1. Investigation of Consolidation Promoting Effect by Field and Model Test for Vacuum Consolidation Method
Nagasaki University
H.Mihara
Y.Tanabasi
Y.Jiang
T.Shiono
Maruyama Industry Co,Ltd
真空圧密工法の室内模型試験と試験施工による圧密促進効果の解明と題しまして、長崎大学三原が発表させて頂きます。
Thank you Mr.chairman.
Ladies and gentlemen, my topic is investigation of consolidation promoting effect by field and model test for vacuum consolidation method.

2. Background of research
soft ground Reinforcement
Pre-loading method
Deep mixing stabilization method
Vacuum consolidation method
Social demand
Less cost
Less constructing period
Improvement of vacuum consolidation technology
Construction cases using vacuum consolidation method are increasing
Vacuum consolidation method
まず初めに研究背景です。
近年、様々な軟弱地盤対策技術が日本で普及しています。
As the background of this research, a variety of countermeasures for soft ground spread in Japan recently.
その中で社会的要求や真空圧密技術の向上に伴い、真空圧密工法による施工事例が増加しています。
Construction cases using vacuum consolidation method are increasing by the reasons of social demand and improvement of vacuum consolidation technology.
しかし、挙動予測や施工管理は経験的手法に依存し、又周辺地盤への影響が拡大しているのが現状です。
However, behavior prediction and site management remain empirical, and the influence on peripheral ground is large.
Behavior prediction and site management remain empirical
Influence on peripheral ground is large

3. Purpose of research Model test Field investigation
Countermeasure for peripheral ground hasn’t been specified
Influence range of vacuum consolidation remains uncertain
Behavior prediction of the ground remains empirical
Effect of vacuum-filling combined consolidation method hasn’t been clarified
Model test
Behavior prediction of the ground remains empirical
Effect of vacuum-filling combined consolidation method hasn’t been clarified
Prediction of behavior of the ground remains empirical
Effect of vacuum-filling combined consolidation method hasn’t been clarified
Field investigation
Countermeasure for peripheral ground hasn’t been specified
Influence range of vacuum consolidation remains uncertain
次に本研究の目的です。
周辺地盤対策工の未確立と真空圧影響範囲の未把握という課題を解決するために試験施工を実施しました。
As the purpose of this research, field investigation was carried out to solve the problems that the countermeasure for peripheral ground hadn’t been specified and the influence range of vacuum consolidation remained uncertain.
又、経験的手法による実現場挙動予測と真空圧密併用載荷盛土の効果の未解明という課題を解決するために室内模型試験を行いました。
Moreover, model test was carried out to solve the problems that the behavior prediction of the ground remained empirical and the effect of vacuum-filling combined consolidation method hadn’t been clarified.
それら試験施工と室内模型試験から真空圧による圧密促進効果の解明を図ることとします。
The consolidation promoting effect of vacuum consolidation method is clarified by field investigation and model test.
Investigation of consolidation promoting effect of vacuum consolidation method

4. Outline of field investigation
Construction period
20 November. 2003～
Improved area
About 3300m2
Improved depth
About 12m
Loading vacuum pressure
About -68kPa
Construction spot panorama
試験施工について説明します。
At first, field investigation is explained.
試験施工は佐賀県で実施された。
Field investigation was carried out in Saga province, Japan in 2003.
写真は施工地点の全景であり、試験施工は第4工区で実施されました。
A photograph is construction spot panorama, it was carried out in 4th construction field.
試験工区の概要は、工期は平成15年11月20日から、改良面積は約3300m2、良深度は約12m、載荷真空圧力は-63kPaとなっています。
Construction period is from 20 November. 2003, improved area is about 3300m2, improved depth is about 12m, Loading vacuum pressure is about –68kPa.
赤い部分に各種計器を設置しました。
Various instruments were installed in red zone.
17.6m
187m
162
160
158
166
164
4th construction field

