Bs 1377 Plate Load Test Pdf

[Bartie Spalitto]

Whilesite investigations for most projects consider ground conditions at depth, the strength and variability of the near surface ground is critical for the design and operation of working platforms. The plate bearing test is typically used in the design of temporary working structures such as working platforms for piling rigs or pads for crane outriggers. Approximate equivalent CBR values can be derived from the Modulus of sub grade reaction by use of mathematical relationship.

The plate bearing test is carried out in accordance with BS 1377 Part 9: 1990. It basically consists of loading a steel plate of known diameter and recording the settlements corresponding to each load increment. The test load is gradually increased till the plate starts to settle at a rapid rate. The total value of load on the plate divided by the area of the steel plate gives the value of the ultimate bearing capacity of soil. A factor of safety is applied to give the safe bearing capacity of soil.

The plate bearing test is normally carried out at foundation level, either on the surface or in a shallow pit. Plates of varying sizes up to 720mm diameter are available. The loading plate is placed on the ground and connected via a load cell to a reaction load. Due to the larger size of the plate used (compared with a CBR test) this test is more suitable for testing larger aggregate backfills, however, it requires a larger reaction load. Typically, a minimum 15tonne tracked excavator or other suitable plant is required for us to use as a reaction load.

Our engineers will advise on the plate diameter required to match the anticipated design load and reaction load required (i.e. size of excavator) to be made available for us on site. We will typically complete 4-6 tests in a day subject to site conditions and can provide you with the results the following day.

If you have any questions about our services or would like to discuss how we could help you, please get in touch using our contact form below. Please provide as much information as possible about the nature of your enquiry, particularly the purpose of the investigation, the site address and postcode.

The truth will set you free. Best of luck. Geodude RE: Plate Loading Tests Focht3 (Geotechnical)7 May 03 17:41BigH:

I haven't "heard" from DirtDoc in awhile, either. If he's 'out there' and not posting, we miss you! Please come back!

I'm trying to find out if he's still around - another way...

RE: Plate Loading Tests jheidt2543 (Civil/Environmental)8 May 03 09:20Having just finished my "equine excrement" sandwitch I'll get back in this discussion. My, how much has transpired in one day!

Sugarcane's posting of the specification clarifies what is asked for - a test. The AVERAGE testing lab will perform the test in the field and the soil either withstands (passes) "twice the required ground bearing capacity" or it doesn't (fails). The fact that the test maybe meaningless in this application is beside the point for the time being, that is what the specification calls for. This could be the end of the discussion.

Focht3 and BigH rightly raise the red flag, this is the wrong test to answer the contractor's main concern, "am I meeting the required bearing capacity?" The specification writer either pulled the wrong spec. off the shelf or didn't understand what test or series of tests should be called for.

Following up on Focht3's Question #1, I agree that acceptance or rejection of the test results lay with the specifing authority. However, the contractor certainly has a vested interest too. As his work progresses, he has to know whether he is meeting the specifications or whether he has to stop and rework an area. This has to be decided in "REAL TIME" and wrong decisions cost real money. I think we can all agree that halting work to wait for the formal report is unrealistic, hence the contractor's question.

My original post was to raise the point that we can't leave the contractor hanging in mid air. If the answer to the question can't be had because the wrong test is specified, I think the testing lab has a professional responsibilty to say so and recommend to whom ever hired him, the contractor or the specifying authority, the correct testing proceedure.

An aside: this has been a fun discussion, it ruined my taste buds, but I thought about a lot of engineering. Thanks! RE: Plate Loading Tests SUGARCANE (Geotechnical)(OP)8 May 03 12:00To clarify for jheidt2543, we will always inform our clients where (and why) we have any reservations with any testing requirements, whether it be for plates or any other part of our service. We are a proactive lab and frequently get involved with problem solving, suggesting alternatives for consideration as we fell appropriate.

For the example specification quoted above, it was agreed with our Client and their Consultantants prior to commencing any testing that we load the plate to 160kN/m2 in 6 approx equal increments. We just reported the settlement values and the data is all yours and our jobs done (sorry, i should say ours and yours, were all in this together, yeah right!).

I thought I'd had enough of this subject but someone just dumped another plate test specification on my desk. This goes as follows:

Load 600mm plate in increments upto 300kN/m2

at 100kN/m2 settlement should be less than 3mm

at 300kN/m2 settlement should be less than 10mm

Now at least with this spec we have clealy defined acceptablity limits which we can all understand and more importantly for our contractor, we can tell him in 'Real Time' if his fill is up to scratch.

For this site, again the fill area is shallow, only 1 or 2m is some places. I'm not sure on final use of site, likely to be light industrial.I know it note a lot to go on but can anyone fill me in on what is the designer trying to model here! He's come up with acceptability limits, How!

