and the existing superstructure. The present article introduces a classification of the various kinds of load transfer structures. In addition, the article proposes a new way of modeling underpinning using an adapted UML (Unified Modeling LanguageTM) sequence diagram. The adaptation of UML modeling allows the linking of the installation process and its various stages with the structural descriptions of, e.g., structural members and force diagrams. The classification can be used to support planning decisions, or to estimate costs or duration from the owner´s point of view.

KEYWORDS: underpinning, micropile, jet grouting, load transfer structure, seismic retrofit, UML modeling

INTRODUCTION

Major renovation measures, such as foundation underpinning, are usually taken either at the end of the life cycle of the structural components or in connection with major amendment work (Wong 2000). Aikivuori (1994) lists five reasons for refurbishment: (i) failure in the building due to deterioration, (ii) change in use, (iii) optimization of economic factors, (iv) subjective features of decision maker, and (v) change of circumstances.

Renovation measures can result in visible changes or, on the other hand, the results can be invisible (Chau et al. 2003). Renovation projects at the end of a building’s life cycle are unavoidable if the building is to continue being used for at least one more life cycle. Most renovation projects (those relating to the building services or the facade, for example) are of a nature that concerns all buildings. Typically, underpinning is only necessary in buildings where the foundation is supported by wood piles or wood rafts (Hartikainen, 2000). The need for foundation underpinning arises as the underground wooden structures rot or when it is desirable

Vol. 15 [2010], Bund. C 296 to reduce the settlement of structures, e.g. when existing foundations are disturbed by underground construction, such as tunneling (Han and Ye, 2006a; Han and Ye, 2006b). Also, the load-bearing capacity of foundations may require enhancement because of increased loads due to, for instance, the construction of an additional floor (Han and Ye, 2006a; Han and Ye, 2006b, Lehtonen, 2009). In addition, in seismic zones the safety of foundations is improved by using micropiles to provide additional foundation support (Bromenschenkel, 1997; Herbst, 1997; Mason, 1997; Miura, 1997; Okahara, 1997; Okahara et al., 1997; Schlosser and Frank, 1997; Tatsuta et al., 1997; Tsukada and Ichimuda, 1997; Misra et al., 1999; Okumatsu, 1999; Armour, 2002; Fukui, 2006). However, foundations are frequently underpinned only when the uneven settlement or cracks have reached harmful proportions (Lizzi, 1982; Thorburn, 1993).

During different periods, various underpinning techniques have been applied (Mason and Kulhawy, 1999; Thornburn, 1993). Until the 1980s, the methods used included, in particular, foundation extension by deepening and broadening, different kinds of pile work, soil nailing, and chemical grouting (Bradbury, 1993; Bruce, 1993; Cole, 1993; Hutchison, 1993; Littlejohn, 1993; Lizzi, 1982; Pryke, 1993; Thorburn, 1993; Gould et al., 2002; Perko, 2005). Micropiles and jet grouting have been common underpinning methods since the 1980s (Eronen, 1997; Schlosser and Frank, 1997; Klosinski, 2000; Fross, 2006; Nicholson and Pinyot, 2006). The steel-structured micropiles are installed by drilling, driving, jacking, or screwing, depending on the circumstances and the installation equipment available (Lizzi, 1982; Lizzi, 1993; Korkeakoski et al., 2000; Ruben et al., 2000; Lehtonen, 2001; Pienpaalutusohje, PPO 2007).

In underpinning, the existing superstructure is structurally integrated with new piles (Bruce, 1989) or, for example, jet grouted columns. Tawast (1993) has suggested a specific classification of the so called load transfer structures, based on a force diagram separately depicting the occurrence of compression and tension forces (Fig. 2 and Fig. 3.). Lizzi (1982) describes foundation underpinning without pile preloading, i.e., following Tawast’s Cases 1 and 2. On the other hand, pile preloading by means of hydraulic jacks is also common following Cases 3 and 4, Fig. 2 (Gupte, 1989; O´Neill and Pierry, 1989; Bradbury, 1993; Cole, 1993; Hutchison, 1993; Vehmas, 2000). Preloading has also been applied in foundation deepening (Pryke, 1993) and piles have been installed by jacking, whereby the installation even produces preloading (Bradbury 1993). Preloading has further been implemented by mounting a tendon inside the micropile and by grouting it to the tip of the pile. By pulling at the tendon and using the pile head as support, elastic contraction of the pile is achieved (Bruce et al., 1990; Hayward Baker, 2005). In addition to pile installation and preloading, jacks have been used to straighten or lift the superstructure (Vehmas, 2000; Smith, 2003; Perälä, 2009; Vunneli 2009).

