What is Soil Investigation

Soil investigation is the process of collecting and analysing information about the soil at a specific location to determine its physical and engineering properties. This information is used to design foundations, slopes, and other structures, as well as to plan for construction, agricultural, and environmental projects.

Types of Soil Investigation

There are several different types of soil investigation techniques, each with their own advantages and disadvantages. Some of the most common types include:

  • Machine  boring: This method involves drilling a hole into the ground using a drilling rig. Soil samples can then be collected and analyzed to determine soil properties.
  • Hand augering: This method is similar to boring, but it is done manually using a hand-held auger. It is typically used for shallow soil investigations and is less expensive than drilling.
  • Cone penetration testing (CPT): This method involves pushing a cone-shaped probe into the soil and measuring the resistance encountered to determine soil properties such as density and strength.
  • Trenching: This method involves excavating a trench in the soil to observe soil profile, and collect soil samples for laboratory testing.
  • Geophysical methods: These methods include electrical resistivity imaging, ground-penetrating radar, and seismic refraction, which are used to create subsurface maps of soil and rock layers without drilling or excavating.
  • Chemical analysis: This method involves taking soil samples and analyzing their chemical composition to determine if there is any contamination present.

The specific method or combination of methods used will depend on the type of project and the soil conditions at the site.

Uses of Soil Investigation

Soil investigation serves several important functions in the design and construction of foundations, slopes, and other structures, as well as in planning for construction, agricultural, and environmental projects. Some of the main functions of soil investigation include:

  • Determining soil properties: Soil investigation is used to determine the physical and engineering properties of the soil at a specific location, such as its type, strength, compressibility, water content, and Atterberg limits. This information is critical for designing foundations, slopes, and other structures that will be built on the site.
  • Identifying potential hazards: Soil investigation can be used to identify potential hazards such as soil liquefaction, landslides, or unstable slopes that could affect the stability of structures built on the site.
  • Planning for construction: Soil investigation can be used to plan for construction activities, such as determining the most suitable locations for foundations, or identifying areas where additional soil stabilization measures may be required.
  • Environmental protection: Soil investigation can be used to identify soil contamination, as well as potential sources of pollution and to plan for environmental cleanup and mitigation measures.
  • Agricultural purpose: Soil investigation can be used to identify soil type, fertility, and water holding capacity to plan for crop production and irrigation.
  • Cost savings: Soil investigation can save costs in the long run by identifying potential problems and providing solutions before the construction phase. Improper foundation design or not taking into account soil conditions can lead to costly repairs or even building failures.
  • In summary, soil investigation provides crucial information that is necessary for the safe and efficient design and construction of structures, as well as for the protection of the environment and agricultural production.

Dangers of Inadqeuate Soil Investigation

One example of a failure due to inadequate soil investigation is the collapse of the Silver Bridge in West Virginia, USA in 1967. The bridge was a suspension bridge that connected Point Pleasant, West Virginia to Gallipolis, Ohio over the Ohio River.

The collapse was caused by a failure in a single eyebar within a suspension chain, which led to the failure of the entire bridge. After the collapse, it was discovered that the failure was due to a design error, specifically the lack of redundancy in the suspension chains. However, the root cause of the design error was inadequate soil investigation. The soils at the site were composed of soft clay, which was not properly taken into account during the design of the bridge’s foundations. The soft clay caused the bridge’s piers to settle unevenly, which put additional stress on the suspension chains and ultimately led to their failure. The collapse of the Silver Bridge resulted in the deaths of 46 people and was a tragic reminder of the importance of proper soil investigation in the design and construction of structures.

Another example is the failure of the St. Francis Dam in California in 1928. The dam was a concrete gravity dam and was built to supply water to Los Angeles. The dam failed within hours of filling, killing more than 400 people. The cause of the failure was determined to be the dam being built on a weak foundation of loose soil and rock. The investigation revealed that the geology of the area was not properly studied, and the weak foundation material was not identified during the construction.

Building failures due to soil investigation in Indonesia is not well documented and due to lack of public knowledge and the desire from clients to hide the nature of accidents the cases are not well known. But the author of this article has know several failure and all was due to poor soil investigation. These examples demonstrate the importance of proper soil investigation in the design and construction of structures, as failure to do so can lead to tragic consequences.