What Is Dry Masonry?

Dry masonry is a block masonry that does not require cement. It depends on the weight of the stones and the friction between the contact surfaces of the stones to maintain stability under the action of external forces. It is usually used in retaining walls, slope protection, embankment and other projects ^[1] . Dry masonry technology is considered to be a better wall structure, of course, there are also stone houses, stone bridges and other structures.

The foundation of dry stone buildings should be excavated or filled in accordance with the required depth, width, length, and slope of the design, and then cleaned and strengthened before laying the stones. The stones transported to the site should be laid flat and easy to choose.

Before the stone is built, the dirt on the surface should be removed and the sharp edges and thin edges should be knocked off. The dry stone should be placed smoothly, the joints should be tight, pressed against each other, and the shape should be flat. Tight, so that each stone can be kept stable and combined with each other into a whole. Large-volume dry block stone retaining walls or buildings shall be arranged in layers according to the design standards, and the layers shall be staggered from top to bottom and inside and outside. The masonry method of laying the face stone on the inside and outside first and filling in the middle cannot be adopted. Stones should not be added to the bonding surfaces of the upper and lower layers. The corners, junctions and sections of each layer of masonry should be made of larger flat stones. The exposed surface of the dry block stone wall must be set with boulder (racket stone). The boulder should be evenly distributed. The length of boulder in the same layer should be equal to the wall thickness when the wall thickness is equal to or less than 40 cm; when the wall thickness is greater than 40 cm, two internal and external boulder stones are required to overlap with each other. It should be less than 15 cm, and the length of one piece should not be less than 2/3 of the wall thickness. For example, when using stone to build a retaining wall, one layer should be laid on every two layers. If Dingshun group is used for the same layer, the stone distance should not be more than 2 meters ^[1]

Dry-built stone dams are river dams whose main body is made of dry stones. The masonry materials are required to be fresh and complete. The upstream impervious body generally uses concrete panels or straight masonry walls. It can also be made into an overflow dam. Only one layer of concrete shell is required on the dam top and downstream dam surface. Overflow dry masonry dams with a height of more than 20m, the maximum single width flow rate does not exceed 20m ³ / (s · m). The advantage is that the material is collected in situ, which saves engineering amount. The disadvantage is that the impervious body is easy to crack ^[3] .

Dry stone advantages

Obtain materials on site; Save more cement and wood than concrete dams; Less engineering volume than earth-rock dams; Flood discharge and diversion layout are simpler and safety is higher than earth-rock dams; Its main disadvantage is that it consumes more labor, it is difficult to use mechanized construction, and the construction period is longer. This type of dam has been rarely adopted in developed countries, but it is still being built in developing countries. According to the dam type, stone masonry dams are divided into stone masonry gravity dams, stone masonry arch dams and stone masonry pier dams. According to the masonry methods, they can be divided into dry masonry dams and mortar masonry dams. Most contemporary masonry dams are mortar masonry Dam ^[4] .

Dry masonry material

The stone of the dam body should be uniform in texture, without cracks, not easy to weather, and its saturated compressive strength should not be lower than 30 40MPa, the water absorption rate should not exceed 10%, and the softening coefficient should not be lower than 0.7. Commonly used stones are wool, block and strip. Cement mortar is commonly used for grouting and cementing materials. There are also small stone cement mortar, fine aggregate concrete, cement lime mortar, cement clay mortar and other materials ^[4] .

Characteristics of dry stone structure

The design and calculation of stone masonry dams are basically the same as concrete dams. The physical and mechanical indexes of masonry mainly depend on the cementitious material and the compactness of masonry. As the joints between the stones are difficult to fill and compact, it is necessary to set an impervious layer on the upstream face of the dam body or near the upstream part, such as concrete impervious panel, asphalt concrete impervious panel, steel mesh cement shotcrete surface, cement mortar hook Seams and other impervious layers. Unlike concrete dams, stone masonry dams are generally not provided with longitudinal and transverse joints; when transverse joints are provided, the gaps between the joints are large; usually, no cooling or cooling measures are taken ^[4] .

Development and examples of dry masonry

Long ago, humans built dams with stones. The oldest stone masonry dams in China that are still in operation today are: dry-coated pebble diversion weirs built on the Dujiangyan Junction in Sichuan Province around 250 BC; completed on the Lingqu (Xianggui Canal) in 219 BC Dry block stone and pebble overflow dam. After 1949, China built many stone-built dams, especially stone-built arch dams. According to incomplete statistics in 1997, China has built 1,741 stone masonry dams over 15m in height, of which 986 stone masonry arch dams account for 56.7% of the total number of stone masonry dams; 549 stone masonry gravity dams account for 31.5%; 206 stone masonry piers and other dam types account for 11.8%. ^[4]

India's Nagarjun-nasagar stone masonry gravity dam, with a height of 125m and a volume of 5.61 million m ³ , is the world's tallest and largest cubic masonry dam. The highest masonry gravity dam in China is the masonry dam of Zhuzhuang Reservoir in Hebei Province, with a dam height of 95m. The tallest stone masonry arch dam in the world is Qunyingjiang Stone Masonry Gravity Arch Dam, Henan Province, China, with a height of 101m. Dongfeng Plastered Stone Double-curved Arch Dam in Shandong Province, China, with a dam height of 84m and a thickness-to-height ratio of 0.16. Since the 1970s, China has also built many new types of stone masonry dams, such as the Yanwutan Stone Masonry Open Web Gravity Dam (66m high) ), Daxilong dry-stone masonry overflow dam (27m high) in Zhejiang Province and Xiaolongtan slurry masonry slag-filled gravity dam (39.6m high) in Hebei Province, Datian Hexagon Palace fine-grain concrete stone masonry arch dam ( 79m high) ^[4] .