Design Guide for MassBlocä Retaining Walls - CSP · PDF fileDesign Guide for...

Design Guide for MassBloc Retaining Walls

(less than 3m high)

Version 1.0 May 2002

CSP Pacific www.csppacific.co.nz Ph 0800 655 200 Version 1.0 May 2002


(less than 3m high)

CSP Pacific www.csppacific.co.nz Ph 0800 655 200

Table of Contents

No. Section Page

1. General 2

2. Applications 3

3. Advantages 4

4. Design Approach 5

5. Technical Specifications 7

6. Installation Guide 10

7. Standard Design Guide 12

8. Supply Information 16


(less than 3m high)


1.0 General These notes have been compiled to aid in the design of MassBlocTM retaining walls. The standard design tables presented in this guide shall be only used for preliminary design of walls LESS THAN 3m high ( 3 standard blocks high ). All walls shall require detailed investigation and specific design by a suitably qualified Engineer.


(less than 3m high)


2.0 Applications MassBlocTM can be used in a variety of situations with the flexibility of a number of different design solutions available, which allows them to be applied to difficult sites. • Retaining walls • Facing for bridge abutments • Stream channelisation and erosion protection • Coastal protection (beach front erosion protection) • Tunnel entrance walls • Culvert wing walls • Slip repairs • Temporary traffic parking barriers • Temporary bin storage


(less than 3m high)


3.0 Advantages Performance: MassBlocs™ are relatively flexible structures that are typically based on a compacted aggregate foundation. As wall construction is mortarless this dry stacked system can tolerate movement and settlement without causing visual distress at the face. Permeability: MassBlocs™ are highly permeable. This permeability can be supplemented by draincoil, which will further reduce the development of hydrostatic pressure behind the blocks. Durability: MassBlocs™ are manufactured from wet-cast concrete that results in a durable retaining wall system. The blocks are resistant to cracking and do not rust or deform like gabions. Speedy Installation: Two experienced workers and an excavator can place up to 70m² of wall per day. Blocks are placed using the galvanised lifting eye, which is cast into the top of each block. Ecologically Friendly: MassBlocs™ are an ecologically safe building component. The blocks are manufactured from naturally occurring materials that are in abundant supply and are extracted with minimal environmental impact. MassBlocs™ are eco-friendly! Economics: MassBlocs™ are competitively priced and when all project costs are measured and compared against the speed of installation, durability and in-situ performance they represent excellent value for the construction dollars invested. No other system can beat MassBlocs™ in terms of speedy installation, durability and in-site performance.


(less than 3m high)


4.0 Design Approach MassBlocsTM are essentially a gravity wall structure that depends on the mass of the blocks to resist the destabilising forces due to the retained soil and surcharge loadings. As with all gravity type wall structures, there are three modes of failure by which a wall can fail. All three require careful analysis to ensure both safety and performance of the wall is maintained for the design life of the structure. 4.1 External Stability The three modes for which gravity retaining walls must be designed to ensure external stability are: • Overturning: the wall fails by rotating about the toe of the wall

• Sliding: outward movement of the wall along its base • Bearing Capacity: failure of the foundations causing the wall to lean over To guard against any of these failure modes occurring, the common practice is to design the wall with a predetermined factor of safety designed in. These predetermined factors of safety are outlined below and are consistent with currently accepted design practice.

Failure Mode Recommended Minimum Factor of Safety Overturning 2.0

Sliding 1.5 Bearing Capacity 2.0

As for all structures, the degree of uncertainty over design parameters - and the consequences of the structure failing - dictate the level of safety required. For the designs contained in this document, the factors of safety are defined above. In situations where the structure is to become a critical structure, where failure would cause significant property damage or even loss of life, then we recommend that higher safety factors be used. It is recommended that a suitably qualified geotechnical engineer undertake a detailed soils investigation. 4.2 Internal Stability When considering the reinforced earth retaining wall utilising geogrid the number and layout must also be determined to ensure that the reinforced fill does not fail internally. Two modes of failure have been checked and allowed for in the design charts. • Pull out failure: the geogrid pulls out of the soil without rupture • Tensile rupture of the geogrid: the geogrid is stressed beyond its allowable tensile limit.


