The definitions of negative skin friction （NSF） and neutral point show that the variation of NSF from both sides of the tope of pile to the neutral point is not uniform

within which there might be a maximum value of NSF. This has been confirmed by recently obtained data from in situ tests in collapsing loess ground. It is necessary to determine the position of the maximum NSF on pile in order to obtain the theoretic curve of the variation of NSF versus depth

which may help to understand how the NSF takes place and calculate the value of NSF. To date

there have been few studies on this problem. Using the data obtained from tests in the collapsing loess ground

this paper studies the position of the maximum NSF by theoretical analysis. It shows that the variation of NSF with depth is likely to be influenced by the effective weight of the soil body above certain depth （such as the depth of maximum NSF） and the settlement of the soil body around the pile at that depth in the collpasing loess ground. Furthermore

the principle is derived

which determines the position of maximum NSF on piles in loess ground with different water col-lapsibility. Compared with in situ measurements

the method proposed in this paper for the determination of the position of maximum NSF is theoretically reasonable and the estimation of the total NSF on piles with this method is more rational than other applications using the effective stress method （ESM）

with which the neutral point is usually taken as the computing depth for the calculation of the NSF value and the oversimplication of the computing depth violates the difinition of the nertral point

where the NSF value equals zero.