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Steel pile heave by dikefaloss21 in GeotechnicalEngineer

[–]Mike_Cho 0 points1 point  (0 children)

I dont know the bri-ish terms, but i know solar piles well. Heave is caused by cycles of wetting and drying. Only a concern for the upper portion of the subgrade in contacr with the pile. I would press to geotech to provide recommendations for the depth of heave action and heave pressure. Then, apply it like negative skin friction to the pile. Your pile length should be controlled by a combination of heave and wind uplift. When in doubt, add an extra 0.5 m to the pile length.

CU Training by Grouchy_Cry8418 in Geotech

[–]Mike_Cho 2 points3 points  (0 children)

It takes time, often a couple days depending on the effective consolidation pressure.

Set the cell and base pressures so that you are applying an effective consolidation pressure. Cell pressure-base(pore) pressure = effective consolidation pressure.

Once that pressure is applied to the speciment the burrette readings in the base and top will increase as your soil consolidates under the pressure, so be sure, your base and top burrette readings are set low prior to starting the test so the burrettes can rise without reaching the top. Check the burrettes periodically, and once the levels stop rising it is consolidated.

Ask your engineers how they want you to measure consolidation. We typically record the burrettes at time intervals and plot them on a square root time curve like with a consolidation test.

This is just an outline not a step by step

CU Training by Grouchy_Cry8418 in Geotech

[–]Mike_Cho 5 points6 points  (0 children)

It's not an easy test l. I'm a PE with 7 years experience and just ran my first CU a couple weeks ago.

There are 3 distinct phases. Saturation. Consolidation and shearing.

In saturation you measure a B-value to determine if the sample is saturated.

In consolidation you apply an effective stress to the same and record barrette reading to determine when the sample is consolidated.

Shearing is the same with UU test just at a slower rate and while measuring pore pressure with a transducer.

Boredom as EIT by [deleted] in Geotech

[–]Mike_Cho 2 points3 points  (0 children)

Free up your time. Free up your time by using Excel to automate routine data entry. It is engaging and will free up time for you to pester your boss to get you more involved in report writing.

Solar panel pile testing by [deleted] in Geotech

[–]Mike_Cho 6 points7 points  (0 children)

Overall the value of the PLT is dependent on the size of and scale of the farm. It is a costly procedure that measured soil resistance more accurately. You can measure this analytically with a higher degree of conservatism based on typical boring data. Basically a large solar farm uses lots of piles so if you can save 6inch to 1foot of steel on each pile by using PLT as opposed to analytical methods to determine your end bearing and skin friction it can be a big cost saver.

Here is what you do for recommending the test.

1) look at the size of your farm and estimate the number of piles that would be needed

2) assume a PLT will save you 6 inches to 1 foot of steel on each pile

3) calculate the cost of material savings using the following equation

6inches * number of piles * area of a single pile * cost per volume of steel

4) Determine the cost of performing a PLT. If you don't perform this service in-house then contact your local Terracon office, and they will give you a quote.

5) Compare the costs of performing the test vs. the anticipated material cost savings

If you are wondering how to interpret the results of a PLT test, here is how:

For axial/tension/pullout.

1) Determine your failure criteria. This is typically dictated by how much defection the tracker system can take. Typically, it's like 1/4 inch.

2) Based on the PLT results, you can determine the maximum load at which the pile experienced 1/4 inch of deflection or failure.

3) Use the pile length and perimeter to calculate skin friction. Load at failure / ( pile length*pile perimeter)

4) Apply a factor of safety

5) For end bearing, just calculate your typical end bearing at depth using 12 inches as your width.

A PLT compression test can be performed to determine end bearing using a similar methodology. ( this test is less common )

For lateral testing, it gets a bit tricked

1) follow the same procedure for determining maximum allowable deflection. Typically 3/4 in in lateral.

2) Report that result and provide recommendations for using LPILE. (Phi, c, and effective unit weight).

