Last week’s post covered the most primitive method of foundation used in minka, the horidate-bashira method, in which timber posts are set directly into shallow excavations. It also briefly touched on a later improvement over that method: ishiba-date (石場建て), the practice of using foundation stones (礎石, soseki) under the timber posts. This week I would like to look at this method in more detail.

In many cases, the foundation stones used in minka are used in their natural state, without any working or dressing. Typically these are large, attractive river stones known as tama-ishi (玉石) or gorotaishi (ごろた石), whose edges have been rounded smooth by centuries of water action.

Natural, unworked river stones used as post foundations in a *minka.*

Another example, here below a raised floor.

On important buildings such as temples, the head or ‘column seat’ of the stone, that part visible above ground, would be finely worked into a circular pad, resulting in a composition very similar in appearance to the base of one of the simpler orders of classical Greek or Roman columns. With the passing of time, the soseki of abandoned temples, known as ‘temple stones’ (伽藍石, garan-ishi), became particularly prized for use in landscape gardens. Worked soseki can also occasionally be found amongst more recent and ‘high-end’ minka, where they are called ‘shoe stones’ (沓石, kutsu-ishi).

A foundation stone, presumably in a temple, with its ‘column seat' worked into a disc shape.

In order to lay the foundation stone, the first stage of foundation construction is no different for minka than it is for concrete foundations in modern buildings: the ground is excavated down to the depth of the bearing layer (jiban 地盤 or jiyama 地山), i.e. the level at which the soil is deemed hard enough or well-structured enough to support the weight of the building. This stage is known as ne-giri (根伐り) or ‘root cutting’. In minka, foundation construction in general is called chigyou (地形); isolated pad footings for individual posts are called tsubo-gata-gyou (壺型形) or ‘pot-form’ footings, and strip footings are known as nuno-chigyou (布地形) or ‘bolt-form’ (literally ‘cloth-form’) footings.

The foundation stone does not bear directly on the soil at the base of the excavation: a layer of large, split stones known as wariguri-ishi (割栗石) are first laid in the pit, oriented in a standing position, i.e. with their long axis vertical (koba-date, 小端建) so that their pointy ends penetrate into the bearing layer. These stones are then usually covered by a layer of sharp gravel. Again, this practice is strikingly similar to that followed in modern concrete foundation construction.

Various methods of founding stones on *wariguri-ish*i. Top: an isolated timber post on a foundation stone. Bottom left: a continuous timber groundsill on intermittent foundation stones. Bottom right: a continuous timber groundsill on a continuous dressed stone strip footing.

Compaction (chizuki 地搗き ‘earth pounding’ or touzuki 胴搗き ‘trunk pounding’) is achieved by the use of various implements: at the smaller scale ranging from a simple disc-shaped ‘mortar stone’ (usu-jou no ishi 臼状の石) with ropes tied around it, called a ‘turtle pounder’ (kame-no-ko-zuki 亀の子搗き), ‘flat turtle’ (hira-game平亀) or ‘flat octopus’ (平蛸 hira-dako); or a hard timber ‘trunk’ (tou 胴) with two or four wooden handles, for use by as many men, called variously an ‘octopus trunk pounder’ (tako-tou-tsuki 蛸胴搗き) ‘small octopus’ (ko-dako 子蛸 or ‘big octopus’ ou-dako 大蛸) On larger projects, a method known as yoitomake (ヨイトマケ) was employed: either ‘oar trunk pounding’ (yaguratou-tsuki 櫓胴搗き) or ‘pole trunk pounding’ (shinboutou-tsuki 真棒胴搗き), where a large timber trunk is suspended from a tripod or scaffold by means of pulleys and ropes.

An illustration of the various implements used for foundation compaction.

The shinboutou-tsuki method required the participation of the whole village: the villagers would raise the trunk by pulling on the ropes, then release the ropes in unison, dropping it into the hole. Naturally work songs and chants arose to aid the villagers in the co-ordination of their actions and to relieve the monotony of the work; these songs and chants show great variation across the different regions of the country.