Foundation Failure: Causes, Prevention and the Role of Civil Engineers

RC foundations are the most important elements in any type of structure, as they transfer all the loads that come on the superstructure to the ground below. RC foundations are designed such that the safe bearing capacity of the soil at the site is not exceeded, and have adequate safety against sliding, overturning, or pull-out, and keep the total and the differential settlements within allowable limits.

Foundation failures are difficult to rectify and may endanger the entire building. In addition, as foundations will be buried inside the ground, it is difficult to monitor or repair them. Failure of foundations may occur due to poor soil conditions, improper drainage, changes in the water table, tree roots, construction errors, weather conditions or expansive soils. If any foundation failure is noticed or suspected, it is important to have the foundation inspected by a qualified geotechnical engineer and remedial measures undertaken. Soil failures are classified as bearing capacity failures, bulging or swelling of soil, sliding, liquefaction, and lateral spreading. A few notable soil failures are discussed. Foundation engineers are urged to study such failures, in order to avoid repeating such mistakes in their projects.

Introduction

Civil engineering is one of the most important professions today, but when civil engineers make mistakes, the consequences can be catastrophic as they can result in loss of property and human life and may even affect the economy of the state. Structural engineers must also consider the environmental and economic outcomes of their work.

A major concern is safety. The safety of structures is achieved by analyzing the building using appropriate software to resist various possible loads and their combinations as specified in the codes released by the Bureau of Indian Standards (e.g. various parts of IS 875 and IS 1893). Then the different elements of the building have to be designed and detailed properly using IS 456:2000. Finally, the building has to be executed at the site using quality materials under strict supervision.

RC foundations are the most important elements in any type of structure, as they transfer all the loads that come on the superstructure to the ground below. Due to the complex nature of soils and their behaviour, a hybrid approach is usually adopted in foundation design in which soil bearing pressures are checked based on the working stress method and members of the foundation are designed using the limit states method (Subramanian, 2013). There should not be any compromise in their analysis, design, and execution, as any error in them may lead to the failure of the whole structure.

RC foundations are to be designed keeping in mind the following (Varghese, 2005):

1. All the applied vertical and horizontal loads and moments have to be resisted by the soil pressure, which should not exceed the safe bearing capacity of the soil at the site.
2. The foundation should have adequate safety against sliding, overturning, or pull-out (in case of tensile loads due to wind or earthquake).
3. The total settlement and the differential settlements of the structure should be within the allowable limits as prescribed in IS 1904.

It must be remembered that a non-uniform pressure under the foundation in compressible (clay) soils can lead to long-term effect of tilting of the foundation. It is also important to conduct enough soil investigations at the site using geotechnical engineers, and determine soil properties at foundation level, the type of soil below the foundation up to the required level of dispersion of load, and to determine the type of foundation for the structure at hand.

Usually, the factor of safety adopted for the soil is in the range of 2.0 to 4.0, depending on the type of structure as compared with the factor of safety of 1.5 adopted for concrete or steel structures. In general, foundations in clays should be given a larger factor of safety against shear failure than foundations in sands (Varghese, 2005). A higher factor of safety for soils is used because the properties of soil can vary greatly depending on the location, the type of soil, and the depth of the soil. This variability makes it difficult to accurately predict the behavior of soil under load. Foundation failures are difficult to rectify and may endanger the entire building. In addition, as the foundation will be at a depth from the ground level, it will not be visible for monitoring. Hence, it is important to design them conservatively.