FOUNDATION UNDERPINNING IN TURKU

Underpinning is particularly common in Turku, Finland. At the moment, the total number and extent of projects in Turku is exceptionally great even internationally speaking. A database containing about 200 different parameters from some 100 underpinning projects has been compiled (DATU 2008). This database, called DATU, is one of the most extensive of its kind in the world. The data has been gathered from the property owners, the project planners, and from the building supervision authority in Turku.

Vol. 15 [2010], Bund. C 297

Figure 1: Load transfer cases 1 and 2 in underpinning (Tawast, 1993)

Vol. 15 [2010], Bund. C 298

Figure 2: Load transfer cases 3…5 in underpinning (Tawast, 1993)

Vol. 15 [2010], Bund. C 299

Figure 3: Load transfer cases 6 and 7 in underpinning (Tawast, 1993)

The user interface can be accessed by a web browser and it is possible to work in the database over the world wide web system. Both Finnish- and English-language versions of the user interface are available.

In Turku, the thickness of the soft clay layer (Fig. 4) varies from a couple of meters to as much as 60 m (Korkeakoski et al., 2000). If the thickness of the soft soil layers under a building in Turku exceeds 15 m, micropiles are usually used, whereas in areas with soft layers of less than 15 m in thickness, either micropiles or jet grouting is used. The costs of underpinning usually amount to 150...450 €/net m2 (Lehtonen, 2008).

Vol. 15 [2010], Bund. C 300

Figure 4: Soil profile in Turku city centre.

Before the 1940s, floating piles or cohesive piles, were commonly used. Foundations underpinned in this manner tend to sink if the soil layers consist of very soft clay (su < 15 kN/m2), as they do in Turku. Attempts have been made to even out the settlement by piling, but buildings underpinned with cohesive piles have suffered uneven settlement of harmful proportions. Wooden cohesive piling may remain unaffected by rot for a great length of time unless the groundwater table sinks to a level below that of the foundation. The characteristic tendency of a construction supported by cohesive piling to settle renders the supportive piling safer through two mechanisms: (i) the settlement partly reduces the effect of groundwater recession, and (ii) no cavity is formed under the foundation, as is easily the case with supportive piling. From the 1950s and until the end of the 1960s, supporting piles were used in Turku, with tips extending to the bearing stratum or bedrock. Wooden foundations with supporting piles are especially exposed to decay by rotting due to drops in the groundwater level and when, in addition, a void is created under the foundation as a result of soil layer consolidation. Damage in buildings with wooden piling may also be due to other reasons such as vibration caused by traffic, leaking sewerage, and additional loads on the superstructure (Lehtonen, 2009).

LOAD TRANSFER STRUCTURES IN UNDERPINNING

UML modeling

In this study, the new method applied comprises an adapted UML (Unified Modeling LanguageTM) modeling sequence diagram to illustrate the transfer of forces (in the manner of a force diagram) parallel with the timing of the various construction steps. The UML sequence diagram shows how a group of objects interact in a given example (object source). The modified UML sequence diagram allows the combination of the process flowchart and the force diagram. In this case, the horizontal axis represents time and the forces are depicted vertically, compression as a downward arrow and tension as an upward one. The different steps are depicted in chronological order. An underpinning step such as the installation of a new pile is depicted as an

Vol. 15 [2010], Bund. C 301 object in the model, symbolized by a rectangle over the effective time of the step. An object may cease to exist, whereby the completion of the measure is indicated by a cross. (Bell 2010)

Load transfer cases

The classification by Tawast was primarily based on the use of force diagrams. Various kinds of load transfer structures are estimated to have an effect on the costs and duration of underpinning (Tawast 1993).

