| Good soil information can lead to substantial savings | | | | corners sharp or irregular. |
| and tighter foundation design because the design | | | | Boulders: |
| parameters are well defined. The more | | | | Boulders are fragments of rock larger than |
| comprehensive the information, the more economically | | | | 200mm.Once the soil is classified and the composition |
| can a good structure be built. The object is to build a | | | | of the grain particles are determined, one can make a |
| good building cheaply and not to build a cheap building. | | | | recommendation as to which type of foundation or pile |
| Geo-technical site investigations may cost up to 2% | | | | structure should be used. |
| of the total project cost, but is very necessary as | | | | There are various types of clay and not all of them |
| geo-technical engineers often say: you will pay for | | | | may be regarded as bad. Some are soft but are still |
| your geo-technical investigation | | | | stable. |
| anyway!GEOTECHNICAL INVESTIGATION | | | | Collapsible soils are usually not very dense because |
| PROCEDUREInitially one should find geological | | | | of the high proportion of voids present.Heaving or |
| information for a specific site about the original rock | | | | active clays contain minerals which cause the soil |
| type of the area and the soils which are the | | | | mass to react strongly to changes regarding moisture |
| weathered rock. This can be done at either the | | | | content. These clays will swell when more moisture is |
| government printer or your local geological board. | | | | added and will shrink as they dry out. The treatment of |
| If in doubt regarding the characteristics of the soil, | | | | soft soils is usually to make the foundations wider to |
| consult an engineer or take soil samples from a test | | | | reduce the pressure to an acceptable level so that the |
| hole to a soil laboratory for analysis. Based on the | | | | soil will be able to withstand the load with little or no |
| results of this analysis, a recommendation can be | | | | settlement. Should the soil prove to be too soft or wet |
| made regarding the best foundation structure to | | | | then a raft foundation or piling is recommended. A pile |
| use.CLASSIFICATION OF SOIL TYPESSand: | | | | is a concrete column driven into the earth which either |
| Sand consists of discrete particles normally visible to | | | | carries the load down to a stronger soil or rock below |
| the naked eye. Sand is clearly distinguishable by the | | | | or by hanging in friction on the soil around its |
| presence of gritty particles which do not break down | | | | shank.RECOMMENDATIONS FOR PROBLEM |
| when rubbed on the palm of the hand. | | | | SOILSClay soils |
| Silt: | | | | Clay is generally smooth and has no visible particles, it |
| Silt consists of fine particles. In general silt particles are | | | | retains water and does not drain well. The presence |
| barely felt when rubbed with water on the palm. When | | | | of clay is sometimes indicated by cracks on the |
| this wetted soil is placed on the tongue, the particles | | | | surface of the ground. This type of soil could pose a |
| can be felt grating the against the enamel of the teeth. | | | | problem although some soft clays are quite stable. |
| Clay: | | | | Heaving clay is very problematic and changes a lot |
| Clay consists of very fine particles. The particles are | | | | when the moisture content changes.Recommendation: |
| flaky and when rubbed on the palm with water has a | | | | One should lay a compacted hardcore (of broken |
| soapy or greasy feeling. No sensation of grittiness can | | | | bricks, stones etc.) under the concrete foundations but |
| be detected when tasted. | | | | for heaving clay a raft foundation will often have to be |
| Gravel: | | | | used; also, depending on the extremeness of the |
| Gravel consists of fragments of rock. The shape of | | | | heaving clay, the site can be thoroughly soaked once |
| the particles should be described as: rounded shape, | | | | the trenches have been dug and building can then |
| oval shape, rounded corners, corners slightly bevelled, | | | | begin when it has dried sufficiently. |