PE Civil WRE

conceptual questions for PE Civil WRE

What is a compaction curve?

Dry unit weight vs moisture content

What happens to the effective stress at any point below the groundwater table if the table fluctuates but remains below ground surface?

Effective stress decreases with the rise of a groundwater table.

What soil “actions” depend greatly on effective stress?

Soil Compressibility, Soil Shear Strength, Soil Consolidation

What is soil consolidation?

Consolidation is a natural (long term) process caused by pressure from buildings or natural structures. It expels water from the soil & compresses soil particles, reducing volume

What is soil compaction?

Compaction is the application of external forces on soil that remove air pockets & reduce volume. It increases load-bearing capacity, reduces permeability, and increases stability.

What is the difference between compaction & consolidation?

Compaction is quick process caused by machinery to increase certain soil properties. Consolidation is a long process caused by existing structures that reduce soil volume. IE: compaction is intentional, consolidation is a byproduct

Local shear failure mode is for what types of soil?

Sands or Clays of medium compaction

General shear failure mode is for what types of soil?

Dense Sands & Siff Clays

Punching shear failure mode is used for what type of soil?

Loose Soil

What is fineness modulus (FM)?

An empirical value that describes the average size of particles in a sample of aggregate. It provides a way to estimate the amount of aggregate needed to proportion mix designs.

What is aggregate?

Aggregates are granular materials like gravel, sand, or crushed rock.

What has an affect on the compressive strength (f’c) of concrete?

• the type of coarse aggregate used

• the amount of water used

• how the concrete was cured

How does calcium chloride change cement hydration when used as an additive in concrete?

It is used to accelerate cement hydration & reduce set time. (like an enzyme)

What is cement hydration?

The chemical reaction between water & cement that produces heat.

How is the fineness modulus (FM) scale used?

The higher the FM, the larger the aggregate size (IE the smaller the FM, the smaller the aggregate size).

What test is used for concrete compaction?

The split tensile test (ASTM C496), which splits the concrete test cylinders.

What tensile stresses are applied during the split tensile test?

Perpendicular tensile stresses that would cause the structure to split or fracture.

What does fly ash do in a cement mix?

Reduces cement volume

What is cement? Portland cement?

Powder used to create concrete. The most common type is portland cement, which is made by combining limestone, sand, bauxite, gypsum, and other raw materials.

How is portland cement made?

Heating all raw materials together until they are cooled (the clinker). The clinker is then ground into a fine powder.

What is concrete?

TThe combination of an aggregate, sand, portland cement, and water. The main mix can be manipulated to achieve different necessary properties (IE better at freeze/thaw cycles)

What are the basic types of portland cement?

Type I, Type II, Type III, Type IV, Type V

What is Type I portland cement?

Normal/ General Purpose: general, all-purpose cement. It is useful when the special properties of the other cement types are not required.

What is Type II portland cement?

Moderate Sulfate Resistance: the concrete product requires increased resistance to sulfates. It can be useful for underground structures in areas where soil and groundwater contain moderate levels of sulfates or in roadways & transportation products.

What is Type III portland cement?

High Early Strength: offers expedited early-age strength development which is a benefit for concrete used in cold weather applications as it expedites the strength development in the early stages of hydration.

What is Type IV cement?

Low Heat of Hydration: generates less heat during hydration & curing. This is used primarily for large-volume concrete products to reduce the risk of flash setting or thermal shock. This is also beneficial in hot weather where fresh concrete may cure at an expedited rate due to high temps.

What is Type V cement?

High Sulfate Resistance: the concrete product requires extreme sulfate resistance. This is used in coastal structures, piers, underwater tunnels, submerged structures, foundations, and roadways/transportation products.

What does fly ash do in a concrete mix?

• increases workability

• reduces air content

• reduces water

What is laminar flow according to the Reynolds number? What does that mean? (PIPES)

Re < 2000. This means that viscosity is dominant over inertial forces.

What is transitional flow according to the Reynolds number? What does that mean? (PIPES)

2000 < Re < 4000. This means that neither viscosity nor inertial forces are dominant.

What is turbulent flow according to the Reynolds number? What does that mean? (PIPES)

Re > 4000. This means that inertial forces are dominant over viscosity. Dominant velocity can lead to flow disruptions.

What is laminar flow according to the Reynolds number? What does that mean? (OPEN CHANNEL)

Re < 500. This means that viscosity is dominant over inertial forces.

