7_engineering geology and soil mechanics_chapter 8_consolidation

固結

剪切破壞

過度沉降

淺地基

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ENGINEERING GEOLOGY AND SOIL MECHANICS

8.1

沉降不均勻整體

最重要的類型

土層

土層剖面

土壤性質

dimensions

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恆載

不等

不均勻整體沉降

適用性,使用極限

居住

複雜,精心製作的1. 2. 3.

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建築上

彈性(瞬時)沉降應變反應

固結沉降體積應變

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泊松比

自由排水

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滲透性

彈性沉降

逐步的

主固結

二次固結

持續荷載

水動力滯後

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滑移重新定向

卡爾太沙基

skeleton 骨架

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盒彈簧

spaces

(loosely compacted soil)

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Refer to Fig. 9.6a

Refer to Fig. 9.6b

Refer to Fig. 9.6c

Refer to Fig. 9.6d

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達西定律

1.

2.

3.

4.

5.

6.

7.

v=ki

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Drainage

SAND

CLAY

SAND

Ground level

G.W.T.

Foundation stress

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Pore water

固結儀、壓縮儀試驗

體積壓縮係數

固結係數

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Rectangle

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Rectangle

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Administrator

Text Box

0.5649

Administrator

Text Box

0.584-0.5649

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先期固結壓力先期固結土

Time factor, a pre-determined dimensionless numberbased on different presumed drainage conditions

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Rectangle

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Worked Examples

1.

2.

mv

cv

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Worked Examples

1

Cc

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Worked Examples

Initial Final FinalInitial

Vv

Vs e=

Vs:unchanged

Important assumption

A A

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Worked Examples

h0

h

e0

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Worked Examples

Relative to thereading at the end ofthe test

Alternative mehtod of determination of mv

0.067dh=

We only know this value

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Worked Examples

Before excavation for and construction of foundation

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Worked Examples

Solution:

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After excavation for and construction of foundation

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Worked Examples

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IVE(TY) Chapter 9_Consolidation Soil Mechanics & Geology

Soil Mechanics_Chapter 9_Class Practice_2011 Page 1 Prepared by Jimmy Yan

Chapter 9_Consolidation Class Practice 1 A layer of sand 5 metres deep overlies a 6-metre thick clay. The ground water

level is at the ground surface at the top of the sand layer. A 4-metre thick fill is then placed on the top of the sand layer over a wide area. The properties of the materials are:

Sand: unit weight, �sat = 19 kN/m3 Clay: unit weight, �sat = 20 kN/m3 Coefficient of volume compressibility, mv = 2.3 x 10-4 m2/kN Fill: unit weight, �d = 20 kN/m3

(i) Determine the vertical effective stress at the centre of the clay layer:

� before the layer of fill is placed � immediately after the fill layer is placed � after the fill is placed and all drainage in the clay layer is complete

(ii) Calculate the final primary consolidation settlement in the clay layer.

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75 kN/m2

75 kN/m2

155 kN/m2

0.11 m

Chapter 8_Consolidation


Soil Mechanics_Chapter 8_Class Practice_2011

固結度

時間因數

(Expressed in terms of %)

LOADINGLOADING

is related toso-called time factor Tv, a dimensionless number

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雙排水層(Theoretical)

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CHAPTER 8

Take Case 1 as an example as referred to Figure 9.10

(0.197)

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Ans: 80 mm

Ans: 7.84 months

Ans: 20 mm

Ans: 18.8 months

Ans: 1.54 x 10-10 m/s

100 kPa

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CHAPTER 8Class Exercise: Question 1

IVE(TY) Chapter 9_Consolidation Soil Mechanics & Geology

Soil Mechanics_Chapter 9_Class Practice_2011 Page 2 Prepared by Jimmy Yan

Chapter 9_Consolidation Class Practice 2 A uniform vertical stress of 200 kN/m2 is applied on the ground surface of a site with underground profile as shown in Figure 2. The properties of the clay layer are as below:

Coefficient of volume change, mv = 9.71 x 10-4 m2/kN Coefficient of consolidation, cv = 2.1 x 10-8 m2/s.

Find: (i) the permeability of the clay layer in m/s; (ii) the total consolidation settlement of the clay layer due to the 200 kN/m2

increase of effective vertical stress; (iii) the time required (in days) for 90% of the settlement to complete if the time

factor, Tv, for 90 % consolidation is 0.848. (iv) Suggest two methods to speed up the rate of consolidation settlement.

Figure 2

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2.04 x 10-10 m/s

1.17 m

4206 days



Soil Mechanics_Chapter 8_Class Practice_2011

Ans: 250 mmAns: 2.21 months

Ans: 57 mm

Ans: 8.9 months

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Class Exercise: Question 2

7_engineering geology and soil mechanics_chapter 8_consolidation

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