Causes of Building Foundation Failures

If the footing is not of the required thickness, there is a danger of the column piercing through the foundation (punching failures). Several failures (both partial and total) in the past have demonstrated the importance of foundation failures, especially in poor soils. There may be many causes of building foundation failures. Some of the most common are given below:

• Poor soil conditions: If the soil beneath a foundation is not strong enough to support the weight of the building, it can cause the foundation to fail. This can happen if the soil is too soft, too sandy, or too wet.
• Improper drainage: If water is not properly drained away from the foundation, it can seep into the soil and cause the foundation to become weak and unstable.
• Changes in the water table: If the water table rises, it can put extra pressure on the foundation and cause it to fail. This can happen due to heavy rains, melting of excessive snow, or other factors.
• Tree roots: Tree roots can grow under a foundation and cause it to heave or shift. This can damage the foundation and make it unstable (Vivek and Subramanian, 2021). Trees near a building may also affect the moisture in the soil below foundations and cause problems, especially in expansive soils (Wray, 1995).
• Construction errors: If a foundation is not built properly, it can be more likely to fail. This can happen due to mistakes in the design, construction, or materials used.
• Weather events: Extreme weather events, such as earthquakes, floods, or hurricanes, can damage foundations. This can happen due to the force of the wind or water, or due to the shaking of the ground.
• Expansive soils: Some clays such as kaolinite, illite, and smectite, shrink and swell in the presence of moisture. Expansive soils can cause foundations to crack, heave, or tilt. This can lead to damage of the structure above the foundation, such as walls, floors, and ceilings, especially in single storey buildings or light buildings (Wray, 1995). In expansive soils, it is better to adopt under-reamed piles. Some signs of foundation failure:
• Cracks: Cracks in the foundation are a common sign of failure. These cracks can be small or large, and they may be vertical, horizontal, or diagonal.
• Sagging floors: If the floors of a building are sagging, it may be a sign that the foundation is failing. This is especially true if the sagging is only in one area of the home.
• Water leaks: If there is water leak in the basement, it may be a sign that the foundation is failing. This is because water can seep into the soil and cause the foundation to become weak.
• Doors and windows that stick: If doors and windows in a building are sticking, it may be a sign that the foundation is failing. This is because the foundation is shifting, which can cause the doors and windows to become misaligned.

If any of these signs are noticed or suspected, it is important to have the foundation inspected by a qualified geotechnical engineer who will be able to assess the damage and recommend the best course of action.

Types of Soil Failure

There are many different types of soil failures, but some of the most common include:

• Bearing capacity failure: There are two types of this failure: General shear failure and local shear failure. General shear failure occurs when the shear stresses in the soil are evenly distributed over a large area. This type of failure is more common in dense soils. Local shear failure occurs when the shear stresses in the soil are concentrated in a small area. This type of failure is more common in loose soils. Shear failure can be caused by a number of factors, including the weight of a building, the force of water, or the shaking of an earthquake. Bearing capacity failure can have serious consequences, including structural damage, flooding, and loss of life.
• Bulging or Swelling of Soil: This type of failure occurs when the soil is unable to support the weight of a building and starts to bulge out. Bulging can be caused by the same factors that cause shear failure, as well as by the expansion of clay soils when they are wet.
• Sliding: This type of failure occurs when the soil on a slope starts to slide down the slope. Sliding can be caused by the weight of the soil, the force of water, or earthquakes.
• Liquefaction: This type of failure occurs when saturated soil loses its strength and behaves like a liquid. Liquefaction can be caused by earthquakes or by the sudden release of water from the soil (see Fig.1).
• Lateral spreading: This type of failure occurs when the soil on a slope starts to move sideways. Lateral spreading can be caused by the weight of the soil, the force of water, or earthquakes.

Figure 1: Overturning failure of apartment complex buildings during Niigata 1964 earthquake (Courtesy: USGS)

The type of soil failure that occurs will depend on the specific conditions of the soil and the loading conditions. It is important to have a qualified engineer test and evaluate the soil conditions before building on a site to determine the risk of any possible soil failure.