Cases 1 through 7 (Figs. 1, 2 and 3) were originally introduced by Tawast, while Cases 8 through 12 (Figs. 5 and 6) were identified in Turku underpinning projects. In addition, research literature has reported Case 10 (Richards and Kartofilis, 2006) and Case 13, Fig. 6 (Bruce, 1990; Hayward Baker, 2005). All the cases are analyzed considering existing wood piles and potential interaction between the foundation and soil has not covered. In the classification, credit has been given to the following factors which may be deemed to influence the costs or duration of the construction project:

i. Transfer of forces in the form of compression and tension ii. Use of separate structures to transfer forces from the superstructure to the new piles

iii. Eventual pile preloading, i.e., the use of a hydraulic jack.

Table 1 shows the occurrence of load transfer cases in underpinning projects saved in the DATU database. The load transfer cases can be divided into two main groups: firstly, methods where the foundation suffers small settlement (typically 10 to 30 mm) due to the elastic contraction of the new piles, and secondly, methods where there is no post-settlement (typical target <10 mm). Cases 1…13 can be classified as Categories A…D, Table 2, for further analyses on the costs (Table 3) and duration of underpinning (Fig. 7).

The load transfer structure in Category A includes minimum consumption of steel and concrete. An additional beam or enlargement of existing columns have been used in Categories B and D causing increase of steel and concrete consumption (Table 3). Category C reflects to Category A in material consumption. Jacking is an additional cost for Categories C and D.

Vol. 15 [2010], Bund. C 302

Table 1: Underpinning, load transfer cases in the DATU database (DATU 2008)

Case No.

Number of

piles in the

DATU

database

(totally 58

sites)

Small settlement

in the

superstructure

after underpinning

(no jacking during

installation)

No movement of

superstructure

after

underpinning

(installation with

jacking)

Superstructure

rests on new

pile directly or

over minor load

transfer

structure

Separate load

transfer structure

between

superstructure

and pile

1 1475 x x

2 3025 x x

3 642 x x

4 696 x x

5 12 x x

6 707 x x

7 5 x x

8 938 x x

9 119 x x

10 197 x x

11 55 x x

12 216 x x

13 0 x x x

unknown 511

totally 8598

Vol. 15 [2010], Bund. C 303

Table 2: Categories of load transfer structures in underpinning Category covering cases of load transfer structures

Direct support or minor load

transfer structure

Separate load transfer structure

Small settlement of

superstructure after underpinning

(no jacking during installation)

A: 1, 8 B: 2

No movement of superstructure

after underpinning (installation

with jacking)

C: 9, 10, 13 D: 3, 4, 5, 6, 7, 11, 12

Table 3: Costs of load transfer structures can vary widely depending on the categories of load transfer structures (Lehtonen and Kiiras, 2010)

Task or resource Load Transfer Categories

A B C D

Demolition € 300 300 300 300

Load-bearing

steel components

kg 50 200 100 200

€ 100 400 200 400

Concrete

structures

m3 0.5 2 1 2

€ 100 400 200 400

Jacking € 500 500

Total € 500 1,100 1,200 1,600

Vol. 15 [2010], Bund. C 304

Figure 5: Load transfer cases 8…10

Vol. 15 [2010], Bund. C 305

Figure 6: Load transfer cases 11, 12 and Case 13 (preloading using a tendon inside the micropile.)

Vol. 15 [2010], Bund. C 306

Figure 7: Duration of underpinning in Turku by consumption of piles (underpinning site number N = 49) grouped by Load Transfer Category (Lehtonen and Hattara, 2009).

SUMMARY

Foundations are underpinned mainly to prevent harmful settlement, to enhance bearing capacity, or for seismic retrofit. In many cases, the need for repair work on foundations is due to rot in wooden piles. Many methods are available for foundation underpinning, micropiles and jet grouting having been common in recent times. A new micropile or a jet grouted column is attached to the existing superstructure, often by means of an even highly complex load transfer structure. The aim is often to mobilize the elastic transformation of the micropile already during the installation phase by using jacks.

The article puts forward a classification of underpinning methods and a new modeling system based on adapting the UML sequence diagram. The classification is scrutinized more thoroughly through underpinning projects in Turku.

Developers can use the classification presented in this article as a tool in selecting planning solutions, and in cost and duration estimation.

