Geotechnical Investigation
Geotechnical Investigation: Where Every Design Starts
What Is Geotechnical Investigation?
Every design starts right here: geotechnical investigation characterizes a site’s soil and groundwater and produces the parameters every later design decision — from pile diameter to retaining wall type — is built on. Without this stage, any support or foundation method is just an assumption, not an engineering design.
Borehole Drilling and Sampling
Fieldwork begins with drilling boreholes at pre-planned locations across the site. Each borehole logs the soil stratigraphy and yields samples: disturbed samples for classification and SPT testing, and undisturbed samples — typically thin-walled Shelby tube samples — for more precise strength and consolidation testing in the lab.
In-Situ Tests
The Standard Penetration Test (SPT), run during drilling, measures soil density or consistency at each depth and is the primary basis for initial strength estimates. Depending on the project, supplementary tests such as CPT (cone penetration), pressuremeter testing, or pumping tests for permeability are also used to build a more precise picture of the soil’s in-situ behavior. Laboratory Testing
Samples collected in the field are examined from several angles in the lab: classification tests (grain-size distribution, Atterberg limits, natural moisture content) identify the soil type; strength tests (direct shear, triaxial) yield shear strength parameters; consolidation testing predicts expected settlement in cohesive soils; and chemical tests (sulfate, pH, chloride) measure how aggressive the soil and groundwater are toward concrete and steel — data that directly shapes concrete cover design for piles or corrosion protection for micropiles.
Groundwater Regime
Groundwater level and its seasonal fluctuation are usually monitored with piezometers or observation wells, while permeability is estimated through in-situ or laboratory testing. This data directly determines whether dewatering or a cutoff wall is needed, which retaining wall type fits the site, and whether concrete below the water table has to be placed by the tremie method. Soil Profile and Geotechnical Model Data from drilling, in-situ tests, and laboratory testing are ultimately combined into a layered model of the site: layer boundaries, the strength and deformation parameters of each layer, and how they’re likely to vary across the site. This model is the direct input to numerical analyses such as PLAXIS and to the design of every excavation support system on the site.
From Report to Design
The report ends exactly where design begins: not with a pile of raw data, but with recommended design parameters, the site’s geotechnical model, and risks and uncertainties stated explicitly — not hidden in an appendix. Borehole spacing, the possibility of soft or loose pockets between the points actually drilled, and the assumptions behind each chosen parameter all belong in the body of the report, not in a footnote that’s rarely read. Why Geotechnical Investigation Underpins Every Other Method Every support and foundation method described elsewhere on this site — top-down construction, soil nailing and anchoring, cross-lot bracing, truss bracing, jet grouting, and piles and micropiles — builds its design directly on parameters from this same investigation: pile bearing capacity, nail or anchor bond strength, the permeability that drives a jet-grouting decision, all trace back to this same report. Geotechnical investigation isn’t a separate page alongside the others; it’s the shared starting point for all of them. Where Does Geotechnical Investigation Apply? No excavation, deep foundation, or slope stabilization project can be designed with real confidence without this stage; even on seemingly straightforward sites, an unexpected soil layer or groundwater level can change the entire choice of method.
Frequently Asked Questions
How many boreholes does a project need?
The number and depth of boreholes depend on site size, soil variability, and the planned depth of the structure; the goal is enough coverage to catch layer changes between drilled points, not a fixed number that applies to every project.
Why do soil chemical tests matter?
Sulfate and chloride in soil or groundwater can attack concrete and steel; the results directly shape the concrete cover and corrosion protection chosen for piles, micropiles, nails, and anchors. At Ziggurat, every design starts with borehole drilling, in-situ and laboratory testing, the groundwater regime, and the soil profile, and we hand over a report with parameters, model, and risks stated explicitly.