Civil Engineering Chapter 22 Homework The Follow The Rough Trench Excavate Level

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CAUTION

Exercise 22

Wall Base Preparation

and Wall First Course

Installation/Stepping

First Course

OBJECTIVE

The objectives of this exercise are to install base material

and properly install the first course of a landscape retain-

ing wall using ties/timbers, segmental concrete wall units

Follow manufacturer’s instructions when using

equipment. Use caution when cutting and

installing wall materials. Obtain assistance when

lifting wall materials.

TEXTBOOK REFERENCE

Information related to this activity can be found in the

INTRODUCTION

The longevity of a landscape retaining wall depends on

several factors, including the quality of the base upon

which the wall rests. Proper preparation of the site and

Base Installation

To prepare a granular base for a landscape retaining wall,

use the following steps:

• Lay out the wall alignment and grades.

• Excavate sod from 2 feet in front of to 2 feet

behind the wall for the entire wall alignment

(Figure 22–1).

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Exercise 22 Wall Base Preparation and Wall First Course Installation/Stepping First Course 93

is placed below finish grade. The trench should

follow the elevation of the alignment. Excavate

stepped portions of the wall separately. When

excavating, any loose or unstable materials

encountered should be removed and replaced

with granular backfill.

3/4 inch to 1 inch crushed stone.

• Level the base material end to end and front to

back for each level of the wall.

• Compact using a vibratory plate compactor.

• The addition of a 1/2 inch to 1 inch layer of finer

granular material will accommodate the leveling

of the first course of wall material when placed in

the trench. Crushed stone that passes a 3/8inch

sieve is suitable for this purpose. Relevel and

recompact after granular material is added.

changes. Failure to properly level a wall will create prob-

lems that multiply as wall height increases. Stepping

the first course up a hillside can also create potential

problems if the level and alignment are not maintained

through the steps. When walls encounter embankments,

this stepping may occur rapidly. Walls should never step

• Place a tie/timber on the base material, ensuring

the tie/timber’s front is properly aligned. If the

project requires the top of the wall stop at a

particular elevation, use a survey instrument to

verify elevations (Figure 22–2).

• Using a carpenter’s level, check for level end to

end. If tie/timber is not level, add or remove base

material under the tie/timber as necessary.

• Using a carpenter’s level, check for level front to

back or for the proper leaning batter. If the level is

not correct, tip the tie/timber forward or backward

and remove or add base material as necessary.

Wall material

(any material selected)

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94 Exercise 22 Wall Base Preparation and Wall First Course Installation/Stepping First Course

Stepping First Course

• In instances where the wall steps up, complete the

lower course of wall to the point where the step

occurs.

Segmental Unit and Stone Walls

Perform the following checks before placing the first

course for segmental units:

pins and the bottom should have openings to

receive pins. For lipped units the bottom will

have a thickened lip. This lip should be knocked

off with a hammer for all blocks used on the base

base to speed the leveling process.

• Place the first unit or stone, ensuring the front of

the block is properly aligned (Figure 22–3).

• Check for level side to side. If the block is not

level, adjustments may be made by scratching

away base material or adding base material under

Front of wall

A. Position with proper

alignment

B. Check for level end to end

(add or remove base material)

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Exercise 22 Wall Base Preparation and Wall First Course Installation/Stepping First Course 95

Stepping First Course

• If the wall is to step up only one course or slowly,

create a base for the upper course using the

instructions provided earlier in this exercise. The

base material for the upper course should be level

with the top of the blocks in the lower course and

Figure 22–3 Installing segmental unit or stone first course.

Front

of wall

A. Position with proper

alignment

B. Check level side to side,

adjust if necessary

E. Recheck level side to side

and front to back before

placing next unit

F. Set next unit. Use palm of hand

to verify and unit is flush with first

unit. Repeat steps A–E for

second unit. Use long level over several

units to check side to side level

2nd unit

1st unit

Cross-Section

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96 Exercise 22 Wall Base Preparation and Wall First Course Installation/Stepping First Course

PREREQUISITE EXERCISES

Students should have successfully completed Exercise 5,

Tool Operation and Construction Techniques, Exercise 6,

Cutting of Paving and Wall Materials, Exercise 8, Construc-

tion Staking, and Exercise 9, Grade Staking, before begin-

ning this exercise.

EXERCISE 22 PART A

MATERIALS REQUIRED

• Square-nosed shovel

• Mason’s level (48 inch preferred)

• Garden rake/screed

• Granular base material, 3/4 inch to 1 inch

• Granular base material, 3/8 inch

EXERCISE DESCRIPTION

To complete this exercise prepare a 20 foot long base for

a landscape retaining wall (Figure 22–5). This base can be

on a level surface that cuts across the run of a slope or can

parallel the run of a slope, gradually stepping up it.

20′

Flat Slope

Note: This exercise practices installation of a base with

relative grades. When construction plans detail a specific

grading scheme, a survey level must be used to establish

the precise elevation of the base.

EXERCISE 22 PART B

MATERIALS REQUIRED

• Proper clothing and safety gear

• Mason’s level (48 inch)

• Torpedo level (6 inch)

• Vibratory plate compactor (prepared for

operation)

• Hydraulic block splitter or cutoff saw, or wet

• Granular base material

EXERCISE DESCRIPTION

To complete this exercise construct a 20 foot long base

segment of landscape retaining wall two courses high

using both ties/timbers and segmental units or stone

(Figure 22–6). This wall should include a 10 foot long level

section and a 10 foot long section that steps up a gradual

slope. Complete the base as directed in Exercise 22 Part A.

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Exercise 22 Wall Base Preparation and Wall First Course Installation/Stepping First Course 97

Note: This exercise practices installation of a wall with

relative grades. When construction plans require specific

Operate power equipment under supervision.

Serious injury or death could result

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