The Importance of a Proper Preliminary Geotechnical Investigation

A Preliminary Geotechnical Investigation Report  is generally a requirement of city and county engineering divisions before any plot of land is approved for development; from the 150 unit house tract, to the big box retail center, all the way down to the custom single family residence.   A preliminary geotechnical investigation defines the geologic formations, soil units, fault zones,hard rock, bedding, expansive soils, and other variables that make up the site.  

One pitfall more and more developers are falling into is what I'm going to call the "cookie-cutter prelim".  When building a custom home, budgets are almost always tight; so when a home builder sees an opportunity to save $800 on ANYTHING taking advantage is imperative. What most people don't understand is that what is required, and what is ultimately beneficial to a project are two different things in regards to a preliminary geotechnical . Moving forward with a consulting firm that produces a prelim that is more comprehensive in nature provides the client with a  much more realistic view of project costs and hazards.  For example, lets pretend I'm planning on building on a custom home.  I meet with a grading contractor ahead of time to discuss what costs I'm going to accrue when getting started on the process.  He refers a geotechnical consultant that is the "cheapest in town" for the required prelim.  When the plans and reports are submitted to the county, they move through with ease and now I'm ready to break ground.  What was never mentioned is that the preliminary geotechnical investigation will not include a comprehensive over-excavations  calculations for the entirety of the project.  At first glance, the prelim does have a "cookie-cutter" statement referring to the 5 foot over excavation of the building pads, with "localized deeper removals" in some areas, but the report does not address removal depths in reference to the entire sight including slope construction.

If a Preliminary Geotechnical Investigation does not define removals throughout the site, a developer is subject to change-orders and extra expense from not only the geotechnical consultant, but also the Grading contractor which can potentially drown a project before any building has even been accomplished .

If a Preliminary Geotechnical Investigation does not define removals throughout the site, a developer is subject to change-orders and extra expense from not only the geotechnical consultant, but also the Grading contractor which can potentially drown a project before any building has even been accomplished.

Of course,  being a homeowner I am ignorant to what could lie ahead; especially when my designs made it through the approval process (city and or county) without any hiccups.  So here is what could happen to me when as I move forward with my project.   I'm going to receive a bid for grading based on what the prelim spells out.  I wont even know i have a problem until grading has started and the over excavation depths spelled out in the prelim prove to be 3 feet shallow.  Now i'm going to be hit by my contractor  for a change order of potentially thousands of dollars because he had to over excavate and re-compact  a significantly larger amount of material.  That bill alone is enough to sink most projects. Its not the grading contractor's fault; its not even the geotechnical consultant's fault. The county approved everything so what was missed?  Unfortunately comprehensive over excavation depths in the report and on the goetechnical/geologic map are not required by most cities and counties, so now I am stuck with a significantly higher bill for grading than I ever anticipated which could be the difference in finishing my project and mothballing it until I save more money.  Is there anything I can do to drop the costs of grading?  Unfortunately in most cases at this point not much can be done. 

LGC Geo-Environmental, Inc.  prides itself on looking at the big picture of even the smallest project.  We believe that service is the product we provide, as well as the preliminary report. A proper preliminary geotechnical investigation can prepare one for the unforeseen expenses that haunt tightly budgeted projects.  Going into any situation with as much information as possible allows for realistic budgets and realistic time frames.  Be diligent now so you're not unpleasantly surprised halfway through the project.  It isn't hard to see how this problem can be amplified when you plug it into a much larger project.  For example, a $10,000 grading change order and 2 weeks of extra grading time for a 4 acre site is one thing, if the site is 20 acres it quickly turns into $50,000 and a month and half of extra grading pushing back the completion of a project more than a month!

Contact LGC Geo-Environmental, Inc.  for your next preliminary geotechnical investigation where you will receive peace of mind from a staff of local geologists with knowledge and experience of the area spanning 4 decades.

When a preliminary geotechnical investigation does a bad job of defining over-excavation depths, it ultimately costs the property owner more money.Every project has a tight time-frame and budget, and issues in grading can increase the length of the project by days, weeks, even months depending on the site.  Contact LGC for your next project.

When a preliminary geotechnical investigation does a bad job of defining over-excavation depths, it ultimately costs the property owner more money.Every project has a tight time-frame and budget, and issues in grading can increase the length of the project by days, weeks, even months depending on the site. Contact LGC for your next project.