def Nch(c, H, D):
    """ Horizontal bearing capacity factor for sand
    """
    if c == 0:
        return 0
    x = H / D
    return min(6.752 + 0.065 * x - 11.063 / (x + 1) ** 2 + 7.119 / (x + 1) **
        3, 9)
