The immediate objective of the operation was for the forces to establish themselves in commanding positions, from which they could operate against tunnels running from the strip into Israel.
...
Before the ground incursion began, a senior officer in the GOC southern command said it would most likely be limited to a depth of three to four kilometers from the Israeli border, and would focus on locating and destroying tunnels. Such an operation, he said, could take between a week and two weeks.
Not as widely known is Egypt's own battle with Gaza tunnels leading into their country. This piece from February of this year:
The Egyptian army has demolished ten more tunnels under the border with the Gaza Strip, which has been under an Israeli blockade for the past 79 months.
The tunnels were destroyed on Saturday as a part of the military-appointed government’s campaign of tightening the noose around the Palestinians living in Gaza.
The Egyptian army has destroyed hundreds of tunnels since it ousted the country’s first democratically elected president, Mohamed Morsi, in a coup in July last year.
The tunnels are the only lifeline for Gazans living under the Israeli siege. Palestinians use the tunnels to bring essential supplies, such as foodstuff, cooking gas, medicines, petrol, and livestock, into the Gaza Strip.
On Saturday, the Egyptian army also destroyed several homes in the Sinai Peninsula as part of a new plan to create a buffer zone along its border with Gaza.
The campaign began with a military operation in the border town of Rafah where tunnels leading into the Gaza Strip were destroyed.
The event preceding Israel's ground incursion into Gaza was the thwarting of an attack inside Israel by Palestinian commandos using one of these tunnels as their entry point:
IDF forces identified some 13 Gaza terrorists who attempted to penetrate into Israel through a tunnel from Gaza Strip Thursday morning.
The IDF forces attacked the group and some direct hits were identified. The attempted attack took place near Kerem Shalom.
At roughly 4:30 am the group attempted to penetrate into Israel through a tunnel which the IDF already identified by IDF lookouts near Kibbutz Suffa.
The soldiers attacked the tunnel's pier and the attack was thwarted, and causalities were sustained to the Hamas men. No Israelis were wounded during the attack but massive IDF forces were present at the scene on the ground and in the sky.
Lt. Col. Peter Lerner, an IDF spokesman, said the IDF believed at least one militant was killed in the strike and that the remaining fighters appeared to have returned to Gaza through the tunnel. Footage released by the IDF showed a number of individuals creeping slowly toward what appeared to be a hole in the ground. A separate shot showed an explosion from an airstrike on the tunnel entrance.
Lerner said the attack "could have had devastating consequences" and said the militants were armed with "extensive weapons," including rocket-propelled grenades.
God, let this end quickly. Be with the innocents involved. Protect them from harm. Thwart the wicked and grant wisdom and resolve to the just.
Amen.