Case Studies of Foundation Failures

A few notable foundation failures are discussed below:

The Tower of Pisa, Italy (Year 1173)

Figure 2: Tower of Pisa, considered as the first foundation failure (Photo: Er. S. Srinivas)

The Tower of Pisa is a freestanding bell tower of the cathedral of the Italian city of Pisa. The tower is a 56.4m tall, circular, eight-storey structure made of white marble. Although intended to stand vertically, the tower began leaning to the southeast soon after the onset of construction in the year 1173 due to a poorly laid 3m deep foundation and weak, unstable subsoil. Prior to restoration work performed between 1990 and 2001, the tower leaned at an angle of 5.5 degrees, but the tower now leans at about 3.99 degrees. This means that the top of the tower is 3.9m away from the vertical plane through the tower (see Fig. 2).

Several attempts have been made to stabilize the foundation movement- details of these may be found in Subramanian and Muthukumar (1998) and Burland et al. (2009). After a decade of corrective reconstruction and stabilization efforts, the tower was declared stable in 2008 and is expected to stand for at least another 200 years.

It may be of interest to note that in June 2010, the Capital Gate building in Abu Dhabi, UAE was certified as the ‘World's Furthest Leaning Man-made Tower’; it has a 18-degree slope, almost five times as that of the Leaning Tower of Pisa; however this tower is deliberately engineered to slant.

Transcona Grain Elevator, Canada (Year 1913)

The Transcona Grain Elevator was a grain storage facility, whose construction started in 1911 at North Transcona, near Winnipeg, Manitoba, for use by the Canadian Pacific Railway. It consisted of a RC work-house and adjoining bin-house. In plan, the work-house measured 21 m × 29 m. The structure was 55 m tall and was founded on a raft foundation, 3.6 m below ground level. The bin-house consisted of five rows of thirteen bins each 4.3 m diameter and 28 m high and rested on a concrete framework, which was supported by RC raft. The bin-house raft measured 23m × 59m and was also founded at a depth of 3.7 m below Ground Level (Peck and Bryant, 1953). The construction was completed in September, 1913.

Immediately after completion, filling of the elevator commenced, and about 31,500 m3 of wheat was distributed as evenly as possible in all the bins. On October 18, 1913, the building began to settle uniformly at the rate of 0.3 m per hour. On the next day, the building began tilting and the inclination reached about 27 degrees to the west (see Fig. 3). The subsoil below consisted of a uniform deposit of clay of thickness 9 to15 m, which was due to the sedimentation in waters of glacial Lake Agassy. No borings were known to have been made for the design of foundation. In 1951, comprehensive geotechnical investigations were undertaken by Peck and Bryant, who drilled additional exploratory boreholes, took undisturbed soil samples, and conducted triaxial tests (Peck and Bryant, 1953). Based on these tests, it was concluded that the elevator foundation had failed due to a bearing failure in the underlying clay. It has to be noted that during 1911, the state-of-the art in geotechnical engineering had not reached the point that ultimate bearing capacity of the foundation could be computed (Stepherd and Frost, 1995). Terzaghi developed his bearing capacity theory only in 1943 (Terzaghi, 1943).

Figure 3: Collapse of Transcona Grain Elevator, Canada (Photo Source: structville.com)

After the accident, remedial work was carried out by the Foundation Company Limited. This remedial work consisted of building supporting structures, gradually excavating the foundation slabs and building the piles in order to return the building to its original condition. The Transcona grain elevator was purchased by the Parrish & Heimbecker Company in 1970. It is still in operation today, under the name Parrish & Heimbecker Grain Elevator (See Fig. 4).

Figure 4: Parrish & Heimbecker Grain Elevator (Source: www.geotech.hr)

The Ocean Tower, USA (Year 2009)

Another example of a famous foundation failure in Texas, USA, is the South Padre Island’s Ocean Tower, which was dubbed later as the ‘leaning tower of South Padre’. Ocean Tower was originally designed to be a 31-storey luxury high-rise building, which housed high-end condominiums (see Fig. 5). It featured 147 residences, a gym, swimming pools, spa, and a media room, with a height of 136 m. The building was designed to withstand extreme winds with three massively reinforced core walls. Each unit was sold for $2 million.

