[21] immediate forward support (IFS) ������֧��

[22] canopy��Һѹ֧�ܶ���

[23] supporting resistances��֧������

[24] lowered and pulled forward������������

[25] hydraulic advancing ram��Һѹ����ǧ�ﶥ

[26] rigidity�����ԣ��ն�

[27] curved or snaked section��������������

[28] panel development�����ε���չ

[29] cribs��ľ��

[30] support density��֧���ܶ�

��һҳ[1][2][3]