(less than 3m high)


To guard against any of these failure modes occurring, the common practice is to design the wall with a predetermined factor of safety designed in. These predetermined factors of safety are outlined below and are consistent with currently accepted design practice.

Failure Mode Recommended Minimum Factor of Safety Pull out failure 1.5

Tensile rupture of the geogrid 1.3 All Geo-grid shown in the design cross sections is Tensar SR 80 and the designs are based exclusively for this type of grid and granular backfill (2mm – 20m). The spacing and number of layers shown in the design guide are only applicable to design parameters shown. The design solutions are only to be used as a guide and where the parameters vary a suitably qualified engineer should be engaged to ensure that the appropriate design solution is chosen. As for all structures the degree of uncertainty over design parameters and the consequences of the structure failing dictate the level of safety required. For the designs contained in this document the factors of safety are defined above. In situations where the structure is to become a critical structure, where failure would cause significant property damage or even loss of life, then we recommend that higher safety factors be used. 4.3 Drainage Considerations MassBlocsTM are constructed from a no fines concrete mix that allows water to easily permeate through the blocks. This effectively allows the wall to drain naturally. Filter fabric and drain coil are also included to ensure that no hydrostatic pore pressure is able to accumulate and destabilise the wall. This is more of a precautionary measure and included as part of good design practice. 4.4 Seismic Considerations MassBlocTM walls are designed to be relatively flexible and can undergo small changes in line and level without adversely affecting their structural integrity. The effects of seismic conditions on 3m high or less walls are minimal and have not been allowed for in this manual. If a situation arises where additional seismic forces need to be allowed for, it is recommended that a suitably qualified structural engineer be engaged to carry out the seismic analysis. 4.5 Global Stability MassBlocTM walls must also be analysed for global stability. This shall be undertaken by a suitably qualified geotechnical engineer. They must consider potential failure surfaces passing through the backfill and foundation soils.


(less than 3m high)


5.0 Technical Specifications Base Unit Dimensions Face width 1185mm Vertical height of front face 1000mm Vertical height of rear face 1000mm Depth of unit 880mm Block weight 1.7 tonne Standard Unit Dimensions Face width 1185mm Vertical height of front face 1000mm Vertical height of rear face 1150mm Depth of unit 880mm Block weight 1.8 tonne For design flexibility, blocks of varying heights and width may be ordered (note: maximum height is 1000mm and maximum width is 1185mm)


(less than 3m high)



(less than 3m high)


6.0 Installation Guide Note: This information is provided as a guide only. The registered engineer's design details shall take precedence if there is any conflict or ambiguity with this information. Step One • Excavate the base to the required depth • This will be site dependent - generally 1200mm wide and 200mm deep Step Two • Place GAP65 (or equivalent) into trench then compact to engineer’s requirements (100kpa as a

basic guide) • Use a laser level for the best result • Place a layer of binding material (e.g. GAP7 on sand) up to 20mm thick over the entire

foundation • Use a screed to achieve a perfect level front to back and end to end

Step Three • Set string line or conduit approximately 10mm from the front of the MassBloc wall • Blocks can be placed onto the base using an excavator with a certified chain and 2.5t swift lift • Should the work area be within reach of the hiab, blocks can be delivered and placed directly

from the truck • Care must be taken so that the block is not damaged when unloading or placing

Step Four • Lower the MassBloc base unit approximately 30mm from the prepared base and move the

unit slowly into position and then lower fully • Each consecutive block is lowered 30mm from base keeping 20mm away from previously

placed block


(less than 3m high)


• Once the front face is positioned correctly, slowly move the block to touch the adjoining block • Using a spirit level, check that each block is level

Step Five • Once the base is level front to back and side to side, standard blocks can be placed on top

