JP4022867B2

JP4022867B2 - Pre-drilling method for soft and viscous ground with high groundwater level

Info

Publication number: JP4022867B2
Application number: JP2002327520A
Authority: JP
Inventors: 博明妹尾; 善一石井; 亮彦鈴木; 智晴大西
Original assignee: Taisei Corp; Fudo Tetra Corp
Current assignee: Taisei Corp; Fudo Tetra Corp
Priority date: 2002-10-07
Filing date: 2002-10-07
Publication date: 2007-12-19
Anticipated expiration: 2022-10-07
Also published as: JP2004124674A

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 excavation part 3, and 5 is sand. Pile, 6 is an enlarged diameter portion of sand pile 5, and 7 is a pumping pipe for groundwater level lowering method.
[0008]
In the method of the present invention, first, the retaining wall 2 is driven along the outer edge of the excavation area of the ground 1, and then a large number of sand piles 5 penetrating the excavation part 3 are formed inside the retaining wall 2. In that case, the diameter of the sand pile 5 is increased to an appropriate height in the vicinity of the lower limit 4 of the excavated portion 3 to provide a diameter-expanded portion 6, and a layer having relatively high permeability near the lower limit 4 of the excavated portion 3. Form.
[0009]
In the case of the illustrated embodiment, the enlarged diameter portion 6 is provided so that the upper end thereof coincides with the lower limit 4 of the excavation portion 3. When constructing a structure on the ground, it is advantageous because the foundation ground of the structure is reinforced by the formation of the enlarged diameter portion 6.
[0010]
In addition, although the enlarged diameter part 6 of the adjacent sand pile 5 may be distant, it is preferable that it is as close as possible, it is contacting like the case of illustration, and the adjacent sand pile 5 is expanded diameter part. The connection at 6 is most preferable.
[0011]
The formation of the enlarged diameter portion 6 of the sand pile 5 is similar to the formation of a general compacted sand pile. After the sand pile formation casing has been penetrated to a predetermined depth of the ground, the casing is drawn out to a predetermined length, and the trace is extracted. After filling the sand, the casing is re-penetrated for a predetermined length and the sand is compacted, and the diameter of the enlarged diameter portion 6 is determined by the outer diameter of the casing, the withdrawal length of the casing, and the re-penetration length ( JP, 9-158166, A).
[0012]
It should be noted that the formation of the portion other than the enlarged-diameter portion 6 of the sand pile 5 is optional whether or not it is made the same as that of the compacted sand pile. Alternatively, the drawing trace may be filled with sand.
[0013]
In the method of the present invention, after the sand pile 5 is formed as described above, the pumping pipe 7 is installed in a layer having a relatively high water permeability near the lower limit 4 of the excavation part 3 provided with the enlarged diameter part 6. The groundwater level lowering method is applied to lower the groundwater level of the excavation part 3. The groundwater level lowering method to be applied may be either the dave well method or the well point method.
[0014]
In addition, the arrow of FIG. 2 has shown the behavior of the groundwater of the excavation part 3 at the time of the above-mentioned groundwater level fall construction method implementation.
[0015]
In FIG. 3 illustrating the arrangement mode of the sand piles 5 in the method of the present invention, (a) shows that the sand piles 5 are arranged in a plurality of rows in two vertical and horizontal directions, and the enlarged diameter portions 6 of the adjacent sand piles 5 are all. In the case where the sand piles 5 are in contact with each other, (b) indicates that the sand piles 5 are arranged in a rectangular frame shape, and in the case where the enlarged diameter portions 6 of the adjacent sand piles 5 are in contact with each other, (c) indicates that the sand pile 5 Are arranged in two vertical and horizontal directions, and the enlarged diameter portions 6 of adjacent sand piles 5 are adjacent in one direction, but separated in the other direction. When the enlarged diameter portions 6 of the adjacent sand piles 5 are all separated from each other, (e) indicates that the sand piles 5 are arranged in a rectangular frame shape and a diagonal shape, and the adjacent sand piles 5 are expanded. This is a case where the diameter portions 6 are in contact with each other, and (A) is the most preferable.
[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

When drilling a ground water level is high soft viscous land board, and construct a large number of sand piles penetrating the excavation drilling zone, compacted and ground of the excavation, with increase its strength, the lower limit of the excavation The diameter of the sand pile is enlarged in the vicinity, a layer with relatively high water permeability is artificially formed, and the groundwater level lowering method is applied using this layer to lower the groundwater level of the excavated part. Pre-drilling method for soft and viscous ground with high groundwater level.