r/GeotechnicalEngineer

I have been accepted for an MSc in geotechnical engineering while my bsc was in geology with physical geography. I am considering a switch to geological engineering, as I am mainly interested in bedrock rather than soils. Would it be beneficial to swap or would having a geology background with a geotechnical masters open up more doors. I am very early in my career and I do not want to pigeon hole myself into one route, but I do want to become a chartered geologist. Currently I am thinking that the geotech route will still allow me to do work in bedrocks and hazards. I would love some advice on this subject!

Going to try and make a long story short.

We are adding onto our home which the existing is single story, tearing down a non-load bearing wall with a gable end, and opening it up for our addition.

Initially, we didn’t have a soil boring test done, that was until the proposed footing depth on the addition went beyond the called for 4’ stem wall as it was about 5’5” down from the floor elevation due to the grade of the property.

Soil borings were completed. Boring taken near the house showed red clay about 4’ down and they hit limestone at 15’. Second boring at the opposite corner/furthest point from existing but a couple feet from the addition showed no clay until 6’ down and no limestone was hit all the way to 20’ down.

Plans called for a 2x2 pad thats 16” thick to support the load for a 6x6 post that will carry 50% of the load of the addition. Now structural engineer is backtracking saying that pad needs to be 4x4 and 18” thick, and after communication with the geotech they’ve concluded that helical piles need to be drilled into the existing foundation to support the load of the header because the existing is too close to the clay and that’s the only way to beef it up.

My only other option is to change the truss layout, which has already been built and I’d be out about $10k, so that the addition ties into a gable ending versus a hip and the load is more evenly distributed across the new stem wall. I’m leaning more towards that option, but my foundation guy says in all his time building foundations he has never had two engineers go so far down a rabbit hole like this and has never heard of helical piles outside of marshy areas or coastal regions.

I am mostly venting because I will never, no matter what, ever do a home addition again. Were over 10 months in and have gotten basically nowhere, and have spent hours on the phone with engineers.

I plan to seek out analysis from another geotech firm as well and see if they might be willing to conduct their own independent analysis and foundation recommendations based on the borings that I have.

How would people approach this usually?

Timber pile retaining wall, cohesive soils (max retained height about 1.8m). Soils routinely manage a 90 degree cut (a lot of our historical roads have this batter all over the place, sidle fill construction) and only come undone during extreme storm events where the top layers (1m or so) lose suction.

Using slope stability software to get a design action for a modified broms (a la caltrans) style equation gives me a very high load that would require hefty steel sections.

WALLAP is fine until I go to do seismic checks and switch to wedge stability. Switching to wedge stability gives even my pre excavation stages metres of movement. Modelling backslope as a surcharge as per their guidance. Using a boussinesq method to derive a resultant force from the retained backslope causes the model to fail even before wedge stability is turned on.

I'm at a small regional design consultancy so I only have limited software available.

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!

I'm currently investigating the possibility of building a house here in the the UK, but with foundations (and heavy frame) designed to be as long-lasting as possible. *Certainly hundreds of years, maybe even a thousand or more. So far my reading has taken me to a method outlined on the Construction Physics website of unreinforced concrete pilings down to bedrock, topped with an unreinforced concrete slab. (Not sure if I can post a link but the page is titled "How to design a house to last for 1000 years (part III)")

My question is about choosing the location for the house within the UK. Looking at the British Geological Survey website they have interactive maps and downloads showing the bedrock type across the UK. There are many types of bedrock from "very weak" mudstone and chalk, "strong limestone", to "very strong" Gneiss. This is an engineering map I'm looking at so not sure what the strengths are relative to. Are all of these bedrock-types suitable for supporting a thousand-year foundation, or are things like the wet-sounding mudstone going to allow subsidence or shift over time?

The map is on a page titled "Engineering geology (bedrock) map of the United Kingdom" at NORA NERC. I'll attempt to post links in a follow-up reply. Thanks!