The purpose of an in situ soil sample collection and testing
is to carry out an analysis of the soil quality and its features so as to
smoothen the process of design. Understanding the subsoil information and the
engineering properties, such as the strength, permeability and deformation, allows
appropriate choice of building foundation and structure depending on the types,
consistency, condition, etc. Through these analysis, stakeholders can select
the most suitable and cost effective way of construction with minimum or
Therefore soil samples are
collected through various soil sampling methods:
1. Trial pits
(trial pit 1)
(trial pit 2)
Trial pit is the excavation of a pit
as deep as 1.5m or more depending on the soil conditions, which is usually left
unsupported. Any trial pits deeper than 1.5m are dangerous. The excavation is
being done manually by hand or by a mechanical excavator. After excavation, visual
examination of strata, soil layering, soil discontinuity and soil conditions
are carried out onsite. At the same time large amount of soil samples will be
obtained for further investigation. During a trial pits investigation, an
experienced supervisor or engineer whom has thorough knowledge of geology and
soil mechanic will be present to provide advices or feedbacks.
Generally, the trial pits method
produces a comprehensive examination results. However, there still advantages
and disadvantages while executing the method.
1. More efficient method of investigation compared
to other methods (such as window drilling).
1. Trial pits deeper than 1.5m are dangerous due to
the lack of support.
2. Soil strata can be visually examined as it is.
2. Instability of side walls occurs & loss of
original sample when there is presence of water.
3. Large amount of soil samples can be obtained for
3. Difficulty of excavation where services are laid
4. Lesser cost compared to boreholes & probe
2. Dynamic Probe Testing
The dynamic probe testing method
provides an estimation of the subsoil conditions. It is carried out by driving
a marked steel bar or cone (e.g. marked 100mm interval) cyclically to penetrate
it into the ground. The steel bar or cone is driven by a free falling hammer
repeatedly and number of blows are recorded (e.g. number of blows per 100mm
movement). In order to determine the soil features, from time to time the bar
or cone is extracted out so as to examine the soil sample on it. This process
is repeated until the probe reaches the requirement depth or when there is no
penetration due to the hard stratum underground.
1. Light and easy usage.
1. Human error in records.
2. Disturbed soil sample obtained for moisture
2. Limited depth penetration due to penetration
3. Cost efficient.
3. Difficulty in penetrating into tougher stratum.
4. No requirement of a experienced or skill worker.
4. No visual or detailed strata information.
The boreholes method is basically
to create bore holes in the ground and obtaining the soil samples. Depth and
quantity of boreholes are determine by various factor such as the structure and
loading type, and the soil characteristics. However, the type of boring method also
differs depending on the ground condition, depth, accessibility and the ground
Types of boring
– Auger Boring
The auger boring is the most
simplified method of boring, usually operated manually by hand or mechanically
by power driven machinery. This method is preferred when there is presence of
soft soil above the water table. However, the soil samples that are being
recovered are badly disturbed and can only be use for visual identification
– Percussion Drilling
The percussion drilling is the
method of heavy drilling, in a manner when repetitive blows of a drill rod/bit
breaking the soil formation while advancing into the ground. This method of
boring allows advancement of holes into different types of soil. Due to the
heavy drilling and impact, the soil formation would be disturbed.
– Rotary drilling
The rotary drilling is a fastest
method of making a borehole. Similarly to a drill, the drill bit(attached at
the bottom of the drilling rod) are placed in contact with the bottom of the
ground and having the ability to cut through soil or rock formation. During
intervals, the sampler will replace the drill bit so as to collect soil samples.
4. Window Sampling