Levelling in Construction for Beginners - Mastering a Laser

LEVELLING - For us it's all activities regarding the setting the levels, taking information from the drawings and communicating with the team. Either we call it setting reduced levels & using a benchmark - or just setting levels & using a datum doesn't really matter - what matters is that you understand what you are doing, are able to get the info needed, communicate with the team and double check your calcs so there won't be mistakes.

Please have a look and read the attached Ordnance Survey book - Copyright Ordnance Survey 2018 - this will give you a lot of theory for all our setting out activities, not only levelling!

We work in metric system and datums will be set in metres with the tolerance to milimetres eg. 40.500 ---> means fourty and a half metre above m.s.l.

40.500m (there is a dot!) = 40500mm

In general:

Datum - Main one set  by Ordnace Survey 0.00m (the M.S.L - mean sea level) in Cornwall calculated for years in Newlyn - ODN (Ordnance Datum Newlyn). Point of reference.

Benchmark - point with established elevation (height)

TBM - Temporary Benchmark - our site datum (mark on the wall, columns, slab etc) - a point of height reference - we will be calling it a DATUM on site - don't worry about the definitions too much, just make sure you're using the right one!

Level - all depends on the context ?

Engineer, we need the level! - laser has to be set up :)

The 'Level' will also refer to a spirit level, the construction element's designed level (eg. SSL  40.210m), or just any height value above MSL -  Reduced Level eg. 30.385m

Where to find a Datum/Level on site - at this point (Assistant Engineer) it should be given to you - don't try to do some transfers yourself you are a beginner! - later you will be able to establish your own datums and control, but for now this information should be provided to you! Typically set by a surveyor with the main job control.

HPC - Height of Collimation (our Intrument height)

* The video I mentioned about is in the last section, as will be much easier for you to understand after you will go through the lessons below.

Main types of lasers used in Construction:

Rotating lasers - basic plane laser, Gradient Laser.

Pipe Lasers - 'Drainage' laser - used inside pipes & manholes with set gradient (fall).

Line lasers - similar to rotating laser in principle, but with the visible line - very useful on slipforms structures.

Plumb Laser - used to check the cores verticality and to transfer setting out points - plummet points

(I will be covering all above types on the intermediate level course)

Accuracy on tapes depending on Lenghts at 20 deg Temperature (class II):

3m  -----> ± 0.9mm

5m ----->  ± 1.3mm

8m ----->  ± 1.9mm

10m ---->  ± 2.3mm

20m ---->  ± 4.3mm

30m ---->  ± 6.3mm

50m ---->  ± 10.3mm

100m ---->  ± 20.3mm

Class I tapes would give a half of the above numbers.

When we talk about long tapes, please remember that the lenght of the tape will change with the Temperature and about the Tension and Sag on the tape. Accuracies are assumed when pulling with 50N force - which is ar. 5kg (so you should pull your tape like you would hold a 5L bottle ;)

On the 100m long tape there could be easily over 25mm difference between winter & summer.

I really recommend to spend few extra pounds and get a good measure tape (class II is enough) for yourself - don't count on getting a tape on site and come with your own one!

Typically you will be working with 5 metre telescopic staff with E graduation on the front and millimetre graduation on the back.

Remember to always check the bottom of staff if it's clean and check if the staff is fully extended - it's often when mistakes happen followed by errors (when staff is used & dirty it might give impression of being extended) - always a quick visual check is recommended before use!

If buying a Spirit Level don't go for the cheapest one!

Always make sure the Spirit Level is clean and care for it.

There are also digital spirit levels showing the fall on the screen available to make our lives easier ?

1. Laser (? obviously) - might be different types, but box might be even the same

2. Charger - important to keep the laser charged - your responsibility!

3. Receiver (Rod Eye) + Bracket

4. Manual, User guide and Calibration Certificate

5. First CHECKS - visual and calibration cert. check! Do a good visual check as in most cases this will be used equipment, often delivered from other site (site to site) nad not checked in between - that's why we will be always doing a first time on site check.

Your job is limited to do a proper visual check and calibration cert. check,  anything worrying should be reported to your engineer and laser replaced if needed. We're not doing any DIY instrument corrections on site although it's possible.

Your role is just to check the calibration certificate, copy it and upload to your company calibration log folder - check if the sticker is on the laser / if the serial number corresponds the actual tool and then error check it (in one of the next lessons)

We will be checking the laser's error on regular basis comparing it with allowed limits!

If you have a chance, try to get the Rod Eye 160 on site (unfortunately, as it's more expensive, bring it). Try always to have an extra receiver and staff. Remember red light - down, blue - up, green - on grade.  Always have spare batteries for the receiver!

hold buttons for settings - change for mm in case your receiver will come set to imperial units.

(for more info please refer to laser manual from the previous lesson)

Few points about the Laser:

Self levelling to certain degree - depending on the laser but typically 5deg.

Creates a level plane to which we will be refering etc

The Laser creates a level plane to which we are referring to. Make sure the laser is set correctly - levelling itself and showing continuous green light. Don't forget to charge the laser, the worst thing can happen is to start a day with a 'dead' laser when it's most needed. Some sites are run on generators which are switched off after work so be careful as your laser won't charge at night. You won't be using the laser in manual mode and adjusting it using the hidden buttons - anything worrying you will report to your engineer who should double check and replace it, or calibrate him/herself.

I recommend to check the laser as per video & attached manual. Please always refer to site specific ITP as it's often copied from job to job with 2peg test for lasers. What really matters if that the laser is really checked and error logged and 2 peg test is not practical really.

Height of Instrument | Height of Collimation:

Laser beam (HPC) is below the datum - take off (deduct) the height difference between the datum and the laser reading.

Laser beam (HPC) is above the datum - add the height difference between the datum and the laser reading.

I still would like you to know how the Dumpy Level (Optical Level, or Automatic Level) works - if you have a chance to work & exercise with a dumpy level then setting the laser will be a 'piece of cake' for you.

Following lessons I recorded some time ago, so sorry for the quality, but content you need it there.

FROM BEFORE

In general 2 peg test will be used to check other surveying instruments too, so you need to understand it.

First setup - in between the points (15-16m between points is well enough) backsight to point 01 and foresight to point 02

Second setup - behind the point 02 (ar. 2m from the point, so you can see the staff) backsight to point 02 and foresight to point 01

Also, you can add the backsight readings and the foresight readings - the difference between foresights and backsights will be your error

example from video: 1601 + 1450 = 3.051 & 1.592 + 1.460 = 3.052 ----> 3.052 - 3.051 = 0.001m = 1mm

I always keep it simple though and do like on the lesson, but if you don't want to mix the reading & points you can go the 'surveyor way' ?

Some people levelling instrument the way the collimation matches the datum taking off any calculations. I find it time consuming, but if you would master setting the dumpy this way, who knows ;)

Congratulations!!

You are now ready to start on construction site and take the first levelling tasks with more confidence. I hope you will find a job in construction asap and invite you to the 'Site Engineer - Intermediate - Levelling' Course where you will learn more advanced techniques and equipment to progress to a Site / Setting Out Engineer position!

Please don't forget to leave a review and let me know what I can do better to make learning easier others!

All the best!

Greg