Geotechnical Investigation is very important before any structure is built

No matter what structure is built it will require a geotechnical investigation to determine the soil / rock properties that it will be founded upon.  Poor investigation can lead to unforeseen issues whereas a thorough investigation can minimise risks when more is known.

Site Geotechnical Pty Ltd are in the business of enhancing engineering projects through ‘Soil Investigation Testing and Evaluation’ beginning at the soil foundation.

Although affordability is an important factor, other factors are more long-term. Risk management is a large consideration and the more that is known about a site, the better the ability to make decisions. The use of less accurate (rule of thumb) soil testing methods may save money at the start of the project, however it is important to recognize that the soil test is generally only a small fraction of the total project cost (often less than 1%). Conservative, incomplete, or incorrect information provided at the soil testing stage may eventually result in greater costs than that saved by undertaking a cheaper soil test. To ensure a solid start to any building project – and minimize problems or delays later in the build – it is wise to first focus on getting a quality soil test completed by a reputable company.

Given that soil provides the support for a structure, a soil test is essential for obtaining the parameters for design and identifying any constraints on construction. The information provided within a soil report should assist structural engineers in designing appropriate slabs, footings, or deep foundations (if required) to ensure your structure is safe and appropriately designed i.e. less prone to cosmetic defects such as cracking.

The more information you have, the more specific and appropriate the design for your structure. The Australian Standard AS 2870 sets out the method for determining the classification of a site and the design and construction requirements for slabs on ground, stiffened rafts, waffle slabs, strip footings, pad footings and piled footings. Structural Engineers and Builders are increasingly adopting the use of deep or piled foundations, requiring more detailed investigation to ensure the appropriateness of your design as well as providing better quantified options.

The main items required as part of the soil test are listed below. Having a good understanding of the ground conditions should assist in proper design and performance.

• The Expansive Nature of the Soil. Seasonal swelling and shrinkage of soil plays a significant part of the final design.
• Moisture Conditions. Trees and drainage can affect moisture and subsequent shrink-swell movement and strength of soil. If moisture conditions are likely to change during the life of the structure, the design should account for this change.
• Compressibility of the Soil. This can influence the settlement potential and the allowable bearing capacity of soils. Poor support is often associated with soft or filled soil. Sites that have deep fill will sometimes require deeper drilling beyond the normal depths quoted. This is usually charged at a rate over what is included unless it is accounted for within the investigation.
• Topography. Steepness of the site can affect the design, method of construction and/or stability. If the site falls within a designated Erosion Management Overlay (EMO), the report needs to follow specific guidelines relating to slope stability, landslip risk and the council’s specific schedule.
• Flexibility or Lack of Flexibility of the Structure. Timber structures can move with less possibility of noticeable distress while the effects on solid brick (rigid or brittle) structures are often more susceptible to noticeable cracking. 5mm cracks within brickwork may be acceptable from a structural perspective, however, may not be acceptable from an aesthetic viewpoint.
• Existing Structures and Footing Exposures. A great deal can be learned about the soils and existing footing performance by undertaking a footing exposure. If you are completing an upper story extension or building up against a neighboring building, it is often beneficial to undertake a footing exposure. This is where we would expose, measure, and confirm foundation material, condition and bearing of the footing and provide information so that your structural engineer can design appropriately. Things that can affect footing probe fees are if there is concrete paving or other obstruction. Concrete can be arranged to be cut for an added fee.
• Deep Foundations or Piles. These are often needed for deep fill, soft soils, reactive soils, high loadings, lighting poles, retaining walls, basements and the like. These types of projects require detailed Geotechnical Site Investigation.

The cost of completing a geotechnical investigation is dependent on the project, engineers brief and site requirements.