Transcript SETTLEMENT - Universitas Brawijaya

SETTLEMENT
C
YULVI ZAIKA
OUTCOMES OF STUDY
• Introduce consolidation settlement
• Understand 3 conditions primary consolidation based on pre consolidation stress
• Calculation primary consolidation settlement
• Calculation secondary consolidation settlement
COMPRESION OF SOIL
• If the clay layer of thickness H when subjected to an increase in average effective
overburden pressure from ´0 to ´1 ( ´0+´) there will be consolidation settlement
of H.
• 𝜀=
∆𝐻
𝐻
in field
∆𝑒
𝜀 = 1+𝑒 in laboratory
0
Equating:
∆𝐻
𝐻
∆𝑒
∆𝑒
= 1+𝑒 then ∆𝐻 = 1+𝑒 H
0
0
H: settlement
CALCULATION SETTLEMENT
• There are two different methods to calculate settlement:
1. Using mv : 𝑆𝑐 = 𝑚𝑣 ∆𝜎 𝐻
∆𝑒
2. Using e – log  diagram 𝑆𝑐 = 1+𝑒 𝐻
0
SETTLEMENT COMPUTATION
computing e using e log v’ plot
• If the clay is normally consolidation, the
entire loading path along virgin
consolidated line (VCL)
• 𝑆𝑐 =
𝐶𝑐 𝐻
𝜎0′ +∆𝜎
log ′
1+𝑒0
𝜎0
e0
e
e1
VCL
0’
0’+
SETTLEMENT COMPUTATION
computing e using e log v’ plot
• If the clay is over consolidation and
remain so by the end of consolidation
• 𝑆𝑐 =
𝐶𝑟 𝐻
𝜎0′ +∆𝜎
log 𝜎′
1+𝑒0
0
e0
e1
e
VCL
0’
0’+
SETTLEMENT COMPUTATION
computing e using e log v’ plot
• If the over consolidated clay become
normal consolidation by the end of
consolidation
• 𝑆𝑐 =
𝐻
1+𝑒0
𝐶𝑟 𝑙𝑜𝑔
𝜎𝑐
𝜎0
+ 𝐶𝑐 log
𝜎0′ +∆𝜎
𝜎𝑐
e0
e
e1
VCL
0’
c
0’+
SECONDARY CONSOLIDATION SETTLEMENT
This is also called Secondary compression
(Creep). “It is the change in volume of a
fine grained soil due to rearrangement of
soil particles (fabric) at constant effective
stress”.
The
rate
of
secondary
consolidation
is
very
slow
when
compared with primary consolidation.
The secondary compression index:
∆𝑒
𝐶𝛼 =
log 𝑡2 𝑡1
Where e : change in void ratio
𝐶𝛼
𝐶′𝛼 =
1 + 𝑒𝑝
ep : void ratio at the end of primary consolidation
𝑡2
𝑆𝑠𝑐 = 𝐶′𝛼 log
𝑡1
Ssc : Settlement of secondary consolidation
Flow chart for calculation primary
consolidation settlement
Data: soil characteristic(,Cc,Cs,c,e0)
soil layers
load of upper structure
If clay layer is more than 2 m
Divide layer in to some thick layers.
Define the reference point for every layer
Calculate overburden pressure from
soil surface to the reference points
Calculate applied load from foundation base ()
To reference points
Calculte 𝜎1 ′ = 𝜎0 ′ + ∆𝜎
If 𝜎𝑐 < 𝜎0′ < 𝜎1′ normal
consolidation (NC)
If 𝜎0 ′ < 𝜎𝑐 < 𝜎1′ over
consolidation (OC)
𝐶𝑐 𝐻
𝜎0′ + ∆𝜎
𝑆𝑐 =
log
1 + 𝑒0
𝜎0′
Summation settlement of every layers
If 𝜎0 ′ < 𝜎1′ < 𝜎𝑐 over
consolidation (OC)