Abstract:A collapsed incident occurred on 10 October 2016 in Wenzhou City, China, which resulted in 22 casualties and 6 injuries. Most of victims were migrant laborers (rural dwellers who move to urban for a temporary work), who rented apartments in these residential buildings, which were originally constructed by local rural residents. This case report investigates the collapsed incident as well as other similar previous incidents. From the perspectives of both social and technical aspects, this report analyzed the Chinese rural land use policy with relevant technical factors. These incidents reveal social problems of the existing dual structure land-use policy in China. Chinese dual structure land-use policy caused deficiencies in the supervision of the construction market in rural area so that the following technical factors were not well supervised by the various quality control departments: (1) poorly quality of residential buildings, (2) unauthorized rooftop additions, and (3) differential settlement caused by the uneven distribution of underlying Wenzhou clay under creep conditions. Mandatory regulation by the government for any construction in China, particularly for the construction of self-constructed house building sites in rural areas, was recommended to minimize the resettlement issue of migrant workers.

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The interface shear strength properties of geogrid-reinforced recycled construction and demolition (C&D) materials were determined in this research to assess the viability of using geogrid-reinforced C&D materials as alternative construction materials. The C&D materials investigated were recycled concrete aggregate (RCA), crushed brick (CB), and reclaimed asphalt pavement (RAP). Biaxial and triaxial geogrids were tested as the geogrid-reinforcement materials. The interface shear strength properties of the C&D materials were ascertained by using a large direct shear test (DST) equipment. Large-scale DST was conducted for unreinforced and geogrid-reinforced C&D materials. The interface peak and residual shear strength property of unreinforced and geogrid-reinforced RCA was found to be higher than that of CB and RAP. RAP was found to have the lowest interface shear strength properties of the C&D materials. The higher strength triaxial geogrids were found to attain higher interface shear strength properties than that of the lower strength biaxial geogrids. The DST results, however, indicated that the interface shear strength properties of the geogrid-reinforced C&D materials were less than that of the respective material without reinforcement. This can be attributed to the lack of interlock between the geogrids and the recycled C&D aggregates, as well as the current conventional testing method for DST that induces a shear plane at the boundary between the lower and upper boxes where the geogrid is placed. The unreinforced and geogrid-reinforced RCA, CB, and RAP were found to meet the peak and residual shear strength requirements for typical construction materials in civil engineering applications.

Laboratory large-scale direct shear tests were carried out on five different recycled construction and demolition materials, such as crushed concrete (CC), crushed rock (CR), crushed brick (CB), reclaimed asphalt pavement (RAP), and recycled glass (RG). The shear strength parameters were evaluated with a large shear test machine for different values of normal stress ranging from 30 to 200 kPa. Resulting values of cohesion were found to vary in a wide range between 8.55 kPa to 284.5 kPa, whereas coefficient of internal friction varies between 44.6° to 52.1°. The failure envelopes for all materials investigated are straight-line failure envelopes. Crushed rock and crushed concrete showed high cohesion of 284 kPa and 154 kPa, respectively, whereas reclaimed asphalt pavement and recycled glass showed low cohesion of 8.55 kPa and 14 kPa, respectively. Meanwhile, crushed brick showed a medium cohesion of 61.2 kPa. Further, the volumetric behaviours of the recycled materials are dilatancy except for reclaimed asphalt pavement at low normal stress. The results of the shear strength tests indicate that CR, CC, and CB and blends of RAP and medium recycled glass (MRG) with other materials can be viable materials to be sustainably used in pavement sub-base applications.

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