5. Setting positions of instruments
No.164
Center of improved area
　　water-level observation well
W-1
GL‐13.00m
GL‐6.00m
W-2
8.8m
8.0m
2.4m
W-1
GL‐13.00m
　　water-level observation well
　　ground inclinometer
　　differential settlement gauge
　　pore water piezometer
2.0m
P GL‐3.50m
P GL‐8.50m
P GL‐3.50m
P GL‐8.50m
‐8.50m
P-1-3
‐5.20m
P-1-2
GL‐3.50m
P-1-1
‐13.00m
S-3
‐11.30m
S-2
GL‐5.10m
S-1
GL‐6.00m
W-2
road
　　differential settlement gauge
GL‐5.10m
S-1
‐11.30m
S-2
‐13.00m
S-3
　　ground inclinometer
　　pore water piezometer
GL‐3.50m
P-1-1
‐5.20m
P-1-2
‐8.50m
P-1-3
P GL‐8.50m
P GL‐3.50m
P GL‐8.50m
P GL‐3.50m
End of improved area
3.8m
図は、試験工区の計器設置平面図です。
The setting positions of instruments are shown.
水位観測井戸は2箇所、地中傾斜計は1箇所、層別沈下計は3箇所、間隙水圧計は7箇所設置しました。
Water level observation well was installed at two places, ground inclinometer was installed at one place, differential settlement gauge was installed at three places, pore water piezometer was installed was installed at seven places.
また、クラック制御孔を改良域端部から2ｍ程度離れた位置に設置しました。
Moreover, crack control hole was installed in the position left about 2m from the end of improved area.
Crack control hole
2.0m
Crack control hole

6. Construction situation
Situation of countermeasure for peripheral ground
Situation of operation of vacuum pump
Before vacuum pump operating
Installation of crack control hole
To pre-estimate the influence on peripheral ground
20 November ～26 December. 2003
Vacuum pump operating for 9 hours a day
7 December. 2003
Installation of relief well
To reduce the influence on peripheral ground
5 January ～
Vacuum pump operating for all the day
試験工区の施工状況についてです。
This page explains construction situation.
真空ポンプ稼動前にクラック制御孔を設置しました。
Crack control hole was installed before vacuum pump was operated.
更に、周辺地盤への影響を考慮して平成15年11月20日～平成15年12月27日までは真空ポンプを昼間のみ9時間稼動させました。
In addition, vacuum pump was operated for 9 hours from 20 November to 26 December to pre-estimate the influence on peripheral ground
しかし、周辺地盤への影響が見られたので平成15年12月7日からリチャージウェルを設置しました。
However, relief well was installed from 7 December because the influence on peripheral ground occurred.
これにより周辺地盤への影響の減少が見られたので、平成16年1月5日からは真空ポンプを24時間稼動させました。
As a result, the influence on peripheral ground decreased.
Therefore, vacuum pump was operated all the day from 5 January. 2004

7. To place crack control hole for monitoring
End of improved area
30cm
Sand layer
30cm 2m
Improved area 6m
15cm in diameter 6m
図はクラック制御孔についての概要図です。
Crack control hole is shown.
改良域端部から2m程度離れた位置に、直径15cm、高さ6mの孔を30cm間隔で形成することにより、クラックの発生する場所を制御します。
The hole is 15cm in diameter and 6m in height, and, it is formed at intervals of 30cm in the position left about 2m from the end of improved area to monitor the crack. 2m
15cm in diameter

8. Relief well To prevent seepage from peripheral ground
Supply of the water
To prevent seepage from peripheral ground
Water level observation well W-2
End of improved area
30cm
Improved area 6m
Sand layer
次にリチャージウェルについて説明したいと思います。
Relief well is shown.
中間砂層からの水の流入が周辺地盤への影響の原因として考えられます。
The seepage from peripheral ground is thought as the cause of the influence on peripheral ground.
そこで、先程のクラック制御孔に水を供給することで周辺地盤からの水の流入を阻止し、周辺地盤への影響を減少させます。
So relief well prevents the seepage by supplying the water into crack control hole, and the influence on peripheral ground decreases.
また、水位観測井戸W-2を設置し、地下水位状況を計測しました。
Moreover, water level observation well W-2 was installed, and the situation of groundwater level was measured. 2m
15cm in diameter

