STUDY OF CAUSES OF FOUNDATION FAILURES (A CASE STUDY OF RIVERS STATE)
The research focuses on the causes and possible solution to common foundation failures to building in Nigeria. The occurrence of foundation failures and collapse of building has become a major issue of concern in the development on this nation as the magnitudes of this incident are becoming very alarming. This paper therefore examines the incident of foundation failure and collapse in swampy/expansive areas in Nigeria. By focusing on some states from each of the five geopolitical region of the country as case study. The paper examined the contributory role of the informal sector to this decadence. The study indicated that the failure and collapse of foundation in building stem principally from hasty construction, low quality workmanship, poor supervision, inexperience (use of incompetent hands), ignorance non-compliance with building regulations. Questionnaires were administered to few selected, architects, town planners, civil engineers and clients within reach also filed trips made to Lagos to ascertain common failures. Secondary data were obtained from the websites of the Nigerian Institute of Building (NIOB). The research outcome revealed that all parties in the building industry, clients, architects, design engineers, local authority (town planners) and contractors are contributing immensely to foundation building failure in various dimensions. This study has revealed that more than 70% of the reported cases of foundation collapse and failure in Nigeria stemmed from the informal sector. It further showed that 70-0%, 23-3% and 6.7% of the reported cases occurred in private, public and corporate organization respectively. Common failures with proper assurance of competent professionals and strict enforcement of ethical standards by the Nigeria society of engineers, the NIOB and the NIA would reduce the problems identified to the minimum.
1.1 BACKGROUND OF THE STUDY
Failure is an unaccepted difference between expected and observed performance. A failure can be considered as occurring in a component when that component can no longer be relied upon to fulfill its principal functions. Limited deflection and settlement in a foundation which caused a certain amount of cracking and distortion of partitions could reasonably be considered as a deflect but not failure, where an excessive settlement and deflection resulting in serious damage to partitions, ceiling and flour finishes could be caused as a failure (Roddies, 1993). Frequently, consultants in the office, when they visit sites, see the mistakes being made time and time again. Many of these are indicators of lack of knowledge on the part of the people undertaking the construction.
The type of foundation failure commonly encountered in soft ground and in construction field as a whole can be classified into the following categories;
Inadequate protection resulted in weakening of foundation soil leading in instability and failure of the foundation. Two (2) earth slopes on Aghaji crescent, GRA, Enugu failed during a prolonged rainfall period in August 10th 2009 and affected the safety of two (2) residential building situated on top of failed slopes. According to the results of the study both slope failures are found to be attributed to the effect of soil saturation and buildup of pure water pressure in the slop, which in turn became threat to the foundation of the buildings.
Failure due to incompetent bearing stratum resulted in collapse or excessive deformation of foundation soil under the imposed loads. An example is seen in the reported cases of collapsed building in Victoria Island Lagos in July 18, 1985 when a residential building claimed the life of 13 people all of the same family.
Failure due to improper sequence and method of construction. This was encountered in a mult-storey building under construction located at Mokola, Ibadan Oyo state in October 1974. one was founded on footing foundation embedded at deep depth in ground consisting of residual soil and the other one was supported by RC driven pile embedded in soft ground close to a river. The piles and pile caps were constructed by the pilling contractor but without the construction of ground beams. Serious offset of column stump positions were founded in both projects after the completion of soil back filling surround the footing and pile caps. Pit exploration was carried out at the disturbed foundation locations found that shear failure of ground/ beams/ stumps of footing bending failure of RC piles occurred at the offset stump locations. The results of investigation showed that the caused of failures were likely due to improper backfilling and surcharge effects of heavy machine resulting in additional stress and soil movement in vicinity of the footings.
Design consideration and preventive measures. It is noted that many foundation failures could be avoided if the design does not take into consideration of the most critical condition and adequate protection to ensure integrity of design in long term.
The foundation shall be designed to withstand the most critical combination of load which the foundation may be subjected to during its services, period. Addition forces included by down drag effects, of subsiding ground on piles, rising of groundwater tables (swampy grounds) on retaining well and effect of wetting band on slope stability shall also be considered.
The characteristics of foundation soil including its mode of failure shall be well delineated for ensuring the most representative approach of analysis and valid assumption in the design be analyzed and checked for both drained and undrained cases to determine its safe bearing capacity. When compressible materials exist within influence zone of foundation, settlement of the foundation should also be assessed to ensure that no excessive settlement will be induced under the design foundation pressure.
Suitable types of filed and laboratory test shall be assigned based on the soil types, exiting and failure stress conditions to determine the representative soil parameters.
