Setting Out and Site Investigation

Question 1

What would the development of the means of measurement do to facilitate the planning of the exact location of a building and agreement with the statutory authorities?

Answer 1

Demarcate the site boundary;
Demarcate the building footprint;
Demarcate the major components of the building - to set out the relevant components at the right location, angle, alignment and level.

Question 2

What does setting out mean?

Answer 2

Setting out means providing the necessary control lines and reference lines on site so that the workmen can identify where to put the building, the individual building elements, and components as specified on the drawings.

Question 3

What are control lines?

Answer 3

Control lines comprise two main groups:
City grids - control lines designated by the government to demarcate the local geographical areas via a system of coordinates on a horizontal plane.
Building grids - control lines designated by the architects of a building to demarcate the building lines and principal elements, like columns and/or load-bearing walls, of a building via a system of coordinates and/or measurements on a horizontal plane.
Set by someone of authority.

Question 4

What are reference lines?

Answer 4

Reference lines mean any lines provided by the setter out (or surveyor) to facilitate the work of the workmen.
There can be many reference lines and most of them are temporary (covered up or rubbed away).
They are usually provided at a convenient location close to work (10 cm to few m away).
Setter out (or surveyor) is regarded as part of the construction team.

Question 5

What are the parties involved in setting out and what are their roles?

Answer 5

Survey Office of HKSAR: Set control points/survey stations in various parts of HK
Registered land surveyors: May help the employer transfer proper control points to somewhere close to his development area before the commencement of construction work, and set out the site boundary

Question 6

In construction, what is the vertical level termed? What is it measured from and where is it usually?

Answer 6

Elevation.
It is measured from the principal datum and the mean sea level is usually regarded as the principal datum (0.000)

Question 7

What makes reference to their differences to the principal datum?

Answer 7

Elevation marks used in the construction process.

Question 8

Transfer of the survey stations and/or benchmarks relies on one or more of which survey tools and equipment?

Answer 8

Measuring tape, optical surveying equipment, and levelling rod (aka “staff”)

Question 9

Data collected by the use of optical surveying equipment (+ measuring tape and levelling rod) can be processed by simple calculations based on ____________ to work out the physical distance of different objects with great precision.

Answer 9

Trigonometric theories.

Question 10

What are the basic types of surveying instruments?

Answer 10

The level, the level transit, and the theodolite/total station.

Question 11

What does a level (builder’s level) do?

Answer 11

A level operates in a horizontal plane only, so it can only measure horizontal angles and differences in elevation.

Question 12

What does a level transit do?

Answer 12

Besides turning in a horizontal plane, it will also tilt in a vertical arc, up to 45° from the horizontal position.
It is able to measure vertical angles and running lines. It has all the basic parts of a level + those involved in vertical movement.

Question 13

What does a theodolite do?

Answer 13

It measures horizontal and vertical angles, but the gradations on the scales are finer, providing greater accuracy in angular readings than most levels or level transits.

Question 14

What does a total station do?

Answer 14

It is a theodolite with an integrated distance meter that can measure angles and distances simultaneously.
Theodolites measure horizontal and vertical angles only. We can calculate distances using trigonometric calculations. A total station can measure angles and distances electronically and process them trigonometrically to give us position coordinates in space.

Question 15

Before architects can proceed to the design of the building, they must know the site conditions in what regard?

Answer 15

The topography of the site (e.g. site boundary, elevations, existing structures, trees, and other features) and its neighbouring structure/street;
The soil conditions of the site;
The underground water table of the site.

Question 16

Elaborate on topographic surveys.

Answer 16

Topographic surveys are conducted by land surveyors.
Information on the topography of a site helps architects determine how to form the building platform of the proposed building, the shape and size of the building footprint, the design of the access road, the need for site formation works, etc.

Question 17

Elaborate on soil investigation.

Answer 17

Specific information of sub-soil conditions must be made available before a foundation system can be elected and designed.
So, accurate information on sub-soil conditions of the site must be collected before proceeding to the design of the building.

Question 18

Regarding soil investigation, information on what aspects must be collected for the consideration of engineers?

Answer 18

Soil type, composition and profile;
Grain size of the soft material (of the sub-soil);
Moisture content of the soft material (of the sub-soil);
Engineering properties (e.g compressive strength and shear strength) of the sub-soil;
The underground water table (measured at different seasons since it is subject to change at different time of a year).

