Applied Field Engineering

A slope can be quoted three ways, and every trade prefers a different one. Roads and drainage use percent. Geotechnical drawings and embankment sections use H:V ratios.

A grade on its own is a shape.

Earthwork is measured by slicing the job into cross sections and putting the volume back together between them. Two formulas do almost all of it, and the choice between them is a choice about how much you measured.

A cubic metre of soil is three different volumes in the course of a single day, and every quantity on an earthworks job belongs to exactly one of them.

The last thing a field calculation does is put a number on a delivery docket, and each material is bought in its own currency.

A horizontal curve is a piece of a circle dropped into the corner where two straights meet. Everything a crew needs to stake it is written as eight quantities, and the whole of curve design is knowing which one you are holding.

Given a radius and a deflection, the whole curve falls out. Three relations do most of the work on a plan sheet.

An arc is a poor thing to measure. Three straight distances describe it well enough to stake, and all three are the radius multiplied by some function of half the deflection angle.

The curve table says where the curve is. It does not put a single stake in the ground.

Where a road's profile changes grade, the two tangents are joined by a parabola — not a circle.

Three relations decide whether a geometry is safe at a speed. They chain: how far a driver needs to see, then how long a crest must be to deliver it, then how hard a bend may be taken.

A traverse is a chain of measured courses round a parcel. Each course carries a length and a direction, and the whole method rests on turning that pair into two components that can simply be added up.

A level does one thing: it gives a perfectly horizontal line of sight.

A stack file arrives as a stack of numbers, and before any of them can be used they have to be sorted.

Before a plume can be modelled, the air it is going into has to be described. Two profiles do almost all of that work: how the temperature falls with height, and how the pressure does.

Every plume-rise and dispersion equation in this chapter divides by u, the wind speed at stack height. Every anemometer in the country stands at 10 m.

Before any plume, the stack. Three relations answer almost everything a designer asks of one.

A plume leaves a stack hot and moving, and it keeps climbing.

An analyser gives a reading.

This is the equation regulatory air quality runs on, worldwide.

Two numbers close this chapter out: how much a control device removes, and whether the measurement proving it is admissible at all.

Noise work goes wrong in one place more than any other: somebody adds two decibels together. So before a single relation, the scale itself.

Two identical compressors, each 80 dBA at the operator's ear. Switch the second one on and the meter reads 83. Not 160, and not 85 either.

A point source in the open radiates onto an expanding sphere. Double the radius and the same power is spread over four times the area, so the intensity falls to a quarter — and a quarter of the energy is −6 dB.

Stop a sound in a hard room and it does not stop.

Absorption keeps a room from ringing. Transmission loss is the other job entirely: keeping sound from crossing into the next space.

Hearing loss from noise is cumulative, permanent and painless while it happens.

The exposure clock protects one worker over one shift. A site also has neighbours, and they are protected by a different instrument: a twenty-four-hour average with the night made to count for more.

Irrigation is arithmetic on a depth of water — millimetres, exactly as rainfall is measured — because a depth is the only figure that compares a centre pivot to a drip line to a thunderstorm.

FAO-56 splits crop water use into two questions that can be measured separately, and that separation is the whole method.

Three relations here, and they stack: rain reduces what you owe, efficiency inflates what you pump, and uniformity caps how good efficiency can ever be.

Everything in this lesson is the depth identity from the first teach card, used in anger: 1 mm over 1 ha is 10 m³, exactly.

A fertiliser rate 20% out costs money. A pesticide rate 20% out is either a failed application or an illegal residue, and the second one can end a shipment, a contract or a licence.

Calibration settles the rate.

A grower does not want seeds; a grower wants plants, at a target density, on a date. Everything between the two is loss, and every loss divides.

C = wSe — read aloud C equals w S e. C is the effective field capacity, the ground actually covered per hour; w is the working width of the machine — the swath it really cuts, not the width of the frame; S is the field speed while working…

Every navigation problem splits into a direction and a distance. The compass handles the direction. The distance comes from one of two places — the paper, or your own legs — and a working field engineer checks each against the other.

A map is a plan view: every distance on it is horizontal. The ground is not, and two right triangles reconcile the two.

William Naismith was a Scottish mountaineer, and in 1892 he wrote down the sentence that still plans hill days: allow an hour for every three miles on the map, plus an hour for every 2,000 feet of ascent.

Nothing has moved but the observer. The discipline is the wrap. Add 180; if the result passes 360, take 360 off. Below 180 you may subtract instead and the two routes agree.

On a sphere the shortest path between two points is an arc of the great circle — the circle whose centre is the centre of the earth.

This chapter's marine and airborne lessons run in knots and nautical miles, and not out of nostalgia. One nautical mile is one minute of latitude, by definition.

An aircraft flies through air, and the air is going somewhere itself. Draw the vectors and everything follows: your true airspeed through the air, the wind across the ground, and the resultant — what you actually make over the earth.

Two small relations that make the earth's shape and spin useful on a working day.

Engineering economy has almost no formulas in it. It has one idea — a dollar has a date attached — and a small family of factors for moving dollars between dates.

Everything else in the chapter is assembled from this one relation.

A rate on a quotation is a headline, and three separate things can sit between the headline and what the plant actually pays.

Almost nothing in a plant happens once. Energy is saved every year, chemical is bought every year, a reserve is funded every year.

Take a sum today and ask what equal amount, every period, would pay it back with interest. That question has one answer and two names, and knowing they are the same thing is worth more than either formula alone.

Five factors are on the shelf already: a single sum moved forward and back, a series moved forward and back, and capital recovery.

Two machines do the same duty. One is expensive and lasts fifteen years; the other is cheap and lasts eight. Nearly every instinct available to you is wrong here, and there is exactly one honest comparison.

A private firm asks whether a project makes money.

Not every decision earns a discounted analysis. Three screens run in seconds, appear in every business case ever written, and each one is honest only if you say what it leaves out.

Depreciation is an accounting schedule, not an economic one: it spreads a cost you have already paid across the years that use it.