The construction of Ocean Tower began on April 5, 2006, after soil testing (the exploratory borings were no deeper than 30m). It continued for two years with much of the main structure completed until differential settlement made the building to sink by over 360 mm. The 401 numbers 400 mm diameter auger-cast piles of length 28.95 m in the expansive clay caused problems, stressing beams and columns, causing cracking, spalling, and breaking (see Fig. 5). The building leaned towards the northwest corner, cracking the wall of the adjacent garage, which abutted the tower. In addition, there was a differential settlement, due to which the tower's core sank 360 to 410 mm, while the attached parking lot sank less than half that amount. Construction was halted in the summer of 2008.

Figure 5: The Ocean Tower, Texas, and the failure of columns (Photo source: www.walterpmoore.com/projects/ocean-tower-failure-analysis)

During the forensic investigation, the company Walter P Moore performed a detailed evaluation and used computer modeling to analyze the causes of failure, as well as predict any future failure of structural elements. On November 4, 2008, it was felt that the work needed to fix the building would prevent the project from becoming economically viable. Hence, the development was stopped and on December 13, 2009, the tower was imploded by Controlled Demolition, Inc. The building weighed 50,000 t when it fell, and became the tallest and largest reinforced concrete structure to be imploded, till then.

The developers filed a $125 million lawsuit against geotechnical engineering firm Raba-Kistner Engineering and Consulting of San Antonio and structural engineers Datum Engineers of Austin and Dallas (en.wikipedia.org/wiki/Ocean_Tower). In 2010, the Cameron County District Court dismissed all claims against the structural engineering firm.

Rare Foundation Failure in China (2009)

On June 27, 2009, an unoccupied 13-storey block of flat building, still under construction, at Lianhuanan Road in the Minhang district of Shanghai city, China toppled over and ended up lying on its side in a muddy construction field (see Fig. 6). One worker was killed.

Figure 6: Toppling of a complete 13-storey building in China [Source: Basulto, David. "Building collapse in Shanghai" 30 Jun 2009. (www.archdaily.com/27245]

The cause of this building collapse was due to a pressure difference on two sides of the structure, according to an investigation report. The report claimed that the collapse was caused by earth, excavated along the building on one side with a depth of 4.6 m, for an underground car park, and piled up to a height of up to 10 m on the other side of the structure. The weight of overburden earth created a pressure differential, which led to a shift in the soil structure, eventually weakening the pile foundation and causing it to fail. This situation might have been aggravated by several days of heavy rain leading up to the collapse, but investigators did not site this as a crucial factor. The sequence of failure of this building is shown in Fig. 7. More details about this failure may be found in Subramanian (2009). This failure underlined the importance of not disturbing the soil near a construction, even if the building is supported on piles.

Figure 7: Sequence of foundation failure of a tall building in Shanghai, China

The Millennium Tower –Most Expensive Foundation Failure (2016-22)

Figure 8: The 58-storey Millennium Tower, San Francisco (Source:en.wikipedia.org)

The Millennium Tower is located in the South of Market district of downtown San Francisco, USA. It is a mixed-use, primarily residential high rise and is the sixth tallest building in San Francisco. It is a 58 storey, 197m tall building, with 366 luxury condominium units (see. Fig.8). The adjacent 12-storey tower, in the same property has 53 units and is a 13m tall, two-storey glass atrium connecting these two towers. This US$350 million (originally estimated cost) project was designed by Handel Architects, engineered by DeSimone Consulting Engineers, built by Webcor Builders, and developed by Mission Street Development LLC, an affiliate of Millennium Partners. Treadwell & Rollo acted as the geotechnical engineer.

This is a slender tower with each floor having an area of 1,300 m2. The tower opened to residents in 2009. But the building was slowly sinking into the ground and has tilted to one side. In May 2016, residents were informed that this tower was both sinking and tilting, resulting in nine separate lawsuits involving 400 individuals. As of 2018, the sinking had increased to 460 mm with a lean of 360 mm. Measurements in 2022 showed that the tilt increased to 710 mm, as measured from the roof top (https://en.wikipedia.org). The sinking and tilting of The Millennium Tower was believed to have been caused by a number of factors, including the building's pile foundation not reaching the bedrock, the soft soil on which it was built, and the heavy weight of the building.

