N tt
P
tt
M .y
x max
M tt .x
max
(3.25)
i
max n
y
i
n c n c
min
c y 2 i 1
x 2 i 1
In which: N tt ; M tt x ; M tt y ; Q tt x ; Q tt y : Total force system about the center of gravity of the foundation bottom:
+ N tt
N tt nF .h .
0 mm tb
M
M
+
tt tt
x 0x
M
M
+
tt tt
y 0 y
Q tt .h
0 y
0x
m
m
Q tt .h
+ n = 1.15 is the overload factor
+ x i , y i are the coordinates of the i-th pile
Q tt
N
tt
0
0
M
tt 0
ptt
min
ptt
max
x
P i
y i
y
y max
L m
H m
h m
b) Plane problem
x i
x max
B m
Figure 3.7: Diagram of force calculation transmitted to piles
- Force acting on pile i:
Pi
N tt M tt .y
i
n n c
(3.26)
i
c y 2
i 1
- The largest and smallest forces acting on the edge piles:
P max
N tt
n
M tt .y
n c
max
(3.27)
min
c y 2
i
i 1
In there:
+ N tt
N tt nF .h . ;
0 mm tb
+ M tt
M tt Q tt .h ;
0 0 m
+ n = 1.15: is the overload factor.
+ x i , y i : are the coordinates of the i-th pile.
3.1.7.2 Test conditions
P max + P c P cp (3.28)
P min ≥ 0 (3.29)
In there:
+P c : is the weight of the pile;
+ In case P min <0, pile pulling must be checked.
3.1.8 Calculation and settlement check (TTGH 2)
3.1.8.1 Stress check at conventional block foundation
- The foundation of the pile foundation resists deformation very little, always satisfying the deformation condition so there is no need to check. The foundation of the friction pile foundation must be checked according to the deformation condition. It is believed that thanks to the friction force between the surrounding surface of the pile and the soil surrounding the pile, the load of the foundation is transmitted over the area.
wider, starting from the outer edge of the pile at the base of the pedestal at an angle
tb
4
1 h 1 2 h 2 ... n h n
(3.30)
tb
In there:
h 1 h 2
... h n
+ i : is the internal friction angle of the soil layer i;
+ h i : is the thickness of the i-th soil layer that the pile passes through.
- The conventional foundation block (abcd) is considered as a shallow foundation on natural ground and the settlement of the ground under that foundation is calculated. To calculate the settlement of the ground under that foundation, the relationship between deformation and stress is linear.
a) Conventional block foundation size
B qu = B m + 2L c .tgα (3.31)
L qu = L m + 2L c .tgα (3.32)
b) Stress at conventional block foundation
- Stress distribution at the bottom of the conventional block:
P
tc max
N tc
qu (1
F
6e L
L
6e B )
B
(3.33)
min
In there:
monster
+ N tc
N tc F
.(h
L ). ;
number 0
monster
c tbqu
M
+
tc xqu
M
+
tc yqu
tc 0x
M
M
tc 0 y
M tc
Q tc .(h
0 y
0x
m
m
Q tc .(h
L c ) ;
L c ) ;
+ e xqu : eccentricity in direction L m ;
N
L tc
the
M tc
+ e yqu : eccentricity in direction B m ;
N
B tc
the
+ F qu = B qu .L qu : conventional block foundation area.
- Average stress at conventional block foundation:
p
p tc p tc
l 2
l 1
h m
tc max min tb2
a
Q tc
N
tc
0
0
M
tc
0
b
P tc
min
d
P tc
max
c
z
l n
...
l i
...
L c
Figure 3.8: Diagram of stress testing under conventional block foundation
c) Calculated strength of the soil at the bottom of the conventional foundation
- Driven and pressed pile foundation: Due to the volume of driven and pressed piles occupying the soil, making the ground compacted. Therefore, the soil parameters increase, R is determined:
the
R m 1 m 2 (1,1A.B
k tc
- Bored pile foundation:
. 1,1.B.(h m
L c
) .
tbqu
3.Dc)
(3.34)
the
R m 1 m 2 (AB k tc
. B.(h m
L c
) .
tbqu
Dc)
(3.35)
In there:
+ A, B, D are load carrying coefficients depending on the internal friction angle , see table 2.2;
+ tbqu : is the average density of soil within the scope of the standard block foundation
wish:
1 l 1 2 l 2 ... n l n
(3.36)
tbqu
l 1 l 2 ... l n
d) Testing conditions
p
tc max
1.2R
p
R
tc tb
3.1.8.2 Calculation and checking of settlement
a) Settlement stress at the bottom of the conventional foundation
gl p tc .(h L )
(3.37)
0 tb tbqu mc
b) Divide the soil under the foundation into many homogeneous element layers h i ≤ B qu /4
Note: You should choose h i = B qu /5 to easily use the coefficient lookup table k 0 .
c) Calculate the self-stress at the bottom of the element layers and draw the self-stress diagram.
close:
- At the bottom of the conventional foundation:
0
t
tbqu
(h m
L c )
(3.38)
- At the bottom of the element layers:
n
bt bt h (3.39)
i 0 iii 1
d) Calculate the subsidence stress at the bottom of the element layers and draw the subsidence stress diagram.
