Retaining Walls

5.5.1.1 Gravity Type (Concrete or Stone Masonry)

These walls can sustain the earth pressure by means of its own weight and can be built more easily than the other types of retaining walls. They are often adopted when the height is relatively low (less than 4 m.) and the ground foundation has a good bearing stratum. This type of wall can be adopted also as catchwall as shown in Figure 5.33.

Figure 5.34 Gravity Type (Rock Catcher Retaining Wall) 5.5.1.2 Leaning Type (Concrete or Stone Masonry)

This type of wall acts against the soil pressure not only by its own weight but also by the weight of soil as shown in Figure 5.34.

Figure 5.35 Leaning Type Retaining Wall

The advantages in adopting stone masonry over concrete are that the gradient, length and horizontal alignment could be done easily to match the profile of an existing section and it is more economical. Moreover, if it will function as catch wall (with steel-framed catch fence), reinforced concrete retaining wall is advisable.

Stone Masonry consists of stones with sizes as shown in Table 5.7 laid in accordance with the lines and grades as shown in the plans or as directed by the Engineer, jointed by cement mortar of 1 (cement) : 2 (sand) at trowel consistency.

Ws Wc Leaning Type Retaining Wall

where:

Wc = Weight of Concrete Ws = Weight of Soil

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The construction steps are shown below.

1. Prepare the foundation bed, compact and moisten as per

Specifications. Mortar that is not used

within 90 minutes after the water has been added shall be discarded. Re-tempering of mortar is not permitted.

Weepholes shall be provided unless otherwise shown on the plans or as directed by the Engineer.

2. Lay 5-10 cm thick mortar

3. Embed Stones of specified size

4. Fill the spaces between stones with new mortar

5. Repeat steps 2-4 until the required dimension is attained.

Figure 5.36 Construction steps for Stone Masonry

5.5.2 Grouted Riprap

Grouted riprap shall consist of the furnishing and placing of riprap with filter backing, furnished and constructed in accordance with the specification and as to lines and grades and dimensions shown on the plans. This is commonly used in slope protections, abutments, lined canals and other places called for in the plans.

(c) (d) (e) Surfacing

Figure 5.37 Construction steps for Grouted Riprap

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Grouted riprap shall be constructed in accordance with the following steps:

(a) Prepare the foundation bed, compacted specified sizes into the fresh mortar.

(d) Fill the voids in between the stones with mortar.

(e) Repeat the above steps a until the specified dimensions are attained.

Figure 5.38 Grouted Riprap

Table 5.7 Materials Requirement for Grouted Riprap and Stone Masonry

Item Grouted riprap

(Item 505）

Thickness: 150 mm or more Width: 150% of respective thickness or more

Length; 150% of respective width or more

Horizontally at the lowest points,

Not more than 2.0 m center to center in a staggered manner. The length should not be less than the thickness of the walls, at least 100 mm dia.

PVC is recommended.

(Source: DPWH Standard Specifications for Highways, Bridges and Airports, 2013Edition)

5.5.3 Cribwall

5.5.3.1 Stone Masonry and/or Reinforced Concrete Cribwall

It is a type of retaining wall particularly made up of concrete or stone masonry (or a combination of both) and supported with reinforced concrete frame. Generally, a double frame type is adopted for a 3.5 to 5.5 m. height of slope.

On rock slopes with many joints or loose talus and where concrete spraying is inappropriate, concrete cribwall is advisable.

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Figure 5.39 Stone Masonry Cribwall

←Fourth Level: Stone Masonry Cribwall

←Third and Second Level: Concrete Cribwall

←First Level: Concrete Retaining Wall

←Second Level: Stone Masonry Cribwall

←First Level: Concrete Cribwall

Figure 5.40 Reinforced Concrete Crib and Pitching Wall

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5.5.3.2 Reinforced Concrete Frame with Vegetation Works

This type is ideal for high slope composed of weathered rock or unstable soil with seepage or springs.

Figure 5.41 Reinforced Concrete Frame with Vegetation Works Source: DPWH/JICA Technical Standards and Guidelines for Planning and Design Vol. IV,

2002 Natural Slope Failure Countermeasures

5.5.4 Gabion Wall

Gabions are used where there are springs on a slope and sediments are likely to be washed out and where a collapsed portion is to be restored.

The lengths should be multiples of two (2), three (3) or four (4) times the width of the gabions and the height should be 0.50 meter to 1.0 meter. The horizontal width should not be less than 1.0 meter. Gabion furnished shall be of uniform width.

Figure 5.42 Gabion Wall

Gabion wires are double twisted meshed conforming to ASTM 641 or 856 or 809. Rock pieces must be uniformly graded 100 mm to 200mm. No rock size shall exceed 2/3 the mattress depth. Filled gabions shall have a minimum density of 1,400 kg/m3.

If spring water amount is big, drainage should be installed at the foot of the gabion. Filter fabric shall be placed between the slope surface and gabion materials. The filter fabric shall be rolled out into a flat non-rutted surface free from sharp objects.

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Figure 5.43 Constructed Gabion Wall at a Location with Seepage

5.5.5 Mechanically Stabilized Embankment Wall (MSE Wall)

Reinforced embankment walls are of two types 1) Geotextile-reinforced and 2) Terre Armee.

Figure 5.44 Mechanically Stabilized Embankment by means of Geotextile fabrics

Front View

Rear View

Slip Bars Slip Connection Clamp

Figure 5.45 Mechanically Stabilized Embankment Wall (Terree Armee Wall)

Collapse surface of road slip

Bedrock

Road

Ground line before road slip Embackment Work

Terre Armee Wall

9.0 m

Embankment

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