Narrow-space excavations.
Ways of spreading narrow-space excavations: a) in essence succinctly, b), c) in the soil not very cohesive and loose, d) complex way, e) in loose soil with the use of vertical logs, f) in loose ground - mining method.
Narrow-space excavations, which are used for deeper foundation or sewage works, can be secured using the braces shown in the drawing. In the case of compact soil - easily sustained - the expansion of the excavation consists of lining the walls of the excavation with single boards or several boards together (in groups), at fairly considerable intervals, the smaller ones at the bottom of the trench and the larger ones at the top.
Between the formwork of the excavation walls, struts made of wooden logs are firmly stretched with wedges. The struts are usually installed horizontally, they can also be arranged with a slight slope.
The walls of the trench are made with a slight slope to the level (rys.a), which gives you more confidence, that the stretching will not loosen. However, such excavations have this disadvantage, that the struts at the bottom are shorter than at the top.
When spreading more than one horizontal board, vertical boards should be placed between the boarding and the struts. The boards arranged in groups can be connected with crossbars.
Distortion in less cohesive soils, easily slipping, made of planks that are butt-jointed or with small gaps - with gaps. Vertical overlay boards are used in short sections at the ends of the struts. During the execution of works, these sections are replaced with longer sections. After excavation is completed, these boards are usually replaced with long boards, which require fewer supports.
If there is more space in the field, the expansion can be made as shown in the drawing d; the bottom of the wall is stretched, and at the top an offset with a working footbridge and a slope without protection.