u/No_Preparation8438

Hi everyone!
I’m currently helping prepare a geotechnical investigation report for a project with 5 boreholes, and I’d really appreciate some guidance from people with more experience in geotechnical design/reporting.

My professor is asking us to include the following in the final project output:

1. nterpretation of results, conclusions, and recommendations
2. Recommendations for the type of foundation
3. Soil bearing capacity calculations for foundations
4. Settlement assessment of critical areas

The challenge is that the investigation did not include UDS sampling, so we don’t have direct shear strength or consolidation test results.

The available data/tests are mainly:
SPT results
USCS classification
Sieve analysis
Hydrometer analysis
Atterberg limits
Specific gravity
Natural moisture content
Flexible-wall permeability
Groundwater observations
Borehole logs

There were no consolidation tests, UU/triaxial tests, UCS, or direct shear tests.

My initial thought is to use corrected SPT values and published correlations to estimate parameters such as friction angle for granular soils and possibly undrained shear strength for cohesive soils, then use these for preliminary bearing-capacity calculations.

For settlement, I understand that SPT-based methods can be used for granular soils, but I’m less confident about how to properly evaluate settlement in cohesive soils without consolidation parameters such as Cc, Cr, e0, and preconsolidation pressure.

I’d really appreciate advice on:
What methodology would you normally use with this level of available data?

Which SPT corrections/correlations would you recommend?

What parameters would you derive from the available tests?

How would you approach settlement for cohesive soils without consolidation testing?

Would you calculate bearing capacity per borehole, or group similar boreholes into geotechnical zones and use representative/critical BHs?

What additional information should I request from the structural/client side before starting, such as footing size, founding depth, column loads, or allowable settlement?

What references/books/standards would you recommend for learning how to do this properly?
I’m still learning and I want to make sure the analysis is technically defensible rather than just plugging numbers into equations.

Any advice, references, example workflows, or things I should watch out for would be greatly appreciated.
Thank you!

Good day everyone,

I'm a civil engineer working in geotechnical engineering, and I'm trying to deepen my understanding of how experienced engineers plan subsurface investigations.

I know there are general rules of thumb (e.g., borehole spacing based on project type or site area), but I'm more interested in the engineering judgment behind deciding:

• How do you determine the appropriate number of boreholes for a project?
• How do you decide the required depth of each borehole?
• What factors (geology, foundation type, project risk, budget, etc.) have the biggest influence on your decisions?
• Are there any widely accepted guidelines or references that you rely on (e.g., BS 5930, Eurocode 7, FHWA manuals, ASTM, local standards, or textbooks)?
• How do you approach this during the proposal stage when little site information is available versus after obtaining preliminary investigation results?

I'm looking for both practical advice from industry experience and recommendations for authoritative references. My goal is to become proficient in planning geotechnical investigations rather than simply following rules of thumb.

I'd really appreciate hearing how senior geotechnical engineers approach this problem in practice.

Thanks in advance!

Has anyone here used the Prilonski (1952) criterion / Liquidity Index as a preliminary indicator for collapsible soils?

I came across this interpretation:

• LI < 0 → highly collapsible soils
• LI = 0 to 0.5 → slightly to moderately collapsible?
• LI = 0.5 to 1 → non-collapsible
• LI > 1 → swelling soils

Equation used:

LI = (NMC - PL) / PI

What I’m unsure about is the interpretation of the range between 0 and 0.5. I can’t seem to find a direct statement from Prilonski regarding this interval, and it looks more like an interpolated engineering interpretation from later references.

Is there any published reference or accepted practice that defines the 0–0.5 range more clearly in terms of degree of collapsibility?

Also, do you personally consider the Prilonski criterion reliable for preliminary collapse assessment?

Would appreciate insights from anyone who has worked with collapsible soils.

Hi everyone,
I’m currently working on a project where we performed Dynamic Cone Penetrometer (DCP) tests and obtained DCPI values (mm/blow). I would like to estimate equivalent SPT N-values from the DCPI results.
I understand that:

1. DCPI ↔ CBR correlations are fairly well established in pavement/subgrade evaluation.
2. Direct DCPI ↔ SPT N correlations are less common and appear to be soil-specific.
3. Some researchers suggest site-specific regression if paired DCP and SPT data are available.

My questions are:

1. Are there any well-cited studies or published correlations directly relating DCPI to SPT N?
2. Is it more defensible to go DCPI → CBR → SPT N using existing empirical relationships?
3. From a practical standpoint, would you recommend developing a site-specific correlation instead of relying on published equations?

I’m mainly looking for a defensible approach for reporting purposes (preliminary evaluation, not final foundation design).
Any references, papers, or field experience would be greatly appreciated.
Thanks in advance!