9. Settlement Settlement (cm) Time (day)
Vacuum pump operating all the day ① ②
-5.1m
S-1
-11.3m
S-2
-13.0m
S-3
S-3(GL-13.0m)
layer②
Settlement (cm)
layer①
ground surface
次に層別沈下計より計測された沈下量から算出した区間圧縮量の経時変化を示します。
The variation of settlement with time is shown.
沈下計S-3には全く沈下が見られないのでS-3以深には真空圧密の影響はないと考えられます。
Vacuum consolidation didn’t take its effect under the depth of S-3 because no settlement was observed at settlement gauge S-3.
①層と②層を比較してみると、両層とも同等の沈下が生じており、深層にまで圧密促進効果が促進されていると言える。
As compared layer① and layer②, it is believed that the consolidation promoting effect of vacuum consolidation is promoted to deep soil because both layer① and layer② sink similarly.
Time (day)
Installation depth of differential settlement gauge

10. Groundwater level Water pressure (kPa) Measuring day (date)
W-1(Inside of improved area GL-13.0m)
The water is supplied into relief well
Vacuum pump operating all the day
次に地下水位の経時変化を示します。
The variation of groundwater level with time is shown.
W-1には真空ポンプの稼動の有無に関わらず明確な反応は見られないので、深度13m以深には真空圧密の影響はないと言えます。
Vacuum consolidation is thought no effect under the depth of 13m because the water pressure at W-1 has no response to the operation of vacuum pump.
W-2には真空圧による地下水位の変化が見られます。
The intense variation of groundwater level was observed at W-2.
しかし、リチャージウェルを設置してからはその効果が明確に現われています。
However, relief well took its effect after the water was supplied into it.
W-2(Outside of improved area GL-6.0m)

11. Summary of field investigation
Countermeasure for peripheral ground
Deformation on peripheral ground is reduced
Installation of relief well as countermeasure for peripheral ground
Installation of relief well as countermeasure for peripheral ground
Influence range of vacuum consolidation
There was no reaction both differential settlement gauge S-3 and water level observation well W-1
There is no effect of vacuum consolidation under improved depth
There was no reaction both differential settlement gauge S-3 and water level observation well W-1
試験施工のまとめです。
周辺地盤沈下対策としてリチャージウェルを設置することにより、周辺地盤の変状の軽減を図ることが出来ました。
As the summary of field investigation, the deformation on peripheral ground could be reduced by installing relief well as countermeasure for peripheral ground.
また層別沈下計、水位観測井戸共に反応が無かったことから、改良深度以深の層には影響しないという知見が得られました。
Moreover, it is thought that there is no effect of vacuum consolidation under improved depth because there was no reaction both differential settlement gauge S-3 and water level observation well W-1

12. Model test Triaxial chamber General drawing of Experimental apparatus
Loading device
Displacement gauge
Load cell
Triaxial chamber
General drawing of Experimental apparatus
Operation panel
Triaxial chamber
Pore water gauge
Specimen
Drain
Vacuum pressure
–68kPa
Lateral pressure
Axial force
Water
これより、室内模型試験について説明します。
Next, model test is explained.
図は試験装置の全体図です。
This figure shows the general drawing of experimental apparatus.
真空ポンプにより真空圧-68kPaを供試体に作用させ、図のような圧力を加え、供試体から水を排水させます。
The vacuum pressure of –68kPa was loaded on specimen.
The axial force and the lateral pressure loaded on specimen were the initial stress of each specimen, the water was drained from specimen.

