What is meant by a dry stack retaining wall?<\/h2>\n
A dry stack retaining wall is a self-supporting masonry structure made exclusively with carefully positioned and interlocked natural stones without the use of binders or mortars<\/strong>. The longevity of dry stone constructions derives precisely from the absence of a binder like mortar, which tends to deteriorate, break, or crumble over time, thus compromising the structural stability of walls and buildings. The main function of the dry stack retaining wall is to counteract the pressure of the earth behind it, ensuring the stability of slopes, embankments, or terraces.<\/p>\n The stability of the wall is achieved thanks to its own weight (gravity stability), friction, and the mechanical interlocking between the stones, while its intrinsic permeability allows for the natural drainage of water, reducing hydrostatic pressure. It is therefore useful for containing the soil and ensuring the stability of slopes, reducing the risk of erosion and landslides.<\/p>\n Two main categories of dry constructions can be distinguished: “rich walls” and “poor walls.”<\/p>\n With the advent of agricultural industrialization in the 20th century, many of the more difficult-to-work surfaces were progressively abandoned, both due to high costs and a decrease in the need to exploit them. Abandonment has led to the rapid degradation of these structures, causing in many cases the complete disappearance of dry walls and artifacts.<\/p>\n A dry stack retaining wall is made up of a series of parts:<\/p>\n The terracing with dry stack retaining walls<\/strong> allows for the optimization and increase of arable land, expanding workable areas. With an inclination of only 80\u00b0, approximately 20-25 cm in height is lost for every meter, meaning that a wall 2 meters high reduces the horizontal projection of the slope by just over one third. Compared to a grassy edge, whose stability depends on soil cohesion, a dry stack wall inclined between 45\u00b0 and 55\u00b0 (which results in a horizontal loss of 80-100 cm per meter of height) offers a clear advantage, recovering up to 60-80 cm of surface for every meter of height.<\/p>\n In areas traditionally dedicated to viticulture, dry stack retaining walls have been used to optimize space<\/strong> on particularly unfavorable slopes. In addition to expanding arable land, these walls offer an additional agronomic advantage: the ability to regulate the microclimate of the terrace<\/strong>. The stones, in fact, accumulate heat during the day and release it at night, mitigating temperature fluctuations. This phenomenon allows for the cultivation of agricultural species even in seemingly unsuitable areas.<\/p>\n The construction techniques of dry stack retaining walls represent one of the oldest practices developed by humans to build stone structures. The careful arrangement of stones, sometimes shaped, has been documented since the earliest times in human history. It is significant to note how these skills have been found in archaeological discoveries scattered across almost all continents and belonging to very different cultures and societies.<\/p>\n In recent decades, however, the construction of dry stack retaining walls has seen renewed interest<\/strong>, especially in the context of designing green spaces, both public and private. Their unique aesthetics and architectural value have made them a valued choice for creating harmonious and sustainable landscapes.<\/p>\n We can distinguish two phases: a preliminary phase leading to the subsequent one, which focuses on the geotechnical study of the site where the wall will be built and the selection of suitable stones; the subsequent phase is the construction phase. Let’s analyze them in detail.<\/p>\n Preliminary Phase<\/strong><\/p>\n Before construction, it is essential to conduct a thorough analysis of the soil<\/strong>. The main parameters to evaluate are:<\/p>\n The calculation of soil pressure<\/strong> follows the classical equations of soil mechanics (for example, Rankine or Coulomb theory). In particular, for a dry stack retaining wall, it is necessary to consider the most critical condition, namely the active pressure:<\/p>\n P\u03b1<\/sub>\u200b = 1\/2\u200b\u22c5\u03b3 \u22c5 H2 <\/sup>\u22c5 K\u03b1<\/sub><\/strong><\/p>\n where:<\/p>\n The choice of stones for the construction of dry stack retaining walls is closely related to the local geology, as the material used generally comes from the surrounding environment or, alternatively, from a nearby quarry. The hardness<\/strong> of the stones is a determining factor to ensure the stability and durability of the wall over time. It is essential to verify that the material is sufficiently resistant and not prone to fracturing under the action of weather agents, temperature variations, or the pressure exerted by the overlying courses. If the available material is not very compact, the assembly technique must provide for minimal joints between the stones to prevent the disintegration of the material from causing voids that would weaken the structure.