Fore design of foundation located on slopes the effect of ground profile on the bearing capacity of foundation should be properly analyzed to determine the possible reduction of soil bearing capacity. Earth slopes supporting foundations of structures should be adequately designed in terms of effective stresses taken into consideration of the most critical peizometric profile which may be included by the critical rain storm, flood and the worst loading condition during service period. Adequate surface and sub soil drains shall be provided to prevent surface erosion and soil disturbance due to infiltration of rainfall.
1.2 STATEMENT OF THE PROBLEMS
Many foundations failures are known to be attributed to inadequate protection of foundation soil, lack of consideration in the engineering characteristics of soils under different stress and loading conditions, improper construction sequence and inadequacy of design against possible worst condition in long terms. This failures are caused by the types of soil the foundation are found. Some other effects on foundation which leads to failure and continuous movement and cracking includes.
IMPROPER GROUND PREPARATION: In most cases, site preparation includes properly removing inadequate soil from the site, usually the top several inches. This allows the house to be built on original undistributed ground. However, Sometimes the site requires fill dirt to be placed to level the building foundation. If this material is not properly compacted, it can settle. This settlement causes foundation failures and interior home cracks.
EVAPORATION: Due to the fluctions in day to day weather conditions, the soil can experience expansion and contraction especially in swampy ground due to changes in moisture levels. As the moisture evaporates from the soil, it contracts and the foundation settles. When the moisture is returned through rainfall and percolation, the soil swells again. This type of foundation problem is cyclic, meaning the building will experience settlement then upliftment depending on the current soil conditions.
WATER TABLE LEVEL: Unlike evaporation charges in the water table happen less quickly under normal circumstances. Typically due to seasonal changes or more gradual short term climate shifts in the area, swampy and riverline areas. These foundation issues are more difficult to diagnose due to their slow progressive.
TRANSFORMATION: Tree, large plants, or large amounts of vegetation require large amount of water. Through not frequent in swampy areas. But if planted too closely to foundation, water will be removed from the soil and cause foundation settlement. Root of trees can also be a problem in foundation of building around or close to them. Root can break drains leading to more water and saturation of the surrounding soil and possible soil heave or weakening the soil.
IMPROPER DRAINAGE AND PLUMBING LEAKS: Drainage is a key concern of most properties water shed should be accomplished in most cases through adequate grade near the building. Another common issue is gutter down sputs draining near the foundation.
This adds excessive amount of water near the foundation that will cause foundation movements among other problems. Leaking pipes depending on the severity of the leak and if left untreated causes more progress to foundation failures.
INADEQUATE FOUNDATION CONSTRUCTION: Foundation construction techniques vary widely depending on the age, location and type of building.
This introduces problem that require the analysis of a licensed professional to determine the adequacy of the foundation. Investigation should be made to determine the size and material of the foundation.
Typical problems of poor foundation construction are
Incorrect mixing of concrete
Use of contaminated aggregates or old cement
Inadequate cleaning trenches before concrete is poured
Concreting in freezing weather
Avoiding excess water to help the concrete flow round the trench
POOR SOIL CONDITIONS: Soil condition vary based on general location of the building. However, the soil conditions can drastically differ from one property to the next. Underlying issues within the soil can also play a role in overall stability of the soil. Sometimes hidden layers of inadequate soil is located below support layers of acceptable materials.
DIFFERENTIAL MOVEMENT: Similar problems of cracking can occur if houses foundations of uneven depth and an example of this is housed with partial basement.
There is a danger that the shallow foundation may settle at a greater rate that the seep foundation and this differential movement will cause cracking. Similarly when extending houses, it is wise to ensure that the foundations to the new extension are at the same depth as the original property to prevent future problems of differential settlement. The porch extension added to several original constructions in building leads to quick failure especially one with quite shallow foundations.
CHEMICAL ATTACK: Some soils, particularly clays containing a high proportion of sulfate can attack the foundation concrete. In wet condition the sulfates combine with a by-product of the cement to produce a material called tricalcium sulfoaluminate. The crystals of this compound expands as they form and gradually cause pieces of concrete to break away. It can be prevented by the use of sulfate resisting cement and by protecting the external faces of the concrete with a bituminous compound.
BUILDING ON EXISTING SITES: If old foundations are not removed they can cause problems of differential settlement. This should of course be spotted at the site investigation stage. Some existing sites may be contaminated by toxic substances the ground can be “capped off” with an inert layer such as clean earth or stone to isolate these substances if it is impractical to excavate and remove the contaminated ground.
SIGNS OF FOUNDATION FAILURE
Misaligned doors and windows cracks in the sheetrock sloping of the floor cracks in the floor or title cracks on walls cracking of the foundation etc.
