1 of 19

Soil Improvement

Dr Adewale Abimbola, FHEA, GMICE

www.edulibrary.co.uk

2 of 19

Aim and Objectives

Aim: Soil Improvement/Remediation.

Objectives: At the end of the lesson, the students should be able to:

  • Identify various soil improvement/remediation techniques.
  • Describe at least any two techniques used for soil or ground improvement remediating of a site prior to construction commencing.

3 of 19

LO3 | P5 - Learning Outcomes and Assessment Criteria

4 of 19

Introduction

  • Shallow foundations are suitable for soils with high bearing capacity near the surface.
  • In cases of lower surface soil bearing capacity, deep foundations like piles or piers are used to transfer the load to firmer strata below.
  • Soil improvement, also known as soil stabilisation, is another economical choice or method to modify soil properties to enhance its engineering performance.
  • Soil improvement:
  • Increases shear strength
  • Reduces permeability
  • Reduces compressibility.

​

Figure 1. Stabilisation of leaning tower of Pisa (Leaning Tower Pisa, 2024)

5 of 19

Introduction - Why soil remediation or improvement is required?

  • Failure of slope/Land slide

​

  • Effects of liquefaction

​

https://www.youtube.com/watch?v=IRLLKziZ7Io

  • Sink hole

​

6 of 19

  • When a project encounters difficult foundation conditions, possible alternative solutions include:

 Avoid the particular site

Remove and replace unsuitable soils

 Enable cost effective foundation design

 Reduce the effects of contaminated soils

 Ensure sustainability in construction projects using soil improvement techniques

 Etc.

The Need for Ground Improvement?

7 of 19

Soil or Ground Improvement Techniques

  • Ground improvement can be done through various mechanisms:

Compaction

 Admixtures or grouting

 Reinforcement

Dewatering (This would be considered in our next lesson)

8 of 19

Soil Improvement/Remediation Techniques – Stone Column

  • Also termed as vibro-replacement or vibro-displacement, this technique enhances ground stability.
  • The process involves creating dense aggregate columns through soil layers.
  • A vibrator reaches the desired depth using vibration combined with air or water jetting.
  • Gravel is introduced at the vibrator's tip, and repeated vibrator movements distribute the gravel into the soil.
  • This technique forms a soil-column matrix, significantly improving the soil's shear strength and reducing its compressibility.

Vibro-Replacement (Stone Columns) - Dry Bottom Feed Animation – YouTube

Figure 2. Stone column (The Constructor, 2021)

9 of 19

Soil Improvement/Remediation Techniques – Vibro Compaction

  • This process stabilises loose sands, creating firm foundation soils.
  • Utilises a vibrator, often with water jetting, to reposition soil particles into a tighter arrangement, achieving 70-85% relative density.
  • Effective in both above and below water table environments.
  • Implemented in Dubai, notably for the Palm Islands construction.
  • Vibro compaction equipment is often equipped with advanced instrumentation, including onboard computers for real-time monitoring and adjustment, ensuring adherence to project specifications.

Figure 3. Compaction process during deep vibro compaction and the deep vibrator. (Nagy, et al.,, 2018)

Figure 4. Compaction process during deep vibro compaction and the deep vibrator. (Bhosale, 2014)

10 of 19

Soil Improvement/Remediation Techniques – Dynamic Compaction

 Dynamic consolidation involves applying dynamic energy to pressurise the pore water and to accelerate consolidation of the underlying soft ground. It is useful for soft clay.

 Traditionally employs tall cranes and free-falling weights.

 Best suited for sandy soils, less effective on fine-grained materials.

 Dynamic Consolidation Technique utilises dynamic energy to compress pore water and accelerates consolidation in soft ground, particularly effective for soft clay.

 Further details on various compaction methods are presented in subsequent slides.

