Laboratory Test On Some Engineering Characteristics Of Salt Rock In Lop Nur Area

Due to its special natural climate conditions,the surface of Lop Nur area is covered by a largenumber of salt rocks,and the available water resources are scarce.The groundwater is saturated brine.In the local highway construction,in line with the principle of local materials,green environmental protection and local conditions,this paper uses the thick layer of crazing salt rock in the center of Lop Nur Lake Basin as the subgrade filler to solve the problems of lack of local subgrade filler and high transportation cost,analyzes the formation mechanism of remolded salt rock strength and the law of salt expansion change,and uses inorganic binder to reinforce remolded salt rock The water stability and mechanical properties were studied in laboratory.In this paper,according to the local materials,the thick layer of crazing salt rock(mainly composed of sodium chloride,gypsum and calcium sulfate)in the center of Lop Nur Lake Basin is used.Because the natural salt rock has the problems of uneven pore division and large gap in mechanical properties,it is crushed and screened,compacted according to the maximum dry density,and treated as subgrade filler by curing,which can improve the mechanical properties of remolded salt rock subgrade Indoor compaction test,shear strength test,unconfined compressive strength test and uniaxial compression test were carried out.It can be seen from the test results that the maximum dry density and the best moisture content of the thick layer of crazing salt rock in the center of Lop Nur Lake Basin are 1.613g/cm3 and 5.42% respectively;the shear strength,unconfined compressive strength and rebound modulus of the remolded salt rock are in direct proportion to the curing age,with the friction angle of 46.04 ° and cohesion of 462.160 kpa in the 28 day old period.From 0 to 14 days old,the values of C and φ change greatly,with obvious increase.After 14 days of age,they increase slightly,but with little increase.At 28 days old,the unconfined compressive strength is 7.40 mpa,with no obvious change.In uniaxial compression test of salt rock,the three deformation stages of salt rock in uniaxial compression process are determined according to the stress-strain curve determined by the test The results show that the elastic modulus and Poisson’s ratio are 2.3gpa and 0.32 at the age of 28 days.Because the remolded salt rock is easy to dissolve in water and produce a series of diseases,considering that Lop Nur is dry all the year round and there is almost no rainfall,its main water distribution is underground saturated brine,the remolded salt rock is soaked in saturated brine,and its water stability is studied.After soaking in saturated brine,each mechanical property index has a certain degree of decline,and in the early stage of curing,the immersion brine is loose,with the increase of curing age,its water stability has improved.According to the comprehensive experimental results and the comparison with the improved saline soil used as subgrade filler in the saline soil area,based on the premise of drought and less rainfall in Lop Nur area,the local saline rock used as subgrade filler has a series of advantages,such as high strength,high hardness,strong self cementation ability,self-made slab and so on,compared with the traditional improved saline soil.Secondly,when salt rock is used as subgrade filling material,salt swelling occurs due to the infiltration of underground saturated brine and the change of external temperature.The laboratory salt swelling test of remolded salt rock was carried out.It can be seen from the test results that when the external temperature changes,salt swelling will occur in remolded salt rock,which is irreversible and cumulative,and is directly proportional to its liquid content and inversely proportional to the degree of compaction,but less affected by its degree of compaction,and greatly affected by the liquid content.When the liquid content is 9.5%,the salt swelling rate is as high as 2.5%,and the accumulated salt swelling rate is 6% after three freeze-thaw cycles.Based on the principle of phase equilibrium,the crystallization rules of chloride and sulfate are analyzed when salt swelling occurs.The temperature range of salt swelling is determined and the reason of the change is explained.The comprehensive test results show that the remolded salt rock belongs to the light salt swelling grade.At last,different proportion of lime and fly ash are used to strengthen and stabilize salt rock,and indoor mechanical property tests are carried out.It can be seen that in the early stage of maintenance,the water stability of salt rock strengthened by lime and fly ash is not improved much,and its strength is even decreased,but with the increase of maintenance age,its water stability is improved more and more.At the later stage of curing,its water stability is better.But with the increase of lime fly ash content,the salt swelling deformation of remolded salt rock increases.Therefore,combined with the local hydrogeological conditions and test results,remolded salt rock can be used as subgrade filler in this area.