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Building firm foundations

Archive for July, 2006

Modular Retaining Wall Components

Posted by Kshitija Nadgouda on July 26, 2006

Since my article on Retaining Walls, I received queries regarding the components of a modular block retaining wall. So I deceided to write this post to supplemnt my earlier article.

(Courtsey Versa-Lok)
A modular block (or segmental) retaining wall consists of the following components:

  1. Modular blocks (Facing Unit)
  2. Levelling pad
  3. Drainage Material
  4. Engineered Fill
  5. Geosynthetic Reinforcement
  6. Impervious Fill
  7. Retained Backfill

Modular blocks are the facing units – the aesthetic component of the wall that meets the eye. There are several companies like VERSA-LOK, KEYSTONE, ALLAN BLOCK, MESA BLOCK , etc that sell these inter-locking units.
Levelling Pad refers to the base of the “founding” element of the retaining wall. It provides a level base for the retaining blocks.
Drainage material is placed immediately behind the facing units to ensure that any moisture or groundwater is drained away and doesn’t exert excess pressure on the facing units.
Engineered Fill refers to the soil that replaces the material excavated from the natural slope. Typically a silty sand is used as engineered fill.
Geosynthetic Reinforcement are the sheets or grids of geosynthetic reinforcement that are used to strengthen the system. Tensar and Mirafi are two of the popular companies that manufacture geosynthetic reinforcement sheets and grids in the US, while Techfab India provides these materials in India,
Impervious fill is used to cap the backfill behind the facing units so that rain water or other surficial water doesn’t permeate into it.
Retained backfill is the part of the natural slope or natural terrain that is still undisturbed.

Geogrid Retaining Wall Systems, Incorported has an excellent series of photographs showing the step-by-step construction of a segmental retaining wall.

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Posted by Kshitija Nadgouda on July 15, 2006

This post is about foundations of structures built over the sea, in response to two questions posted by Sachin Choughule on the post about the Bandra Worli Sea Link.

Most bridge foundations over the sea are caissons that are embedded into the river-bed (or ocean floor) until a suitable firm stratum is encountered. A caisson foundation, in simple words, is like a can (although it need not be circular!). It is a watertight chamber that facilitates the operation of construction equipment by workers within it.

Small Caisson
(Courtsey Manitoba Labour and Immigration)

The workers operate construction equipment and excavate the soil within the caisson walls thus sinking the caisson into the river-bed (or ocean floor). Compressed air is pumped into the caisson and regulated to ensure that the caisson remains stable and soil/mud/water do not rush in through the bottom.

(Courtsey Carol Denney)

Some interesting information:

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Landslide along Mumbai-Pune Expressway

Posted by Kshitija Nadgouda on July 6, 2006

Heavy rains on Monday caused a landslide along the Mumbai-Pune Expresway near Khandala. It would be more accurate to call it a rock slide rather than a landslide since the hillslope is primarily a deccan trap rock formation. Big boulders and stones came toppiling down on to the expressway, obstructing traffic along two of the six lanes.

Simple preventive or mitigation measures such as nets should be proposed along the expressway in potential shallow landslide prone areas. Geologic mapping of the area should be carried out to determine such potential landslide prone areas or aras that have seen landslides historically.

Landslides along the Mumbai-Pune expressway have unfortunately become an annual feature with at least one landslide each year in the monsoons. The concerned agencies must take preventive and proactive mitigation measures to ensure this doesn’t continue. Will the authorites wake up only after loss of life occurs due to these landslides?

Get more information about the Mumbai-Pune expressway at:
or at the Road Traffic Technology site.
And photos at:
Amit Kulkarni’s site
or Shantanu’s gallery
The Pune Lifestyle webpage also has some great photos.

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