1. General Concept of Soil Category

Soil particle size determines name. Name indicates properties. From soil mechanics perspective, the following sorting roughly indicates the soil from "soft" to "hard" OR from "Clay" to "Rocky" type:

Peat > Silt > Clay > Sand > Gravel: 泥炭 > 淤泥 > 粘土 > 沙 > 石

Further, the suffix "y" or "ed" to describe sort of that type as:

Peaty: 泥炭质的
Silty: 淤泥质的
Clayed: 粘土质的
Sandy: 沙质的

The above adjectives can be used to describe the soil name, giving more detailed characteristics of that type of soil. For example: Silty Clay.

An example of soil profile is like this:

From geological strata's perspective, the ground is categorised according to its layers. Here is one example (from top to down layer):

Fill 填土层
Kalang Formation (contains Marine Clay)
Alluvium 冲积层

2.1. Geological Map of Singapore and Soil Category

Soil category associated with location to have general concept of the soil type:


Source: Straits Times, April 6, 2009

2.2. Soil Category and Description

Reference Soil and Rock Type General Description
M Marine Very soft to soft blue or gray clay
E Estuarine (Transitional) Peats, peaty and organic clays
B Beach (Littoral) Sandy, sometimes silty, with gravels, coral and shells
F Alluvial Sands, peaty and organic clays
O Old Alluvium Silty sand to silty clay
S Sedimentaries (Rocks and Associated Soils) Sandstones, siltstones, mudstones, limestones and conglomerates
G Granite (Rocks and Associated Residual Soils)  

3.1 Indicative Standard Penetration Test (SPT) Vs. Soil Category

3.2. Standard Penetration Test (SPT) Vs. Soil Characteristics

Sand

Clay and Silt
N-value (blows / 300mm of penetration) Relative Density N-value (blows / 300mm of penetration) Consistency
0-4 Very loose <2 Very soft
4-10 Loose 2-4 Soft
10-30 Medium dense 4-8 Firm
30-50 Dense 8-15 Stiff
>50 Very dense 15-30 Very Stiff
    >30 Hard

4. Temporary Earth Retaining System (TERS)

When open cut excavation is not possible in the downtown area, the earth retaining wall is necessary. The complete earth retaining system includes earth retaining wall and strutting system. There are many types of earth retaining structures available depending on the site suitability (site constraints and soil parameters γ, c, φ). Often, there are many strutting methods available for the earth retaining wall. Sometimes, the slope stabilization method such as guniting or shotcreting and ground improvement measures such as JGP are supplemented with earth retaining structures. The followings are common earth retaining structures starting from the stiffest type.

5. Strutting System

6. Slope Stabilization and Protection

7. Ground Improvement

8. Temporary Decking

When the site is so constraint that there is no access between the basement wall and the boundary hoarding, temporary decking may be considered. When designing decking, the following points shall take into account:

9. Cofferdam

10. Caisson

11. Type of Piles