When building a new house, house addition or any kind of heavy structure, having knowledge of the soil conditions on your property can be very advantageous. Doing an in depth investigation on your property before construction can save you a lot of time and money.
Everyone knows a solid foundation is the most important element to any house and making a mistake with foundation selection can be extremely costly. The knowledge from your investigation will be key when selecting the best foundation for your project whether it be helical piles, strip footings, concrete piers, micropiles or driven piles.As a homeowner, there are a few things you can do to gain further insight into the soil conditions existing on your property which will help you in making decisions around foundation selection. Before we get into the process of doing an investigation and determining which investigation is correct for you, we need to look at the common soil types in Ontario.
The first thing that we will let you know is that soil conditions can change drastically on the same building site. You could have strong soils in one area of your site and 20’ away can be very weak fill material.
Toronto soil type is different than Ottawa soil type and London Ontario soil type will be different than the soil type in Hamilton Ontario (You get the point!!). An investigation will answer all these questions for you!
Let’s dive into the different types of Toronto geology. This also applies to the Golden Horseshoe area and many other areas, but we will focus on Toronto soil types as that is where a majority of our work takes place. This is very technical information that geotechnical engineers use but it’s important to have a general understanding of soil characteristics on your site.
There are 3 types of soil classifications that we need to be aware of when choosing a foundation;
- Coarse Grained Soils (sand and gravel)
- Fine Grained Soils (clays and silts)
- Organic Soils (peat)
To break these classifications down further, there are 6 main types of soil;
Sand – Granular material consisting of many small rocks
Silt – Fine bits of clay and sand that settle at the bottom of a river,
Clay – Fined grained material that is typically hard and sticky
Organics – Material that has decomposed. Typically wet.
Fill – Material that has been moved from its original location either by man or nature.
Gravel – Stone and rock that varies in shape and size.
The main reason helical piles are so often deployed in Toronto geology is that there is a lot of fill material present. What this means is, the government soil maps from yesterday aren’t reliable down to your individual construction site.What may have been there 50 years ago has very likely been contaminated with fill or material from another region.
Soil maps of yesterday are not particularly reliable.
Fill can be described as soil material that has been excavated from one location and moved to a different location to fill a hole or raise the property elevation. It can be from the same site or come from a far away location.
The 3 main type of fill material are;
Engineered Fill – A mixture of material determined by an engineer that will provide the required support for the project.
Undocumented Fill – This is unknown fill. No one knows where it came from. There is no documentation available for the material.
Hydraulic Fill – A fill material that has moved naturally by a flowing river/stream
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Some are better than others but they all have their challenges. If you do have poor soil conditions on your site, it’s best to bring in a geotechnical engineer.
A geotechnical engineer is worth his weight in gold when problem soils are an issue. They will be able to provide you with the most economical solution and save a bunch of potential headaches
Now we have looked at some of the common soil types in Ontario, let’s look at a few ways we can do our own soil investigation. Please note that none of these investigations replace a competent geotechnical engineer on your project. Although the investigations below are helpful, there are many conditions that can go unforeseen. So please proceed at your own risk.
This is the most practical, easiest and most economical type of soil investigation that you can do. Talking with your neighbours and others in your neighbourhood can be very insightful as it is almost guaranteed that someone has installed some sort of foundation in your neighbourhood at some point.
They would be able to let you know if the water table is high or if bedrock will be encountered 10’ below grade. This is very valuable information. We have even had customers that were able to get full geotechnical investigations from one of their neighbours.
As this is the cheapest form of investigation, its is also the least reliable as soil conditions can be different from property to property (your soil conditions may be different than your neighbours).
Digging a test pit involves excavating into the ground to determine the strength of soil at the desired depth. The excavation can be done by excavator, auger, hand shovel or any other means you have to expose the soil on your property.
Samples can be taken at prescribed depths and sent to a local lab analysis or a local engineer can be consulted to make observations. This will give you direct soil information that will allow you to make sound decisions with regards to your future foundation.
It is best to dig more than 1 test pit depending on the size of the structure as soil conditions can differ from one side of the house to the other. Be warned that competent soil conditions may be beyond the digging depth of your chosen excavation equipment.
You could spend the money to hire an excavator to find out that the soil conditions are still poor and the excavator cannot dig any deeper.
One of the many advantages of helical piles is that we are running a test during the entire installation. When installing helical piles, we use specialized equipment that measures the amount or torque required to drive the pile deeper into the ground. There is a direct correlation between installation torque and pile capacity.
Depending on the size and criticality of the project, we will sometimes go to site before hand to install a test pile. For a house foundation project, we would do 2-3 tests depending on the project budget. Recording the output torque at 1-foot intervals allows us to get a very accurate idea of the soil conditions that are present and how deep we will have to go to be in competent soil.
This pretty much helps us learn if your foundation is going to have to be 10’ deep or 50’ deep. The difference in these depths will greatly affect the budget and would result in a shocking invoice at the end of the job if not expected.This form of testing is very reliable and fairly cost effective. Helical pile contractors typically will not charge for this work if you end up using them for the project.
This investigation is the most accurate and preferred but also the most expensive. This would involve contacting a local Geotechnical Engineering company who would consult on site soil condition and give recommendations on foundation type as well as many other aspects of the project.A soil sampling drill will be brought to site and samples will be taken at various depths. At the same time they are testing the soil using a penetrating device giving important information about the strength of this soil at different depths. You will be provided a detailed report outlining the soil condition on your property that will be used to make important decisions about the design of your foundation.
Having a geotechnical investigation performed can also bring cost savings in some scenarios. A Structural Engineer prefers to have the detailed information a geotechnical report will provide.
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This extra information will make the engineer more comfortable with the project and mitigate an over design (designing a foundation than is larger than necessary). The Engineer may also specify an onsite load test if the required detailed soil information isn’t available.
We receive calls from customers all the time that have begun excavation for their house foundation. They have excavated to the design footing elevation and have realized that the soil at that depth will not support their house if they use strip footings alone.
They can not dig any deeper as they would be undermining existing adjacent structures. Putting up a shoring wall is not really an option at this point. Utilizing helical piles to keep the footings at the same elevation is the answer. The problem now is that they are at a stand still with their project until a helical pile contractor can perform the work.
This could take 2-3 weeks in peak season. If there was an investigation performed before hand, this information would already be available, and the issue would be mitigated before hand. Not to mention they do not have an understanding of how bad the soil conditions are or how deep the helical piles will need to go to reach component soil.
If you have any questions at all about helical piles, no matter where you are or what kind of questions you have, please contact us. We are willing and want to answer any questions that you have.