Two-dimensional inversion of spectral induced polarization data using MPI parallel algorithm in data space

Traditional two-dimensional（2D） complex resistivity forward modeling is based on Poisson＇s equation but spectral induced polarization（SIP） data are the coproducts of the induced polarization（IP） and the electromagnetic induction（EMI） effects.This is especially true under high frequencies,where the EMI effect can exceed the IP effect.2D inversion that only considers the IP effect reduces the reliability of the inversion data.In this paper,we derive differential equations using Maxwell＇s equations.With the introduction of the Cole-Cole model,we use the finite-element method to conduct2 D SIP forward modeling that considers the EMI and IP effects simultaneously.The data-space Occam method,in which different constraints to the model smoothness and parametric boundaries are introduced,is then used to simultaneously obtain the four parameters of the Cole-Cole model using multi-array electric field data.This approach not only improves the stability of the inversion but also significantly reduces the solution ambiguity.To improve the computational efficiency,message passing interface programming was used to accelerate the 2D SIP forward modeling and inversion.Synthetic datasets were tested using both serial and parallel algorithms,and the tests suggest that the proposed parallel algorithm is robust and efficient.

Monitoring lime and cement improvement using spectral induced polarization and bender element techniques

Spectral induced polarization(SIP)and bender element(BE)techniques show a high sensitivity to particle size,particle distribution and content of generated hydration products,which essentially govern the efficiency of ground improvement.In this context,both SIP and BE were integrated on a column setup to monitor the processes of lime and cement stabilization.A 5 mmol/L Na2CO3 solution was injected into the sand-lime mixture to produce CaCO3 precipitation,while deionized water was injected into the sandcement mixture to induce the hydration of cement.The average diameters of the precipitated particles or clusters were calculated from the relaxation time,which was a significant parameter of SIP signals,via the Schwarz equation.Two pairs of BE were used to demonstrate the heterogeneity of the product precipitation,which was probably caused by the location of the inflow and outflow on the SIP-BE column.SIP and BE showed the capability of nondestructively monitoring the spatiotemporal chemical evolution processes,which could be helpful for engineering applications.