Electrochemical Modified Mechanism Of Physicochemical Soft Rock

The physicochemical soft rock is a kind of rock in which containing a great amount of clay minerals. Under engineering disturbance conditions, it is easy to produce swell and shrink by wetting and drying and to reduce rapidly its engineering properties. It is one of the biggest rock mechanics problems in geotechnical engineering. It is usually controlling methods about soft rock engineering that bolting and shotcreting, grouting reinforcement, strengthening rack supporting, arching and close concrete camber. These methods all base on equilibrium of forces and not base on its physical, chemical and mechanical properties. In the paper electrochemical modified method is introduced, which can change mineralogical composition, crystal structure, the pore stuctue, and control the stability of soft rock engineering. The method can provide the theoretical reference and technical supporting for the controlling of the disaster of soft rock engineering, and has significant scientific value and extensive application value for decreasing and preventing the disaster of soft rock engineering.According to the crystal structure and anodic exchange capacity, the montmorillonitic soft rock and illitic soft rock are taken as the researth object. Based on the theory of electric double layer in the electrochemical treatment, the electrochemical modified mechanism of the physicochemical soft rock was theoretical analyzed; the mineral properties of montmorillonitic soft rock related to the electrochemical modification was experimental analyzed, which main including in charge property, electric double layer, the pH value, the point of zero charge(pHZPNC), the permanent charge density(σP), the specific surface area, porosity and pore aperture; the change rule of mineralogical composition and crystal structure of montmorillonitic soft rock was analyzed; the effect on subsidence and expandability of montmorillonitic soft rock particles was studied; and the modification about the pore structure and mechanical property of illitic soft rock was analyzed. The following is main research results:1. The electrochemical modified mechanism about clay minerals and soft rock in electrochemical modification was summarized, which is the electrochmical phenomenon of clay mineral and soft rock, such as electroosmosis, electrophoresis, and electrolysis. Under the electrochemical treatment, the mineralogical composition of soft rock will alert and generate new minerals, and change the physical and mechanical properties by electroosmotic drainage.2. The mineral parameters of the physicochemical soft rock which including in cation types, pHZPNC,σP, theζpotential, the isoelectric point, the specific surface area, the pore volume–diameter distribution, et al. was analyzed systemically by X-ray diffraction, X-ray fluorescence spectral analysis, potentiometric titration, electrophoresis, and nitrogen adsorption isotherm under modified and unmodified conditions.3. With different CaCl2 electrolyte concentration and different electric gradient, the mineralogical composition of soft rock is altered; the newly formed minerals are calcite, gibbsite, anhydrite and allophane. The montmorillonitic content in the anodic, cathodic and intermediate zones of soft rock decreases under electrochemical treatment. The electrochemical modification can result in a change of montmorillonitic crystal structure in soft rock also, and the crystallographic planes in all zones exponent increases. Under different CaCl2 electrolyte concentration, with increasing the concentration, the crystalline size in anodic and intermediate zones change by exponent rule, and the size in cathodic zone change by Gauss rule. Under different electric gradient, with increasing the electric gradient, the crystalline sizes in all zones change by Gauss rule.4. The subsidence process of montmorillonitic soft rock particles is wetting slowly, subsiding accelerately, and volume steady. The treatment of electrochemical modification can change subsidence rate of soft rock particles in distilled water and not affect its volume expandability when the subsidence is in stable state.5. The combination of micro-CT, digital image processing and three-dimensional reconstruction can provide a new, simple and feasible method for the analysis of rock pore structure. The single digital image is processed by image segmentation, binarization and compression, and the new images with different resolutions are generated. When the pixel size of the new image is taken as the pore aperture, the rule of the rock porosity variation with the pore aperture is estimated from Micro-CT single image. The volume rendering algorithm of visualized reconstruction can make the single image become the image sequence, and generate three-dimensional digital image. The rule of the rock porosity variation with the pore aperture is estimated on the base of the image sequence. Electrochemical modification can increase the mechanical property of soft rock. The mean tensile strength of the original sample is 1.31MPa; after merging in distilled water it changes to 0.81MPa, and with electrochemical modification it will increase by 16.79%-116.03%.