Hydraulic Load Of Underground Structure In Pore Water Bearing Rock

It is a growing issue that high-pressure pore water can lead to increasing damage to underground structure lining in rock aquifer with the increase of burial depth. In order to establish a design theory on underground structure lining of pore water bearing rock, hydraulic load of underground structure in pore water bearing rock is studied by means of analytical analysis, numerical simulation, physical simulation and field measurement. Study results are shown as follows.First, the impact of pore water pressure on rock mechanics parameters is studied. Through theoretical analysis, the study discovers the mechanism of pore water pressure affecting elasticity modulus, Poisson’s ratio and lateral pressure coefficient of rocks: the pore water pressure affects pore deformation rigidity and pore water pressure change leads to pore expansion or contraction which in turn affects elasticity modulus, Poisson’s ratio and lateral pressure coefficient; a theoretical analysis model is built to obtain analytic solution to the change of elasticity modulus, Poisson’s ratio and lateral pressure coefficient with the pore water pressure and other factors; random numerical model of microcosmic rock pore is built to master the law of porosity factor, pore water pressure and other factors affecting equivalent elastic modulus, equivalent Poisson’s ratio and equivalent lateral pressure coefficient of rocks by means of large-scale numerical computation. Study shows that, the equivalent elastic modulus, equivalent Poisson’s ratio and equivalent lateral pressure coefficient all increase linearly with pore water pressure.Second, hydraulic load of underground structure under the pore water pressure is studied. The study revealed the formation mechanism for hydraulic load of underground structure in pore water bearing rock: change of the pore water pressure leads to pore expansion or contraction in surrounding rocks which results in change of underground structure loads, similar to the structure loads arising from thermal expansion and contraction of surrounding rocks; a mechanical model is built for the interaction between pore water bearing surrounding rocks and underground structure based on the mechanism of water pressure-caused expansion in order to obtain the analytic solution to hydraulic load; a microcosmic rock pore space axial-symmetrical random numerical model is built for the interaction between surrounding rocks and underground structure in order to master the law of hydraulic load changing with factors by means of large-scale numerical calculation; the law of hydraulic load changing with pore water pressure is discovered by means of large-scale simulation test and field measurement study.Study shows that, hydraulic load of underground structure is proportional to the pore water pressure; hydraulic load increases with porosity of surrounding rock; hydraulic load increases with deformation rigidity of lining relative to surrounding rocks(thickness and elasticity modulus); hydraulic load increases with Poisson’s ratio of surrounding rocks; Poisson’s ratio of the lining has no significant effect on hydraulic load. Study indicates that hydraulic load is far lower than static water pressure and hydraulic load value of existing design method is too large; the lining may be stripped from surrounding rock and the stripping surface will bear water pressure to increase external load of the lining. This finding has an important theoretical and practical significance on design of underground structure in water bearing rock.Finally, a design principle is put forward for water seal lining of underground engineering in pore water bearing surrounding rock according to the above study results. Hydraulic load is far lower than the pore water pressure and is one of the key external loads on the lining, so the lining needs to have enough strength to resist hydraulic load, surrounding rock deformation pressure and other external loads; the lining shall has reasonable stiffness to maintain the contact between the lining and the surrounding rock and reasonably reduce hydraulic load of underground structure; it can effectively reduce hydraulic load on the water seal lining to improve quality of contact between the lining and the surrounding rock and inject slurry into pores and fractures behind the dense wall.