Using filter paper method the measured water content is different due to the different distances between filter paper and soil surface

and the relevant soil suction is also different.For this purpose

tests were carried out to measure the total suction of expansive soil under different distances between filter paper and soil surface

and the relationship between water content of filter paper and distance was obtained.When the dry density of soil is small

the water content of filter paper decreased firstly

then increased and finally decreased with increasing distances.When the dry density is large

the water content of filter paper decreased with increasing distances and then remained stable.The dispersion degree of soil suction is lesser at a distance of3 cm than at other distances;hence

this distance could be regarded as a standard distance for measuring soil suction.The total suction-distance relationship was established by introducing the concept of pseudo matrix suction

and the relevant pseudo matrix suction was obtained.The true matrix suction has a linear correlation with the pseudo matrix suction under different dry densities and water contents.This method can provide a new idea for the determination of field soil matrix suction.