JP4022867B2 - Pre-drilling method for soft and viscous ground with high groundwater level - Google Patents
Pre-drilling method for soft and viscous ground with high groundwater level Download PDFInfo
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- JP4022867B2 JP4022867B2 JP2002327520A JP2002327520A JP4022867B2 JP 4022867 B2 JP4022867 B2 JP 4022867B2 JP 2002327520 A JP2002327520 A JP 2002327520A JP 2002327520 A JP2002327520 A JP 2002327520A JP 4022867 B2 JP4022867 B2 JP 4022867B2
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- Prior art keywords
- groundwater level
- sand
- ground
- soft
- excavation
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- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Description
【0001】
【発明が属する技術分野】
本発明は、地下水位が高い軟弱粘性土地盤を掘削する際の前処理の技術に関するものである。
【0002】
【従来の技術】
軟弱粘性土地盤を掘削する際に、掘削域に掘削部を貫通する多数の砂杭を造成し、掘削部の地盤を圧密しその強度を高めて、掘削作業を容易にするとともに、産業廃棄物化した掘削土が生じないようにする技術は、本出願人らによって先に発明され、公知である(特開2000−199220号公報参照)。
【0003】
ところで、前記公知技術を地下水位が高い軟弱粘性土地盤に適用する場合は、地下水位を下げて、掘削作業の容易性が阻害されないようにすることが望ましいが、従来は、地盤にもともと存在する天然の透水層に揚水管を設置して地下水位低下工法を施すようにしていたため、地盤に透水層がない場合や、あっても非常に深いところにある場合は、地下水位を下げることができないか、できても施工やコストの面で大変であった。
【0004】
【発明が解決しようとする課題】
本発明が解決しようとする課題(本発明の目的)は、前記実情に鑑み、地下水位が高い軟弱粘性土地盤を、掘削部の地盤強度が増大し、かつ、掘削部の地下水位が低くなるように前処理する新規技術を提供することにある。
【0005】
【課題を解決するための手段】
前記課題を解決するために、本発明の地下水位が高い軟弱粘性土地盤の掘削前処理方法(以下、本発明の方法という)では、地下水位が高い軟弱粘性土地盤を掘削する際に、掘削域に掘削部を貫通する多数の砂杭を造成して、掘削部の地盤を圧密し、その強度を増大させるとともに、掘削部の下限付近で前記砂杭の径を拡大して、人工的に比較的透水性の高い層を形成し、この層を利用して地下水位低下工法を施し、掘削部の地下水位を下げるようにしている。
【0006】
なお、本発明の方法でいう砂には、砂以外に、砂利、砕石、ドレーン材として使用できる現場発生土、産業廃棄物と見做されない砂類似粒状物を含む。
【0007】
【発明の実施の形態】
以下、本発明の方法の実施態様を図面に基づいて説明すると、図1,図2において、1は地盤、2は土留め壁、3は掘削部、4は掘削部3の下限、5は砂杭、6は砂杭5の拡径部、7は地下水位低下工法用の揚水管である。
【0008】
本発明の方法では、先ず、地盤1の掘削域の外縁に沿って土留め壁2を打設した後、土留め壁2の内方において掘削部3を貫通する多数の砂杭5を造成し、その際、掘削部3の下限4付近で適宜高さに亙って砂杭5の径を大きくして拡径部6を設け、掘削部3の下限4付近に透水性が比較的高い層を形成する。
【0009】
図示の実施態様の場合は、拡径部6をその上端が掘削部3の下限4に一致するようにして設けているが、このようにすると、掘削部3をその下限4まで掘削して底の地盤上に構造物を構築する場合に、構造物の基礎地盤が拡径部6の造成で強化されていることになるので有利である。
【0010】
なお、隣接の砂杭5の拡径部6は離れていてもよいが、成るべく接近しているのが好ましく、図示の場合のように接触していて、隣接の砂杭5が拡径部6のところで接続した状態になっているのが最も好ましい。
【0011】
砂杭5の拡径部6の造成は、一般の締固め砂杭の造成と同様に、砂杭造成用のケーシングを地盤の所定深度まで貫入した後、ケーシングを所定長さ引き抜き、引き抜き跡に砂を充填してから、ケーシングを所定長さ再貫入して砂を締め固めるという態様でなされ、拡径部6の径は、ケーシングの外径とケーシングの引き抜き長と再貫入長とによって定まる(特開平9−158166号公報参照)。
【0012】
なお、砂杭5の拡径部6以外の部分の造成は、締固め砂杭と同様にするか否かは任意であり、締固め砂杭と同様にしないで、ケーシングを連続的に引き抜きつつ、引き抜き跡に砂を充填するという態様で行ってもよい。
【0013】
本発明の方法では、前述のようにして砂杭5を造成した後、拡径部6が設けられている掘削部3の下限4付近の透水性が比較的高い層に揚水管7を設置し、地下水位低下工法を施して、掘削部3の地下水位を下げるが、施す地下水位低下工法はディーブウエル工法とウエルポイント工法の何れでもよい。
【0014】
なお、図2の矢印は、前述の地下水位低下工法実施時における掘削部3の地下水の挙動を示している。
【0015】
本発明の方法における砂杭5の配置態様を例示する図3において、(イ)は、砂杭5が縦横2方向に複数列に列設され、隣接の砂杭5の拡径部6が全て相接している場合、(ロ)は、砂杭5が方形枠状に列設され、隣接の砂杭5の拡径部6が相接している場合、(ハ)は、砂杭5が縦横2方向に列設され、隣接の砂杭5の拡径部6が、一方向では相接しているが、他方向では離れている場合、(ニ)は、砂杭5が縦横2方向に列設され、隣接の砂杭5の拡径部6が全て離れている場合、(ホ)は、砂杭5が方形枠状と対角線状に列設され、隣接の砂杭5の拡径部6が相接している場合であり、この内、(イ)が最も好ましい。
【図面の簡単な説明】
【図1】本発明の方法の実施態様説明用の断面図である。
【図2】本発明の方法の地下水位低下工法実施時の地下水の動きを示す斜視図である。
【図3】(イ)〜(ホ)は、それぞれ本発明の方法における砂杭の配置態様例の平面図である。
【符号の説明】
1:軟弱粘性土地盤、2:土留め壁、3:掘削部、4:下限、5:砂杭、6:拡径部、7:揚水管。[0001]
[Technical field to which the invention belongs]
The present invention relates to a pretreatment technique when excavating a soft viscous ground with a high groundwater level.
