Yes , here are several research papers (or preprints) on effective thermal conductivity of granular (or porous) materials that you can access via HTTPS links:

Open-Access / Free-PDF Papers & Preprints

Effective thermal conductivity in granular media with devolatilization: the Lattice Boltzmann modelling A. Grucelski et al. (2021) — Open access article. https://link.springer.com/article/10.1007/s40789-020-00395-0

Measurement of effective thermal conductivity of compacted granular beds W. Dai et al. (2017) — uses transient plane source method; full PDF available. https://www.epj-conferences.org/articles/epjconf/pdf/2017/09/epjconf162400.pdf

Determination of the effective thermal conductivity of granular materials under varying pressure E. S. Huetter et al. (2008) — full article (or at least full abstract with PDF link) https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2008JE003085

Thermal Conductivity of Granular Porous Media: A Pore-Scale Computational Approach R. Askari et al. (2015) — describes numerical modelling of effective conductivity in porous/granular media https://pubs.aip.org/aip/adv/article/5/9/097106/896880/Thermal-conductivity-of-granular-porous-media-A

The effects of packing structure on the effective thermal conductivity of granular media: A grain-scale investigation Weijing Dai, Dorian Hanaor, Yixiang Gan (2018) — preprint on arXiv, free access https://arxiv.org/abs/1809.01379

Maxwell-type models for the effective thermal conductivity of a porous material with radiative transfer in the voids Kristian B. Kiradjiev et al. (2018) — looks at models including radiative contributions, open version via arXiv https://arxiv.org/abs/1812.11696