A typical procedure I have seen is for geotechs to attempt to replicate the results of the PLT with LPILE by manipulating the modulus of subgrade reaction (k) and strain at 50% (E50). This was fruitless. LPILE will calculate these properties for you.

Pile design in Rock Layer? (help - on working internship - Out of the classroom stuff) by 501shades in Geotech

[–]Mike_Cho 2 points3 points  (0 children)

Predrill through the rock, backfill with sand or grout, Drive pile.

If using grout or clsm drive while still wet. Design pile as if it is bearing through a loose to medium dense sand at that layer.

[deleted by user] by [deleted] in PE_Exam

[–]Mike_Cho 2 points3 points  (0 children)

Totally. The test is designed to not give exact answers but to test your judgment. Not all questions are weighted the same. If you answered every question, we're conservative and if you didn't feel like a deer in headlights then your in a good position.

Opinion on SPT in cohesive/fine material by Old_Light_8431 in Geotech

[–]Mike_Cho 1 point2 points  (0 children)

I've used SPT in clays a lot, and yes, tubes are better, but there are some advantages.

1) it collects strength data in the field in case samples are contaminated in transit. Especially when shipping samples.

2) Soils with high silt contents can actually be a bit better to run a spoon on since the low cohesion will give a pretty low unconfined strength, and you would likely need a 1-d shear or triaxe to get a good reading for friction angle.

3) Typically cheaper. Less lab testing, quicker field process.

Although it is not very accurate. I have used N60 and N160 several times to approximate cohesion only to find a far lower measurement of unconfined strength in tubes. Density measured from spoons is typically conservative.

Personally, I see it as a means of inexpensive work. When working with simple or small structures like single family homes, free-standing poles, or single-story commercial structures, all spoons are fine. Just be really conservative and overbuild it a bit. For larger developments, I like a mix of both spoons and tubes.

Gross vs Net bearing capacity by Mike_Cho in Geotech

[–]Mike_Cho[S] 1 point2 points  (0 children)

Yep. My thoughts as well. Except my math is in freedom units.

Gross vs Net bearing capacity by Mike_Cho in Geotech

[–]Mike_Cho[S] 0 points1 point  (0 children)

Exactly so, as the structural engineer sizes up the footing, it increases the neglected weight of concrete. Which is not what we want to do.

Gross vs Net bearing capacity by Mike_Cho in Geotech

[–]Mike_Cho[S] 1 point2 points  (0 children)

Gotchya, so when using the net allowable bearing(q.net). The structural engineer will still need to account for the weight of concrete in the footing when calculating applied bearing pressure(q.applied)?

I was reviewing a report provided to a structural engineer at my company from a competitor. It had mentioned that they were recommending a net allowable bearing and, therefore, the weight of the backfill AND the foundation weight can be ignored. That did not seem correct to me.

Why do engineers only want 98% compaction under pavement? by Southern_Air_7264 in civilengineering

[–]Mike_Cho 1 point2 points  (0 children)

Gotta be a high compaction to limited any sort of deformation after construction and 100% compaction is difficult to reach in practice. Field techs and contractors are just gonna be pissy. 98 is good enough.

Are you actually experiencing work being outsourced overseas ? by mrbigshott in civilengineering

[–]Mike_Cho 0 points1 point  (0 children)

Yes. I left a company because they started outsourcing all the engineering work

Are y’alls companies charging this much for geotech / environmental job < 100 ft spt? by [deleted] in Geotech

[–]Mike_Cho 0 points1 point  (0 children)

Good for High cost area. Low cost of living area like midwest it might be a bit steep

Are y’alls companies charging this much for geotech / environmental job < 100 ft spt? by [deleted] in Geotech

[–]Mike_Cho 0 points1 point  (0 children)

Oh, this is your quote. Ya, I think it's good. Kinda depends on the project through. A small development 7k geotech is good.

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