An improved framework for volume change of shrink/swell soils subjected to time-varying climatic effects

Abstract

The ability to estimate soil volume change as a function of time is a valuable tool in the design or forensic analysis of shallow foundations and pavement structures. This paper presents an improved framework for estimating the volume change of shrink/swell soils due to time-varying climatic effects using the Lytton et al. (2005) approach with the suction envelope models created by Vann & Houston (2021) and updated considerations of short-term varying climate. The procedure can be easily implemented in any country due to its mechanistic-empirical nature. The authors present an example calculation of the proposed framework using the data from an American Association of State Highway and Transportation Officials (AASHTO) Long-Term Pavement Performance (LTPP) Seasonal Monitoring Program (SMP) section, located approximately 80 miles northeast of Dallas, Texas. The volume change estimated from the proposed framework was compared to 70 measured data points from sections from the SMP study and the results look promising. The models are universal and can be used in any part of the world provided measured data is available to calibrate for local conditions. Ongoing calibration effort with the remaining LTPP SMP sections will allow obtaining calibration factors for the proposed framework that will improve the estimation of the volume change predictions under pavements and facilitate the implementation into current design procedures.

Climate-driven soil suction variation using a natural-order Fourier series approach

“…This improvement can be observed in Fig. 1, adapted from [19], which presents the estimated monthly suction near the ground surface over a 20-year period, which resulted in a better representation of the shifts from dry (high suction) to wet (low suction) periods and a significant increase of the adjusted-R 2 from 0.33 with a periodic fit to 0.73 with an 8th-order Fourier fit, as well as a decrease in the sum of square errors from 13.3 to 5.4, respectively. The improved goodness-of-fit with increased Fourier series order (k) is promising, however there are considerable limitations when applying a fixed order fit to time series data.…”

“…Although the TMI-P200/wPI model was originally developed using a long-term average TMIeq, the model has potential to characterize seasonal climate-soil interaction near the ground surface (or just below the pavement surface), by substituting the long-term TMIeq in Equation (1) with a shorter-term average TMI, referred to by the authors as the seasonal TMI (TMIsn). The seasonal TMI adopted herein represents a 1-year average TMI calculated on a monthly basis and has been previously demonstrated as a useful parameter for describing time-varying climate-suction relationships [5,19,22,23].…”

“…In 1979, Mitchell also proposed that an improved representation of the irregular patterns of the surface flux boundary condition could be achieved using a Fourier analysis [1]. Follow up studies by Aubeny & Long [18] and Olaiz et al [19] preliminary demonstrated how the Fourier series can improve the representation of the climate-driven variation of surficial suction compared to a periodic fit. This improvement can be observed in Fig.…”

A Unified Two Independent Stress Variable Approach to Moisture-Change-Induced Unsaturated Soil Volume Change

“…There are numerous soil index propertybased methods for expansion response, and relatively fewer for collapse response. Olaiz, et al [45] present a series of suction-controlled oedometer tests performed on clay soils exhibiting predominantly expansion response to wetting, with the data demonstrating that empirical relationships based on soil index properties alone are inadequate for making quantitative volume change estimates due to heavy dependence of the suction volume change index on stress history. Fig.…”

“…Oedometer devices that provide for measurement and/or control of soil suction and net total vertical stress, allowing stress-path testing for 1-D, Ko conditions, are available to the practice community. One such device is an oedometer pressure plate device (OPPD), which uses axis-translation suction-control methods [45]. Other suction-controlled oedometers include osmotic suctioncontrol and high capacity tensiometer measurement methods [66][67][68][69].…”