Step Six • Back filling - the engineer's details will provide the required method. Options include: • Firth no fines concrete mix (Flowable Fill™) • Reid Bars • Manta Rays • Geogrids between each unit


(less than 3m high)


7.0 Standard Design Guide GRAVITY WALL / LEVEL BACKFILL / VEHICLE SURCHARGE

g = 20kN/m3 C = 0 F = 300

Retaining wallheight, H

1.02.02.53.0

12kPaNoneNone0.250.6

Note: Concrete placed behind the wall is to be 1.0m high

Massbloc Gravity Retaining Wall With Additional Concrete Mass For a Vehicle Surcharge of 12kPa

Vehicle Surcharge


(less than 3m high)


GRAVITY WALL / SLOPING BACKFILL / NO SURCHARGE

g = 20kN/m3 C = 0 F = 300

Retaining wallheight, H 0 10 15 20 25

1.0 None None None None None2.0 None None None None None2.5 None 0.1 0.15 0.25 0.43.0 0.35 0.45 0.55 0.65 0.85

Note: Concrete placed behind the wall is to be 1.0m high

For Various Backfill Slopes

W = Width of concrete required from back of blocks

Backfill slope in degrees

Massbloc Gravity Retaining Wall With Additional Concrete Mass


(less than 3m high)


REINFORCED EARTH WALL / SLOPING BACKFILL / NO SURCHARGE

g = 20kN/m3

C = 0 F = 300

Retaining wall Backfill slope Number Geogrid Placementheight, H in degrees of Layers Length = L above base (m)

0 None None None10 None None None

1m 15 None None None20 None None None25 None None None0 None None None10 None None None

2m 15 None None None20 None None None25 None None None0 2 1.9m 2m, 1m10 2 1.9m 2m, 1m

2.5m 15 2 1.9m 2m, 1m20 2 1.9m 2m, 1m25 3 1.9m 2m, 1.5m, 1m0 2 2.3m 2m, 1m10 3 2.3m 2.5m, 2m, 1m

3m 15 3 2.3m 2.5m, 2m, 1m20 3 2.3m 2.5m, 2m, 1m25 3 2.3m 2.5m, 2m, 1m

Note: Geogrid to be Tensar SR 80 and backfill to be granular fill, 2mm - 20mm.

For Various Backfill Slopes


(less than 3m high)


REINFORCED EARTH WALL / LEVEL BACKFILL / VEHICLE SURCHARGE

g = 20kN/m3 C = 0 F = 300

Retaining wall Vehicle Number Geogrid Placementheight, H surcharge of Layers Length (m) above base (m)

1m 12kPa None None None2m 12kPa 2 1.5 1.5m, 1.0m

2.5m 12kPa 3 1.9m 2.0m, 1.5m, 1.0m3m 12kPa 3 2.3m 2.5m, 2m, 1m

Note: Geogrid to be Tensar SR 80 and backfill to be granular fill, 2mm - 20mm.

For a Vehicle Surcharge of 12kPaMassbloc Reinforced Earth Retaining Wall With Tensar SR80 Geogrid

NOTES:

1. All designs have been based on conservative design parameters and therefore should only be used for preliminary design. A suitably qualified Engineer should be engaged to assess site specific design parameters and produce the final design.

2. Concrete placed behind the wall is to be no fines Masstec mix. The designer shall allow for the hydrostatic pressure of the wet concrete during construction.

3. All Geo-grid shown in the design cross sections is Tensar SR 80 and the designs are based exclusively for this type of grid and granular backfill (2mm – 20m)

4. No allowance for seismic loadings, global stability or hydrostatic pressure has been allowed for.


(less than 3m high)


8.0 Supply Information Made locally, manufactured nationally by approved suppliers. Blocks are stocked at various locations around New Zealand in small quantities. There is a lead time to manufacture larger quantities of blocks. Lead times will vary depending on the number of MassBlocs™ required and the demand from the market. Contact CSP Pacific for more information. CSP Pacific Ph 0800 655 200 or your local CSP Pacific Sales Engineers (see our website for details : www.csppacific.com )

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