What is transitional flow according to the Reynolds number? What does that mean? (OPEN CHANNEL)

500 < Re < 2000. This means that neither viscosity nor inertial forces are dominant

What is turbulent flow according to the Reynolds number? What does that mean? (OPEN CHANNEL)

Re > 2000. This means that inertial forces are dominant over viscosity. Dominant velocity can lead to flow disruptions.

What are the components of Total Kjeldahl Nitrogen (TKN)? Are the components organic or inorganic?

• Nitrogen from organic substances

• Ammonia (inorganic)

• Ammonium (inorganic)

What is direct inflow in a WWTP?

Inflow that rapidly increases shortly after the start of a storm & decreases quickly after the conclusion of a storm.

What is peak inflow in a WWTP?

The largest rate difference in an hour between the storm event flow and the dry weather flow.

What is delayed inflow in a WWTP?

Inflow that decreases gradually after the conclusion of a storm and after the peak inflow.

What is estimated inflow in a WWTP?

Inflow that is a calculated approximation of the inflow.

Gases created at a WWTP are strictly inorganic?

FALSE - gases created at a WWTP can be organic

What is a disadvantage of a trickling filtration system?

Trickling filtration systems are extremely temperature dependent. Extreme heat or cold can have negative effects on the effectiveness of the filtration.

Are particles only skimmed off the top of the tank during air flotation treatment at a WWTP?

No, particles can also settle at the bottom of the tank and be removed.

What is Monod kinetics?

Monod kinetics is the empirical equation for microorganism growth that relates microbial growth rates to the concentration of a limiting nutrient or substrate

What is the variable μ in Monod kinetics?

μ is the growth rate of the organism

• μ_max is the maximum growth rate of any specific organism and is an empirical coefficient

What is the variable [S] in Monod kinetics?

[S] is the concentration of the limiting substrate or nutrient

What is the variable K_s in Monod kinetics?

K_s is the “half-velocity” constant (i.e. the value of [S] when μ/μ_max is 0.5)

• K_s is an empirical coefficient

How do you go from calcium concentration to calcium hardness as CaCO₃?

(calcium hardness as CaCO₃) = (calcium concentration)

(equivalent weight of CaCO₃) (equivalent weight of calcium)

When using a paddle to mix water in a flocculator, is the velocity of the paddle or water greater?

The velocity of the paddle is greater due to the “slip” of the water. The “slip” is the relative between the paddle and water. You need the paddle to move quicker than the water to get the correct velocity gradient that force particles to collide = flocc

What are two categories of coagulating chemicals used in drinking water treatment?

Hydrolyzing Metal Ions and Ionic Polymers

How is natural methane gas removed from groundwater?

Aeration - air is mixed into the water which forces the gas to vent into the surrounding area.

What type of settling occurs when individual particles settle independently?

Discrete settling

Which type of hydrograph is obtained by using storm characteristics and watershed parameters to simulate a natural hydrograph?

Synthetic Hydrograph

Describe the loose cubic yard to bank cubic yard relationships.

• Loose cubic yard = bank cubic yard (1 + decimal swell)

  • A loose cubic yard is equal to the bank cubic yard times the decimal swell + one

• Loose cubic yard = bank cubic yard / load factor

  • A loose cubic yard is equal to the bank cubic yard divided by the load factor

What happens when you increase the water content in a concrete batch mix?

This increases the workability (aka slump), but will decrease strength due to the increased porosity from the additional water.

• The reason for increased porosity is because not all water is consumed during the cement hydration

How do you calculate the N-value using blow counts from a boring log?

The N-value is calculated by summing the number of blows required for the second and third 6-inches of penetration.

What is a strip footing?

A strip footing is used for a load-bearing wall or for a row of columns that are closely spaced. (aka Continuous Footing)

What is an isolated footing?

An isolated footing is provided to support an individual column. Usually a circular, square, or rectangular slab of uniform thickness. (aka Pad Footing)

What is a mat foundation?

A mat foundation is a large slab supporting a number of columns and walls under the entire structure or a majority of the structure (aka Raft Foundation)

Is a Pile Foundation a shallow foundation?

No, piles are deep foundations.

What type of shallow foundation should be used when the allowable soil pressure is low or where an array of columns and/or walls are so close that individual footings would overlap or nearly touch each other?

Mat or Raft Foundation

• strip footings cannot be used for an array of columns

• isolated footings are for individual columns

What nondestructive testing methods can be used for concrete thickness?

• impact echo

• ground penetrating radar

• ultrasonic echo

What nondestructive testing methods can be used for concrete density?