It appears to me that he is trying to model a foundation which will exert somewhere between 100-300kN/m2 presumably. If my assumtion is right, surely such foundations will influence more than the 1.2m that the plate will. We are then back to why we are doing them. Are plate tests anygood at all for confirming foundation designs.

I NO LONGER UNDERSTAND WHY PEOPLE WANT PLATE TESTS FOR EARTHWORKS FILL OPERATIONS. AAAAARGGG! Still, brings in good money, ha ha.

Given that the plate tests are coupled with insitu density tests to confirm compaction less that 5% AV and lab tests to confirm MC is with acceptable limits based on PL and OMC, isn't it just a little bit overkill to ask for plate tests as well.

Hell, your gonna wish I'd never started this. RE: Plate Loading Tests Focht3 (Geotechnical)8 May 03 12:30SUGARCANE posted the following questions & comments (in italics) and I responded in plain text:

Are plate tests anygood at all for confirming foundation designs.

I don't think so - unless the plate and footing are about the same size and the sustained footing loads will be quite low.

I NO LONGER UNDERSTAND WHY PEOPLE WANT PLATE TESTS FOR EARTHWORKS FILL OPERATIONS.

It's a "feel good" test. It doesn't really help evaluate the problem, but they feel like they have done something meaningful. And the person that specifies the PLT doesn't understand geotechnical engineering.

Given that the plate tests are coupled with insitu density tests to confirm compaction less that 5% AV and lab tests to confirm MC is with acceptable limits based on PL and OMC, isn't it just a little bit overkill to ask for plate tests as well.

Absolutely. PLTs are a waste of time and money when you have monitored the fill placement, and the placement guidelines are appropriate to the intended use.

Hell, your gonna wish I'd never started this.

Nah!

RE: Plate Loading Tests BigH (Geotechnical)9 May 03 20:40Finally - and I see it in India - you may just have real "old" guys specifying the works and as "they have always done PLTs, they continue to put them in." These are guys who wouldn't really know the nuances about tests - just that they ARE done as a matter of course. Just when you think the the "cancer's" relapsed, it rages again! FUN ! ! ! RE: Plate Loading Tests BigH (Geotechnical)11 May 03 13:43Sorry guys/gals I ! ! I meant that when you think that the cancer's has gone into remission, then it turns out for a relapse. (now - I think I got that right; sometimes at 0300h, the mine wanders!) RE: Plate Loading Tests Focht3 (Geotechnical)11 May 03 16:27jheidt2543:

I'd have bought you a better lunch than that - or at least something cold and fermented to wash out the taste. (I missed the start of your May 8, 2002 post somehow. Speed reading can get you in trouble sometimes...)

You made a good point about the contractor's need for timely information. Unfortunately contractors can get saddled with a difficult site and an inexperienced engineer, and it costs the contractors money. Those circumstances really suck. I do not mean to imply that the contractor should be put in any kind of a bind; my point is that plate load tests should not be specified at all for evaluating the allowable bearing pressure beneath "large" footings. It's really a problem with specifications, not the contractor. Unless the contractor tries to use the PLT to "prove" he has met some other project requirements.

RE: Plate Loading Tests jheidt2543 (Civil/Environmental)12 May 03 08:14Focht3,

Thanks for quenching my thirst!

Now, back to Sugarcane's problem. Since we all agree that the plate load test is out, can you outline for him, and us, what testing proceedure should be used to answer the question "does this fill meet the specified bearing capacity"? RE: Plate Loading Tests BigH (Geotechnical)12 May 03 15:49Actually, we may have missed something - I don't see, in my review speed reading - the types of fills that he is placing. Are they cohesionless fills (sands) or better sand and gravel? Are they cohesive fills - assuming non-swelling/non-shrinking?

If the engineer specified an engineered fill compacted to a specific relative compaction (or relative density), he is happy with the material underlying the fill, then we (say I, if under my control) would be happy that that one can reach 75-150kPa bearing on such engineered fills. 75 to 150kPa for normal footing sizes (say up to 1 to 2m =B) is not that onerous. Even if this was clay (not fill) this would be in the range of 40kPa to 80kPa undrained shear strengths. For granular fills less a problem as compacted fills to 95% MDD (heavy tamping) leads to low void ratios - leads to little settlement on applied loads. It is the poor compaction practices that could get you in trouble.

Hence - for engineered fills, I would be happy with normal compaction confirmation tests (sand cone; nuke; etc.). If you are worried, try taking out a small drill rig and driving 50mm dia dynamic cones (65kg hammer dropping 75mm) - or take SPTs in the fill. If cohesive fills, take a tube sample and do a UU test.

It all boils down to choosing the right test at the "right site". So I think . . . googletag.cmd.push(function() googletag.display('div-gpt-ad-1406030293255-2'); ); Red Flag This PostPlease let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

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