Assessment of Topographic, Geological and Hydrological Conditions

N gxt = 1.8.( 2.5  1.7 ).27.1 =19.5 T;

2

In there:

p tt  p tt

25.8  28.4 2

p

+

tt

2tb

2 max

2

=27.1 T/m

2

p

 p

+

tt tt

2 min

tt max

 p

tt min

)( L m  L xt )

 (p

2L

m

= 12.4  (28.4  12.4)( 2.5  1.7 ) =25.8T/m 2

2.2.5

- Determine the penetration resistance:

N cxt = 0.75.R bt .H 0 . b c  B xt =0.75.100.0.7. 0.2  1.6 = 47.3T

2 2

- Check the penetration condition: N cxt = 47.3T ≥ N gxt = 19.5 T

- So the selected foundation height satisfies the penetration condition.

2.2.8 Steel calculation

2.2.8.1 Calculation of reinforcement according to the side direction L m

- Bending moment along the side L m

M  1 .p tt .B .(L  l ) 2 = 1 .24,9.1,8.(2.5  0.3) 2 = 27.1 Tm

L8 1tb mmc8

In there:

p

 p

+

tt tt

1 min

tt max

tt min

)( L m  l c )

 (p

 p

2L

m

= 12.4  (28.4  12.4)( 2.5  0.3) =21.4 T/m 2 .

2.2.5

p

+

1tb

p tt  p tt



1 max =

2

21.4  28.4

2

=24.9 T/m 2 .

- Steel reinforcement calculated according to side direction L m

tt M

M 27.1.10 52

A sL LL = 15.4 cm

 R s H 0 0.9.R s H 0 0.9.2800.70

- Reinforcement steel structure according to L m direction

A



ct

sL min

.B m

.H 0

= 0.1%.180.70 = 12.6 cm 2

- Steel reinforcement arranged in the direction of edge L m

A sL = max ( A ct ; A tt ) = 15.4 cm 2

sL sL

- Selecting steel arrangement  12 we have: f a

 1.2 .3.14  1.13 cm 2

2

4

- Total number of steel bars in L m direction :

n  A sL = 15.4 = 14 bars

f

a

L 1.13

- Reinforcement step in L m direction :

@ L =

B m  100  1800  100 = 130

14  1

- So the steel is arranged along the edge L m direction :  12@130

2.2.8.2 Calculation of reinforcement according to side direction B m

- Bending moment along side B m

M  1 .p tt .L .(B  b ) 2 = 1 .20,4.2,5.(1.8  0.2) 2 = 16.3 Tm

B 8 tb mmc8

In there:

tt p tt  p tt

12.4  28.4 2

+ p tb min max=

2

=20.4 T/m .

2

- Steel reinforcement calculated according to side direction B m

tt M

M 16.3.10 52

A sB BB = 9.2 cm

 R s H 0 0.9.R s H 0 0.9.2800.70

- Steel reinforcement is constructed according to the direction of edge B m

A



ct

sB min

.L m

.H 0

= 0.1%.250.70 = 17.5 cm 2

- Steel reinforcement arranged in the direction of edge B m

A sB = max ( A ct ; A tt ) = 17.5 cm 2

sB sB

- Selecting steel arrangement  12 we have: f a

 1.2 .3.14  1.13 cm 2

2

4

- Total number of steel bars in direction B m :

n  A sB = 17.5 = 16 bars

f

a

B 1.13

- Reinforcement step in direction B m : @ B =

L m  100  2500  100 = 160

- So the steel is arranged along the edge direction Bm:  12@160

-

16  1

N

tt 0

Q tt tt

H m

1  @130

0 M 0

h m

 @1602

p tt = 12.4T/m 2

p

min

B

L

tt

p

m

tb

.p tt 1

tt max

=28.4T/m 2

c

b c

B m = 1.8m

2  @160 l

1 @130

L m = 2.5m

.p tt

L

B m .p tt

B m 1

max

Figure 2.12: Steel calculation diagram

2.2.9 Drawing representation

40Þ

Column steel

± 0.000

300

-0.300

NATURAL GROUND

1250

Þ8@100 3

Tripod

-2,300

2000

500

2 Þ12@160

50

300

400 50

Þ12@130 1

100250

BT STONE LINING 4x6 M100 100 THICK

100

1250 1250

2500

BB CROSS SECTION

TL:1/25

100

900

100

400

1800

300

50 1 50150 50

B 50 200 200 50 B

900

Þ12@160 2

100

Þ12@130 1

100 1250 1250

2500

100

NOTE:

NAIL (1800x2500)

TL:1/25

* STONE CONCRETE 10X20 GRADE 250 (DURABILITY LEVEL B20)

* STEEL < 10 .Rs = 2250 kg/cm2 (AI STEEL)

* STEEL >= 10 .Rs = 2800 kg/cm2 (AII STEEL)

Figure 2.13: Drawing showing single foundation

Chapter 3

PILE FOUNDATION DESIGN

3.1 LOW PILE FOUNDATION DESIGN PROCEDURE

3.1.1 Determine the load on the foundation

- The load on the foundation can be at the natural ground level or the top of the foundation. When determining the load on the foundation, it is necessary to determine the load combination for the most dangerous calculated internal force as follows:

 N tt

 N tt

 N tt

 M

max

practice

practice

 M

TT

 Q tt

or

tt max

 Q tt

or

TT

 M

 Q tt

(3.1)

practice

practice

max

- The standard is divided into 2 types of loads:

+ Standard load: Used for calculation and testing according to TTGH II.

+ Design load: Used for calculation and testing according to TTGH I.

 N tt  Ntc

0 0

0

 M tt

 Q tt

= n  M tc

0

 Q tc

(3.2)

0 0

with n = 1.15 being the average overload factor.

3.1.2 Assessment of topographic, geological and hydrological conditions

3.1.2.1 Terrain conditions

- Current terrain conditions of the construction site at a scale of 1/500 need to be clarified:

Before and after filling;

- Underground pipes, equipment, ... passing through the construction site.

3.1.2.2 Synthesis of geological and hydrological survey data for design

Based on the "Construction geological survey report" the designer

Synthesize necessary data for foundation design calculations:

- Field test parameters:

+ Penetration test: static penetration test (CPT) and standard penetration test (SPT);

+ Field test (if any): Static axial compression test,

Field compression test, horizontal compression test.

- Laboratory test parameters:

+ Physical indicators: Types of bulk density  , specific gravity  , humidity W, limits

yield limit W l , plastic limit W p , saturation, porosity, void ratio and other parameters

Numbers to evaluate soil condition such as: relative density D, consistency I l , index

plastic I p .

+ Strength indicators: Internal friction angle  , adhesion force c;

+ Deformation indicators: Total deformation modulus E 0 , compression coefficient a, relative compression coefficient a 0 , compression-settlement relationship charts such as: e - p, a 0 – p; a - p,..;

- Groundwater level (if any) is shown in geological cylinders. Design work must take into account seasonal and temporal changes in groundwater level.

- Geological cross-section, borehole cylinders, borehole layout plan.

3.1.3 Select the depth of the base of the platform (h m )

- Normally, the depth of the pile foundation should not be too shallow or too deep. The depth of the pile foundation is usually chosen as h m = (1.0 – 3.0) m and satisfies the condition h min .

Natural ground

Q tt

tt

N

0 tt

0 M 0

h m

E p

L c

Figure 3.1: Depth of pile foundation

- For low pile foundations, when choosing the depth of the foundation, it is important to note that h m is large enough so that the shear force Q tt 0 is balanced with the soil pressure, meaning:

0

γB m

2Q tt

φ

In there:

h m  h min = 0.7tg(45 0 - )

2

(3.3)

+  : Unit weight of soil on the foundation bottom;

+  : Internal friction angle of soil on the bottom of the foundation;

+ B m : Foundation width, initially can assume B m = 5d (d: edge or line)

pile glass).

+ Q tt 0 : Shear force transmitted to the foundation.

3.1.4 Selection of pile type, pile material, construction method and expected depth of lowering

pile

3.1.4.1 Selection of pile type, materials and construction methods

a) Concrete piles

- Reinforced concrete square piles are usually constructed by driving or

pressed, bored pile: Grade  250 (B20);

- Prestressed centrifugal concrete piles: Grade  600 (B50);

b) Pile reinforcement

- Reinforced steel: is ribbed steel, commonly used types:

+ AII; AIII; AIV;

+ SD295; SD390; SD490;

+ CB300; CB400; CB500-V;

- Belt: Usually use AI; CI smooth steel

Table 3.2: Design strengths of concrete R b, R bt when calculating according to the first limit states, MPa (according to TCVN 5574:2012)

Status

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