Десмонд Бэгли - Landslide

I took a deep breath. ‘They never found out what triggered that one off. But here’s another one. This happened in a place called Surte in Sweden, and Surte is quite a big town. Trouble was it slid into the Gota river. Over a hundred million cubic feet of topsoil went on the rampage and it took with it a railroad, a highway and the homes of three hundred people. That one left a hole half a mile long and a third of a mile wide. It was started by someone using a pile-driver on a new building foundation.’

‘A pile-driver!’ Mac’s mouth stayed open.

‘It doesn’t take much vibration to set quick clay on the move. I told you it was thixotropic, it changes by touch — and it doesn’t need much of a touch if the conditions are right. And when it happens the whole of a wide area changes from solid to liquid and the topsoil starts to move — and it moves damn’ fast. The Surte disaster took three minutes from start to finish. One house moved four hundred and fifty feet — how would you like to be in a house that took off at nearly twenty miles an hour?’

‘I wouldn’t,’ said Mac grimly.

I said, ‘Do you remember what happened to Anchorage?’

‘Worst disaster Alaska ever had,’ said Mac. ‘But that was a proper earthquake.’

‘Oh, there was an earthquake, but it wasn’t that that did the damage to Anchorage. It did trigger off a quick clay slide, though. Most of the town happened to be built on quick clay and Anchorage took off for the wide blue yonder, which happened to be in the direction of the Pacific Ocean.’

‘I didn’t know that,’ said Mac.

‘There are dozens of other examples,’ I said. ‘During the war British bombers attacking a chemical factory in Norway set off a slide over an area of fifty thousand square yards. And there was Aberfan in South Wales: that was an artificial situation — the slag heap of a coal mine — but the basic cause was the interaction of clay and water. It killed a schoolful of children.’

Clare said, ‘And you think the dam is in danger?’

I gestured at the cores on the table. ‘I took three samples from across the escarpment, and they show quick clay right across. I don’t know how far it extends up and down, but it’s my guess that it’s all the way. There’s an awful lot of mud appeared down at the bottom. A quick clay slide can travel at twenty miles an hour on a slope of only one degree. The gradient of that escarpment must average fifteen degrees, so that when it goes, it’ll go fast. That power plant will be buried under a hundred feet of mud and it’ll probably jerk the foundations from under the dam, too. If that happens, then the whole of the new Matterson Lake will follow the mud. I doubt if there’d be much left of the power plant.’

‘Or anyone in it,’ said Clare quietly.

‘Or anyone in it,’ I agreed.

Mac hunched his shoulders and stared loweringly at the cores. ‘What I don’t understand is why it hasn’t gone before now. I can remember when they were logging on the escarpment and cutting big trees at that. A full grown Douglas fir hits the ground with a mighty big thump — harder than a pile-driver. The whole slope should have collapsed years ago.’

I said, ‘I think the dam is responsible. I think the quick clay layer surfaces somewhere the other side of the dam. Everything was all right until the dam was built, but then they closed the sluices and the water started backing up and covering the quick clay outcropping. Now it’s seeping down in the quick clay all under the escarpment.’

Mac nodded. ‘That figures.’

‘What are you going to do about it?’ asked Clare.

‘I’ll have to tell the Mattersons somehow,’ I said. ‘I tried to tell Howard this afternoon but he shut me up. In my report I even told him to watch out for quick clay, but I don’t think he even read it. You’re right, Clare: he’s a sloppy businessman.’ I stretched. ‘But right now I want to find out more about these samples — the water content especially.’

‘How will you do that?’ asked Mac interestedly.

‘Easy. I cut a sample and weigh it, then cook the water out on that stove there, then weigh it again. It’s just a sum in subtraction from then on.’

‘I’ll make supper first,’ said Clare. ‘Right now you’d better clear up this mess you’ve made.’

After supper I got down to finding the water content. The shear strength of quick clay depends on the mineral constituents and the amount of water held — it was unfortunate that this particular clay was mainly montmorillonite and deficient in strength. That, combined with a water content of forty per cent, averaged out over three samples, gave it a shear strength of about one ton per square foot.

If I was right and water was seeping into the quick clay strata from the new lake, then conditions would rapidly become worse. Double the water percentage and the shear strength would drop to a mere 500 pounds a square foot, and a heavy-footed construction man could start the whole hillside sliding.

Clare said, ‘Is there anything that can be done about it — to save the dam, I mean?’

I sighed. ‘I don’t know, Clare. They’ll have to open the sluices again and get rid of the water in the lake, locate where the clay comes to the surface and then, maybe, they can seal it off. Put a layer of concrete over it, perhaps. But that still leaves the quick clay under the escarpment in a dangerous condition.’

‘So what do you do then?’ asked Mac.

I grinned. ‘Pump some more water into it.’ I laughed outright at the expression on his face. ‘I mean it, Mac; but we pump in a brine solution with plenty of dissolved salts. That will put in some glue to hold it together and it will cease to be thixotropic.’

‘Full of smart answers, aren’t you?’ said Mac caustically. ‘Well, answer this one. How do you propose getting the Matterson Corporation to listen to you in the first place? I can’t see you popping into Howard’s office tomorrow and getting him to open those sluices. He’d think you were nuts.’

‘I could tell him,’ said Clare.

Mac snorted in disgust. ‘From Howard’s point of view, you and Bob have gypped him out of four million bucks that were rightly his. If you tried to get him to close down construction on the dam he’d think you were planning another fast killing. He wouldn’t be able to figure how you’re going to do it, but he’d be certain you were pulling a fast one.’

I said, ‘What about old Bull? He might listen.’

‘He might,’ said Mac. ‘On the other hand, you asked me to spread that story around Fort Farrell and he might have got his dander up about it. I wouldn’t bank on him listening to anything you have to say.’

‘Oh, hell!’ I said. ‘Let’s sleep on it. Maybe we’ll come up with something tomorrow.’

I bedded down in the clearing because Clare had my bed, and I stayed awake thinking of what I had done. Had I achieved anything at all? Fort Farrell had been a murky enough pool when I arrived, but now the waters were stirred up into muddiness and nothing at all could be seen. I was still butting my head against the mystery of the Trinavants and, so far, nothing had come of my needling the Mattersons.

I began to think about that and came up against something odd. Old Bull had known who I was right from the start and he had got stirred up pretty fast. From that I argued that there was something he had to hide with regard to the Mattersons — and perhaps I was right, because it was he who had clamped down on the name of Trinavant.

Howard, on the other hand, had been stirred up about other things — our argument about Clare, his defeat in the matter of my prospecting on Crown land, another defeat in the matter of the cutting of the lumber on Clare’s land. But then I had asked Mac to spread around the story that I was the survivor of the Trinavant auto smash — and Howard had immediately blown his top and given me twenty-four hours to get out of town.