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