The Millennium Tower’s foundation consisted of a 3 m-thick concrete raft slab supported by 942 numbers prestressed concrete friction piles (see Fig.9). These piles extended only to a depth of 18-27m below the ground into Colma sand formation, which consists of dense clay and silty sand. Beneath the Colma Formation, there is a 50m of marine and alluvial deposit, the upper layers of which are a stiff clay material, known locally as Old Bay Clay (www.geoengineer.org). If end-bearing piles had been used for the Millennium Tower, they would have been up to three times longer than the existing piles.

Figure 9: Original fix proposed for the rectification of the tilt of the Millennium Tower (adapted from www.enr.com)

In May 2020, the $100m remediation plan was suggested by Ronald Hamburger, the senior principal engineer at Simpson Gumpertz & Heger and his team. This plan proposed the construction of a perimeter pile upgrade of 52 concrete piles with 1.8m spacing, to anchor the building to a stable bedrock layer 75m below the ground (see Fig. 9). Also, an extension of the existing mat foundation was decided, to encompass the new piles together with jacking of 3560 kN of load from the existing building onto each of the new piles. The design goal was to relieve a portion of the stress on the Old Bay Clay soils along the building’s north and west sides, to stop further settlement, and to recover a portion of the building’s tilt. Shortly after the works began, the tilting and the sinking of the tower accelerated.

In May 2021 crews began to dig down to install 910 mm diameter pile casings along Fremont Street and by June 2021 the building had tilted approximately 63 mm more to the west. In early July the contractor started to install 910 mm diameter pile casings along Mission Street, which resulted in a small increase in the rate of tilting to the north. In mid-July, the contractor started to install 610 mm diameter piles along Fremont Street, which again resulted in an increase in the tilt rate to the west.

The repair project was halted in August 2021 when it was found that the building had unexpectedly sunk an additional 25 mm on the Fremont Street side, after 39 of the 52 piles were installed (https://en.wikipedia.org). The engineer and contractor then developed a revised design comprising just 18 piles as opposed to the original 52 pile design and improved techniques for their installations. The fix involved driving 18 concrete piles into bedrock deep under the property at 301 Mission Street and shifting a portion of the building's load onto the new piles. The piles were designed to support the building for the next 150 years. The $100 million engineering fix, which was completed in June 2023, has successfully stabilized the building. The building has not sunk or tilted any further since the fix was completed. The fix has also been praised by city officials, who said that it is a success story for San Francisco. The cost of compensating residents for their losses is still being determined, but it is estimated to be in the tens of millions of dollars (https://en.wikipedia.org).

The Millennium Tower subsidence problems prompted San Francisco Department of Building Inspection to issue guidelines for foundation peer review and monitoring of new buildings, taller than 73 m. New guidelines include procedures for structural, geotechnical and seismic-hazard engineering design review.

Summary and Conclusion

In any structure, RC foundations transfer all the loads that come on the superstructure to the ground below and hence are most important for the proper functioning of the structure. They are designed such that the pressure under the foundation does not exceed the safe bearing capacity of the soil at the site. In addition, the foundation is designed to have adequate safety against sliding, overturning, or pull-out, and the total and the differential settlements are also within allowable limits.

Foundation failures are difficult to monitor and rectify, as the foundations are buried in the soil. Foundation failures may endanger the entire building. Poor soil conditions, improper drainage, changes in the water table, tree roots, construction errors, weather conditions, and the presence of expansive soils or soils with destructive chemicals are the main causes of any foundation failure. If any foundation failure is noticed, it has to be inspected by a qualified geotechnical engineer and remedial measures are to be undertaken.