13. Outline of sample Upper layer Lower layer
Result of laboratory soil testing left 2m from sample
Result of laboratory soil testing left 2m from sample
depth
（GL－m）
specimen
No.
water content
Wn （%）
porosity e0
degree of saturation
Sr (%)
unconfined
compressive
strength
qu (kN/m2)
2.00～2.90
T-2
147.1
3.816
100
21.1
3.00～3.90
T-3
136.3
3.585
26.5
4.00～4.90
not adopted
107.2
2.875
99.2
28.3
6.00～6.90
T-6
119.2
3.132
45.1
7.00～7.90
T-7
125.7
3.318
38.5
8.00～8.90
T-8
115.1
3.008
48.9
9.00～9.90
T-9
116.5
3.088
44.1
10.00～10.90
90.0
2.444
98.9
64.7
11.00～11.90
67.4
1.782
60.7
7.4㎝
15cm
Specimen
Upper layer
Lower layer
試料の概要です。
The outline of sample is shown.
本試験で使用した試料は、平成15年に佐賀県小城郡で行った実地盤試験施工の際に不撹乱採取した有明粘土を使用した。
The sample used in this research is the undisturbed Ariake soft clay taken in the field investigation.
この土質試験結果は室内模型試験で使用した試料から2m離れた地点のものです。
This table shows the result of laboratory soil testing left 2m from it.
本試験では、深度3.00～3.90mと深度7.00～7.90mの試料を用いた。
The sample were used, which was the depth of 3.00m-3.90m and 7.00m-7.90m.
深度5.00m付近に存在する中間砂層より上方を上層、下方を下層と呼ぶこととする。
The sample above and under the depth of 5.00m are called upper layer and lower layer.

14. Vacuum pressure transmitting rate (Upper layer)
Time (day)
Vacuum pressure transmitting rate (%)
Field(GL-3.5m)
Model(2003)
Model(2004)
Vacuum pressure transmitting rate
Pore water pressure
Vacuum pressure
×100(%)
40%
The variation of vacuum pressure transmitting rate of upper layer with time is shown.
Vacuum pressure transmitting rate is calculated by this equation.
About 40% tolerance was showed between model test of 2003 and field investigation.
However, model test of 2004 accord with field investigation well.

15. Vacuum pressure transmitting rate (Lower layer)
Model(2003)
40%
Field(GL-8.5m)
Model(2004)
The variation of vacuum pressure transmitting rate of lower layer with time is shown.
Lower layer also had about 40% tolerance between model test of 2003 and field investigation.
Moreover, model test of 2004 accord with field investigation as well as upper layer.
Time (day)

16. To estimate the limit height of filling
Stage loading test
Purpose
To estimate the limit height of filling
Simulation of rapid fill on soft ground when vacuum-filling combined consolidation method used
Simulation of rapid fill on soft ground when vacuum-filling combined consolidation method used
Outline of stage loading test
Vacuum pressure of –68kPa is acted on specimen
Vacuum pressure of –68kPa is acted on specimen
Stage load of 17.7kPa(Height of filling of 1.0m) is added
Vacuum pressure transmitting rate reaches 60%
Next, stage loading test is explained.
As the purpose of the test, the limit height of filling is estimated by simulating the rapid fill on soft ground when vacuum-filling combined consolidation method used.
As the outline of stage loading test, the vacuum pressure of –68kPa was acted on specimen, and then the stage load of 17.7kPa was added when vacuum pressure transmitting rate reached 60%.
After the excess pore water pressure dissipated, it was added when vacuum pressure transmitting rate reached 60% again.
This process was repeated until specimen failed.
Stage load of 17.7kPa(Height of filling of 1.0m) is added
Stage load is added when vacuum pressure transmitting rate reaches 60% again
Failure
Failure