​

Compaction by tamper

11 of 19

Soil Improvement Techniques – Dynamic Compaction

Deep Dynamic Compaction (DDC) with drop weights:

  • Involves dropping weights ranging from 5 to 20 tons from heights up to 20 meters using a crane.
  • Common applications include strengthening reclaimed areas and rehabilitating landfills.
  • Effective for reducing settlement risks in treated areas.

Dynamic Compaction - YouTube

Impact Rolling using High Impact Energy Dynamic Compaction (HIEDYC)

  • Energy impact reaches depths between 2 to 5 meters.
  • Produces relatively low vibration levels, making it suitable near existing structures.
  • HIEDYC ground treatment, part of this technique, is applicable to a variety of soil types including landfills, sands, silts, and clays.

Figure 5. Visuals of Tria (3-sided), Qadra (4-sided) and Penta (5sided) HIEDYC modules (L to R) (Choy et al., 2019).

https://www.youtube.com/watch?v=zjcT1cO9th4

12 of 19

Soil Improvement/Remediation Techniques – Dynamic Compaction

Rapid Impact Compactor (RIC)

  • The RIC is typically mounted on a 35 to 70 tonne tracked base excavator, enhancing mobility and site access.
  • Its adaptability allows operation in confined spaces, including inside warehouses and urban areas.
  • Operates at a rate of 10-60 blows per minute, utilising drop weights of 5, 7, 9, or 12 tonnes.
  • The drop height for the weight ranges from 1 to 2 meters.

​

  • Faster than traditional Deep Dynamic Compaction (DDC) but with less energy per impact.
  • The technique involves creating imprints with each blow, which are then filled with granular material.

https://www.youtube.com/watch?v=McIcn5t_vHs

Figure 6. Rapid impact compactor (Menard Canada, 2024)

13 of 19

Stabilisation Using Admixtures

  • Portland Cement is the most widely used admixture.
  • Mixing soil with Portland Cement creates soil-cement, akin to a less robust form of concrete.
  • Other notable admixtures are lime and asphalt.
  • The primary goal is to artificially cement the soil, enhancing its strength and decreasing its compressibility and permeability.
  • Effective in minimising the expansion properties of clay soils.
  • Commonly applied in surface mixing processes
  • In addition, contaminated soil can be mixed with binders (e.g., lime, cement, pozzolans) to lock contaminants in place and improve soil stiffness.

https://www.youtube.com/watch?v=t1BkutBj6Qs

14 of 19

Group-assessment Task

1. On a construction site with loose sandy soil and a planned multi-story building, which soil improvement method is most appropriate to increase density and bearing capacity without adding significant new materials?

  1. Installing deep soil mixing columns
  2. Dynamic compaction with heavy tamping
  3. Capping with a thick granular replacement layer
  4. Chemical grouting of the sand layer

2. A construction project encounters expansive clay that causes heave beneath lightly loaded slabs. Which soil treatment strategy primarily targets reducing the soil’s swell potential?

  1. Using a thicker, more heavily reinforced concrete slab without soil treatment
  2. Replacing a shallow layer of clay with compacted gravel only
  3. Lime stabilisation of the clay subgrade
  4. Installing stone columns beneath the slab

3. Which statement best explains why preloading with vertical drains is used for soft clay ground improvement under an embankment?

  1. It replaces the clay with granular soil to eliminate settlement.
  2. It increases permeability of the clay so that it behaves like sand indefinitely.
  3. It strengthens the clay by cementing particles together chemically.
  4. It accelerates consolidation by shortening drainage paths for pore water.

15 of 19

Reinforcement/Reinforced Soil/Earth Wall Construction

  • Soil is stronger in compression than in tension
  • To improve strength in tension, geosynthetics placed in soil for soil reinforcement

                               

                                

                               

                               

https://www.youtube.com/watch?v=2A581dzTsBs

https://www.youtube.com/shorts/HQz6kn-kvEw

Figure 7. Reinforced earth wall construction (Hood, 2019).

Figure 8. Reinforcement (Hood, 2019).

