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88

Exercise 21

Wall Material Calculations

OBJECTIVE

The objective of this exercise is to correctly calculate wall

material quantities.

TEXTBOOK REFERENCE

Information related to this activity can be found in the

INTRODUCTION

Determining wall material needs requires calculating the

surface area of the wall to be built and information from

the manufacturer regarding how much surface area is

If the wall is variable in height over its entire length

(Figure 21–1B), use the following steps:

• Obtain the average height of the wall by taking

multiple measurements (where the wall is the

tallest and the shortest), adding measurements

• Add 1 foot to the height measurement to

accommodate a buried base, and multiply by the

length to obtain square footage of the wall.

If the wall is consistent in height except for a few small

sections, such as return or cheek walls (Figure 21–1C),

use the following steps:

• Add 1 foot to the height measurement to

accommodate a buried base, and multiply by the

length to obtain square footage of the wall.

If the project contains multiple walls, the square foot-

age of each wall must be measured and added to obtain

one unit (typical areas range from .5 SF to 1.25 SF). Divide

the wall square footage by the surface area of one unit to

obtain the number of total units required for the wall.

Segmental Unit Capstone Calculations

Capstones are usually ordered by the number of linear

97171_21_ch21_p088-091.indd 88 14/06/10 8:58 PM

Exercise 21 Wall Material Calculations 89

Tie/Timber Calculations

Calculations for ties and timbers require the same area

calculations just performed, but the area is divided by

conversion numbers to determine the number of ties and

timbers to order. Find the material being used in the fol-

lowing list, and then divide the square footage of the wall

divide by 3.7.

• Timber 6 feet long by 6 inches height: divide

by 2.8.

To calculate the number of ties/timbers required for

deadmen or verticals, divide the total wall length by 5.

Add the wall ties/timbers numbers to the deadmen or

Figure 21–1 Wall material calculations.

H1

H2

H3

H4

H5

Add 1' to

height for buried

course

A. Consistent height retaining wall

(H + 1') × L = SF

C. Variable height retaining wall

where wall ends in hillside

(same formula as B)

A.

Formulas: Examples:

(5' + 4' + 7' + 5')

(5.25' + 1') × 30' = 187.5 SF

4= ave. HT. of 5.25

30'

C.

5'

5'

4' 7'

L

© Delmar/Cengage Learning.

97171_21_ch21_p088-091.indd 89 14/06/10 8:58 PM

90 Exercise 21 Wall Material Calculations

vertical numbers to determine the number of ties/tim-

bers to order.

Backfill Calculations

To calculate the amount of free-draining angular fill

Drainage Tile Calculations

To obtain the linear feet of drainage tile necessary to

PREREQUISITE EXERCISES

Students should have successfully completed Exercise 1,

Construction Math, before beginning this exercise.

MATERIALS REQUIRED

• Wall construction plans, including plan view,

• Calculator

• Writing paper and instrument

EXERCISE DESCRIPTION—PART A

• Timbers (assuming timbers 8 feet long and

6 inches in height)

• Segmental wall units (assuming .9 SF per unit

drawing negates the need to add one foot to the height

measurement (for the buried base) when calculating the

surface area of the wall. Record answers in the worksheet

provided in Figure 21–3.

EXERCISE DESCRIPTION—PART B

Using construction documents provided by the instruc-

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Exercise 21 Wall Material Calculations 91

Segmental Units Units Conversion Factor Quantity Notes/Comments

Segmental Units Each 1 unit =

Stone Units Conversion Factor Quantity Notes/Comments

Dry-Laid Stone Ton 1 Ton =

Backfill CF Same as CF above

Drainage Tile LF Same as LF above

Drainage T’s EA Count

Drainage Caps EA Count

Ties/Timbers Units Conversion Factor Quantity Notes/Comments

Timbers Each 1 timber =

Sqare Footage of Wall: Length of Wall: Cubic Footage of Fill:

97171_21_ch21_p088-091.indd 91 14/06/10 8:58 PM

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