<\/p>\n The dimensions<\/strong> of the stones vary based on their function within the wall: the foundations require larger blocks, while the upper courses need progressively smaller stones. To improve the stability of the wall, it is advisable to insert “binding stones,” which are longer elements that cross the outer facing and anchor to the underlying ground. It is advisable to avoid excessively large stones that are difficult to handle, and stones with overly smooth surfaces, such as river pebbles, as they limit the stability of the interlocking.<\/p>\n In the reconstruction of a collapsed wall<\/strong>, there is a tendency to reuse the existing stones, recovering them from the rubble. During this phase, it is essential to classify and separate the stones by shape and size to facilitate the restoration work. Since the stones of the original wall were already selected by the builder, it is rarely necessary to modify them; it is preferable to reposition them in the structure while maintaining their original shape.<\/p>\n For new constructions<\/strong>, it is recommended to use local stones or, in any case, materials that harmonize with the landscape context, preserving the environmental identity of the place. The ideal stones for masonry should have at least one flat face to be used for the outer facing. A shape as square as possible is preferable, as it ensures a greater bearing surface and a more stable interlocking between the various elements.<\/p>\n Construction phase<\/strong><\/p>\n The foundations are essential for the stability of the dry stack retaining wall. They are placed below the ground level, where larger stones than the rest of the structure are used. The foundations must be built on compact soil, preferably on rocky substrate, to prevent settling and landslides. In unstable soils or with significant elevation changes, it may be necessary to use larger stones and arrange them to distribute the weight evenly.<\/p>\n Once the foundations are in place, the construction of the wall facing begins, which represents the visible part of the wall. This layer is made up of stones arranged in an orderly manner, paying attention to their stability and interlocking. The stones are selected based on their shape to facilitate the proper fitting and achieve a solid structure. Each stone must be laid so that its weight contributes to maintaining the balance of the entire wall.<\/p>\n The wall is built in layers, called \u201ccourses<\/strong>,\u201d which overlap each other. Each course is made up of stones of similar sizes, and their height depends on the sizes of the stones used in the outer facing. It is important that there is good interlocking between one course and the next, so that the wall gains solidity and does not lose cohesion over time. At regular intervals, wider stones, called “binding stones,” are inserted, which cross the wall to anchor it securely to the ground and prevent movement.<\/p>\n During the construction of the wall, it is necessary to provide a layer of drainage material behind the wall facing, between the wall and the ground. This material, generally made up of small stones, serves to allow rainwater runoff and to prevent moisture accumulation, which could compromise the stability of the wall over time. Drainage is essential, especially in particularly sloped or exposed soils.<\/p>\n Once the construction of the wall is completed, the final part, the capping, is carried out. This phase consists of placing the largest or flattest stones on top of the wall, which serve to protect the structure from wear caused by rainwater and weather conditions. The capping is also aesthetically important, as it contributes to giving a finished appearance to the wall and ensuring its durability.<\/p>\n The last phase involves a final check of the stability of the wall. The interlocking between the stones, the cohesion of the courses, and the effectiveness of the drainage are checked. Any irregularities are corrected, and the structure is consolidated if necessary. Finally, any debris is removed, and the exterior appearance of the wall is finished so that it harmoniously integrates with the surrounding landscape.<\/p>\n <\/p>\nRich walls and poor walls<\/h3>\n
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Dry stack retaining walls: the components<\/h2>\n
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Dry Stack Retaining Walls: Terracing<\/h2>\n
How to Build a Dry Stack Retaining Wall<\/h2>\n
Geotechnical Study of the Site<\/h3>\n
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The choice of materials<\/h3>\n
P<\/strong>lacement of the foundations<\/h3>\n
Construction of the wall facing<\/h3>\n
Creation of the courses<\/h3>\n
Placement of drainage<\/h3>\n
Closure and capping<\/h3>\n
Final check and finishing touches<\/h3>\n
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