• gamma radiometry

What nondestructive testing methods can be used for determining bar size of rebar in concrete?

• covermeter

What nondestructive testing methods can be used for in-place strength of concrete?

• pullout test

• pull-off test (bond strength)

• probe penetration

• maturity method (new construction)

What nondestructive testing methods can be used for locating near-surface defects of concrete?

• sounding

• infrared thermography

What nondestructive testing methods can be used for general quality & uniformity of concrete?

• visual inspection

• rebound hammer

• pulse velocity

What nondestructive testing methods can be used for dynamic modulus of elasticity of concrete?

• resonate frequency (small specimens)

What nondestructive testing methods can be used for locating reinforcement locations in concrete?

• covermeter

• ground-penetrating radar

What nondestructive testing methods can be used for determining the corrosion state of steel reinforcement in concrete?

• half-cell potential

• polarization resistance

What nondestructive testing methods can be used for locating internal defects of concrete?

• impact-echo

• ultrasonic echo

• impulse response

What is a cost-plus fixed fee procurement method?

Provides reimbursement for all costs associate with the construction AND a fixed fee

What is a cost-plus percentage fee procurement method?

Provides reimbursement for all costs associated with the construction AND a percentage fee to help with overhead & profit

What is a unit price procurement method?

Contracts are estimates based on how much each part of the project should cost. The projected vs billed amount are likely to vary.

What is a lump sum procurement method?

Provides a fixed price for completing a construction project.

In reference to the Schedule Performance Indicator (SPI), describe the relationship between earned and planned.

Earned is the budgeted cost of work performed

Planned is the budgeted cost of work scheduled

What does a SPI > 1 indicate?

If the the SPI > 1, that means more work has been completed than what was scheduled & the project is ahead of schedule.

What does a SPI < 1 indicate?

If the the SPI < 1, that means less work has been completed than what was scheduled & the project is behind schedule.

Is incineration a common method for sludge disposal?

No, it is expensive to heat up the sludge due to the high water content

100 meters is how many centimeters?

10,000 cm (multiply by 100)

100 kilograms is how many grams?

100,000 g (multiply by 1000)

10 micrograms is how many grams?

0.00001 g (divide by 1000)

100000 micrograms is how many kilograms?

100 kg (divide by 1e9)

Should there be an aeration zone in a settling tank?

No, the goal is for particles to settle and aeration will prevent that.

What type of sedimentation has the highest concentration of particles in a sedimentation basin?

Compression sedimentation. Concentration is increased via the compressing of particles beneath them.

What is a water quality model used for when determining a TMDL for a particular water body?

The model is used to determine the loading that must exist in order to meet water quality standards.

What assumption can be made if the reaeration and deoxygenation coefficients in the stream are equal?

The dissolved oxygen concentration will be uniform / steady state.

Is COD always greater than BOD?

Yes, because COD measures all chemically oxidizable organic matter and BOD measures only biologically degraded matter. COD can oxidize material in a more complete way than BOD can.

How do you calculate velocity head?

V² / 2g

How many gallons/day is 0.34 MGD?

340,000 gallons/day (0.34 × 1e6)

What geosynthetics are used for soil stablization?

Geotextiles and Geogrids

What is another term for torque?

Moment of force

Where is the centroid of the moment located in a triangle?

2/3 away from the point

Where is the centroid of the moment located in a rectangle?

½ away from the point

What does the force do as you go deeper in the soil?

The force increases steadily the deeper you go

The theoretical bearing pressure at which shear failure will occur is:

The ultimate bearing capacity.

Which of the following is not a component of biogas?

• methane

• carbon dioxide

• carbon monoxide

• hydrogen sulfide

Carbon Monoxide. Biogas is a product of anaerobic digestion and is composed of methane, hydrogen sulfide, carbon dioxide, and trace amounts of nitrogen, oxygen, and volatile hydrocarbons.

What is surface loading rate a relationship between?

Loading rates are a relationship between the flow rate and surface area. So Q/A

How do you calculate the weir length of a circular weir?

π * diameter

Which of the following is a factor that affects the efficiency of primary sedimentation?

• the shape of the tank

• the type of wastewater entering

• tank capacity

All are factors that effect efficiency of primary sedimentation.

• tank shape determines whether tank conditions are calm enough to allow for settling to occur

• wastewater type is important because wastewater conditions (eg density or temperature) can affect settlement

• tank capacity determines whether the tank conditions are calm enough to allow for settling to occur