0
subsidence:
i
oh
gl k
. gl
(3.40)
In there:
+ k 0i : is the stress coefficient at the center of the rectangle (L qu /B qu ; 2z i /B qu ) look up
Table 2.1
0
l i
...
l 2
l 1
L c
h m
+ gl : is the settlement stress at the bottom of the foundation.
a
Q tc
N
tc
0
0
M
tc
0
b
gl
d
c
0
bt
0
bt
0
1
2
...
i
i
...
gl = p
ii
n
z
l n
...
h n
...
h i
...
h 2
h 1
h dl
Figure 3.9: Settlement calculation diagram
e) Check the subsidence stop condition
- The depth satisfies the settlement stop calculation so that:
bt 5 gl
zz
f) Determine total settlement and check settlement
- The final (stable) settlement is determined by one of the following formulas:
following formula:
n
S
i 1
e 1i e 2i h 1 e 1i
(3.41)
i
n
S a oi p i h i
i 1
(3.42)
n
S
i ph
(3.43)
E
In there:
i 1
ii
oh
i
+ e 1i ; is the void ratio corresponding to the load level p 1i = bt ;
+ e 2i : is the void ratio corresponding to the load level p 2i = bt gl ;
ii
+ h i : is the thickness of the i-th element soil layer;
+ pi : is the average subsidence stress of the i-th element layer;
+ a 0i : is the relative compression coefficient of the ith soil layer.
+ i = 0.8 for all soil layers;
+ E 0i : is the total deformation modulus of the ith element soil layer;
- Settlement test conditions: S S gh , S gh is taken according to Table 3.14
Table 3.14: Limit deformation of foundation S gh according to TCVN 10304:2014
Project
Limit deformation of foundation | |||
Differential settlement | Degree | Absolute settlement | |
relative | lean | s gh or settlement | |
s/L | i u | average | |
cm | |||
1. Manufacturer, one-story residential house and multi-storey frame structure buildings: | |||
- Reinforced concrete frame; | 0.002 | - | 10 |
- Reinforced concrete frame with additional bracing | 0.003 | - | 15 |
Reinforced concrete or monolithic roof slab and construction | |||
full block | |||
- Steel frame | 0.004 | - | 15 |
- Steel frame with additional reinforced concrete bracing or | 0.005 | - | 18 |
monolithic roof deck | |||
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2. Houses and buildings do not appear
additional internal force in the structure when subjected to subsidence
deviated
0.006 | - | 20 | |
3. Multi-storey house without structure frame, load-bearing structure is: | |||
- Large panels - Large blocks or bricks are not steel | 0.0016 0.0020 | - - | 12 12 |
- As above, but reinforced, in It has reinforced concrete bracing or monolithic roof as well as monolithic structure house. | 0.0024 | - | 18 |
4. Reinforced concrete tube structure: | |||
- Manufacturer and monolithic structural silo | - | 0.003 | 40 |
on a nail plate; | |||
- As above for assembled structure | - | 0.003 | 30 |
- Silo with independent monolithic structure | - | 0.004 | 40 |
- As above, assembled structure | - | 0.004 | 30 |
5. Chimney height H, m: | |||
H ≤ 100 | - | 0.005 | 40 |
100 < H ≤ 200 | - | 1/(2H) | 30 |
200 < H ≤ 300 | - | 1/(2H) | 20 |
H>300 | - | 1/(2H) | 10 |
6. Hard structural works up to 100m high m, except for the works in points 4 and 5 | - | 0.004 | 20 |
7. Communication antenna project: | |||
- The tower body is attached to the ground. | - | 0.002 | 20 |
- As above, insulation | - | 0.001 | 10 |
- Radio station | 0.002 | - | - |
- Shortwave radio station | 0.0025 | - | - |
- Individual stations | 0.002 | - | - |
8. Overhead power line poles: - Intermediate pillar | 0.003 | - | - |
- Anchors, corner anchors, intermediate corner posts,
0.0025 | - | - | |
pillars in the arc, pillars of the distribution equipment | |||
open style | 0.002 | - | - |
- Special transfer post |
- Note:
+ Settlement limit value s gh is used for construction works on individual foundations on natural (artificial) ground or on pile foundations with individual pile caps (pile strip or pile foundation under column ...).
+ Average settlement limit value
s gh
used for construction works
on monolithic reinforced concrete foundations for continuous structures (crossing strip or raft foundations on natural or artificial foundations, pile foundations with continuous raft caps, raft-pile foundations, etc.).
3.1.9 Determine the working height of the foundation
3.1.9.1 Determining the minimum height of the foundation
- Minimum height of foundation according to experience:
H min = 2d+a (3.44)
In there:
+ d: is the edge or diameter of the pile;
+ a: is the pile section attached to the foundation, take a = (50 ÷ 100).
3.1.9.2 Check height H m under puncture condition
- Penetration tower size:
B xt = b c + 2H 0 (3.44)
L xt = l c + 2H 0 (3.45)
- Force causing penetration:
N gxt
n
i
P tt (outside the penetration tower) (3.46)
i
- Penetration resistance:
N cxt 0.75R bt .H 0 .U tb
N cxt
0.75R bt .H 0 .(b c l c B xt L xt )
(3.47)