[0002]
[Prior art]
When excavating soft viscous ground, many sand piles that penetrate the excavated area are created in the excavated area, the ground of the excavated area is consolidated and its strength is increased, making excavation work easier and making it industrial waste A technique for preventing the excavated soil from being generated has been invented by the present applicants and is well known (see Japanese Patent Application Laid-Open No. 2000-199220).
[0003]
By the way, when applying the above-mentioned known technology to soft and viscous ground with a high groundwater level, it is desirable to lower the groundwater level so that the ease of excavation work is not hindered. Since the groundwater level was lowered by installing a pumping pipe in a natural permeable layer, the groundwater level cannot be lowered if there is no permeable layer in the ground or if it is in a very deep place. But even if it was possible, it was difficult in terms of construction and cost.
[0004]
[Problems to be solved by the invention]
The problem to be solved by the present invention (the purpose of the present invention) is that, in view of the above situation, the ground strength of the excavation part is increased and the groundwater level of the excavation part is lowered in the soft and viscous ground having a high groundwater level. Thus, it is to provide a new technique for preprocessing.
[0005]
[Means for Solving the Problems]
In order to solve the above-described problem, the excavation pretreatment method (hereinafter referred to as the method of the present invention) for soft viscous ground with high groundwater level according to the present invention excavates when excavating soft viscous ground with high groundwater level. A large number of sand piles penetrating the excavation part in the area, consolidating the ground of the excavation part, increasing its strength, and increasing the diameter of the sand pile near the lower limit of the excavation part, artificially A layer with relatively high water permeability is formed, and the groundwater level lowering method is applied using this layer to lower the groundwater level of the excavated part.
[0006]
In addition to the sand, the sand referred to in the method of the present invention includes gravel, crushed stone, on-site generated soil that can be used as a drain material, and sand-like granular material that is not regarded as industrial waste.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the method of the present invention will be described below with reference to the drawings. In FIGS. 1 and 2, 1 is the ground, 2 is the retaining wall, 3 is the excavation part, 4 is the lower limit of the
[0008]
In the method of the present invention, first, the
[0009]
In the case of the illustrated embodiment, the enlarged
[0010]
In addition, although the enlarged
[0011]
The formation of the enlarged
[0012]
It should be noted that the formation of the portion other than the enlarged-
[0013]
In the method of the present invention, after the
[0014]
In addition, the arrow of FIG. 2 has shown the behavior of the groundwater of the
[0015]
In FIG. 3 illustrating the arrangement mode of the
[Brief description of the drawings]
FIG. 1 is a sectional view for explaining an embodiment of a method of the present invention.
FIG. 2 is a perspective view showing the movement of groundwater when the groundwater level lowering method according to the method of the present invention is performed.
FIGS. 3A to 3E are plan views of examples of arrangement modes of sand piles in the method of the present invention, respectively.
[Explanation of symbols]
1: soft-viscous ground, 2: retaining wall, 3: excavation part, 4: lower limit, 5: sand pile, 6: diameter-expanded part, 7: pumping pipe.
Claims (1)
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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JP2002327520A JP4022867B2 (en) | 2002-10-07 | 2002-10-07 | Pre-drilling method for soft and viscous ground with high groundwater level |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
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JP2002327520A JP4022867B2 (en) | 2002-10-07 | 2002-10-07 | Pre-drilling method for soft and viscous ground with high groundwater level |
Publications (2)
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JP2004124674A JP2004124674A (en) | 2004-04-22 |
JP4022867B2 true JP4022867B2 (en) | 2007-12-19 |
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JP2002327520A Expired - Fee Related JP4022867B2 (en) | 2002-10-07 | 2002-10-07 | Pre-drilling method for soft and viscous ground with high groundwater level |
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JP5426321B2 (en) * | 2009-10-29 | 2014-02-26 | 五洋建設株式会社 | Sand pile construction method and improved ground in floating sand compaction pile method |
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