Basic Of Retaining Wall Design

Chapter 1 

1 .Evolution of Retaining Structures

In the year one-million BC, or thereabouts, an anonymous man, or woman, laid a row of stones atop another row to keep soil from sliding into their camp. Thus was constructed an early retaining wall, and we've been keeping soil in place ever since. with increasingly better methods and understanding.

The early engineers in ancient cultures of Egypt, Greece, Rome, and the Mayans, were masters at invention and experimentation, learning primarily through intuition and trial-and-error what worked and what didn't We marvel at their achievements. Even the most casual observer looks in wonder at the magnificent structures they created and have stood for thousands of years including countless retaining walls. With great skill they cut, shaped, and set stone with such precision that the joints were paper thin. Reinforced concrete would not be developed for thousands of years, but they used what they had, and learned how to do it better with each succeeding structure. The Great Wall of China, for example, transverse bamboo poles were used to tie the walls togethera forerunner of today's "mechanically stabilized earth". These early engineers also discovered that by battering a wall so that it leaned slightly backward the lateral pressure was relieved and the height could be extended an intuitive understanding of the soil wedge theory. Any student of ancient construction methods is awed by their ingenuity and accomplishments

Major advances in understanding how retaining walls work and how soil generates forces appeared in the 18th and 19th centuries with the work of French engineer Charles Coulomb 1776, and who is better remembered for his work on electricity, and later by William Rankine in 1857. Today, their equations are familiar to every civil engineer. A significant body of work was the introduction of soil mechanics as a science through the pioneering work of Karl Terrzaghi in the 1920s.

Indeed, soil mechanics and the design of retaining structures has advanced dramatically in recent decades giving us new design concepts, and a better understanding of soil behavior, and hopefully safer and more economical designs.

A Definition:

A retaining wall is any constructed wall that holds back soil, a liquid or other materials, where there is an abrupt change in elevation.

The Precision Illusion

Let's not fool ourselves. Even though the science of soil mechanics is well developed and reasonably well understood, it is still not an exact science and remains both an art as well as a science. Soil is a mixture of earth materials and although its characteristics can be closely defined its actual in situ behavior will not precisely fit theory. For example: the straight line we assume for the angle of rupture is actually

somewhat concave, and, the "equivalent fluid pressure" of soil is not truly triangular. We makem Smplifying assumptions to make our designs manageable. As the adage goes: engineering is an exactscience based upon assumptions. Our calculations are the best we can do with assumptions we make andthe results are never fully accurate. That's why we use factors of safety. So keep precision in mind when

calculating beyond the first decimal point.