Duration of underpinning by length of piles

0 m

2,000 m

4,000 m

6,000 m

8,000 m

10,000 m

12,000 m

14,000 m

16,000 m

0 d 50 d 100 d 150 d 200 d 250 d 300 d 350 d 400 d 450 d 500 d

Duration (days)

Leng

th o

f pile

s (m

eter

s) Load Transfer Category-A

LTC-B

LTC-C

LTC-D

Linear (LTC-A)

Linear (LTC-B)

Linear (LTC-C)

Linear (LTC-D)

Vol. 15 [2010], Bund. C 307

CONCLUSIONS

This study introduces a comprehensive classification of underpinning methods, resulting in 13 different main cases of load transfer structures. The main cases can be grouped into four main categories, whereby the aim is to apply these main categories in further research to predict the cost of underpinning and the duration of repair work on a foundation.

The article proposes a new method based on the UML sequence diagram for the classification of underpinning projects. In UML modeling, the underpinning process can be combined with force diagrams previously described in research literature. Force diagrams have thus far ignored the process aspect of the matter: an underpinning project often consists of an initial state, the preloading of piles, and the implementation of the final load transfer structure. The underpinning process, then, as construction processes in general, is in research literature usually described in the form of a flowchart, often combined with a time factor. Such timetable charts, however, lack a force diagram depicting how demanding the underpinning project is and at the same time probably also indicating the magnitude of costs.

ACKNOWLEDGEMENTS

The authors wish to acknowledge a number of researchers who have worked in the DATU database project, including E. Lehtonen, S. Lehti-Koivunen, A. Nyrhinen and J. Hattara.

REFERENCES 1. Aikivuori, A. (1994) Classification of demand for refurbishment projects. Acta Universitas

Ouluensis C77

2. Ansari, N. and Bruce, J. (2003) Credit Valley Hospital Pre-loaded Micropiles for Vertical Expansion of Parking Garage. Proceedings of the 5th International Workshop on Micropiles, Seattle.

3. Armour, T.A. (2002) Hewlett Packard Building 5, seismic upgrade. Corvallis, Oregon, USA. Proceedings of the International Workshop on Micropiles, Venice.

4. Bell, D. (2010) UML basics: The sequence diagram. [referred 17.2.2010] Available http:// www.ibm.com/developerworks/rational/library/3101.html.

5. Bradbury, H. (1993) The Bullivant system. In Underpinning and Retention (ed. Thorburn, S. and Littlejohn, G.S.) Blackie Academic & Professional.

6. Bromenschenkel (1997) Use of micropiles for seismic retrofit. International Workshop on Micropiles, Seattle.

7. Bruce, D.A. (1989) American developments in the use of small diameter inserts as piles and insitu reinforcement. Proceedings of the International Conference on Piling and Deep Foundations, Lontoo.

8. Bruce, D.A., Pearlman, S.L. and Clark, J.H. (1990) Foundation rehabilitation of the Pocomoke River Bridge, MD using high capacity preloaded Pin Pilessm. Proceedings of the 7th International Bridge Conference, Pittsburgh.

Vol. 15 [2010], Bund. C 308 9. Bruce, D.A. (1993) In-situ earth reinforcing by soil nailing. In Underpinning and Retention

(ed. Thorburn, S. and Littlejohn, G.S.) Blackie Academic & Professional.

10. Bruce, D.A. and Juran, I. (1997) Drilled and grouted micropiles. US. Department of Transportation, Federal Highway Administration reports No. FHWA-RD-96-016…19.

11. Chau, K.W., Leung, A.Y.T, Iyu, C.Y. and Wong, S.K. (2003) Estimating the value enhancement effects of refurbishment. Facilities Vol. 21 No. 1/2, s. 13-19.

12. Cole, K.W. (1993) Conventional piles in underpinning. In Underpinning and Retention (ed. Thorburn, S. and Littlejohn, G.S.) Blackie Academic & Professional.

13. DATU (2008) Database on Turku Underpinning Projects, Turun ammattikorkeakoulun tietokanta Turun perustustenvahvistuksista. [referred 16.5.2008] Available http://www.datu.info/.

