Compaction of Sediments Underlying Areas of Land Subsidence in Central California GEOLOGICAL SURVEY PROFESSIONAL PAPER 497-D Compaction of Sediments Underlying Areas of Land Subsidence in Central California By ROBERT H. MEADE MECHANICS OF AQUIFER SYSTEMS GEOLOGICAL SURVEY PROFESSIONAL PAPER 497-D A study) partly statistical^ of the factors that influence the pore volume and fabric of water-bearing sediments compacted by effective overburden loads ranging from J to JO kilograms per square centimeter UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1968 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY William T. Pecora, Director For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price 35 cents (paper cover) CONTENTS Page Page Abstract_ _---------_-____________________________ Dl Combined effects of overburden load and particle Introduction- -_-------_____________________________ 1 size______________________---____ D23 Purpose of report_______________________________ 2 Effect of particle sorting________________________ 24 Acknowledgments__ __________________________ 2 Combined effects of selected physical and chemical Review of factors influencing compaction of clays and factors.______--_--____--______-_-_------_--- 25 sands__________________________________________ 3 Fabric of the sediments and its relation to overburden Removal of water from clays.____________________ 3 load and other factors.____________________________ 28 Rearrangement of clay-mineral particles. __________ 5 Orientation of clay-mineral particles_____________ 28 Development of preferred orientation_______ Observation and measurement______________ 28 Development of turbostratic orientation. ______ Relation to depth of burial and type of sedi­ Reduction of pore volume in sands at pressures less mentary deposit._________________________ 29 than 100 kilograms per square centimeter..______ Relation to particle size and chemical factors 31 Influence of particle size.____________________ 9 Domainlike aggregates._____________-_--_--- 31 Influence of particle sorting._________________ 11 Distribution of montmorillonite orientation Influence of particle roundness.______________ 12 within the sediments,_____________________ 32 Influence of mica particles.__________________ 12 Fabric of sands___________-.________-__----_---_ 32 Influence of interstitial water.________________ 12 Preparation of thin sections._________________ 32 Pore volume of sandstones at pressures greater than Distortion of compressible grains._______--__- 32 100 kilograms per square centimeter__________ 12 Orientation of mica particles___________---- 34 Summary of petrology of sediments in areas of land Conclusions.___________________________-_--_-----_- 34 subsidence _______________________________________ 14 Glossary of statistical terms_________________-___-_--- 36 Analysis of factors influencing compaction of the sedi­ References.________________________________________ 37 ments. __________________________________________ 17 Appendix A. Samples used in statistical studies.-_______ 39 Use of multiple-regression statistics for analysis.____ 17 Appendix B. Effective overburden loads at different Effect of overburden load________________________ 18 depths in the cored sections at time of coring._____ 39 Effect of particle size__________________________ 22 ILLUSTRATIONS Page FIGURE 1. Graphs showing influence of different factors on the relations between void ratio and pressure in clayey materials_________________________________________________________________________________ D4 2. Graph showing influence of pH on relations between void ratio and pressure in <4-micron fractions of kao- linite mixed with 10~3 M sodium chloride solution____-____-_--_-_--------------------_--------- 5 3. Sketches showing idealized clay-mineral particle arrangements that may be formed during compaction _ __ 6 4-8. Graphs showing: 4. Influence of particle size on void ratio of silts, sands, and sandstones______________-_----_---_ 11 5. Influence of particle sorting on void ratio of sands_______--_------------------------_____---_- H 6. Influence of degree of roundness of pure quartz, 420 to 840 microns in size, on relation between void ratio and pressure______--___________________________________-___-_---__----------- 12 7. Influence of proportion and size of mica particles on relations between void ratio and pressure in sands and silts___________________________________________________________________________ 13 8. Influence of interstitial water on relation between void ratio and pressure in well-sorted clean quartz sands_____________________________________________________________________________ 14 9. Map showing locations of core holes in central California._________________-_-_-__-_--___---------- 15 10.. Composite logs of petrologic characteristics of sediments cored in areas of land subsidence in central California. _________________________________________________________________________________ 16 11. Graphs and diagrams showing simple relations between void ratio and effective overburden load in fresh­ water-bearing alluvial sediments._____________________________________-_-_-_-___----_--------- 20 IV CONTENTS FIGURES 12-17. Graphs showing: Page 12. Relations between median diameter and the residuals of the void ratio-load regressions.________ D22 13. Simple relations between void ratio and median particle diameter in fresh-water-bearing alluvial sediments____ ____________________________________________________________________ 23 14. Influence of particle size on relations between void ratio and effective overburden load.__________ 23 15. Relations between quartile deviation and the residuals of void ratio-load-Md^ and void ratio- Md<t> regressions___________________________________________________________________ 25 16. Simple relation between void ratio and quartile deviation in silty sands from Los Banos-Kettleman City area___________________________-____-______--__-----------------------______ 25 17. Relations of void ratio of fine sediments in Richgrove core to depth of burial, type of sedimentary deposit, and effective overburden load_______________________-___-_________________^__ 26 18-20. Diagrams showing: 18. Relations of montmorillonite-particle orientation to depth of burial and type of deposit represented by fine sediments cored in Los Banos-Kettleman City area_____________________________ 30 19. Relations of montmorillonite-particle orientation to depth of burial and type of deposit represented by fine sediments in Richgrove core _________________________________________________ 31 20. Orientation of montmorillonite in sections cut at different angles to the bedding of sediments from Huron and Richgrove cores_________________________________________________________ 33 21. Sketches showing distortion of compressible sand grains____________________________________________ 34 22. Sketches showing sections of micaceous sands from Mendota core-____-------------_----_-------______ 35 TABLES Page TABLE 1. Summary of experimental data on compaction of unconsolidated sands_______________________________ DIO 2. Details of significant regressions of void ratio on effective overburden load, median particle diameter, and quartile deviation of particle-size distribution____-_______-______-_-----------------_-_------__ 21 3. Selected properties of fine sediments in Richgrove core____________________________________________ 27 4. Selected details of multiple regressions of void ratio on different combinations of variables, representing properties of selected fine sediments in Richgrove core_________________________________________ 27 5. Selected details of multiple regressions of orientation ratio on different combinations of variables representing properties of marine siltstone in Richgrove core______________________________________________ 31 MECHANICS OF AQUIFER SYSTEMS COMPACTION OF SEDIMENTS UNDERLYING AREAS OF LAND SUBSIDENCE IN CENTRAL CALIFORNIA By ROBERT H. MEADE ABSTRACT and such chemical properties as the composition and An increase in effective overburden load from 3 to 70 kilo­ concentration of the material dissolved in the interstitial grams per square centimeter, partly natural and partly man- waters. Our understanding of the process of compaction, made, has caused an average reduction of 10 to 15 percent in therefore, involves understanding how these factors the volume of alluvial sediments in the San Joaquin and Santa Clara Valleys of California. The effects of load, however, are interact with each other and with increasing overburden complicated by the effects of other factors on the pore volume. loads to inhibit or to enhance the removal of fluids and The most easily discerned of these factors in the alluvial sedi­ the reduction of pore volume in sediments. ments are particle size and particle sorting. The variation in The compaction of the water-bearing sediments in pore volume that is related to differences in average particle three areas of land-surface subsidence in the San size is of the same order as the variation related to differences in load. The effects of particle sorting are probably subsidiary to Joaquin and Santa Clara Valleys of California is the the effects of load and average particle size. subject of this report. The historic compaction and land A multiple-regression analysis of the pore volume, overburden subsidence in these areas are clearly related to'the load, and selected