Dependence of sand soil compressibility on soil physical properties

I.S.Vak hrin ,G.P.Kuzmin

Melnikov Permafrost Institute,Siberian Branch of the Russian Academy of Sciences,Yakutsk 677010,Russia

1 Introduction

In the Lena River flood plain of Yakutsk,Russia,a new residential quarter is being constructed on hydraulically filled sand soils,with water contents varying with depth from a few percent to the maximal water capacity.This area was hydraulically filled in 1990–1992 and now contains a suprapermafrost talik.Of practical significance is the definition of thawed soil compressibility under construction pressure and their dependence on principal soil physical properties.The possibility of data extension obtained from standard compression tests and a certain dependence of thawed soil compressibility on soil physical properties are presented.

2 Definition of physical soil property methods

A relationship between physical properties of thawed soils is expressed by the following formula(Kuzmin,2011):whereva/vis soil relative air content;ρd,ρs,andρware density of dry soil,solid particles and water,respectively;wis soil water content.

As presented in formula(1),physical parameters of thawed soils depend on two other parameters.

In compression tests of soil samples with sequentially increasing loads and no possibility of lateral extension,dry soil density is calculated by the following formula:

whereρd0is initial soil porosity factor;h0is initial sample height;Δhis the change of sample height under increased loading.

Based onformula(2),at each level of sample load,soil porosity factor can be defined as:

Therefore,according to results of standard compression tests for each soil sample,dependency of soil compressibility factor on the density of dry soil and the porosity factor under alternating applied load can be identified.Compression factor dependency on water content and relative air content of soils calculated by formula(1)can only be determined based on data received from sample compression tests with one increment of load,as it is impossible to determine variablewandva/v,with subsequent loading increments.

Sample preparation for compression tests consist of the following:(1) The tested soil mass was previously watered to a certain level of the water content.(2) The mass was then compacted into a metallic cylinder using a GT 1.1.4 compressive device (Geoteck Ltd.,Penza) at 0.05 MPa.(3) Finally,physical and compressive properties of the compacted soil sample are defined.

3 Experimental results

The granulometric composition of the soil is defined as fine-grained sand which is predominating in the hydraulically filled massif of Yakutsk (Table 1).

Table 1 Granulometric composition of soils

Table 2 Results of compression tests and definitions of va/v,ρd and e

The results of soil compression tests with differing water content and calculated values of air content,changes of density and porosity factors are presented in table 2.

Dependency of the soil compression factor on water content and relative air content after the first increment of sample loading (0.05 MPa) are presented in figure 1.

Compression factor reduction with increasing soil water content and its rise with air content increase is evidently connected with differing viscosity of these two soil components.

Figure 1 Dependency of compression factor on water content (a) and relative air content (b)

The alterations of soil density of differing water content on the load value using a logarithmic scale are presented in figure 2.

Figure 2 Dependency of dry soil density with various load degrees of water content.1:w=8.0%;2:w=11.5%;3:w=13.7%;4:w=20.0%

As presented in figure 2,soil density increases with an increase of water content and load.Regularities of dry soil density varying in load dependence are described by the following equation:whereAandkare constants depending on soil typeand water content.

Dependency of the compression factor on dry soil density and porosity factor is presented in figure 3.Compression factor alterations dependent on density and porosity factors are described by the following equations:

whereB,C,tandlare constants depending on type and degree of soil water content.

Considering equations(5)and(6),correspondingly,(2)and(3)are given in the following form:Constants of equations(4)–(8)are presented in table 3.

Figure 3 Dependency of the compression factor of soil with various water contents on dry soil density (a) and porosity factor (b).1:w = 8.0%;2:w = 11.5%;3:w = 13.7%;4:w = 20.0%

Table 3 Constants in empirical dependency

As presented in table 3,the constants in equations(4)–(8)with an exception ofl,depend to a certain extent on soil water content.With a change of soil water content from 8.0% to 20.0%,A,kandtchange insignificantly,whileCchanges considerably andBchanges markedly.

4 Conclusions

1) Experimental research of sand soils has identified as the following:

·soil compression factor decreases with an increase of water content and rises with an increase of air content,which is explained by differing viscosity of water and air;

·the compression factor decreases with increasing soil density,caused by a decrease of its porosity.

2) Dependence of the compression factor on soil density and porosity is expressed by the exponential function.

Kuzmin GP,2011.Relationship among the physical properties of soils.Proceedings of the 9thInternational Symposium on Permafrost Engineering.September 3–7,2011,Mirny,Russia.