14. Dietz, K. and Schurman, A. (2006) Foundation improvement of historical buildings by micropiles: Museum Island Berlin, St. Kolumba Cologne. Proceedings of the 7th International Workshop on Micropiles, Schrobenhausen.

15. Eronen, S. (1997) Drilled piles in Scandinavia. Tampere University of Technology, Geotechnics, Publication 40.

16. Fross, M. (2006) 35 years of application of micropiles in Austria. Proceedings of the 7th International Workshop on Micropiles, Schrobenhausen.

17. Fukui, J. (2006) Performance of seismic retrofits with high capacity micropiles. Lizzi Lecture 2006, Proceedings of the 7th International Workshop on Micropiles, Schrobenhausen.

18. Gould, R.A., Bedell, P.R. and Muckle, J.G. (2002) Construction over organic soils in an urban environment: four case histories. Canadian Geotechnical Journal 39, p. 345-356.

19. Gupte, A.A. (1989) Design, construction and applications of auger piling system for earth retention and underpinning of structures. Proceedings of the International Conference on Piling and Deep Foundations, Lontoo.

20. Han, J and Ye, S.-L. (2006a) A field study on the behavior of micropiles in clay under compression or tension. Canadian Geotechnical Journal 43, p. 19-29.

21. Han, J. and Ye, S.-L. (2006b) A field study on the behavior of a foundation underpinned by micropiles. Canadian Geotechnical Journal 43, p. 30-42.

22. Harris, J.S. (1993) Ground freezing. In Underpinning and Retention (ed. Thorburn, S. and Littlejohn, G.S.) Blackie Academic & Professional.

23. Hartikainen, J. (2000) Why wooden piles in Turku are decaying? The 3rd International Workshop on Micropiles, Turku.

24. Hayward Baker Inc. (2005) Post-tensioned micropile detail, Biloxi, MS. Design sheet SK-01.

25. Herbst, T. (1997) Micropiles – steel reinforcement. International Workshop on Micropiles, Seattle.

26. Hutchison, J.F. (1993) Traditional methods of support. In Underpinning and Retention (ed. Thorburn, S. and Littlejohn, G.S.) Blackie Academic & Professional.

27. Klosinski, B. (2000) Micropiles in Poland. The 3rd International Workshop on Micropiles, Turku.

Vol. 15 [2010], Bund. C 309 28. Korkeakoski, P., Lehtonen J. and Heikinheimo, R. (2000) Underpinning with steel pipe piles.

Proceedings of the 25th Annual Meeting and 8th International DFI Conference.

29. Lehtonen, J. (2001) Shaft bearing micropiles. Tampere University of Technology. Post-graduate thesis.

30. Lehtonen, J. (2008) Real estate value impacts caused by major refurbishment projects (available only in Finnish: Suuren korjaushankkeen vaikutus kiinteistön arvoon). Maanmittaus 83:2.

31. Lehtonen, J. Ed. (2009) Underpinning – Nordic practice. Course material from Turku University of Applied Sciences 46.

32. Lehtonen, J. and Hattara, J. (2009) Duration of the micropile underpinning projects in Turku. Proceedings of the 9th International Workshop on Micropiles, London.

33. Lehtonen J. and Kiiras J. (2010) Cost modelling in underpinning projects. Manuscript for Construction Management and Economics, a peer-reviewed publication.

34. Littlejohn, G.S. (1993) Underpinning by chemical grouting. In Underpinning and Retention (ed. Thorburn, S. and Littlejohn, G.S.) Blackie Academic & Professional.

35. Lizzi, F. (1982) The static restoration of monuments. International Society for Micropiles & The International Association of Foundation Drilling.

36. Lizzi, F. (1993) “Pali radice” structures. In Underpinning and Retention (ed. Thorburn, S. and Littlejohn, G.S.) Blackie Academic & Professional.

37. Mason, J.A. (1997) Seismic design concepts and issues for reticulated micropile foundation systems. International Workshop on Micropiles, Seattle.

38. Mason, J.A. and Kulhawy, F.H. (1999) Notes on improvement and underpinning of foundations of historic structures with reticulated micropiles. Proceedings of the 2nd International Workshop on Micropiles, Ube.