17. Test result (GL-7.0m～GL-7.9m)
Load・Pressure (kPa)
Strain・Vacuum pressure transmitting rate (%)
Time (min)
4630min
460.1kPa
Failure
Vacuum pressure transmitting rate
Volumetric strain
177kPa
4180min
Load
Axial strain
The test result of stage loading test is shown.
The sample of the depth of 7.0m-7.9m was used in this test.
Stage load kept being added until 4180 minutes but specimen didn’t fail.
However, when the stage load was added at 4630 minutes, where the load was 460.1kPa and 2.5 times of design load.
Vacuum pressure

18. Prediction of behavior of the ground
Summary of model test
Prediction of behavior of the ground
Pore water pressure of the ground can be forecasted by model test
Vacuum pressure transmitting rate of 2004 accords with field investigation well
Vacuum pressure transmitting rate of 2004 accords with field investigation well
Effect of vacuum-filling combined consolidation method
Limit filling load is circumscribed within range of 177kPa～460.1kPa
Fill of 10m or more is allowable on the ground since load of 177kPa is equivalent to pressure of 10m filling high
Limit filling load is circumscribed within range of 177kPa～460.1kPa
As the summary of model test, the pore water pressure of the ground can be forecasted by model test because the vacuum pressure transmitting rate of 2004 accords with field investigation well.
Moreover, limit filling load was circumscribed within the range of 177kPa-460.1kPa.
Therefore, the fill of 10m or more is allowable on the ground since the load of 177kPa is equivalent to the pressure of 10m filling high.

19. Conclusion Field investigation Model test
Pore water pressure of the ground could be forecasted by model test
Fill of 10m or more is allowable on the ground when vacuum-filling combined consolidation method used
Pore water pressure of the ground could be forecasted by model test
Fill of 10m or more is allowable on the ground when vacuum-filling combined consolidation method used
A effective countermeasure for peripheral ground was specified
Influence depth of vacuum consolidation could be estimate
A effective countermeasure for peripheral ground was specified
Influence depth of vacuum consolidation could be estimate
As the conclusion of this research, a effective countermeasure for peripheral ground could be specified by field investigation.
Moreover, the influence depth of vacuum consolidation could be estimate.
On the other hand, the pore water pressure of the ground could be forecasted by model test.
Moreover, the fill of 10m or more is allowable on the ground when vacuum-filling combined consolidation method used.
From these, consolidation promoting effect of vacuum consolidation method could be clarified partially.
Consolidation promoting effect of vacuum consolidation method could be clarified partially

20. Thank you for your attention.

21. Vacuum consolidation method
Flow of drainage Direction of force
Horizontal drain
Vertical drain
Airtight sheet
Perforated drainage pipe
Vacuum pump

22. Pore water pressure Pore water pressure (kPa) GL-8.5m GL-3.5m
Improved area
End of improved area
Vacuum pump operating all the day (1/5)
Vacuum pump operating for 9 hours (11/20)
Pore water pressure (kPa)
Measuring day (date)
GL-8.5m
1.8m
GL-3.5m
グラフは間隙水圧の経時変化を示しています。
The variation of pore water pressure with time is shown.
緑色の部分は深度8.5m、茶色の部分は深度3.5mの間隙水圧である。
Green zone is the pore water pressure of the depth of 8.5m, brown zone is the one of 3.5m.
改良域内では、真空ポンプ稼動後間隙水圧の低下が確認出来ます。
Pore water pressure began to decrease inside improved area after vacuum pump operating for 9 hours
また真空ポンプを24時間連続稼動にしてからは、顕著な間隙水圧の低下が見られます。
Moreover, the rapid falling of one was observed after vacuum pump operating all the day.
改良域外では、真空ポンプ稼動後間隙水圧の低下は見られなかった。
On the other hand, the falling of pore water pressure was not observed outside improved area after vacuum pump operating for 9 hours.
しかし真空ポンプ24時間連続稼動、クラック制御孔外では反応が特に見られないのに対し、クラック制御孔内では間隙水圧の低下が確認出来る。
However, the falling of one was observed inside crack control hole after vacuum pump operating all the day, whereas no variation outside crack control hole.
Crack control hole
1.8m
Setting position of pore water piezometer