Study On The Thermal Conductivity And Anti Erosion Of GSHP Buried PIPE Backfill Material In Karst Area

Ground source heat pump buried pipe backfill option has its particularity in karst area. The main topics for ground source heat pump buried karst area pipe backfill material as the research object, thermal performance test through the actual backfill for buried pipe of ground source heat pump engineering, Guilin University of Technology of materials and anti scour simulation, feasibility of backfill to analysis and verification in practical engineering.In the karst area, because of the long-term effects of infiltration of surface water and groundwater, underground rock cave development with various different sizes, the shuttle in the groundwater flow. Ground source heat pump engineering, Guilin University of Technology through the underground water cave in the vertical drilling, with sand and bentonite backfill can easily be washed away the groundwater found in backfill process, resulting in the loss of the backfill material in great quantities, blocked two partial backfill material connected caves, not sand and bentonite rapid condensation heat transfer protective effect of buried pipe and play. According to the construction experience, the construction side to choose powder instead of sand as backfill material for backfill, through on-site construction situation, mixed with bentonite backfill material in powder, to achieve the desired effect, show the back filling powder and bentonite can be more rapid condensation protection of buried pipe piles in continuous erosion karst groundwater, the backfill process completed successfully.But the powder and bentonite as backfill is real and long withstand the groundwater erosion, and the sand and bentonite has better thermal performance, still needs further study. This article is to powder and bentonite and sand and bentonite were used as backfill a contrast material, through the indoor thermal performance test and anti erosion test, combined with the special properties of powder itself, backfill to judge the powder is suitable for special geological conditions in karst area of ground source heat pump.Firstly, comparative measurement of thermal conductivity of the soil thermal properties analysis of sand and bentonite, powder and bentonite were used as backfill when found powder and sand, as with thermal good rate, volumetric heat capacity and thermal diffusivity; powder adding bentonite as backfill thermal coefficient of2.127W/(m-k); similar properties of powder and sand, with the change trend of the same heat and sand, the thermal conductivity increases with the increase of moisture content and dry density increased. Powder is a very good thermal conductivity of backfill material.Secondly, from the mixture experiment of sample preparation and the dry density, in addition to the same water, powder with fluidity and cementing performance was better in the sand; stone powder in water with compressibility than the sand is much higher, density is bigger, better water retention properties.Third, given the powder in water with good water absorption, adhesion and compression performance, adding a certain amount of the powder and bentonite sand test, test results show that the back filling powder and sand and bentonite with high thermal conductivity and high thermal conductivity, up to2.600W/(m·k) above the effect of heat transfer, has the very good, volumetric heat capacity reaches2.500[MJ/(m3·k)] above, thermal diffusivity changes in0.600～0.900[mm2/s]. Powder with sand and bentonite backfill compaction, permeability, water absorption and cohesiveness is good, is a very good back packing, the recommended ratio of sand、stone powder bentonite、water:50%、 30%、5%、15%.Fourth, powder backfill in the moisture content of w=18.81%～19.86%range, thermal conductivity peak, water is back filling rate control in18%～20%, can obtain the best effect of heat transfer.Finally, through the flume apparatus to simulate underground karst water to flour as the scour process of backfill material, through four kinds of erosion three velocities and erosion shows, in the scouring process, only a very small amount of filler particles is taken away by water flow, erosion amount shall not exceed5%of the total weight of the sample. The back filling powder has good anti scouring ability, suitable for drilling in karst area of backfill material.