According to most building codes, the unsupported height of masonry piers shall not exceed ten times their least dimension. This ensures the stability and safety of the structure. So, none of the options in the question (three, four, five, or six times their least dimension) are correct.
The piers are usually made of concrete, although they can also be made of brick, stone, or wood. They're typically around 4 feet tall and spaced evenly apart (8-10 feet).
Common practice when exceeding the prescriptive 30-ft (9.14 m) height limitation for brick veneer on wood framing has been to follow Section 12.2. 1 of the masonry code, Alternative design of anchored masonry veneer, which allows an alternate method to be used.
Masonry Opening Height
The MO height is the measurement of the opening from the header masonry to subfloor. When determining the Masonry Opening, there is a 1/4″ adder to each piece of brickmould to account for the backer rod that is used. The unit sits in the Masonry Opening.
The maximum height is 48 inches as measured from the top of the footer to the top of the last concrete block. Piers of greater heights are allowed if they are within limits established in adopted federal standards. The pier is capped with a minimum 16x16x4 concrete cap. Open cells must be vertical and in alignment.
Piers between 36 and 80 inches (914 and 2032 mm) in height and all corner piers greater than 24 inches (610 mm) in height shall be at least 16 inches by 16 inches (406 mm by 406 mm) consisting of interlocking masonry units and shall be fully capped with minimum 4-inch (102 mm) solid masonry units or equivalent.
Planning a Block Retaining Wall
Interlocking retaining wall block can be stacked to build walls up to 24 to 36 inches high, depending on the size of the block.
All masonry walls over eight feet in height shall be adequately braced to prevent overturning and to prevent collapse unless the wall is adequately supported so that it will not overturn or collapse. The bracing shall remain in place until permanent supporting elements of the structure are in place.
AS 3700, also known as the Masonry Structures Standard, is a comprehensive set of guidelines that outline the design and construction requirements for masonry structures. These standards ensure that masonry structures are built to withstand various environmental and load conditions, ensuring their longevity and safety.
Structural Integrity: Unlike rough openings in wood or metal-framed walls, a masonry opening is cut directly into masonry materials. These openings need to be reinforced properly to maintain the overall strength and stability of the wall.
Lintels are required for all openings over timber frames greater than 600mm in width, & for all openings over steel frames greater than 900mm.
The maximum unsupported height of any masonry wall during the period of construction shall be two stories or twenty-six feet, unless satisfactory support is provided and specific approval of the superintendent obtained, except when walls are carried separately by structural members on each story.
A partition wall constructed of 12” block can span up to 28 feet high as an unreinforced masonry wall. As we increase in height and/or reduce in wall thickness, light reinforcement is needed to resist the interior pressure of 5 psf.
Piers are the concrete columns or piles that rest on top of the footings, usually connected using steel rebar.
But how often should you use brick piers in a wall? Well, a single-brick wall that's more than 12 inches high should have brick piers at least every 3 metres. You'll also need your brick wall and piers to rest on a foundation.
BS 5628 - Code of practice for use of masonry.
In accordance with BS EN 1996-2:2006 and NHBC requirements all external wall lintels MUST be installed with a flexible damp proof course with the exception of those adequately protected by an eaves overhang or similar form of protection. Masonry should not overhang any flange by more than 25mm.
The most common wall assembly is defined by a facing of thin brick between 1/2" to 11/2" in thickness applied over a plaster backing. If this combined masonry layer is 13/4", the masonry side of the assembly qualifies for a 1-hr fire rating.
a) The maximum length of unsupported external masonry wall should not exceed 9000mm between buttressing walls, piers or chimneys and the minimum thickness of the unsupported cavity wall is 190mm.
OSHA's Adequate Bracing Requirement
OSHA also requires that all masonry walls over eight feet in height must be adequately braced to prevent overturning and to prevent collapse, unless the wall is adequately supported so that it will not overturn or collapse.
Maximum pour heights and the minimum dimensions of spaces provided for grout placement shall conform to Table R606. 3.5. 1. Grout shall be poured in lifts with a maximum height of 8 feet (2438 mm).
(b) Frame piers 36 inches to 67 inches high and corner piers. (1) All frame piers between 36 inches and 67 inches high and all corner piers over three blocks high must be constructed out of double, interlocked concrete blocks, as shown in Figure B to this section, when the design capacity of the block is not exceeded.
The length of the deadman anchor should equal the height of your wall. So a 4-ft tall wall would require 4-ft long deadman anchors. Deadman anchors are spaced 8-ft apart on each row of timber, except the top and bottom coarse. Pro tip: buy timbers in 8-ft sections to limit the amount of cutting.
Rather than how many, it depends more on what can be laid in your situation. If too many blocks go up in one go, the mortar gets squashed out, so in your situation, I'd expect this to be a two day job. All being well. You are looking at 200 blocks on a good day.