What is the first stage of shaft sinking through subsoil?
C
Surface preparation and site clearing
Analysis & Theory
Sinking begins with clearing the surface area and preparing the site for excavation.
Which technique is commonly used to prevent water inflow during sinking through subsoil?
Analysis & Theory
Grouting is used to seal off water-bearing zones and reduce water ingress.
Why is caisson sinking used in soft subsoil?
A
To increase blasting efficiency
C
To provide support and resist collapse
D
To reduce noise pollution
Analysis & Theory
Caissons provide structural support and prevent collapse in loose or soft subsoil.
What is the purpose of dewatering during shaft sinking?
B
To provide drinking water
C
To lower groundwater level and keep the shaft dry
Analysis & Theory
Dewatering keeps the excavation area dry by controlling groundwater inflow.
What type of lining is initially used in subsoil shaft sinking?
Analysis & Theory
Cast iron rings are often used for initial support in soft ground due to their strength and ease of assembly.
Which stage follows the excavation of soft subsoil in shaft sinking?
Analysis & Theory
After excavation, lining and support structures are installed to stabilize the shaft walls.
Which equipment is primarily used for mucking in subsoil excavation?
C
Grab buckets or clam-shells
Analysis & Theory
Grab buckets or clam-shells are commonly used for removing loose excavated material in soft ground.
In which condition is ground freezing used during shaft sinking?
C
In water-logged or unstable subsoil
Analysis & Theory
Ground freezing temporarily stabilizes water-bearing loose soils to allow safe excavation.
Why is shaft collaring important in shaft sinking through subsoil?
A
To increase blasting pressure
B
To hold the shaft mouth and prevent collapse
Analysis & Theory
Shaft collaring reinforces the upper part of the shaft to prevent caving or collapse at the start.
What marks the transition from subsoil sinking to rock sinking?
A
Completion of shaft collar
C
Encountering hard rock strata
D
Construction of surface buildings
Analysis & Theory
The sinking method changes once the soft subsoil ends and hard rock is encountered.