16 of 19

Soil Improvement/Remediation Techniques – Jet/Pressure Grouting

  • Utilises high-pressure jets of grout, water, air, or a combination to simultaneously erode and inject grout into the soil using a jet monitor.
  • The process involves inserting pipes to the required depth, then raising and rotating them during injection to form a column of treated soil.
  • Primarily used to enhance strength or diminish water permeability in various formations.
  • Employed in repairing faults in concrete and masonry structures.
  • Its high-pressure application makes it suitable for a broad range of soil types.
  • Applicable in reinforcing existing structures or stabilising foundations that have experienced shifts.

Figure 9. Pressure Grouting (Hubbard, 2019).

17 of 19

Soil Improvement/Remediation Technique - Soil Nailing

  • Involves reinforcing soil through the insertion of closely spaced passive elements.
  • Aims to transform the existing soil into a unified gravity-supported structure.
  • Enhances the overall shear strength of the soil and limits its displacement.

https://www.youtube.com/watch?v=44waiItHM1w

https://www.youtube.com/shorts/cRAEZTOCBm0

Figure 10. Soil nailing (Utama, 2009).

18 of 19

Self-assessment Task

Describe any TWO techniques used for soil improvement/remediation technique of a site prior to construction commencing.

Note:

  • A paragraph of about 5-6 lines for each of the technique.
  • Use illustration to support your description.
  • Ensure you provide the source of the information.

19 of 19

References/Bibliography

Bhosale, N. (2014) Ground Improvement Techniques. Available at: https://www.slideshare.net/nileshbhosale6/gt-39281373 (Accessed: 26 January 2024).

Choy, L. E., Rusli, Q. N., Razali, M., K. and Andy, R. (2019) ‘A case study of soft ground improvement by dynamic consolidation approach’, IOP Conf. Series: Materials Science and Engineering 512 012052. Available at: https://iopscience.iop.org/article/10.1088/1757-899X/512/1/012052/pdf (Accessed: 28 January 2023).

Hood, A. (2020) Soil improvement. Available at: https://slideplayer.com/slide/12639909/ (Accessed: 26 January 2024).

Hubbard, H. (2019) Unit i-sub structure construction. Available at: https://slideplayer.com/slide/12161516/ (Accessed: 26 January 2024).

Kazemain, S. and Barghchi, M. (2012) ‘Review of soft soils stabilization by grouting and injection methods with different chemical binders ’, Scientific Research and Essays, 7(24), pp 2104 - 2111. Available at: https://academicjournals.org/article/article1380880431_Kazemian%20and%20Barghchi.pdf (Accessed: 29 January 2023)

Keller (2018) Jet Grouting (Soilcrete®). Available at: https://www.keller.co.uk/sites/keller-uk/files/2019-03/jet-grouting-brochure-keller-uk.pdf (Accessed: 29 January 2023).

Leaning Tower Pisa (2024) HOW was the Leaning Tower of Pisa stabilized? Available at: https://leaningtowerpisa.com/facts/how-pisa-leaning-tower-was-stabilized (Accessed: 26 January 2024).

Nagy, P., Adam, D., Kopf, F. and FREITAG, P. (2018). Experimental and theoretical investigation of deep vibro compaction. ce/papers. 2. 7, pp 25-730. 10.1002/cepa.756.

Robbins, B. A., Stephens, I. J. and Marcuson III, W. F. (2021) Geotechnical engineering. Encyclopedia of geology, 2nd edn. pp 377-392.

TerraSystems (2023) Stone columns. Available at: http://www.terrasystems.com/services/stone-columns.html#:~:text=The%20stone%20column%20technique%2C%20also,the%20soils%20to%20be%20improved (Accessed: 28 January 2023).

The Constructor (2021) Ground improvement. Available at: https://theconstructor.org/geotechnical/ground-improvement/page/3/ (Accessed: 26 January 2024).

Utama, G. (2009) Services. Available at: https://www.geonusa.com/services_en.htm (Accessed: 26 January 2024).