1.3 PURPOSE OF THE STUDY
While it is certain that buildings are prone to deterioration and many not be possible to generally aver failure, it is also expedient that the rate of collapse and the associated loss shield be greatly reduced. Based on the results obtained by Folagbade (2001), 75% of the reported foundation collapse in building as of 1980 in 1999 were private buildings, then activities of the informal sector need to be investigated. This project report therefore takes agential look at the incessant causes of foundation building failure and collapse especially swampy grounds by identifying the likely causes and also investigate the activities of the informal sector in this context. The main objectives are to identify the likely causes of building collapses and foundation failure of Nigeria.
The Oxford Advances Learner’s Dictionary defined informal sector as a released and friendly sector, not following strict rules of how to behave or do. In the same vein Uwakweh (2000) describes the informed sector as “that segment of firms or industrial that engage in construction or other activities without obtaining the necessary design, planning and construction documents”. This project report aim to see how this informal sectors help and in other hand attribute to this failure.
Registration categories of contractors with the federation board registration of Nigeria and the number of permanent employees in their pay roll.
Registration categories, No of permanent employee
Category No of respondent % response Classification No of respondents % respondents
A 72 80.0 1 to 10 81 90.0
B 12 13.3 Up to 50 6 6.7
C 4 4.5 Up to 80 2 2.2
D 2 2.2 Above 100 1 1.1
Effectiveness of monitoring of construction activities by the relevant government agencies.
No of respondents
No of respondents
% of respondents
1.4 JUSTIFICATION OF THE STUDY
This report presents guidance and information for the geotechnical investigation necessary for the selection and design of foundation for heavy and light military type building constructed in expansive clay soil areas. The information in this report is generally applicable to many types of structure such as residence, ware house and multistory buildings. Emphasis’s given to the maintenance of an environment that encourages constant moisture conditions in the foundation soils during and following constructions.
Special attention must always be given to specific requirements of the structure such as limitations allowable differential movement. The guidance and information provided in this report can significantly reduce the risk of undesirable and severe damages to many studies for numerous expensive soil conditions.
However, complete solution for some swampy or expansive soil are not yet available, for example the depth and amount of future soil moisture changes may be difficult to predict. This report presents guidance for selecting economical foundation or swampy and expansive tolerable levels and guidance for minimizing problems that may occur in footings and structures on expansive and swampy soils.1.5 RESEARCH QUESTIONS
What are the causes of foundation failures
What are the causes of ground water effects on structures.
How can foundation failures be avoided?
What are the causes of ground movements?
What are the causes of heave in ground?
How can design cause foundation failure?
Whose fault is it, the constructors or the clients?
Do the architects have hands in foundation failure?
What are the effects of soil test in foundation?
How can the down planners authority prevent or help prevent founded failure?
Can foundation failure be avoided?
What are the remedical measures to foundation failure?
1.6 SCOPE AND DELIMITATION
Guidelines of the geotechnical investigation and analysis necessary for selection and design of foundation in buildings constructed in expansive clay soil areas, consisting of methods and applications of methodology for prediction of volume changes in swelling foundation soil. However, much of the basis information presented is broadly applicable to the investigation and analysis of volume changes in soils supporting these structures and method for minimizing potential soil volume changes. Audience is also not specifically provided for the design of structure in areas susceptible to soil volume changes from forest heave and chemical reactions in the example oxidation of iron pyrite, although much of the information presented can be useful toward those designs.
1.7 LIMITATIONS OF THE STUDY
This report is concerned with settle med and heaves caused by change in soil moisture in non-frozen soil which in turn causes failure in the foundation. Foundation materials that exhibit volume change from change in soil moisture are referred to as expansive or swelling materials. They are highly plastic clays and clay shales that often contains colloidal clay materials such are used as the montmorillonites. Expensive soil are used in this report also include marls, clayey silt stones, and saprhtes especially swampy regions.
DAMAGES FROM DIFFERENTIAL MOVEMENT
The differential movement caused by swell or shrinkage and difference in water level expansive soils can increase the probability of damage to the foundation and super structure. Differential rather than total movements of the foundation soil are generally responsible for the major structural damage. Deferential movement redistribute the structure loads causing concentration and large changes in movement and shear forces in structure not previously accounted for in standard design practice.
OCCURRENCE OF DAMAGES: Damages can occur within a few months following construction, may develop slowly over a period of about 5 years, or may for many years until some activity occur to disturb construction and effects of occupancy tend to promote moisture changes on the soil.
STUDY OF CAUSES OF FOUNDATION FAILURES (A CASE STUDY OF RIVERS STATE)