Soil failures are classified as bearing capacity failures, bulging or swelling of soil, sliding, liquefaction, and lateral spreading. The 1173 failure of the Tower of Pisa, Italy (which is considered as a successful foundation failure), the 1913 Transcona Grain Elevator failure at Canada (due to the non-availability of theories to estimate safe bearing capacities), The 2009 Ocean Tower failure at Texas, USA (which resulted in the demolition of the entire building), the 2009 rare foundation failure in China (which resulted in the toppling of the entire 13-storey building as a unit on ground), and the 2016-22 failure of the Millennium Tower at San Francisco, USA (due to the reliance of friction piles to carry the heavy loads) have been discussed. A study of such failures is important for foundation engineers so that such mistakes are avoided in their projects.

References

1. Burland, J.B., Jamiolkowski, M.B. and Viggiani, C. (2009) “Leaning Tower of Pisa: Behaviour after Stabilization Operations”, International Journal of Geoengineering Case Histories, Vol. 1, No. 3, pp. 156-169. http://casehistories.geoengineer.org/volume/volume1/issue3/IJGCH_1_3_2.pdf
2. Peck, R.B. and Bryant, F.G.(1953) “The bearing Capacity Failure of the Transcona Elevator”, Geotechnique, Vol. III, pp. 201-208.
3. Stepherd, R., and Frost, J.D. (Editors) (1995) Failures in Civil Engineering: Structural, Foundation, and Geoenvironmental Case Studies, American Society of Civil Engineers, New York, 92 pp.
4. Subramanian, N. (2009) “Rare Foundation Failure”, New Building Materials & Construction World, Vol. 16, No.2, Aug 2009, pp.100-105.
5. Subramanian N. (2013) Design of Reinforced Concrete Structures, Oxford University Press, New Delhi, 880 pp.
6. Subramanian, N. and Muthukumar, D. (1998) “Leaning Tower of Pisa - will it be reopened for tourists?”, Bulletin of the Indian Concrete Institute, No.63, April-June 1998, pp. 13-16.
7. Subramanian, N. (2014) “The Failures that Changed the Perception of Our Designs”, The Bridge and Structural Engineer, Journal of ING/IABSE, Vol. 44, No.4, Dec., pp. 29-51.
8. Terzaghi, K. (1943) Theoretical Soil Mechanics, John Wiley and Sons, New York, 510 pp.
9. Varghese, P.C. (2005) Foundation Engineering, Prentice-Hall of India Pvt. Ltd, New Delhi, 570 pp.
10. Vivek, A., and Subramanian, N. (2021) “Planting Trees-Precautions and Care”, New Building Materials & Construction World (NBM & CW), Vol. 27, No.6, Dec., pp. 106-112.
11. Wray, W.K. (Editor) (1995) So Your Home is Built on Expansive Soils-A Discussion on How Expansive Soils Affect Buildings, American Society of Civil Engineers, New York, 59 pp.
12. https://en.wikipedia.org/wiki/Millennium_Tower_(San_Francisco)
13. https://www.geoengineer.org/news/san-franciscos-troubled-millennium-tower-continues-to-sink
14. https://www.geoengineer.org/news/new-guidance-for-san-francisco-high-rise-foundations

About the Author

Dr. N. Subramanian, Ph.D., FNAE, is a consulting engineer, now living in Maryland, USA. He earned his PhD from IIT Madras in 1978 and has 46 years of professional experience which includes teaching, research, and consultancy in India and abroad. Dr. Subramanian has authored 25 books and more than 310 technical papers, published in international and Indian journals and conferences. He has won the Tamil Nadu Scientist Award, the Lifetime Achievement Award from the Indian Concrete Institute (ICI), Gourav Award of ACCE(I), and the ACCE(I)-Nagadi best book award for three of his books. He also served as the past vice-president of ICI and ACCE(I).

Acknowledgement: The article has been reprinted from the Journal of the Indian Concrete Institute, Vol. 24, No.4, Oct.-Dec.2023, pp. 15-22., with due permission of the author.