39. Misra, A., Oberoi, R. and Kleiber, A. (1999) Micropiles for seismic retrofitting of highway interchange foundation. Proceedings of the 2nd International Workshop on Micropiles, Ube.

40. Miura, F. (1997) Lessons from the damage caused by past earthquakes. International Workshop on Micropiles, Seattle.

41. Nicholson, P.J. and Pinyot, D.E. (2006) The evolution of micropiles in America. Proceedings of the 7th International Workshop on Micropiles, Schrobenhausen.

42. Okahara, M. (1997) Outline of the 1996 seismic design criteria of highway bridges in Japan. International Workshop on Micropiles, Seattle.

43. Okahara, M., Fukui, J. and Kimura, Y. (1997) Damage to bridge foundations during the Hanshin earthquake. International Workshop on Micropiles, Seattle.

44. Okumatsu, T. (1999) Micropile projects in United States. Proceedings of the 2nd International Workshop on Micropiles, Ube.

45. O´Neill, M.W and Pierry, R.F. (1989) Behavior of mini-piles in foundation underpinning in Beaumont Clay, Houston, Texas, USA. Proceedings of the International Conference on Piling and Deep Foundations, Lontoo.

Vol. 15 [2010], Bund. C 310 46. Perko, H.A. (2005) Underpinning and shoring for underground MRI Research Facility at

Ohio State University. Proceedings of the Spec. Sem. “Underground Construction in Urban Environments” ASCE Metropolitan Section Geotechnical Group, Geo-Institute of ASCE.

47. Perälä A. (2009) Structural engineering for underpinning. In Underpinning – Nordic practice. (ed. Lehtonen, J.). Course material from Turku University of Applied Sciences 46.

48. Pienpaaluohje PPO (2007) Micropiles Standard. RIL 230-2007. (available only in Finnish: Teräksiset lyönti-, pora- ja puristuspaalut)

49. Pryke, J.F.S. (1993) The Pynford underpinning method. In Underpinning and Retention (ed. Thorburn, S. and Littlejohn, G.S.) Blackie Academic & Professional.

50. Richards, T.D. and Kartofilis, D. (2006) Micropile underpinning of the Mandalay Bay Hotel & Casino. Proceedings of the 54th Annual Geotechnical Engineering Conference, University of Minnesota.

51. Ruben, T., Mets, M. and Eskel, U. (2000) Micropiles. Proceedings of the 9th Baltic Geotechnical Conference, Tallinn.

52. Samchek, G. (2003) Western Canada micropiles. Proceedings of the 5th International Workshop on Micropiles, Seattle.

53. Schlosser, F. and Frank, R. (1997) Review of French “FOREVER” project. International Workshop on Micropiles, Seattle.

54. Siel, B.D. (2006) Micropiles and the FHWA 30 years of implementation. Proceedings of the 7th International Workshop on Micropiles, Schrobenhausen.

55. Smith, G. (2003) Rehabilitation of a sinking townhome. Proceedings of the 5th International Workshop on Micropiles, Seattle.

56. Tatsuta, M, Shioi, Y., Kimura, M., Shimazu, A., Yoshida, E. and Takano, K. (1997). Experimental study on ultimate behavior of steel pipe pile group. International Workshop on Micropiles, Seattle.

57. Tawast, I. (1993) Underpinning (in Finnish: Perustusten vahvistusmenetelmät korjausrakentamisessa) Laboratory of Foundation and Earth Structures, Report 26. Tampere University of Technology.

58. Thorburn, S. (1993) Introduction. In Underpinning and Retention (ed. Thorburn, S. and Littlejohn, G.S.) Blackie Academic & Professional.

59. Tsukada, Y. and Ichimura, Y. (1997) Micropiles in Japan: present status and future prospects. International Workshop on Micropiles, Seattle.

60. Vehmas, H. (2000) The city hall of Porvoo – the reinforcing of the foundation and leveling of the building. The 3rd International Workshop on Micropiles, Turku.

61. Vunneli, J. (2009) Underpinning methods. In Underpinning – Nordic practice. (ed. Lehtonen, J.). Course material from Turku University of Applied Sciences 46.

62. Wong, K.C. (2000) Valuing the refurbishment cycle. Property Managementt Vol. 18 No. 1, s. 16-24.

© 2010 ejge