Question 19

Elaborate on underground water table.

Answer 19

It refers to the level at which water can be found at the sub-soil.
Changes in the moisture content of sub-soil may affect its engineering properties.
The underground water table must be detected and monitored where shallow foundations are adopted, but not deep foundations.
Underground water table may affect excavation works and it can also cause problems when a dry working condition is required in the course of construction.
For any works involving excavation , engineers would need to consider the underground water table of the site to elect an appropriate working method for the project.

Question 20

Before the commencement of any design work or construction work, ____________ shall be conducted. The primary ____________ is usually done in which two stages?

Answer 20

Site investigation.
A surface evaluation of the building site;
A sub-surface investigation

Question 21

Elaborate on surface evaluation.

Answer 21

The surface evaluation of the site normally consists of a topographic survey to establish the site boundary, grades and other features (e.g. access, existing structures, trees, and utility lines and ducting).
A study of the record drawings shall help identify these utility facilities’ existence and their alignments and levels.

Question 22

Elaborate on sub-surface evaluation. What information can be collected in regards to it?

Answer 22

Sub-surface evaluation consists of evaluating the soil below the surface to establish the criteria for the foundation requirements of the proposed structure.
The bearing capacity of the soil;
The profile (variation of soil) of the subsoil strata;
The underground water table.

Question 23

For relatively shallow foundations, how may sub-surface samples be obtained?

Answer 23

From a simple trial pit 1-2 meters deep.

Question 24

For deep foundations, how may sub-surface samples be obtained?

Answer 24

They are obtained at various depths up to 30 meters or more below the ground surface.
A drill rig is used to provide the test borehole, and special methods (e.g. split spoon sampler or Shelby tube) are used for extracting the required samples.

Question 25

What is a bore log?

Answer 25

The information collected from the surface/sub-surface soil samples will be compiled into a soil investigation report (or bore log).

Question 26

Why is sub-surface exploration of prime importance?

Answer 26

It is of prime importance to designers in gathering information for the design of the building foundations.

Question 27

What do large buildings that impose substantial loads on their foundations depend on to provide the necessary support? What will the depth of that dictate?

Answer 27

Soil of good bearing capacity, bedrock in some cases.
The depth at which this bearing is available will dictate the type and cost of the foundation.

Question 28

What foundation can low-rise buildings benefit from and why?

Answer 28

Shallow foundation.
They are relatively light and subject to relatively low wind load; thus can be founded on soil of relatively low load-bearing capacity, which is usually available close by the ground surface.

Question 29

What foundation can high-rise buildings benefit from and why?

Answer 29

Deep foundation.
They are very heavy and subject to high wind loads; thus they are usually founded on bedrock and anchored to a significant depth of the ground (to overcome the possible lateral force caused by wind). Frequently, high quality bedrock is only available at a great depth, about 35 to 50 m below the ground surface.

Question 30

What are the types of soil in descending order of size?

Answer 30

Cobbles and boulders, gravel, sand, silts, and clay.

Question 31

What are cohesionless and cohesive soils?

Answer 31

Cohesionless soils include sand and gravel soils in which the particles have little or no tendency to stick together under pressure.
Cohesive soils include dense silt, medium dense silt, hard clay, stiff clay, firm clay, and soft clay. The particles of these soils tend to stick together, particularly with the addition of water.

Question 32

What are miscellaneous soils?

Answer 32

Glacial tills and conglomerate (a mixture of sand, gravel and clay, with the clay acting as a cement to hold the particles together).

Question 33

What are the four types of rocks and their properties?

Answer 33

Massive rocks.
They are very hard, have no visible bedding planes or laminations, and have widely spaced, nearly vertical or horizontal joints. They are comparable to the best concrete in compressive strength.
Foliated rocks.
They are also hard, but have sloping joints which preclude equal compressive strength in all directions. They are comparable to sound structural concrete.
Sediment rocks.
They include hard shales, sandstones, limestones and siltstones, with softer components. Rocks in this category may be likened to good quality brick masonry.
Soft or shattered rocks.
They include those that are soft or broken but not displaced from their natural beds. They do not become plastic when wet and their compressive strength is comparable to poor brick masonry.