This document discusses deep excavation methods used for underground construction. Deep excavation is defined as deeper than 15 feet and requires retaining structures like walls, piles, or sheets. Common methods are bottom-up, top-down, and cut-and-cover. Retaining structures are installed, then the soil is excavated in levels while installing horizontal steel struts for bracing before further excavation. Dewatering using sumps, pumps, and wells is also required to control groundwater levels during excavation. Deep excavation is used to construct underground metro stations, tunnels, buildings, and dams.

2.  An Excavation in soil or rock more than 15ft/4.5m is called deep excavation.
 It has some retaining system with soil/rock.
 Deep excavation employed for the construction of underground metro
stations, cut and cover tunnels, power houses, Dams and high rise
buildings.

3.  Deep Excavtion carried out by:
 Bottom up method
 Top down method
 Cut and cover method
1. Retaining wall construction
a. Diaphragm Walls
b. Soldier Piles
c. Secant Piles
d. Sheet Piles
2. Strut installation and fixing/Ground anchors installation
3. Dewatering

4.  Panels excavated under
support fluid
(Bentonite/Polymer)
 Reinforced concrete panels
cast using tremie
 Waterstop included across
panel joints

5.  Bored cast-in-situ piles
inserted with ISMB.
 Wooden lagging inserted
between the ISMB to control
to retain the soil.
 Horizontal movements control
by Strut arrangements.

6.  Bored cast-in-situ piles
alternately driven soft and
hard piles under support fluid
(Bentonite/Polymer)
 Horizontal movements control
by Strut arrangements.

7.  Thick MS sheets driven by
Vibro hammer.
 Horizontal movements control
by Strut arrangements.

8.  Placement of horizontal struts in front of retaining
structures
 Earth pressure transfer to horizontal struts through
wallers
 Center posts prevent the failure of struts due to their
own weight.

9.  Stage 1- Installation of Retaining walls: Retaining walls are installed before excavation commences.
Depending on site condition, soil type and excavation depth, retaining walls can be concrete walls,
concrete bored piles or steel sheet pile walls.

10.  Stage 2- Excavation and bracing steel strut installation: The soil is excavated to the first
strut level. The first level struts must be installed before excavation proceeds further

11.  While doing excavation we should maintain ground water level always 2m
below the excavation level.
 Stage 3- Excavation and bracing steel strut installation: The soil is excavated to the next strut level and
second level struts are installed. This process progresses until it reaches the final depth or formation
level. The number of strut levels depends on the excavation depth

13.  Anchors are installed to counter act against earth pressure
 Bonded portion of the anchor provides anchoring force that works against earth
pressure unbonded part of the anchored transfer pressure to the anchor head
 Anchor head transfer loads to the retaining wall
 The anchoring force is greatly based on the soil strength.
 The higher the soil strength the greater the anchoring forces

14.  Dewatering means “the separation of water from the soil,” or perhaps “taking
the water out of the particular construction problem completely.”
 There are several methods commonly used to drain or dewater a construction
site:
 Gravity flow
 Deep well Pumping

15.  The site is drained through
channels placed at intervals,
that permit the water to flow
away from the high points and
collecting in Sumps.
 De-watering/Submersible
pumps placed in Sumps and
water will pump out to the
Drains.

16.  Dewatering wells driven by
Auger boring
 Bore hole encased with slotted
casing.
 Install submersible pump inside
the casing.
 Outlet of submersible pump
connected to the drains.
 Surrounding Ground water
near the well flow through the
slotted holes.
 The collected water pump out
through the submersible pump.

17. Water ingress through the joints leads caving behind the
structures.
Improper Dewatering leads slush formation
Heavy floods leads surface water flow to the excavated
area.
Ground settlement surrounding locations.
Toxic gases leads Health problems.