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PE Civil Construction · Complete public sample

Soil quantities and moisture bases

Keep dry solids separate from water when converting borrow quantities into compacted fill.

Understand the governing concept.

Loose, bank, and compacted cubic yards describe different volumes of the same material. Without loss of solids, the conserved quantity is dry soil mass, not volume. A wet unit weight includes water; dividing by one plus the decimal water content gives the dry unit weight needed for a solids balance.

Gravimetric water content is water mass divided by dry-solids mass. To change moisture content, multiply the change in that ratio by the dry-solids mass. A four-percentage-point increase is 0.04 times dry mass, not four percent of the original wet mass. State the volume condition and moisture basis beside every quantity.

By the end of this refresher

  • Explain the basis or assumption controlling this decision.
  • Apply the method within its stated limits.
  • Check the result and choose a related study task.
γd=γwet1+w,Vc=Vlγd,lγd,c,ΔWw=(w2−w1)Wd\gamma_d=\frac{\gamma_{\mathrm{wet}}}{1+w},\quad V_c=V_l\frac{\gamma_{d,l}}{\gamma_{d,c}},\quad \Delta W_w=(w_2-w_1)W_d

Convert to a dry-solids basis before calculating compacted volume or water adjustment.

Define the basis before substituting a value
SymbolMeaningUnit or basis
γd\gamma_dDry unit weightlb/ft³
γwet\gamma_{\mathrm{wet}}Total moist unit weightlb/ft³
wwWater mass / dry-solids massdecimal
Vl,VcV_l,V_cLoose and compacted volumessame volume unit
WdW_dDry-solids weightlb
ΔWw\Delta W_wAdditional water weightlb

When the method applies

  • Assume no discarded material, solids loss, or change in the soil composition; account for such losses separately when they are specified.
  • Added-water calculations here neglect evaporation, drainage, and absorption changes. Field conditioning may require additional water or drying.
Connect the physical model and the decisionConnect the equipment to the calculation

01 · Equipment view

An illustrative earthwork site connects excavation, stockpile, hauling and compaction.

Excavation · borrow pile · hauling · compacted fill

Illustrative site context; no volume or density is inferred from the image.

02 · Exam-style model

Zoom in to read every label.

Connect the physical model and the decision

100%Open in a new tab

Scroll or swipe inside the viewport. Read the units and assumptions with the labelled components.

Loose borrow, conserved dry-solids mass and compacted fill are separate states; adding water does not create more dry solids.

Keep soil quantities on a stated mass and volume basis. Use the worked-case givens and limits below.

Original teaching figure. The schematic and stated givens define the model; the 3D view illustrates the hardware. These are not actual examination exhibits.

Original teaching case

Work the decision, then cross-check it.

There are 1,000 loose yd³ of soil at a moist unit weight of 108 lb/ft³ and water content of 8%. The target compacted dry unit weight is 125 lb/ft³. Raise water content to 12%. Use 27 ft³/yd³ and water weight of 8.34 lb/gal; assume no loss.

  1. Compute the loose dry unit weight: 108/1.08 = 100 lb/ft³.
  2. Compute dry-solids weight: 1,000 × 27 × 100 = 2,700,000 lb.
  3. Conserve dry solids to obtain compacted volume: 1,000 × 100/125 = 800 yd³.
  4. Additional water is (0.12 − 0.08) × 2,700,000 = 108,000 lb. Convert to gallons: 108,000/8.34 ≈ 12,950 gal.
Vc=800 yd3,Vw,add≈12,950 galV_c=800\ \mathrm{yd^3},\qquad V_{w,\mathrm{add}}\approx12{,}950\ \mathrm{gal}

Decision

Plan on 800 compacted yd³ from this borrow quantity under the stated assumptions; the separate moisture adjustment is approximately 12,950 gal.

Independent check

800 × 27 × 125 returns 2,700,000 lb of dry solids. Original water is 216,000 lb; after adding 108,000 lb, water/dry solids = 324,000/2,700,000 = 12%.

A fresh application

Use the concept under changed conditions.

Choose a response before inspecting the reasoning. This is a learning check, separate from scored diagnostic and mock attempts.

A stockpile contains 450 loose yd³ at moist unit weight 114 lb/ft³ and water content 14%. With no loss of solids, how much compacted fill results at dry unit weight 125 lb/ft³?

Connect this refresher to your program.

The NCEES Civil handbook and the standards listed in the specification are supplied references. Refresh the engineering behavior and assumptions that help you select and apply them. This topic is classified as understanding and application; no individual reference omission has been verified.

Original ReasonSpan™ teaching material. AI-assisted checks are complete; independent specialist review remains pending.