What a Geotechnical Report should contain
In all projects, a number of contractors and engineers will be required. Whether constructing a commercial project or building a new agricultural facility or nutrient storage facility, the soil conditions and bearing capacity are some of the most important factors in building a suitable structure. In order to build an agricultural structure, the owner must conform to the regulations of the Nutrient Management Act. To address these requirements, and ensure your structure is built on a structurally adequate base, the services of a Geotechnical Engineer may be required.
A Geoscientist or Geotechnical Engineer is an expert at evaluating soil and groundwater conditions as they relate to design and construction. They are commonly used for proposed manure storage facilities, as well as for general and pre-construction geotechnical investigations.
A site characterization study is usually completed if a new nutrient management storage is to be constructed or in situations where the ground conditions appear questionable for construction. Geotechnical investigations for proposed nutrient management storage assess the soil’s ability to support the required bearing capacity as well as determine the site characteristics meet the minimum guidelines and regulations for the type of storage structure and to ensure two levels of groundwater protection.
In combination with the required setback distances from water wells, the minimum criteria is intended to provide protection against groundwater contamination. Two layers of protection are required to minimize any leakage from liquid manure storage from reaching groundwater - the structure being one layer and hydraulically secure soil (or liner) being the second. During the investigation, the groundwater elevation and bedrock elevations are noted, as well as open water sources and nearby structures to ensure that proper separation distances are provided to protect sensitive areas.
A Geotechnical Engineer should not only provide the required assessment during your planning process, but should be onsite during construction. This onsite inspection helps to ensure that soils are consistent with the initial report and any unforeseen soil conditions experienced during excavation are addressed and remediated prior to construction.
When selecting a Geotechnical Engineer, there are many factors to keep in mind - cost, efficiency to complete the work required onsite and thoroughness in their testing and reporting.
When having your site characterization report completed, it is best to follow up with your geotechnical engineer to ensure that the following basics are noted in your report.
the size (diameter and depth) of the manure storage;
all testing was completed in accordance with the requirements of the Nutrient Management Act (Ontario Regulation 267/03, as amended), including the depth of testing and number of test holes;
the founding elevation of the proposed tank;
location of any groundwater or bedrock to a depth of 1.5m below the founding elevation;
the soil bearing capacity at the proposed depth of tank (SLS and ULS) as well as anticipated settlement
confirmation that the geotechnical engineering firm will be completing an onsite inspection upon completion of the excavation to verify the soil conditions
Ensuring your geotechnical engineer intends to include this information in their report prior to testing will ensure that your engineer has the necessary information to prepare your permit drawings. When setting up your geotechnical services, knowing what to ask for is the key to getting the most from these services.
WHEN ELSE MIGHT YOU NEED A GEOTECHNICAL ENGINEER?
Outside of the utilization of a geotechnical engineer for your site characterization, there are other instances where one would be required for your project.
When constructing a building, onsite sewage disposal or storm water management projects or projects where grading and soil stability may be concerning factors, a Geotechnical Engineer will be required. In these instances borehole samples of soil are analyzed for grain size, moisture content and stability.
Since a solid base of suitable soil is critical to having a sound structure, we provide the following recommendations:
All footings should be on native, undisturbed soil, where possible;
If more than 36 inches of structural fill is to be used, a Geotechnical Engineer should be contacted, prior to fill placement, to provide compaction recommendations and to perform the necessary testing;
If on-farm or graded fill is to be used, a geotechnical professional should inspect the material prior to placement to determine its suitability. If suitable, the Geotechnical Engineer should also provide a procedure for compaction and perform the necessary compaction testing;
Where soil bearing capacity is in question, a Geotechnical Engineer should be contacted to confirm that the onsite conditions are consistent with the design assumption.
If the foundation for a new structure is to be near existing structures or manure tanks, the new foundation must be located so as not to impart any additional loading on the existing facility. This is usually achieved through the use of step footings. However, in some instances, the soil against the existing building must be excavated. In this instance, a Geotechnical Engineer can help determine a safe course of action and review any undermined footings.
It is important to ensure your geotechnical engineer provides their approval on your soil conditions prior to continuing with the construction of your project. When the structural engineer is onsite to do the initial footing inspection, ensure they receive a copy of any geotechnical reports. This will ensure that your building’s base has been approved and any issues addressed before a foundation is poured.
Information for this article was provided courtesy of Kyle Hilliar, C. Tech., Field Services Manager at CMT Engineering Inc., St. Clements, Ontario. For more information, visit their website at www.cmtinc.net.