Kazusa Bori - Kazusa Bori

This is a method of digging water wells that has been used since ancient times in the Kazusa region of Chiba Prefecture. The surface equipment includes a wooden tower and a twisted wheel. Several stalks of moso bamboo are tied together at the top of the tower, their bases fixed in place, and their ends facing the well mouth. This is called a bow bamboo. The tool used to dig into the earth's stratum is called a hori-tetsu-kan, a pipe with a rock-crushing blade attached to the end and a valve that opens upwards attached to the top. The hori-tetsu-kan is suspended from the ground surface by twisted bamboo. The twisted bamboo is made by splitting bamboo, cutting it into pieces about 3 cm wide, and joining them together with iron rings and wedges. The twisted bamboo is connected to the end of the bow bamboo, which is made of moso bamboo bundled together, by a digging rope. When the digging rope is pulled down by hand, the hori-tetsu-kan breaks up the earth's stratum, and when the force is released, the hori-tetsu-kan bounces up. When the pipe of the well is full of rock fragments, it is pulled up using a twisting wheel. Several people get into the twisting wheel, turn it, and wrap the twisting bamboo around it. If there are any rock fragments remaining in the well, a pipe with a valve attached to the bottom end called a suction pipe is lowered to collect the rock fragments.

It was first used in 1893 (Meiji 26) to drill oil wells in the Niitsu oil field in Niigata Prefecture, and various improvements were made thereafter, such as to the iron pipe lifting device. In 1935 (Showa 10), a well dug using the Kazusa-bori method at the Yabase oil field in Akita Prefecture struck an oil layer at a depth of 203 meters, causing a massive oil gush, which marked the beginning of the discovery of the Yabase oil field, Japan's largest oil field. Today, the Kazusa-bori method is rarely used.

[Shozo Tanaka]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

千葉県上総地方で古くより行われていた水井戸を掘る掘削法。地表装置としては木製櫓(やぐら)とヒネ車がある。櫓の上部にはモウソウチク数本を束ね、その根本を固定し、その末端が坑口に臨むようにする。これを弓竹という。地層を掘削する器具を掘鉄管といい、パイプの先端に岩石を砕く刃を接着し、その上に上方に開く弁が取り付けてある。掘鉄管はヒネ竹で地表より吊(つ)り下げられる。ヒネ竹は竹を裂き、幅3センチメートルぐらいに削ったものを鉄の輪と楔(くさび)で長く継ぎ合わせたものである。ヒネ竹はモウソウチクを束ねた弓竹の末端と掘綱で結ばれている。掘綱を人力で引き下げれば、掘鉄管は地層を破砕し、力を緩めれば掘鉄管は跳ね上がる。掘鉄管のパイプ中に岩石の破片がいっぱいになれば掘鉄管を引き上げる。引き上げにはヒネ車を用いる。ヒネ車に人が数名入り、車を回してヒネ竹を巻き付ける。井戸に岩石破片が残っているときはスイコー（吸子）という、パイプの下端に弁をつけたものを降ろし、岩石破片を回収する。

　1893年（明治26）に新潟県新津(にいつ)油田の石油井掘削に用いられ、以後鉄管の昇降装置などに種々改良がなされた。1935年（昭和10）秋田県八橋(やばせ)油田で上総掘りで掘った坑井が深度203メートルで油層にあたり、大噴油をおこし、日本最大の油田である八橋油田発見の端緒となった。現在は上総掘りはほとんど使用されていない。

［田中正三］

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